Gitiles
Code Review Sign In
gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / e264f62ca09a8f65c87a46d562a4d0f9ec5d457e / . / docs / SourceLevelDebugging.html
blob: e1c78a9d375af19278d269112f3ca7debdcb2e47 [file] [log] [blame]
Shih-wei Liaoe264f622010-02-10 11:10:31 -0800[diff] [blame^]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
3<html>
4<head>
5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
6 <title>Source Level Debugging with LLVM</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
10
11<div class="doc_title">Source Level Debugging with LLVM</div>
12
13<table class="layout" style="width:100%">
14 <tr class="layout">
15 <td class="left">
16<ul>
17 <li><a href="#introduction">Introduction</a>
18 <ol>
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>
22 </ol></li>
23 <li><a href="#format">Debugging information format</a>
24 <ol>
25 <li><a href="#debug_info_descriptors">Debug information descriptors</a>
26 <ul>
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>
37 </ul></li>
38 <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
39 <ul>
40 <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
41 <li><a href="#format_common_value">llvm.dbg.value</a></li>
42 </ul></li>
43 </ol></li>
44 <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
45 <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
46 <ol>
47 <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
48 <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
49 <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
50 <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
51 <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
52 <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
53 <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
54 </ol></li>
55</ul>
56</td>
57<td class="right">
58<img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
59height="369">
60</td>
61</tr></table>
62
63<div class="doc_author">
64 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
65 and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
66</div>
67
68
69<!-- *********************************************************************** -->
70<div class="doc_section"><a name="introduction">Introduction</a></div>
71<!-- *********************************************************************** -->
72
73<div class="doc_text">
74
75<p>This document is the central repository for all information pertaining to
76 debug information in LLVM. It describes the <a href="#format">actual format
77 that the LLVM debug information</a> takes, which is useful for those
78 interested in creating front-ends or dealing directly with the information.
79 Further, this document provides specific examples of what debug information
80 for C/C++.</p>
81
82</div>
83
84<!-- ======================================================================= -->
85<div class="doc_subsection">
86 <a name="phil">Philosophy behind LLVM debugging information</a>
87</div>
88
89<div class="doc_text">
90
91<p>The idea of the LLVM debugging information is to capture how the important
92 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
93 Several design aspects have shaped the solution that appears here. The
94 important ones are:</p>
95
96<ul>
97 <li>Debugging information should have very little impact on the rest of the
98 compiler. No transformations, analyses, or code generators should need to
99 be modified because of debugging information.</li>
100
101 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
102 easily described ways</a> with the debugging information.</li>
103
104 <li>Because LLVM is designed to support arbitrary programming languages,
105 LLVM-to-LLVM tools should not need to know anything about the semantics of
106 the source-level-language.</li>
107
108 <li>Source-level languages are often <b>widely</b> different from one another.
109 LLVM should not put any restrictions of the flavor of the source-language,
110 and the debugging information should work with any language.</li>
111
112 <li>With code generator support, it should be possible to use an LLVM compiler
113 to compile a program to native machine code and standard debugging
114 formats. This allows compatibility with traditional machine-code level
115 debuggers, like GDB or DBX.</li>
116</ul>
117
118<p>The approach used by the LLVM implementation is to use a small set
119 of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
120 mapping between LLVM program objects and the source-level objects. The
121 description of the source-level program is maintained in LLVM metadata
122 in an <a href="#ccxx_frontend">implementation-defined format</a>
123 (the C/C++ front-end currently uses working draft 7 of
124 the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
125 standard</a>).</p>
126
127<p>When a program is being debugged, a debugger interacts with the user and
128 turns the stored debug information into source-language specific information.
129 As such, a debugger must be aware of the source-language, and is thus tied to
130 a specific language or family of languages.</p>
131
132</div>
133
134<!-- ======================================================================= -->
135<div class="doc_subsection">
136 <a name="consumers">Debug information consumers</a>
137</div>
138
139<div class="doc_text">
140
141<p>The role of debug information is to provide meta information normally
142 stripped away during the compilation process. This meta information provides
143 an LLVM user a relationship between generated code and the original program
144 source code.</p>
145
146<p>Currently, debug information is consumed by the DwarfWriter to produce dwarf
147 information used by the gdb debugger. Other targets could use the same
148 information to produce stabs or other debug forms.</p>
149
150<p>It would also be reasonable to use debug information to feed profiling tools
151 for analysis of generated code, or, tools for reconstructing the original
152 source from generated code.</p>
153
154<p>TODO - expound a bit more.</p>
155
156</div>
157
158<!-- ======================================================================= -->
159<div class="doc_subsection">
160 <a name="debugopt">Debugging optimized code</a>
161</div>
162
163<div class="doc_text">
164
165<p>An extremely high priority of LLVM debugging information is to make it
166 interact well with optimizations and analysis. In particular, the LLVM debug
167 information provides the following guarantees:</p>
168
169<ul>
170 <li>LLVM debug information <b>always provides information to accurately read
171 the source-level state of the program</b>, regardless of which LLVM
172 optimizations have been run, and without any modification to the
173 optimizations themselves. However, some optimizations may impact the
174 ability to modify the current state of the program with a debugger, such
175 as setting program variables, or calling functions that have been
176 deleted.</li>
177
178 <li>LLVM optimizations gracefully interact with debugging information. If
179 they are not aware of debug information, they are automatically disabled
180 as necessary in the cases that would invalidate the debug info. This
181 retains the LLVM features, making it easy to write new
182 transformations.</li>
183
184 <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
185 debugging information, allowing them to update the debugging information
186 as they perform aggressive optimizations. This means that, with effort,
187 the LLVM optimizers could optimize debug code just as well as non-debug
188 code.</li>
189
190 <li>LLVM debug information does not prevent many important optimizations from
191 happening (for example inlining, basic block reordering/merging/cleanup,
192 tail duplication, etc), further reducing the amount of the compiler that
193 eventually is "aware" of debugging information.</li>
194
195 <li>LLVM debug information is automatically optimized along with the rest of
196 the program, using existing facilities. For example, duplicate
