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11 <div class="doc_title">Source Level Debugging with LLVM</div>
13 <table class="layout" style="width:100%">
17 <li><a href="#introduction">Introduction</a>
19 <li><a href="#phil">Philosophy behind LLVM debugging information</a></li>
20 <li><a href="#consumers">Debug information consumers</a></li>
21 <li><a href="#debugopt">Debugging optimized code</a></li>
23 <li><a href="#format">Debugging information format</a>
25 <li><a href="#debug_info_descriptors">Debug information descriptors</a>
27 <li><a href="#format_compile_units">Compile unit descriptors</a></li>
28 <li><a href="#format_files">File descriptors</a></li>
29 <li><a href="#format_global_variables">Global variable descriptors</a></li>
30 <li><a href="#format_subprograms">Subprogram descriptors</a></li>
31 <li><a href="#format_blocks">Block descriptors</a></li>
32 <li><a href="#format_basic_type">Basic type descriptors</a></li>
33 <li><a href="#format_derived_type">Derived type descriptors</a></li>
34 <li><a href="#format_composite_type">Composite type descriptors</a></li>
35 <li><a href="#format_subrange">Subrange descriptors</a></li>
36 <li><a href="#format_enumeration">Enumerator descriptors</a></li>
37 <li><a href="#format_variables">Local variables</a></li>
39 <li><a href="#format_common_intrinsics">Debugger intrinsic functions</a>
41 <li><a href="#format_common_declare">llvm.dbg.declare</a></li>
42 <li><a href="#format_common_value">llvm.dbg.value</a></li>
45 <li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
46 <li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a>
48 <li><a href="#ccxx_compile_units">C/C++ source file information</a></li>
49 <li><a href="#ccxx_global_variable">C/C++ global variable information</a></li>
50 <li><a href="#ccxx_subprogram">C/C++ function information</a></li>
51 <li><a href="#ccxx_basic_types">C/C++ basic types</a></li>
52 <li><a href="#ccxx_derived_types">C/C++ derived types</a></li>
53 <li><a href="#ccxx_composite_types">C/C++ struct/union types</a></li>
54 <li><a href="#ccxx_enumeration_types">C/C++ enumeration types</a></li>
59 <img src="img/venusflytrap.jpg" alt="A leafy and green bug eater" width="247"
64 <div class="doc_author">
65 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>
66 and <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
70 <!-- *********************************************************************** -->
71 <div class="doc_section"><a name="introduction">Introduction</a></div>
72 <!-- *********************************************************************** -->
74 <div class="doc_text">
76 <p>This document is the central repository for all information pertaining to
77 debug information in LLVM. It describes the <a href="#format">actual format
78 that the LLVM debug information</a> takes, which is useful for those
79 interested in creating front-ends or dealing directly with the information.
80 Further, this document provides specific examples of what debug information
81 for C/C++ looks like.</p>
85 <!-- ======================================================================= -->
86 <div class="doc_subsection">
87 <a name="phil">Philosophy behind LLVM debugging information</a>
90 <div class="doc_text">
92 <p>The idea of the LLVM debugging information is to capture how the important
93 pieces of the source-language's Abstract Syntax Tree map onto LLVM code.
94 Several design aspects have shaped the solution that appears here. The
95 important ones are:</p>
98 <li>Debugging information should have very little impact on the rest of the
99 compiler. No transformations, analyses, or code generators should need to
100 be modified because of debugging information.</li>
102 <li>LLVM optimizations should interact in <a href="#debugopt">well-defined and
103 easily described ways</a> with the debugging information.</li>
105 <li>Because LLVM is designed to support arbitrary programming languages,
106 LLVM-to-LLVM tools should not need to know anything about the semantics of
107 the source-level-language.</li>
109 <li>Source-level languages are often <b>widely</b> different from one another.
110 LLVM should not put any restrictions of the flavor of the source-language,
111 and the debugging information should work with any language.</li>
113 <li>With code generator support, it should be possible to use an LLVM compiler
114 to compile a program to native machine code and standard debugging
115 formats. This allows compatibility with traditional machine-code level
116 debuggers, like GDB or DBX.</li>
119 <p>The approach used by the LLVM implementation is to use a small set
120 of <a href="#format_common_intrinsics">intrinsic functions</a> to define a
121 mapping between LLVM program objects and the source-level objects. The
122 description of the source-level program is maintained in LLVM metadata
123 in an <a href="#ccxx_frontend">implementation-defined format</a>
124 (the C/C++ front-end currently uses working draft 7 of
125 the <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3
128 <p>When a program is being debugged, a debugger interacts with the user and
129 turns the stored debug information into source-language specific information.
