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5 <title>Source Level Debugging with LLVM</title>
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10 <div class="doc_title">Source Level Debugging with LLVM</div>
12 <table class="layout" style="width:100%">
16 <li><a href="#introduction">Introduction</a>
18 <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
19 <li><a href="#consumers">Debug information consumers</a></li>
20 <li><a href="#debugopt">Debugging optimized code</a></li>
22 <li><a href="#format">Debugging information format</a>
24 <li><a href="#debug_info_descriptors">Debug information descriptors</a>
26 <li><a href="#format_anchors">Anchor descriptors</a></li>
27 <li><a href="#format_compile_units">Compile unit descriptors</a></li>
28 <li><a href="#format_global_variables">Global variable descriptors</a></li>
29 <li><a href="#format_subprograms">Subprogram descriptors</a></li>
30 <li><a href="#format_blocks">Block descriptors</a></li>
31 <li><a href="#format_basic_type">Basic type descriptors</a></li>
32 <li><a href="#format_derived_type">Derived type descriptors</a></li>
33 <li><a href="#format_composite_type">Composite type descriptors</a></li>
34 <li><a href="#format_subrange">Subrange descriptors</a></li>
35 <li><a href="#format_enumeration">Enumerator descriptors</a></li>
36 <li><a href="#format_variables">Local variables</a></li>
38 <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
40 <li><a href="#format_common_stoppoint">llvm.dbg.stoppoint</a></li>
41 <li><a href="#format_common_func_start">llvm.dbg.func.start</a></li>
42 <li><a href="#format_common_region_start">llvm.dbg.region.start</a></li>
43 <li><a href="#format_common_region_end">llvm.dbg.region.end</a></li>
44 <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
46 <li><a href="#format_common_stoppoints">Representing stopping points in the
47 source program</a></li>
49 <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
51 <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
52 <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
53 <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
54 <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
55 <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
56 <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
57 <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
62 <img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
67 <div class="doc_author">
68 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
69 and <a href="mailto:jlaskey@apple.com">Jim Laskey</a></p>
73 <!-- *********************************************************************** -->
74 <div class="doc_section"><a name="introduction">Introduction</a></div>
75 <!-- *********************************************************************** -->
77 <div class="doc_text">
79 <p>This document is the central repository for all information pertaining to
80 debug information in LLVM. It describes the <a href="#format">actual format
81 that the LLVM debug information</a> takes, which is useful for those interested
82 in creating front-ends or dealing directly with the information. Further, this
83 document provides specifc examples of what debug information for C/C++.</p>
87 <!-- ======================================================================= -->
88 <div class="doc_subsection">
89 <a name="phil">Philosophy behind LLVM debugging information</a>
92 <div class="doc_text">
94 <p>The idea of the LLVM debugging information is to capture how the important
95 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
96 Several design aspects have shaped the solution that appears here. The
97 important ones are:</p>
100 <li>Debugging information should have very little impact on the rest of the
101 compiler. No transformations, analyses, or code generators should need to be
102 modified because of debugging information.</li>
104 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
105 easily described ways</a> with the debugging information.</li>
107 <li>Because LLVM is designed to support arbitrary programming languages,
108 LLVM-to-LLVM tools should not need to know anything about the semantics of the
109 source-level-language.</li>
111 <li>Source-level languages are often <b>widely</b> different from one another.
112 LLVM should not put any restrictions of the flavor of the source-language, and
113 the debugging information should work with any language.</li>
115 <li>With code generator support, it should be possible to use an LLVM compiler
116 to compile a program to native machine code and standard debugging formats.
117 This allows compatibility with traditional machine-code level debuggers, like
122 <p>The approach used by the LLVM implementation is to use a small set of <a
123 href="#format_common_intrinsics">intrinsic functions</a> to define a mapping
124 between LLVM program objects and the source-level objects. The description of
125 the source-level program is maintained in LLVM global variables in an <a
126 href="#ccxx_frontend">implementation-defined format</a> (the C/C++ front-end
127 currently uses working draft 7 of the <a
128 href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3 standard</a>).</p>
130 <p>When a program is being debugged, a debugger interacts with the user and
131 turns the stored debug information into source-language specific information.
132 As such, a debugger must be aware of the source-language, and is thus tied to
133 a specific language of family of languages.</p>
137 <!-- ======================================================================= -->
138 <div class="doc_subsection">
139 <a name="consumers">Debug information consumers</a>
142 <div class="doc_text">
143 <p>The role of debug information is to provide meta information normally
144 stripped away during the compilation process. This meta information provides an
145 llvm user a relationship between generated code and the original program source
148 <p>Currently, debug information is consumed by the DwarfWriter to produce dwarf
149 information used by the gdb debugger. Other targets could use the same
150 information to produce stabs or other debug forms.</p>
152 <p>It would also be reasonable to use debug information to feed profiling tools
153 for analysis of generated code, or, tools for reconstructing the original source
154 from generated code.</p>
156 <p>TODO - expound a bit more.</p>
160 <!-- ======================================================================= -->
161 <div class="doc_subsection">
162 <a name="debugopt">Debugging optimized code</a>
165 <div class="doc_text">
167 <p>An extremely high priority of LLVM debugging information is to make it
168 interact well with optimizations and analysis. In particular, the LLVM debug
169 information provides the following guarantees:</p>
173 <li>LLVM debug information <b>always provides information to accurately read the
174 source-level state of the program</b>, regardless of which LLVM optimizations
175 have been run, and without any modification to the optimizations themselves.
