</head>
<body>
-<div class="doc_title">Source Level Debugging with LLVM</div>
+<h1>Source Level Debugging with LLVM</h1>
<table class="layout" style="width:100%">
<tr class="layout">
<li><a href="#debug_info_descriptors">Debug information descriptors</a>
<ul>
<li><a href="#format_compile_units">Compile unit descriptors</a></li>
+ <li><a href="#format_files">File descriptors</a></li>
<li><a href="#format_global_variables">Global variable descriptors</a></li>
<li><a href="#format_subprograms">Subprogram descriptors</a></li>
<li><a href="#format_blocks">Block descriptors</a></li>
</ul></li>
<li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
<ul>
- <li><a href="#format_common_stoppoint">llvm.dbg.stoppoint</a></li>
- <li><a href="#format_common_func_start">llvm.dbg.func.start</a></li>
- <li><a href="#format_common_region_start">llvm.dbg.region.start</a></li>
- <li><a href="#format_common_region_end">llvm.dbg.region.end</a></li>
<li><a href="#format_common_declare">llvm.dbg.declare</a></li>
+ <li><a href="#format_common_value">llvm.dbg.value</a></li>
</ul></li>
- <li><a href="#format_common_stoppoints">Representing stopping points in the
- source program</a></li>
</ol></li>
+ <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
<li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
<ol>
<li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
<li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
<li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
</ol></li>
+ <li><a href="#llvmdwarfextension">LLVM Dwarf Extensions</a>
+ <ol>
+ <li><a href="#objcproperty">Debugging Information Extension
+ for Objective C Properties</a>
+ <ul>
+ <li><a href="#objcpropertyintroduction">Introduction</a></li>
+ <li><a href="#objcpropertyproposal">Proposal</a></li>
+ <li><a href="#objcpropertynewattributes">New DWARF Attributes</a></li>
+ <li><a href="#objcpropertynewconstants">New DWARF Constants</a></li>
+ </ul>
+ </li>
+ <li><a href="#acceltable">Name Accelerator Tables</a>
+ <ul>
+ <li><a href="#acceltableintroduction">Introduction</a></li>
+ <li><a href="#acceltablehashes">Hash Tables</a></li>
+ <li><a href="#acceltabledetails">Details</a></li>
+ <li><a href="#acceltablecontents">Contents</a></li>
+ <li><a href="#acceltableextensions">Language Extensions and File Format Changes</a></li>
+ </ul>
+ </li>
+ </ol>
+ </li>
</ul>
</td>
<td class="right">
<!-- *********************************************************************** -->
-<div class="doc_section"><a name="introduction">Introduction</a></div>
+<h2><a name="introduction">Introduction</a></h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>This document is the central repository for all information pertaining to
debug information in LLVM. It describes the <a href="#format">actual format
that the LLVM debug information</a> takes, which is useful for those
interested in creating front-ends or dealing directly with the information.
Further, this document provides specific examples of what debug information
- for C/C++.</p>
-
-</div>
+ for C/C++ looks like.</p>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="phil">Philosophy behind LLVM debugging information</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>The idea of the LLVM debugging information is to capture how the important
pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
<p>The approach used by the LLVM implementation is to use a small set
of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
mapping between LLVM program objects and the source-level objects. The
- description of the source-level program is maintained in LLVM global
-
variables in an <a href="#ccxx_frontend">implementation-defined format</a>
+ description of the source-level program is maintained in LLVM metadata
+ in an <a href="#ccxx_frontend">implementation-defined format</a>
(the C/C++ front-end currently uses working draft 7 of
the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
standard</a>).</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="consumers">Debug information consumers</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>The role of debug information is to provide meta information normally
stripped away during the compilation process. This meta information provides
an LLVM user a relationship between generated code and the original program
source code.</p>
-<p>Currently, debug information is consumed by the DwarfWriter to produce dwarf
+<p>Currently, debug information is consumed by DwarfDebug to produce dwarf
information used by the gdb debugger. Other targets could use the same
information to produce stabs or other debug forms.</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="debugopt">Debugging optimized code</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>An extremely high priority of LLVM debugging information is to make it
interact well with optimizations and analysis. In particular, the LLVM debug
as setting program variables, or calling functions that have been
deleted.</li>
- <li>LLVM optimizations gracefully interact with debugging information. If
- they are not aware of debug information, they are automatically disabled
- as necessary in the cases that would invalidate the debug info. This
- retains the LLVM features, making it easy to write new
- transformations.</li>
-
<li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
debugging information, allowing them to update the debugging information
as they perform aggressive optimizations. This means that, with effort,
the LLVM optimizers could optimize debug code just as well as non-debug
code.</li>
- <li>LLVM debug information does not prevent many important optimizations from
+ <li>LLVM debug information does not prevent optimizations from
happening (for example inlining, basic block reordering/merging/cleanup,
- tail duplication, etc), further reducing the amount of the compiler that
- eventually is "aware" of debugging information.</li>
+ tail duplication, etc).</li>
<li>LLVM debug information is automatically optimized along with the rest of
the program, using existing facilities. For example, duplicate
</div>
+</div>
+
<!-- *********************************************************************** -->
-<div class="doc_section">
+<h2>
<a name="format">Debugging information format</a>
-</div>
+</h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>LLVM debugging information has been carefully designed to make it possible
for the optimizer to optimize the program and debugging information without
necessarily having to know anything about debugging information. In
- particular, the global constant merging pass automatically eliminates
- duplicated debugging information (often caused by header files), the global
- dead code elimination pass automatically deletes debugging information for a
- function if it decides to delete the function, and the linker eliminates
- debug information when it merges <tt>linkonce</tt> functions.</p>
+ particular, the use of metadata avoids duplicated debugging information from
+ the beginning, and the global dead code elimination pass automatically
+ deletes debugging information for a function if it decides to delete the
+ function. </p>
<p>To do this, most of the debugging information (descriptors for types,
variables, functions, source files, etc) is inserted by the language
- front-end in the form of LLVM global variables. These LLVM global variables
- are no different from any other global variables, except that they have a web
- of LLVM intrinsic functions that point to them. If the last references to a
- particular piece of debugging information are deleted (for example, by the
- <tt>-globaldce</tt> pass), the extraneous debug information will
- automatically become dead and be removed by the optimizer.</p>
+ front-end in the form of LLVM metadata. </p>
<p>Debug information is designed to be agnostic about the target debugger and
debugging information representation (e.g. DWARF/Stabs/etc). It uses a
- generic machine debug information pass to decode the information that
- represents variables, types, functions, namespaces, etc: this allows for
- arbitrary source-language semantics and type-systems to be used, as long as
- there is a module written for the target debugger to interpret the
- information. In addition, debug global variables are declared in
- the <tt>"llvm.metadata"</tt> section. All values declared in this section
- are stripped away after target debug information is constructed and before
- the program object is emitted.</p>
+ generic pass to decode the information that represents variables, types,
+ functions, namespaces, etc: this allows for arbitrary source-language
+ semantics and type-systems to be used, as long as there is a module
+ written for the target debugger to interpret the information. </p>
<p>To provide basic functionality, the LLVM debugger does have to make some
assumptions about the source-level language being debugged, though it keeps
these to a minimum. The only common features that the LLVM debugger assumes
- exist are <a href="#format_compile_units">source files</a>,
+ exist are <a href="#format_files">source files</a>,
and <a href="#format_global_variables">program objects</a>. These abstract
objects are used by a debugger to form stack traces, show information about
local variables, etc.</p>
common to any source-language. The <a href="#ccxx_frontend">next section</a>
describes the data layout conventions used by the C and C++ front-ends.</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="debug_info_descriptors">Debug information descriptors</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>In consideration of the complexity and volume of debug information, LLVM
- provides a specification for well formed debug global variables. The
- constant value of each of these globals is one of a limited set of
- structures, known as debug descriptors.</p>
+ provides a specification for well formed debug descriptors. </p>
<p>Consumers of LLVM debug information expect the descriptors for program
objects to start in a canonical format, but the descriptors can include
way. Also, all debugging information objects start with a tag to indicate
what type of object it is. The source-language is allowed to define its own
objects, by using unreserved tag numbers. We recommend using with tags in
- the range 0x1000 thru 0x2000 (there is a defined enum DW_TAG_user_base =
+ the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
0x1000.)</p>
-<p>The fields of debug descriptors used internally by LLVM (MachineModuleInfo)
- are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>,
- <tt>bool</tt>, <tt>float</tt>, <tt>double</tt>, <tt>i8*</tt> and
- <tt>{ }*</tt>. References to arbitrary values are handled using a
- <tt>{ }*</tt> and a cast to <tt>{ }*</tt> expression; typically
- references to other field descriptors, arrays of descriptors or global
- variables.</p>
+<p>The fields of debug descriptors used internally by LLVM
+ are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
+ <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
<div class="doc_code">
<pre>
-%llvm.dbg.object.type = type {
- uint, ;; A tag
+!1 = metadata !{
+ i32, ;; A tag
...
}
</pre>
</div>
<p><a name="LLVMDebugVersion">The first field of a descriptor is always an
- <tt>uint</tt> containing a tag value identifying the content of the
+ <tt>i32</tt> containing a tag value identifying the content of the
descriptor. The remaining fields are specific to the descriptor. The values
of tags are loosely bound to the tag values of DWARF information entries.
However, that does not restrict the use of the information supplied to DWARF
targets. To facilitate versioning of debug information, the tag is augmented
- with the current debug version (LLVMDebugVersion = 4 << 16 or 0x40000 or
- 262144.)</a></p>
-
-<p>The details of the various descriptors follow.</p>
+ with the current debug version (LLVMDebugVersion = 8 << 16 or
+ 0x80000 or 524288.)</a></p>
-</div>
+<p>The details of the various descriptors follow.</p>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_compile_units">Compile unit descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type {
- i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_compile_unit)
- { }*, ;; Compile unit anchor = cast = (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*)
- i32, ;; DWARF language identifier (ex. DW_LANG_C89)
- i8*, ;; Source file name
- i8*, ;; Source file directory (includes trailing slash)
- i8* ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
- i1, ;; True if this is a main compile unit.
- i1, ;; True if this is optimized.
- i8*, ;; Flags
- i32 ;; Runtime version
+!0 = metadata !{
+ i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_compile_unit)
+ i32, ;; Unused field.
+ i32, ;; DWARF language identifier (ex. DW_LANG_C89)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
+ i1, ;; True if this is a main compile unit.
+ i1, ;; True if this is optimized.
+ metadata, ;; Flags
+ i32 ;; Runtime version
+ metadata ;; List of enums types
+ metadata ;; List of retained types
+ metadata ;; List of subprograms
+ metadata ;; List of global variables
}
</pre>
</div>
that produced it.</p>
<p>Compile unit descriptors provide the root context for objects declared in a
- specific source file. Global variables and top level functions would be
- defined using this context. Compile unit descriptors also provide context
- for source line correspondence.</p>
+ specific compilation unit. File descriptors are defined using this context.
+ These descriptors are collected by a named metadata
+ <tt>!llvm.dbg.cu</tt>. Compile unit descriptor keeps track of subprograms,
+ global variables and type information.
