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
72 \item Either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of
73 attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute whose values encode the
74 contiguous or non\dash contiguous address ranges, respectively,
75 of the machine instructions generated for the compilation
76 unit (see Section {chap:codeaddressesandranges}).
77 A \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute may also
78 be specified in combination with \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} to specify the
79 default base address for use in location lists (see Section
80 \refersec{chap:locationlists}) and range lists
81 (see Section \refersec{chap:noncontiguousaddressranges}).
83 \item A \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute whose value is a null\dash terminated
85 \hypertarget{chap:DWATnamepathnameofcompilationsource}
86 containing the full or relative path name of the primary
87 source file from which the compilation unit was derived.
89 \item A \livelink{chap:DWATlanguage}{DW\-\_AT\-\_language} attribute whose constant value is an
90 \hypertarget{chap:DWATlanguageprogramminglanguage}
91 integer code indicating the source language of the compilation
92 unit. The set of language names and their meanings are given
94 Figure \refersec{fig:languagenames}.
98 \caption{Language names}
99 \label{fig:languagenames}
101 Language name & Meaning\\ \hline
102 \livetarg{chap:DWLANGAda83}{DW\-\_LANG\-\_Ada83} \dag&ISO Ada:1983 \addtoindexx{Ada} \\
103 \livetarg{chap:DWLANGAda95}{DW\-\_LANG\-\_Ada95} \dag&ISO Ada:1995 \addtoindexx{Ada} \\
104 \livetarg{chap:DWLANGC}{DW\-\_LANG\-\_C}&Non-standardized C, such as K\&R \\
105 \livetarg{chap:DWLANGC89}{DW\-\_LANG\-\_C89}&ISO C:1989 \\
106 \livetarg{chap:DWLANGC99}{DW\-\_LANG\-\_C99} & ISO C:1999 \\
107 \livetarg{chap:DWLANGCplusplus}{DW\-\_LANG\-\_C\-\_plus\-\_plus}&ISO C++:1998 \\
108 \livetarg{chap:DWLANGCobol74}{DW\-\_LANG\-\_Cobol74}& ISO Cobol:1974 \\
109 \livetarg{chap:DWLANGCobol85}{DW\-\_LANG\-\_Cobol85} & ISO Cobol:1985 \\
110 \livetarg{chap:DWLANGD}{DW\-\_LANG\-\_D} \dag & D \\
111 \livetarg{chap:DWLANGFortran77}{DW\-\_LANG\-\_Fortran77} &ISO FORTRAN 77\\
112 \livetarg{chap:DWLANGFortran90}{DW\-\_LANG\-\_Fortran90} & ISO Fortran 90\\
113 \livetarg{chap:DWLANGFortran95}{DW\-\_LANG\-\_Fortran95} & ISO Fortran 95\\
114 \livetarg{chap:DWLANGJava}{DW\-\_LANG\-\_Java} & Java\\
115 \livetarg{chap:DWLANGModula2}{DW\-\_LANG\-\_Modula2} & ISO Modula\dash 2:1996\\
116 \livetarg{chap:DWLANGObjC}{DW\-\_LANG\-\_ObjC} & Objective C\\
117 \livetarg{chap:DWLANGObjCplusplus}{DW\-\_LANG\-\_ObjC\-\_plus\-\_plus} & Objective C++\\
118 \livetarg{chap:DWLANGPascal83}{DW\-\_LANG\-\_Pascal83} & ISO Pascal:1983\\
119 \livetarg{chap:DWLANGPLI}{DW\-\_LANG\-\_PLI} \dag & ANSI PL/I:1976\\
120 \livetarg{chap:DWLANGPython}{DW\-\_LANG\-\_Python} \dag & Python\\
121 \livetarg{chap:DWLANGUPC}{DW\-\_LANG\-\_UPC} &Unified Parallel C\\ \hline
122 \dag \ \ Support for these languages is limited.& \\
126 \item A \livelink{chap:DWATstmtlist}{DW\-\_AT\-\_stmt\-\_list} attribute whose value is a section
127 \hypertarget{chap:DWATstmtlistlinenumberinformationforunit}
128 offset to the line number information for this compilation
129 unit. This information is placed in a separate object file
130 section from the debugging information entries themselves. The
131 value of the statement list attribute is the offset in the
132 \addtoindex{.debug\_line} section of the first byte of the line number
133 information for this compilation unit
134 (see Section \refersec{chap:linenumberinformation}).
136 \item A \livelink{chap:DWATmacroinfo}{DW\-\_AT\-\_macro\-\_info} attribute whose value is a section
137 \hypertarget{chap:DWATmacroinfomacroinformation}
138 offset to the macro information for this compilation unit.
139 This information is placed in a separate object file section
140 from the debugging information entries themselves. The
141 value of the macro information attribute is the offset in
142 the \addtoindex{.debug\_macinfo} section of the first byte of the macro
143 information for this compilation unit
144 (see Section \refersec{chap:macroinformation}).
147 \livelink{chap:DWATcompdir}{DW\-\_AT\-\_comp\-\_dir}
149 \hypertarget{chap:DWATcompdircompilationdirectory}
151 null\dash terminated string containing the current working directory
152 of the compilation command that produced this compilation
153 unit in whatever form makes sense for the host system.
155 \item A \livelink{chap:DWATproducer}{DW\-\_AT\-\_producer} attribute whose value is a null\dash
156 terminated string containing information about the compiler
157 \hypertarget{chap:DWATproducercompileridentification}
158 that produced the compilation unit. The actual contents of
159 the string will be specific to each producer, but should
160 begin with the name of the compiler vendor or some other
161 identifying character sequence that should avoid confusion
162 with other producer values.
165 \item A \livelink{chap:DWATidentifiercase}{DW\-\_AT\-\_identifier\-\_case}
166 attribute whose integer
167 \hypertarget{chap:DWATidentifiercaseidentifiercaserule}
168 constant value is a code describing the treatment
169 of identifiers within this compilation unit. The
170 set of identifier case codes is given in Figure
171 \refersec{fig:identifiercasecodes}.
174 \autorows[0pt]{c}{1}{l}{
175 \livelink{chap:DWIDcasesensitive}{DW\-\_ID\-\_case\-\_sensitive},
176 \livelink{chap:DWIDupcase}{DW\-\_ID\-\_up\-\_case},
177 \livelink{chap:DWIDdowncase}{DW\-\_ID\-\_down\-\_case},
178 \livelink{chap:DWIDcaseinsensitive}{DW\-\_ID\-\_case\-\_insensitive}
180 \caption{Identifier case codes}\label{fig:identifiercasecodes}
183 \livetarg{chap:DWIDcasesensitive}{DW\-\_ID\-\_case\-\_sensitive} is the default for all compilation units
184 that do not have this attribute. It indicates that names given
185 as the values of \livelink{chap:DWATname}{DW\-\_AT\-\_name} attributes in debugging information
186 entries for the compilation unit reflect the names as they
187 appear in the source program. The debugger should be sensitive
188 to the case of identifier names when doing identifier lookups.
190 \livetarg{chap:DWIDupcase}{DW\-\_ID\-\_up\-\_case} means that the producer of the debugging
191 information for this compilation unit converted all source
192 names to upper case. The values of the name attributes may not
193 reflect the names as they appear in the source program. The
194 debugger should convert all names to upper case when doing
197 \livetarg{chap:DWIDdowncase}{DW\-\_ID\-\_down\-\_case} means that the producer of the debugging
198 information for this compilation unit converted all source
199 names to lower case. The values of the name attributes may not
200 reflect the names as they appear in the source program. The
201 debugger should convert all names to lower case when doing
204 \livetarg{chap:DWIDcaseinsensitive}{DW\-\_ID\-\_case\-\_insensitive} means that the values of the name
205 attributes reflect the names as they appear in the source
206 program but that a case insensitive lookup should be used to
209 \item A \livelink{chap:DWATbasetypes}{DW\-\_AT\-\_base\-\_types} attribute whose value is a reference.