176 However, some optimizations may impact the ability to modify the current state
177 of the program with a debugger, such as setting program variables, or calling
178 function that have been deleted.</li>
180 <li>LLVM optimizations gracefully interact with debugging information. If they
181 are not aware of debug information, they are automatically disabled as necessary
182 in the cases that would invalidate the debug info. This retains the LLVM
183 features making it easy to write new 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 as they
187 perform aggressive optimizations. This means that, with effort, the LLVM
188 optimizers could optimize debug code just as well as non-debug code.</li>
190 <li>LLVM debug information does not prevent many important optimizations from
191 happening (for example inlining, basic block reordering/merging/cleanup, tail
192 duplication, etc), further reducing the amount of the compiler that eventually
193 is "aware" of debugging information.</li>
195 <li>LLVM debug information is automatically optimized along with the rest of the
196 program, using existing facilities. For example, duplicate information is
197 automatically merged by the linker, and unused information is automatically
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 and
206 accurate for reading (e.g., you get accurate stack traces despite tail call
207 elimination and inlining), but you might lose the ability to modify the program
208 and call functions where were optimized out of the program, or inlined away
213 <!-- *********************************************************************** -->
214 <div class="doc_section">
215 <a name="format">Debugging information format</a>
217 <!-- *********************************************************************** -->
219 <div class="doc_text">
221 <p>LLVM debugging information has been carefully designed to make it possible
222 for the optimizer to optimize the program and debugging information without
223 necessarily having to know anything about debugging information. In particular,
224 the global constant merging pass automatically eliminates duplicated debugging
225 information (often caused by header files), the global dead code elimination
226 pass automatically deletes debugging information for a function if it decides to
227 delete the function, and the linker eliminates debug information when it merges
228 <tt>linkonce</tt> functions.</p>
230 <p>To do this, most of the debugging information (descriptors for types,
231 variables, functions, source files, etc) is inserted by the language front-end
232 in the form of LLVM global variables. These LLVM global variables are no
233 different from any other global variables, except that they have a web of LLVM
234 intrinsic functions that point to them. If the last references to a particular
235 piece of debugging information are deleted (for example, by the
236 <tt>-globaldce</tt> pass), the extraneous debug information will automatically
237 become dead and be removed by the optimizer.</p>
239 <p>Debug information is designed to be agnostic about the target debugger and
240 debugging information representation (e.g. DWARF/Stabs/etc). It uses a generic
241 machine debug information pass to decode the information that represents
242 variables, types, functions, namespaces, etc: this allows for arbitrary
243 source-language semantics and type-systems to be used, as long as there is a
244 module written for the target debugger to interpret the information. In
245 addition, debug global variables are declared in the <tt>"llvm.metadata"</tt>
246 section. All values declared in this section are stripped away after target
247 debug information is constructed and before the program object is emitted.</p>
249 <p>To provide basic functionality, the LLVM debugger does have to make some
250 assumptions about the source-level language being debugged, though it keeps
251 these to a minimum. The only common features that the LLVM debugger assumes
252 exist are <a href="#format_compile_units">source files</a>, and <a
253 href="#format_global_variables">program objects</a>. These abstract objects are
254 used by a debugger to form stack traces, show information about local
257 <p>This section of the documentation first describes the representation aspects
258 common to any source-language. The <a href="#ccxx_frontend">next section</a>
259 describes the data layout conventions used by the C and C++ front-ends.</p>
263 <!-- ======================================================================= -->
264 <div class="doc_subsection">
265 <a name="debug_info_descriptors">Debug information descriptors</a>
268 <div class="doc_text">
269 <p>In consideration of the complexity and volume of debug information, LLVM
270 provides a specification for well formed debug global variables. The constant
271 value of each of these globals is one of a limited set of structures, known as
272 debug descriptors.</p>
274 <p>Consumers of LLVM debug information expect the descriptors for program
275 objects to start in a canonical format, but the descriptors can include
276 additional information appended at the end that is source-language specific. All
277 LLVM debugging information is versioned, allowing backwards compatibility in the
278 case that the core structures need to change in some way. Also, all debugging
279 information objects start with a tag to indicate what type of object it is. The
280 source-language is allowed to define its own objects, by using unreserved tag
281 numbers. We recommend using with tags in the range 0x1000 thru 0x2000 (there is
282 a defined enum DW_TAG_user_base = 0x1000.)</p>
284 <p>The fields of debug descriptors used internally by LLVM (MachineDebugInfo)
285 are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>,
286 <tt>bool</tt>, <tt>float</tt>, <tt>double</tt>, <tt>sbyte*</tt> and <tt> { }*
287 </tt>. References to arbitrary values are handled using a <tt> { }* </tt> and a
288 cast to <tt> { }* </tt> expression; typically references to other field
289 descriptors, arrays of descriptors or global variables.</p>
292 %llvm.dbg.object.type = type {
298 <p>The first field of a descriptor is always an <tt>uint</tt> containing a tag
299 value identifying the content of the descriptor. The remaining fields are
300 specific to the descriptor. The values of tags are loosely bound to the tag
301 values of Dwarf information entries. However, that does not restrict the use of
302 the information supplied to Dwarf targets.</p>
304 <p>The details of the various descriptors follow.</p>
308 <!-- ======================================================================= -->
309 <div class="doc_subsubsection">
310 <a name="format_anchors">Anchor descriptors</a>
313 <div class="doc_text">
316 %<a href="#format_anchors">llvm.dbg.anchor.type</a> = type {
318 uint ;; Tag of descriptors grouped by the anchor
322 <p>One important aspect of the LLVM debug representation is that it allows the
323 LLVM debugger to efficiently index all of the global objects without having the
324 scan the program. To do this, all of the global objects use "anchor"
325 descriptors with designated names. All of the global objects of a particular
326 type (e.g., compile units) contain a pointer to the anchor. This pointer allows
327 a debugger to use def-use chains to find all global objects of that type.</p>
329 <p>The following names are recognized as anchors by LLVM:</p>
332 %<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 } ;; DW_TAG_compile_unit
333 %<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 } ;; DW_TAG_variable
