1 \chapter{Program Scope Entries}
2 \label{chap:programscopeentries}
3 This section describes debugging information entries that
4 relate to different levels of program scope: compilation,
5 module, subprogram, and so on. Except for separate type
6 entries (see Section \refersec{chap:separatetypeunitentries}),
7 these entries may be thought of
8 as bounded by ranges of text addresses within the program.
10 \section{Unit Entries}
11 An object file may contain one or more compilation units,
12 of which there are three kinds: normal compilation units,
13 partial compilation units and type units. A partial compilation
14 unit is related to one or more other compilation units that
15 import it. A type unit represents a single complete type in a
16 separate unit. Either a normal compilation unit or a partial
17 compilation unit may be logically incorporated into another
18 compilation unit using an imported unit entry.
20 \subsection[Normal and Partial CU Entries]{Normal and Partial Compilation Unit Entries}
21 \label{chap:normalandpartialcompilationunitentries}
23 A normal compilation unit is represented by a debugging
24 information entry with the
25 tag \livetarg{chap:DWTAGcompileunit}{DW\-\_TAG\-\_compile\-\_unit}. A partial
26 compilation unit is represented by a debugging information
28 tag \livetarg{chap:DWTAGpartialunit}{DW\-\_TAG\-\_partial\-\_unit}.
30 In a simple normal compilation, a single compilation unit with
32 \livelink{chap:DWTAGcompileunit}{DW\-\_TAG\-\_compile\-\_unit} represents a complete object file
34 \livelink{chap:DWTAGpartialunit}{DW\-\_TAG\-\_partial\-\_unit} is not used.
36 employing the DWARF space compression and duplicate elimination
38 Appendix \refersec{app:usingcompilationunits},
39 multiple compilation units using
41 \livelink{chap:DWTAGcompileunit}{DW\-\_TAG\-\_compile\-\_unit} and/or
42 \livelink{chap:DWTAGpartialunit}{DW\-\_TAG\-\_partial\-\_unit} are
43 used to represent portions of an object file.
45 \textit{A normal compilation unit typically represents the text and
46 data contributed to an executable by a single relocatable
47 object file. It may be derived from several source files,
48 including pre\dash processed ``include files.'' A partial
49 compilation unit typically represents a part of the text
50 and data of a relocatable object file, in a manner that can
51 potentially be shared with the results of other compilations
52 to save space. It may be derived from an ``include file'',
53 template instantiation, or other implementation\dash dependent
54 portion of a compilation. A normal compilation unit can also
55 function in a manner similar to a partial compilation unit
58 A compilation unit entry owns debugging information
59 entries that represent all or part of the declarations
60 made in the corresponding compilation. In the case of a
61 partial compilation unit, the containing scope of its owned
62 declarations is indicated by imported unit entries in one
63 or more other compilation unit entries that refer to that
64 partial compilation unit (see
65 Section \refersec{chap:importedunitentries}).
68 Compilation unit entries may have the following attributes:
71 \item Either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of
72 attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute whose values encode the
73 contiguous or non\dash contiguous address ranges, respectively,
74 of the machine instructions generated for the compilation
75 unit (see Section {chap:codeaddressesandranges}).
76 A \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute may also
77 be specified in combination with \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} to specify the
78 default base address for use in location lists (see Section
79 \refersec{chap:locationlists}) and range lists
80 (see Section \refersec{chap:noncontiguousaddressranges}).
82 \item A \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute whose value is a null\dash terminated
84 \hypertarget{chap:DWATnamepathnameofcompilationsource}
85 containing the full or relative path name of the primary
86 source file from which the compilation unit was derived.
88 \item A \livelink{chap:DWATlanguage}{DW\-\_AT\-\_language} attribute whose constant value is an
89 integer code indicating the source language of the compilation
90 unit. The set of language names and their meanings are given
92 Figure \refersec{fig:languagenames}.
96 \caption{Language names}
97 \label{fig:languagenames}
99 Language name & Meaning\\ \hline
100 \livetarg{chap:DWLANGAda83}{DW\-\_LANG\-\_Ada83} \dag&ISO Ada:1983 \\
101 \livetarg{chap:DWLANGAda95}{DW\-\_LANG\-\_Ada95} \dag&ISO Ada:1995 \\
102 \livetarg{chap:DWLANGC}{DW\-\_LANG\-\_C}&Non-standardized C, such as K\&R \\
103 \livetarg{chap:DWLANGC89}{DW\-\_LANG\-\_C89}&ISO C:1989 \\
104 \livetarg{chap:DWLANGC99}{DW\-\_LANG\-\_C99} & ISO C:1999 \\
105 \livetarg{chap:DWLANGCplusplus}{DW\-\_LANG\-\_C\-\_plus\-\_plus}&ISO C++:1998 \\
106 \livetarg{chap:DWLANGCobol74}{DW\-\_LANG\-\_Cobol74}& ISO Cobol:1974 \\
107 \livetarg{chap:DWLANGCobol85}{DW\-\_LANG\-\_Cobol85} & ISO Cobol:1985 \\
108 \livetarg{chap:DWLANGD}{DW\-\_LANG\-\_D} \dag & D \\
109 \livetarg{chap:DWLANGFortran77}{DW\-\_LANG\-\_Fortran77} &ISO FORTRAN 77\\
110 \livetarg{chap:DWLANGFortran90}{DW\-\_LANG\-\_Fortran90} & ISO Fortran 90\\
111 \livetarg{chap:DWLANGFortran95}{DW\-\_LANG\-\_Fortran95} & ISO Fortran 95\\
112 \livetarg{chap:DWLANGJava}{DW\-\_LANG\-\_Java} & Java\\
113 \livetarg{chap:DWLANGModula2}{DW\-\_LANG\-\_Modula2} & ISO Modula\dash 2:1996\\
114 \livetarg{chap:DWLANGObjC}{DW\-\_LANG\-\_ObjC} & Objective C\\
115 \livetarg{chap:DWLANGObjCplusplus}{DW\-\_LANG\-\_ObjC\-\_plus\-\_plus} & Objective C++\\
116 \livetarg{chap:DWLANGPascal83}{DW\-\_LANG\-\_Pascal83} & ISO Pascal:1983\\
117 \livetarg{chap:DWLANGPLI}{DW\-\_LANG\-\_PLI} \dag & ANSI PL/I:1976\\
118 \livetarg{chap:DWLANGPython}{DW\-\_LANG\-\_Python} \dag & Python\\
119 \livetarg{chap:DWLANGUPC}{DW\-\_LANG\-\_UPC} &Unified Parallel C\\ \hline
120 \dag \ \ Support for these languages is limited.& \\
124 \item A \livelink{chap:DWATstmtlist}{DW\-\_AT\-\_stmt\-\_list} attribute whose value is a section
125 \hypertarget{chap:DWATstmtlistlinenumberinformationforunit}
126 offset to the line number information for this compilation
127 unit. This information is placed in a separate object file
128 section from the debugging information entries themselves. The
129 value of the statement list attribute is the offset in the
130 .debug\_line section of the first byte of the line number
131 information for this compilation unit
132 (see Section \refersec{chap:linenumberinformation}).
134 \item A \livelink{chap:DWATmacroinfo}{DW\-\_AT\-\_macro\-\_info} attribute whose value is a section
135 \hypertarget{chap:DWATmacroinfomacroinformation}
136 offset to the macro information for this compilation unit.
137 This information is placed in a separate object file section
138 from the debugging information entries themselves. The
139 value of the macro information attribute is the offset in
140 the .debug\_macinfo section of the first byte of the macro
141 information for this compilation unit
142 (see Section \refersec{chap:macroinformation}).