213 \hypertarget{chap:DWATbasetypesprimitivedatatypesofcompilationunit}
215 \addtoindexx{base types attribute}
216 points to a debugging information entry
217 representing another compilation unit. It may be used
218 to specify the compilation unit containing the base type
219 entries used by entries in the current compilation unit
220 (see Section \refersec{chap:basetypeentries}).
222 This attribute provides a consumer a way to find the definition
223 of base types for a compilation unit that does not itself
224 contain such definitions. This allows a consumer, for example,
225 to interpret a type conversion to a base type
226 % getting this link target at the right spot is tricky.
227 \hypertarget{chap:DWATuseUTF8compilationunitusesutf8strings}
230 \item A \livelink{chap:DWATuseUTF8}{DW\-\_AT\-\_use\-\_UTF8} attribute,
231 which is a \livelink{chap:flag}{flag} whose
232 presence indicates that all strings (such as the names of
233 declared entities in the source program) are represented
234 using the UTF\dash 8 representation
235 (see Section \refersec{datarep:attributeencodings}).
238 \item A \livelink{chap:DWATmainsubprogram}{DW\-\_AT\-\_main\-\_subprogram} attribute, which is a \livelink{chap:flag}{flag}
239 whose presence indicates
240 \hypertarget{chap:DWATmainsubprogramunitcontainingmainorstartingsubprogram}
241 that the compilation unit contains a
242 subprogram that has been identified as the starting function
243 of the program. If more than one compilation unit contains
244 this \nolink{flag}, any one of them may contain the starting function.
246 \textit{Fortran has a PROGRAM statement which is used
247 to specify and provide a user\dash specified name for the main
248 subroutine of a program. C uses the name “main” to identify
249 the main subprogram of a program. Some other languages provide
250 similar or other means to identify the main subprogram of
255 The base address of a compilation unit is defined as the
256 value of the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute, if present; otherwise,
257 it is undefined. If the base address is undefined, then any
258 DWARF entry or structure defined in terms of the base address
259 of that compilation unit is not valid.
262 \subsection{Imported Unit Entries}
263 \label{chap:importedunitentries}
265 \hypertarget{chap:DWATimportimportedunit}
266 place where a normal or partial unit is imported is
267 represented by a debugging information entry with the
268 tag \livetarg{chap:DWTAGimportedunit}{DW\-\_TAG\-\_imported\-\_unit}.
269 An imported unit entry contains a
270 \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute whose value is a reference to the
271 normal or partial compilation unit whose declarations logically
272 belong at the place of the imported unit entry.
274 An imported unit entry does not necessarily correspond to
275 any entity or construct in the source program. It is merely
276 “glue” used to relate a partial unit, or a compilation
277 unit used as a partial unit, to a place in some other
280 \subsection{Separate Type Unit Entries}
281 \label{chap:separatetypeunitentries}
282 An object file may contain any number of separate type
283 unit entries, each representing a single complete type
284 definition. Each type unit must be uniquely identified by
285 a 64\dash bit signature, stored as part of the type unit, which
286 can be used to reference the type definition from debugging
287 information entries in other compilation units and type units.
289 A type unit is represented by a debugging information entry
290 with the tag \livetarg{chap:DWTAGtypeunit}{DW\-\_TAG\-\_type\-\_unit}.
291 A type unit entry owns debugging
292 information entries that represent the definition of a single
293 type, plus additional debugging information entries that may
294 be necessary to include as part of the definition of the type.
296 A type unit entry may have a \livelink{chap:DWATlanguage}{DW\-\_AT\-\_language} attribute, whose
297 constant value is an integer code indicating the source
298 language used to define the type. The set of language names
299 and their meanings are given in Figure \refersec{fig:languagenames}.
301 A type unit entry for a given type T owns a debugging
302 information entry that represents a defining declaration
303 of type T. If the type is nested within enclosing types or
304 namespaces, the debugging information entry for T is nested
305 within debugging information entries describing its containers;
306 otherwise, T is a direct child of the type unit entry.
308 A type unit entry may also own additional debugging information
309 entries that represent declarations of additional types that
310 are referenced by type T and have not themselves been placed in
311 separate type units. Like T, if an additional type U is nested
312 within enclosing types or namespaces, the debugging information
313 entry for U is nested within entries describing its containers;
314 otherwise, U is a direct child of the type unit entry.
316 The containing entries for types T and U are declarations,
317 and the outermost containing entry for any given type T or
318 U is a direct child of the type unit entry. The containing
319 entries may be shared among the additional types and between
320 T and the additional types.
322 Types are not required to be placed in type units. In general,
323 only large types such as structure, class, enumeration, and
324 union types included from header files should be considered
325 for separate type units. Base types and other small types
326 are not usually worth the overhead of placement in separate
327 type units. Types that are unlikely to be replicated, such
328 as those defined in the main source file, are also better
329 left in the main compilation unit.
331 \section{Module, Namespace and Importing Entries}
332 \textit{Modules and namespaces provide a means to collect related
333 entities into a single entity and to manage the names of
336 \subsection{Module Entries}
337 \label{chap:moduleentries}
338 \textit{Several languages have the concept of a ``module.''
339 A Modula\dash 2 definition module may be represented by a module
340 entry containing a declaration attribute (\livelink{chap:DWATdeclaration}{DW\-\_AT\-\_declaration}). A
341 Fortran 90 module may also be represented by a module entry
342 (but no declaration attribute is warranted because Fortran
343 has no concept of a corresponding module body).}
345 A module is represented by a debugging information entry
347 tag \livetarg{chap:DWTAGmodule}{DW\-\_TAG\-\_module}.
348 Module entries may own other
349 debugging information entries describing program entities
350 whose declaration scopes end at the end of the module itself.
352 If the module has a name, the module entry has a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
353 attribute whose value is a null\dash terminated string containing
354 the module name as it appears in the source program.
356 The module entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
357 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
358 whose values encode the contiguous or non\dash contiguous address
359 ranges, respectively, of the machine instructions generated for
360 the module initialization code
361 (see Section \refersec{chap:codeaddressesandranges}).
362 \hypertarget{chap:DWATentrypcentryaddressofmoduleinitialization}
364 have a \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute whose value is the address of
365 the first executable instruction of that initialization code
366 (see Section \refersec{chap:entryaddress}).
369 \hypertarget{chap:DWATprioritymodulepriority}
370 the module has been assigned a priority, it may have a
371 \livelink{chap:DWATpriority}{DW\-\_AT\-\_priority} attribute. The value of this attribute is a
372 reference to another debugging information entry describing
373 a variable with a constant value. The value of this variable
374 is the actual constant value of the module’s priority,
375 represented as it would be on the target architecture.
377 \subsection{Namespace Entries}
378 \label{chap:namespaceentries}
379 \textit{C++ has the notion of a namespace, which provides a way to
380 implement name hiding, so that names of unrelated things
381 do not accidentally clash in the global namespace when an
382 application is linked together.}
384 A namespace is represented by a debugging information entry
386 tag \livetarg{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace}.
387 A namespace extension is
388 \hypertarget{chap:DWATextensionpreviousnamespaceextensionororiginalnamespace}
390 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace} entry
392 \livelink{chap:DWATextension}{DW\-\_AT\-\_extension}
393 attribute referring to the previous extension, or if there
394 is no previous extension, to the original
395 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace}
396 entry. A namespace extension entry does not need to duplicate
397 information in a previous extension entry of the namespace
398 nor need it duplicate information in the original namespace
399 entry. (Thus, for a namespace with a name,
400 a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
401 attribute need only be attached directly to the original
402 \livelink{chap:DWTAGnamespace}{DW\-\_TAG\-\_namespace} entry.)