334 %<a href="#format_subprograms">llvm.dbg.subprograms</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> { uint 0, uint 46 } ;; DW_TAG_subprogram
337 <p>Using anchors in this way (where the compile unit descriptor points to the
338 anchors, as opposed to having a list of compile unit descriptors) allows for the
339 standard dead global elimination and merging passes to automatically remove
340 unused debugging information. If the globals were kept track of through lists,
341 there would always be an object pointing to the descriptors, thus would never be
346 <!-- ======================================================================= -->
347 <div class="doc_subsubsection">
348 <a name="format_compile_units">Compile unit descriptors</a>
351 <div class="doc_text">
354 %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type {
355 uint, ;; Tag = 17 (DW_TAG_compile_unit)
356 { }*, ;; Compile unit anchor = cast = (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*)
357 uint, ;; LLVM debug version number = 3
358 uint, ;; Dwarf language identifier (ex. DW_LANG_C89)
359 sbyte*, ;; Source file name
360 sbyte*, ;; Source file directory (includes trailing slash)
361 sbyte* ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
365 <p>These descriptors contain the version number for the debug info (currently
366 3), a source language ID for the file (we use the Dwarf 3.0 ID numbers, such as
367 <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>, <tt>DW_LANG_Cobol74</tt>,
368 etc), three strings describing the filename, working directory of the compiler,
369 and an identifier string for the compiler that produced it.</p>
371 <p> Compile unit descriptors provide the root context for objects declared in a
372 specific source file. Global variables and top level functions would be defined
373 using this context. Compile unit descriptors also provide context for source
374 line correspondence.</p>
378 <!-- ======================================================================= -->
379 <div class="doc_subsubsection">
380 <a name="format_global_variables">Global variable descriptors</a>
383 <div class="doc_text">
386 %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type {
387 uint, ;; Tag = 52 (DW_TAG_variable)
388 { }*, ;; Global variable anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*),
389 { }*, ;; Reference to context descriptor
391 { }*, ;; Reference to compile unit where defined
392 uint, ;; Line number where defined
393 { }*, ;; Reference to type descriptor
394 bool, ;; True if the global is local to compile unit (static)
395 bool, ;; True if the global is defined in the compile unit (not extern)
396 { }* ;; Reference to the global variable
400 <p>These descriptors provide debug information about globals variables. The
401 provide details such as name, type and where the variable is defined.</p>
405 <!-- ======================================================================= -->
406 <div class="doc_subsubsection">
407 <a name="format_subprograms">Subprogram descriptors</a>
410 <div class="doc_text">
413 %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type {
414 uint, ;; Tag = 46 (DW_TAG_subprogram)
415 { }*, ;; Subprogram anchor = cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*),
416 { }*, ;; Reference to context descriptor
418 { }*, ;; Reference to compile unit where defined
419 uint, ;; Line number where defined
420 { }*, ;; Reference to type descriptor
421 bool, ;; True if the global is local to compile unit (static)
422 bool ;; True if the global is defined in the compile unit (not extern)
426 <p>These descriptors provide debug information about functions, methods and
427 subprograms. They provide details such as name, return types and the source
428 location where the subprogram is defined.</p>
431 <!-- ======================================================================= -->
432 <div class="doc_subsubsection">
433 <a name="format_blocks">Block descriptors</a>
436 <div class="doc_text">
439 %<a href="#format_blocks">llvm.dbg.block</a> = type {
440 uint, ;; Tag = 13 (DW_TAG_lexical_block)
441 { }* ;; Reference to context descriptor
445 <p>These descriptors provide debug information about nested blocks within a
446 subprogram. The array of member descriptors is used to define local variables
447 and deeper nested blocks.</p>
451 <!-- ======================================================================= -->
452 <div class="doc_subsubsection">
453 <a name="format_basic_type">Basic type descriptors</a>
456 <div class="doc_text">
459 %<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type {
460 uint, ;; Tag = 36 (DW_TAG_base_type)
461 { }*, ;; Reference to context (typically a compile unit)
462 sbyte*, ;; Name (may be "" for anonymous types)
463 { }*, ;; Reference to compile unit where defined (may be NULL)
464 uint, ;; Line number where defined (may be 0)
465 uint, ;; Size in bits
466 uint, ;; Alignment in bits
467 uint, ;; Offset in bits
468 uint ;; Dwarf type encoding
472 <p>These descriptors define primitive types used in the code. Example int, bool
473 and float. The context provides the scope of the type, which is usually the top
474 level. Since basic types are not usually user defined the compile unit and line
475 number can be left as NULL and 0. The size, alignment and offset are expressed
476 in bits and can be 64 bit values. The alignment is used to round the offset
477 when embedded in a <a href="#format_composite_type">composite type</a>
478 (example to keep float doubles on 64 bit boundaries.) The offset is the bit
479 offset if embedded in a <a href="#format_composite_type">composite
482 <p>The type encoding provides the details of the type. The values are typically
483 one of the following;</p>
490 DW_ATE_signed_char = 6
492 DW_ATE_unsigned_char = 8
497 <!-- ======================================================================= -->
498 <div class="doc_subsubsection">
499 <a name="format_derived_type">Derived type descriptors</a>
502 <div class="doc_text">
505 %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> = type {
506 uint, ;; Tag (see below)
507 { }*, ;; Reference to context
508 sbyte*, ;; Name (may be "" for anonymous types)
509 { }*, ;; Reference to compile unit where defined (may be NULL)
510 uint, ;; Line number where defined (may be 0)
511 uint, ;; Size in bits
512 uint, ;; Alignment in bits
513 uint, ;; Offset in bits
514 { }* ;; Reference to type derived from
518 <p>These descriptors are used to define types derived from other types. The
519 value of the tag varies depending on the meaning. The following are possible
523 DW_TAG_formal_parameter = 5
525 DW_TAG_pointer_type = 15
526 DW_TAG_reference_type = 16
528 DW_TAG_const_type = 38
529 DW_TAG_volatile_type = 53
530 DW_TAG_restrict_type = 55
533 <p> <tt>DW_TAG_member</tt> is used to define a member of a <a
534 href="#format_composite_type">composite type</a> or <a
535 href="#format_subprograms">subprogram</a>. The type of the member is the <a
536 href="#format_derived_type">derived type</a>. <tt>DW_TAG_formal_parameter</tt>
537 is used to define a member which is a formal argument of a subprogram.</p>
539 <p><tt>DW_TAG_typedef</tt> is used to
540 provide a name for the derived type.</p>
542 <p><tt>DW_TAG_pointer_type</tt>,
543 <tt>DW_TAG_reference_type</tt>, <tt>DW_TAG_const_type</tt>,
544 <tt>DW_TAG_volatile_type</tt> and <tt>DW_TAG_restrict_type</tt> are used to
545 qualify the <a href="#format_derived_type">derived type</a>. </p>
547 <p><a href="#format_derived_type">Derived type</a> location can be determined