130 As such, a debugger must be aware of the source-language, and is thus tied to
131 a specific language or family of languages.</p>
135 <!-- ======================================================================= -->
136 <div class="doc_subsection">
137 <a name="consumers">Debug information consumers</a>
140 <div class="doc_text">
142 <p>The role of debug information is to provide meta information normally
143 stripped away during the compilation process. This meta information provides
144 an LLVM user a relationship between generated code and the original program
147 <p>Currently, debug information is consumed by DwarfDebug to produce dwarf
148 information used by the gdb debugger. Other targets could use the same
149 information to produce stabs or other debug forms.</p>
151 <p>It would also be reasonable to use debug information to feed profiling tools
152 for analysis of generated code, or, tools for reconstructing the original
153 source from generated code.</p>
155 <p>TODO - expound a bit more.</p>
159 <!-- ======================================================================= -->
160 <div class="doc_subsection">
161 <a name="debugopt">Debugging optimized code</a>
164 <div class="doc_text">
166 <p>An extremely high priority of LLVM debugging information is to make it
167 interact well with optimizations and analysis. In particular, the LLVM debug
168 information provides the following guarantees:</p>
171 <li>LLVM debug information <b>always provides information to accurately read
172 the source-level state of the program</b>, regardless of which LLVM
173 optimizations have been run, and without any modification to the
174 optimizations themselves. However, some optimizations may impact the
175 ability to modify the current state of the program with a debugger, such
176 as setting program variables, or calling functions that have been
179 <li>LLVM optimizations gracefully interact with debugging information. If
180 they are not aware of debug information, they are automatically disabled
181 as necessary in the cases that would invalidate the debug info. This
182 retains the LLVM features, making it easy to write new
183 transformations.</li>
185 <li>As desired, LLVM optimizations can be upgraded to be aware of the LLVM
186 debugging information, allowing them to update the debugging information
187 as they perform aggressive optimizations. This means that, with effort,
188 the LLVM optimizers could optimize debug code just as well as non-debug
191 <li>LLVM debug information does not prevent many important optimizations from
192 happening (for example inlining, basic block reordering/merging/cleanup,
193 tail duplication, etc), further reducing the amount of the compiler that
194 eventually is "aware" of debugging information.</li>
196 <li>LLVM debug information is automatically optimized along with the rest of
197 the program, using existing facilities. For example, duplicate
198 information is automatically merged by the linker, and unused information
199 is automatically removed.</li>
202 <p>Basically, the debug information allows you to compile a program with
203 "<tt>-O0 -g</tt>" and get full debug information, allowing you to arbitrarily
204 modify the program as it executes from a debugger. Compiling a program with
205 "<tt>-O3 -g</tt>" gives you full debug information that is always available
206 and accurate for reading (e.g., you get accurate stack traces despite tail
207 call elimination and inlining), but you might lose the ability to modify the
208 program and call functions where were optimized out of the program, or
209 inlined away completely.</p>
211 <p><a href="TestingGuide.html#quicktestsuite">LLVM test suite</a> provides a
212 framework to test optimizer's handling of debugging information. It can be
215 <div class="doc_code">
217 % cd llvm/projects/test-suite/MultiSource/Benchmarks # or some other level
222 <p>This will test impact of debugging information on optimization passes. If
223 debugging information influences optimization passes then it will be reported
224 as a failure. See <a href="TestingGuide.html">TestingGuide</a> for more
225 information on LLVM test infrastructure and how to run various tests.</p>
229 <!-- *********************************************************************** -->
230 <div class="doc_section">
231 <a name="format">Debugging information format</a>
233 <!-- *********************************************************************** -->
235 <div class="doc_text">
237 <p>LLVM debugging information has been carefully designed to make it possible
238 for the optimizer to optimize the program and debugging information without
239 necessarily having to know anything about debugging information. In
240 particular, the use of metadata avoids duplicated debugging information from
241 the beginning, and the global dead code elimination pass automatically
242 deletes debugging information for a function if it decides to delete the
245 <p>To do this, most of the debugging information (descriptors for types,
246 variables, functions, source files, etc) is inserted by the language
247 front-end in the form of LLVM metadata. </p>
249 <p>Debug information is designed to be agnostic about the target debugger and
250 debugging information representation (e.g. DWARF/Stabs/etc). It uses a
251 generic pass to decode the information that represents variables, types,
252 functions, namespaces, etc: this allows for arbitrary source-language
253 semantics and type-systems to be used, as long as there is a module
254 written for the target debugger to interpret the information. </p>
256 <p>To provide basic functionality, the LLVM debugger does have to make some
257 assumptions about the source-level language being debugged, though it keeps
258 these to a minimum. The only common features that the LLVM debugger assumes
259 exist are <a href="#format_files">source files</a>,
260 and <a href="#format_global_variables">program objects</a>. These abstract
261 objects are used by a debugger to form stack traces, show information about
262 local variables, etc.</p>
264 <p>This section of the documentation first describes the representation aspects
265 common to any source-language. The <a href="#ccxx_frontend">next section</a>
266 describes the data layout conventions used by the C and C++ front-ends.</p>
270 <!-- ======================================================================= -->
271 <div class="doc_subsection">
272 <a name="debug_info_descriptors">Debug information descriptors</a>
275 <div class="doc_text">
277 <p>In consideration of the complexity and volume of debug information, LLVM
278 provides a specification for well formed debug descriptors. </p>
280 <p>Consumers of LLVM debug information expect the descriptors for program
281 objects to start in a canonical format, but the descriptors can include
282 additional information appended at the end that is source-language
283 specific. All LLVM debugging information is versioned, allowing backwards
284 compatibility in the case that the core structures need to change in some
285 way. Also, all debugging information objects start with a tag to indicate
286 what type of object it is. The source-language is allowed to define its own
287 objects, by using unreserved tag numbers. We recommend using with tags in
288 the range 0x1000 through 0x2000 (there is a defined enum DW_TAG_user_base =
291 <p>The fields of debug descriptors used internally by LLVM
292 are restricted to only the simple data types <tt>i32</tt>, <tt>i1</tt>,
293 <tt>float</tt>, <tt>double</tt>, <tt>mdstring</tt> and <tt>mdnode</tt>. </p>
295 <div class="doc_code">
304 <p><a name="LLVMDebugVersion">The first field of a descriptor is always an
305 <tt>i32</tt> containing a tag value identifying the content of the
306 descriptor. The remaining fields are specific to the descriptor. The values
307 of tags are loosely bound to the tag values of DWARF information entries.
308 However, that does not restrict the use of the information supplied to DWARF
309 targets. To facilitate versioning of debug information, the tag is augmented
310 with the current debug version (LLVMDebugVersion = 8 << 16 or 0x80000 or
313 <p>The details of the various descriptors follow.</p>
317 <!-- ======================================================================= -->
318 <div class="doc_subsubsection">
319 <a name="format_compile_units">Compile unit descriptors</a>
322 <div class="doc_text">
324 <div class="doc_code">
327 i32, ;; Tag = 17 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
328 ;; (DW_TAG_compile_unit)
329 i32, ;; Unused field.
330 i32, ;; DWARF language identifier (ex. DW_LANG_C89)
331 metadata, ;; Source file name
332 metadata, ;; Source file directory (includes trailing slash)
333 metadata ;; Producer (ex. "4.0.1 LLVM (LLVM research group)")
334 i1, ;; True if this is a main compile unit.
335 i1, ;; True if this is optimized.
