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11 <div class="doc_title">Source Level Debugging with LLVM</div>
13 <table class="layout" style="width:100%">
17 <li><a href="#introduction">Introduction</a>
19 <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
20 <li><a href="#consumers">Debug information consumers</a></li>
21 <li><a href="#debugopt">Debugging optimized code</a></li>
23 <li><a href="#format">Debugging information format</a>
25 <li><a href="#debug_info_descriptors">Debug information descriptors</a>
27 <li><a href="#format_compile_units">Compile unit descriptors</a></li>
28 <li><a href="#format_files">File descriptors</a></li>
29 <li><a href="#format_global_variables">Global variable descriptors</a></li>
30 <li><a href="#format_subprograms">Subprogram descriptors</a></li>
31 <li><a href="#format_blocks">Block descriptors</a></li>
32 <li><a href="#format_basic_type">Basic type descriptors</a></li>
33 <li><a href="#format_derived_type">Derived type descriptors</a></li>
34 <li><a href="#format_composite_type">Composite type descriptors</a></li>
35 <li><a href="#format_subrange">Subrange descriptors</a></li>
36 <li><a href="#format_enumeration">Enumerator descriptors</a></li>
37 <li><a href="#format_variables">Local variables</a></li>
39 <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
41 <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
42 <li><a href="#format_common_value">llvm.dbg.value</a></li>
45 <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
46 <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
48 <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
49 <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
50 <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
51 <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
52 <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
53 <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
54 <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
59 <img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
64 <div class="doc_author">
65 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
66 and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
70 <!-- *********************************************************************** -->
71 <div class="doc_section"><a name="introduction">Introduction</a></div>
72 <!-- *********************************************************************** -->
74 <div class="doc_text">
76 <p>This document is the central repository for all information pertaining to
77 debug information in LLVM. It describes the <a href="#format">actual format
78 that the LLVM debug information</a> takes, which is useful for those
79 interested in creating front-ends or dealing directly with the information.
80 Further, this document provides specific examples of what debug information
81 for C/C++ looks like.</p>
85 <!-- ======================================================================= -->
86 <div class="doc_subsection">
87 <a name="phil">Philosophy behind LLVM debugging information</a>
90 <div class="doc_text">
92 <p>The idea of the LLVM debugging information is to capture how the important
93 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
94 Several design aspects have shaped the solution that appears here. The
95 important ones are:</p>
98 <li>Debugging information should have very little impact on the rest of the
99 compiler. No transformations, analyses, or code generators should need to
100 be modified because of debugging information.</li>
102 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
103 easily described ways</a> with the debugging information.</li>
105 <li>Because LLVM is designed to support arbitrary programming languages,
106 LLVM-to-LLVM tools should not need to know anything about the semantics of
107 the source-level-language.</li>
109 <li>Source-level languages are often <b>widely</b> different from one another.
110 LLVM should not put any restrictions of the flavor of the source-language,
111 and the debugging information should work with any language.</li>
113 <li>With code generator support, it should be possible to use an LLVM compiler
114 to compile a program to native machine code and standard debugging
115 formats. This allows compatibility with traditional machine-code level
116 debuggers, like GDB or DBX.</li>
119 <p>The approach used by the LLVM implementation is to use a small set
120 of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
121 mapping between LLVM program objects and the source-level objects. The
122 description of the source-level program is maintained in LLVM metadata
123 in an <a href="#ccxx_frontend">implementation-defined format</a>
124 (the C/C++ front-end currently uses working draft 7 of
125 the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
128 <p>When a program is being debugged, a debugger interacts with the user and
129 turns the stored debug information into source-language specific information.
130 As such, a debugger must be aware of the source-language, and is thus tied to
131 a specific language or family of languages.</p>
135 <!-- ======================================================================= -->
136 <div class="doc_subsection">
137 <a name="consumers">Debug information consumers</a>
140 <div class="doc_text">
142 <p>The role of debug information is to provide meta information normally
143 stripped away during the compilation process. This meta information provides
144 an LLVM user a relationship between generated code and the original program
147 <p>Currently, debug information is consumed by DwarfDebug to produce dwarf
148 information used by the gdb debugger. Other targets could use the same
149 information to produce stabs or other debug forms.</p>
151 <p>It would also be reasonable to use debug information to feed profiling tools
152 for analysis of generated code, or, tools for reconstructing the original
153 source from generated code.</p>
155 <p>TODO - expound a bit more.</p>
159 <!-- ======================================================================= -->
160 <div class="doc_subsection">
161 <a name="debugopt">Debugging optimized code</a>
164 <div class="doc_text">
166 <p>An extremely high priority of LLVM debugging information is to make it
167 interact well with optimizations and analysis. In particular, the LLVM debug
168 information provides the following guarantees:</p>
171 <li>LLVM debug information <b>always provides information to accurately read
172 the source-level state of the program</b>, regardless of which LLVM
173 optimizations have been run, and without any modification to the
174 optimizations themselves. However, some optimizations may impact the
175 ability to modify the current state of the program with a debugger, such
176 as setting program variables, or calling functions that have been
179 <li>LLVM optimizations gracefully interact with debugging information. If
180 they are not aware of debug information, they are automatically disabled
181 as necessary in the cases that would invalidate the debug info. This
182 retains the LLVM features, making it easy to write new
183 transformations.</li>
185 <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
186 debugging information, allowing them to update the debugging information
187 as they perform aggressive optimizations. This means that, with effort,
188 the LLVM optimizers could optimize debug code just as well as non-debug
191 <li>LLVM debug information does not prevent many important optimizations from
192 happening (for example inlining, basic block reordering/merging/cleanup,
193 tail duplication, etc), further reducing the amount of the compiler that