548 from the compile unit and line number. The size, alignment and offset are
549 expressed in bits and can be 64 bit values. The alignment is used to round the
550 offset when embedded in a <a href="#format_composite_type">composite type</a>
551 (example to keep float doubles on 64 bit boundaries.) The offset is the bit
552 offset if embedded in a <a href="#format_composite_type">composite
555 <p>Note that the <tt>void *</tt> type is expressed as a
556 <tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt> and
557 NULL derived type.</p>
561 <!-- ======================================================================= -->
562 <div class="doc_subsubsection">
563 <a name="format_composite_type">Composite type descriptors</a>
566 <div class="doc_text">
569 %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> = type {
570 uint, ;; Tag (see below)
571 { }*, ;; Reference to context
572 sbyte*, ;; Name (may be "" for anonymous types)
573 { }*, ;; Reference to compile unit where defined (may be NULL)
574 uint, ;; Line number where defined (may be 0)
575 uint, ;; Size in bits
576 uint, ;; Alignment in bits
577 uint, ;; Offset in bits
578 bool, ;; Is vector flag
579 { }* ;; Reference to array of member descriptors
583 <p>These descriptors are used to define types that are composed of 0 or more
584 elements. The value of the tag varies depending on the meaning. The following
585 are possible tag values;</p>
588 DW_TAG_array_type = 1
589 DW_TAG_enumeration_type = 4
590 DW_TAG_structure_type = 19
591 DW_TAG_union_type = 23
594 <p>The vector flag indicates that an array type is a native packed vector.</p>
596 <p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) are <a
597 href="#format_subrange">subrange descriptors</a>, each representing the range of
598 subscripts at that level of indexing.</p>
600 <p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
601 <a href="#format_enumeration">enumerator descriptors</a>, each representing the
602 definition of enumeration value
605 <p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
606 = <tt>DW_TAG_union_type</tt>) types are any one of the <a
607 href="#format_basic_type">basic</a>, <a href="#format_derived_type">derived</a>
608 or <a href="#format_composite_type">composite</a> type descriptors, each
609 representing a field member of the structure or union.</p>
611 <p><a href="#format_composite_type">Composite type</a> location can be
612 determined from the compile unit and line number. The size, alignment and
613 offset are expressed in bits and can be 64 bit values. The alignment is used to
614 round the offset when embedded in a <a href="#format_composite_type">composite
615 type</a> (as an example, to keep float doubles on 64 bit boundaries.) The offset
616 is the bit offset if embedded in a <a href="#format_composite_type">composite
621 <!-- ======================================================================= -->
622 <div class="doc_subsubsection">
623 <a name="format_subrange">Subrange descriptors</a>
626 <div class="doc_text">
629 %<a href="#format_subrange">llvm.dbg.subrange.type</a> = type {
630 uint, ;; Tag = 33 (DW_TAG_subrange_type)
636 <p>These descriptors are used to define ranges of array subscripts for an array
637 <a href="#format_composite_type">composite type</a>. The low value defines the
638 lower bounds typically zero for C/C++. The high value is the upper bounds.
639 Values are 64 bit. High - low + 1 is the size of the array. If
640 low == high the array will be unbounded.</p>
644 <!-- ======================================================================= -->
645 <div class="doc_subsubsection">
646 <a name="format_enumeration">Enumerator descriptors</a>
649 <div class="doc_text">
652 %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> = type {
653 uint, ;; Tag = 40 (DW_TAG_enumerator)
659 <p>These descriptors are used to define members of an enumeration <a
660 href="#format_composite_type">composite type</a>, it associates the name to the
665 <!-- ======================================================================= -->
666 <div class="doc_subsubsection">
667 <a name="format_variables">Local variables</a>
670 <div class="doc_text">
672 %<a href="#format_variables">llvm.dbg.variable.type</a> = type {
673 uint, ;; Tag (see below)
676 { }*, ;; Reference to compile unit where defined
677 uint, ;; Line number where defined
678 { }* ;; Type descriptor
682 <p>These descriptors are used to define variables local to a sub program. The
683 value of the tag depends on the usage of the variable;</p>
686 DW_TAG_auto_variable = 256
687 DW_TAG_arg_variable = 257
688 DW_TAG_return_variable = 258
691 <p>An auto variable is any variable declared in the body of the function. An
692 argument variable is any variable that appears as a formal argument to the
693 function. A return variable is used to track the result of a function and has
694 no source correspondent.</p>
696 <p>The context is either the subprogram or block where the variable is defined.
697 Name the source variable name. Compile unit and line indicate where the
698 variable was defined. Type descriptor defines the declared type of the
703 <!-- ======================================================================= -->
704 <div class="doc_subsection">
705 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
708 <div class="doc_text">
710 <p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
711 provide debug information at various points in generated code.</p>
715 <!-- ======================================================================= -->
716 <div class="doc_subsubsection">
717 <a name="format_common_stoppoint">llvm.dbg.stoppoint</a>
720 <div class="doc_text">
722 void %<a href="#format_common_stoppoint">llvm.dbg.stoppoint</a>( uint, uint, { }* )
725 <p>This intrinsic is used to provide correspondence between the source file and
726 the generated code. The first argument is the line number (base 1), second
727 argument si the column number (0 if unknown) and the third argument the source
728 <tt>%<a href="#format_compile_units">llvm.dbg.compile_unit</a>*</tt> cast to a
729 <tt>{ }*</tt>. Code following a call to this intrinsic will have been defined
730 in close proximity of the line, column and file. This information holds until
731 the next call to <tt>%<a
732 href="#format_common_stoppoint">lvm.dbg.stoppoint</a></tt>.</p>
736 <!-- ======================================================================= -->
737 <div class="doc_subsubsection">
738 <a name="format_common_func_start">llvm.dbg.func.start</a>
741 <div class="doc_text">
743 void %<a href="#format_common_func_start">llvm.dbg.func.start</a>( { }* )
746 <p>This intrinsic is used to link the debug information in <tt>%<a
747 href="#format_subprograms">llvm.dbg.subprogram</a></tt> to the function. It also
748 defines the beginning of the function's declarative region (scope.) The
749 intrinsic should be called early in the function after the all the alloca
750 instructions. It should be paired off with a closing <tt>%<a
751 href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The function's
752 single argument is the <tt>%<a
753 href="#format_subprograms">llvm.dbg.subprogram.type</a></tt>.</p>
757 <!-- ======================================================================= -->
758 <div class="doc_subsubsection">
759 <a name="format_common_region_start">llvm.dbg.region.start</a>
762 <div class="doc_text">
764 void %<a href="#format_common_region_start">llvm.dbg.region.start</a>( { }* )
767 <p>This intrinsic is used to define the beginning of a declarative scope (ex.