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="format_files">File descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!0 = metadata !{
+ i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_file_type)
+ metadata, ;; Source file name
+ metadata, ;; Source file directory (includes trailing slash)
+ metadata ;; Unused
+}
+</pre>
+</div>
-<p>Each input file is encoded as a separate compile unit in LLVM debugging
- information output. However, many target specific tool chains prefer to
- encode only one compile unit in an object file. In this situation, the LLVM
- code generator will include debugging information entities in the compile
- unit that is marked as main compile unit. The code generator accepts maximum
- one main compile unit per module. If a module does not contain any main
- compile unit then the code generator will emit multiple compile units in the
- output object file.</p>
+<p>These descriptors contain information for a file. Global variables and top
+ level functions would be defined using this context.k File descriptors also
+ provide context for source line correspondence. </p>
+
+<p>Each input file is encoded as a separate file descriptor in LLVM debugging
+ information output. </p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_global_variables">Global variable descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type {
- i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_variable)
- { }*, ;; Global variable anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*),
- { }*, ;; Reference to context descriptor
- i8*, ;; Name
- i8*, ;; Display name (fully qualified C++ name)
- i8*, ;; MIPS linkage name (for C++)
- { }*, ;; Reference to compile unit where defined
- i32, ;; Line number where defined
- { }*, ;; Reference to type descriptor
- i1, ;; True if the global is local to compile unit (static)
- i1, ;; True if the global is defined in the compile unit (not extern)
- { }* ;; Reference to the global variable
+!1 = metadata !{
+ i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_variable)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1, ;; True if the global is defined in the compile unit (not extern)
+ {}* ;; Reference to the global variable
}
</pre>
</div>
<p>These descriptors provide debug information about globals variables. The
-provide details such as name, type and where the variable is defined.</p>
+provide details such as name, type and where the variable is defined. All
+global variables are collected inside the named metadata
+<tt>!llvm.dbg.cu</tt>.</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_subprograms">Subprogram descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type {
- i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subprogram)
- { }*, ;; Subprogram anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*),
- { }*, ;; Reference to context descriptor
- i8*, ;; Name
- i8*, ;; Display name (fully qualified C++ name)
- i8*, ;; MIPS linkage name (for C++)
- { }*, ;; Reference to compile unit where defined
- i32, ;; Line number where defined
- { }*, ;; Reference to type descriptor
- i1, ;; True if the global is local to compile unit (static)
- i1 ;; True if the global is defined in the compile unit (not extern)
+!2 = metadata !{
+ i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_subprogram)
+ i32, ;; Unused field.
+ metadata, ;; Reference to context descriptor
+ metadata, ;; Name
+ metadata, ;; Display name (fully qualified C++ name)
+ metadata, ;; MIPS linkage name (for C++)
+ metadata, ;; Reference to file where defined
+ i32, ;; Line number where defined
+ metadata, ;; Reference to type descriptor
+ i1, ;; True if the global is local to compile unit (static)
+ i1, ;; True if the global is defined in the compile unit (not extern)
+ i32, ;; Line number where the scope of the subprogram begins
+ i32, ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual
+ i32, ;; Index into a virtual function
+ metadata, ;; indicates which base type contains the vtable pointer for the
+ ;; derived class
+ i32, ;; Flags - Artifical, Private, Protected, Explicit, Prototyped.
+ i1, ;; isOptimized
+ Function *,;; Pointer to LLVM function
+ metadata, ;; Lists function template parameters
+ metadata ;; Function declaration descriptor
+ metadata ;; List of function variables
}
</pre>
</div>
<p>These descriptors provide debug information about functions, methods and
subprograms. They provide details such as name, return types and the source
- location where the subprogram is defined.</p>
+ location where the subprogram is defined.
+</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_blocks">Block descriptors</a>
+</h4>
+
+<div>
+
+<div class="doc_code">
+<pre>
+!3 = metadata !{
+ i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
+ metadata,;; Reference to context descriptor
+ i32, ;; Line number
+ i32, ;; Column number
+ metadata,;; Reference to source file
+ i32 ;; Unique ID to identify blocks from a template function
+}
+</pre>
</div>
-<div class="doc_text">
+<p>This descriptor provides debug information about nested blocks within a
+ subprogram. The line number and column numbers are used to dinstinguish
+ two lexical blocks at same depth. </p>
<div class="doc_code">
<pre>
-%<a href="#format_blocks">llvm.dbg.block</a> = type {
- i32, ;; Tag = 13 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
- { }* ;; Reference to context descriptor
+!3 = metadata !{
+ i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
+ metadata ;; Reference to the scope we're annotating with a file change
+ metadata,;; Reference to the file the scope is enclosed in.
}
</pre>
</div>
-<p>These descriptors provide debug information about nested blocks within a
- subprogram. The array of member descriptors is used to define local
- variables and deeper nested blocks.</p>
+<p>This descriptor provides a wrapper around a lexical scope to handle file
+ changes in the middle of a lexical block.</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_basic_type">Basic type descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type {
- i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_base_type)
- { }*, ;; Reference to context (typically a compile unit)
- i8*, ;; Name (may be "" for anonymous types)
- { }*, ;; Reference to compile unit where defined (may be NULL)
- i32, ;; Line number where defined (may be 0)
- i64, ;; Size in bits
- i64, ;; Alignment in bits
- i64, ;; Offset in bits
- i32, ;; Flags
- i32 ;; DWARF type encoding
+!4 = metadata !{
+ i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_base_type)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ i32 ;; DWARF type encoding
}
</pre>
</div>
<p>These descriptors define primitive types used in the code. Example int, bool
and float. The context provides the scope of the type, which is usually the
- top level. Since basic types are not usually user defined the compile unit
+ top level. Since basic types are not usually user defined the context
and line number can be left as NULL and 0. The size, alignment and offset
are expressed in bits and can be 64 bit values. The alignment is used to
round the offset when embedded in a
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_derived_type">Derived type descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> = type {
- i32, ;; Tag (see below)
- { }*, ;; Reference to context
- i8*, ;; Name (may be "" for anonymous types)
- { }*, ;; Reference to compile unit where defined (may be NULL)
- i32, ;; Line number where defined (may be 0)
- i32, ;; Size in bits
- i32, ;; Alignment in bits
- i32, ;; Offset in bits
- { }* ;; Reference to type derived from
+!5 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags to encode attributes, e.g. private
+ metadata, ;; Reference to type derived from
+ metadata, ;; (optional) Name of the Objective C property associated with
+ ;; Objective-C an ivar
+ metadata, ;; (optional) Name of the Objective C property getter selector.
+ metadata, ;; (optional) Name of the Objective C property setter selector.
+ i32 ;; (optional) Objective C property attributes.
}
</pre>
</div>
<p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
-<p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
- <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
- and <tt>DW_TAG_restrict_type</tt> are used to qualify
+<p><tt>DW_TAG_pointer_type</tt>, <tt>DW_TAG_reference_type</tt>,
+ <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt> and
+ <tt>DW_TAG_restrict_type</tt> are used to qualify
the <a href="#format_derived_type">derived type</a>. </p>
<p><a href="#format_derived_type">Derived type</a> location can be determined
- from the compile unit and line number. The size, alignment and offset are
+ from the context and line number. The size, alignment and offset are
expressed in bits and can be 64 bit values. The alignment is used to round
the offset when embedded in a <a href="#format_composite_type">composite
type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
the bit offset if embedded in a <a href="#format_composite_type">composite
type</a>.</p>
-<p>Note that the <tt>void *</tt> type is expressed as a
- <tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt>
- and <tt>NULL</tt> derived type.</p>
+<p>Note that the <tt>void *</tt> type is expressed as a type derived from NULL.
+</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_composite_type">Composite type descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_composite_type">llvm.dbg.compositetype.type</a> = type {
- i32, ;; Tag (see below)
- { }*, ;; Reference to context
- i8*, ;; Name (may be "" for anonymous types)
- { }*, ;; Reference to compile unit where defined (may be NULL)
- i32, ;; Line number where defined (may be 0)
- i64, ;; Size in bits
- i64, ;; Alignment in bits
- i64, ;; Offset in bits
- i32, ;; Flags
- { }*, ;; Reference to type derived from
- { }*, ;; Reference to array of member descriptors
- i32 ;; Runtime languages
+!6 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Reference to context
+ metadata, ;; Name (may be "" for anonymous types)
+ metadata, ;; Reference to file where defined (may be NULL)
+ i32, ;; Line number where defined (may be 0)
+ i64, ;; Size in bits
+ i64, ;; Alignment in bits
+ i64, ;; Offset in bits
+ i32, ;; Flags
+ metadata, ;; Reference to type derived from
+ metadata, ;; Reference to array of member descriptors
+ i32 ;; Runtime languages
}
</pre>
</div>
<p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
<a href="#format_enumeration">enumerator descriptors</a>, each representing
- the definition of enumeration value for the set.</p>
+ the definition of enumeration value for the set. All enumeration type
+ descriptors are collected inside the named metadata
+ <tt>!llvm.dbg.cu</tt>.</p>
<p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
= <tt>DW_TAG_union_type</tt>) types are any one of
the formal arguments to the subroutine.</p>
<p><a href="#format_composite_type">Composite type</a> location can be
- determined from the compile unit and line number. The size, alignment and
+ determined from the context and line number. The size, alignment and
offset are expressed in bits and can be 64 bit values. The alignment is used
to round the offset when embedded in
a <a href="#format_composite_type">composite type</a> (as an example, to keep
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_subrange">Subrange descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_subrange">llvm.dbg.subrange.type</a> = type {
+!42 = metadata !{
i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
i64, ;; Low value
i64 ;; High value
<a href="#format_composite_type">composite type</a>. The low value defines
the lower bounds typically zero for C/C++. The high value is the upper
bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
- == high the array will be unbounded.</p>
+ > high the array bounds are not included in generated debugging information.
+</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_enumeration">Enumerator descriptors</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_enumeration">llvm.dbg.enumerator.type</a> = type {
- i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_enumerator)
- i8*, ;; Name
- i64 ;; Value
+!6 = metadata !{
+ i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
+ ;; (DW_TAG_enumerator)
+ metadata, ;; Name
+ i64 ;; Value
}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="format_variables">Local variables</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_variables">llvm.dbg.variable.type</a> = type {
- i32, ;; Tag (see below)
- { }*, ;; Context
- i8*, ;; Name
- { }*, ;; Reference to compile unit where defined
- i32, ;; Line number where defined
- { }* ;; Type descriptor
+!7 = metadata !{
+ i32, ;; Tag (see below)
+ metadata, ;; Context
+ metadata, ;; Name
+ metadata, ;; Reference to file where defined
+ i32, ;; 24 bit - Line number where defined
+ ;; 8 bit - Argument number. 1 indicates 1st argument.
+ metadata, ;; Type descriptor
+ i32, ;; flags
+ metadata ;; (optional) Reference to inline location
}
</pre>
</div>
has no source correspondent.</p>
<p>The context is either the subprogram or block where the variable is defined.