337 i32 ;; Runtime version
342 <p>These descriptors contain a source language ID for the file (we use the DWARF
343 3.0 ID numbers, such as <tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>,
344 <tt>DW_LANG_Cobol74</tt>, etc), three strings describing the filename,
345 working directory of the compiler, and an identifier string for the compiler
346 that produced it.</p>
348 <p>Compile unit descriptors provide the root context for objects declared in a
349 specific compilation unit. File descriptors are defined using this context.</p>
353 <!-- ======================================================================= -->
354 <div class="doc_subsubsection">
355 <a name="format_files">File descriptors</a>
358 <div class="doc_text">
360 <div class="doc_code">
363 i32, ;; Tag = 41 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
364 ;; (DW_TAG_file_type)
365 metadata, ;; Source file name
366 metadata, ;; Source file directory (includes trailing slash)
367 metadata ;; Reference to compile unit where defined
372 <p>These descriptors contain information for a file. Global variables and top
373 level functions would be defined using this context.k File descriptors also
374 provide context for source line correspondence. </p>
376 <p>Each input file is encoded as a separate file descriptor in LLVM debugging
377 information output. Each file descriptor would be defined using a
382 <!-- ======================================================================= -->
383 <div class="doc_subsubsection">
384 <a name="format_global_variables">Global variable descriptors</a>
387 <div class="doc_text">
389 <div class="doc_code">
392 i32, ;; Tag = 52 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
394 i32, ;; Unused field.
395 metadata, ;; Reference to context descriptor
397 metadata, ;; Display name (fully qualified C++ name)
398 metadata, ;; MIPS linkage name (for C++)
399 metadata, ;; Reference to file where defined
400 i32, ;; Line number where defined
401 metadata, ;; Reference to type descriptor
402 i1, ;; True if the global is local to compile unit (static)
403 i1, ;; True if the global is defined in the compile unit (not extern)
404 {}* ;; Reference to the global variable
409 <p>These descriptors provide debug information about globals variables. The
410 provide details such as name, type and where the variable is defined.</p>
414 <!-- ======================================================================= -->
415 <div class="doc_subsubsection">
416 <a name="format_subprograms">Subprogram descriptors</a>
419 <div class="doc_text">
421 <div class="doc_code">
424 i32, ;; Tag = 46 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
425 ;; (DW_TAG_subprogram)
426 i32, ;; Unused field.
427 metadata, ;; Reference to context descriptor
429 metadata, ;; Display name (fully qualified C++ name)
430 metadata, ;; MIPS linkage name (for C++)
431 metadata, ;; Reference to file where defined
432 i32, ;; Line number where defined
433 metadata, ;; Reference to type descriptor
434 i1, ;; True if the global is local to compile unit (static)
435 i1 ;; True if the global is defined in the compile unit (not extern)
436 i32 ;; Virtuality, e.g. dwarf::DW_VIRTUALITY__virtual
437 i32 ;; Index into a virtual function
438 metadata, ;; indicates which base type contains the vtable pointer for the
442 Function *;; Pointer to LLVM function
447 <p>These descriptors provide debug information about functions, methods and
448 subprograms. They provide details such as name, return types and the source
449 location where the subprogram is defined.</p>
453 <!-- ======================================================================= -->
454 <div class="doc_subsubsection">
455 <a name="format_blocks">Block descriptors</a>
458 <div class="doc_text">
460 <div class="doc_code">
463 i32, ;; Tag = 11 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_lexical_block)
464 metadata,;; Reference to context descriptor
466 i32, ;; Column number
467 metadata,;; Reference to source file
468 i32 ;; Unique ID to identify blocks from a template function
473 <p>These descriptors provide debug information about nested blocks within a
474 subprogram. The line number and column numbers are used to dinstinguish
475 two lexical blocks at same depth. </p>
479 <!-- ======================================================================= -->
480 <div class="doc_subsubsection">
481 <a name="format_basic_type">Basic type descriptors</a>
484 <div class="doc_text">
486 <div class="doc_code">
489 i32, ;; Tag = 36 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
490 ;; (DW_TAG_base_type)
491 metadata, ;; Reference to context (typically a compile unit)
492 metadata, ;; Name (may be "" for anonymous types)
493 metadata, ;; Reference to file where defined (may be NULL)
494 i32, ;; Line number where defined (may be 0)
496 i64, ;; Alignment in bits
497 i64, ;; Offset in bits
499 i32 ;; DWARF type encoding
504 <p>These descriptors define primitive types used in the code. Example int, bool
505 and float. The context provides the scope of the type, which is usually the
506 top level. Since basic types are not usually user defined the compile unit
507 and line number can be left as NULL and 0. The size, alignment and offset
508 are expressed in bits and can be 64 bit values. The alignment is used to
509 round the offset when embedded in a
510 <a href="#format_composite_type">composite type</a> (example to keep float
511 doubles on 64 bit boundaries.) The offset is the bit offset if embedded in
512 a <a href="#format_composite_type">composite type</a>.</p>
514 <p>The type encoding provides the details of the type. The values are typically
515 one of the following:</p>
517 <div class="doc_code">
523 DW_ATE_signed_char = 6
525 DW_ATE_unsigned_char = 8
531 <!-- ======================================================================= -->
532 <div class="doc_subsubsection">
533 <a name="format_derived_type">Derived type descriptors</a>
536 <div class="doc_text">
538 <div class="doc_code">
541 i32, ;; Tag (see below)
542 metadata, ;; Reference to context
543 metadata, ;; Name (may be "" for anonymous types)
544 metadata, ;; Reference to file where defined (may be NULL)
545 i32, ;; Line number where defined (may be 0)
547 i64, ;; Alignment in bits
548 i64, ;; Offset in bits
549 metadata ;; Reference to type derived from
554 <p>These descriptors are used to define types derived from other types. The
555 value of the tag varies depending on the meaning. The following are possible
558 <div class="doc_code">
560 DW_TAG_formal_parameter = 5
562 DW_TAG_pointer_type = 15
563 DW_TAG_reference_type = 16
565 DW_TAG_const_type = 38
566 DW_TAG_volatile_type = 53
567 DW_TAG_restrict_type = 55
571 <p><tt>DW_TAG_member</tt> is used to define a member of
572 a <a href="#format_composite_type">composite type</a>
573 or <a href="#format_subprograms">subprogram</a>. The type of the member is
574 the <a href="#format_derived_type">derived
575 type</a>. <tt>DW_TAG_formal_parameter</tt> is used to define a member which
576 is a formal argument of a subprogram.</p>
578 <p><tt>DW_TAG_typedef</tt> is used to provide a name for the derived type.</p>
580 <p><tt>DW_TAG_pointer_type</tt>,<tt>DW_TAG_reference_type</tt>,
581 <tt>DW_TAG_const_type</tt>, <tt>DW_TAG_volatile_type</tt>
582 and <tt>DW_TAG_restrict_type</tt> are used to qualify
583 the <a href="#format_derived_type">derived type</a>. </p>
585 <p><a href="#format_derived_type">Derived type</a> location can be determined
586 from the compile unit and line number. The size, alignment and offset are
587 expressed in bits and can be 64 bit values. The alignment is used to round
588 the offset when embedded in a <a href="#format_composite_type">composite
589 type</a> (example to keep float doubles on 64 bit boundaries.) The offset is
590 the bit offset if embedded in a <a href="#format_composite_type">composite
593 <p>Note that the <tt>void *</tt> type is expressed as a type derived from NULL.