768 block) for local language elements. It should be paired off with a closing
769 <tt>%<a href="#format_common_region_end">llvm.dbg.region.end</a></tt>. The
770 function's single argument is the <tt>%<a
771 href="#format_blocks">llvm.dbg.block</a></tt> which is starting.</p>
776 <!-- ======================================================================= -->
777 <div class="doc_subsubsection">
778 <a name="format_common_region_end">llvm.dbg.region.end</a>
781 <div class="doc_text">
783 void %<a href="#format_common_region_end">llvm.dbg.region.end</a>( { }* )
786 <p>This intrinsic is used to define the end of a declarative scope (ex. block)
787 for local language elements. It should be paired off with an opening <tt>%<a
788 href="#format_common_region_start">llvm.dbg.region.start</a></tt> or <tt>%<a
789 href="#format_common_func_start">llvm.dbg.func.start</a></tt>. The function's
790 single argument is either the <tt>%<a
791 href="#format_blocks">llvm.dbg.block</a></tt> or the <tt>%<a
792 href="#format_subprograms">llvm.dbg.subprogram.type</a></tt> which is
797 <!-- ======================================================================= -->
798 <div class="doc_subsubsection">
799 <a name="format_common_declare">llvm.dbg.declare</a>
802 <div class="doc_text">
804 void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, { }* )
807 <p>This intrinsic provides information about a local element (ex. variable.) The
808 first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The
809 second argument is the <tt>%<a
810 href="#format_variables">llvm.dbg.variable</a></tt> containing the description
811 of the variable, also cast to a <tt>{ }*</tt>.</p>
815 <!-- ======================================================================= -->
816 <div class="doc_subsection">
817 <a name="format_common_stoppoints">
818 Representing stopping points in the source program
822 <div class="doc_text">
824 <p>LLVM debugger "stop points" are a key part of the debugging representation
825 that allows the LLVM to maintain simple semantics for <a
826 href="#debugopt">debugging optimized code</a>. The basic idea is that the
827 front-end inserts calls to the <a
828 href="#format_common_stoppoint">%<tt>llvm.dbg.stoppoint</tt></a> intrinsic
829 function at every point in the program where a debugger should be able to
830 inspect the program (these correspond to places a debugger stops when you
831 "<tt>step</tt>" through it). The front-end can choose to place these as
832 fine-grained as it would like (for example, before every subexpression
833 evaluated), but it is recommended to only put them after every source statement
834 that includes executable code.</p>
836 <p>Using calls to this intrinsic function to demark legal points for the
837 debugger to inspect the program automatically disables any optimizations that
838 could potentially confuse debugging information. To non-debug-information-aware
839 transformations, these calls simply look like calls to an external function,
840 which they must assume to do anything (including reading or writing to any part
841 of reachable memory). On the other hand, it does not impact many optimizations,
842 such as code motion of non-trapping instructions, nor does it impact
843 optimization of subexpressions, code duplication transformations, or basic-block
844 reordering transformations.</p>
849 <!-- ======================================================================= -->
850 <div class="doc_subsection">
851 <a name="format_common_lifetime">Object lifetimes and scoping</a>
854 <div class="doc_text">
855 <p>In many languages, the local variables in functions can have their lifetime
856 or scope limited to a subset of a function. In the C family of languages, for
857 example, variables are only live (readable and writable) within the source block
858 that they are defined in. In functional languages, values are only readable
859 after they have been defined. Though this is a very obvious concept, it is also
860 non-trivial to model in LLVM, because it has no notion of scoping in this sense,
861 and does not want to be tied to a language's scoping rules.</p>
863 <p>In order to handle this, the LLVM debug format uses the notion of "regions"
864 of a function, delineated by calls to intrinsic functions. These intrinsic
865 functions define new regions of the program and indicate when the region
866 lifetime expires. Consider the following C fragment, for example:</p>
880 <p>Compiled to LLVM, this function would be represented like this:</p>
891 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 )
893 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 )
895 call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...)
896 call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %Y, ...)
898 <i>;; Evaluate expression on line 2, assigning to X.</i>
900 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 )
902 <i>;; Evaluate expression on line 3, assigning to Y.</i>
904 call void %<a href="#format_common_stoppoint">llvm.region.start</a>()
905 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 )
906 call void %<a href="#format_common_declare">llvm.dbg.declare</a>({}* %X, ...)
908 <i>;; Evaluate expression on line 5, assigning to Z.</i>
910 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 )
911 call void %<a href="#format_common_region_end">llvm.region.end</a>()
913 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 )
915 call void %<a href="#format_common_region_end">llvm.region.end</a>()
921 <p>This example illustrates a few important details about the LLVM debugging
922 information. In particular, it shows how the various intrinsics are applied
923 together to allow a debugger to analyze the relationship between statements,
924 variable definitions, and the code used to implement the function.</p>
926 <p>The first intrinsic <tt>%<a
927 href="#format_common_func_start">llvm.dbg.func.start</a></tt> provides
928 a link with the <a href="#format_subprograms">subprogram descriptor</a>
929 containing the details of this function. This call also defines the beginning
930 of the function region, bounded by the <tt>%<a
931 href="#format_common_region_end">llvm.region.end</a></tt> at the end of
932 the function. This region is used to bracket the lifetime of variables declared
933 within. For a function, this outer region defines a new stack frame whose
934 lifetime ends when the region is ended.</p>
936 <p>It is possible to define inner regions for short term variables by using the
937 %<a href="#format_common_stoppoint"><tt>llvm.region.start</tt></a> and <a
938 href="#format_common_region_end"><tt>%llvm.region.end</tt></a> to bound a
939 region. The inner region in this example would be for the block containing the
940 declaration of Z.</p>
942 <p>Using regions to represent the boundaries of source-level functions allow
943 LLVM interprocedural optimizations to arbitrarily modify LLVM functions without
944 having to worry about breaking mapping information between the LLVM code and the
945 and source-level program. In particular, the inliner requires no modification
946 to support inlining with debugging information: there is no explicit correlation
947 drawn between LLVM functions and their source-level counterparts (note however,
948 that if the inliner inlines all instances of a non-strong-linkage function into
949 its caller that it will not be possible for the user to manually invoke the
950 inlined function from a debugger).</p>
952 <p>Once the function has been defined, the <a
953 href="#format_common_stoppoint"><tt>stopping point</tt></a> corresponding to
954 line #2 (column #2) of the function is encountered. At this point in the
955 function, <b>no</b> local variables are live. As lines 2 and 3 of the example
956 are executed, their variable definitions are introduced into the program using
957 %<a href="#format_common_declare"><tt>llvm.dbg.declare</tt></a>, without the
958 need to specify a new region. These variables do not require new regions to be
959 introduced because they go out of scope at the same point in the program: line
962 <p>In contrast, the <tt>Z</tt> variable goes out of scope at a different time,
963 on line 7. For this reason, it is defined within the inner region, which kills
964 the availability of <tt>Z</tt> before the code for line 8 is executed. In this
965 way, regions can support arbitrary source-language scoping rules, as long as
966 they can only be nested (ie, one scope cannot partially overlap with a part of
969 <p>It is worth noting that this scoping mechanism is used to control scoping of
970 all declarations, not just variable declarations. For example, the scope of a
971 C++ using declaration is controlled with this couldchange how name lookup is
978 <!-- *********************************************************************** -->
979 <div class="doc_section">
980 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
982 <!-- *********************************************************************** -->
984 <div class="doc_text">
986 <p>The C and C++ front-ends represent information about the program in a format
987 that is effectively identical to <a
988 href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3.0</a> in terms of
989 information content. This allows code generators to trivially support native
990 debuggers by generating standard dwarf information, and contains enough
991 information for non-dwarf targets to translate it as needed.</p>
993 <p>This section describes the forms used to represent C and C++ programs. Other
994 languages could pattern themselves after this (which itself is tuned to
995 representing programs in the same way that Dwarf 3 does), or they could choose
996 to provide completely different forms if they don't fit into the Dwarf model.