- Name the source variable name. Compile unit and line indicate where the
+ Name the source variable name. Context and line indicate where the
variable was defined. Type descriptor defines the declared type of the
variable.</p>
</div>
+</div>
+
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="format_common_intrinsics">Debugger intrinsic functions</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
provide debug information at various points in generated code.</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_common_stoppoint">llvm.dbg.stoppoint</a>
-</div>
+<h4>
+ <a name="format_common_declare">llvm.dbg.declare</a>
+</h4>
-<div class="doc_text">
+<div>
<pre>
- void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint, uint, { }* )
+ void %<a href="#format_common_declare">llvm.dbg.declare</a>(metadata, metadata)
</pre>
-<p>This intrinsic is used to provide correspondence between the source file and
- the generated code. The first argument is the line number (base 1), second
- argument is the column number (0 if unknown) and the third argument the
- source <tt>%<a href="#format_compile_units">llvm.dbg.compile_unit</a>*</tt>
- cast to a <tt>{ }*</tt>. Code following a call to this intrinsic will
- have been defined in close proximity of the line, column and file. This
- information holds until the next call
- to <tt>%<a href="#format_common_stoppoint">lvm.dbg.stoppoint</a></tt>.</p>
-
+<p>This intrinsic provides information about a local element (e.g., variable). The
+ first argument is metadata holding the alloca for the variable. The
+ second argument is metadata containing a description of the variable.</p>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_common_func_start">llvm.dbg.func.start</a>
-</div>
+<h4>
+ <a name="format_common_value">llvm.dbg.value</a>
+</h4>
-<div class="doc_text">
+<div>
<pre>
- void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( { }* )
+ void %<a href="#format_common_value">llvm.dbg.value</a>(metadata, i64, metadata)
</pre>
-<p>This intrinsic is used to link the debug information
- in <tt>%<a href="#format_subprograms">llvm.dbg.subprogram</a></tt> to the
- function. It defines the beginning of the function's declarative region
- (scope). It also implies a call to
- %<tt><a href="#format_common_stoppoint">llvm.dbg.stoppoint</a></tt> which
- defines a source line "stop point". The intrinsic should be called early in
- the function after the all the alloca instructions. It should be paired off
- with a closing
- <tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>.
- The function's single argument is
- the <tt>%<a href="#format_subprograms">llvm.dbg.subprogram.type</a></tt>.</p>
-
+<p>This intrinsic provides information when a user source variable is set to a
+ new value. The first argument is the new value (wrapped as metadata). The
+ second argument is the offset in the user source variable where the new value
+ is written. The third argument is metadata containing a description of the
+ user source variable.</p>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_common_region_start">llvm.dbg.region.start</a>
</div>
-<div class="doc_text">
-<pre>
- void %<a href="#format_common_region_start">llvm.dbg.region.start</a>( { }* )
-</pre>
+<!-- ======================================================================= -->
+<h3>
+ <a name="format_common_lifetime">Object lifetimes and scoping</a>
+</h3>
-<p>This intrinsic is used to define the beginning of a declarative scope (ex.
- block) for local language elements. It should be paired off with a closing
- <tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The
- function's single argument is
- the <tt>%<a href="#format_blocks">llvm.dbg.block</a></tt> which is
- starting.</p>
+<div>
+<p>In many languages, the local variables in functions can have their lifetimes
+ or scopes limited to a subset of a function. In the C family of languages,
+ for example, variables are only live (readable and writable) within the
+ source block that they are defined in. In functional languages, values are
+ only readable after they have been defined. Though this is a very obvious
+ concept, it is non-trivial to model in LLVM, because it has no notion of
+ scoping in this sense, and does not want to be tied to a language's scoping
+ rules.</p>
+<p>In order to handle this, the LLVM debug format uses the metadata attached to
+ llvm instructions to encode line number and scoping information. Consider
+ the following C fragment, for example:</p>
+<div class="doc_code">
+<pre>
+1. void foo() {
+2. int X = 21;
+3. int Y = 22;
+4. {
+5. int Z = 23;
+6. Z = X;
+7. }
+8. X = Y;
+9. }
+</pre>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_common_region_end">llvm.dbg.region.end</a>
-</div>
+<p>Compiled to LLVM, this function would be represented like this:</p>
-<div class="doc_text">
+<div class="doc_code">
<pre>
- void %<a href="#format_common_region_end">llvm.dbg.region.end</a>( { }* )
-</pre>
-
-<p>This intrinsic is used to define the end of a declarative scope (ex. block)
- for local language elements. It should be paired off with an
- opening <tt>%<a href="#format_common_region_start">llvm.dbg.region.start</a></tt>
- or <tt>%<a href="#format_common_func_start">llvm.dbg.func.start</a></tt>.
- The function's single argument is either
- the <tt>%<a href="#format_blocks">llvm.dbg.block</a></tt> or
- the <tt>%<a href="#format_subprograms">llvm.dbg.subprogram.type</a></tt>
- which is ending.</p>
+define void @foo() nounwind ssp {
+entry:
+ %X = alloca i32, align 4 ; <i32*> [#uses=4]
+ %Y = alloca i32, align 4 ; <i32*> [#uses=4]
+ %Z = alloca i32, align 4 ; <i32*> [#uses=3]
+ %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7
+ store i32 21, i32* %X, !dbg !8
+ %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10
+ store i32 22, i32* %Y, !dbg !11
+ %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1]
+ call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14
+ store i32 23, i32* %Z, !dbg !15
+ %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
+ %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
+ %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
+ store i32 %add, i32* %Z, !dbg !16
+ %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
+ store i32 %tmp2, i32* %X, !dbg !17
+ ret void, !dbg !18
+}
+declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
+
+!0 = metadata !{i32 459008, metadata !1, metadata !"X",
+ metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
+ metadata !"foo", metadata !3, i32 1, metadata !4,
+ i1 false, i1 true}; [DW_TAG_subprogram ]
+!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
+ metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
+ i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
+!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
+ i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
+!5 = metadata !{null}
+!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
+ i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!8 = metadata !{i32 2, i32 3, metadata !1, null}
+!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!10 = metadata !{i32 3, i32 7, metadata !1, null}
+!11 = metadata !{i32 3, i32 3, metadata !1, null}
+!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
+ metadata !6}; [ DW_TAG_auto_variable ]
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
+!15 = metadata !{i32 5, i32 5, metadata !13, null}
+!16 = metadata !{i32 6, i32 5, metadata !13, null}
+!17 = metadata !{i32 8, i32 3, metadata !1, null}
+!18 = metadata !{i32 9, i32 1, metadata !2, null}
+</pre>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_common_declare">llvm.dbg.declare</a>
-</div>
+<p>This example illustrates a few important details about LLVM debugging
+ information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
+ intrinsic and location information, which are attached to an instruction,
+ are applied together to allow a debugger to analyze the relationship between
+ statements, variable definitions, and the code used to implement the
+ function.</p>
-<div class="doc_text">
+<div class="doc_code">
<pre>
- void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, { }* )
+call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7
</pre>
-
-<p>This intrinsic provides information about a local element (ex. variable.) The
- first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The
- second argument is
- the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
- the description of the variable, also cast to a <tt>{ }*</tt>.</p>
-
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsection">
- <a name="format_common_stoppoints">
- Representing stopping points in the source program
- </a>
-</div>
-
-<div class="doc_text">
-
-<p>LLVM debugger "stop points" are a key part of the debugging representation
- that allows the LLVM to maintain simple semantics
- for <a href="#debugopt">debugging optimized code</a>. The basic idea is that
- the front-end inserts calls to
- the <a href="#format_common_stoppoint">%<tt>llvm.dbg.stoppoint</tt></a>
- intrinsic function at every point in the program where a debugger should be
- able to inspect the program (these correspond to places a debugger stops when
- you "<tt>step</tt>" through it). The front-end can choose to place these as
- fine-grained as it would like (for example, before every subexpression
- evaluated), but it is recommended to only put them after every source
- statement that includes executable code.</p>
-
-<p>Using calls to this intrinsic function to demark legal points for the
- debugger to inspect the program automatically disables any optimizations that
- could potentially confuse debugging information. To
- non-debug-information-aware transformations, these calls simply look like
- calls to an external function, which they must assume to do anything
- (including reading or writing to any part of reachable memory). On the other
- hand, it does not impact many optimizations, such as code motion of
- non-trapping instructions, nor does it impact optimization of subexpressions,
- code duplication transformations, or basic-block reordering
- transformations.</p>
+<p>The first intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for the variable <tt>X</tt>. The metadata
+ <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
+ variable <tt>X</tt>.</p>
+<div class="doc_code">
+<pre>
+!7 = metadata !{i32 2, i32 7, metadata !1, null}
+!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
+!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
+ metadata !"foo", metadata !"foo", metadata !3, i32 1,
+ metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
+</pre>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsection">
- <a name="format_common_lifetime">Object lifetimes and scoping</a>
-</div>
+<p>Here <tt>!7</tt> is metadata providing location information. It has four
+ fields: line number, column number, scope, and original scope. The original
+ scope represents inline location if this instruction is inlined inside a
+ caller, and is null otherwise. In this example, scope is encoded by
+ <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
+ <tt>!2</tt>, where <tt>!2</tt> is a
+ <a href="#format_subprograms">subprogram descriptor</a>. This way the
+ location information attached to the intrinsics indicates that the
+ variable <tt>X</tt> is declared at line number 2 at a function level scope in
+ function <tt>foo</tt>.</p>
-<div class="doc_text">
-<p>In many languages, the local variables in functions can have their lifetime
- or scope limited to a subset of a function. In the C family of languages,
- for example, variables are only live (readable and writable) within the
- source block that they are defined in. In functional languages, values are
- only readable after they have been defined. Though this is a very obvious
- concept, it is also non-trivial to model in LLVM, because it has no notion of
- scoping in this sense, and does not want to be tied to a language's scoping
- rules.</p>
-
-<p>In order to handle this, the LLVM debug format uses the notion of "regions"
- of a function, delineated by calls to intrinsic functions. These intrinsic
- functions define new regions of the program and indicate when the region
- lifetime expires. Consider the following C fragment, for example:</p>
+<p>Now lets take another example.</p>
<div class="doc_code">
<pre>
-1. void foo() {
-2. int X = ...;
-3. int Y = ...;
-4. {
-5. int Z = ...;
-6. ...
-7. }
-8. ...
-9. }
+call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
</pre>
</div>
-<p>Compiled to LLVM, this function would be represented like this:</p>
+<p>The second intrinsic
+ <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
+ encodes debugging information for variable <tt>Z</tt>. The metadata
+ <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
+ the variable <tt>Z</tt>.</p>
<div class="doc_code">
<pre>
-void %foo() {
-entry:
- %X = alloca int
- %Y = alloca int
- %Z = alloca int
-
- ...
-
- call void @<a href="#format_common_func_start">llvm.dbg.func.start</a>( %<a href="#format_subprograms">llvm.dbg.subprogram.type</a>* @llvm.dbg.subprogram )
-
- call void @<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 2, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* @llvm.dbg.compile_unit )
-
- call void @<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...)
- call void @<a href="#format_common_declare">llvm.dbg.declare</a>({}* %Y, ...)
-
- <i>;; Evaluate expression on line 2, assigning to X.</i>
-
- call void @<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 3, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* @llvm.dbg.compile_unit )
-
- <i>;; Evaluate expression on line 3, assigning to Y.</i>
-
- call void @<a href="#format_common_stoppoint">llvm.region.start</a>()
- call void @<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 5, uint 4, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* @llvm.dbg.compile_unit )
- call void @<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...)