145 \livelink{chap:DWATcompdir}{DW\-\_AT\-\_comp\-\_dir}
147 \hypertarget{chap:DWATcompdircompilationdirectory}
149 null\dash terminated string containing the current working directory
150 of the compilation command that produced this compilation
151 unit in whatever form makes sense for the host system.
153 \item A \livelink{chap:DWATproducer}{DW\-\_AT\-\_producer} attribute whose value is a null\dash
154 terminated string containing information about the compiler
155 \hypertarget{chap:DWATproducercompileridentification}
156 that produced the compilation unit. The actual contents of
157 the string will be specific to each producer, but should
158 begin with the name of the compiler vendor or some other
159 identifying character sequence that should avoid confusion
160 with other producer values.
163 \item A \livelink{chap:DWATidentifiercase}{DW\-\_AT\-\_identifier\-\_case} attribute whose integer
164 constant value is a code describing the treatment
165 of identifiers within this compilation unit. The
166 set of identifier case codes is given in Figure
167 \refersec{fig:identifiercasecodes}.
170 \autorows[0pt]{c}{1}{l}{
171 \livelink{chap:DWIDcasesensitive}{DW\-\_ID\-\_case\-\_sensitive},
172 \livelink{chap:DWIDupcase}{DW\-\_ID\-\_up\-\_case},
173 \livelink{chap:DWIDdowncase}{DW\-\_ID\-\_down\-\_case},
174 \livelink{chap:DWIDcaseinsensitive}{DW\-\_ID\-\_case\-\_insensitive}
176 \caption{Identifier case codes}\label{fig:identifiercasecodes}
179 \livetarg{chap:DWIDcasesensitive}{DW\-\_ID\-\_case\-\_sensitive} is the default for all compilation units
180 that do not have this attribute. It indicates that names given
181 as the values of \livelink{chap:DWATname}{DW\-\_AT\-\_name} attributes in debugging information
182 entries for the compilation unit reflect the names as they
183 appear in the source program. The debugger should be sensitive
184 to the case of identifier names when doing identifier lookups.
186 \livetarg{chap:DWIDupcase}{DW\-\_ID\-\_up\-\_case} means that the producer of the debugging
187 information for this compilation unit converted all source
188 names to upper case. The values of the name attributes may not
189 reflect the names as they appear in the source program. The
190 debugger should convert all names to upper case when doing
193 \livetarg{chap:DWIDdowncase}{DW\-\_ID\-\_down\-\_case} means that the producer of the debugging
194 information for this compilation unit converted all source
195 names to lower case. The values of the name attributes may not
196 reflect the names as they appear in the source program. The
197 debugger should convert all names to lower case when doing
200 \livetarg{chap:DWIDcaseinsensitive}{DW\-\_ID\-\_case\-\_insensitive} means that the values of the name
201 attributes reflect the names as they appear in the source
202 program but that a case insensitive lookup should be used to
205 \item A \livelink{chap:DWATbasetypes}{DW\-\_AT\-\_base\-\_types} attribute whose value is a reference.
209 \hypertarget{chap:DWATbasetypesprimitivedatatypesofcompilationunit}
210 attribute points to a debugging information entry
211 representing another compilation unit. It may be used
212 to specify the compilation unit containing the base type
213 entries used by entries in the current compilation unit
214 (see Section \refersec{chap:basetypeentries}).
216 This attribute provides a consumer a way to find the definition
217 of base types for a compilation unit that does not itself
218 contain such definitions. This allows a consumer, for example,
219 to interpret a type conversion to a base type correctly.
221 \item A \livelink{chap:DWATuseUTF8}{DW\-\_AT\-\_use\-\_UTF8} attribute,
222 which is a \livelink{chap:flag}{flag} whose
223 presence indicates that all strings (such as the names of
224 declared entities in the source program) are represented
225 using the UTF\dash 8 representation
226 (see Section \refersec{datarep:attributeencodings}).
229 \item A \livelink{chap:DWATmainsubprogram}{DW\-\_AT\-\_main\-\_subprogram} attribute, which is a \livelink{chap:flag}{flag}
230 whose presence indicates
231 \hypertarget{chap:DWATmainsubprogramunitcontainingmainorstartingsubprogram}
232 that the compilation unit contains a
233 subprogram that has been identified as the starting function
234 of the program. If more than one compilation unit contains
235 this \nolink{flag}, any one of them may contain the starting function.
237 \textit{Fortran has a PROGRAM statement which is used
238 to specify and provide a user\dash specified name for the main
239 subroutine of a program. C uses the name “main” to identify
240 the main subprogram of a program. Some other languages provide
241 similar or other means to identify the main subprogram of
246 The base address of a compilation unit is defined as the
247 value of the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute, if present; otherwise,
248 it is undefined. If the base address is undefined, then any
249 DWARF entry or structure defined in terms of the base address
250 of that compilation unit is not valid.
253 \subsection{Imported Unit Entries}
254 \label{chap:importedunitentries}
255 The place where a normal or partial unit is imported is
256 represented by a debugging information entry with the
257 tag \livetarg{chap:DWTAGimportedunit}{DW\-\_TAG\-\_imported\-\_unit}.
258 An imported unit entry contains a
259 \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute whose value is a reference to the
260 normal or partial compilation unit whose declarations logically
261 belong at the place of the imported unit entry.
263 An imported unit entry does not necessarily correspond to
264 any entity or construct in the source program. It is merely
265 “glue” used to relate a partial unit, or a compilation
266 unit used as a partial unit, to a place in some other
269 \subsection{Separate Type Unit Entries}
270 \label{chap:separatetypeunitentries}
271 An object file may contain any number of separate type
272 unit entries, each representing a single complete type
273 definition. Each type unit must be uniquely identified by
274 a 64\dash bit signature, stored as part of the type unit, which
275 can be used to reference the type definition from debugging
276 information entries in other compilation units and type units.
278 A type unit is represented by a debugging information entry
279 with the tag \livetarg{chap:DWTAGtypeunit}{DW\-\_TAG\-\_type\-\_unit}.
280 A type unit entry owns debugging
281 information entries that represent the definition of a single
282 type, plus additional debugging information entries that may
283 be necessary to include as part of the definition of the type.
285 A type unit entry may have a \livelink{chap:DWATlanguage}{DW\-\_AT\-\_language} attribute, whose
286 constant value is an integer code indicating the source
287 language used to define the type. The set of language names
288 and their meanings are given in Figure \refersec{fig:languagenames}.
290 A type unit entry for a given type T owns a debugging
291 information entry that represents a defining declaration
292 of type T. If the type is nested within enclosing types or
293 namespaces, the debugging information entry for T is nested
294 within debugging information entries describing its containers;
295 otherwise, T is a direct child of the type unit entry.
297 A type unit entry may also own additional debugging information
298 entries that represent declarations of additional types that
299 are referenced by type T and have not themselves been placed in
300 separate type units. Like T, if an additional type U is nested
301 within enclosing types or namespaces, the debugging information
302 entry for U is nested within entries describing its containers;
303 otherwise, U is a direct child of the type unit entry.
305 The containing entries for types T and U are declarations,
306 and the outermost containing entry for any given type T or
307 U is a direct child of the type unit entry. The containing
308 entries may be shared among the additional types and between
309 T and the additional types.
311 Types are not required to be placed in type units. In general,
312 only large types such as structure, class, enumeration, and
313 union types included from header files should be considered
314 for separate type units. Base types and other small types
315 are not usually worth the overhead of placement in separate
316 type units. Types that are unlikely to be replicated, such
317 as those defined in the main source file, are also better
318 left in the main compilation unit.
320 \section{Module, Namespace and Importing Entries}
321 \textit{Modules and namespaces provide a means to collect related
322 entities into a single entity and to manage the names of
325 \subsection{Module Entries}
326 \label{chap:moduleentries}
327 \textit{Several languages have the concept of a ``module.''