997 As support for debugging information gets added to the various LLVM
998 source-language front-ends, the information used should be documented here.</p>
1000 <p>The following sections provide examples of various C/C++ constructs and the
1001 debug information that would best describe those constructs.</p>
1005 <!-- ======================================================================= -->
1006 <div class="doc_subsection">
1007 <a name="ccxx_compile_units">C/C++ source file information</a>
1010 <div class="doc_text">
1012 <p>Given the source files "MySource.cpp" and "MyHeader.h" located in the
1013 directory "/Users/mine/sources", the following code;</p>
1016 #include "MyHeader.h"
1018 int main(int argc, char *argv[]) {
1023 <p>a C/C++ front-end would generate the following descriptors;</p>
1028 ;; Define types used. In this case we need one for compile unit anchors and one
1029 ;; for compile units.
1031 %<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
1032 %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = type { uint, { }*, uint, uint, sbyte*, sbyte*, sbyte* }
1035 ;; Define the anchor for compile units. Note that the second field of the
1036 ;; anchor is 17, which is the same as the tag for compile units
1037 ;; (17 = DW_TAG_compile_unit.)
1039 %<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"
1042 ;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp".
1044 %<a href="#format_compile_units">llvm.dbg.compile_unit1</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> {
1046 { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*),
1049 sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0),
1050 sbyte* getelementptr ([21 x sbyte]* %str2, int 0, int 0),
1051 sbyte* getelementptr ([33 x sbyte]* %str3, int 0, int 0) }, section "llvm.metadata"
1054 ;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h".
1056 %<a href="#format_compile_units">llvm.dbg.compile_unit2</a> = internal constant %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> {
1058 { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_units</a> to { }*),
1061 sbyte* getelementptr ([11 x sbyte]* %str4, int 0, int 0),
1062 sbyte* getelementptr ([21 x sbyte]* %str2, int 0, int 0),
1063 sbyte* getelementptr ([33 x sbyte]* %str3, int 0, int 0) }, section "llvm.metadata"
1066 ;; Define each of the strings used in the compile units.
1068 %str1 = internal constant [13 x sbyte] c"MySource.cpp\00", section "llvm.metadata";
1069 %str2 = internal constant [21 x sbyte] c"/Users/mine/sources/\00", section "llvm.metadata";
1070 %str3 = internal constant [33 x sbyte] c"4.0.1 LLVM (LLVM research group)\00", section "llvm.metadata";
1071 %str4 = internal constant [11 x sbyte] c"MyHeader.h\00", section "llvm.metadata";
1077 <!-- ======================================================================= -->
1078 <div class="doc_subsection">
1079 <a name="ccxx_global_variable">C/C++ global variable information</a>
1082 <div class="doc_text">
1084 <p>Given an integer global variable declared as follows;</p>
1090 <p>a C/C++ front-end would generate the following descriptors;</p>
1094 ;; Define types used. One for global variable anchors, one for the global
1095 ;; variable descriptor, one for the global's basic type and one for the global's
1098 %<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
1099 %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> = type { uint, { }*, { }*, sbyte*, { }*, uint, { }*, bool, bool, { }*, uint }
1100 %<a href="#format_basic_type">llvm.dbg.basictype.type</a> = type { uint, { }*, sbyte*, { }*, int, uint, uint, uint, uint }
1101 %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ...
1104 ;; Define the global itself.
1106 %MyGlobal = global int 100
1109 ;; Define the anchor for global variables. Note that the second field of the
1110 ;; anchor is 52, which is the same as the tag for global variables
1111 ;; (52 = DW_TAG_variable.)
1113 %<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"
1116 ;; Define the global variable descriptor. Note the reference to the global
1117 ;; variable anchor and the global variable itself.
1119 %<a href="#format_global_variables">llvm.dbg.global_variable</a> = internal constant %<a href="#format_global_variables">llvm.dbg.global_variable.type</a> {
1121 { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_global_variables">llvm.dbg.global_variables</a> to { }*),
1122 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1123 sbyte* getelementptr ([9 x sbyte]* %str1, int 0, int 0),
1124 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1126 { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*),
1129 { }* cast (int* %MyGlobal to { }*) }, section "llvm.metadata"
1132 ;; Define the basic type of 32 bit signed integer. Note that since int is an
1133 ;; intrinsic type the source file is NULL and line 0.
1135 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1137 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1138 sbyte* getelementptr ([4 x sbyte]* %str2, int 0, int 0),
1144 uint 5 }, section "llvm.metadata"
1147 ;; Define the names of the global variable and basic type.