194 eventually is "aware" of debugging information.</li>
196 <li>LLVM debug information is automatically optimized along with the rest of
197 the program, using existing facilities. For example, duplicate
198 information is automatically merged by the linker, and unused information
199 is automatically removed.</li>
202 <p>Basically, the debug information allows you to compile a program with
203 "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
204 modify the program as it executes from a debugger. Compiling a program with
205 "<tt>-O3 -g</tt>" gives you full debug information that is always available
206 and accurate for reading (e.g., you get accurate stack traces despite tail
207 call elimination and inlining), but you might lose the ability to modify the
208 program and call functions where were optimized out of the program, or
209 inlined away completely.</p>
211 <p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
212 framework to test optimizer's handling of debugging information. It can be
215 <div class="doc_code">
217 % cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
222 <p>This will test impact of debugging information on optimization passes. If
223 debugging information influences optimization passes then it will be reported
224 as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
225 information on LLVM test infrastructure and how to run various tests.</p>
229 <!-- *********************************************************************** -->
230 <div class="doc_section">
231 <a name="format">Debugging information format</a>
233 <!-- *********************************************************************** -->
235 <div class="doc_text">
237 <p>LLVM debugging information has been carefully designed to make it possible
238 for the optimizer to optimize the program and debugging information without
239 necessarily having to know anything about debugging information. In
240 particular, the use of metadata avoids duplicated debugging information from
241 the beginning, and the global dead code elimination pass automatically
242 deletes debugging information for a function if it decides to delete the
245 <p>To do this, most of the debugging information (descriptors for types,
246 variables, functions, source files, etc) is inserted by the language
247 front-end in the form of LLVM metadata. </p>
249 <p>Debug information is designed to be agnostic about the target debugger and
250 debugging information representation (e.g. DWARF/Stabs/etc). It uses a
251 generic pass to decode the information that represents variables, types,
252 functions, namespaces, etc: this allows for arbitrary source-language
253 semantics and type-systems to be used, as long as there is a module
254 written for the target debugger to interpret the information. </p>
256 <p>To provide basic functionality, the LLVM debugger does have to make some
257 assumptions about the source-level language being debugged, though it keeps
258 these to a minimum. The only common features that the LLVM debugger assumes
259 exist are <a href="#format_files">source files</a>,
260 and <a href="#format_global_variables">program objects</a>. These abstract
261 objects are used by a debugger to form stack traces, show information about
262 local variables, etc.</p>
264 <p>This section of the documentation first describes the representation aspects
265 common to any source-language. The <a href="#ccxx_frontend">next section</a>
266 describes the data layout conventions used by the C and C++ front-ends.</p>
270 <!-- ======================================================================= -->
271 <div class="doc_subsection">
272 <a name="debug_info_descriptors">Debug information descriptors</a>
275 <div class="doc_text">
277 <p>In consideration of the complexity and volume of debug information, LLVM
278 provides a specification for well formed debug descriptors. </p>
280 <p>Consumers of LLVM debug information expect the descriptors for program
281 objects to start in a canonical format, but the descriptors can include
282 additional information appended at the end that is source-language
283 specific. All LLVM debugging information is versioned, allowing backwards
284 compatibility in the case that the core structures need to change in some
285 way. Also, all debugging information objects start with a tag to indicate
286 what type of object it is. The source-language is allowed to define its own
287 objects, by using unreserved tag numbers. We recommend using with tags in
288 the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
291 <p>The fields of debug descriptors used internally by LLVM
292 are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
293 <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
295 <div class="doc_code">
304 <p><a name="LLVMDebugVersion">The first field of a descriptor is always an
305 <tt>i32</tt> containing a tag value identifying the content of the
306 descriptor. The remaining fields are specific to the descriptor. The values
307 of tags are loosely bound to the tag values of DWARF information entries.
308 However, that does not restrict the use of the information supplied to DWARF
309 targets. To facilitate versioning of debug information, the tag is augmented
310 with the current debug version (LLVMDebugVersion = 8 << 16 or 0x80000 or
313 <p>The details of the various descriptors follow.</p>
317 <!-- ======================================================================= -->
318 <div class="doc_subsubsection">
319 <a name="format_compile_units">Compile unit descriptors</a>
322 <div class="doc_text">
324 <div class="doc_code">
327 i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
328 ;; (DW_TAG_compile_unit)
329 i32, ;; Unused field.
330 i32, ;; DWARF language identifier (ex. DW_LANG_C89)
331 metadata, ;; Source file name
332 metadata, ;; Source file directory (includes trailing slash)
333 metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
334 i1, ;; True if this is a main compile unit.
335 i1, ;; True if this is optimized.
337 i32 ;; Runtime version
342 <p>These descriptors contain a source language ID for the file (we use the DWARF
343 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
344 <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
345 working directory of the compiler, and an identifier string for the compiler
346 that produced it.</p>
348 <p>Compile unit descriptors provide the root context for objects declared in a
349 specific compilation unit. File descriptors are defined using this context.</p>
353 <!-- ======================================================================= -->
354 <div class="doc_subsubsection">
355 <a name="format_files">File descriptors</a>
358 <div class="doc_text">
360 <div class="doc_code">
363 i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
364 ;; (DW_TAG_file_type)
365 metadata, ;; Source file name
366 metadata, ;; Source file directory (includes trailing slash)
367 metadata ;; Reference to compile unit where defined
372 <p>These descriptors contain information for a file. Global variables and top
373 level functions would be defined using this context.k File descriptors also
374 provide context for source line correspondence. </p>
376 <p>Each input file is encoded as a separate file descriptor in LLVM debugging
377 information output. Each file descriptor would be defined using a
382 <!-- ======================================================================= -->
383 <div class="doc_subsubsection">
384 <a name="format_global_variables">Global variable descriptors</a>
387 <div class="doc_text">
389 <div class="doc_code">
392 i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
394 i32, ;; Unused field.