197 information is automatically merged by the linker, and unused information
198 is automatically removed.</li>
199</ul>
200
201<p>Basically, the debug information allows you to compile a program with
202 "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
203 modify the program as it executes from a debugger. Compiling a program with
204 "<tt>-O3 -g</tt>" gives you full debug information that is always available
205 and accurate for reading (e.g., you get accurate stack traces despite tail
206 call elimination and inlining), but you might lose the ability to modify the
207 program and call functions where were optimized out of the program, or
208 inlined away completely.</p>
209
210<p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
211 framework to test optimizer's handling of debugging information. It can be
212 run like this:</p>
213
214<div class="doc_code">
215<pre>
216% cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
217% make TEST=dbgopt
218</pre>
219</div>
220
221<p>This will test impact of debugging information on optimization passes. If
222 debugging information influences optimization passes then it will be reported
223 as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
224 information on LLVM test infrastructure and how to run various tests.</p>
225
226</div>
227
228<!-- *********************************************************************** -->
229<div class="doc_section">
230 <a name="format">Debugging information format</a>
231</div>
232<!-- *********************************************************************** -->
233
234<div class="doc_text">
235
236<p>LLVM debugging information has been carefully designed to make it possible
237 for the optimizer to optimize the program and debugging information without
238 necessarily having to know anything about debugging information. In
239 particular, te use of metadadta avoids duplicated dubgging information from
240 the beginning, and the global dead code elimination pass automatically
241 deletes debugging information for a function if it decides to delete the
242 function. </p>
243
244<p>To do this, most of the debugging information (descriptors for types,
245 variables, functions, source files, etc) is inserted by the language
246 front-end in the form of LLVM metadata. </p>
247
248<p>Debug information is designed to be agnostic about the target debugger and
249 debugging information representation (e.g. DWARF/Stabs/etc). It uses a
250 generic pass to decode the information that represents variables, types,
251 functions, namespaces, etc: this allows for arbitrary source-language
252 semantics and type-systems to be used, as long as there is a module
253 written for the target debugger to interpret the information. </p>
254
255<p>To provide basic functionality, the LLVM debugger does have to make some
256 assumptions about the source-level language being debugged, though it keeps
257 these to a minimum. The only common features that the LLVM debugger assumes
258 exist are <a href="#format_compile_units">source files</a>,
259 and <a href="#format_global_variables">program objects</a>. These abstract
260 objects are used by a debugger to form stack traces, show information about
261 local variables, etc.</p>
262
263<p>This section of the documentation first describes the representation aspects
264 common to any source-language. The <a href="#ccxx_frontend">next section</a>
265 describes the data layout conventions used by the C and C++ front-ends.</p>
266
267</div>
268
269<!-- ======================================================================= -->
270<div class="doc_subsection">
271 <a name="debug_info_descriptors">Debug information descriptors</a>
272</div>
273
274<div class="doc_text">
275
276<p>In consideration of the complexity and volume of debug information, LLVM
277 provides a specification for well formed debug descriptors. </p>
278
279<p>Consumers of LLVM debug information expect the descriptors for program
280 objects to start in a canonical format, but the descriptors can include
281 additional information appended at the end that is source-language
282 specific. All LLVM debugging information is versioned, allowing backwards
283 compatibility in the case that the core structures need to change in some
284 way. Also, all debugging information objects start with a tag to indicate
285 what type of object it is. The source-language is allowed to define its own
286 objects, by using unreserved tag numbers. We recommend using with tags in
287 the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
288 0x1000.)</p>
289
290<p>The fields of debug descriptors used internally by LLVM
291 are restricted to only the simple data types <tt>int</tt>, <tt>uint</tt>,
292 <tt>bool</tt>, <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and
293 <tt>mdnode</tt>. </p>
294
295<div class="doc_code">
296<pre>
297!1 = metadata !{
298 uint, ;; A tag
299 ...
300}
301</pre>
302</div>
303
304<p><a name="LLVMDebugVersion">The first field of a descriptor is always an
305 <tt>uint</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 = 7 << 16 or 0x70000 or
311 458752.)</a></p>
312
313<p>The details of the various descriptors follow.</p>
314
315</div>
316
317<!-- ======================================================================= -->
318<div class="doc_subsubsection">
319 <a name="format_compile_units">Compile unit descriptors</a>
320</div>
321
322<div class="doc_text">
323
324<div class="doc_code">
325<pre>
326!0 = metadata !{
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.
336 metadata, ;; Flags
337 i32 ;; Runtime version
338}
339</pre>
340</div>
341
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>
347
348<p>Compile unit descriptors provide the root context for objects declared in a
349 specific source file. Global variables and top level functions would be
350 defined using this context. Compile unit descriptors also provide context
351 for source line correspondence.</p>
352
353<p>Each input file is encoded as a separate compile unit in LLVM debugging
354 information output. However, many target specific tool chains prefer to
355 encode only one compile unit in an object file. In this situation, the LLVM
356 code generator will include debugging information entities in the compile
357 unit that is marked as main compile unit. The code generator accepts maximum
358 one main compile unit per module. If a module does not contain any main
359 compile unit then the code generator will emit multiple compile units in the
360 output object file.</p>
361
362</div>
363
364<!-- ======================================================================= -->
365<div class="doc_subsubsection">
366 <a name="format_global_variables">Global variable descriptors</a>
367</div>
368
369<div class="doc_text">
370
371<div class="doc_code">
372<pre>
373!1 = metadata !{
374 i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
375 ;; (DW_TAG_variable)
376 i32, ;; Unused field.
377 metadata, ;; Reference to context descriptor
378 metadata, ;; Name
379 metadata, ;; Display name (fully qualified C++ name)
380 metadata, ;; MIPS linkage name (for C++)
381 metadata, ;; Reference to compile unit where defined
382 i32, ;; Line number where defined
383 metadata, ;; Reference to type descriptor
384 i1, ;; True if the global is local to compile unit (static)
385 i1, ;; True if the global is defined in the compile unit (not extern)
386 { }* ;; Reference to the global variable
387}
388</pre>
389</div>
390
391<p>These descriptors provide debug information about globals variables. The
392provide details such as name, type and where the variable is defined.</p>
393
394</div>
395
396<!-- ======================================================================= -->
397<div class="doc_subsubsection">
398 <a name="format_subprograms">Subprogram descriptors</a>
399</div>
400
401<div class="doc_text">
402
403<div class="doc_code">
404<pre>
405!2 = metadata !{
406 i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
407 ;; (DW_TAG_subprogram)
408 i32, ;; Unused field.