-
- <i>;; Evaluate expression on line 5, assigning to Z.</i>
-
- call void @<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 7, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* @llvm.dbg.compile_unit )
- call void @<a href="#format_common_region_end">llvm.region.end</a>()
-
- call void @<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint 9, uint 2, %<a href="#format_compile_units">llvm.dbg.compile_unit</a>* @llvm.dbg.compile_unit )
-
- call void @<a href="#format_common_region_end">llvm.region.end</a>()
-
- ret void
-}
+!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
+!14 = metadata !{i32 5, i32 9, metadata !13, null}
</pre>
</div>
-<p>This example illustrates a few important details about the LLVM debugging
- information. In particular, it shows how the various intrinsics are applied
- together to allow a debugger to analyze the relationship between statements,
- variable definitions, and the code used to implement the function.</p>
-
-<p>The first
- intrinsic <tt>%<a href="#format_common_func_start">llvm.dbg.func.start</a></tt>
- provides a link with the <a href="#format_subprograms">subprogram
- descriptor</a> containing the details of this function. This call also
- defines the beginning of the function region, bounded by
- the <tt>%<a href="#format_common_region_end">llvm.region.end</a></tt> at the
- end of the function. This region is used to bracket the lifetime of
- variables declared within. For a function, this outer region defines a new
- stack frame whose lifetime ends when the region is ended.</p>
-
-<p>It is possible to define inner regions for short term variables by using the
- %<a href="#format_common_stoppoint"><tt>llvm.region.start</tt></a>
- and <a href="#format_common_region_end"><tt>%llvm.region.end</tt></a> to
- bound a region. The inner region in this example would be for the block
- containing the declaration of Z.</p>
-
-<p>Using regions to represent the boundaries of source-level functions allow
- LLVM interprocedural optimizations to arbitrarily modify LLVM functions
- without having to worry about breaking mapping information between the LLVM
- code and the and source-level program. In particular, the inliner requires
- no modification to support inlining with debugging information: there is no
- explicit correlation drawn between LLVM functions and their source-level
- counterparts (note however, that if the inliner inlines all instances of a
- non-strong-linkage function into its caller that it will not be possible for
- the user to manually invoke the inlined function from a debugger).</p>
-
-<p>Once the function has been defined,
- the <a href="#format_common_stoppoint"><tt>stopping point</tt></a>
- corresponding to line #2 (column #2) of the function is encountered. At this
- point in the function, <b>no</b> local variables are live. As lines 2 and 3
- of the example are executed, their variable definitions are introduced into
- the program using
- %<a href="#format_common_declare"><tt>llvm.dbg.declare</tt></a>, without the
- need to specify a new region. These variables do not require new regions to
- be introduced because they go out of scope at the same point in the program:
- line 9.</p>
-
-<p>In contrast, the <tt>Z</tt> variable goes out of scope at a different time,
- on line 7. For this reason, it is defined within the inner region, which
- kills the availability of <tt>Z</tt> before the code for line 8 is executed.
- In this way, regions can support arbitrary source-language scoping rules, as
- long as they can only be nested (ie, one scope cannot partially overlap with
- a part of another scope).</p>
-
-<p>It is worth noting that this scoping mechanism is used to control scoping of
- all declarations, not just variable declarations. For example, the scope of
- a C++ using declaration is controlled with this and could change how name
- lookup is performed.</p>
+<p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
+ column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
+ itself resides inside of lexical scope <tt>!1</tt> described above.</p>
+
+<p>The scope information attached with each instruction provides a
+ straightforward way to find instructions covered by a scope.</p>
+
+</div>
</div>
<!-- *********************************************************************** -->
-<div class="doc_section">
+<h2>
<a name="ccxx_frontend">C/C++ front-end specific debug information</a>
-</div>
+</h2>
<!-- *********************************************************************** -->
-<div class="doc_text">
+<div>
<p>The C and C++ front-ends represent information about the program in a format
that is effectively identical
<p>The following sections provide examples of various C/C++ constructs and the
debug information that would best describe those constructs.</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_compile_units">C/C++ source file information</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
<pre>
...
;;
-;; Define types used. In this case we need one for compile unit anchors and one
-;; for compile units.
+;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
;;
-%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
-%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type { uint, { }*, uint, uint, i8*, i8*, i8* }
-...
-;;
-;; Define the anchor for compile units. Note that the second field of the
-;; anchor is 17, which is the same as the tag for compile units
-;; (17 = DW_TAG_compile_unit.)
-;;
-%<a href="#format_compile_units">llvm.dbg.compile_units</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 17 }, section "llvm.metadata"
+!2 = metadata !{
+ i32 524305, ;; Tag
+ i32 0, ;; Unused
+ i32 4, ;; Language Id
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
+ i1 true, ;; Main Compile Unit
+ i1 false, ;; Optimized compile unit
+ metadata !"", ;; Compiler flags
+ i32 0} ;; Runtime version
;;
-;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp".
+;; Define the file for the file "/Users/mine/sources/MySource.cpp".
;;
-%<a href="#format_compile_units">llvm.dbg.compile_unit1</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> {
- uint add(uint 17, uint 262144),
- { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*),
- uint 1,
- uint 1,
- i8* getelementptr ([13 x i8]* %str1, i32 0, i32 0),
- i8* getelementptr ([21 x i8]* %str2, i32 0, i32 0),
- i8* getelementptr ([33 x i8]* %str3, i32 0, i32 0) }, section "llvm.metadata"
-
-;;
-;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h".
-;;
-%<a href="#format_compile_units">llvm.dbg.compile_unit2</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> {
- uint add(uint 17, uint 262144),
- { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*),
- uint 1,
- uint 1,
- i8* getelementptr ([11 x i8]* %str4, int 0, int 0),
- i8* getelementptr ([21 x i8]* %str2, int 0, int 0),
- i8* getelementptr ([33 x i8]* %str3, int 0, int 0) }, section "llvm.metadata"
+!1 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"MySource.cpp",
+ metadata !"/Users/mine/sources",
+ metadata !2 ;; Compile unit
+}
;;
-;; Define each of the strings used in the compile units.
+;; Define the file for the file "/Users/mine/sources/Myheader.h"
;;
-%str1 = internal constant [13 x i8] c"MySource.cpp\00", section "llvm.metadata";
-%str2 = internal constant [21 x i8] c"/Users/mine/sources/\00", section "llvm.metadata";
-%str3 = internal constant [33 x i8] c"4.0.1 LLVM (LLVM research group)\00", section "llvm.metadata";
-%str4 = internal constant [11 x i8] c"MyHeader.h\00", section "llvm.metadata";
+!3 = metadata !{
+ i32 524329, ;; Tag
+ metadata !"Myheader.h"
+ metadata !"/Users/mine/sources",
+ metadata !2 ;; Compile unit
+}
+
...
</pre>
</div>
+<p>llvm::Instruction provides easy access to metadata attached with an
+instruction. One can extract line number information encoded in LLVM IR
+using <tt>Instruction::getMetadata()</tt> and
+<tt>DILocation::getLineNumber()</tt>.
+<pre>
+ if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
+ DILocation Loc(N); // DILocation is in DebugInfo.h
+ unsigned Line = Loc.getLineNumber();
+ StringRef File = Loc.getFilename();
+ StringRef Dir = Loc.getDirectory();
+ }
+</pre>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_global_variable">C/C++ global variable information</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given an integer global variable declared as follows:</p>
<div class="doc_code">
<pre>
;;
-;; Define types used. One for global variable anchors, one for the global
-;; variable descriptor, one for the global's basic type and one for the global's
-;; compile unit.
-;;
-%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
-%<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type { uint, { }*, { }*, i8*, { }*, uint, { }*, bool, bool, { }*, uint }
-%<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type { uint, { }*, i8*, { }*, int, uint, uint, uint, uint }
-%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ...
-...
-;;
;; Define the global itself.
;;
%MyGlobal = global int 100
...
;;
-;; Define the anchor for global variables. Note that the second field of the
-;; anchor is 52, which is the same as the tag for global variables
-;; (52 = DW_TAG_variable.)
+;; List of debug info of globals
;;
-%<a href="#format_global_variables">llvm.dbg.global_variables</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 52 }, section "llvm.metadata"
+!llvm.dbg.cu = !{!0}
+
+;; Define the compile unit.
+!0 = metadata !{
+ i32 786449, ;; Tag
+ i32 0, ;; Context
+ i32 4, ;; Language
+ metadata !"foo.cpp", ;; File
+ metadata !"/Volumes/Data/tmp", ;; Directory
+ metadata !"clang version 3.1 ", ;; Producer
+ i1 true, ;; Deprecated field
+ i1 false, ;; "isOptimized"?
+ metadata !"", ;; Flags
+ i32 0, ;; Runtime Version
+ metadata !1, ;; Enum Types
+ metadata !1, ;; Retained Types
+ metadata !1, ;; Subprograms
+ metadata !3 ;; Global Variables
+} ; [ DW_TAG_compile_unit ]
+
+;; The Array of Global Variables
+!3 = metadata !{
+ metadata !4
+}
+
+!4 = metadata !{
+ metadata !5
+}
;;
-;; Define the global variable descriptor. Note the reference to the global
-;; variable anchor and the global variable itself.
+;; Define the global variable itself.
+;;
+!5 = metadata !{
+ i32 786484, ;; Tag
+ i32 0, ;; Unused
+ null, ;; Unused
+ metadata !"MyGlobal", ;; Name
+ metadata !"MyGlobal", ;; Display Name
+ metadata !"", ;; Linkage Name
+ metadata !6, ;; File
+ i32 1, ;; Line
+ metadata !7, ;; Type
+ i32 0, ;; IsLocalToUnit
+ i32 1, ;; IsDefinition
+ i32* @MyGlobal ;; LLVM-IR Value
+} ; [ DW_TAG_variable ]
+
;;
-%<a href="#format_global_variables">llvm.dbg.global_variable</a> = internal constant %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> {
- uint add(uint 52, uint 262144),
- { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([9 x i8]* %str1, int 0, int 0),
- i8* getelementptr ([1 x i8]* %str2, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- uint 1,
- { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*),
- bool false,
- bool true,
- { }* cast (int* %MyGlobal to { }*) }, section "llvm.metadata"
-
+;; Define the file
;;
-;; Define the basic type of 32 bit signed integer. Note that since int is an
-;; intrinsic type the source file is NULL and line 0.
-;;
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([4 x i8]* %str3, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 5 }, section "llvm.metadata"
+!6 = metadata !{
+ i32 786473, ;; Tag
+ metadata !"foo.cpp", ;; File
+ metadata !"/Volumes/Data/tmp", ;; Directory
+ null ;; Unused
+} ; [ DW_TAG_file_type ]
;;
-;; Define the names of the global variable and basic type.
+;; Define the type
;;
-%str1 = internal constant [9 x i8] c"MyGlobal\00", section "llvm.metadata"
-%str2 = internal constant [1 x i8] c"\00", section "llvm.metadata"
-%str3 = internal constant [4 x i8] c"int\00", section "llvm.metadata"
+!7 = metadata !{
+ i32 786468, ;; Tag
+ null, ;; Unused
+ metadata !"int", ;; Name
+ null, ;; Unused
+ i32 0, ;; Line
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+} ; [ DW_TAG_base_type ]
+
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_subprogram">C/C++ function information</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given a function declared as follows:</p>
<div class="doc_code">
<pre>
-;;
-;; Define types used. One for subprogram anchors, one for the subprogram
-;; descriptor, one for the global's basic type and one for the subprogram's
-;; compile unit.
-;;
-%<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { uint, { }*, { }*, i8*, { }*, bool, bool }
-%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
-%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ...
-
;;
;; Define the anchor for subprograms. Note that the second field of the
;; anchor is 46, which is the same as the tag for subprograms
;; (46 = DW_TAG_subprogram.)
;;
-%<a href="#format_subprograms">llvm.dbg.subprograms</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 46 }, section "llvm.metadata"
-
-;;
-;; Define the descriptor for the subprogram. TODO - more details.
-;;
-%<a href="#format_subprograms">llvm.dbg.subprogram</a> = internal constant %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> {
- uint add(uint 46, uint 262144),
- { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([5 x i8]* %str1, int 0, int 0),
- i8* getelementptr ([1 x i8]* %str2, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- uint 1,
- { }* null,
- bool false,
- bool true }, section "llvm.metadata"
-
-;;
-;; Define the name of the subprogram.