395 metadata, ;; Reference to context descriptor
397 metadata, ;; Display name (fully qualified C++ name)
398 metadata, ;; MIPS linkage name (for C++)
399 metadata, ;; Reference to file where defined
400 i32, ;; Line number where defined
401 metadata, ;; Reference to type descriptor
402 i1, ;; True if the global is local to compile unit (static)
403 i1, ;; True if the global is defined in the compile unit (not extern)
404 {}* ;; Reference to the global variable
409 <p>These descriptors provide debug information about globals variables. The
410 provide details such as name, type and where the variable is defined. All
411 global variables are collected by named metadata <tt>!llvm.dbg.gv</tt>.</p>
415 <!-- ======================================================================= -->
416 <div class="doc_subsubsection">
417 <a name="format_subprograms">Subprogram descriptors</a>
420 <div class="doc_text">
422 <div class="doc_code">
425 i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
426 ;; (DW_TAG_subprogram)
427 i32, ;; Unused field.
428 metadata, ;; Reference to context descriptor
430 metadata, ;; Display name (fully qualified C++ name)
431 metadata, ;; MIPS linkage name (for C++)
432 metadata, ;; Reference to file where defined
433 i32, ;; Line number where defined
434 metadata, ;; Reference to type descriptor
435 i1, ;; True if the global is local to compile unit (static)
436 i1 ;; True if the global is defined in the compile unit (not extern)
437 i32 ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual
438 i32 ;; Index into a virtual function
439 metadata, ;; indicates which base type contains the vtable pointer for the
443 Function *;; Pointer to LLVM function
444 metadata ;; Lists function template parameters
449 <p>These descriptors provide debug information about functions, methods and
450 subprograms. They provide details such as name, return types and the source
451 location where the subprogram is defined.
452 All subprogram descriptors are collected by a named metadata
453 <tt>!llvm.dbg.sp</tt>.
458 <!-- ======================================================================= -->
459 <div class="doc_subsubsection">
460 <a name="format_blocks">Block descriptors</a>
463 <div class="doc_text">
465 <div class="doc_code">
468 i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
469 metadata,;; Reference to context descriptor
471 i32, ;; Column number
472 metadata,;; Reference to source file
473 i32 ;; Unique ID to identify blocks from a template function
478 <p>These descriptors provide debug information about nested blocks within a
479 subprogram. The line number and column numbers are used to dinstinguish
480 two lexical blocks at same depth. </p>
484 <!-- ======================================================================= -->
485 <div class="doc_subsubsection">
486 <a name="format_basic_type">Basic type descriptors</a>
489 <div class="doc_text">
491 <div class="doc_code">
494 i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
495 ;; (DW_TAG_base_type)
496 metadata, ;; Reference to context (typically a compile unit)
497 metadata, ;; Name (may be "" for anonymous types)
498 metadata, ;; Reference to file where defined (may be NULL)
499 i32, ;; Line number where defined (may be 0)
501 i64, ;; Alignment in bits
502 i64, ;; Offset in bits
504 i32 ;; DWARF type encoding
509 <p>These descriptors define primitive types used in the code. Example int, bool
510 and float. The context provides the scope of the type, which is usually the
511 top level. Since basic types are not usually user defined the compile unit
512 and line number can be left as NULL and 0. The size, alignment and offset
513 are expressed in bits and can be 64 bit values. The alignment is used to
514 round the offset when embedded in a
515 <a href="#format_composite_type">composite type</a> (example to keep float
516 doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
517 a <a href="#format_composite_type">composite type</a>.</p>
519 <p>The type encoding provides the details of the type. The values are typically
520 one of the following:</p>
522 <div class="doc_code">
528 DW_ATE_signed_char = 6
530 DW_ATE_unsigned_char = 8
536 <!-- ======================================================================= -->
537 <div class="doc_subsubsection">
538 <a name="format_derived_type">Derived type descriptors</a>
541 <div class="doc_text">
543 <div class="doc_code">
546 i32, ;; Tag (see below)
547 metadata, ;; Reference to context
548 metadata, ;; Name (may be "" for anonymous types)
549 metadata, ;; Reference to file where defined (may be NULL)
550 i32, ;; Line number where defined (may be 0)
552 i64, ;; Alignment in bits
553 i64, ;; Offset in bits
554 metadata, ;; Reference to type derived from
555 metadata, ;; (optional) Name of the Objective C property assoicated with
556 ;; Objective-C an ivar
557 metadata, ;; (optional) Name of the Objective C property getter selector.
558 metadata, ;; (optional) Name of the Objective C property setter selector.
559 i32 ;; (optional) Objective C property attributes.