328 A Modula\dash 2 definition module may be represented by a module
329 entry containing a declaration attribute (\livelink{chap:DWATdeclaration}{DW\-\_AT\-\_declaration}). A
330 Fortran 90 module may also be represented by a module entry
331 (but no declaration attribute is warranted because Fortran
332 has no concept of a corresponding module body).}
334 A module is represented by a debugging information entry
336 tag \livetarg{chap:DWTAGmodule}{DW\-\_TAG\-\_module}.
337 Module entries may own other
338 debugging information entries describing program entities
339 whose declaration scopes end at the end of the module itself.
341 If the module has a name, the module entry has a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
342 attribute whose value is a null\dash terminated string containing
343 the module name as it appears in the source program.
345 The module entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
346 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
347 whose values encode the contiguous or non\dash contiguous address
348 ranges, respectively, of the machine instructions generated for
349 the module initialization code
350 (see Section \refersec{chap:codeaddressesandranges}).
351 \hypertarget{chap:DWATentrypcentryaddressofmoduleinitialization}
353 have a \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute whose value is the address of
354 the first executable instruction of that initialization code
355 (see Section \refersec{chap:entryaddress}).
358 \hypertarget{chap:DWATprioritymodulepriority}
359 the module has been assigned a priority, it may have a
360 \livelink{chap:DWATpriority}{DW\-\_AT\-\_priority} attribute. The value of this attribute is a
361 reference to another debugging information entry describing
362 a variable with a constant value. The value of this variable
363 is the actual constant value of the module’s priority,
364 represented as it would be on the target architecture.
366 \subsection{Namespace Entries}
367 \label{chap:namespaceentries}
368 \textit{C++ has the notion of a namespace, which provides a way to
369 implement name hiding, so that names of unrelated things
370 do not accidentally clash in the global namespace when an
371 application is linked together.}
373 A namespace is represented by a debugging information entry
375 tag \livetarg{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace}.
376 A namespace extension is
377 \hypertarget{chap:DWATextensionpreviousnamespaceextensionororiginalnamespace}
379 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace} entry
381 \livelink{chap:DWATextension}{DW\-\_AT\-\_extension}
382 attribute referring to the previous extension, or if there
383 is no previous extension, to the original
384 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace}
385 entry. A namespace extension entry does not need to duplicate
386 information in a previous extension entry of the namespace
387 nor need it duplicate information in the original namespace
388 entry. (Thus, for a namespace with a name,
389 a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
390 attribute need only be attached directly to the original
391 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace} entry.)
393 Namespace and namespace extension entries may own other
394 debugging information entries describing program entities
395 whose declarations occur in the namespace.
397 \textit{For C++, such owned program entities may be declarations,
398 including certain declarations that are also object or
399 function definitions.}
401 If a type, variable, or function declared in a namespace is
402 defined outside of the body of the namespace declaration,
403 that type, variable, or function definition entry has a
404 \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} attribute whose value is a reference to the
405 debugging information entry representing the declaration of
406 the type, variable or function. Type, variable, or function
407 entries with a \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} attribute do not need
408 to duplicate information provided by the declaration entry
409 referenced by the specification attribute.
411 \textit{The C++ global namespace (the namespace referred to by
412 ``::f'', for example) is not explicitly represented in
413 DWARF with a namespace entry (thus mirroring the situation
414 in C++ source). Global items may be simply declared with no
415 reference to a namespace.}
417 \textit{The C++ compilation unit specific ``unnamed namespace'' may
418 be represented by a namespace entry with no name attribute in
419 the original namespace declaration entry (and therefore no name
420 attribute in any namespace extension entry of this namespace).
423 \textit{A compiler emitting namespace information may choose to
424 explicitly represent namespace extensions, or to represent the
425 final namespace declaration of a compilation unit; this is a
426 quality\dash of\dash implementation issue and no specific requirements
427 are given here. If only the final namespace is represented,
428 it is impossible for a debugger to interpret using declaration
429 references in exactly the manner defined by the C++ language.
432 \textit{Emitting all namespace declaration information in all
433 compilation units can result in a significant increase in the
434 size of the debug information and significant duplication of
435 information across compilation units. The C++ namespace std,
436 for example, is large and will probably be referenced in
437 every C++ compilation unit.
440 \textit{For a C++ namespace example, see Appendix \refersec{app:namespaceexample}.
445 \subsection{Imported (or Renamed) Declaration Entries}
446 \label{chap:importedorrenameddeclarationentries}
447 \textit{Some languages support the concept of importing into or making
448 accessible in a given unit declarations made in a different
449 module or scope. An imported declaration may sometimes be
453 An imported declaration is represented by one or
454 more debugging information entries with the
455 tag \livetarg{chap:DWTAGimporteddeclaration}{DW\-\_TAG\-\_imported\-\_declaration}.
456 When an overloaded entity
457 is imported, there is one imported declaration entry for
458 each overloading. Each imported declaration entry has a
459 \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute, whose value is a reference to the
460 debugging information entry representing the declaration that
463 An imported declaration may also have a \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute
464 whose value is a null\dash terminated string containing the
465 name, as it appears in the source program, by which the
466 imported entity is to be known in the context of the imported
467 declaration entry (which may be different than the name of
468 the entity being imported). If no name is present, then the
469 name by which the entity is to be known is the same as the
470 name of the entity being imported.
472 An imported declaration entry with a name attribute may be
473 used as a general means to rename or provide an alias for
474 an entity, regardless of the context in which the importing
475 declaration or the imported entity occurs.
477 \textit{A C++ namespace alias may be represented by an imported
478 declaration entry with a name attribute whose value is
479 a null\dash terminated string containing the alias name as it
480 appears in the source program and an import attribute whose
481 value is a reference to the applicable original namespace or
482 namespace extension entry.
485 \textit{A C++ using declaration may be represented by one or more
486 imported declaration entries. When the using declaration
487 refers to an overloaded function, there is one imported
488 declaration entry corresponding to each overloading. Each
489 imported declaration entry has no name attribute but it does
490 have an import attribute that refers to the entry for the
491 entity being imported. (C++ provides no means to ``rename''
492 an imported entity, other than a namespace).
495 \textit{A Fortran use statement with an ``only list'' may be
496 represented by a series of imported declaration entries,
497 one (or more) for each entity that is imported. An entity
498 that is renamed in the importing context may be represented
499 by an imported declaration entry with a name attribute that
500 specifies the new local name.
503 \subsection{Imported Module Entries}
504 \label{chap:importedmoduleentries}
506 \textit{Some languages support the concept of importing into or making
507 accessible in a given unit all of the declarations contained
508 within a separate module or namespace.
511 An imported module declaration is represented by a debugging
512 information entry with the
513 tag \livetarg{chap:DWTAGimportedmodule}{DW\-\_TAG\-\_imported\-\_module}.
515 imported module entry contains a \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute
516 whose value is a reference to the module or namespace entry
517 containing the definition and/or declaration entries for
518 the entities that are to be imported into the context of the
519 imported module entry.
521 An imported module declaration may own a set of imported
522 declaration entries, each of which refers to an entry in the
523 module whose corresponding entity is to be known in the context
524 of the imported module declaration by a name other than its
525 name in that module. Any entity in the module that is not
526 renamed in this way is known in the context of the imported
527 module entry by the same name as it is declared in the module.
529 \textit{A C++ using directive may be represented by an imported module
530 entry, with an import attribute referring to the namespace
531 entry of the appropriate extension of the namespace (which
532 might be the original namespace entry) and no owned entries.