404 Namespace and namespace extension entries may own other
405 debugging information entries describing program entities
406 whose declarations occur in the namespace.
408 \textit{For C++, such owned program entities may be declarations,
409 including certain declarations that are also object or
410 function definitions.}
412 If a type, variable, or function declared in a namespace is
413 defined outside of the body of the namespace declaration,
414 that type, variable, or function definition entry has a
415 \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} attribute whose value is a reference to the
416 debugging information entry representing the declaration of
417 the type, variable or function. Type, variable, or function
418 entries with a \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} attribute do not need
419 to duplicate information provided by the declaration entry
420 referenced by the specification attribute.
422 \textit{The C++ global namespace (the namespace referred to by
423 ``::f'', for example) is not explicitly represented in
424 DWARF with a namespace entry (thus mirroring the situation
425 in C++ source). Global items may be simply declared with no
426 reference to a namespace.}
428 \textit{The C++ compilation unit specific ``unnamed namespace'' may
429 be represented by a namespace entry with no name attribute in
430 the original namespace declaration entry (and therefore no name
431 attribute in any namespace extension entry of this namespace).
434 \textit{A compiler emitting namespace information may choose to
435 explicitly represent namespace extensions, or to represent the
436 final namespace declaration of a compilation unit; this is a
437 quality\dash of\dash implementation issue and no specific requirements
438 are given here. If only the final namespace is represented,
439 it is impossible for a debugger to interpret using declaration
440 references in exactly the manner defined by the C++ language.
443 \textit{Emitting all namespace declaration information in all
444 compilation units can result in a significant increase in the
445 size of the debug information and significant duplication of
446 information across compilation units. The C++ namespace std,
447 for example, is large and will probably be referenced in
448 every C++ compilation unit.
451 \textit{For a C++ namespace example, see Appendix \refersec{app:namespaceexample}.
456 \subsection{Imported (or Renamed) Declaration Entries}
457 \label{chap:importedorrenameddeclarationentries}
458 \textit{Some languages support the concept of importing into or making
459 accessible in a given unit declarations made in a different
460 module or scope. An imported declaration may sometimes be
465 imported declaration is represented by one or
466 \addtoindex{imported declaration entry}
467 more debugging information entries with the
468 tag \livetarg{chap:DWTAGimporteddeclaration}{DW\-\_TAG\-\_imported\-\_declaration}.
470 \hypertarget{chap:DWATimportimporteddeclaration}
472 is imported, there is one imported declaration entry for
473 each overloading. Each imported declaration entry has a
474 \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute, whose value is a reference to the
475 debugging information entry representing the declaration that
478 An imported declaration may also have a
479 \livelink{chap:DWATname}{DW\-\_AT\-\_name}
481 whose value is a null\dash terminated string containing the
482 name, as it appears in the source program, by which the
483 imported entity is to be known in the context of the imported
484 declaration entry (which may be different than the name of
485 the entity being imported). If no name is present, then the
486 name by which the entity is to be known is the same as the
487 name of the entity being imported.
489 An imported declaration entry with a name attribute may be
490 used as a general means to rename or provide an alias for
491 \addtoindexx{alias declaration|see{imported declaration entry}}
492 an entity, regardless of the context in which the importing
493 declaration or the imported entity occurs.
495 \textit{A C++ namespace alias may be represented by an imported
496 \hypertarget{chap:DWATimportnamespacealias}
497 declaration entry with a name attribute whose value is
498 a null\dash terminated string containing the alias name as it
499 appears in the source program and an import attribute whose
500 value is a reference to the applicable original namespace or
501 namespace extension entry.
504 \textit{A C++ using declaration may be represented by one or more
505 \hypertarget{chap:DWATimportnamespaceusingdeclaration}
506 imported declaration entries. When the using declaration
507 refers to an overloaded function, there is one imported
508 declaration entry corresponding to each overloading. Each
509 imported declaration entry has no name attribute but it does
510 have an import attribute that refers to the entry for the
511 entity being imported. (C++ provides no means to ``rename''
512 an imported entity, other than a namespace).
515 \textit{A Fortran use statement with an ``only list'' may be
516 represented by a series of imported declaration entries,
517 one (or more) for each entity that is imported. An entity
518 that is renamed in the importing context may be represented
519 by an imported declaration entry with a name attribute that
520 specifies the new local name.
523 \subsection{Imported Module Entries}
524 \label{chap:importedmoduleentries}
526 \textit{Some languages support the concept of importing into or making
527 accessible in a given unit all of the declarations contained
528 within a separate module or namespace.
531 An imported module declaration is represented by a debugging
532 information entry with the
533 tag \livetarg{chap:DWTAGimportedmodule}{DW\-\_TAG\-\_imported\-\_module}.
535 imported module entry contains a \livelink{chap:DWATimport}{DW\-\_AT\-\_import} attribute
536 whose value is a reference to the module or namespace entry
537 containing the definition and/or declaration entries for
538 the entities that are to be imported into the context of the
539 imported module entry.
541 An imported module declaration may own a set of imported
542 declaration entries, each of which refers to an entry in the
543 module whose corresponding entity is to be known in the context
544 of the imported module declaration by a name other than its
545 name in that module. Any entity in the module that is not
546 renamed in this way is known in the context of the imported
547 module entry by the same name as it is declared in the module.
549 \textit{A C++ using directive may be represented by an imported module
550 \hypertarget{chap:DWATimportnamespaceusingdirective}
551 entry, with an import attribute referring to the namespace
552 entry of the appropriate extension of the namespace (which
553 might be the original namespace entry) and no owned entries.
556 \textit{A Fortran use statement with a “rename list” may be
557 represented by an imported module entry with an import
558 attribute referring to the module and owned entries
559 corresponding to those entities that are renamed as part of
563 \textit{A Fortran use statement with neither a “rename list” nor
564 an “only list” may be represented by an imported module
565 entry with an import attribute referring to the module and
566 no owned child entries.
569 \textit{A use statement with an “only list” is represented by a
570 series of individual imported declaration entries as described
571 in Section \refersec{chap:importedorrenameddeclarationentries}.
574 \textit{A Fortran use statement for an entity in a module that is
575 itself imported by a use statement without an explicit mention
576 may be represented by an imported declaration entry that refers
577 to the original debugging information entry. For example, given
593 the imported declaration entry for Q within module C refers
594 directly to the variable declaration entry for A in module A
595 because there is no explicit representation for X in module B.
597 A similar situation arises for a C++ using declaration that
598 imports an entity in terms of a namespace alias. See
599 Appendix \refersec{app:namespaceexample}
603 \section{Subroutine and Entry Point Entries}
604 \label{chap:subroutineandentrypointentries}
606 The following tags exist to describe debugging information entries for subroutines and entry
609 \begin{tabular}{lp{9.0cm}}
610 \livetarg{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} & A subroutine or function. \\
611 \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine} & A particular inlined
612 instance of a subroutine or function. \\
613 \livetarg{chap:DWTAGentrypoint}{DW\-\_TAG\-\_entry\-\_point} & An alternate entry point. \\
616 \subsection{General Subroutine and Entry Point Information}
617 \label{chap:generalsubroutineandentrypointinformation}
619 It may also have a \livelink{chap:DWATlinkagename}{DW\-\_AT\-\_linkage\-\_name} attribute as
620 described in Section \refersec{chap:linkagenames}.
622 If the name of the subroutine described by an entry with the
623 tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}
624 is visible outside of its containing
625 \hypertarget{chap:DWATexternalexternalsubroutine}
626 compilation unit, that entry has a
627 \livelink{chap:DWATexternal}{DW\-\_AT\-\_external} attribute,
628 which is a \livelink{chap:flag}{flag}.