564 <p>These descriptors are used to define types derived from other types. The
565 value of the tag varies depending on the meaning. The following are possible
568 <div class="doc_code">
570 DW_TAG_formal_parameter = 5
572 DW_TAG_pointer_type = 15
573 DW_TAG_reference_type = 16
575 DW_TAG_const_type = 38
576 DW_TAG_volatile_type = 53
577 DW_TAG_restrict_type = 55
581 <p><tt>DW_TAG_member</tt> is used to define a member of
582 a <a href="#format_composite_type">composite type</a>
583 or <a href="#format_subprograms">subprogram</a>. The type of the member is
584 the <a href="#format_derived_type">derived
585 type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
586 is a formal argument of a subprogram.</p>
588 <p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
590 <p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
591 <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
592 and <tt>DW_TAG_restrict_type</tt> are used to qualify
593 the <a href="#format_derived_type">derived type</a>. </p>
595 <p><a href="#format_derived_type">Derived type</a> location can be determined
596 from the compile unit and line number. The size, alignment and offset are
597 expressed in bits and can be 64 bit values. The alignment is used to round
598 the offset when embedded in a <a href="#format_composite_type">composite
599 type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
600 the bit offset if embedded in a <a href="#format_composite_type">composite
603 <p>Note that the <tt>void *</tt> type is expressed as a type derived from NULL.
608 <!-- ======================================================================= -->
609 <div class="doc_subsubsection">
610 <a name="format_composite_type">Composite type descriptors</a>
613 <div class="doc_text">
615 <div class="doc_code">
618 i32, ;; Tag (see below)
619 metadata, ;; Reference to context
620 metadata, ;; Name (may be "" for anonymous types)
621 metadata, ;; Reference to file where defined (may be NULL)
622 i32, ;; Line number where defined (may be 0)
624 i64, ;; Alignment in bits
625 i64, ;; Offset in bits
627 metadata, ;; Reference to type derived from
628 metadata, ;; Reference to array of member descriptors
629 i32 ;; Runtime languages
634 <p>These descriptors are used to define types that are composed of 0 or more
635 elements. The value of the tag varies depending on the meaning. The following
636 are possible tag values:</p>
638 <div class="doc_code">
640 DW_TAG_array_type = 1
641 DW_TAG_enumeration_type = 4
642 DW_TAG_structure_type = 19
643 DW_TAG_union_type = 23
644 DW_TAG_vector_type = 259
645 DW_TAG_subroutine_type = 21
646 DW_TAG_inheritance = 28
650 <p>The vector flag indicates that an array type is a native packed vector.</p>
652 <p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
653 (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
654 descriptors</a>, each representing the range of subscripts at that level of
657 <p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
658 <a href="#format_enumeration">enumerator descriptors</a>, each representing
659 the definition of enumeration value for the set. All enumeration type
660 descriptors are collected by named metadata <tt>!llvm.dbg.enum</tt>.</p>
662 <p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
663 = <tt>DW_TAG_union_type</tt>) types are any one of
664 the <a href="#format_basic_type">basic</a>,
665 <a href="#format_derived_type">derived</a>
666 or <a href="#format_composite_type">composite</a> type descriptors, each
667 representing a field member of the structure or union.</p>
669 <p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
670 provide information about base classes, static members and member
671 functions. If a member is a <a href="#format_derived_type">derived type
672 descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
673 represents a base class. If the member of is
674 a <a href="#format_global_variables">global variable descriptor</a> then it
675 represents a static member. And, if the member is
676 a <a href="#format_subprograms">subprogram descriptor</a> then it represents
677 a member function. For static members and member
678 functions, <tt>getName()</tt> returns the members link or the C++ mangled
679 name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
681 <p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
682 elements is the return type for the subroutine. The remaining elements are
683 the formal arguments to the subroutine.</p>
685 <p><a href="#format_composite_type">Composite type</a> location can be
686 determined from the compile unit and line number. The size, alignment and
687 offset are expressed in bits and can be 64 bit values. The alignment is used
688 to round the offset when embedded in
689 a <a href="#format_composite_type">composite type</a> (as an example, to keep
690 float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
691 in a <a href="#format_composite_type">composite type</a>.</p>
695 <!-- ======================================================================= -->
696 <div class="doc_subsubsection">
697 <a name="format_subrange">Subrange descriptors</a>
700 <div class="doc_text">
702 <div class="doc_code">
705 i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
712 <p>These descriptors are used to define ranges of array subscripts for an array
713 <a href="#format_composite_type">composite type</a>. The low value defines
714 the lower bounds typically zero for C/C++. The high value is the upper
715 bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
716 > high the array bounds are not included in generated debugging information.
721 <!-- ======================================================================= -->
722 <div class="doc_subsubsection">
723 <a name="format_enumeration">Enumerator descriptors</a>
726 <div class="doc_text">
728 <div class="doc_code">
731 i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
732 ;; (DW_TAG_enumerator)
739 <p>These descriptors are used to define members of an
740 enumeration <a href="#format_composite_type">composite type</a>, it
741 associates the name to the value.</p>
745 <!-- ======================================================================= -->
746 <div class="doc_subsubsection">
747 <a name="format_variables">Local variables</a>
750 <div class="doc_text">
752 <div class="doc_code">
755 i32, ;; Tag (see below)
758 metadata, ;; Reference to file where defined
759 i32, ;; 24 bit - Line number where defined
760 ;; 8 bit - Argument number. 1 indicates 1st argument.
761 metadata ;; Type descriptor
766 <p>These descriptors are used to define variables local to a sub program. The
767 value of the tag depends on the usage of the variable:</p>
769 <div class="doc_code">
771 DW_TAG_auto_variable = 256
772 DW_TAG_arg_variable = 257
773 DW_TAG_return_variable = 258
777 <p>An auto variable is any variable declared in the body of the function. An
778 argument variable is any variable that appears as a formal argument to the
779 function. A return variable is used to track the result of a function and
780 has no source correspondent.</p>
782 <p>The context is either the subprogram or block where the variable is defined.