535 \textit{A Fortran use statement with a “rename list” may be
536 represented by an imported module entry with an import
537 attribute referring to the module and owned entries
538 corresponding to those entities that are renamed as part of
542 \textit{A Fortran use statement with neither a “rename list” nor
543 an “only list” may be represented by an imported module
544 entry with an import attribute referring to the module and
545 no owned child entries.
548 \textit{A use statement with an “only list” is represented by a
549 series of individual imported declaration entries as described
550 in Section \refersec{chap:importedorrenameddeclarationentries}.
553 \textit{A Fortran use statement for an entity in a module that is
554 itself imported by a use statement without an explicit mention
555 may be represented by an imported declaration entry that refers
556 to the original debugging information entry. For example, given
572 the imported declaration entry for Q within module C refers
573 directly to the variable declaration entry for A in module A
574 because there is no explicit representation for X in module B.
576 A similar situation arises for a C++ using declaration that
577 imports an entity in terms of a namespace alias. See
578 Appendix \refersec{app:namespaceexample}
582 \section{Subroutine and Entry Point Entries}
583 \label{chap:subroutineandentrypointentries}
585 The following tags exist to describe debugging information entries for subroutines and entry
588 \begin{tabular}{lp{9.0cm}}
589 \livetarg{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} & A subroutine or function. \\
590 \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine} & A particular inlined
591 instance of a subroutine or function. \\
592 \livetarg{chap:DWTAGentrypoint}{DW\-\_TAG\-\_entry\-\_point} & An alternate entry point. \\
595 \subsection{General Subroutine and Entry Point Information}
596 \label{chap:generalsubroutineandentrypointinformation}
598 It may also have a \livelink{chap:DWATlinkagename}{DW\-\_AT\-\_linkage\-\_name} attribute as
599 described in Section \refersec{chap:linkagenames}.
601 If the name of the subroutine described by an entry with the
602 tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}
603 is visible outside of its containing
604 \hypertarget{chap:DWATexternalexternalsubroutine}
605 compilation unit, that entry has a
606 \livelink{chap:DWATexternal}{DW\-\_AT\-\_external} attribute,
607 which is a \livelink{chap:flag}{flag}.
609 \textit{Additional attributes for functions that are members of a
610 class or structure are described in
611 Section \refersec{chap:memberfunctionentries}.
615 \hypertarget{chap:DWATmainsubprogrammainorstartingsubprogram}
616 subroutine entry may contain a \livelink{chap:DWATmainsubprogram}{DW\-\_AT\-\_main\-\_subprogram}
618 a \livelink{chap:flag}{flag} whose presence indicates that the
619 subroutine has been identified as the starting function of
620 the program. If more than one subprogram contains this
622 any one of them may be the starting subroutine of the program.
624 \textit{Fortran has a PROGRAM statement which is used to specify
625 and provide a user\dash supplied name for the main subroutine of
629 \textit{A common debugger feature is to allow the debugger user to call
630 a subroutine within the subject program. In certain cases,
631 however, the generated code for a subroutine will not obey
632 the standard calling conventions for the target architecture
633 and will therefore not be safe to call from within a debugger.
636 A subroutine entry may
637 \hypertarget{chap:DWATcallingconventionsubprogramcallingconvention}
639 \livelink{chap:DWATcallingconvention}{DW\-\_AT\-\_calling\-\_convention}
640 attribute, whose value is an integer constant. The set of
641 calling convention codes is given in
642 Figure \refersec{fig:callingconventioncodes}.
645 \autorows[0pt]{c}{1}{l}{
646 \addtoindex{DW\-\_CC\-\_normal},
647 \addtoindex{DW\-\_CC\-\_program},
648 \addtoindex{DW\-\_CC\-\_nocall},
650 \caption{Calling convention codes}\label{fig:callingconventioncodes}
653 If this attribute is not present, or its value is the constant
654 \livetarg{chap:DWCCnormal}{DW\-\_CC\-\_normal}, then the subroutine may be safely called by
655 obeying the ``standard'' calling conventions of the target
656 architecture. If the value of the calling convention attribute
657 is the constant \livetarg{chap:DWCCnocall}{DW\-\_CC\-\_nocall}, the subroutine does not obey
658 standard calling conventions, and it may not be safe for the
659 debugger to call this subroutine.
661 If the semantics of the language of the compilation unit
662 containing the subroutine entry distinguishes between ordinary
663 subroutines and subroutines that can serve as the ``main
664 program,'' that is, subroutines that cannot be called
665 directly according to the ordinary calling conventions,
666 then the debugging information entry for such a subroutine
667 may have a calling convention attribute whose value is the
668 constant \livetarg{chap:DWCCprogram}{DW\-\_CC\-\_program}.
670 \textit{The \livelink{chap:DWCCprogram}{DW\-\_CC\-\_program} value is intended to support Fortran main
671 programs which in some implementations may not be callable
672 or which must be invoked in a special way. It is not intended
673 as a way of finding the entry address for the program.
676 \textit{In C there is a difference between the types of functions
677 declared using function prototype style declarations and
678 those declared using non\dash prototype declarations.
681 A subroutine entry declared with a function prototype style
682 declaration may have a
683 \livelink{chap:DWATprototyped}{DW\-\_AT\-\_prototyped} attribute, which is
684 a \livelink{chap:flag}{flag}.
686 \textit{The Fortran language allows the keywords elemental, pure
687 and recursive to be included as part of the declaration of
688 a subroutine; these attributes reflect that usage. These
689 attributes are not relevant for languages that do not support
690 similar keywords or syntax. In particular, the \livelink{chap:DWATrecursive}{DW\-\_AT\-\_recursive}
691 attribute is neither needed nor appropriate in languages such
692 as C where functions support recursion by default.
696 \hypertarget{chap:DWATelementalelementalpropertyofasubroutine}
698 \livelink{chap:DWATelemental}{DW\-\_AT\-\_elemental} attribute, which
699 is a \livelink{chap:flag}{flag}.
700 The attribute indicates whether the subroutine
701 or entry point was declared with the ``elemental'' keyword
705 \hypertarget{chap:DWATpurepurepropertyofasubroutine}
706 subprogram entry may have a
707 \livelink{chap:DWATpure}{DW\-\_AT\-\_pure} attribute, which is
708 a \livelink{chap:flag}{flag}.
709 The attribute indicates whether the subroutine was
710 declared with the ``pure'' keyword or property.
713 \hypertarget{chap:DWATrecursiverecursivepropertyofasubroutine}
714 subprogram entry may have a
715 \livelink{chap:DWATrecursive}{DW\-\_AT\-\_recursive} attribute, which
716 is a \livelink{chap:flag}{flag}.
717 The attribute indicates whether the subroutine
718 or entry point was declared with the ``recursive'' keyword
723 \subsection{Subroutine and Entry Point Return Types}
724 \label{chap:subroutineandentrypointreturntypes}
726 If the subroutine or entry point is a function that returns a
727 value, then its debugging information entry has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type}
728 attribute to denote the type returned by that function.
730 \textit{Debugging information entries for C void functions should
731 not have an attribute for the return type. }
734 \subsection{Subroutine and Entry Point Locations}
735 \label{chap:subroutineandentrypointlocations}
737 A subroutine entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
738 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
739 whose values encode the contiguous or non\dash contiguous address
740 ranges, respectively, of the machine instructions generated
741 for the subroutine (see
742 Section \refersec{chap:codeaddressesandranges}).
745 \hypertarget{chap:DWATentrypcentryaddressofsubprogram}
746 subroutine entry may also have a
747 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute
748 whose value is the address of the first executable instruction
749 of the subroutine (see
750 Section \refersec{chap:entryaddress}).
752 An entry point has a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute whose value is the
753 relocated address of the first machine instruction generated
756 \textit{While the \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute might also seem appropriate
757 for this purpose, historically the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute
758 was used before the \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} was introduced (in DWARF
759 Version 3). There is insufficient reason to change this.}
762 Subroutines and entry points
763 \hypertarget{chap:DWATaddressclasssubroutineorsubroutinetype}
765 \livelink{chap:DWATsegment}{DW\-\_AT\-\_segment}
767 \livelink{chap:DWATaddressclass}{DW\-\_AT\-\_address\-\_class} attributes,
768 as appropriate, to specify
769 which segments the code for the subroutine resides in and
770 the addressing mode to be used in calling that subroutine.