630 \textit{Additional attributes for functions that are members of a
631 class or structure are described in
632 Section \refersec{chap:memberfunctionentries}.
636 \hypertarget{chap:DWATmainsubprogrammainorstartingsubprogram}
637 subroutine entry may contain a \livelink{chap:DWATmainsubprogram}{DW\-\_AT\-\_main\-\_subprogram}
639 a \livelink{chap:flag}{flag} whose presence indicates that the
640 subroutine has been identified as the starting function of
641 the program. If more than one subprogram contains this
643 any one of them may be the starting subroutine of the program.
645 \textit{Fortran has a PROGRAM statement which is used to specify
646 and provide a user\dash supplied name for the main subroutine of
650 \textit{A common debugger feature is to allow the debugger user to call
651 a subroutine within the subject program. In certain cases,
652 however, the generated code for a subroutine will not obey
653 the standard calling conventions for the target architecture
654 and will therefore not be safe to call from within a debugger.
657 A subroutine entry may
658 \hypertarget{chap:DWATcallingconventionsubprogramcallingconvention}
660 \livelink{chap:DWATcallingconvention}{DW\-\_AT\-\_calling\-\_convention}
661 attribute, whose value is an integer constant. The set of
662 calling convention codes is given in
663 Figure \refersec{fig:callingconventioncodes}.
666 \autorows[0pt]{c}{1}{l}{
667 \addtoindex{DW\-\_CC\-\_normal},
668 \addtoindex{DW\-\_CC\-\_program},
669 \addtoindex{DW\-\_CC\-\_nocall},
671 \caption{Calling convention codes}\label{fig:callingconventioncodes}
674 If this attribute is not present, or its value is the constant
675 \livetarg{chap:DWCCnormal}{DW\-\_CC\-\_normal}, then the subroutine may be safely called by
676 obeying the ``standard'' calling conventions of the target
677 architecture. If the value of the calling convention attribute
678 is the constant \livetarg{chap:DWCCnocall}{DW\-\_CC\-\_nocall}, the subroutine does not obey
679 standard calling conventions, and it may not be safe for the
680 debugger to call this subroutine.
682 If the semantics of the language of the compilation unit
683 containing the subroutine entry distinguishes between ordinary
684 subroutines and subroutines that can serve as the ``main
685 program,'' that is, subroutines that cannot be called
686 directly according to the ordinary calling conventions,
687 then the debugging information entry for such a subroutine
688 may have a calling convention attribute whose value is the
689 constant \livetarg{chap:DWCCprogram}{DW\-\_CC\-\_program}.
691 \textit{The \livelink{chap:DWCCprogram}{DW\-\_CC\-\_program} value is intended to support Fortran main
692 programs which in some implementations may not be callable
693 or which must be invoked in a special way. It is not intended
694 as a way of finding the entry address for the program.
697 \textit{In C there is a difference between the types of functions
698 declared using function prototype style declarations and
699 those declared using non\dash prototype declarations.
702 A subroutine entry declared with a function prototype style
703 declaration may have a
704 \livelink{chap:DWATprototyped}{DW\-\_AT\-\_prototyped} attribute, which is
705 a \livelink{chap:flag}{flag}.
707 \textit{The Fortran language allows the keywords elemental, pure
708 and recursive to be included as part of the declaration of
709 a subroutine; these attributes reflect that usage. These
710 attributes are not relevant for languages that do not support
711 similar keywords or syntax. In particular, the \livelink{chap:DWATrecursive}{DW\-\_AT\-\_recursive}
712 attribute is neither needed nor appropriate in languages such
713 as C where functions support recursion by default.
717 \hypertarget{chap:DWATelementalelementalpropertyofasubroutine}
719 \livelink{chap:DWATelemental}{DW\-\_AT\-\_elemental} attribute, which
720 is a \livelink{chap:flag}{flag}.
721 The attribute indicates whether the subroutine
722 or entry point was declared with the ``elemental'' keyword
726 \hypertarget{chap:DWATpurepurepropertyofasubroutine}
727 subprogram entry may have a
728 \livelink{chap:DWATpure}{DW\-\_AT\-\_pure} attribute, which is
729 a \livelink{chap:flag}{flag}.
730 The attribute indicates whether the subroutine was
731 declared with the ``pure'' keyword or property.
734 \hypertarget{chap:DWATrecursiverecursivepropertyofasubroutine}
735 subprogram entry may have a
736 \livelink{chap:DWATrecursive}{DW\-\_AT\-\_recursive} attribute, which
737 is a \livelink{chap:flag}{flag}.
738 The attribute indicates whether the subroutine
739 or entry point was declared with the ``recursive'' keyword
744 \subsection{Subroutine and Entry Point Return Types}
745 \label{chap:subroutineandentrypointreturntypes}
748 \hypertarget{chap:DWATtypetypeofsubroutinereturn}
749 the subroutine or entry point is a function that returns a
750 value, then its debugging information entry has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type}
751 attribute to denote the type returned by that function.
753 \textit{Debugging information entries for C void functions should
754 not have an attribute for the return type. }
757 \subsection{Subroutine and Entry Point Locations}
758 \label{chap:subroutineandentrypointlocations}
760 A subroutine entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
761 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
762 whose values encode the contiguous or non\dash contiguous address
763 ranges, respectively, of the machine instructions generated
764 for the subroutine (see
765 Section \refersec{chap:codeaddressesandranges}).
768 \hypertarget{chap:DWATentrypcentryaddressofsubprogram}
769 subroutine entry may also have a
770 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute
771 whose value is the address of the first executable instruction
772 of the subroutine (see
773 Section \refersec{chap:entryaddress}).
775 An entry point has a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute whose value is the
776 relocated address of the first machine instruction generated
779 \textit{While the \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} attribute might also seem appropriate
780 for this purpose, historically the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute
781 was used before the \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc} was introduced (in DWARF
782 Version 3). There is insufficient reason to change this.}
788 \addtoindexx{address class!attribute}
790 \hypertarget{chap:DWATaddressclasssubroutineorsubroutinetype}
792 \livelink{chap:DWATsegment}{DW\-\_AT\-\_segment}
794 \livelink{chap:DWATaddressclass}{DW\-\_AT\-\_address\-\_class} attributes,
795 as appropriate, to specify
796 which segments the code for the subroutine resides in and
797 the addressing mode to be used in calling that subroutine.
799 A subroutine entry representing a subroutine declaration
800 that is not also a definition does not have code address or
804 \subsection{Declarations Owned by Subroutines and Entry Points}
805 \label{chap:declarationsownedbysubroutinesandentrypoints}
807 The declarations enclosed by a subroutine or entry point are
808 represented by debugging information entries that are owned
809 by the subroutine or entry point entry. Entries representing
810 the formal parameters of the subroutine or entry point appear
811 in the same order as the corresponding declarations in the
814 \textit{There is no ordering requirement for entries for declarations
815 that are children of subroutine or entry point entries but
816 that do not represent formal parameters. The formal parameter
817 entries may be interspersed with other entries used by formal
818 parameter entries, such as type entries.}
820 The unspecified parameters of a variable parameter list are
821 represented by a debugging information entry with the tag
822 \livetarg{chap:DWTAGunspecifiedparameters}{DW\-\_TAG\-\_unspecified\-\_parameters}.
824 The entry for a subroutine that includes a
825 Fortran \livelink{chap:fortrancommonblock}{common} \livelink{chap:commonblockentry}{block}
826 \addtoindexx{common block|see{Fortran common block}}
827 has a child entry with the
828 tag \livetarg{chap:DWTAGcommoninclusion}{DW\-\_TAG\-\_common\-\_inclusion}.