598 <!-- ======================================================================= -->
599 <div class="doc_subsubsection">
600 <a name="format_composite_type">Composite type descriptors</a>
603 <div class="doc_text">
605 <div class="doc_code">
608 i32, ;; Tag (see below)
609 metadata, ;; Reference to context
610 metadata, ;; Name (may be "" for anonymous types)
611 metadata, ;; Reference to file where defined (may be NULL)
612 i32, ;; Line number where defined (may be 0)
614 i64, ;; Alignment in bits
615 i64, ;; Offset in bits
617 metadata, ;; Reference to type derived from
618 metadata, ;; Reference to array of member descriptors
619 i32 ;; Runtime languages
624 <p>These descriptors are used to define types that are composed of 0 or more
625 elements. The value of the tag varies depending on the meaning. The following
626 are possible tag values:</p>
628 <div class="doc_code">
630 DW_TAG_array_type = 1
631 DW_TAG_enumeration_type = 4
632 DW_TAG_structure_type = 19
633 DW_TAG_union_type = 23
634 DW_TAG_vector_type = 259
635 DW_TAG_subroutine_type = 21
636 DW_TAG_inheritance = 28
640 <p>The vector flag indicates that an array type is a native packed vector.</p>
642 <p>The members of array types (tag = <tt>DW_TAG_array_type</tt>) or vector types
643 (tag = <tt>DW_TAG_vector_type</tt>) are <a href="#format_subrange">subrange
644 descriptors</a>, each representing the range of subscripts at that level of
647 <p>The members of enumeration types (tag = <tt>DW_TAG_enumeration_type</tt>) are
648 <a href="#format_enumeration">enumerator descriptors</a>, each representing
649 the definition of enumeration value for the set.</p>
651 <p>The members of structure (tag = <tt>DW_TAG_structure_type</tt>) or union (tag
652 = <tt>DW_TAG_union_type</tt>) types are any one of
653 the <a href="#format_basic_type">basic</a>,
654 <a href="#format_derived_type">derived</a>
655 or <a href="#format_composite_type">composite</a> type descriptors, each
656 representing a field member of the structure or union.</p>
658 <p>For C++ classes (tag = <tt>DW_TAG_structure_type</tt>), member descriptors
659 provide information about base classes, static members and member
660 functions. If a member is a <a href="#format_derived_type">derived type
661 descriptor</a> and has a tag of <tt>DW_TAG_inheritance</tt>, then the type
662 represents a base class. If the member of is
663 a <a href="#format_global_variables">global variable descriptor</a> then it
664 represents a static member. And, if the member is
665 a <a href="#format_subprograms">subprogram descriptor</a> then it represents
666 a member function. For static members and member
667 functions, <tt>getName()</tt> returns the members link or the C++ mangled
668 name. <tt>getDisplayName()</tt> the simplied version of the name.</p>
670 <p>The first member of subroutine (tag = <tt>DW_TAG_subroutine_type</tt>) type
671 elements is the return type for the subroutine. The remaining elements are
672 the formal arguments to the subroutine.</p>
674 <p><a href="#format_composite_type">Composite type</a> location can be
675 determined from the compile unit and line number. The size, alignment and
676 offset are expressed in bits and can be 64 bit values. The alignment is used
677 to round the offset when embedded in
678 a <a href="#format_composite_type">composite type</a> (as an example, to keep
679 float doubles on 64 bit boundaries.) The offset is the bit offset if embedded
680 in a <a href="#format_composite_type">composite type</a>.</p>
684 <!-- ======================================================================= -->
685 <div class="doc_subsubsection">
686 <a name="format_subrange">Subrange descriptors</a>
689 <div class="doc_text">
691 <div class="doc_code">
694 i32, ;; Tag = 33 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a> (DW_TAG_subrange_type)
701 <p>These descriptors are used to define ranges of array subscripts for an array
702 <a href="#format_composite_type">composite type</a>. The low value defines
703 the lower bounds typically zero for C/C++. The high value is the upper
704 bounds. Values are 64 bit. High - low + 1 is the size of the array. If low
705 == high the array will be unbounded.</p>
709 <!-- ======================================================================= -->
710 <div class="doc_subsubsection">
711 <a name="format_enumeration">Enumerator descriptors</a>
714 <div class="doc_text">
716 <div class="doc_code">
719 i32, ;; Tag = 40 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
720 ;; (DW_TAG_enumerator)
727 <p>These descriptors are used to define members of an
728 enumeration <a href="#format_composite_type">composite type</a>, it
729 associates the name to the value.</p>
733 <!-- ======================================================================= -->
734 <div class="doc_subsubsection">
735 <a name="format_variables">Local variables</a>
738 <div class="doc_text">
740 <div class="doc_code">
743 i32, ;; Tag (see below)
746 metadata, ;; Reference to file where defined
747 i32, ;; 24 bit - Line number where defined
748 ;; 8 bit - Argument number. 1 indicates 1st argument.
749 metadata ;; Type descriptor
754 <p>These descriptors are used to define variables local to a sub program. The
755 value of the tag depends on the usage of the variable:</p>
757 <div class="doc_code">
759 DW_TAG_auto_variable = 256
760 DW_TAG_arg_variable = 257
761 DW_TAG_return_variable = 258
765 <p>An auto variable is any variable declared in the body of the function. An
766 argument variable is any variable that appears as a formal argument to the
767 function. A return variable is used to track the result of a function and
768 has no source correspondent.</p>
770 <p>The context is either the subprogram or block where the variable is defined.