409 metadata, ;; Reference to context descriptor
410 metadata, ;; Name
411 metadata, ;; Display name (fully qualified C++ name)
412 metadata, ;; MIPS linkage name (for C++)
413 metadata, ;; Reference to compile unit where defined
414 i32, ;; Line number where defined
415 metadata, ;; Reference to type descriptor
416 i1, ;; True if the global is local to compile unit (static)
417 i1 ;; True if the global is defined in the compile unit (not extern)
418}
419</pre>
420</div>
421
422<p>These descriptors provide debug information about functions, methods and
423 subprograms. They provide details such as name, return types and the source
424 location where the subprogram is defined.</p>
425
426</div>
427
428<!-- ======================================================================= -->
429<div class="doc_subsubsection">
430 <a name="format_blocks">Block descriptors</a>
431</div>
432
433<div class="doc_text">
434
435<div class="doc_code">
436<pre>
437!3 = metadata !{
438 i32, ;; Tag = 13 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
439 metadata ;; Reference to context descriptor
440}
441</pre>
442</div>
443
444<p>These descriptors provide debug information about nested blocks within a
445 subprogram. The array of member descriptors is used to define local
446 variables and deeper nested blocks.</p>
447
448</div>
449
450<!-- ======================================================================= -->
451<div class="doc_subsubsection">
452 <a name="format_basic_type">Basic type descriptors</a>
453</div>
454
455<div class="doc_text">
456
457<div class="doc_code">
458<pre>
459!4 = metadata !{
460 i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
461 ;; (DW_TAG_base_type)
462 metadata, ;; Reference to context (typically a compile unit)
463 metadata, ;; Name (may be "" for anonymous types)
464 metadata, ;; Reference to compile unit where defined (may be NULL)
465 i32, ;; Line number where defined (may be 0)
466 i64, ;; Size in bits
467 i64, ;; Alignment in bits
468 i64, ;; Offset in bits
469 i32, ;; Flags
470 i32 ;; DWARF type encoding
471}
472</pre>
473</div>
474
475<p>These descriptors define primitive types used in the code. Example int, bool
476 and float. The context provides the scope of the type, which is usually the
477 top level. Since basic types are not usually user defined the compile unit
478 and line number can be left as NULL and 0. The size, alignment and offset
479 are expressed in bits and can be 64 bit values. The alignment is used to
480 round the offset when embedded in a
481 <a href="#format_composite_type">composite type</a> (example to keep float
482 doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
483 a <a href="#format_composite_type">composite type</a>.</p>
484
485<p>The type encoding provides the details of the type. The values are typically
486 one of the following:</p>
487
488<div class="doc_code">
489<pre>
490DW_ATE_address = 1
491DW_ATE_boolean = 2
492DW_ATE_float = 4
493DW_ATE_signed = 5
494DW_ATE_signed_char = 6
495DW_ATE_unsigned = 7
496DW_ATE_unsigned_char = 8
497</pre>
498</div>
499
500</div>
501
502<!-- ======================================================================= -->
503<div class="doc_subsubsection">
504 <a name="format_derived_type">Derived type descriptors</a>
505</div>
506
507<div class="doc_text">
508
509<div class="doc_code">
510<pre>
511!5 = metadata !{
512 i32, ;; Tag (see below)
513 metadata, ;; Reference to context
514 metadata, ;; Name (may be "" for anonymous types)
515 metadata, ;; Reference to compile unit where defined (may be NULL)
516 i32, ;; Line number where defined (may be 0)
517 i32, ;; Size in bits
518 i32, ;; Alignment in bits
519 i32, ;; Offset in bits
520 metadata ;; Reference to type derived from
521}
522</pre>
523</div>
524
525<p>These descriptors are used to define types derived from other types. The
526value of the tag varies depending on the meaning. The following are possible
527tag values:</p>
528
529<div class="doc_code">
530<pre>
531DW_TAG_formal_parameter = 5
532DW_TAG_member = 13
533DW_TAG_pointer_type = 15
534DW_TAG_reference_type = 16
535DW_TAG_typedef = 22
536DW_TAG_const_type = 38
537DW_TAG_volatile_type = 53
538DW_TAG_restrict_type = 55
539</pre>
540</div>
541
542<p><tt>DW_TAG_member</tt> is used to define a member of
543 a <a href="#format_composite_type">composite type</a>
544 or <a href="#format_subprograms">subprogram</a>. The type of the member is
545 the <a href="#format_derived_type">derived
546 type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
547 is a formal argument of a subprogram.</p>
548
549<p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
550
551<p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
552 <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
553 and <tt>DW_TAG_restrict_type</tt> are used to qualify
554 the <a href="#format_derived_type">derived type</a>. </p>
555
556<p><a href="#format_derived_type">Derived type</a> location can be determined
557 from the compile unit and line number. The size, alignment and offset are
558 expressed in bits and can be 64 bit values. The alignment is used to round
559 the offset when embedded in a <a href="#format_composite_type">composite
560 type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
561 the bit offset if embedded in a <a href="#format_composite_type">composite
562 type</a>.</p>
563
564<p>Note that the <tt>void *</tt> type is expressed as a
565 <tt>llvm.dbg.derivedtype.type</tt> with tag of <tt>DW_TAG_pointer_type</tt>
566 and <tt>NULL</tt> derived type.</p>
567
568</div>
569
570<!-- ======================================================================= -->
571<div class="doc_subsubsection">
572 <a name="format_composite_type">Composite type descriptors</a>
573</div>
574
575<div class="doc_text">
576
577<div class="doc_code">
578<pre>
579!6 = metadata !{
580 i32, ;; Tag (see below)
581 metadata, ;; Reference to context
582 metadata, ;; Name (may be "" for anonymous types)
583 metadata, ;; Reference to compile unit where defined (may be NULL)
584 i32, ;; Line number where defined (may be 0)
585 i64, ;; Size in bits
586 i64, ;; Alignment in bits
587 i64, ;; Offset in bits
588 i32, ;; Flags
589 metadata, ;; Reference to type derived from
590 metadata, ;; Reference to array of member descriptors
591 i32 ;; Runtime languages
592}
593</pre>
594</div>
595
596<p>These descriptors are used to define types that are composed of 0 or more
597elements. The value of the tag varies depending on the meaning. The following
598are possible tag values:</p>
599
600<div class="doc_code">
601<pre>
602DW_TAG_array_type = 1
603DW_TAG_enumeration_type = 4
604DW_TAG_structure_type = 19
605DW_TAG_union_type = 23
606DW_TAG_vector_type = 259
607DW_TAG_subroutine_type = 21
608DW_TAG_inheritance = 28
609</pre>
610</div>
611
612<p>The vector flag indicates that an array type is a native packed vector.</p>
613
614<p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
615 (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
616 descriptors</a>, each representing the range of subscripts at that level of
617 indexing.</p>
618
619<p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
620 <a href="#format_enumeration">enumerator descriptors</a>, each representing
621 the definition of enumeration value for the set.</p>
622
623<p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
624 = <tt>DW_TAG_union_type</tt>) types are any one of
625 the <a href="#format_basic_type">basic</a>,
626 <a href="#format_derived_type">derived</a>
627 or <a href="#format_composite_type">composite</a> type descriptors, each
628 representing a field member of the structure or union.</p>
629
630<p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
631 provide information about base classes, static members and member