830 \hypertarget{chap:commonreferencecommonblockusage}
831 common inclusion entry has a
832 \livelink{chap:DWATcommonreference}{DW\-\_AT\-\_common\-\_reference} attribute
833 whose value is a reference to the debugging information entry
834 for the common \nolink{block} being included
835 (see Section \refersec{chap:commonblockentries}).
837 \subsection{Low-Level Information}
838 \label{chap:lowlevelinformation}
841 \hypertarget{chap:DWATreturnaddrsubroutinereturnaddresssavelocation}
842 subroutine or entry point entry may have a
843 \livelink{chap:DWATreturnaddr}{DW\-\_AT\-\_return\-\_addr}
844 attribute, whose value is a location description. The location
845 calculated is the place where the return address for the
846 subroutine or entry point is stored.
849 \hypertarget{chap:DWATframebasesubroutineframebaseaddress}
850 subroutine or entry point entry may also have a
851 \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute, whose value is a location
852 description that computes the “frame base” for the
853 subroutine or entry point. If the location description is
854 a simple register location description, the given register
855 contains the frame base address. If the location description is
856 a DWARF expression, the result of evaluating that expression
857 is the frame base address. Finally, for a location list,
858 this interpretation applies to each location description
859 contained in the list of location list entries.
861 \textit{The use of one of the \livelink{chap:DWOPreg}{DW\-\_OP\-\_reg}~\textless~n~\textgreater
863 context is equivalent to using
864 \livelink{chap:DWOPbreg}{DW\-\_OP\-\_breg}~\textless~n~\textgreater(0)
866 compact. However, these are not equivalent in general.}
868 \textit{The frame base for a procedure is typically an address fixed
869 relative to the first unit of storage allocated for the
870 procedure’s stack frame. The \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute
871 can be used in several ways:}
873 \begin{enumerate}[1.]
874 \item \textit{In procedures that need location lists to locate local
875 variables, the \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} can hold the needed location
876 list, while all variables’ location descriptions can be
877 simpler ones involving the frame base.}
879 \item \textit{It can be used in resolving ``up\dash level'' addressing
880 within nested routines.
881 (See also \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link}, below)}
882 %The -See also- here is ok, the DW\-\_AT should be
883 %a hyperref to the def itself, which is earlier in this document.
886 \textit{Some languages support nested subroutines. In such languages,
887 it is possible to reference the local variables of an
888 outer subroutine from within an inner subroutine. The
889 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link} and \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attributes allow
890 debuggers to support this same kind of referencing.}
893 \hypertarget{chap:DWATstaticlinklocationofuplevelframe}
895 \addtoindexx{address!uplevel|see{static link attribute}}
896 subroutine or entry point is nested, it may have a
897 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link}
898 attribute, whose value is a location
899 description that computes the frame base of the relevant
900 instance of the subroutine that immediately encloses the
901 subroutine or entry point.
903 In the context of supporting nested subroutines, the
904 \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} attribute value should obey the following
907 \begin{enumerate}[1.]
908 \item It should compute a value that does not change during the
909 life of the procedure, and
911 \item The computed value should be unique among instances of
912 the same subroutine. (For typical \livelink{chap:DWATframebase}{DW\-\_AT\-\_frame\-\_base} use, this
913 means that a recursive subroutine’s stack frame must have
917 \textit{If a debugger is attempting to resolve an up\dash level reference
918 to a variable, it uses the nesting structure of DWARF to
919 determine which subroutine is the lexical parent and the
920 \livelink{chap:DWATstaticlink}{DW\-\_AT\-\_static\-\_link} value to identify the appropriate active
921 frame of the parent. It can then attempt to find the reference
922 within the context of the parent.}
926 \subsection{Types Thrown by Exceptions}
927 \label{chap:typesthrownbyexceptions}
929 \textit{In C++ a subroutine may declare a set of types which
930 it may validly throw.}
932 If a subroutine explicitly declares that it may throw
933 an exception for one or more types, each such type is
934 represented by a debugging information entry with the tag
935 \livetarg{chap:DWTAGthrowntype}{DW\-\_TAG\-\_thrown\-\_type}.
936 Each such entry is a child of the entry
937 representing the subroutine that may throw this type. Each
938 thrown type entry contains a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute, whose
939 value is a reference to an entry describing the type of the
940 exception that may be thrown.
942 \subsection{Function Template Instantiations}
943 \label{chap:functiontemplateinstantiations}
945 \textit{In C++, a function template is a generic definition of
946 a function that is instantiated differently when called with
947 values of different types. DWARF does not represent the generic
948 template definition, but does represent each instantiation.}
950 A template instantiation is represented by a debugging
951 information entry with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}. With four
952 exceptions, such an entry will contain the same attributes and
953 will have the same types of child entries as would an entry
954 for a subroutine defined explicitly using the instantiation
955 types. The exceptions are:
957 \begin{enumerate}[1.]
958 \item Each formal parameterized type declaration appearing in the
959 template definition is represented by a debugging information
961 tag \livetarg{chap:DWTAGtemplatetypeparameter}{DW\-\_TAG\-\_template\-\_type\-\_parameter}.
963 such entry has a \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute, whose value is a
964 null\dash terminated string containing the name of the formal
965 type parameter as it appears in the source program. The
966 template type parameter entry also has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute
967 describing the actual type by which the formal is replaced
968 for this instantiation.
970 \item The subprogram entry and each of its child entries reference
971 a template type parameter entry in any circumstance where
972 the template definition referenced a formal parameterized type.
974 \item If the compiler has generated a special compilation unit
975 to hold the template instantiation and that compilation unit
976 has a different name from the compilation unit containing
977 the template definition, the name attribute for the debugging
978 information entry representing that compilation unit is empty
981 \item If the subprogram entry representing the template
982 instantiation or any of its child entries contain declaration
983 coordinate attributes, those attributes refer to the source
984 for the template definition, not to any source generated
985 artificially by the compiler for this instantiation.
990 \subsection{Inlinable and Inlined Subroutines}
991 A declaration or a definition of an inlinable subroutine
992 is represented by a debugging information entry with the
994 \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}.
995 The entry for a subroutine that is
996 \hypertarget{chap:DWATinlineinlinedsubroutine}
997 explicitly declared to be available for inline expansion or
998 that was expanded inline implicitly by the compiler has a
999 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is an integer constant. The
1000 set of values for the \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute is given in
1001 Figure \refersec{fig:inlinecodes}.
1003 \begin{figure}[here]
1005 \caption{Inline codes}
1006 \label{fig:inlinecodes}
1007 \begin{tabular}{lp{9cm}}
1008 Name&Meaning\\ \hline
1009 \livetarg{chap:DWINLnotinlined}{DW\-\_INL\-\_not\-\_inlined} & Not delared inline nor inlined by the
1010 compiler(equivalent to the absense of the containing
1011 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute) \\
1012 \livetarg{chap:DWINLinlined}{DW\-\_INL\-\_inlined} & Not declared inline but inlined by the compiler \\
1013 \livetarg{chap:DWINLdeclarednotinlined}{DW\-\_INL\-\_declared\-\_not\-\_inlined} & Declared inline but
1014 not inlined by the compiler \\
1015 \livetarg{chap:DWINLdeclaredinlined}{DW\-\_INL\-\_declared\-\_inlined} & Declared inline and inlined by the compiler \\
1019 \textit{In C++, a function or a constructor declared with
1020 constexpr is implicitly declared inline. The abstract inline
1021 instance (see below) is represented by a debugging information
1022 entry with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}. Such an entry has a
1023 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is \livelink{chap:DWINLinlined}{DW\-\_INL\-\_inlined}.}
1026 \paragraph{Abstract Instances}
1027 \label{chap:abstractinstances}
1028 Any debugging information entry that is owned (either
1029 \hypertarget{chap:DWATinlineabstracttinstance}
1030 directly or indirectly) by a debugging information entry
1032 \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute is referred to
1033 \addtoindexx{abstract instance!entry}
1034 as an ``abstract instance entry.''