771 Name the source variable name. Compile unit and line indicate where the
772 variable was defined. Type descriptor defines the declared type of the
777 <!-- ======================================================================= -->
778 <div class="doc_subsection">
779 <a name="format_common_intrinsics">Debugger intrinsic functions</a>
782 <div class="doc_text">
784 <p>LLVM uses several intrinsic functions (name prefixed with "llvm.dbg") to
785 provide debug information at various points in generated code.</p>
789 <!-- ======================================================================= -->
790 <div class="doc_subsubsection">
791 <a name="format_common_declare">llvm.dbg.declare</a>
794 <div class="doc_text">
796 void %<a href="#format_common_declare">llvm.dbg.declare</a>(metadata, metadata)
799 <p>This intrinsic provides information about a local element (ex. variable.) The
800 first argument is metadata holding alloca for the variable.</tt>. The
801 second argument is metadata containing description of the variable. </p>
804 <!-- ======================================================================= -->
805 <div class="doc_subsubsection">
806 <a name="format_common_value">llvm.dbg.value</a>
809 <div class="doc_text">
811 void %<a href="#format_common_value">llvm.dbg.value</a>(metadata, i64, metadata)
814 <p>This intrinsic provides information when a user source variable is set to a
815 new value. The first argument is the new value (wrapped as metadata). The
816 second argument is the offset in the user source variable where the new value
817 is written. The third argument is metadata containing description of the
818 user source variable. </p>
821 <!-- ======================================================================= -->
822 <div class="doc_subsection">
823 <a name="format_common_lifetime">Object lifetimes and scoping</a>
826 <div class="doc_text">
827 <p>In many languages, the local variables in functions can have their lifetimes
828 or scopes limited to a subset of a function. In the C family of languages,
829 for example, variables are only live (readable and writable) within the
830 source block that they are defined in. In functional languages, values are
831 only readable after they have been defined. Though this is a very obvious
832 concept, it is non-trivial to model in LLVM, because it has no notion of
833 scoping in this sense, and does not want to be tied to a language's scoping
836 <p>In order to handle this, the LLVM debug format uses the metadata attached to
837 llvm instructions to encode line number and scoping information. Consider
838 the following C fragment, for example:</p>
840 <div class="doc_code">
854 <p>Compiled to LLVM, this function would be represented like this:</p>
856 <div class="doc_code">
858 define void @foo() nounwind ssp {
860 %X = alloca i32, align 4 ; <i32*> [#uses=4]
861 %Y = alloca i32, align 4 ; <i32*> [#uses=4]
862 %Z = alloca i32, align 4 ; <i32*> [#uses=3]
863 %0 = bitcast i32* %X to {}* ; <{}*> [#uses=1]
864 call void @llvm.dbg.declare(metadata !{i32 * %X}, metadata !0), !dbg !7
865 store i32 21, i32* %X, !dbg !8
866 %1 = bitcast i32* %Y to {}* ; <{}*> [#uses=1]
867 call void @llvm.dbg.declare(metadata !{i32 * %Y}, metadata !9), !dbg !10
868 store i32 22, i32* %Y, !dbg !11
869 %2 = bitcast i32* %Z to {}* ; <{}*> [#uses=1]
870 call void @llvm.dbg.declare(metadata !{i32 * %Z}, metadata !12), !dbg !14
871 store i32 23, i32* %Z, !dbg !15
872 %tmp = load i32* %X, !dbg !16 ; <i32> [#uses=1]
873 %tmp1 = load i32* %Y, !dbg !16 ; <i32> [#uses=1]
874 %add = add nsw i32 %tmp, %tmp1, !dbg !16 ; <i32> [#uses=1]
875 store i32 %add, i32* %Z, !dbg !16
876 %tmp2 = load i32* %Y, !dbg !17 ; <i32> [#uses=1]
877 store i32 %tmp2, i32* %X, !dbg !17
881 declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
883 !0 = metadata !{i32 459008, metadata !1, metadata !"X",
884 metadata !3, i32 2, metadata !6}; [ DW_TAG_auto_variable ]
885 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
886 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo", metadata !"foo",
887 metadata !"foo", metadata !3, i32 1, metadata !4,
888 i1 false, i1 true}; [DW_TAG_subprogram ]
889 !3 = metadata !{i32 458769, i32 0, i32 12, metadata !"foo.c",
890 metadata !"/private/tmp", metadata !"clang 1.1", i1 true,
891 i1 false, metadata !"", i32 0}; [DW_TAG_compile_unit ]
892 !4 = metadata !{i32 458773, metadata !3, metadata !"", null, i32 0, i64 0, i64 0,
893 i64 0, i32 0, null, metadata !5, i32 0}; [DW_TAG_subroutine_type ]
894 !5 = metadata !{null}
895 !6 = metadata !{i32 458788, metadata !3, metadata !"int", metadata !3, i32 0,
896 i64 32, i64 32, i64 0, i32 0, i32 5}; [DW_TAG_base_type ]
897 !7 = metadata !{i32 2, i32 7, metadata !1, null}
898 !8 = metadata !{i32 2, i32 3, metadata !1, null}
899 !9 = metadata !{i32 459008, metadata !1, metadata !"Y", metadata !3, i32 3,
900 metadata !6}; [ DW_TAG_auto_variable ]
901 !10 = metadata !{i32 3, i32 7, metadata !1, null}
902 !11 = metadata !{i32 3, i32 3, metadata !1, null}
903 !12 = metadata !{i32 459008, metadata !13, metadata !"Z", metadata !3, i32 5,
904 metadata !6}; [ DW_TAG_auto_variable ]
905 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
906 !14 = metadata !{i32 5, i32 9, metadata !13, null}
907 !15 = metadata !{i32 5, i32 5, metadata !13, null}
908 !16 = metadata !{i32 6, i32 5, metadata !13, null}
909 !17 = metadata !{i32 8, i32 3, metadata !1, null}
910 !18 = metadata !{i32 9, i32 1, metadata !2, null}
914 <p>This example illustrates a few important details about LLVM debugging
915 information. In particular, it shows how the <tt>llvm.dbg.declare</tt>
916 intrinsic and location information, which are attached to an instruction,
917 are applied together to allow a debugger to analyze the relationship between
918 statements, variable definitions, and the code used to implement the
921 <div class="doc_code">
923 call void @llvm.dbg.declare(metadata, metadata !0), !dbg !7
927 <p>The first intrinsic
928 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
929 encodes debugging information for the variable <tt>X</tt>. The metadata
930 <tt>!dbg !7</tt> attached to the intrinsic provides scope information for the
931 variable <tt>X</tt>.</p>
933 <div class="doc_code">