772 A subroutine entry representing a subroutine declaration
773 that is not also a definition does not have code address or
777 \subsection{Declarations Owned by Subroutines and Entry Points}
778 \label{chap:declarationsownedbysubroutinesandentrypoints}
780 The declarations enclosed by a subroutine or entry point are
781 represented by debugging information entries that are owned
782 by the subroutine or entry point entry. Entries representing
783 the formal parameters of the subroutine or entry point appear
784 in the same order as the corresponding declarations in the
787 \textit{There is no ordering requirement for entries for declarations
788 that are children of subroutine or entry point entries but
789 that do not represent formal parameters. The formal parameter
790 entries may be interspersed with other entries used by formal
791 parameter entries, such as type entries.}
793 The unspecified parameters of a variable parameter list are
794 represented by a debugging information entry with the tag
795 \livetarg{chap:DWTAGunspecifiedparameters}{DW\-\_TAG\-\_unspecified\-\_parameters}.
797 The entry for a subroutine that includes a
798 Fortran \livelink{chap:fortrancommonblock}{common} \livelink{chap:commonblockentry}{block}
799 \index{common block|see{Fortran common block}}
800 has a child entry with the
801 tag \livetarg{chap:DWTAGcommoninclusion}{DW\-\_TAG\-\_common\-\_inclusion}.
803 \hypertarget{chap:commonreferencecommonblockusage}
804 common inclusion entry has a
805 \livelink{chap:DWATcommonreference}{DW\-\_AT\-\_common\-\_reference} attribute
806 whose value is a reference to the debugging information entry
807 for the common \nolink{block} being included
808 (see Section \refersec{chap:commonblockentries}).
810 \subsection{Low-Level Information}
811 \label{chap:lowlevelinformation}
814 \hypertarget{chap:DWATreturnaddrsubroutinereturnaddresssavelocation}
815 subroutine or entry point entry may have a
816 \livelink{chap:DWATreturnaddr}{DW\-\_AT\-\_return\-\_addr}
817 attribute, whose value is a location description. The location
818 calculated is the place where the return address for the
819 subroutine or entry point is stored.
821 A subroutine or entry point entry may also have a
822 \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute, whose value is a location
823 description that computes the “frame base” for the
824 subroutine or entry point. If the location description is
825 a simple register location description, the given register
826 contains the frame base address. If the location description is
827 a DWARF expression, the result of evaluating that expression
828 is the frame base address. Finally, for a location list,
829 this interpretation applies to each location description
830 contained in the list of location list entries.
832 \textit{The use of one of the \livelink{chap:DWOPreg}{DW\-\_OP\-\_reg}~\textless~n~\textgreater
834 context is equivalent to using
835 \livelink{chap:DWOPbreg}{DW\-\_OP\-\_breg}~\textless~n~\textgreater(0)
837 compact. However, these are not equivalent in general.}
839 \textit{The frame base for a procedure is typically an address fixed
840 relative to the first unit of storage allocated for the
841 procedure’s stack frame. The \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute
842 can be used in several ways:}
844 \begin{enumerate}[1.]
845 \item \textit{In procedures that need location lists to locate local
846 variables, the \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} can hold the needed location
847 list, while all variables’ location descriptions can be
848 simpler ones involving the frame base.}
850 \item \textit{It can be used in resolving ``up\dash level'' addressing
851 within nested routines.
852 (See also \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link}, below)}
853 %The -See also- here is ok, the DW\-\_AT should be
854 %a hyperref to the def itself, which is earlier in this document.
857 \textit{Some languages support nested subroutines. In such languages,
858 it is possible to reference the local variables of an
859 outer subroutine from within an inner subroutine. The
860 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link} and \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attributes allow
861 debuggers to support this same kind of referencing.}
864 \hypertarget{chap:DWATstaticlinklocationofuplevelframe}
865 a subroutine or entry point is nested, it may have a
866 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link}
867 attribute, whose value is a location
868 description that computes the frame base of the relevant
869 instance of the subroutine that immediately encloses the
870 subroutine or entry point.
872 In the context of supporting nested subroutines, the
873 \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute value should obey the following
876 \begin{enumerate}[1.]
877 \item It should compute a value that does not change during the
878 life of the procedure, and
880 \item The computed value should be unique among instances of
881 the same subroutine. (For typical \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} use, this
882 means that a recursive subroutine’s stack frame must have
886 \textit{If a debugger is attempting to resolve an up\dash level reference
887 to a variable, it uses the nesting structure of DWARF to
888 determine which subroutine is the lexical parent and the
889 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link} value to identify the appropriate active
890 frame of the parent. It can then attempt to find the reference
891 within the context of the parent.}
895 \subsection{Types Thrown by Exceptions}
896 \label{chap:typesthrownbyexceptions}
898 \textit{In C++ a subroutine may declare a set of types which
899 it may validly throw.}
901 If a subroutine explicitly declares that it may throw
902 an exception for one or more types, each such type is
903 represented by a debugging information entry with the tag
904 \livetarg{chap:DWTAGthrowntype}{DW\-\_TAG\-\_thrown\-\_type}.
905 Each such entry is a child of the entry
906 representing the subroutine that may throw this type. Each
907 thrown type entry contains a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute, whose
908 value is a reference to an entry describing the type of the
909 exception that may be thrown.
911 \subsection{Function Template Instantiations}
912 \label{chap:functiontemplateinstantiations}
914 \textit{In C++, a function template is a generic definition of
915 a function that is instantiated differently when called with
916 values of different types. DWARF does not represent the generic
917 template definition, but does represent each instantiation.}
919 A template instantiation is represented by a debugging
920 information entry with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}. With four
921 exceptions, such an entry will contain the same attributes and
922 will have the same types of child entries as would an entry
923 for a subroutine defined explicitly using the instantiation
924 types. The exceptions are:
926 \begin{enumerate}[1.]
927 \item Each formal parameterized type declaration appearing in the
928 template definition is represented by a debugging information
930 tag \livetarg{chap:DWTAGtemplatetypeparameter}{DW\-\_TAG\-\_template\-\_type\-\_parameter}.
932 such entry has a \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute, whose value is a
933 null\dash terminated string containing the name of the formal
934 type parameter as it appears in the source program. The
935 template type parameter entry also has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute
936 describing the actual type by which the formal is replaced
937 for this instantiation.
939 \item The subprogram entry and each of its child entries reference
940 a template type parameter entry in any circumstance where
941 the template definition referenced a formal parameterized type.
943 \item If the compiler has generated a special compilation unit
944 to hold the template instantiation and that compilation unit
945 has a different name from the compilation unit containing
946 the template definition, the name attribute for the debugging
947 information entry representing that compilation unit is empty
950 \item If the subprogram entry representing the template
951 instantiation or any of its child entries contain declaration
952 coordinate attributes, those attributes refer to the source
953 for the template definition, not to any source generated
954 artificially by the compiler for this instantiation.