1035 Any subroutine entry
1036 that contains a \livelink{chap:DWATinline}{DW\-\_AT\-\_inline} attribute whose value is other
1037 than \livelink{chap:DWINLnotinlined}{DW\-\_INL\-\_not\-\_inlined}
1039 \addtoindexx{abstract instance!root}
1040 an ``abstract instance root.''
1041 Any set of abstract instance entries that are all
1042 children (either directly or indirectly) of some abstract
1043 instance root, together with the root itself, is known as
1044 \addtoindexx{abstract instance!tree}
1045 an ``abstract instance tree.'' However, in the case where
1046 an abstract instance tree is nested within another abstract
1047 instance tree, the entries in the nested abstract instance
1048 tree are not considered to be entries in the outer abstract
1051 Each abstract instance root is either part of a larger
1052 \addtoindexx{abstract instance!root}
1053 tree (which gives a context for the root) or uses
1054 \livelink{chap:DWATspecification}{DW\-\_AT\-\_specification} to refer to the declaration in context.
1056 \textit{For example, in C++ the context might be a namespace
1057 declaration or a class declaration.}
1059 \textit{Abstract instance trees are defined so that no entry is part
1060 of more than one abstract instance tree. This simplifies the
1061 following descriptions.}
1063 A debugging information entry that is a member of an abstract
1064 instance tree should not contain any attributes which describe
1065 aspects of the subroutine which vary between distinct inlined
1066 expansions or distinct out\dash of\dash line expansions. For example,
1067 the \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc},
1068 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc}, \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges},
1069 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc}, \livelink{chap:DWATlocation}{DW\-\_AT\-\_location},
1070 \livelink{chap:DWATreturnaddr}{DW\-\_AT\-\_return\-\_addr}, \livelink{chap:DWATstartscope}{DW\-\_AT\-\_start\-\_scope}, and
1071 \livelink{chap:DWATsegment}{DW\-\_AT\-\_segment}
1072 attributes typically should be omitted; however, this list
1075 \textit{It would not make sense normally to put these attributes into
1076 abstract instance entries since such entries do not represent
1077 actual (concrete) instances and thus do not actually exist at
1078 run\dash time. However,
1079 see Appendix \refersec{app:inlineouteronenormalinner}
1080 for a contrary example.}
1082 The rules for the relative location of entries belonging to
1083 abstract instance trees are exactly the same as for other
1084 similar types of entries that are not abstract. Specifically,
1085 the rule that requires that an entry representing a declaration
1086 be a direct child of the entry representing the scope of the
1087 declaration applies equally to both abstract and non\dash abstract
1088 entries. Also, the ordering rules for formal parameter entries,
1089 member entries, and so on, all apply regardless of whether
1090 or not a given entry is abstract.
1092 \paragraph{Concrete Inlined Instances}
1093 \label{chap:concreteinlinedinstances}
1095 Each inline expansion of a subroutine is represented
1096 by a debugging information entry with the
1097 tag \livetarg{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}.
1098 Each such entry should be a direct
1099 child of the entry that represents the scope within which
1100 the inlining occurs.
1102 Each inlined subroutine entry may have either a
1103 \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc}
1104 and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges}
1105 attribute whose values encode the contiguous or non\dash contiguous
1106 address ranges, respectively, of the machine instructions
1107 generated for the inlined subroutine (see
1108 Section \refersec{chap:codeaddressesandranges}).
1110 \hypertarget{chap:DWATentrypcentryaddressofinlinedsubprogram}
1111 inlined subroutine entry may also contain a
1112 \livelink{chap:DWATentrypc}{DW\-\_AT\-\_entry\-\_pc}
1113 attribute, representing the first executable instruction of
1114 the inline expansion (see
1115 Section \refersec{chap:entryaddress}).
1117 % Positions of the 3 targets here is a bit arbitrary.
1119 \hypertarget{chap:DWATcalllinelinenumberofinlinedsubroutinecall}
1121 \hypertarget{chap:DWATcallcolumncolumnpositionofinlinedsubroutinecall}
1123 \hypertarget{chap:DWATcallfilefilecontaininginlinedsubroutinecall}
1124 may also have \livelink{chap:DWATcallfile}{DW\-\_AT\-\_call\-\_file},
1125 \livelink{chap:DWATcallline}{DW\-\_AT\-\_call\-\_line} and \livelink{chap:DWATcallcolumn}{DW\-\_AT\-\_call\-\_column} attributes,
1127 value is an integer constant. These attributes represent the
1128 source file, source line number, and source column number,
1129 respectively, of the first character of the statement or
1130 expression that caused the inline expansion. The call file,
1131 call line, and call column attributes are interpreted in
1132 the same way as the declaration file, declaration line, and
1133 declaration column attributes, respectively (see
1134 Section \refersec{chap:declarationcoordinates}).
1136 The call file, call line and call column coordinates do not
1137 describe the coordinates of the subroutine declaration that
1138 was inlined, rather they describe the coordinates of the call.
1140 An inlined subroutine entry
1141 \hypertarget{chap:DWATconstexprcompiletimeconstantfunction}
1143 \livelink{chap:DWATconstexpr}{DW\-\_AT\-\_const\-\_expr}
1144 attribute, which is a \livelink{chap:flag}{flag}
1145 whose presence indicates that the
1146 subroutine has been evaluated as a compile\dash time constant. Such
1147 an entry may also have a \livelink{chap:DWATconstvalue}{DW\-\_AT\-\_const\-\_value} attribute,
1148 whose value may be of any form that is appropriate for the
1149 representation of the subroutine's return value. The value of
1150 this attribute is the actual return value of the subroutine,
1151 represented as it would be on the target architecture.
1153 \textit{In C++, if a function or a constructor declared with constexpr
1154 is called with constant expressions, then the corresponding
1155 concrete inlined instance has a \livelink{chap:DWATconstexpr}{DW\-\_AT\-\_const\-\_expr} attribute,
1156 as well as a \livelink{chap:DWATconstvalue}{DW\-\_AT\-\_const\-\_value} attribute whose value represents
1157 the actual return value of the concrete inlined instance.}
1159 Any debugging information entry that is owned (either
1160 directly or indirectly) by a debugging information entry
1161 with the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine} is referred to as a
1162 ``concrete inlined instance entry.'' Any entry that has
1163 the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}
1164 is known as a ``concrete inlined instance root.'' Any set of concrete inlined instance
1165 entries that are all children (either directly or indirectly)
1166 of some concrete inlined instance root, together with the root
1167 itself, is known as a ``concrete inlined instance tree.''
1168 However, in the case where a concrete inlined instance tree
1169 is nested within another concrete instance tree, the entries
1170 in the nested concrete instance tree are not considered to
1171 be entries in the outer concrete instance tree.
1173 \textit{Concrete inlined instance trees are defined so that no entry
1174 is part of more than one concrete inlined instance tree. This
1175 simplifies later descriptions.}
1177 Each concrete inlined instance tree is uniquely associated
1178 with one (and only one) abstract instance tree.
1180 \textit{Note, however, that the reverse is not true. Any given abstract
1181 instance tree may be associated with several different concrete
1182 inlined instance trees, or may even be associated with zero
1183 concrete inlined instance trees.}
1185 Concrete inlined instance entries may omit attributes that
1186 are not specific to the concrete instance (but present in
1187 the abstract instance) and need include only attributes that
1188 are specific to the concrete instance (but omitted in the
1189 abstract instance). In place of these omitted attributes, each
1190 \hypertarget{chap:DWATabstractorigininlineinstance}
1191 concrete inlined instance entry
1192 \addtoindexx{abstract origin attribute}
1194 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin}
1195 attribute that may be used to obtain the missing information
1196 (indirectly) from the associated abstract instance entry. The
1197 value of the abstract origin attribute is a reference to the
1198 associated abstract instance entry.