935 !7 = metadata !{i32 2, i32 7, metadata !1, null}
936 !1 = metadata !{i32 458763, metadata !2}; [DW_TAG_lexical_block ]
937 !2 = metadata !{i32 458798, i32 0, metadata !3, metadata !"foo",
938 metadata !"foo", metadata !"foo", metadata !3, i32 1,
939 metadata !4, i1 false, i1 true}; [DW_TAG_subprogram ]
943 <p>Here <tt>!7</tt> is metadata providing location information. It has four
944 fields: line number, column number, scope, and original scope. The original
945 scope represents inline location if this instruction is inlined inside a
946 caller, and is null otherwise. In this example, scope is encoded by
947 <tt>!1</tt>. <tt>!1</tt> represents a lexical block inside the scope
948 <tt>!2</tt>, where <tt>!2</tt> is a
949 <a href="#format_subprograms">subprogram descriptor</a>. This way the
950 location information attached to the intrinsics indicates that the
951 variable <tt>X</tt> is declared at line number 2 at a function level scope in
952 function <tt>foo</tt>.</p>
954 <p>Now lets take another example.</p>
956 <div class="doc_code">
958 call void @llvm.dbg.declare(metadata, metadata !12), !dbg !14
962 <p>The second intrinsic
963 <tt>%<a href="#format_common_declare">llvm.dbg.declare</a></tt>
964 encodes debugging information for variable <tt>Z</tt>. The metadata
965 <tt>!dbg !14</tt> attached to the intrinsic provides scope information for
966 the variable <tt>Z</tt>.</p>
968 <div class="doc_code">
970 !13 = metadata !{i32 458763, metadata !1}; [DW_TAG_lexical_block ]
971 !14 = metadata !{i32 5, i32 9, metadata !13, null}
975 <p>Here <tt>!14</tt> indicates that <tt>Z</tt> is declared at line number 5 and
976 column number 9 inside of lexical scope <tt>!13</tt>. The lexical scope
977 itself resides inside of lexical scope <tt>!1</tt> described above.</p>
979 <p>The scope information attached with each instruction provides a
980 straightforward way to find instructions covered by a scope.</p>
984 <!-- *********************************************************************** -->
985 <div class="doc_section">
986 <a name="ccxx_frontend">C/C++ front-end specific debug information</a>
988 <!-- *********************************************************************** -->
990 <div class="doc_text">
992 <p>The C and C++ front-ends represent information about the program in a format
993 that is effectively identical
994 to <a href="http://www.eagercon.com/dwarf/dwarf3std.htm">DWARF 3.0</a> in
995 terms of information content. This allows code generators to trivially
996 support native debuggers by generating standard dwarf information, and
997 contains enough information for non-dwarf targets to translate it as
1000 <p>This section describes the forms used to represent C and C++ programs. Other
1001 languages could pattern themselves after this (which itself is tuned to
1002 representing programs in the same way that DWARF 3 does), or they could
1003 choose to provide completely different forms if they don't fit into the DWARF
1004 model. As support for debugging information gets added to the various LLVM
1005 source-language front-ends, the information used should be documented
1008 <p>The following sections provide examples of various C/C++ constructs and the
1009 debug information that would best describe those constructs.</p>
1013 <!-- ======================================================================= -->
1014 <div class="doc_subsection">
1015 <a name="ccxx_compile_units">C/C++ source file information</a>
1018 <div class="doc_text">
1020 <p>Given the source files <tt>MySource.cpp</tt> and <tt>MyHeader.h</tt> located
1021 in the directory <tt>/Users/mine/sources</tt>, the following code:</p>
1023 <div class="doc_code">
1025 #include "MyHeader.h"
1027 int main(int argc, char *argv[]) {
1033 <p>a C/C++ front-end would generate the following descriptors:</p>
1035 <div class="doc_code">
1039 ;; Define the compile unit for the main source file "/Users/mine/sources/MySource.cpp".
1044 i32 4, ;; Language Id
1045 metadata !"MySource.cpp",
1046 metadata !"/Users/mine/sources",
1047 metadata !"4.2.1 (Based on Apple Inc. build 5649) (LLVM build 00)",
1048 i1 true, ;; Main Compile Unit
1049 i1 false, ;; Optimized compile unit
1050 metadata !"", ;; Compiler flags
1051 i32 0} ;; Runtime version
1054 ;; Define the file for the file "/Users/mine/sources/MySource.cpp".
1058 metadata !"MySource.cpp",
1059 metadata !"/Users/mine/sources",
1060 metadata !2 ;; Compile unit
1064 ;; Define the file for the file "/Users/mine/sources/Myheader.h"
1068 metadata !"Myheader.h"
1069 metadata !"/Users/mine/sources",
1070 metadata !2 ;; Compile unit
1077 <p>llvm::Instruction provides easy access to metadata attached with an
1078 instruction. One can extract line number information encoded in LLVM IR
1079 using <tt>Instruction::getMetadata()</tt> and
1080 <tt>DILocation::getLineNumber()</tt>.
1082 if (MDNode *N = I->getMetadata("dbg")) { // Here I is an LLVM instruction
1083 DILocation Loc(N); // DILocation is in DebugInfo.h
1084 unsigned Line = Loc.getLineNumber();
1085 StringRef File = Loc.getFilename();
1086 StringRef Dir = Loc.getDirectory();
1091 <!-- ======================================================================= -->
1092 <div class="doc_subsection">
1093 <a name="ccxx_global_variable">C/C++ global variable information</a>
1096 <div class="doc_text">
1098 <p>Given an integer global variable declared as follows:</p>
1100 <div class="doc_code">
1106 <p>a C/C++ front-end would generate the following descriptors:</p>
1108 <div class="doc_code">
1111 ;; Define the global itself.
1113 %MyGlobal = global int 100
1116 ;; List of debug info of globals
1118 !llvm.dbg.gv = !{!0}
1121 ;; Define the global variable descriptor. Note the reference to the global
1122 ;; variable anchor and the global variable itself.
1127 metadata !1, ;; Context
1128 metadata !"MyGlobal", ;; Name
1129 metadata !"MyGlobal", ;; Display Name
1130 metadata !"MyGlobal", ;; Linkage Name
1131 metadata !3, ;; Compile Unit
1132 i32 1, ;; Line Number
1133 metadata !4, ;; Type
1134 i1 false, ;; Is a local variable
1135 i1 true, ;; Is this a definition
1136 i32* @MyGlobal ;; The global variable
1140 ;; Define the basic type of 32 bit signed integer. Note that since int is an
1141 ;; intrinsic type the source file is NULL and line 0.