-;;
-%str1 = internal constant [5 x i8] c"main\00", section "llvm.metadata"
-%str2 = internal constant [1 x i8] c"\00", section "llvm.metadata"
-
+!6 = metadata !{
+ i32 524334, ;; Tag
+ i32 0, ;; Unused
+ metadata !1, ;; Context
+ metadata !"main", ;; Name
+ metadata !"main", ;; Display name
+ metadata !"main", ;; Linkage name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ metadata !4, ;; Type
+ i1 false, ;; Is local
+ i1 true, ;; Is definition
+ i32 0, ;; Virtuality attribute, e.g. pure virtual function
+ i32 0, ;; Index into virtual table for C++ methods
+ i32 0, ;; Type that holds virtual table.
+ i32 0, ;; Flags
+ i1 false, ;; True if this function is optimized
+ Function *, ;; Pointer to llvm::Function
+ null ;; Function template parameters
+}
;;
;; Define the subprogram itself.
;;
-int %main(int %argc, i8** %argv) {
+define i32 @main(i32 %argc, i8** %argv) {
...
}
</pre>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_basic_types">C/C++ basic types</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>The following are the basic type descriptors for C/C++ core types:</p>
-</div>
-
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_type_bool">bool</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([5 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 2 }, section "llvm.metadata"
-%str1 = internal constant [5 x i8] c"bool\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"bool", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 2 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_char">char</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([5 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 8,
- uint 8,
- uint 0,
- uint 6 }, section "llvm.metadata"
-%str1 = internal constant [5 x i8] c"char\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"char", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 6 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_unsigned_char">unsigned char</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([14 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 8,
- uint 8,
- uint 0,
- uint 8 }, section "llvm.metadata"
-%str1 = internal constant [14 x i8] c"unsigned char\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned char",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 8, ;; Size in Bits
+ i64 8, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 8 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_short">short</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([10 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 16,
- uint 16,
- uint 0,
- uint 5 }, section "llvm.metadata"
-%str1 = internal constant [10 x i8] c"short int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_unsigned_short">unsigned short</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([19 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 16,
- uint 16,
- uint 0,
- uint 7 }, section "llvm.metadata"
-%str1 = internal constant [19 x i8] c"short unsigned int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"short unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 16, ;; Size in Bits
+ i64 16, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_int">int</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([4 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 5 }, section "llvm.metadata"
-%str1 = internal constant [4 x i8] c"int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
</pre></div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_unsigned_int">unsigned int</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([13 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 7 }, section "llvm.metadata"
-%str1 = internal constant [13 x i8] c"unsigned int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_long_long">long long</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([14 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 64,
- uint 64,
- uint 0,
- uint 5 }, section "llvm.metadata"
-%str1 = internal constant [14 x i8] c"long long int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 5 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([23 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 64,
- uint 64,
- uint 0,
- uint 7 }, section "llvm.metadata"
-%str1 = internal constant [23 x 8] c"long long unsigned int\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"long long unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_float">float</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([6 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 4 }, section "llvm.metadata"
-%str1 = internal constant [6 x i8] c"float\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"float",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsubsection">
+<h4>
<a name="ccxx_basic_double">double</a>
-</div>
+</h4>
-<div class="doc_text">
+<div>
<div class="doc_code">
<pre>
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- 8* getelementptr ([7 x 8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 64,
- uint 64,
- uint 0,
- uint 4 }, section "llvm.metadata"
-%str1 = internal constant [7 x 8] c"double\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"double",;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in Bits
+ i64 64, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 4 ;; Encoding
+}
</pre>
</div>
</div>
+</div>
+
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_derived_types">C/C++ derived types</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given the following as an example of C/C++ derived type:</p>
;;
;; Define the typedef "IntPtr".
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 22, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([7 x 8]* %str1, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 1,
- uint 0,
- uint 0,
- uint 0,
- { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*) }, section "llvm.metadata"
-%str1 = internal constant [7 x 8] c"IntPtr\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524310, ;; Tag
+ metadata !1, ;; Context
+ metadata !"IntPtr", ;; Name
+ metadata !3, ;; File
+ i32 0, ;; Line number
+ i64 0, ;; Size in bits
+ i64 0, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !4 ;; Derived From type
+}
;;
;; Define the pointer type.
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 15, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* null,
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) }, section "llvm.metadata"
-
+!4 = metadata !{
+ i32 524303, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 64, ;; Size in bits
+ i64 64, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
;;
;; Define the const type.
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 38, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* null,
- { }* null,
- int 0,
- uint 0,
- uint 0,
- uint 0,
- { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype1</a> to { }*) }, section "llvm.metadata"
-
+!5 = metadata !{
+ i32 524326, ;; Tag
+ metadata !1, ;; Context
+ metadata !"", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !6 ;; Derived From type
+}
;;
;; Define the int type.
;;
-%<a href="#format_basic_type">llvm.dbg.basictype1</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- 8* getelementptr ([4 x 8]* %str2, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 5 }, section "llvm.metadata"
-%str2 = internal constant [4 x 8] c"int\00", section "llvm.metadata"
+!6 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"int", ;; Name
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ 5 ;; Encoding
+}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_composite_types">C/C++ struct/union types</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given the following as an example of C/C++ struct type:</p>
;;
;; Define basic type for unsigned int.
;;
-%<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
- uint add(uint 36, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([13 x i8]* %str1, int 0, int 0),
- { }* null,
- int 0,
- uint 32,
- uint 32,
- uint 0,
- uint 7 }, section "llvm.metadata"
-%str1 = internal constant [13 x i8] c"unsigned int\00", section "llvm.metadata"
-
+!5 = metadata !{
+ i32 524324, ;; Tag
+ metadata !1, ;; Context
+ metadata !"unsigned int",
+ metadata !1, ;; File
+ i32 0, ;; Line number
+ i64 32, ;; Size in Bits
+ i64 32, ;; Align in Bits
+ i64 0, ;; Offset in Bits
+ i32 0, ;; Flags
+ i32 7 ;; Encoding
+}
;;
;; Define composite type for struct Color.
;;
-%<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> {
- uint add(uint 19, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([6 x i8]* %str2, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 1,
- uint 96,
- uint 32,
- uint 0,
- { }* null,
- { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata"
-%str2 = internal constant [6 x i8] c"Color\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524307, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Color", ;; Name
+ metadata !1, ;; Compile unit
+ i32 1, ;; Line number
+ i64 96, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime Language
+}
;;
;; Define the Red field.
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 13, uint 262144),
- { }* null,
- i8* getelementptr ([4 x i8]* %str3, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 2,
- uint 32,
- uint 32,
- uint 0,
- { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
-%str3 = internal constant [4 x i8] c"Red\00", section "llvm.metadata"
+!4 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Red", ;; Name
+ metadata !1, ;; File
+ i32 2, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
;;
;; Define the Green field.
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 13, uint 262144),
- { }* null,
- i8* getelementptr ([6 x i8]* %str4, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 3,
- uint 32,
- uint 32,
- uint 32,
- { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
-%str4 = internal constant [6 x i8] c"Green\00", section "llvm.metadata"
+!6 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Green", ;; Name
+ metadata !1, ;; File
+ i32 3, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 32, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
;;
;; Define the Blue field.
;;
-%<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
- uint add(uint 13, uint 262144),
- { }* null,
- i8* getelementptr ([5 x i8]* %str5, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 4,
- uint 32,
- uint 32,
- uint 64,
- { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
-%str5 = internal constant [5 x 8] c"Blue\00", section "llvm.metadata"
+!7 = metadata !{
+ i32 524301, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Blue", ;; Name
+ metadata !1, ;; File
+ i32 4, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 64, ;; Offset in bits
+ i32 0, ;; Flags
+ metadata !5 ;; Derived From type
+}
;;
;; Define the array of fields used by the composite type Color.
;;
-%llvm.dbg.array = internal constant [3 x { }*] [
- { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype1</a> to { }*),
- { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*),
- { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) ], section "llvm.metadata"
+!3 = metadata !{metadata !4, metadata !6, metadata !7}
</pre>
</div>
</div>
<!-- ======================================================================= -->
-<div class="doc_subsection">
+<h3>
<a name="ccxx_enumeration_types">C/C++ enumeration types</a>
-</div>
+</h3>
-<div class="doc_text">
+<div>
<p>Given the following as an example of C/C++ enumeration type:</p>
;;
;; Define composite type for enum Trees
;;
-%<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> {
- uint add(uint 4, uint 262144),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- i8* getelementptr ([6 x i8]* %str1, int 0, int 0),
- { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
- int 1,
- uint 32,
- uint 32,
- uint 0,
- { }* null,
- { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata"
-%str1 = internal constant [6 x i8] c"Trees\00", section "llvm.metadata"
+!2 = metadata !{
+ i32 524292, ;; Tag
+ metadata !1, ;; Context
+ metadata !"Trees", ;; Name
+ metadata !1, ;; File
+ i32 1, ;; Line number
+ i64 32, ;; Size in bits
+ i64 32, ;; Align in bits
+ i64 0, ;; Offset in bits
+ i32 0, ;; Flags
+ null, ;; Derived From type
+ metadata !3, ;; Elements
+ i32 0 ;; Runtime language
+}
+
+;;
+;; Define the array of enumerators used by composite type Trees.
+;;
+!3 = metadata !{metadata !4, metadata !5, metadata !6}
;;
;; Define Spruce enumerator.
;;
-%<a href="#format_enumeration">llvm.dbg.enumerator1</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
- uint add(uint 40, uint 262144),
- i8* getelementptr ([7 x i8]* %str2, int 0, int 0),
- int 100 }, section "llvm.metadata"
-%str2 = internal constant [7 x i8] c"Spruce\00", section "llvm.metadata"
+!4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
;;
;; Define Oak enumerator.
;;
-%<a href="#format_enumeration">llvm.dbg.enumerator2</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
- uint add(uint 40, uint 262144),
- i8* getelementptr ([4 x i8]* %str3, int 0, int 0),
- int 200 }, section "llvm.metadata"
-%str3 = internal constant [4 x i8] c"Oak\00", section "llvm.metadata"
+!5 = metadata !{i32 524328, metadata !"Oak", i64 200}
;;
;; Define Maple enumerator.
;;
-%<a href="#format_enumeration">llvm.dbg.enumerator3</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
- uint add(uint 40, uint 262144),
- i8* getelementptr ([6 x i8]* %str4, int 0, int 0),
- int 300 }, section "llvm.metadata"
-%str4 = internal constant [6 x i8] c"Maple\00", section "llvm.metadata"
+!6 = metadata !{i32 524328, metadata !"Maple", i64 300}
-;;
-;; Define the array of enumerators used by composite type Trees.
-;;
-%llvm.dbg.array = internal constant [3 x { }*] [
- { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator1</a> to { }*),
- { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator2</a> to { }*),
- { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator3</a> to { }*) ], section "llvm.metadata"
</pre>
</div>
</div>
+</div>
+
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="llvmdwarfextension">Debugging information format</a>
+</h2>
+<!-- *********************************************************************** -->
+<div>
+<!-- ======================================================================= -->
+<h3>
+ <a name="objcproperty">Debugging Information Extension for Objective C Properties</a>
+</h3>
+<div>
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertyintroduction">Introduction</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<p>Objective C provides a simpler way to declare and define accessor methods
+using declared properties. The language provides features to declare a
+property and to let compiler synthesize accessor methods.