632 functions. If a member is a <a href="#format_derived_type">derived type
633 descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
634 represents a base class. If the member of is
635 a <a href="#format_global_variables">global variable descriptor</a> then it
636 represents a static member. And, if the member is
637 a <a href="#format_subprograms">subprogram descriptor</a> then it represents
638 a member function. For static members and member
639 functions, <tt>getName()</tt> returns the members link or the C++ mangled
640 name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
641
642<p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
643 elements is the return type for the subroutine. The remaining elements are
644 the formal arguments to the subroutine.</p>
645
646<p><a href="#format_composite_type">Composite type</a> location can be
647 determined from the compile unit and line number. The size, alignment and
648 offset are expressed in bits and can be 64 bit values. The alignment is used
649 to round the offset when embedded in
650 a <a href="#format_composite_type">composite type</a> (as an example, to keep
651 float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
652 in a <a href="#format_composite_type">composite type</a>.</p>
653
654</div>
655
656<!-- ======================================================================= -->
657<div class="doc_subsubsection">
658 <a name="format_subrange">Subrange descriptors</a>
659</div>
660
661<div class="doc_text">
662
663<div class="doc_code">
664<pre>
665%<a href="#format_subrange">llvm.dbg.subrange.type</a> = type {
666 i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
667 i64, ;; Low value
668 i64 ;; High value
669}
670</pre>
671</div>
672
673<p>These descriptors are used to define ranges of array subscripts for an array
674 <a href="#format_composite_type">composite type</a>. The low value defines
675 the lower bounds typically zero for C/C++. The high value is the upper
676 bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
677 == high the array will be unbounded.</p>
678
679</div>
680
681<!-- ======================================================================= -->
682<div class="doc_subsubsection">
683 <a name="format_enumeration">Enumerator descriptors</a>
684</div>
685
686<div class="doc_text">
687
688<div class="doc_code">
689<pre>
690!6 = metadata !{
691 i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
692 ;; (DW_TAG_enumerator)
693 metadata, ;; Name
694 i64 ;; Value
695}
696</pre>
697</div>
698
699<p>These descriptors are used to define members of an
700 enumeration <a href="#format_composite_type">composite type</a>, it
701 associates the name to the value.</p>
702
703</div>
704
705<!-- ======================================================================= -->
706<div class="doc_subsubsection">
707 <a name="format_variables">Local variables</a>
708</div>
709
710<div class="doc_text">
711
712<div class="doc_code">
713<pre>
714!7 = metadata !{
715 i32, ;; Tag (see below)
716 metadata, ;; Context
717 metadata, ;; Name
718 metadata, ;; Reference to compile unit where defined
719 i32, ;; Line number where defined
720 metadata ;; Type descriptor
721}
722</pre>
723</div>
724
725<p>These descriptors are used to define variables local to a sub program. The
726 value of the tag depends on the usage of the variable:</p>
727
728<div class="doc_code">
729<pre>
730DW_TAG_auto_variable = 256
731DW_TAG_arg_variable = 257
732DW_TAG_return_variable = 258
733</pre>
734</div>
735
736<p>An auto variable is any variable declared in the body of the function. An
737 argument variable is any variable that appears as a formal argument to the
738 function. A return variable is used to track the result of a function and
739 has no source correspondent.</p>
740
741<p>The context is either the subprogram or block where the variable is defined.
742 Name the source variable name. Compile unit and line indicate where the
743 variable was defined. Type descriptor defines the declared type of the
744 variable.</p>
745
746</div>
747
748<!-- ======================================================================= -->
749<div class="doc_subsection">
750 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
751</div>
752
753<div class="doc_text">
754
755<p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
756 provide debug information at various points in generated code.</p>
757
758</div>
759
760<!-- ======================================================================= -->
761<div class="doc_subsubsection">
762 <a name="format_common_declare">llvm.dbg.declare</a>
763</div>
764
765<div class="doc_text">
766<pre>
767 void %<a href="#format_common_declare">llvm.dbg.declare</a>( { } *, metadata )
768</pre>
769
770<p>This intrinsic provides information about a local element (ex. variable.) The
771 first argument is the alloca for the variable, cast to a <tt>{ }*</tt>. The
772 second argument is
773 the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
774 the description of the variable. </p>
775
776</div>
777
778<!-- ======================================================================= -->
779<div class="doc_subsubsection">
780 <a name="format_common_value">llvm.dbg.value</a>
781</div>
782
783<div class="doc_text">
784<pre>
785 void %<a href="#format_common_value">llvm.dbg.value</a>( metadata, i64, metadata )
786</pre>
787
788<p>This intrinsic provides information when a user source variable is set to a
789 new value. The first argument is the new value (wrapped as metadata). The
790 second argument is the offset in the user source variable where the new value
791 is written. The third argument is
792 the <tt>%<a href="#format_variables">llvm.dbg.variable</a></tt> containing
793 the description of the user source variable. </p>
794
795</div>
796
797<!-- ======================================================================= -->
798<div class="doc_subsection">
799 <a name="format_common_lifetime">Object lifetimes and scoping</a>
800</div>
801
802<div class="doc_text">
803<p>In many languages, the local variables in functions can have their lifetimes
804 or scopes limited to a subset of a function. In the C family of languages,
805 for example, variables are only live (readable and writable) within the
806 source block that they are defined in. In functional languages, values are
807 only readable after they have been defined. Though this is a very obvious
808 concept, it is non-trivial to model in LLVM, because it has no notion of
809 scoping in this sense, and does not want to be tied to a language's scoping
810 rules.</p>
811
812<p>In order to handle this, the LLVM debug format uses the metadata attached to
813 llvm instructions to encode line nuber and scoping information. Consider the
814 following C fragment, for example:</p>
815
816<div class="doc_code">
817<pre>
8181. void foo() {
8192. int X = 21;
8203. int Y = 22;
8214. {
8225. int Z = 23;
8236. Z = X;
8247. }
8258. X = Y;
8269. }
827</pre>
828</div>
829
830<p>Compiled to LLVM, this function would be represented like this:</p>
831
832<div class="doc_code">
833<pre>
834define void @foo() nounwind ssp {
835entry:
836 %X = alloca i32, align 4 ; &lt;i32*&gt; [#uses=4]
837 %Y = alloca i32, align 4 ; &lt;i32*&gt; [#uses=4]
838 %Z = alloca i32, align 4 ; &lt;i32*&gt; [#uses=3]
839 %0 = bitcast i32* %X to { }* ; &lt;{ }*&gt; [#uses=1]
840 call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
841 store i32 21, i32* %X, !dbg !8
842 %1 = bitcast i32* %Y to { }* ; &lt;{ }*&gt; [#uses=1]
843 call void @llvm.dbg.declare({ }* %1, metadata !9), !dbg !10
844 store i32 22, i32* %Y, !dbg !11
845 %2 = bitcast i32* %Z to { }* ; &lt;{ }*&gt; [#uses=1]
846 call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