783 Name the source variable name. Compile unit and line indicate where the
784 variable was defined. Type descriptor defines the declared type of the
789 <!-- ======================================================================= -->
790 <div class="doc_subsection">
791 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
794 <div class="doc_text">
796 <p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
797 provide debug information at various points in generated code.</p>
801 <!-- ======================================================================= -->
802 <div class="doc_subsubsection">
803 <a name="format_common_declare">llvm.dbg.declare</a>
806 <div class="doc_text">
808 void %<a href="#format_common_declare">llvm.dbg.declare</a>(metadata, metadata)
811 <p>This intrinsic provides information about a local element (ex. variable.) The
812 first argument is metadata holding alloca for the variable. The
813 second argument is metadata containing description of the variable. </p>
816 <!-- ======================================================================= -->
817 <div class="doc_subsubsection">
818 <a name="format_common_value">llvm.dbg.value</a>
821 <div class="doc_text">
823 void %<a href="#format_common_value">llvm.dbg.value</a>(metadata, i64, metadata)
826 <p>This intrinsic provides information when a user source variable is set to a
827 new value. The first argument is the new value (wrapped as metadata). The
828 second argument is the offset in the user source variable where the new value
829 is written. The third argument is metadata containing description of the
830 user source variable. </p>
833 <!-- ======================================================================= -->
834 <div class="doc_subsection">
835 <a name="format_common_lifetime">Object lifetimes and scoping</a>
838 <div class="doc_text">
839 <p>In many languages, the local variables in functions can have their lifetimes
840 or scopes limited to a subset of a function. In the C family of languages,
841 for example, variables are only live (readable and writable) within the
842 source block that they are defined in. In functional languages, values are
843 only readable after they have been defined. Though this is a very obvious
844 concept, it is non-trivial to model in LLVM, because it has no notion of
845 scoping in this sense, and does not want to be tied to a language's scoping
848 <p>In order to handle this, the LLVM debug format uses the metadata attached to
849 llvm instructions to encode line number and scoping information. Consider
850 the following C fragment, for example:</p>
852 <div class="doc_code">
866 <p>Compiled to LLVM, this function would be represented like this:</p>
868 <div class="doc_code">
870 define void @foo() nounwind ssp {
872 %X = alloca i32, align 4 ; <i32*> [#uses=4]
873 %Y = alloca i32, align 4 ; <i32*> [#uses=4]
874 %Z = alloca i32, align 4 ; <i32*> [#uses=3]
875 %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1]
876 call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7
877 store i32 21, i32* %X, !dbg !8
878 %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1]
879 call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10
880 store i32 22, i32* %Y, !dbg !11
881 %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1]
882 call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14
883 store i32 23, i32* %Z, !dbg !15
884 %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
885 %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
886 %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
887 store i32 %add, i32* %Z, !dbg !16
888 %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
889 store i32 %tmp2, i32* %X, !dbg !17
893 declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
895 !0 = metadata !{i32 459008, metadata !1, metadata !"X",
896 metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
897 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
898 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
899 metadata !"foo", metadata !3, i32 1, metadata !4,
900 i1 false, i1 true}; [DW_TAG_subprogram ]
901 !3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
902 metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
903 i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
904 !4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
905 i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
906 !5 = metadata !{null}
907 !6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
908 i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
909 !7 = metadata !{i32 2, i32 7, metadata !1, null}
910 !8 = metadata !{i32 2, i32 3, metadata !1, null}
911 !9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
912 metadata !6}; [ DW_TAG_auto_variable ]
913 !10 = metadata !{i32 3, i32 7, metadata !1, null}
914 !11 = metadata !{i32 3, i32 3, metadata !1, null}
915 !12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
916 metadata !6}; [ DW_TAG_auto_variable ]
917 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
918 !14 = metadata !{i32 5, i32 9, metadata !13, null}
919 !15 = metadata !{i32 5, i32 5, metadata !13, null}
920 !16 = metadata !{i32 6, i32 5, metadata !13, null}
921 !17 = metadata !{i32 8, i32 3, metadata !1, null}
922 !18 = metadata !{i32 9, i32 1, metadata !2, null}
926 <p>This example illustrates a few important details about LLVM debugging
927 information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
928 intrinsic and location information, which are attached to an instruction,
929 are applied together to allow a debugger to analyze the relationship between
930 statements, variable definitions, and the code used to implement the
933 <div class="doc_code">
935 call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7
939 <p>The first intrinsic
940 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
941 encodes debugging information for the variable <tt>X</tt>. The metadata
942 <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
943 variable <tt>X</tt>.</p>
945 <div class="doc_code">
947 !7 = metadata !{i32 2, i32 7, metadata !1, null}
948 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
949 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
950 metadata !"foo", metadata !"foo", metadata !3, i32 1,
951 metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
955 <p>Here <tt>!7</tt> is metadata providing location information. It has four
956 fields: line number, column number, scope, and original scope. The original
957 scope represents inline location if this instruction is inlined inside a
958 caller, and is null otherwise. In this example, scope is encoded by