+</p>
+
+<p>The debugger lets developer inspect Objective C interfaces and their
+instance variables and class variables. However, the debugger does not know
+anything about the properties defined in Objective C interfaces. The debugger
+consumes information generated by compiler in DWARF format. The format does
+not support encoding of Objective C properties. This proposal describes DWARF
+extensions to encode Objective C properties, which the debugger can use to let
+developers inspect Objective C properties.
+</p>
+
+</div>
+
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertyproposal">Proposal</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<p>Objective C properties exist separately from class members. A property
+can be defined only by "setter" and "getter" selectors, and
+be calculated anew on each access. Or a property can just be a direct access
+to some declared ivar. Finally it can have an ivar "automatically
+synthesized" for it by the compiler, in which case the property can be
+referred to in user code directly using the standard C dereference syntax as
+well as through the property "dot" syntax, but there is no entry in
+the @interface declaration corresponding to this ivar.
+</p>
+<p>
+To facilitate debugging, these properties we will add a new DWARF TAG into the
+DW_TAG_structure_type definition for the class to hold the description of a
+given property, and a set of DWARF attributes that provide said description.
+The property tag will also contain the name and declared type of the property.
+</p>
+<p>
+If there is a related ivar, there will also be a DWARF property attribute placed
+in the DW_TAG_member DIE for that ivar referring back to the property TAG for
+that property. And in the case where the compiler synthesizes the ivar directly,
+the compiler is expected to generate a DW_TAG_member for that ivar (with the
+DW_AT_artificial set to 1), whose name will be the name used to access this
+ivar directly in code, and with the property attribute pointing back to the
+property it is backing.
+</p>
+<p>
+The following examples will serve as illustration for our discussion:
+</p>
+
+<div class="doc_code">
+<pre>
+@interface I1 {
+ int n2;
+}
+
+@property int p1;
+@property int p2;
+@end
+
+@implementation I1
+@synthesize p1;
+@synthesize p2 = n2;
+@end
+</pre>
+</div>
+
+<p>
+This produces the following DWARF (this is a "pseudo dwarfdump" output):
+</p>
+<div class="doc_code">
+<pre>
+0x00000100: TAG_structure_type [7] *
+ AT_APPLE_runtime_class( 0x10 )
+ AT_name( "I1" )
+ AT_decl_file( "Objc_Property.m" )
+ AT_decl_line( 3 )
+
+0x00000110 TAG_APPLE_property
+ AT_name ( "p1" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000120: TAG_APPLE_property
+ AT_name ( "p2" )
+ AT_type ( {0x00000150} ( int ) )
+
+0x00000130: TAG_member [8]
+ AT_name( "_p1" )
+ AT_APPLE_property ( {0x00000110} "p1" )
+ AT_type( {0x00000150} ( int ) )
+ AT_artificial ( 0x1 )
+
+0x00000140: TAG_member [8]
+ AT_name( "n2" )
+ AT_APPLE_property ( {0x00000120} "p2" )
+ AT_type( {0x00000150} ( int ) )
+
+0x00000150: AT_type( ( int ) )
+</pre>
+</div>
+
+<p> Note, the current convention is that the name of the ivar for an
+auto-synthesized property is the name of the property from which it derives with
+an underscore prepended, as is shown in the example.
+But we actually don't need to know this convention, since we are given the name
+of the ivar directly.
+</p>
+
+<p>
+Also, it is common practice in ObjC to have different property declarations in
+the @interface and @implementation - e.g. to provide a read-only property in
+the interface,and a read-write interface in the implementation. In that case,
+the compiler should emit whichever property declaration will be in force in the
+current translation unit.
+</p>
+
+<p> Developers can decorate a property with attributes which are encoded using
+DW_AT_APPLE_property_attribute.
+</p>
+
+<div class="doc_code">
+<pre>
+@property (readonly, nonatomic) int pr;
+</pre>
+</div>
+<p>
+Which produces a property tag:
+<p>
+<div class="doc_code">
+<pre>
+TAG_APPLE_property [8]
+ AT_name( "pr" )
+ AT_type ( {0x00000147} (int) )
+ AT_APPLE_property_attribute (DW_APPLE_PROPERTY_readonly, DW_APPLE_PROPERTY_nonatomic)
+</pre>
+</div>
+
+<p> The setter and getter method names are attached to the property using
+DW_AT_APPLE_property_setter and DW_AT_APPLE_property_getter attributes.
+</p>
+<div class="doc_code">
+<pre>
+@interface I1
+@property (setter=myOwnP3Setter:) int p3;
+-(void)myOwnP3Setter:(int)a;
+@end
+
+@implementation I1
+@synthesize p3;
+-(void)myOwnP3Setter:(int)a{ }
+@end
+</pre>
+</div>
+
+<p>
+The DWARF for this would be:
+</p>
+<div class="doc_code">
+<pre>
+0x000003bd: TAG_structure_type [7] *
+ AT_APPLE_runtime_class( 0x10 )
+ AT_name( "I1" )
+ AT_decl_file( "Objc_Property.m" )
+ AT_decl_line( 3 )
+
+0x000003cd TAG_APPLE_property
+ AT_name ( "p3" )
+ AT_APPLE_property_setter ( "myOwnP3Setter:" )
+ AT_type( {0x00000147} ( int ) )
+
+0x000003f3: TAG_member [8]
+ AT_name( "_p3" )
+ AT_type ( {0x00000147} ( int ) )
+ AT_APPLE_property ( {0x000003cd} )
+ AT_artificial ( 0x1 )
+</pre>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewtags">New DWARF Tags</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>TAG</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td>DW_TAG_APPLE_property</td>
+ <td>0x4200</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewattributes">New DWARF Attributes</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>Attribute</th>
+ <th>Value</th>
+ <th>Classes</th>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property</td>
+ <td>0x3fed</td>
+ <td>Reference</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_getter</td>
+ <td>0x3fe9</td>
+ <td>String</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_setter</td>
+ <td>0x3fea</td>
+ <td>String</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_property_attribute</td>
+ <td>0x3feb</td>
+ <td>Constant</td>
+ </tr>
+</table>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h4>
+ <a name="objcpropertynewconstants">New DWARF Constants</a>
+</h4>
+<!-- *********************************************************************** -->
+
+<div>
+<table border="1" cellspacing="0">
+ <col width="200">
+ <col width="200">
+ <tr>
+ <th>Name</th>
+ <th>Value</th>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_readonly</td>
+ <td>0x1</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_readwrite</td>
+ <td>0x2</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_assign</td>
+ <td>0x4</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_retain</td>
+ <td>0x8</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_copy</td>
+ <td>0x10</td>
+ </tr>
+ <tr>
+ <td>DW_AT_APPLE_PROPERTY_nonatomic</td>
+ <td>0x20</td>
+ </tr>
+</table>
+
+</div>
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="acceltable">Name Accelerator Tables</a>
+</h3>
+<!-- ======================================================================= -->
+<div>
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltableintroduction">Introduction</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>The .debug_pubnames and .debug_pubtypes formats are not what a debugger
+ needs. The "pub" in the section name indicates that the entries in the
+ table are publicly visible names only. This means no static or hidden
+ functions show up in the .debug_pubnames. No static variables or private class
+ variables are in the .debug_pubtypes. Many compilers add different things to
+ these tables, so we can't rely upon the contents between gcc, icc, or clang.</p>
+
+<p>The typical query given by users tends not to match up with the contents of
+ these tables. For example, the DWARF spec states that "In the case of the
+ name of a function member or static data member of a C++ structure, class or
+ union, the name presented in the .debug_pubnames section is not the simple
+ name given by the DW_AT_name attribute of the referenced debugging information
+ entry, but rather the fully qualified name of the data or function member."
+ So the only names in these tables for complex C++ entries is a fully
+ qualified name. Debugger users tend not to enter their search strings as
+ "a::b::c(int,const Foo&) const", but rather as "c", "b::c" , or "a::b::c". So
+ the name entered in the name table must be demangled in order to chop it up
+ appropriately and additional names must be manually entered into the table
+ to make it effective as a name lookup table for debuggers to use.</p>
+
+<p>All debuggers currently ignore the .debug_pubnames table as a result of
+ its inconsistent and useless public-only name content making it a waste of
+ space in the object file. These tables, when they are written to disk, are
+ not sorted in any way, leaving every debugger to do its own parsing
+ and sorting. These tables also include an inlined copy of the string values
+ in the table itself making the tables much larger than they need to be on
+ disk, especially for large C++ programs.</p>
+
+<p>Can't we just fix the sections by adding all of the names we need to this
+ table? No, because that is not what the tables are defined to contain and we
+ won't know the difference between the old bad tables and the new good tables.
+ At best we could make our own renamed sections that contain all of the data
+ we need.</p>
+
+<p>These tables are also insufficient for what a debugger like LLDB needs.
+ LLDB uses clang for its expression parsing where LLDB acts as a PCH. LLDB is
+ then often asked to look for type "foo" or namespace "bar", or list items in
+ namespace "baz". Namespaces are not included in the pubnames or pubtypes
+ tables. Since clang asks a lot of questions when it is parsing an expression,
+ we need to be very fast when looking up names, as it happens a lot. Having new
+ accelerator tables that are optimized for very quick lookups will benefit
+ this type of debugging experience greatly.</p>
+
+<p>We would like to generate name lookup tables that can be mapped into
+ memory from disk, and used as is, with little or no up-front parsing. We would
+ also be able to control the exact content of these different tables so they
+ contain exactly what we need. The Name Accelerator Tables were designed
+ to fix these issues. In order to solve these issues we need to:</p>
+
+<ul>
+ <li>Have a format that can be mapped into memory from disk and used as is</li>
+ <li>Lookups should be very fast</li>
+ <li>Extensible table format so these tables can be made by many producers</li>
+ <li>Contain all of the names needed for typical lookups out of the box</li>
+ <li>Strict rules for the contents of tables</li>
+</ul>
+
+<p>Table size is important and the accelerator table format should allow the
+ reuse of strings from common string tables so the strings for the names are
+ not duplicated. We also want to make sure the table is ready to be used as-is
+ by simply mapping the table into memory with minimal header parsing.</p>
+
+<p>The name lookups need to be fast and optimized for the kinds of lookups
+ that debuggers tend to do. Optimally we would like to touch as few parts of
+ the mapped table as possible when doing a name lookup and be able to quickly
+ find the name entry we are looking for, or discover there are no matches. In
+ the case of debuggers we optimized for lookups that fail most of the time.</p>
+
+<p>Each table that is defined should have strict rules on exactly what is in
+ the accelerator tables and documented so clients can rely on the content.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltablehashes">Hash Tables</a>
+</h4>
+<!-- ======================================================================= -->
+
+<div>
+<h5>Standard Hash Tables</h5>
+
+<p>Typical hash tables have a header, buckets, and each bucket points to the
+bucket contents:
+</p>
+
+<div class="doc_code">
+<pre>
+.------------.
+| HEADER |
+|------------|
+| BUCKETS |
+|------------|
+| DATA |
+`------------'
+</pre>
+</div>
+
+<p>The BUCKETS are an array of offsets to DATA for each hash:</p>
+
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001000 | BUCKETS[0]
+| 0x00002000 | BUCKETS[1]
+| 0x00002200 | BUCKETS[2]
+| 0x000034f0 | BUCKETS[3]
+| | ...