959 \subsection{Inlinable and Inlined Subroutines}
960 A declaration or a definition of an inlinable subroutine
961 is represented by a debugging information entry with the
962 tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}. The entry for a subroutine that is
963 explicitly declared to be available for inline expansion or
964 that was expanded inline implicitly by the compiler has a
965 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is an integer constant. The
966 set of values for the \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute is given in
967 Figure \refersec{fig:inlinecodes}.
971 \caption{Inline codes}
972 \label{fig:inlinecodes}
973 \begin{tabular}{lp{9cm}}
974 Name&Meaning\\ \hline
975 \livetarg{chap:DWINLnotinlined}{DW\-\_INL\-\_not\-\_inlined} & Not delared inline nor inlined by the
976 compiler(equivalent to the absense of the containing
977 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute) \\
978 \livetarg{chap:DWINLinlined}{DW\-\_INL\-\_inlined} & Not declared inline but inlined by the compiler \\
979 \livetarg{chap:DWINLdeclarednotinlined}{DW\-\_INL\-\_declared\-\_not\-\_inlined} & Declared inline but
980 not inlined by the compiler \\
981 \livetarg{chap:DWINLdeclaredinlined}{DW\-\_INL\-\_declared\-\_inlined} & Declared inline and inlined by the compiler \\
985 \textit{In C++, a function or a constructor declared with
986 constexpr is implicitly declared inline. The abstract inline
987 instance (see below) is represented by a debugging information
988 entry with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}. Such an entry has a
989 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is \livelink{chap:DWINLinlined}{DW\-\_INL\-\_inlined}.}
992 \paragraph{Abstract Instances}
993 \label{chap:abstractinstances}
994 Any debugging information entry that is owned (either
995 directly or indirectly) by a debugging information entry
996 that contains the \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute is referred to
997 as an ``abstract instance entry.'' Any subroutine entry
998 that contains a \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is other
999 than \livelink{chap:DWINLnotinlined}{DW\-\_INL\-\_not\-\_inlined} is known as
1000 an ``abstract instance root.''
1001 Any set of abstract instance entries that are all
1002 children (either directly or indirectly) of some abstract
1003 instance root, together with the root itself, is known as
1004 an ``abstract instance tree.'' However, in the case where
1005 an abstract instance tree is nested within another abstract
1006 instance tree, the entries in the nested abstract instance
1007 tree are not considered to be entries in the outer abstract
1010 Each abstract instance root is either part of a larger
1011 tree (which gives a context for the root) or uses
1012 \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} to refer to the declaration in context.
1014 \textit{For example, in C++ the context might be a namespace
1015 declaration or a class declaration.}
1017 \textit{Abstract instance trees are defined so that no entry is part
1018 of more than one abstract instance tree. This simplifies the
1019 following descriptions.}
1021 A debugging information entry that is a member of an abstract
1022 instance tree should not contain any attributes which describe
1023 aspects of the subroutine which vary between distinct inlined
1024 expansions or distinct out\dash of\dash line expansions. For example,
1025 the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc},
1026 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc}, \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges},
1027 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc}, \livelink{chap:DWATlocation}{DW\-\_AT\-\_location},
1028 \livelink{chap:DWATreturnaddr}{DW\-\_AT\-\_return\-\_addr}, \livelink{chap:DWATstartscope}{DW\-\_AT\-\_start\-\_scope}, and
1029 \livelink{chap:DWATsegment}{DW\-\_AT\-\_segment}
1030 attributes typically should be omitted; however, this list
1033 \textit{It would not make sense normally to put these attributes into
1034 abstract instance entries since such entries do not represent
1035 actual (concrete) instances and thus do not actually exist at
1036 run\dash time. However,
1037 see Appendix \refersec{app:inlineouteronenormalinner}
1038 for a contrary example.}
1040 The rules for the relative location of entries belonging to
1041 abstract instance trees are exactly the same as for other
1042 similar types of entries that are not abstract. Specifically,
1043 the rule that requires that an entry representing a declaration
1044 be a direct child of the entry representing the scope of the
1045 declaration applies equally to both abstract and non\dash abstract
1046 entries. Also, the ordering rules for formal parameter entries,
1047 member entries, and so on, all apply regardless of whether
1048 or not a given entry is abstract.
1050 \paragraph{Concrete Inlined Instances}
1051 \label{chap:concreteinlinedinstances}
1053 Each inline expansion of a subroutine is represented
1054 by a debugging information entry with the
1055 tag \livetarg{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}.
1056 Each such entry should be a direct
1057 child of the entry that represents the scope within which
1058 the inlining occurs.
1060 Each inlined subroutine entry may have either a
1061 \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc}
1062 and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges}
1063 attribute whose values encode the contiguous or non\dash contiguous
1064 address ranges, respectively, of the machine instructions
1065 generated for the inlined subroutine (see
1066 Section \refersec{chap:codeaddressesandranges}).
1068 \hypertarget{chap:DWATentrypcentryaddressofinlinedsubprogram}
1069 inlined subroutine entry may also contain a
1070 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc}
1071 attribute, representing the first executable instruction of
1072 the inline expansion (see
1073 Section \refersec{chap:entryaddress}).
1075 % Positions of the 3 targets here is a bit arbitrary.
1077 \hypertarget{chap:DWATcalllinelinenumberofinlinedsubroutinecall}
1079 \hypertarget{chap:DWATcallcolumncolumnpositionofinlinedsubroutinecall}
1081 \hypertarget{chap:DWATcallfilefilecontaininginlinedsubroutinecall}
1082 may also have \livelink{chap:DWATcallfile}{DW\-\_AT\-\_call\-\_file},
1083 \livelink{chap:DWATcallline}{DW\-\_AT\-\_call\-\_line} and \livelink{chap:DWATcallcolumn}{DW\-\_AT\-\_call\-\_column} attributes,
1085 value is an integer constant. These attributes represent the
1086 source file, source line number, and source column number,
1087 respectively, of the first character of the statement or
1088 expression that caused the inline expansion. The call file,
1089 call line, and call column attributes are interpreted in
1090 the same way as the declaration file, declaration line, and
1091 declaration column attributes, respectively (see
1092 Section \refersec{chap:declarationcoordinates}).
1094 The call file, call line and call column coordinates do not
1095 describe the coordinates of the subroutine declaration that
1096 was inlined, rather they describe the coordinates of the call.
1098 An inlined subroutine entry
1099 \hypertarget{chap:DWATconstexprcompiletimeconstantfunction}
1101 \livelink{chap:DWATconstexpr}{DW\-\_AT\-\_const\-\_expr}
1102 attribute, which is a \livelink{chap:flag}{flag}
1103 whose presence indicates that the
1104 subroutine has been evaluated as a compile\dash time constant. Such
1105 an entry may also have a \livelink{chap:DWATconstvalue}{DW\-\_AT\-\_const\-\_value} attribute,
1106 whose value may be of any form that is appropriate for the
1107 representation of the subroutine's return value. The value of
1108 this attribute is the actual return value of the subroutine,
1109 represented as it would be on the target architecture.
1111 \textit{In C++, if a function or a constructor declared with constexpr
1112 is called with constant expressions, then the corresponding
1113 concrete inlined instance has a \livelink{chap:DWATconstexpr}{DW\-\_AT\-\_const\-\_expr} attribute,
1114 as well as a \livelink{chap:DWATconstvalue}{DW\-\_AT\-\_const\-\_value} attribute whose value represents
1115 the actual return value of the concrete inlined instance.}
1117 Any debugging information entry that is owned (either
1118 directly or indirectly) by a debugging information entry
1119 with the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine} is referred to as a
1120 ``concrete inlined instance entry.'' Any entry that has
1121 the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}
1122 is known as a ``concrete inlined instance root.'' Any set of concrete inlined instance
1123 entries that are all children (either directly or indirectly)
1124 of some concrete inlined instance root, together with the root
1125 itself, is known as a ``concrete inlined instance tree.''