1200 If an entry within a concrete inlined instance tree contains
1201 attributes describing the declaration coordinates of that
1202 entry, then those attributes should refer to the file, line
1203 and column of the original declaration of the subroutine,
1204 not to the point at which it was inlined. As a consequence,
1205 they may usually be omitted from any entry that has an abstract
1208 For each pair of entries that are associated via a
1209 \addtoindexx{abstract origin attribute}
1210 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attribute, both members of the pair
1211 have the same tag. So, for example, an entry with the tag
1212 \livelink{chap:DWTAGvariable}{DW\-\_TAG\-\_variable} can only be associated with another entry
1213 that also has the tag \livelink{chap:DWTAGvariable}{DW\-\_TAG\-\_variable}. The only exception
1214 to this rule is that the root of a concrete instance tree
1215 (which must always have the tag \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine})
1216 can only be associated with the root of its associated abstract
1217 instance tree (which must have the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram}).
1219 In general, the structure and content of any given concrete
1220 inlined instance tree will be closely analogous to the
1221 structure and content of its associated abstract instance
1222 tree. There are a few exceptions:
1224 \begin{enumerate}[1.]
1225 \item An entry in the concrete instance tree may be omitted if
1227 \addtoindexx{abstract origin attribute}
1228 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attribute and either
1229 has no children, or its children are omitted. Such entries
1230 would provide no useful information. In C\dash like languages,
1231 such entries frequently include types, including structure,
1232 union, class, and interface types; and members of types. If any
1233 entry within a concrete inlined instance tree needs to refer
1234 to an entity declared within the scope of the relevant inlined
1235 subroutine and for which no concrete instance entry exists,
1236 the reference should refer to the abstract instance entry.
1238 \item Entries in the concrete instance tree which are associated
1239 with entries in the abstract instance tree such that neither
1240 has a \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute, and neither is referenced by
1241 any other debugging information entry, may be omitted. This
1242 may happen for debugging information entries in the abstract
1243 instance trees that became unnecessary in the concrete instance
1244 tree because of additional information available there. For
1245 example, an anonymous variable might have been created and
1246 described in the abstract instance tree, but because of
1247 the actual parameters for a particular inlined expansion,
1248 it could be described as a constant value without the need
1249 for that separate debugging information entry.
1251 \item A concrete instance tree may contain entries which do
1252 not correspond to entries in the abstract instance tree
1253 to describe new entities that are specific to a particular
1254 inlined expansion. In that case, they will not have associated
1255 entries in the abstract instance tree, should not contain
1256 \addtoindexx{abstract origin attribute}
1257 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin} attributes, and must contain all their
1258 own attributes directly. This allows an abstract instance tree
1259 to omit debugging information entries for anonymous entities
1260 that are unlikely to be needed in most inlined expansions. In
1261 any expansion which deviates from that expectation, the
1262 entries can be described in its concrete inlined instance tree.
1266 \paragraph{Out-of-Line Instances of Inlined Subroutines}
1267 \label{chap:outoflineinstancesofinlinedsubroutines}
1268 Under some conditions, compilers may need to generate concrete
1269 executable instances of inlined subroutines other than at
1270 points where those subroutines are actually called. Such
1271 concrete instances of inlined subroutines are referred to as
1272 ``concrete out\dash of\dash line instances.''
1274 \textit{In C++, for example, taking the address of a function declared
1275 to be inline can necessitate the generation of a concrete
1276 out\dash of\dash line instance of the given function.}
1278 The DWARF representation of a concrete out\dash of\dash line instance
1279 of an inlined subroutine is essentially the same as for a
1280 concrete inlined instance of that subroutine (as described in
1281 the preceding section). The representation of such a concrete
1282 % It is critical that the hypertarget and livelink be
1283 % separated to avoid problems with latex.
1284 out\dash of\dash line
1285 \addtoindexx{abstract origin attribute}
1287 \hypertarget{chap:DWATabstractoriginoutoflineinstance}
1289 \livelink{chap:DWATabstractorigin}{DW\-\_AT\-\_abstract\-\_origin}
1290 attributes in exactly the same way as they are used for
1291 a concrete inlined instance (that is, as references to
1292 corresponding entries within the associated abstract instance
1295 The differences between the DWARF representation of a
1296 concrete out\dash of\dash line instance of a given subroutine and the
1297 representation of a concrete inlined instance of that same
1298 subroutine are as follows:
1300 \begin{enumerate}[1.]
1301 \item The root entry for a concrete out\dash of\dash line instance
1302 of a given inlined subroutine has the same tag as does its
1303 associated (abstract) inlined subroutine entry (that is, tag
1304 \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} rather than \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}).
1306 \item The root entry for a concrete out\dash of\dash line instance tree
1307 is normally owned by the same parent entry that also owns
1308 the root entry of the associated abstract instance. However,
1309 it is not required that the abstract and out\dash of\dash line instance
1310 trees be owned by the same parent entry.
1314 \paragraph{Nested Inlined Subroutines}
1315 \label{nestedinlinedsubroutines}
1316 Some languages and compilers may permit the logical nesting of
1317 a subroutine within another subroutine, and may permit either
1318 the outer or the nested subroutine, or both, to be inlined.
1320 For a non\dash inlined subroutine nested within an inlined
1321 subroutine, the nested subroutine is described normally in
1322 both the abstract and concrete inlined instance trees for
1323 the outer subroutine. All rules pertaining to the abstract
1324 and concrete instance trees for the outer subroutine apply
1325 also to the abstract and concrete instance entries for the
1328 For an inlined subroutine nested within another inlined
1329 subroutine, the following rules apply to their abstract and
1330 \addtoindexx{abstract instance!nested}
1331 \addtoindexx{concrete instance!nested}
1332 concrete instance trees:
1334 \begin{enumerate}[1.]
1335 \item The abstract instance tree for the nested subroutine is
1336 described within the abstract instance tree for the outer
1337 subroutine according to the rules in
1338 Section \refersec{chap:abstractinstances}, and
1339 without regard to the fact that it is within an outer abstract
1342 \item Any abstract instance tree for a nested subroutine is
1343 always omitted within the concrete instance tree for an
1346 \item A concrete instance tree for a nested subroutine is
1347 always omitted within the abstract instance tree for an
1350 \item The concrete instance tree for any inlined or out-of-line
1351 expansion of the nested subroutine is described within a
1352 concrete instance tree for the outer subroutine according
1354 Sections \refersec{chap:concreteinlinedinstances} or
1355 \refersec{chap:outoflineinstancesofinlinedsubroutines}
1357 and without regard to the fact that it is within an outer
1358 concrete instance tree.
1361 See Appendix \refersec{app:inliningexamples}
1362 for discussion and examples.
1364 \subsection{Trampolines}
1365 \label{chap:trampolines}
1367 \textit{A trampoline is a compiler\dash generated subroutine that serves as
1368 \hypertarget{chap:DWATtrampolinetargetsubroutine}
1369 an intermediary in making a call to another subroutine. It may
1370 adjust parameters and/or the result (if any) as appropriate
1371 to the combined calling and called execution contexts.}
1373 A trampoline is represented by a debugging information entry
1374 with the tag \livelink{chap:DWTAGsubprogram}{DW\-\_TAG\-\_subprogram} or \livelink{chap:DWTAGinlinedsubroutine}{DW\-\_TAG\-\_inlined\-\_subroutine}
1375 that has a \livelink{chap:DWATtrampoline}{DW\-\_AT\-\_trampoline} attribute. The value of that
1376 attribute indicates the target subroutine of the trampoline,
1377 that is, the subroutine to which the trampoline passes
1378 control. (A trampoline entry may but need not also have a
1379 \livelink{chap:DWATartificial}{DW\-\_AT\-\_artificial} attribute.)