+| 0xXXXXXXXX | BUCKETS[n_buckets]
+'------------'
+</pre>
+</div>
+
+<p>So for bucket[3] in the example above, we have an offset into the table
+ 0x000034f0 which points to a chain of entries for the bucket. Each bucket
+ must contain a next pointer, full 32 bit hash value, the string itself,
+ and the data for the current string value.</p>
+
+<div class="doc_code">
+<pre>
+ .------------.
+0x000034f0: | 0x00003500 | next pointer
+ | 0x12345678 | 32 bit hash
+ | "erase" | string value
+ | data[n] | HashData for this bucket
+ |------------|
+0x00003500: | 0x00003550 | next pointer
+ | 0x29273623 | 32 bit hash
+ | "dump" | string value
+ | data[n] | HashData for this bucket
+ |------------|
+0x00003550: | 0x00000000 | next pointer
+ | 0x82638293 | 32 bit hash
+ | "main" | string value
+ | data[n] | HashData for this bucket
+ `------------'
+</pre>
+</div>
+
+<p>The problem with this layout for debuggers is that we need to optimize for
+ the negative lookup case where the symbol we're searching for is not present.
+ So if we were to lookup "printf" in the table above, we would make a 32 hash
+ for "printf", it might match bucket[3]. We would need to go to the offset
+ 0x000034f0 and start looking to see if our 32 bit hash matches. To do so, we
+ need to read the next pointer, then read the hash, compare it, and skip to
+ the next bucket. Each time we are skipping many bytes in memory and touching
+ new cache pages just to do the compare on the full 32 bit hash. All of these
+ accesses then tell us that we didn't have a match.</p>
+
+<h5>Name Hash Tables</h5>
+
+<p>To solve the issues mentioned above we have structured the hash tables
+ a bit differently: a header, buckets, an array of all unique 32 bit hash
+ values, followed by an array of hash value data offsets, one for each hash
+ value, then the data for all hash values:</p>
+
+<div class="doc_code">
+<pre>
+.-------------.
+| HEADER |
+|-------------|
+| BUCKETS |
+|-------------|
+| HASHES |
+|-------------|
+| OFFSETS |
+|-------------|
+| DATA |
+`-------------'
+</pre>
+</div>
+
+<p>The BUCKETS in the name tables are an index into the HASHES array. By
+ making all of the full 32 bit hash values contiguous in memory, we allow
+ ourselves to efficiently check for a match while touching as little
+ memory as possible. Most often checking the 32 bit hash values is as far as
+ the lookup goes. If it does match, it usually is a match with no collisions.
+ So for a table with "n_buckets" buckets, and "n_hashes" unique 32 bit hash
+ values, we can clarify the contents of the BUCKETS, HASHES and OFFSETS as:</p>
+
+<div class="doc_code">
+<pre>
+.-------------------------.
+| HEADER.magic | uint32_t
+| HEADER.version | uint16_t
+| HEADER.hash_function | uint16_t
+| HEADER.bucket_count | uint32_t
+| HEADER.hashes_count | uint32_t
+| HEADER.header_data_len | uint32_t
+| HEADER_DATA | HeaderData
+|-------------------------|
+| BUCKETS | uint32_t[n_buckets] // 32 bit hash indexes
+|-------------------------|
+| HASHES | uint32_t[n_buckets] // 32 bit hash values
+|-------------------------|
+| OFFSETS | uint32_t[n_buckets] // 32 bit offsets to hash value data
+|-------------------------|
+| ALL HASH DATA |
+`-------------------------'
+</pre>
+</div>
+
+<p>So taking the exact same data from the standard hash example above we end up
+ with:</p>
+
+<div class="doc_code">
+<pre>
+ .------------.
+ | HEADER |
+ |------------|
+ | 0 | BUCKETS[0]
+ | 2 | BUCKETS[1]
+ | 5 | BUCKETS[2]
+ | 6 | BUCKETS[3]
+ | | ...
+ | ... | BUCKETS[n_buckets]
+ |------------|
+ | 0x........ | HASHES[0]
+ | 0x........ | HASHES[1]
+ | 0x........ | HASHES[2]
+ | 0x........ | HASHES[3]
+ | 0x........ | HASHES[4]
+ | 0x........ | HASHES[5]
+ | 0x12345678 | HASHES[6] hash for BUCKETS[3]
+ | 0x29273623 | HASHES[7] hash for BUCKETS[3]
+ | 0x82638293 | HASHES[8] hash for BUCKETS[3]
+ | 0x........ | HASHES[9]
+ | 0x........ | HASHES[10]
+ | 0x........ | HASHES[11]
+ | 0x........ | HASHES[12]
+ | 0x........ | HASHES[13]
+ | 0x........ | HASHES[n_hashes]
+ |------------|
+ | 0x........ | OFFSETS[0]
+ | 0x........ | OFFSETS[1]
+ | 0x........ | OFFSETS[2]
+ | 0x........ | OFFSETS[3]
+ | 0x........ | OFFSETS[4]
+ | 0x........ | OFFSETS[5]
+ | 0x000034f0 | OFFSETS[6] offset for BUCKETS[3]
+ | 0x00003500 | OFFSETS[7] offset for BUCKETS[3]
+ | 0x00003550 | OFFSETS[8] offset for BUCKETS[3]
+ | 0x........ | OFFSETS[9]
+ | 0x........ | OFFSETS[10]
+ | 0x........ | OFFSETS[11]
+ | 0x........ | OFFSETS[12]
+ | 0x........ | OFFSETS[13]
+ | 0x........ | OFFSETS[n_hashes]
+ |------------|
+ | |
+ | |
+ | |
+ | |
+ | |
+ |------------|
+0x000034f0: | 0x00001203 | .debug_str ("erase")
+ | 0x00000004 | A 32 bit array count - number of HashData with name "erase"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x........ | HashData[3]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ |------------|
+0x00003500: | 0x00001203 | String offset into .debug_str ("collision")
+ | 0x00000002 | A 32 bit array count - number of HashData with name "collision"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x00001203 | String offset into .debug_str ("dump")
+ | 0x00000003 | A 32 bit array count - number of HashData with name "dump"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ |------------|
+0x00003550: | 0x00001203 | String offset into .debug_str ("main")
+ | 0x00000009 | A 32 bit array count - number of HashData with name "main"
+ | 0x........ | HashData[0]
+ | 0x........ | HashData[1]
+ | 0x........ | HashData[2]
+ | 0x........ | HashData[3]
+ | 0x........ | HashData[4]
+ | 0x........ | HashData[5]
+ | 0x........ | HashData[6]
+ | 0x........ | HashData[7]
+ | 0x........ | HashData[8]
+ | 0x00000000 | String offset into .debug_str (terminate data for hash)
+ `------------'
+</pre>
+</div>
+
+<p>So we still have all of the same data, we just organize it more efficiently
+ for debugger lookup. If we repeat the same "printf" lookup from above, we
+ would hash "printf" and find it matches BUCKETS[3] by taking the 32 bit hash
+ value and modulo it by n_buckets. BUCKETS[3] contains "6" which is the index
+ into the HASHES table. We would then compare any consecutive 32 bit hashes
+ values in the HASHES array as long as the hashes would be in BUCKETS[3]. We
+ do this by verifying that each subsequent hash value modulo n_buckets is still
+ 3. In the case of a failed lookup we would access the memory for BUCKETS[3], and
+ then compare a few consecutive 32 bit hashes before we know that we have no match.
+ We don't end up marching through multiple words of memory and we really keep the
+ number of processor data cache lines being accessed as small as possible.</p>
+
+<p>The string hash that is used for these lookup tables is the Daniel J.
+ Bernstein hash which is also used in the ELF GNU_HASH sections. It is a very
+ good hash for all kinds of names in programs with very few hash collisions.</p>
+
+<p>Empty buckets are designated by using an invalid hash index of UINT32_MAX.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltabledetails">Details</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>These name hash tables are designed to be generic where specializations of
+ the table get to define additional data that goes into the header
+ ("HeaderData"), how the string value is stored ("KeyType") and the content
+ of the data for each hash value.</p>
+
+<h5>Header Layout</h5>
+<p>The header has a fixed part, and the specialized part. The exact format of
+ the header is:</p>
+<div class="doc_code">
+<pre>
+struct Header
+{
+ uint32_t magic; // 'HASH' magic value to allow endian detection
+ uint16_t version; // Version number
+ uint16_t hash_function; // The hash function enumeration that was used
+ uint32_t bucket_count; // The number of buckets in this hash table
+ uint32_t hashes_count; // The total number of unique hash values and hash data offsets in this table
+ uint32_t header_data_len; // The bytes to skip to get to the hash indexes (buckets) for correct alignment
+ // Specifically the length of the following HeaderData field - this does not
+ // include the size of the preceding fields
+ HeaderData header_data; // Implementation specific header data
+};
+</pre>
+</div>
+<p>The header starts with a 32 bit "magic" value which must be 'HASH' encoded as
+ an ASCII integer. This allows the detection of the start of the hash table and
+ also allows the table's byte order to be determined so the table can be
+ correctly extracted. The "magic" value is followed by a 16 bit version number
+ which allows the table to be revised and modified in the future. The current
+ version number is 1. "hash_function" is a uint16_t enumeration that specifies
+ which hash function was used to produce this table. The current values for the
+ hash function enumerations include:</p>
+<div class="doc_code">
+<pre>
+enum HashFunctionType
+{
+ eHashFunctionDJB = 0u, // Daniel J Bernstein hash function
+};
+</pre>
+</div>
+<p>"bucket_count" is a 32 bit unsigned integer that represents how many buckets
+ are in the BUCKETS array. "hashes_count" is the number of unique 32 bit hash
+ values that are in the HASHES array, and is the same number of offsets are
+ contained in the OFFSETS array. "header_data_len" specifies the size in
+ bytes of the HeaderData that is filled in by specialized versions of this
+ table.</p>
+
+<h5>Fixed Lookup</h5>
+<p>The header is followed by the buckets, hashes, offsets, and hash value
+ data.
+<div class="doc_code">
+<pre>
+struct FixedTable
+{
+ uint32_t buckets[Header.bucket_count]; // An array of hash indexes into the "hashes[]" array below
+ uint32_t hashes [Header.hashes_count]; // Every unique 32 bit hash for the entire table is in this table
+ uint32_t offsets[Header.hashes_count]; // An offset that corresponds to each item in the "hashes[]" array above
+};
+</pre>
+</div>
+<p>"buckets" is an array of 32 bit indexes into the "hashes" array. The
+ "hashes" array contains all of the 32 bit hash values for all names in the
+ hash table. Each hash in the "hashes" table has an offset in the "offsets"
+ array that points to the data for the hash value.</p>
+
+<p>This table setup makes it very easy to repurpose these tables to contain
+ different data, while keeping the lookup mechanism the same for all tables.