1126 However, in the case where a concrete inlined instance tree
1127 is nested within another concrete instance tree, the entries
1128 in the nested concrete instance tree are not considered to
1129 be entries in the outer concrete instance tree.
1131 \textit{Concrete inlined instance trees are defined so that no entry
1132 is part of more than one concrete inlined instance tree. This
1133 simplifies later descriptions.}
1135 Each concrete inlined instance tree is uniquely associated
1136 with one (and only one) abstract instance tree.
1138 \textit{Note, however, that the reverse is not true. Any given abstract
1139 instance tree may be associated with several different concrete
1140 inlined instance trees, or may even be associated with zero
1141 concrete inlined instance trees.}
1143 Concrete inlined instance entries may omit attributes that
1144 are not specific to the concrete instance (but present in
1145 the abstract instance) and need include only attributes that
1146 are specific to the concrete instance (but omitted in the
1147 abstract instance). In place of these omitted attributes, each
1148 \hypertarget{chap:DWATabstractorigininlineinstance}
1149 concrete inlined instance entry
1151 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin}
1152 attribute that may be used to obtain the missing information
1153 (indirectly) from the associated abstract instance entry. The
1154 value of the abstract origin attribute is a reference to the
1155 associated abstract instance entry.
1157 If an entry within a concrete inlined instance tree contains
1158 attributes describing the declaration coordinates of that
1159 entry, then those attributes should refer to the file, line
1160 and column of the original declaration of the subroutine,
1161 not to the point at which it was inlined. As a consequence,
1162 they may usually be omitted from any entry that has an abstract
1165 For each pair of entries that are associated via a
1166 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attribute, both members of the pair
1167 have the same tag. So, for example, an entry with the tag
1168 \livelink{chap:DWTAGvariable}{DW\-\_TAG\-\_variable} can only be associated with another entry
1169 that also has the tag \livelink{chap:DWTAGvariable}{DW\-\_TAG\-\_variable}. The only exception
1170 to this rule is that the root of a concrete instance tree
1171 (which must always have the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine})
1172 can only be associated with the root of its associated abstract
1173 instance tree (which must have the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}).
1175 In general, the structure and content of any given concrete
1176 inlined instance tree will be closely analogous to the
1177 structure and content of its associated abstract instance
1178 tree. There are a few exceptions:
1180 \begin{enumerate}[1.]
1181 \item An entry in the concrete instance tree may be omitted if
1182 it contains only a \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attribute and either
1183 has no children, or its children are omitted. Such entries
1184 would provide no useful information. In C\dash like languages,
1185 such entries frequently include types, including structure,
1186 union, class, and interface types; and members of types. If any
1187 entry within a concrete inlined instance tree needs to refer
1188 to an entity declared within the scope of the relevant inlined
1189 subroutine and for which no concrete instance entry exists,
1190 the reference should refer to the abstract instance entry.
1192 \item Entries in the concrete instance tree which are associated
1193 with entries in the abstract instance tree such that neither
1194 has a \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute, and neither is referenced by
1195 any other debugging information entry, may be omitted. This
1196 may happen for debugging information entries in the abstract
1197 instance trees that became unnecessary in the concrete instance
1198 tree because of additional information available there. For
1199 example, an anonymous variable might have been created and
1200 described in the abstract instance tree, but because of
1201 the actual parameters for a particular inlined expansion,
1202 it could be described as a constant value without the need
1203 for that separate debugging information entry.
1205 \item A concrete instance tree may contain entries which do
1206 not correspond to entries in the abstract instance tree
1207 to describe new entities that are specific to a particular
1208 inlined expansion. In that case, they will not have associated
1209 entries in the abstract instance tree, should not contain
1210 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attributes, and must contain all their
1211 own attributes directly. This allows an abstract instance tree
1212 to omit debugging information entries for anonymous entities
1213 that are unlikely to be needed in most inlined expansions. In
1214 any expansion which deviates from that expectation, the
1215 entries can be described in its concrete inlined instance tree.
1219 \paragraph{Out-of-Line Instances of Inlined Subroutines}
1220 \label{chap:outoflineinstancesofinlinedsubroutines}
1221 Under some conditions, compilers may need to generate concrete
1222 executable instances of inlined subroutines other than at
1223 points where those subroutines are actually called. Such
1224 concrete instances of inlined subroutines are referred to as
1225 ``concrete out\dash of\dash line instances.''
1227 \textit{In C++, for example, taking the address of a function declared
1228 to be inline can necessitate the generation of a concrete
1229 out\dash of\dash line instance of the given function.}
1231 The DWARF representation of a concrete out\dash of\dash line instance
1232 of an inlined subroutine is essentially the same as for a
1233 concrete inlined instance of that subroutine (as described in
1234 the preceding section). The representation of such a concrete
1235 % It is critical that the hypertarget and livelink be
1236 % separated to avoid problems with latex.
1237 out\dash of\dash line instance
1238 \hypertarget{chap:DWATabstractoriginoutoflineinstance}
1240 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin}
1241 attributes in exactly the same way as they are used for
1242 a concrete inlined instance (that is, as references to
1243 corresponding entries within the associated abstract instance
1246 The differences between the DWARF representation of a
1247 concrete out\dash of\dash line instance of a given subroutine and the
1248 representation of a concrete inlined instance of that same
1249 subroutine are as follows:
1251 \begin{enumerate}[1.]
1252 \item The root entry for a concrete out\dash of\dash line instance
1253 of a given inlined subroutine has the same tag as does its
1254 associated (abstract) inlined subroutine entry (that is, tag
1255 \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} rather than \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}).
1257 \item The root entry for a concrete out\dash of\dash line instance tree
1258 is normally owned by the same parent entry that also owns
1259 the root entry of the associated abstract instance. However,
1260 it is not required that the abstract and out\dash of\dash line instance
1261 trees be owned by the same parent entry.
1265 \paragraph{Nested Inlined Subroutines}
1266 \label{nestedinlinedsubroutines}
1267 Some languages and compilers may permit the logical nesting of
1268 a subroutine within another subroutine, and may permit either
1269 the outer or the nested subroutine, or both, to be inlined.
1271 For a non\dash inlined subroutine nested within an inlined
1272 subroutine, the nested subroutine is described normally in
1273 both the abstract and concrete inlined instance trees for
1274 the outer subroutine. All rules pertaining to the abstract
1275 and concrete instance trees for the outer subroutine apply
1276 also to the abstract and concrete instance entries for the
1279 For an inlined subroutine nested within another inlined
1280 subroutine, the following rules apply to their abstract and
1281 concrete instance trees:
1283 \begin{enumerate}[1.]
1284 \item The abstract instance tree for the nested subroutine is
1285 described within the abstract instance tree for the outer
1286 subroutine according to the rules in
1287 Section \refersec{chap:abstractinstances}, and
1288 without regard to the fact that it is within an outer abstract
1291 \item Any abstract instance tree for a nested subroutine is
1292 always omitted within the concrete instance tree for an
1295 \item A concrete instance tree for a nested subroutine is
1296 always omitted within the abstract instance tree for an
1299 \item The concrete instance tree for any inlined or out-of-line
1300 expansion of the nested subroutine is described within a
1301 concrete instance tree for the outer subroutine according
1303 Sections \refersec{chap:concreteinlinedinstances} or
1304 \refersec{chap:outoflineinstancesofinlinedsubroutines}
1306 and without regard to the fact that it is within an outer
1307 concrete instance tree.
1310 See Appendix \refersec{app:inliningexamples}
1311 for discussion and examples.