847 store i32 23, i32* %Z, !dbg !15
848 %tmp = load i32* %X, !dbg !16 ; &lt;i32&gt; [#uses=1]
849 %tmp1 = load i32* %Y, !dbg !16 ; &lt;i32&gt; [#uses=1]
850 %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; &lt;i32&gt; [#uses=1]
851 store i32 %add, i32* %Z, !dbg !16
852 %tmp2 = load i32* %Y, !dbg !17 ; &lt;i32&gt; [#uses=1]
853 store i32 %tmp2, i32* %X, !dbg !17
854 ret void, !dbg !18
855}
856
857declare void @llvm.dbg.declare({ }*, metadata) nounwind readnone
858
859!0 = metadata !{i32 459008, metadata !1, metadata !"X",
860 metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
861!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
862!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
863 metadata !"foo", metadata !3, i32 1, metadata !4,
864 i1 false, i1 true}; [DW_TAG_subprogram ]
865!3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
866 metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
867 i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
868!4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
869 i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
870!5 = metadata !{null}
871!6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
872 i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
873!7 = metadata !{i32 2, i32 7, metadata !1, null}
874!8 = metadata !{i32 2, i32 3, metadata !1, null}
875!9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
876 metadata !6}; [ DW_TAG_auto_variable ]
877!10 = metadata !{i32 3, i32 7, metadata !1, null}
878!11 = metadata !{i32 3, i32 3, metadata !1, null}
879!12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
880 metadata !6}; [ DW_TAG_auto_variable ]
881!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
882!14 = metadata !{i32 5, i32 9, metadata !13, null}
883!15 = metadata !{i32 5, i32 5, metadata !13, null}
884!16 = metadata !{i32 6, i32 5, metadata !13, null}
885!17 = metadata !{i32 8, i32 3, metadata !1, null}
886!18 = metadata !{i32 9, i32 1, metadata !2, null}
887</pre>
888</div>
889
890<p>This example illustrates a few important details about LLVM debugging
891 information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
892 intrinsic and location information, which are attached to an instruction,
893 are applied together to allow a debugger to analyze the relationship between
894 statements, variable definitions, and the code used to implement the
895 function.</p>
896
897<div class="doc_code">
898<pre>
899call void @llvm.dbg.declare({ }* %0, metadata !0), !dbg !7
900</pre>
901</div>
902
903<p>The first intrinsic
904 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
905 encodes debugging information for the variable <tt>X</tt>. The metadata
906 <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
907 variable <tt>X</tt>.</p>
908
909<div class="doc_code">
910<pre>
911!7 = metadata !{i32 2, i32 7, metadata !1, null}
912!1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
913!2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
914 metadata !"foo", metadata !"foo", metadata !3, i32 1,
915 metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
916</pre>
917</div>
918
919<p>Here <tt>!7</tt> is metadata providing location information. It has four
920 fields: line number, column number, scope, and original scope. The original
921 scope represents inline location if this instruction is inlined inside a
922 caller, and is null otherwise. In this example, scope is encoded by
923 <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
924 <tt>!2</tt>, where <tt>!2</tt> is a
925 <a href="#format_subprograms">subprogram descriptor</a>. This way the
926 location information attached to the intrinsics indicates that the
927 variable <tt>X</tt> is declared at line number 2 at a function level scope in
928 function <tt>foo</tt>.</p>
929
930<p>Now lets take another example.</p>
931
932<div class="doc_code">
933<pre>
934call void @llvm.dbg.declare({ }* %2, metadata !12), !dbg !14
935</pre>
936</div>
937
938<p>The second intrinsic
939 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
940 encodes debugging information for variable <tt>Z</tt>. The metadata
941 <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
942 the variable <tt>Z</tt>.</p>
943
944<div class="doc_code">
945<pre>
946!13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
947!14 = metadata !{i32 5, i32 9, metadata !13, null}
948</pre>
949</div>
950
951<p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declaread at line number 5 and
952 column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
953 itself resides inside of lexical scope <tt>!1</tt> described above.</p>
954
955<p>The scope information attached with each instruction provides a
956 straightforward way to find instructions covered by a scope.</p>
957
958</div>
959
960<!-- *********************************************************************** -->
961<div class="doc_section">
962 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
963</div>
964<!-- *********************************************************************** -->
965
966<div class="doc_text">
967
968<p>The C and C++ front-ends represent information about the program in a format
969 that is effectively identical
970 to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
971 terms of information content. This allows code generators to trivially
972 support native debuggers by generating standard dwarf information, and
973 contains enough information for non-dwarf targets to translate it as
974 needed.</p>
975
976<p>This section describes the forms used to represent C and C++ programs. Other
977 languages could pattern themselves after this (which itself is tuned to
978 representing programs in the same way that DWARF 3 does), or they could
979 choose to provide completely different forms if they don't fit into the DWARF
980 model. As support for debugging information gets added to the various LLVM
981 source-language front-ends, the information used should be documented
982 here.</p>
983
984<p>The following sections provide examples of various C/C++ constructs and the
985 debug information that would best describe those constructs.</p>
986
987</div>
988
989<!-- ======================================================================= -->
990<div class="doc_subsection">
991 <a name="ccxx_compile_units">C/C++ source file information</a>
992</div>
993
994<div class="doc_text">
995
996<p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
997 in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
998
999<div class="doc_code">
1000<pre>
1001#include "MyHeader.h"
1002
1003int main(int argc, char *argv[]) {
1004 return 0;
1005}
1006</pre>
1007</div>
1008
1009<p>a C/C++ front-end would generate the following descriptors:</p>
1010
1011<div class="doc_code">
1012<pre>
1013...
1014;;
1015;; Define the compile unit for the source file "/Users/mine/sources/MySource.cpp".
1016;;
1017!3 = metadata !{
1018 i32 458769, ;; Tag
1019 i32 0, ;; Unused
1020 i32 4, ;; Language Id
1021 metadata !"MySource.cpp",
1022 metadata !"/Users/mine/sources",
1023 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1024 i1 true, ;; Main Compile Unit
1025 i1 false, ;; Optimized compile unit
1026 metadata !"", ;; Compiler flags
1027 i32 0} ;; Runtime version
1028
1029;;
1030;; Define the compile unit for the header file "/Users/mine/sources/MyHeader.h".
1031;;
1032!1 = metadata !{
1033 i32 458769, ;; Tag
1034 i32 0, ;; Unused
1035 i32 4, ;; Language Id
1036 metadata !"MyHeader.h",
1037 metadata !"/Users/mine/sources",
1038 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1039 i1 false, ;; Main Compile Unit
1040 i1 false, ;; Optimized compile unit
1041 metadata !"", ;; Compiler flags
1042 i32 0} ;; Runtime version
1043
1044...