1149 %str1 = internal constant [9 x sbyte] c"MyGlobal\00", section "llvm.metadata"
1150 %str2 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata"
1155 <!-- ======================================================================= -->
1156 <div class="doc_subsection">
1157 <a name="ccxx_subprogram">C/C++ function information</a>
1160 <div class="doc_text">
1162 <p>Given a function declared as follows;</p>
1165 int main(int argc, char *argv[]) {
1170 <p>a C/C++ front-end would generate the following descriptors;</p>
1174 ;; Define types used. One for subprogram anchors, one for the subprogram
1175 ;; descriptor, one for the global's basic type and one for the subprogram's
1178 %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> = type { uint, { }*, { }*, sbyte*, { }*, bool, bool }
1179 %<a href="#format_anchors">llvm.dbg.anchor.type</a> = type { uint, uint }
1180 %<a href="#format_compile_units">llvm.dbg.compile_unit.type</a> = ...
1183 ;; Define the anchor for subprograms. Note that the second field of the
1184 ;; anchor is 46, which is the same as the tag for subprograms
1185 ;; (46 = DW_TAG_subprogram.)
1187 %<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"
1190 ;; Define the descriptor for the subprogram. TODO - more details.
1192 %<a href="#format_subprograms">llvm.dbg.subprogram</a> = internal constant %<a href="#format_subprograms">llvm.dbg.subprogram.type</a> {
1194 { }* cast (%<a href="#format_anchors">llvm.dbg.anchor.type</a>* %<a href="#format_subprograms">llvm.dbg.subprograms</a> to { }*),
1195 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1196 sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0),
1197 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1201 bool true }, section "llvm.metadata"
1204 ;; Define the name of the subprogram.
1206 %str1 = internal constant [5 x sbyte] c"main\00", section "llvm.metadata"
1209 ;; Define the subprogram itself.
1211 int %main(int %argc, sbyte** %argv) {
1218 <!-- ======================================================================= -->
1219 <div class="doc_subsection">
1220 <a name="ccxx_basic_types">C/C++ basic types</a>
1223 <div class="doc_text">
1225 <p>The following are the basic type descriptors for C/C++ core types;</p>
1229 <!-- ======================================================================= -->
1230 <div class="doc_subsubsection">
1231 <a name="ccxx_basic_type_bool">bool</a>
1234 <div class="doc_text">
1237 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1239 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1240 sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0),
1246 uint 2 }, section "llvm.metadata"
1247 %str1 = internal constant [5 x sbyte] c"bool\00", section "llvm.metadata"
1252 <!-- ======================================================================= -->
1253 <div class="doc_subsubsection">
1254 <a name="ccxx_basic_char">char</a>
1257 <div class="doc_text">
1260 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1262 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1263 sbyte* getelementptr ([5 x sbyte]* %str1, int 0, int 0),
1269 uint 6 }, section "llvm.metadata"
1270 %str1 = internal constant [5 x sbyte] c"char\00", section "llvm.metadata"
1275 <!-- ======================================================================= -->
1276 <div class="doc_subsubsection">
1277 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1280 <div class="doc_text">
1283 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1285 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1286 sbyte* getelementptr ([14 x sbyte]* %str1, int 0, int 0),
1292 uint 8 }, section "llvm.metadata"
1293 %str1 = internal constant [14 x sbyte] c"unsigned char\00", section "llvm.metadata"
1298 <!-- ======================================================================= -->
1299 <div class="doc_subsubsection">
1300 <a name="ccxx_basic_short">short</a>
1303 <div class="doc_text">
1306 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1308 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1309 sbyte* getelementptr ([10 x sbyte]* %str1, int 0, int 0),
1315 uint 5 }, section "llvm.metadata"
1316 %str1 = internal constant [10 x sbyte] c"short int\00", section "llvm.metadata"
1321 <!-- ======================================================================= -->
1322 <div class="doc_subsubsection">
1323 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1326 <div class="doc_text">
1329 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1331 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1332 sbyte* getelementptr ([19 x sbyte]* %str1, int 0, int 0),
1338 uint 7 }, section "llvm.metadata"
1339 %str1 = internal constant [19 x sbyte] c"short unsigned int\00", section "llvm.metadata"
1344 <!-- ======================================================================= -->
1345 <div class="doc_subsubsection">
1346 <a name="ccxx_basic_int">int</a>
1349 <div class="doc_text">
1352 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1354 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1355 sbyte* getelementptr ([4 x sbyte]* %str1, int 0, int 0),
1361 uint 5 }, section "llvm.metadata"
1362 %str1 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata"
1367 <!-- ======================================================================= -->
1368 <div class="doc_subsubsection">
1369 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1372 <div class="doc_text">
1375 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1377 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1378 sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0),
1384 uint 7 }, section "llvm.metadata"
1385 %str1 = internal constant [13 x sbyte] c"unsigned int\00", section "llvm.metadata"
1390 <!-- ======================================================================= -->
1391 <div class="doc_subsubsection">
1392 <a name="ccxx_basic_long_long">long long</a>
1395 <div class="doc_text">
1398 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1400 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1401 sbyte* getelementptr ([14 x sbyte]* %str1, int 0, int 0),
1407 uint 5 }, section "llvm.metadata"
1408 %str1 = internal constant [14 x sbyte] c"long long int\00", section "llvm.metadata"
1413 <!-- ======================================================================= -->
1414 <div class="doc_subsubsection">
1415 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1418 <div class="doc_text">
1421 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1423 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1424 sbyte* getelementptr ([23 x sbyte]* %str1, int 0, int 0),
1430 uint 7 }, section "llvm.metadata"
1431 %str1 = internal constant [23 x sbyte] c"long long unsigned int\00", section "llvm.metadata"
1436 <!-- ======================================================================= -->
1437 <div class="doc_subsubsection">
1438 <a name="ccxx_basic_float">float</a>
1441 <div class="doc_text">
1444 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1446 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1447 sbyte* getelementptr ([6 x sbyte]* %str1, int 0, int 0),
1453 uint 4 }, section "llvm.metadata"
1454 %str1 = internal constant [6 x sbyte] c"float\00", section "llvm.metadata"
1459 <!-- ======================================================================= -->
1460 <div class="doc_subsubsection">
1461 <a name="ccxx_basic_double">double</a>
1464 <div class="doc_text">
1467 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1469 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1470 sbyte* getelementptr ([7 x sbyte]* %str1, int 0, int 0),
1476 uint 4 }, section "llvm.metadata"
1477 %str1 = internal constant [7 x sbyte] c"double\00", section "llvm.metadata"
1482 <!-- ======================================================================= -->
1483 <div class="doc_subsection">
1484 <a name="ccxx_derived_types">C/C++ derived types</a>
1487 <div class="doc_text">
1489 <p>Given the following as an example of C/C++ derived type;</p>
1492 typedef const int *IntPtr;
1495 <p>a C/C++ front-end would generate the following descriptors;</p>
1499 ;; Define the typedef "IntPtr".