1313 \subsection{Trampolines}
1314 \label{chap:trampolines}
1316 \textit{A trampoline is a compiler\dash generated subroutine that serves as
1317 an intermediary in making a call to another subroutine. It may
1318 adjust parameters and/or the result (if any) as appropriate
1319 to the combined calling and called execution contexts.}
1321 A trampoline is represented by a debugging information entry
1322 with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} or \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}
1323 that has a \livelink{chap:DWATtrampoline}{DW\-\_AT\-\_trampoline} attribute. The value of that
1324 attribute indicates the target subroutine of the trampoline,
1325 that is, the subroutine to which the trampoline passes
1326 control. (A trampoline entry may but need not also have a
1327 \livelink{chap:DWATartificial}{DW\-\_AT\-\_artificial} attribute.)
1329 The value of the trampoline attribute may be represented
1330 using any of the following forms, which are listed in order
1334 \item If the value is of class reference, then the value
1335 specifies the debugging information entry of the target
1338 \item If the value is of class address, then the value is
1339 the relocated address of the target subprogram.
1341 \item If the value is of class string, then the value is the
1342 (possibly mangled) name of the target subprogram.
1344 \item If the value is of class \livelink{chap:flag}{flag}, then the value true
1345 indicates that the containing subroutine is a trampoline but
1346 that the target subroutine is not known.
1350 The target subprogram may itself be a trampoline. (A sequence
1351 of trampolines necessarily ends with a non\dash trampoline
1354 \textit{In C++, trampolines may be used to implement derived virtual
1355 member functions; such trampolines typically adjust the
1356 implicit this pointer parameter in the course of passing
1357 control. Other languages and environments may use trampolines
1358 in a manner sometimes known as transfer functions or transfer
1361 \textit{Trampolines may sometimes pass control to the target
1362 subprogram using a branch or jump instruction instead of a
1363 call instruction, thereby leaving no trace of their existence
1364 in the subsequent execution context. }
1366 \textit{This attribute helps make it feasible for a debugger to arrange
1367 that stepping into a trampoline or setting a breakpoint in
1368 a trampoline will result in stepping into or setting the
1369 breakpoint in the target subroutine instead. This helps to
1370 hide the compiler generated subprogram from the user. }
1372 \textit{If the target subroutine is not known, a debugger may choose
1373 to repeatedly step until control arrives in a new subroutine
1374 which can be assumed to be the target subroutine. }
1378 \section{Lexical Block Entries}
1379 \label{chap:lexicalblockentries}
1381 \textit{A lexical \livetargi{chap:lexicalblock}{block}{lexical block} is a bracketed sequence of source statements
1382 that may contain any number of declarations. In some languages
1383 (including C and C++), \nolink{blocks} can be nested within other
1384 \nolink{blocks} to any depth.}
1386 % We do not need to link to the preceeding paragraph.
1387 A lexical \nolink{block} is represented by a debugging information
1389 tag \livetarg{chap:DWTAGlexicalblock}{DW\-\_TAG\-\_lexical\-\_block}.
1391 The lexical \livetargi{chap:lexicalblockentry}{block}{lexical block entry} entry
1393 either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
1394 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of
1395 attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
1396 whose values encode the contiguous or non-contiguous address
1397 ranges, respectively, of the machine instructions generated
1398 for the lexical \livelink{chap:lexicalblock}{block}
1399 (see Section \refersec{chap:codeaddressesandranges}).
1401 If a name has been given to the
1402 lexical \livelink{chap:lexicalblock}{block}
1404 program, then the corresponding
1405 lexical \livelink{chap:lexicalblockentry}{block} entry has a
1406 \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute whose
1407 value is a null\dash terminated string
1408 containing the name of the lexical \livelink{chap:lexicalblock}{block}
1412 \textit{This is not the same as a C or C++ label (see below).}
1414 The lexical \livelink{chap:lexicalblockentry}{block} entry owns
1415 debugging information entries that
1416 describe the declarations within that lexical \livelink{chap:lexicalblock}{block}.
1418 one such debugging information entry for each local declaration
1419 of an identifier or inner lexical \livelink{chap:lexicalblock}{block}.
1421 \section{Label Entries}
1422 \label{chap:labelentries}
1424 A label is a way of identifying a source statement. A labeled
1425 statement is usually the target of one or more ``go to''
1428 A label is represented by a debugging information entry with
1430 tag \livetarg{chap:DWTAGlabel}{DW\-\_TAG\-\_label}.
1431 The entry for a label should be owned by
1432 the debugging information entry representing the scope within
1433 which the name of the label could be legally referenced within
1436 The label entry has a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute whose value
1437 is the relocated address of the first machine instruction
1438 generated for the statement identified by the label in
1439 the source program. The label entry also has a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
1440 attribute whose value is a null-terminated string containing
1441 the name of the label as it appears in the source program.
1444 \section{With Statement Entries}
1445 \label{chap:withstatemententries}
1447 \textit{Both Pascal and Modula\dash 2 support the concept of a ``with''
1448 statement. The with statement specifies a sequence of
1449 executable statements within which the fields of a record
1450 variable may be referenced, unqualified by the name of the
1453 A with statement is represented by a debugging information
1454 entry with the tag \livetarg{chap:DWTAGwithstmt}{DW\-\_TAG\-\_with\-\_stmt}.
1456 A with statement entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
1457 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
1458 whose values encode the contiguous or non\dash contiguous address
1459 ranges, respectively, of the machine instructions generated
1460 for the with statement
1461 (see Section \refersec{chap:codeaddressesandranges}).
1463 The with statement entry has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute, denoting
1464 the type of record whose fields may be referenced without full
1465 qualification within the body of the statement. It also has
1466 a \livelink{chap:DWATlocation}{DW\-\_AT\-\_location} attribute, describing how to find the base
1467 address of the record object referenced within the body of
1470 \section{Try and Catch Block Entries}
1471 \label{chap:tryandcatchblockentries}
1473 \textit{In C++ a lexical \livelink{chap:lexicalblock}{block} may be
1474 designated as a ``catch \nolink{block}.''
1475 A catch \livetargi{chap:catchblock}{block}{catch block} is an
1476 exception handler that handles
1477 exceptions thrown by an immediately
1478 preceding ``try \livelink{chap:tryblock}{block}.''
1479 A catch \livelink{chap:catchblock}{block}
1480 designates the type of the exception that it
1483 A try \livetargi{chap:tryblock}{block}{try block} is represented
1484 by a debugging information entry
1485 with the tag \livetarg{chap:DWTAGtryblock}{DW\-\_TAG\-\_try\-\_block}.
1486 A catch \livelink{chap:catchblock}{block} is represented by
1487 a debugging information entry with
1488 the tag \livetarg{chap:DWTAGcatchblock}{DW\-\_TAG\-\_catch\-\_block}.
1490 % nolink as we have links just above and do not have a combo link for both
1491 Both try and catch \nolink{block} entries may have either a
1492 \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a
1493 \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute whose values encode the contiguous
1494 or non\dash contiguous address ranges, respectively, of the
1495 machine instructions generated for the \livelink{chap:lexicalblock}{block}
1497 \refersec{chap:codeaddressesandranges}).
1499 Catch \livelink{chap:catchblock}{block} entries have at
1500 least one child entry, an
1501 entry representing the type of exception accepted by
1502 that catch \livelink{chap:catchblock}{block}.
1503 This child entry has one of the tags
1504 \livelink{chap:DWTAGformalparameter}{DW\-\_TAG\-\_formal\-\_parameter} or \livelink{chap:DWTAGunspecifiedparameters}{DW\-\_TAG\-\_unspecified\-\_parameters},
1505 and will have the same form as other parameter entries.
1507 The siblings immediately following
1508 a try \livelink{chap:tryblock}{block} entry are its
1509 corresponding catch \livelink{chap:catchblock}{block} entries.