1145 metadata !1, ;; Context
1146 metadata !"int", ;; Name
1147 metadata !1, ;; File
1148 i32 0, ;; Line number
1149 i64 32, ;; Size in Bits
1150 i64 32, ;; Align in Bits
1151 i64 0, ;; Offset in Bits
1161 <!-- ======================================================================= -->
1162 <div class="doc_subsection">
1163 <a name="ccxx_subprogram">C/C++ function information</a>
1166 <div class="doc_text">
1168 <p>Given a function declared as follows:</p>
1170 <div class="doc_code">
1172 int main(int argc, char *argv[]) {
1178 <p>a C/C++ front-end would generate the following descriptors:</p>
1180 <div class="doc_code">
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.)
1190 metadata !1, ;; Context
1191 metadata !"main", ;; Name
1192 metadata !"main", ;; Display name
1193 metadata !"main", ;; Linkage name
1194 metadata !1, ;; File
1195 i32 1, ;; Line number
1196 metadata !4, ;; Type
1197 i1 false, ;; Is local
1198 i1 true ;; Is definition
1201 ;; Define the subprogram itself.
1203 define i32 @main(i32 %argc, i8** %argv) {
1211 <!-- ======================================================================= -->
1212 <div class="doc_subsection">
1213 <a name="ccxx_basic_types">C/C++ basic types</a>
1216 <div class="doc_text">
1218 <p>The following are the basic type descriptors for C/C++ core types:</p>
1222 <!-- ======================================================================= -->
1223 <div class="doc_subsubsection">
1224 <a name="ccxx_basic_type_bool">bool</a>
1227 <div class="doc_text">
1229 <div class="doc_code">
1233 metadata !1, ;; Context
1234 metadata !"bool", ;; Name
1235 metadata !1, ;; File
1236 i32 0, ;; Line number
1237 i64 8, ;; Size in Bits
1238 i64 8, ;; Align in Bits
1239 i64 0, ;; Offset in Bits
1248 <!-- ======================================================================= -->
1249 <div class="doc_subsubsection">
1250 <a name="ccxx_basic_char">char</a>
1253 <div class="doc_text">
1255 <div class="doc_code">
1259 metadata !1, ;; Context
1260 metadata !"char", ;; Name
1261 metadata !1, ;; File
1262 i32 0, ;; Line number
1263 i64 8, ;; Size in Bits
1264 i64 8, ;; Align in Bits
1265 i64 0, ;; Offset in Bits
1274 <!-- ======================================================================= -->
1275 <div class="doc_subsubsection">
1276 <a name="ccxx_basic_unsigned_char">unsigned char</a>
1279 <div class="doc_text">
1281 <div class="doc_code">
1285 metadata !1, ;; Context
1286 metadata !"unsigned char",
1287 metadata !1, ;; File
1288 i32 0, ;; Line number
1289 i64 8, ;; Size in Bits
1290 i64 8, ;; Align in Bits
1291 i64 0, ;; Offset in Bits
1300 <!-- ======================================================================= -->
1301 <div class="doc_subsubsection">
1302 <a name="ccxx_basic_short">short</a>
1305 <div class="doc_text">
1307 <div class="doc_code">
1311 metadata !1, ;; Context
1312 metadata !"short int",
1313 metadata !1, ;; File
1314 i32 0, ;; Line number
1315 i64 16, ;; Size in Bits
1316 i64 16, ;; Align in Bits
1317 i64 0, ;; Offset in Bits
1326 <!-- ======================================================================= -->
1327 <div class="doc_subsubsection">
1328 <a name="ccxx_basic_unsigned_short">unsigned short</a>
1331 <div class="doc_text">
1333 <div class="doc_code">
1337 metadata !1, ;; Context
1338 metadata !"short unsigned int",
1339 metadata !1, ;; File
1340 i32 0, ;; Line number
1341 i64 16, ;; Size in Bits
1342 i64 16, ;; Align in Bits
1343 i64 0, ;; Offset in Bits
1352 <!-- ======================================================================= -->
1353 <div class="doc_subsubsection">
1354 <a name="ccxx_basic_int">int</a>
1357 <div class="doc_text">
1359 <div class="doc_code">
1363 metadata !1, ;; Context
1364 metadata !"int", ;; Name
1365 metadata !1, ;; File
1366 i32 0, ;; Line number
1367 i64 32, ;; Size in Bits
1368 i64 32, ;; Align in Bits
1369 i64 0, ;; Offset in Bits
1377 <!-- ======================================================================= -->
1378 <div class="doc_subsubsection">
1379 <a name="ccxx_basic_unsigned_int">unsigned int</a>
1382 <div class="doc_text">
1384 <div class="doc_code">
1388 metadata !1, ;; Context
1389 metadata !"unsigned int",
1390 metadata !1, ;; File
1391 i32 0, ;; Line number
1392 i64 32, ;; Size in Bits
1393 i64 32, ;; Align in Bits
1394 i64 0, ;; Offset in Bits
1403 <!-- ======================================================================= -->
1404 <div class="doc_subsubsection">
1405 <a name="ccxx_basic_long_long">long long</a>
1408 <div class="doc_text">
1410 <div class="doc_code">
1414 metadata !1, ;; Context
1415 metadata !"long long int",
1416 metadata !1, ;; File
1417 i32 0, ;; Line number
1418 i64 64, ;; Size in Bits
1419 i64 64, ;; Align in Bits
1420 i64 0, ;; Offset in Bits
1429 <!-- ======================================================================= -->
1430 <div class="doc_subsubsection">
1431 <a name="ccxx_basic_unsigned_long_long">unsigned long long</a>
1434 <div class="doc_text">
1436 <div class="doc_code">
1440 metadata !1, ;; Context
1441 metadata !"long long unsigned int",
1442 metadata !1, ;; File
1443 i32 0, ;; Line number
1444 i64 64, ;; Size in Bits
1445 i64 64, ;; Align in Bits
1446 i64 0, ;; Offset in Bits
1455 <!-- ======================================================================= -->
1456 <div class="doc_subsubsection">
1457 <a name="ccxx_basic_float">float</a>
1460 <div class="doc_text">
1462 <div class="doc_code">
1466 metadata !1, ;; Context
1468 metadata !1, ;; File
1469 i32 0, ;; Line number
1470 i64 32, ;; Size in Bits
1471 i64 32, ;; Align in Bits
1472 i64 0, ;; Offset in Bits
1481 <!-- ======================================================================= -->
1482 <div class="doc_subsubsection">
1483 <a name="ccxx_basic_double">double</a>
1486 <div class="doc_text">
1488 <div class="doc_code">
1492 metadata !1, ;; Context
1493 metadata !"double",;; Name
1494 metadata !1, ;; File
1495 i32 0, ;; Line number
1496 i64 64, ;; Size in Bits
1497 i64 64, ;; Align in Bits
1498 i64 0, ;; Offset in Bits
1507 <!-- ======================================================================= -->
1508 <div class="doc_subsection">
1509 <a name="ccxx_derived_types">C/C++ derived types</a>
1512 <div class="doc_text">
1514 <p>Given the following as an example of C/C++ derived type:</p>
1516 <div class="doc_code">
1518 typedef const int *IntPtr;
1522 <p>a C/C++ front-end would generate the following descriptors:</p>
1524 <div class="doc_code">
1527 ;; Define the typedef "IntPtr".