959 <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
960 <tt>!2</tt>, where <tt>!2</tt> is a
961 <a href="#format_subprograms">subprogram descriptor</a>. This way the
962 location information attached to the intrinsics indicates that the
963 variable <tt>X</tt> is declared at line number 2 at a function level scope in
964 function <tt>foo</tt>.</p>
966 <p>Now lets take another example.</p>
968 <div class="doc_code">
970 call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
974 <p>The second intrinsic
975 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
976 encodes debugging information for variable <tt>Z</tt>. The metadata
977 <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
978 the variable <tt>Z</tt>.</p>
980 <div class="doc_code">
982 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
983 !14 = metadata !{i32 5, i32 9, metadata !13, null}
987 <p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
988 column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
989 itself resides inside of lexical scope <tt>!1</tt> described above.</p>
991 <p>The scope information attached with each instruction provides a
992 straightforward way to find instructions covered by a scope.</p>
996 <!-- *********************************************************************** -->
997 <div class="doc_section">
998 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
1000 <!-- *********************************************************************** -->
1002 <div class="doc_text">
1004 <p>The C and C++ front-ends represent information about the program in a format
1005 that is effectively identical
1006 to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
1007 terms of information content. This allows code generators to trivially
1008 support native debuggers by generating standard dwarf information, and
1009 contains enough information for non-dwarf targets to translate it as
1012 <p>This section describes the forms used to represent C and C++ programs. Other
1013 languages could pattern themselves after this (which itself is tuned to
1014 representing programs in the same way that DWARF 3 does), or they could
1015 choose to provide completely different forms if they don't fit into the DWARF
1016 model. As support for debugging information gets added to the various LLVM
1017 source-language front-ends, the information used should be documented
1020 <p>The following sections provide examples of various C/C++ constructs and the
1021 debug information that would best describe those constructs.</p>
1025 <!-- ======================================================================= -->
1026 <div class="doc_subsection">
1027 <a name="ccxx_compile_units">C/C++ source file information</a>
1030 <div class="doc_text">
1032 <p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
1033 in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
1035 <div class="doc_code">
1037 #include "MyHeader.h"
1039 int main(int argc, char *argv[]) {
1045 <p>a C/C++ front-end would generate the following descriptors:</p>
1047 <div class="doc_code">
1051 ;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
1056 i32 4, ;; Language Id
1057 metadata !"MySource.cpp",
1058 metadata !"/Users/mine/sources",
1059 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1060 i1 true, ;; Main Compile Unit
1061 i1 false, ;; Optimized compile unit
1062 metadata !"", ;; Compiler flags
1063 i32 0} ;; Runtime version
1066 ;; Define the file for the file "/Users/mine/sources/MySource.cpp".
1070 metadata !"MySource.cpp",
1071 metadata !"/Users/mine/sources",
1072 metadata !2 ;; Compile unit
1076 ;; Define the file for the file "/Users/mine/sources/Myheader.h"
1080 metadata !"Myheader.h"
1081 metadata !"/Users/mine/sources",
1082 metadata !2 ;; Compile unit
1089 <p>llvm::Instruction provides easy access to metadata attached with an
1090 instruction. One can extract line number information encoded in LLVM IR
1091 using <tt>Instruction::getMetadata()</tt> and
1092 <tt>DILocation::getLineNumber()</tt>.
1094 if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
1095 DILocation Loc(N); // DILocation is in DebugInfo.h
1096 unsigned Line = Loc.getLineNumber();
1097 StringRef File = Loc.getFilename();
1098 StringRef Dir = Loc.getDirectory();
1103 <!-- ======================================================================= -->
1104 <div class="doc_subsection">
1105 <a name="ccxx_global_variable">C/C++ global variable information</a>
1108 <div class="doc_text">
1110 <p>Given an integer global variable declared as follows:</p>
1112 <div class="doc_code">
1118 <p>a C/C++ front-end would generate the following descriptors:</p>
1120 <div class="doc_code">
1123 ;; Define the global itself.
1125 %MyGlobal = global int 100
1128 ;; List of debug info of globals
1130 !llvm.dbg.gv = !{!0}
1133 ;; Define the global variable descriptor. Note the reference to the global
1134 ;; variable anchor and the global variable itself.
1139 metadata !1, ;; Context
1140 metadata !"MyGlobal", ;; Name
1141 metadata !"MyGlobal", ;; Display Name
1142 metadata !"MyGlobal", ;; Linkage Name
1143 metadata !3, ;; Compile Unit
1144 i32 1, ;; Line Number
1145 metadata !4, ;; Type
1146 i1 false, ;; Is a local variable
1147 i1 true, ;; Is this a definition
1148 i32* @MyGlobal ;; The global variable
1152 ;; Define the basic type of 32 bit signed integer. Note that since int is an
1153 ;; intrinsic type the source file is NULL and line 0.
1157 metadata !1, ;; Context
1158 metadata !"int", ;; Name
1159 metadata !1, ;; File
1160 i32 0, ;; Line number
1161 i64 32, ;; Size in Bits
1162 i64 32, ;; Align in Bits
1163 i64 0, ;; Offset in Bits
1173 <!-- ======================================================================= -->
1174 <div class="doc_subsection">
1175 <a name="ccxx_subprogram">C/C++ function information</a>
1178 <div class="doc_text">
1180 <p>Given a function declared as follows:</p>
1182 <div class="doc_code">
1184 int main(int argc, char *argv[]) {
1190 <p>a C/C++ front-end would generate the following descriptors:</p>
1192 <div class="doc_code">
1195 ;; Define the anchor for subprograms. Note that the second field of the
1196 ;; anchor is 46, which is the same as the tag for subprograms
1197 ;; (46 = DW_TAG_subprogram.)
1202 metadata !1, ;; Context
1203 metadata !"main", ;; Name
1204 metadata !"main", ;; Display name
1205 metadata !"main", ;; Linkage name
1206 metadata !1, ;; File
1207 i32 1, ;; Line number
1208 metadata !4, ;; Type
1209 i1 false, ;; Is local
1210 i1 true, ;; Is definition
1211 i32 0, ;; Virtuality attribute, e.g. pure virtual function
1212 i32 0, ;; Index into virtual table for C++ methods
1213 i32 0, ;; Type that holds virtual table.