1381 The value of the trampoline attribute may be represented
1382 using any of the following forms, which are listed in order
1386 \item If the value is of class reference, then the value
1387 specifies the debugging information entry of the target
1390 \item If the value is of class address, then the value is
1391 the relocated address of the target subprogram.
1393 \item If the value is of class string, then the value is the
1394 (possibly mangled) name of the target subprogram.
1396 \item If the value is of class \livelink{chap:flag}{flag}, then the value true
1397 indicates that the containing subroutine is a trampoline but
1398 that the target subroutine is not known.
1402 The target subprogram may itself be a trampoline. (A sequence
1403 of trampolines necessarily ends with a non\dash trampoline
1406 \textit{In C++, trampolines may be used to implement derived virtual
1407 member functions; such trampolines typically adjust the
1408 implicit this pointer parameter in the course of passing
1409 control. Other languages and environments may use trampolines
1410 in a manner sometimes known as transfer functions or transfer
1413 \textit{Trampolines may sometimes pass control to the target
1414 subprogram using a branch or jump instruction instead of a
1415 call instruction, thereby leaving no trace of their existence
1416 in the subsequent execution context. }
1418 \textit{This attribute helps make it feasible for a debugger to arrange
1419 that stepping into a trampoline or setting a breakpoint in
1420 a trampoline will result in stepping into or setting the
1421 breakpoint in the target subroutine instead. This helps to
1422 hide the compiler generated subprogram from the user. }
1424 \textit{If the target subroutine is not known, a debugger may choose
1425 to repeatedly step until control arrives in a new subroutine
1426 which can be assumed to be the target subroutine. }
1430 \section{Lexical Block Entries}
1431 \label{chap:lexicalblockentries}
1433 \textit{A lexical \livetargi{chap:lexicalblock}{block}{lexical block} is a bracketed sequence of source statements
1434 that may contain any number of declarations. In some languages
1435 (including C and C++), \nolink{blocks} can be nested within other
1436 \nolink{blocks} to any depth.}
1438 % We do not need to link to the preceeding paragraph.
1439 A lexical \nolink{block} is represented by a debugging information
1441 tag \livetarg{chap:DWTAGlexicalblock}{DW\-\_TAG\-\_lexical\-\_block}.
1443 The lexical \livetargi{chap:lexicalblockentry}{block}{lexical block entry} entry
1445 either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
1446 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of
1447 attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
1448 whose values encode the contiguous or non-contiguous address
1449 ranges, respectively, of the machine instructions generated
1450 for the lexical \livelink{chap:lexicalblock}{block}
1451 (see Section \refersec{chap:codeaddressesandranges}).
1453 If a name has been given to the
1454 lexical \livelink{chap:lexicalblock}{block}
1456 program, then the corresponding
1457 lexical \livelink{chap:lexicalblockentry}{block} entry has a
1458 \livelink{chap:DWATname}{DW\-\_AT\-\_name} attribute whose
1459 value is a null\dash terminated string
1460 containing the name of the lexical \livelink{chap:lexicalblock}{block}
1464 \textit{This is not the same as a C or C++ label (see below).}
1466 The lexical \livelink{chap:lexicalblockentry}{block} entry owns
1467 debugging information entries that
1468 describe the declarations within that lexical \livelink{chap:lexicalblock}{block}.
1470 one such debugging information entry for each local declaration
1471 of an identifier or inner lexical \livelink{chap:lexicalblock}{block}.
1473 \section{Label Entries}
1474 \label{chap:labelentries}
1476 A label is a way of identifying a source statement. A labeled
1477 statement is usually the target of one or more ``go to''
1480 A label is represented by a debugging information entry with
1482 tag \livetarg{chap:DWTAGlabel}{DW\-\_TAG\-\_label}.
1483 The entry for a label should be owned by
1484 the debugging information entry representing the scope within
1485 which the name of the label could be legally referenced within
1488 The label entry has a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} attribute whose value
1489 is the relocated address of the first machine instruction
1490 generated for the statement identified by the label in
1491 the source program. The label entry also has a \livelink{chap:DWATname}{DW\-\_AT\-\_name}
1492 attribute whose value is a null-terminated string containing
1493 the name of the label as it appears in the source program.
1496 \section{With Statement Entries}
1497 \label{chap:withstatemententries}
1499 \textit{Both Pascal and Modula\dash 2 support the concept of a ``with''
1500 statement. The with statement specifies a sequence of
1501 executable statements within which the fields of a record
1502 variable may be referenced, unqualified by the name of the
1505 A with statement is represented by a debugging information
1506 entry with the tag \livetarg{chap:DWTAGwithstmt}{DW\-\_TAG\-\_with\-\_stmt}.
1508 A with statement entry may have either a \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and
1509 \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute
1510 whose values encode the contiguous or non\dash contiguous address
1511 ranges, respectively, of the machine instructions generated
1512 for the with statement
1513 (see Section \refersec{chap:codeaddressesandranges}).
1515 The with statement entry has a \livelink{chap:DWATtype}{DW\-\_AT\-\_type} attribute, denoting
1516 the type of record whose fields may be referenced without full
1517 qualification within the body of the statement. It also has
1518 a \livelink{chap:DWATlocation}{DW\-\_AT\-\_location} attribute, describing how to find the base
1519 address of the record object referenced within the body of
1522 \section{Try and Catch Block Entries}
1523 \label{chap:tryandcatchblockentries}
1525 \textit{In C++ a lexical \livelink{chap:lexicalblock}{block} may be
1526 designated as a ``catch \nolink{block}.''
1527 A catch \livetargi{chap:catchblock}{block}{catch block} is an
1528 exception handler that handles
1529 exceptions thrown by an immediately
1530 preceding ``try \livelink{chap:tryblock}{block}.''
1531 A catch \livelink{chap:catchblock}{block}
1532 designates the type of the exception that it
1535 A try \livetargi{chap:tryblock}{block}{try block} is represented
1536 by a debugging information entry
1537 with the tag \livetarg{chap:DWTAGtryblock}{DW\-\_TAG\-\_try\-\_block}.
1538 A catch \livelink{chap:catchblock}{block} is represented by
1539 a debugging information entry with
1540 the tag \livetarg{chap:DWTAGcatchblock}{DW\-\_TAG\-\_catch\-\_block}.
1542 % nolink as we have links just above and do not have a combo link for both
1543 Both try and catch \nolink{block} entries may have either a
1544 \livelink{chap:DWATlowpc}{DW\-\_AT\-\_low\-\_pc} and \livelink{chap:DWAThighpc}{DW\-\_AT\-\_high\-\_pc} pair of attributes or a
1545 \livelink{chap:DWATranges}{DW\-\_AT\-\_ranges} attribute whose values encode the contiguous
1546 or non\dash contiguous address ranges, respectively, of the
1547 machine instructions generated for the \livelink{chap:lexicalblock}{block}
1549 \refersec{chap:codeaddressesandranges}).
1551 Catch \livelink{chap:catchblock}{block} entries have at
1552 least one child entry, an
1553 entry representing the type of exception accepted by
1554 that catch \livelink{chap:catchblock}{block}.
1556 This child entry has one of the
1557 \addtoindexx{unspecified parameters entry!in catch block}
1559 \livelink{chap:DWTAGformalparameter}{DW\-\_TAG\-\_formal\-\_parameter} or \livelink{chap:DWTAGunspecifiedparameters}{DW\-\_TAG\-\_unspecified\-\_parameters},
1560 and will have the same form as other parameter entries.
1562 The siblings immediately following
1563 a try \livelink{chap:tryblock}{block} entry are its
1564 corresponding catch \livelink{chap:catchblock}{block} entries.