1045</pre>
1046</div>
1047
1048</div>
1049
1050<!-- ======================================================================= -->
1051<div class="doc_subsection">
1052 <a name="ccxx_global_variable">C/C++ global variable information</a>
1053</div>
1054
1055<div class="doc_text">
1056
1057<p>Given an integer global variable declared as follows:</p>
1058
1059<div class="doc_code">
1060<pre>
1061int MyGlobal = 100;
1062</pre>
1063</div>
1064
1065<p>a C/C++ front-end would generate the following descriptors:</p>
1066
1067<div class="doc_code">
1068<pre>
1069;;
1070;; Define the global itself.
1071;;
1072%MyGlobal = global int 100
1073...
1074;;
1075;; List of debug info of globals
1076;;
1077!llvm.dbg.gv = !{!0}
1078
1079;;
1080;; Define the global variable descriptor. Note the reference to the global
1081;; variable anchor and the global variable itself.
1082;;
1083!0 = metadata !{
1084 i32 458804, ;; Tag
1085 i32 0, ;; Unused
1086 metadata !1, ;; Context
1087 metadata !"MyGlobal", ;; Name
1088 metadata !"MyGlobal", ;; Display Name
1089 metadata !"MyGlobal", ;; Linkage Name
1090 metadata !1, ;; Compile Unit
1091 i32 1, ;; Line Number
1092 metadata !2, ;; Type
1093 i1 false, ;; Is a local variable
1094 i1 true, ;; Is this a definition
1095 i32* @MyGlobal ;; The global variable
1096}
1097
1098;;
1099;; Define the basic type of 32 bit signed integer. Note that since int is an
1100;; intrinsic type the source file is NULL and line 0.
1101;;
1102!2 = metadata !{
1103 i32 458788, ;; Tag
1104 metadata !1, ;; Context
1105 metadata !"int", ;; Name
1106 metadata !1, ;; Compile Unit
1107 i32 0, ;; Line number
1108 i64 32, ;; Size in Bits
1109 i64 32, ;; Align in Bits
1110 i64 0, ;; Offset in Bits
1111 i32 0, ;; Flags
1112 i32 5 ;; Encoding
1113}
1114
1115</pre>
1116</div>
1117
1118</div>
1119
1120<!-- ======================================================================= -->
1121<div class="doc_subsection">
1122 <a name="ccxx_subprogram">C/C++ function information</a>
1123</div>
1124
1125<div class="doc_text">
1126
1127<p>Given a function declared as follows:</p>
1128
1129<div class="doc_code">
1130<pre>
1131int main(int argc, char *argv[]) {
1132 return 0;
1133}
1134</pre>
1135</div>
1136
1137<p>a C/C++ front-end would generate the following descriptors:</p>
1138
1139<div class="doc_code">
1140<pre>
1141;;
1142;; Define the anchor for subprograms. Note that the second field of the
1143;; anchor is 46, which is the same as the tag for subprograms
1144;; (46 = DW_TAG_subprogram.)
1145;;
1146!0 = metadata !{
1147 i32 458798, ;; Tag
1148 i32 0, ;; Unused
1149 metadata !1, ;; Context
1150 metadata !"main", ;; Name
1151 metadata !"main", ;; Display name
1152 metadata !"main", ;; Linkage name
1153 metadata !1, ;; Compile unit
1154 i32 1, ;; Line number
1155 metadata !2, ;; Type
1156 i1 false, ;; Is local
1157 i1 true ;; Is definition
1158}
1159;;
1160;; Define the subprogram itself.
1161;;
1162define i32 @main(i32 %argc, i8** %argv) {
1163...
1164}
1165</pre>
1166</div>
1167
1168</div>
1169
1170<!-- ======================================================================= -->
1171<div class="doc_subsection">
1172 <a name="ccxx_basic_types">C/C++ basic types</a>
1173</div>
1174
1175<div class="doc_text">
1176
1177<p>The following are the basic type descriptors for C/C++ core types:</p>
1178
1179</div>
1180
1181<!-- ======================================================================= -->
1182<div class="doc_subsubsection">
1183 <a name="ccxx_basic_type_bool">bool</a>
1184</div>
1185
1186<div class="doc_text">
1187
1188<div class="doc_code">
1189<pre>
1190!2 = metadata !{
1191 i32 458788, ;; Tag
1192 metadata !1, ;; Context
1193 metadata !"bool", ;; Name
1194 metadata !1, ;; Compile Unit
1195 i32 0, ;; Line number
1196 i64 8, ;; Size in Bits
1197 i64 8, ;; Align in Bits
1198 i64 0, ;; Offset in Bits
1199 i32 0, ;; Flags
1200 i32 2 ;; Encoding
1201}
1202</pre>
1203</div>
1204
1205</div>
1206
1207<!-- ======================================================================= -->
1208<div class="doc_subsubsection">
1209 <a name="ccxx_basic_char">char</a>
1210</div>
1211
1212<div class="doc_text">
1213
1214<div class="doc_code">
1215<pre>
1216!2 = metadata !{
1217 i32 458788, ;; Tag
1218 metadata !1, ;; Context
1219 metadata !"char", ;; Name
1220 metadata !1, ;; Compile Unit
1221 i32 0, ;; Line number
1222 i64 8, ;; Size in Bits
1223 i64 8, ;; Align in Bits
1224 i64 0, ;; Offset in Bits
1225 i32 0, ;; Flags
1226 i32 6 ;; Encoding
1227}
1228</pre>
1229</div>
1230
1231</div>
1232
1233<!-- ======================================================================= -->
1234<div class="doc_subsubsection">
1235 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1236</div>
1237
1238<div class="doc_text">
1239
1240<div class="doc_code">
1241<pre>
1242!2 = metadata !{
1243 i32 458788, ;; Tag
1244 metadata !1, ;; Context
1245 metadata !"unsigned char",
1246 metadata !1, ;; Compile Unit
1247 i32 0, ;; Line number
1248 i64 8, ;; Size in Bits
1249 i64 8, ;; Align in Bits
1250 i64 0, ;; Offset in Bits
1251 i32 0, ;; Flags
1252 i32 8 ;; Encoding
1253}
1254</pre>
1255</div>
1256
1257</div>
1258
1259<!-- ======================================================================= -->
1260<div class="doc_subsubsection">
1261 <a name="ccxx_basic_short">short</a>
1262</div>
1263
1264<div class="doc_text">
1265
1266<div class="doc_code">
1267<pre>
1268!2 = metadata !{
1269 i32 458788, ;; Tag
1270 metadata !1, ;; Context
1271 metadata !"short int",
1272 metadata !1, ;; Compile Unit
1273 i32 0, ;; Line number
1274 i64 16, ;; Size in Bits
1275 i64 16, ;; Align in Bits