1215 i1 false, ;; True if this function is optimized
1216 Function *, ;; Pointer to llvm::Function
1217 null ;; Function template parameters
1220 ;; Define the subprogram itself.
1222 define i32 @main(i32 %argc, i8** %argv) {
1230 <!-- ======================================================================= -->
1231 <div class="doc_subsection">
1232 <a name="ccxx_basic_types">C/C++ basic types</a>
1235 <div class="doc_text">
1237 <p>The following are the basic type descriptors for C/C++ core types:</p>
1241 <!-- ======================================================================= -->
1242 <div class="doc_subsubsection">
1243 <a name="ccxx_basic_type_bool">bool</a>
1246 <div class="doc_text">
1248 <div class="doc_code">
1252 metadata !1, ;; Context
1253 metadata !"bool", ;; Name
1254 metadata !1, ;; File
1255 i32 0, ;; Line number
1256 i64 8, ;; Size in Bits
1257 i64 8, ;; Align in Bits
1258 i64 0, ;; Offset in Bits
1267 <!-- ======================================================================= -->
1268 <div class="doc_subsubsection">
1269 <a name="ccxx_basic_char">char</a>
1272 <div class="doc_text">
1274 <div class="doc_code">
1278 metadata !1, ;; Context
1279 metadata !"char", ;; Name
1280 metadata !1, ;; File
1281 i32 0, ;; Line number
1282 i64 8, ;; Size in Bits
1283 i64 8, ;; Align in Bits
1284 i64 0, ;; Offset in Bits
1293 <!-- ======================================================================= -->
1294 <div class="doc_subsubsection">
1295 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1298 <div class="doc_text">
1300 <div class="doc_code">
1304 metadata !1, ;; Context
1305 metadata !"unsigned char",
1306 metadata !1, ;; File
1307 i32 0, ;; Line number
1308 i64 8, ;; Size in Bits
1309 i64 8, ;; Align in Bits
1310 i64 0, ;; Offset in Bits
1319 <!-- ======================================================================= -->
1320 <div class="doc_subsubsection">
1321 <a name="ccxx_basic_short">short</a>
1324 <div class="doc_text">
1326 <div class="doc_code">
1330 metadata !1, ;; Context
1331 metadata !"short int",
1332 metadata !1, ;; File
1333 i32 0, ;; Line number
1334 i64 16, ;; Size in Bits
1335 i64 16, ;; Align in Bits
1336 i64 0, ;; Offset in Bits
1345 <!-- ======================================================================= -->
1346 <div class="doc_subsubsection">
1347 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1350 <div class="doc_text">
1352 <div class="doc_code">
1356 metadata !1, ;; Context
1357 metadata !"short unsigned int",
1358 metadata !1, ;; File
1359 i32 0, ;; Line number
1360 i64 16, ;; Size in Bits
1361 i64 16, ;; Align in Bits
1362 i64 0, ;; Offset in Bits
1371 <!-- ======================================================================= -->
1372 <div class="doc_subsubsection">
1373 <a name="ccxx_basic_int">int</a>
1376 <div class="doc_text">
1378 <div class="doc_code">
1382 metadata !1, ;; Context
1383 metadata !"int", ;; Name
1384 metadata !1, ;; File
1385 i32 0, ;; Line number
1386 i64 32, ;; Size in Bits
1387 i64 32, ;; Align in Bits
1388 i64 0, ;; Offset in Bits
1396 <!-- ======================================================================= -->
1397 <div class="doc_subsubsection">
1398 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1401 <div class="doc_text">
1403 <div class="doc_code">
1407 metadata !1, ;; Context
1408 metadata !"unsigned int",
1409 metadata !1, ;; File
1410 i32 0, ;; Line number
1411 i64 32, ;; Size in Bits
1412 i64 32, ;; Align in Bits
1413 i64 0, ;; Offset in Bits
1422 <!-- ======================================================================= -->
1423 <div class="doc_subsubsection">
1424 <a name="ccxx_basic_long_long">long long</a>
1427 <div class="doc_text">
1429 <div class="doc_code">
1433 metadata !1, ;; Context
1434 metadata !"long long int",
1435 metadata !1, ;; File
1436 i32 0, ;; Line number
1437 i64 64, ;; Size in Bits
1438 i64 64, ;; Align in Bits
1439 i64 0, ;; Offset in Bits
1448 <!-- ======================================================================= -->
1449 <div class="doc_subsubsection">
1450 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1453 <div class="doc_text">
1455 <div class="doc_code">
1459 metadata !1, ;; Context
1460 metadata !"long long unsigned int",
1461 metadata !1, ;; File
1462 i32 0, ;; Line number
1463 i64 64, ;; Size in Bits
1464 i64 64, ;; Align in Bits
1465 i64 0, ;; Offset in Bits
1474 <!-- ======================================================================= -->
1475 <div class="doc_subsubsection">
1476 <a name="ccxx_basic_float">float</a>
1479 <div class="doc_text">
1481 <div class="doc_code">
1485 metadata !1, ;; Context
1487 metadata !1, ;; File
1488 i32 0, ;; Line number
1489 i64 32, ;; Size in Bits
1490 i64 32, ;; Align in Bits
1491 i64 0, ;; Offset in Bits
1500 <!-- ======================================================================= -->
1501 <div class="doc_subsubsection">
1502 <a name="ccxx_basic_double">double</a>
1505 <div class="doc_text">
1507 <div class="doc_code">
1511 metadata !1, ;; Context
1512 metadata !"double",;; Name
1513 metadata !1, ;; File
1514 i32 0, ;; Line number
1515 i64 64, ;; Size in Bits
1516 i64 64, ;; Align in Bits
1517 i64 0, ;; Offset in Bits
1526 <!-- ======================================================================= -->
1527 <div class="doc_subsection">
1528 <a name="ccxx_derived_types">C/C++ derived types</a>
1531 <div class="doc_text">
1533 <p>Given the following as an example of C/C++ derived type:</p>
1535 <div class="doc_code">
1537 typedef const int *IntPtr;
1541 <p>a C/C++ front-end would generate the following descriptors:</p>
1543 <div class="doc_code">
1546 ;; Define the typedef "IntPtr".