+ This layout also makes it possible to save the table to disk and map it in
+ later and do very efficient name lookups with little or no parsing.</p>
+
+<p>DWARF lookup tables can be implemented in a variety of ways and can store
+ a lot of information for each name. We want to make the DWARF tables
+ extensible and able to store the data efficiently so we have used some of the
+ DWARF features that enable efficient data storage to define exactly what kind
+ of data we store for each name.</p>
+
+<p>The "HeaderData" contains a definition of the contents of each HashData
+ chunk. We might want to store an offset to all of the debug information
+ entries (DIEs) for each name. To keep things extensible, we create a list of
+ items, or Atoms, that are contained in the data for each name. First comes the
+ type of the data in each atom:</p>
+<div class="doc_code">
+<pre>
+enum AtomType
+{
+ eAtomTypeNULL = 0u,
+ eAtomTypeDIEOffset = 1u, // DIE offset, check form for encoding
+ eAtomTypeCUOffset = 2u, // DIE offset of the compiler unit header that contains the item in question
+ eAtomTypeTag = 3u, // DW_TAG_xxx value, should be encoded as DW_FORM_data1 (if no tags exceed 255) or DW_FORM_data2
+ eAtomTypeNameFlags = 4u, // Flags from enum NameFlags
+ eAtomTypeTypeFlags = 5u, // Flags from enum TypeFlags
+};
+</pre>
+</div>
+<p>The enumeration values and their meanings are:</p>
+<div class="doc_code">
+<pre>
+ eAtomTypeNULL - a termination atom that specifies the end of the atom list
+ eAtomTypeDIEOffset - an offset into the .debug_info section for the DWARF DIE for this name
+ eAtomTypeCUOffset - an offset into the .debug_info section for the CU that contains the DIE
+ eAtomTypeDIETag - The DW_TAG_XXX enumeration value so you don't have to parse the DWARF to see what it is
+ eAtomTypeNameFlags - Flags for functions and global variables (isFunction, isInlined, isExternal...)
+ eAtomTypeTypeFlags - Flags for types (isCXXClass, isObjCClass, ...)
+</pre>
+</div>
+<p>Then we allow each atom type to define the atom type and how the data for
+ each atom type data is encoded:</p>
+<div class="doc_code">
+<pre>
+struct Atom
+{
+ uint16_t type; // AtomType enum value
+ uint16_t form; // DWARF DW_FORM_XXX defines
+};
+</pre>
+</div>
+<p>The "form" type above is from the DWARF specification and defines the
+ exact encoding of the data for the Atom type. See the DWARF specification for
+ the DW_FORM_ definitions.</p>
+<div class="doc_code">
+<pre>
+struct HeaderData
+{
+ uint32_t die_offset_base;
+ uint32_t atom_count;
+ Atoms atoms[atom_count0];
+};
+</pre>
+</div>
+<p>"HeaderData" defines the base DIE offset that should be added to any atoms
+ that are encoded using the DW_FORM_ref1, DW_FORM_ref2, DW_FORM_ref4,
+ DW_FORM_ref8 or DW_FORM_ref_udata. It also defines what is contained in
+ each "HashData" object -- Atom.form tells us how large each field will be in
+ the HashData and the Atom.type tells us how this data should be interpreted.</p>
+
+<p>For the current implementations of the ".apple_names" (all functions + globals),
+ the ".apple_types" (names of all types that are defined), and the
+ ".apple_namespaces" (all namespaces), we currently set the Atom array to be:</p>
+<div class="doc_code">
+<pre>
+HeaderData.atom_count = 1;
+HeaderData.atoms[0].type = eAtomTypeDIEOffset;
+HeaderData.atoms[0].form = DW_FORM_data4;
+</pre>
+</div>
+<p>This defines the contents to be the DIE offset (eAtomTypeDIEOffset) that is
+ encoded as a 32 bit value (DW_FORM_data4). This allows a single name to have
+ multiple matching DIEs in a single file, which could come up with an inlined
+ function for instance. Future tables could include more information about the
+ DIE such as flags indicating if the DIE is a function, method, block,
+ or inlined.</p>
+
+<p>The KeyType for the DWARF table is a 32 bit string table offset into the
+ ".debug_str" table. The ".debug_str" is the string table for the DWARF which
+ may already contain copies of all of the strings. This helps make sure, with
+ help from the compiler, that we reuse the strings between all of the DWARF
+ sections and keeps the hash table size down. Another benefit to having the
+ compiler generate all strings as DW_FORM_strp in the debug info, is that
+ DWARF parsing can be made much faster.</p>
+
+<p>After a lookup is made, we get an offset into the hash data. The hash data
+ needs to be able to deal with 32 bit hash collisions, so the chunk of data
+ at the offset in the hash data consists of a triple:</p>
+<div class="doc_code">
+<pre>
+uint32_t str_offset
+uint32_t hash_data_count
+HashData[hash_data_count]
+</pre>
+</div>
+<p>If "str_offset" is zero, then the bucket contents are done. 99.9% of the
+ hash data chunks contain a single item (no 32 bit hash collision):</p>
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001023 | uint32_t KeyType (.debug_str[0x0001023] => "main")
+| 0x00000004 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x........ | uint32_t HashData[2] DIE offset
+| 0x........ | uint32_t HashData[3] DIE offset
+| 0x00000000 | uint32_t KeyType (end of hash chain)
+`------------'
+</pre>
+</div>
+<p>If there are collisions, you will have multiple valid string offsets:</p>
+<div class="doc_code">
+<pre>
+.------------.
+| 0x00001023 | uint32_t KeyType (.debug_str[0x0001023] => "main")
+| 0x00000004 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x........ | uint32_t HashData[2] DIE offset
+| 0x........ | uint32_t HashData[3] DIE offset
+| 0x00002023 | uint32_t KeyType (.debug_str[0x0002023] => "print")
+| 0x00000002 | uint32_t HashData count
+| 0x........ | uint32_t HashData[0] DIE offset
+| 0x........ | uint32_t HashData[1] DIE offset
+| 0x00000000 | uint32_t KeyType (end of hash chain)
+`------------'
+</pre>
+</div>
+<p>Current testing with real world C++ binaries has shown that there is around 1
+ 32 bit hash collision per 100,000 name entries.</p>
+</div>
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltablecontents">Contents</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<p>As we said, we want to strictly define exactly what is included in the
+ different tables. For DWARF, we have 3 tables: ".apple_names", ".apple_types",
+ and ".apple_namespaces".</p>
+
+<p>".apple_names" sections should contain an entry for each DWARF DIE whose
+ DW_TAG is a DW_TAG_label, DW_TAG_inlined_subroutine, or DW_TAG_subprogram that
+ has address attributes: DW_AT_low_pc, DW_AT_high_pc, DW_AT_ranges or
+ DW_AT_entry_pc. It also contains DW_TAG_variable DIEs that have a DW_OP_addr
+ in the location (global and static variables). All global and static variables
+ should be included, including those scoped withing functions and classes. For
+ example using the following code:</p>
+<div class="doc_code">
+<pre>
+static int var = 0;
+
+void f ()
+{
+ static int var = 0;
+}
+</pre>
+</div>
+<p>Both of the static "var" variables would be included in the table. All
+ functions should emit both their full names and their basenames. For C or C++,
+ the full name is the mangled name (if available) which is usually in the
+ DW_AT_MIPS_linkage_name attribute, and the DW_AT_name contains the function
+ basename. If global or static variables have a mangled name in a
+ DW_AT_MIPS_linkage_name attribute, this should be emitted along with the
+ simple name found in the DW_AT_name attribute.</p>
+
+<p>".apple_types" sections should contain an entry for each DWARF DIE whose
+ tag is one of:</p>
+<ul>
+ <li>DW_TAG_array_type</li>
+ <li>DW_TAG_class_type</li>
+ <li>DW_TAG_enumeration_type</li>
+ <li>DW_TAG_pointer_type</li>
+ <li>DW_TAG_reference_type</li>
+ <li>DW_TAG_string_type</li>
+ <li>DW_TAG_structure_type</li>
+ <li>DW_TAG_subroutine_type</li>
+ <li>DW_TAG_typedef</li>
+ <li>DW_TAG_union_type</li>
+ <li>DW_TAG_ptr_to_member_type</li>
+ <li>DW_TAG_set_type</li>
+ <li>DW_TAG_subrange_type</li>
+ <li>DW_TAG_base_type</li>
+ <li>DW_TAG_const_type</li>
+ <li>DW_TAG_constant</li>
+ <li>DW_TAG_file_type</li>
+ <li>DW_TAG_namelist</li>
+ <li>DW_TAG_packed_type</li>
+ <li>DW_TAG_volatile_type</li>
+ <li>DW_TAG_restrict_type</li>
+ <li>DW_TAG_interface_type</li>
+ <li>DW_TAG_unspecified_type</li>
+ <li>DW_TAG_shared_type</li>
+</ul>
+<p>Only entries with a DW_AT_name attribute are included, and the entry must
+ not be a forward declaration (DW_AT_declaration attribute with a non-zero value).
+ For example, using the following code:</p>
+<div class="doc_code">
+<pre>
+int main ()
+{
+ int *b = 0;
+ return *b;
+}
+</pre>
+</div>
+<p>We get a few type DIEs:</p>
+<div class="doc_code">
+<pre>
+0x00000067: TAG_base_type [5]
+ AT_encoding( DW_ATE_signed )
+ AT_name( "int" )
+ AT_byte_size( 0x04 )
+
+0x0000006e: TAG_pointer_type [6]
+ AT_type( {0x00000067} ( int ) )
+ AT_byte_size( 0x08 )
+</pre>
+</div>
+<p>The DW_TAG_pointer_type is not included because it does not have a DW_AT_name.</p>
+
+<p>".apple_namespaces" section should contain all DW_TAG_namespace DIEs. If
+ we run into a namespace that has no name this is an anonymous namespace,
+ and the name should be output as "(anonymous namespace)" (without the quotes).
+ Why? This matches the output of the abi::cxa_demangle() that is in the standard
+ C++ library that demangles mangled names.</p>
+</div>
+
+<!-- ======================================================================= -->
+<h4>
+ <a name="acceltableextensions">Language Extensions and File Format Changes</a>
+</h4>
+<!-- ======================================================================= -->
+<div>
+<h5>Objective-C Extensions</h5>
+<p>".apple_objc" section should contain all DW_TAG_subprogram DIEs for an
+ Objective-C class. The name used in the hash table is the name of the
+ Objective-C class itself. If the Objective-C class has a category, then an
+ entry is made for both the class name without the category, and for the class
+ name with the category. So if we have a DIE at offset 0x1234 with a name
+ of method "-[NSString(my_additions) stringWithSpecialString:]", we would add
+ an entry for "NSString" that points to DIE 0x1234, and an entry for
+ "NSString(my_additions)" that points to 0x1234. This allows us to quickly
+ track down all Objective-C methods for an Objective-C class when doing
+ expressions. It is needed because of the dynamic nature of Objective-C where
+ anyone can add methods to a class. The DWARF for Objective-C methods is also
+ emitted differently from C++ classes where the methods are not usually
+ contained in the class definition, they are scattered about across one or more
+ compile units. Categories can also be defined in different shared libraries.
+ So we need to be able to quickly find all of the methods and class functions
+ given the Objective-C class name, or quickly find all methods and class
+ functions for a class + category name. This table does not contain any selector
+ names, it just maps Objective-C class names (or class names + category) to all
+ of the methods and class functions. The selectors are added as function
+ basenames in the .debug_names section.</p>
+
+<p>In the ".apple_names" section for Objective-C functions, the full name is the
+ entire function name with the brackets ("-[NSString stringWithCString:]") and the
+ basename is the selector only ("stringWithCString:").</p>
+
+<h5>Mach-O Changes</h5>
+<p>The sections names for the apple hash tables are for non mach-o files. For
+ mach-o files, the sections should be contained in the "__DWARF" segment with
+ names as follows:</p>
+<ul>
+ <li>".apple_names" -> "__apple_names"</li>
+ <li>".apple_types" -> "__apple_types"</li>
+ <li>".apple_namespaces" -> "__apple_namespac" (16 character limit)</li>
+ <li> ".apple_objc" -> "__apple_objc"</li>
+</ul>
+</div>
+</div>
+</div>
+
<!-- *********************************************************************** -->
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
+ <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br>
Last modified: $Date$
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