1276 i64 0, ;; Offset in Bits
1277 i32 0, ;; Flags
1278 i32 5 ;; Encoding
1279}
1280</pre>
1281</div>
1282
1283</div>
1284
1285<!-- ======================================================================= -->
1286<div class="doc_subsubsection">
1287 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1288</div>
1289
1290<div class="doc_text">
1291
1292<div class="doc_code">
1293<pre>
1294!2 = metadata !{
1295 i32 458788, ;; Tag
1296 metadata !1, ;; Context
1297 metadata !"short unsigned int",
1298 metadata !1, ;; Compile Unit
1299 i32 0, ;; Line number
1300 i64 16, ;; Size in Bits
1301 i64 16, ;; Align in Bits
1302 i64 0, ;; Offset in Bits
1303 i32 0, ;; Flags
1304 i32 7 ;; Encoding
1305}
1306</pre>
1307</div>
1308
1309</div>
1310
1311<!-- ======================================================================= -->
1312<div class="doc_subsubsection">
1313 <a name="ccxx_basic_int">int</a>
1314</div>
1315
1316<div class="doc_text">
1317
1318<div class="doc_code">
1319<pre>
1320!2 = metadata !{
1321 i32 458788, ;; Tag
1322 metadata !1, ;; Context
1323 metadata !"int", ;; Name
1324 metadata !1, ;; Compile Unit
1325 i32 0, ;; Line number
1326 i64 32, ;; Size in Bits
1327 i64 32, ;; Align in Bits
1328 i64 0, ;; Offset in Bits
1329 i32 0, ;; Flags
1330 i32 5 ;; Encoding
1331}
1332</pre></div>
1333
1334</div>
1335
1336<!-- ======================================================================= -->
1337<div class="doc_subsubsection">
1338 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1339</div>
1340
1341<div class="doc_text">
1342
1343<div class="doc_code">
1344<pre>
1345!2 = metadata !{
1346 i32 458788, ;; Tag
1347 metadata !1, ;; Context
1348 metadata !"unsigned int",
1349 metadata !1, ;; Compile Unit
1350 i32 0, ;; Line number
1351 i64 32, ;; Size in Bits
1352 i64 32, ;; Align in Bits
1353 i64 0, ;; Offset in Bits
1354 i32 0, ;; Flags
1355 i32 7 ;; Encoding
1356}
1357</pre>
1358</div>
1359
1360</div>
1361
1362<!-- ======================================================================= -->
1363<div class="doc_subsubsection">
1364 <a name="ccxx_basic_long_long">long long</a>
1365</div>
1366
1367<div class="doc_text">
1368
1369<div class="doc_code">
1370<pre>
1371!2 = metadata !{
1372 i32 458788, ;; Tag
1373 metadata !1, ;; Context
1374 metadata !"long long int",
1375 metadata !1, ;; Compile Unit
1376 i32 0, ;; Line number
1377 i64 64, ;; Size in Bits
1378 i64 64, ;; Align in Bits
1379 i64 0, ;; Offset in Bits
1380 i32 0, ;; Flags
1381 i32 5 ;; Encoding
1382}
1383</pre>
1384</div>
1385
1386</div>
1387
1388<!-- ======================================================================= -->
1389<div class="doc_subsubsection">
1390 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1391</div>
1392
1393<div class="doc_text">
1394
1395<div class="doc_code">
1396<pre>
1397!2 = metadata !{
1398 i32 458788, ;; Tag
1399 metadata !1, ;; Context
1400 metadata !"long long unsigned int",
1401 metadata !1, ;; Compile Unit
1402 i32 0, ;; Line number
1403 i64 64, ;; Size in Bits
1404 i64 64, ;; Align in Bits
1405 i64 0, ;; Offset in Bits
1406 i32 0, ;; Flags
1407 i32 7 ;; Encoding
1408}
1409</pre>
1410</div>
1411
1412</div>
1413
1414<!-- ======================================================================= -->
1415<div class="doc_subsubsection">
1416 <a name="ccxx_basic_float">float</a>
1417</div>
1418
1419<div class="doc_text">
1420
1421<div class="doc_code">
1422<pre>
1423!2 = metadata !{
1424 i32 458788, ;; Tag
1425 metadata !1, ;; Context
1426 metadata !"float",
1427 metadata !1, ;; Compile Unit
1428 i32 0, ;; Line number
1429 i64 32, ;; Size in Bits
1430 i64 32, ;; Align in Bits
1431 i64 0, ;; Offset in Bits
1432 i32 0, ;; Flags
1433 i32 4 ;; Encoding
1434}
1435</pre>
1436</div>
1437
1438</div>
1439
1440<!-- ======================================================================= -->
1441<div class="doc_subsubsection">
1442 <a name="ccxx_basic_double">double</a>
1443</div>
1444
1445<div class="doc_text">
1446
1447<div class="doc_code">
1448<pre>
1449!2 = metadata !{
1450 i32 458788, ;; Tag
1451 metadata !1, ;; Context
1452 metadata !"double",;; Name
1453 metadata !1, ;; Compile Unit
1454 i32 0, ;; Line number
1455 i64 64, ;; Size in Bits
1456 i64 64, ;; Align in Bits
1457 i64 0, ;; Offset in Bits
1458 i32 0, ;; Flags
1459 i32 4 ;; Encoding
1460}
1461</pre>
1462</div>
1463
1464</div>
1465
1466<!-- ======================================================================= -->
1467<div class="doc_subsection">
1468 <a name="ccxx_derived_types">C/C++ derived types</a>
1469</div>
1470
1471<div class="doc_text">
1472
1473<p>Given the following as an example of C/C++ derived type:</p>
1474
1475<div class="doc_code">
1476<pre>
1477typedef const int *IntPtr;
1478</pre>
1479</div>
1480
1481<p>a C/C++ front-end would generate the following descriptors:</p>
1482
1483<div class="doc_code">
1484<pre>
1485;;
1486;; Define the typedef "IntPtr".
1487;;
1488!2 = metadata !{
1489 i32 458774, ;; Tag
1490 metadata !1, ;; Context
1491 metadata !"IntPtr", ;; Name
1492 metadata !3, ;; Compile unit
1493 i32 0, ;; Line number
1494 i64 0, ;; Size in bits
1495 i64 0, ;; Align in bits
1496 i64 0, ;; Offset in bits
1497 i32 0, ;; Flags
1498 metadata !4 ;; Derived From type
1499}
1500
1501;;
1502;; Define the pointer type.
1503;;
1504!4 = metadata !{
1505 i32 458767, ;; Tag
1506 metadata !1, ;; Context
1507 metadata !"", ;; Name
1508 metadata !1, ;; Compile unit
1509 i32 0, ;; Line number
1510 i64 64, ;; Size in bits
1511 i64 64, ;; Align in bits
1512 i64 0, ;; Offset in bits
1513 i32 0, ;; Flags
1514 metadata !5 ;; Derived From type
1515}
1516;;
1517;; Define the const type.