1550 metadata !1, ;; Context
1551 metadata !"IntPtr", ;; Name
1552 metadata !3, ;; File
1553 i32 0, ;; Line number
1554 i64 0, ;; Size in bits
1555 i64 0, ;; Align in bits
1556 i64 0, ;; Offset in bits
1558 metadata !4 ;; Derived From type
1562 ;; Define the pointer type.
1566 metadata !1, ;; Context
1567 metadata !"", ;; Name
1568 metadata !1, ;; File
1569 i32 0, ;; Line number
1570 i64 64, ;; Size in bits
1571 i64 64, ;; Align in bits
1572 i64 0, ;; Offset in bits
1574 metadata !5 ;; Derived From type
1577 ;; Define the const type.
1581 metadata !1, ;; Context
1582 metadata !"", ;; Name
1583 metadata !1, ;; File
1584 i32 0, ;; Line number
1585 i64 32, ;; Size in bits
1586 i64 32, ;; Align in bits
1587 i64 0, ;; Offset in bits
1589 metadata !6 ;; Derived From type
1592 ;; Define the int type.
1596 metadata !1, ;; Context
1597 metadata !"int", ;; Name
1598 metadata !1, ;; File
1599 i32 0, ;; Line number
1600 i64 32, ;; Size in bits
1601 i64 32, ;; Align in bits
1602 i64 0, ;; Offset in bits
1611 <!-- ======================================================================= -->
1612 <div class="doc_subsection">
1613 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1616 <div class="doc_text">
1618 <p>Given the following as an example of C/C++ struct type:</p>
1620 <div class="doc_code">
1630 <p>a C/C++ front-end would generate the following descriptors:</p>
1632 <div class="doc_code">
1635 ;; Define basic type for unsigned int.
1639 metadata !1, ;; Context
1640 metadata !"unsigned int",
1641 metadata !1, ;; File
1642 i32 0, ;; Line number
1643 i64 32, ;; Size in Bits
1644 i64 32, ;; Align in Bits
1645 i64 0, ;; Offset in Bits
1650 ;; Define composite type for struct Color.
1654 metadata !1, ;; Context
1655 metadata !"Color", ;; Name
1656 metadata !1, ;; Compile unit
1657 i32 1, ;; Line number
1658 i64 96, ;; Size in bits
1659 i64 32, ;; Align in bits
1660 i64 0, ;; Offset in bits
1662 null, ;; Derived From
1663 metadata !3, ;; Elements
1664 i32 0 ;; Runtime Language
1668 ;; Define the Red field.
1672 metadata !1, ;; Context
1673 metadata !"Red", ;; Name
1674 metadata !1, ;; File
1675 i32 2, ;; Line number
1676 i64 32, ;; Size in bits
1677 i64 32, ;; Align in bits
1678 i64 0, ;; Offset in bits
1680 metadata !5 ;; Derived From type
1684 ;; Define the Green field.
1688 metadata !1, ;; Context
1689 metadata !"Green", ;; Name
1690 metadata !1, ;; File
1691 i32 3, ;; Line number
1692 i64 32, ;; Size in bits
1693 i64 32, ;; Align in bits
1694 i64 32, ;; Offset in bits
1696 metadata !5 ;; Derived From type
1700 ;; Define the Blue field.
1704 metadata !1, ;; Context
1705 metadata !"Blue", ;; Name
1706 metadata !1, ;; File
1707 i32 4, ;; Line number
1708 i64 32, ;; Size in bits
1709 i64 32, ;; Align in bits
1710 i64 64, ;; Offset in bits
1712 metadata !5 ;; Derived From type
1716 ;; Define the array of fields used by the composite type Color.
1718 !3 = metadata !{metadata !4, metadata !6, metadata !7}
1724 <!-- ======================================================================= -->
1725 <div class="doc_subsection">
1726 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1729 <div class="doc_text">
1731 <p>Given the following as an example of C/C++ enumeration type:</p>
1733 <div class="doc_code">
1743 <p>a C/C++ front-end would generate the following descriptors:</p>
1745 <div class="doc_code">
1748 ;; Define composite type for enum Trees
1752 metadata !1, ;; Context
1753 metadata !"Trees", ;; Name
1754 metadata !1, ;; File
1755 i32 1, ;; Line number
1756 i64 32, ;; Size in bits
1757 i64 32, ;; Align in bits
1758 i64 0, ;; Offset in bits
1760 null, ;; Derived From type
1761 metadata !3, ;; Elements
1762 i32 0 ;; Runtime language
1766 ;; Define the array of enumerators used by composite type Trees.
1768 !3 = metadata !{metadata !4, metadata !5, metadata !6}
1771 ;; Define Spruce enumerator.
1773 !4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
1776 ;; Define Oak enumerator.
1778 !5 = metadata !{i32 524328, metadata !"Oak", i64 200}
1781 ;; Define Maple enumerator.
1783 !6 = metadata !{i32 524328, metadata !"Maple", i64 300}
1790 <!-- *********************************************************************** -->
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