1531 metadata !1, ;; Context
1532 metadata !"IntPtr", ;; Name
1533 metadata !3, ;; File
1534 i32 0, ;; Line number
1535 i64 0, ;; Size in bits
1536 i64 0, ;; Align in bits
1537 i64 0, ;; Offset in bits
1539 metadata !4 ;; Derived From type
1543 ;; Define the pointer type.
1547 metadata !1, ;; Context
1548 metadata !"", ;; Name
1549 metadata !1, ;; File
1550 i32 0, ;; Line number
1551 i64 64, ;; Size in bits
1552 i64 64, ;; Align in bits
1553 i64 0, ;; Offset in bits
1555 metadata !5 ;; Derived From type
1558 ;; Define the const type.
1562 metadata !1, ;; Context
1563 metadata !"", ;; Name
1564 metadata !1, ;; File
1565 i32 0, ;; Line number
1566 i64 32, ;; Size in bits
1567 i64 32, ;; Align in bits
1568 i64 0, ;; Offset in bits
1570 metadata !6 ;; Derived From type
1573 ;; Define the int type.
1577 metadata !1, ;; Context
1578 metadata !"int", ;; Name
1579 metadata !1, ;; File
1580 i32 0, ;; Line number
1581 i64 32, ;; Size in bits
1582 i64 32, ;; Align in bits
1583 i64 0, ;; Offset in bits
1592 <!-- ======================================================================= -->
1593 <div class="doc_subsection">
1594 <a name="ccxx_composite_types">C/C++ struct/union types</a>
1597 <div class="doc_text">
1599 <p>Given the following as an example of C/C++ struct type:</p>
1601 <div class="doc_code">
1611 <p>a C/C++ front-end would generate the following descriptors:</p>
1613 <div class="doc_code">
1616 ;; Define basic type for unsigned int.
1620 metadata !1, ;; Context
1621 metadata !"unsigned int",
1622 metadata !1, ;; File
1623 i32 0, ;; Line number
1624 i64 32, ;; Size in Bits
1625 i64 32, ;; Align in Bits
1626 i64 0, ;; Offset in Bits
1631 ;; Define composite type for struct Color.
1635 metadata !1, ;; Context
1636 metadata !"Color", ;; Name
1637 metadata !1, ;; Compile unit
1638 i32 1, ;; Line number
1639 i64 96, ;; Size in bits
1640 i64 32, ;; Align in bits
1641 i64 0, ;; Offset in bits
1643 null, ;; Derived From
1644 metadata !3, ;; Elements
1645 i32 0 ;; Runtime Language
1649 ;; Define the Red field.
1653 metadata !1, ;; Context
1654 metadata !"Red", ;; Name
1655 metadata !1, ;; File
1656 i32 2, ;; Line number
1657 i64 32, ;; Size in bits
1658 i64 32, ;; Align in bits
1659 i64 0, ;; Offset in bits
1661 metadata !5 ;; Derived From type
1665 ;; Define the Green field.
1669 metadata !1, ;; Context
1670 metadata !"Green", ;; Name
1671 metadata !1, ;; File
1672 i32 3, ;; Line number
1673 i64 32, ;; Size in bits
1674 i64 32, ;; Align in bits
1675 i64 32, ;; Offset in bits
1677 metadata !5 ;; Derived From type
1681 ;; Define the Blue field.
1685 metadata !1, ;; Context
1686 metadata !"Blue", ;; Name
1687 metadata !1, ;; File
1688 i32 4, ;; Line number
1689 i64 32, ;; Size in bits
1690 i64 32, ;; Align in bits
1691 i64 64, ;; Offset in bits
1693 metadata !5 ;; Derived From type
1697 ;; Define the array of fields used by the composite type Color.
1699 !3 = metadata !{metadata !4, metadata !6, metadata !7}
1705 <!-- ======================================================================= -->
1706 <div class="doc_subsection">
1707 <a name="ccxx_enumeration_types">C/C++ enumeration types</a>
1710 <div class="doc_text">
1712 <p>Given the following as an example of C/C++ enumeration type:</p>
1714 <div class="doc_code">
1724 <p>a C/C++ front-end would generate the following descriptors:</p>
1726 <div class="doc_code">
1729 ;; Define composite type for enum Trees
1733 metadata !1, ;; Context
1734 metadata !"Trees", ;; Name
1735 metadata !1, ;; File
1736 i32 1, ;; Line number
1737 i64 32, ;; Size in bits
1738 i64 32, ;; Align in bits
1739 i64 0, ;; Offset in bits
1741 null, ;; Derived From type
1742 metadata !3, ;; Elements
1743 i32 0 ;; Runtime language
1747 ;; Define the array of enumerators used by composite type Trees.
1749 !3 = metadata !{metadata !4, metadata !5, metadata !6}
1752 ;; Define Spruce enumerator.
1754 !4 = metadata !{i32 524328, metadata !"Spruce", i64 100}
1757 ;; Define Oak enumerator.
1759 !5 = metadata !{i32 524328, metadata !"Oak", i64 200}
1762 ;; Define Maple enumerator.
1764 !6 = metadata !{i32 524328, metadata !"Maple", i64 300}
1771 <!-- *********************************************************************** -->
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