1518;;
1519!5 = metadata !{
1520 i32 458790, ;; Tag
1521 metadata !1, ;; Context
1522 metadata !"", ;; Name
1523 metadata !1, ;; Compile unit
1524 i32 0, ;; Line number
1525 i64 32, ;; Size in bits
1526 i64 32, ;; Align in bits
1527 i64 0, ;; Offset in bits
1528 i32 0, ;; Flags
1529 metadata !6 ;; Derived From type
1530}
1531;;
1532;; Define the int type.
1533;;
1534!6 = metadata !{
1535 i32 458788, ;; Tag
1536 metadata !1, ;; Context
1537 metadata !"int", ;; Name
1538 metadata !1, ;; Compile unit
1539 i32 0, ;; Line number
1540 i64 32, ;; Size in bits
1541 i64 32, ;; Align in bits
1542 i64 0, ;; Offset in bits
1543 i32 0, ;; Flags
1544 5 ;; Encoding
1545}
1546</pre>
1547</div>
1548
1549</div>
1550
1551<!-- ======================================================================= -->
1552<div class="doc_subsection">
1553 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1554</div>
1555
1556<div class="doc_text">
1557
1558<p>Given the following as an example of C/C++ struct type:</p>
1559
1560<div class="doc_code">
1561<pre>
1562struct Color {
1563 unsigned Red;
1564 unsigned Green;
1565 unsigned Blue;
1566};
1567</pre>
1568</div>
1569
1570<p>a C/C++ front-end would generate the following descriptors:</p>
1571
1572<div class="doc_code">
1573<pre>
1574;;
1575;; Define basic type for unsigned int.
1576;;
1577!5 = metadata !{
1578 i32 458788, ;; Tag
1579 metadata !1, ;; Context
1580 metadata !"unsigned int",
1581 metadata !1, ;; Compile Unit
1582 i32 0, ;; Line number
1583 i64 32, ;; Size in Bits
1584 i64 32, ;; Align in Bits
1585 i64 0, ;; Offset in Bits
1586 i32 0, ;; Flags
1587 i32 7 ;; Encoding
1588}
1589;;
1590;; Define composite type for struct Color.
1591;;
1592!2 = metadata !{
1593 i32 458771, ;; Tag
1594 metadata !1, ;; Context
1595 metadata !"Color", ;; Name
1596 metadata !1, ;; Compile unit
1597 i32 1, ;; Line number
1598 i64 96, ;; Size in bits
1599 i64 32, ;; Align in bits
1600 i64 0, ;; Offset in bits
1601 i32 0, ;; Flags
1602 null, ;; Derived From
1603 metadata !3, ;; Elements
1604 i32 0 ;; Runtime Language
1605}
1606
1607;;
1608;; Define the Red field.
1609;;
1610!4 = metadata !{
1611 i32 458765, ;; Tag
1612 metadata !1, ;; Context
1613 metadata !"Red", ;; Name
1614 metadata !1, ;; Compile Unit
1615 i32 2, ;; Line number
1616 i64 32, ;; Size in bits
1617 i64 32, ;; Align in bits
1618 i64 0, ;; Offset in bits
1619 i32 0, ;; Flags
1620 metadata !5 ;; Derived From type
1621}
1622
1623;;
1624;; Define the Green field.
1625;;
1626!6 = metadata !{
1627 i32 458765, ;; Tag
1628 metadata !1, ;; Context
1629 metadata !"Green", ;; Name
1630 metadata !1, ;; Compile Unit
1631 i32 3, ;; Line number
1632 i64 32, ;; Size in bits
1633 i64 32, ;; Align in bits
1634 i64 32, ;; Offset in bits
1635 i32 0, ;; Flags
1636 metadata !5 ;; Derived From type
1637}
1638
1639;;
1640;; Define the Blue field.
1641;;
1642!7 = metadata !{
1643 i32 458765, ;; Tag
1644 metadata !1, ;; Context
1645 metadata !"Blue", ;; Name
1646 metadata !1, ;; Compile Unit
1647 i32 4, ;; Line number
1648 i64 32, ;; Size in bits
1649 i64 32, ;; Align in bits
1650 i64 64, ;; Offset in bits
1651 i32 0, ;; Flags
1652 metadata !5 ;; Derived From type
1653}
1654
1655;;
1656;; Define the array of fields used by the composite type Color.
1657;;
1658!3 = metadata !{metadata !4, metadata !6, metadata !7}
1659</pre>
1660</div>
1661
1662</div>
1663
1664<!-- ======================================================================= -->
1665<div class="doc_subsection">
1666 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1667</div>
1668
1669<div class="doc_text">
1670
1671<p>Given the following as an example of C/C++ enumeration type:</p>
1672
1673<div class="doc_code">
1674<pre>
1675enum Trees {
1676 Spruce = 100,
1677 Oak = 200,
1678 Maple = 300
1679};
1680</pre>
1681</div>
1682
1683<p>a C/C++ front-end would generate the following descriptors:</p>
1684
1685<div class="doc_code">
1686<pre>
1687;;
1688;; Define composite type for enum Trees
1689;;
1690!2 = metadata !{
1691 i32 458756, ;; Tag
1692 metadata !1, ;; Context
1693 metadata !"Trees", ;; Name
1694 metadata !1, ;; Compile unit
1695 i32 1, ;; Line number
1696 i64 32, ;; Size in bits
1697 i64 32, ;; Align in bits
1698 i64 0, ;; Offset in bits
1699 i32 0, ;; Flags
1700 null, ;; Derived From type
1701 metadata !3, ;; Elements
1702 i32 0 ;; Runtime language
1703}
1704
1705;;
1706;; Define the array of enumerators used by composite type Trees.
1707;;
1708!3 = metadata !{metadata !4, metadata !5, metadata !6}
1709
1710;;
1711;; Define Spruce enumerator.
1712;;
1713!4 = metadata !{i32 458792, metadata !"Spruce", i64 100}
1714
1715;;
1716;; Define Oak enumerator.
1717;;
1718!5 = metadata !{i32 458792, metadata !"Oak", i64 200}
1719
1720;;
1721;; Define Maple enumerator.
1722;;
1723!6 = metadata !{i32 458792, metadata !"Maple", i64 300}
1724
1725</pre>
1726</div>
1727
1728</div>
1729
1730<!-- *********************************************************************** -->
1731
1732<hr>
1733<address>
1734 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1735 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
1736 <a href="http://validator.w3.org/check/referer"><img
1737 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
1738
1739 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1740 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
1741 Last modified: $Date: 2010-01-11 14:53:48 -0800 (Mon, 11 Jan 2010) $
1742</address>
1743
1744</body>
1745</html>