1501 %<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1503 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1504 sbyte* getelementptr ([7 x sbyte]* %str1, int 0, int 0),
1505 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1510 { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*) }, section "llvm.metadata"
1511 %str1 = internal constant [7 x sbyte] c"IntPtr\00", section "llvm.metadata"
1514 ;; Define the pointer type.
1516 %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1518 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1525 { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) }, section "llvm.metadata"
1528 ;; Define the const type.
1530 %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1532 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1539 { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype1</a> to { }*) }, section "llvm.metadata"
1542 ;; Define the int type.
1544 %<a href="#format_basic_type">llvm.dbg.basictype1</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1546 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1547 sbyte* getelementptr ([4 x sbyte]* %str2, int 0, int 0),
1553 uint 5 }, section "llvm.metadata"
1554 %str2 = internal constant [4 x sbyte] c"int\00", section "llvm.metadata"
1559 <!-- ======================================================================= -->
1560 <div class="doc_subsection">
1561 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1564 <div class="doc_text">
1566 <p>Given the following as an example of C/C++ struct type;</p>
1576 <p>a C/C++ front-end would generate the following descriptors;</p>
1580 ;; Define basic type for unsigned int.
1582 %<a href="#format_basic_type">llvm.dbg.basictype</a> = internal constant %<a href="#format_basic_type">llvm.dbg.basictype.type</a> {
1584 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1585 sbyte* getelementptr ([13 x sbyte]* %str1, int 0, int 0),
1591 uint 7 }, section "llvm.metadata"
1592 %str1 = internal constant [13 x sbyte] c"unsigned int\00", section "llvm.metadata"
1595 ;; Define composite type for struct Color.
1597 %<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> {
1599 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1600 sbyte* getelementptr ([6 x sbyte]* %str2, int 0, int 0),
1601 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1608 { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata"
1609 %str2 = internal constant [6 x sbyte] c"Color\00", section "llvm.metadata"
1612 ;; Define the Red field.
1614 %<a href="#format_derived_type">llvm.dbg.derivedtype1</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1617 sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0),
1618 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1623 { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
1624 %str3 = internal constant [4 x sbyte] c"Red\00", section "llvm.metadata"
1627 ;; Define the Green field.
1629 %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1632 sbyte* getelementptr ([6 x sbyte]* %str4, int 0, int 0),
1633 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1638 { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
1639 %str4 = internal constant [6 x sbyte] c"Green\00", section "llvm.metadata"
1642 ;; Define the Blue field.
1644 %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> = internal constant %<a href="#format_derived_type">llvm.dbg.derivedtype.type</a> {
1647 sbyte* getelementptr ([5 x sbyte]* %str5, int 0, int 0),
1648 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1653 { }* cast (%<a href="#format_basic_type">llvm.dbg.basictype.type</a>* %<a href="#format_basic_type">llvm.dbg.basictype</a> to { }*) }, section "llvm.metadata"
1654 %str5 = internal constant [5 x sbyte] c"Blue\00", section "llvm.metadata"
1657 ;; Define the array of fields used by the composite type Color.
1659 %llvm.dbg.array = internal constant [3 x { }*] [
1660 { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype1</a> to { }*),
1661 { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype2</a> to { }*),
1662 { }* cast (%<a href="#format_derived_type">llvm.dbg.derivedtype.type</a>* %<a href="#format_derived_type">llvm.dbg.derivedtype3</a> to { }*) ], section "llvm.metadata"
1667 <!-- ======================================================================= -->
1668 <div class="doc_subsection">
1669 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1672 <div class="doc_text">
1674 <p>Given the following as an example of C/C++ enumeration type;</p>
1684 <p>a C/C++ front-end would generate the following descriptors;</p>
1688 ;; Define composite type for enum Trees
1690 %<a href="#format_composite_type">llvm.dbg.compositetype</a> = internal constant %<a href="#format_composite_type">llvm.dbg.compositetype.type</a> {
1692 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1693 sbyte* getelementptr ([6 x sbyte]* %str1, int 0, int 0),
1694 { }* cast (%<a href="#format_compile_units">llvm.dbg.compile_unit.type</a>* %<a href="#format_compile_units">llvm.dbg.compile_unit</a> to { }*),
1701 { }* cast ([3 x { }*]* %llvm.dbg.array to { }*) }, section "llvm.metadata"
1702 %str1 = internal constant [6 x sbyte] c"Trees\00", section "llvm.metadata"
1705 ;; Define Spruce enumerator.
1707 %<a href="#format_enumeration">llvm.dbg.enumerator1</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
1709 sbyte* getelementptr ([7 x sbyte]* %str2, int 0, int 0),
1710 int 100 }, section "llvm.metadata"
1711 %str2 = internal constant [7 x sbyte] c"Spruce\00", section "llvm.metadata"
1714 ;; Define Oak enumerator.
1716 %<a href="#format_enumeration">llvm.dbg.enumerator2</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
1718 sbyte* getelementptr ([4 x sbyte]* %str3, int 0, int 0),
1719 int 200 }, section "llvm.metadata"
1720 %str3 = internal constant [4 x sbyte] c"Oak\00", section "llvm.metadata"
1723 ;; Define Maple enumerator.
1725 %<a href="#format_enumeration">llvm.dbg.enumerator3</a> = internal constant %<a href="#format_enumeration">llvm.dbg.enumerator.type</a> {
1727 sbyte* getelementptr ([6 x sbyte]* %str4, int 0, int 0),
1728 int 300 }, section "llvm.metadata"
1729 %str4 = internal constant [6 x sbyte] c"Maple\00", section "llvm.metadata"
1732 ;; Define the array of enumerators used by composite type Trees.
1734 %llvm.dbg.array = internal constant [3 x { }*] [
1735 { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator1</a> to { }*),
1736 { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator2</a> to { }*),
1737 { }* cast (%<a href="#format_enumeration">llvm.dbg.enumerator.type</a>* %<a href="#format_enumeration">llvm.dbg.enumerator3</a> to { }*) ], section "llvm.metadata"
1742 <!-- *********************************************************************** -->
1746 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1747 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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1751 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1752 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1753 Last modified: $Date$