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:typeunitentries}),
7 these entries may be thought of as
8 ranges of text addresses within the program.
10 \section{Unit Entries}
11 \label{chap:unitentries}
12 A DWARF object file is an object file that contains one or more
13 DWARF compilation units, of which there are these kinds:
14 \addtoindexx{unit|see {compilation unit}}
15 \addtoindexx{compilation unit}
17 \item A \definition{full compilation unit} describes
18 a complete compilation, possibly in combination with
19 related partial compilation units and/or type units.
21 \item A \definition{partial compilation unit} describes
22 a part of a compilation (generally corresponding to an
23 imported module) which is imported into one or more
24 related full compilation units.
26 \item A \definition{type unit} is a specialized unit
27 (similar to a compilation unit) that represents a type
28 whose description may be usefully shared by multiple
32 \index{conventional compilation unit|see{
33 full compilation unit, partial compilation unit, type unit}}
35 \textit{These first three kinds of compilation unit are
36 sometimes called \doublequote{conventional} compilation
37 units--they are kinds of compilation units that were
38 defined prior to \DWARFVersionV. Conventional compilation units
39 are part of the same object file as the compiled code and
40 data (whether relocatable, executable, shared and so on).
41 The word \doublequote{conventional} is usually
42 omitted in these names, unless needed to distinguish them
43 from the similar split compilation units below.}
47 \item A \definition{skeleton compilation unit} represents
48 the DWARF debugging information for a compilation using a
49 minimal description that identifies a separate split
50 compilation unit that provides the remainder (and most)
54 \textit{A skeleton compilation acts as a minimal conventional full
55 compilation (see above) that identifies and is paired with a
56 corresponding split full compilation (as described below). Like
57 the conventional compilation units, a skeleton compilation unit
58 is part of the same object file as the compiled code and data.}
62 \definition{split compilation unit} describes
63 a complete compilation, possibly in combination with
64 related type compilation units. It corresponds
65 to a specific skeleton compilation unit.
67 \item A \definition{split type unit} is a specialized
68 compilation unit that represents a type whose description may
69 be usefully shared by multiple other units.
73 \textit{Split compilation units and split type units may be
74 contained in object files separate from those containing the
75 program code and data.
76 These object files are not processed by a linker; thus,
77 split units do not depend on underlying object file relocations.}
79 \textit{Either a full compilation unit or a partial compilation
80 unit may be logically incorporated into another compilation unit
81 using an \addtoindex{imported unit entry}
82 (see Section \refersec{chap:importedunitentries}).}
85 combined split and partial
86 compilation unit kind is not defined.}
88 \textit{In the remainder of this document, the word
89 \doublequote{compilation} in the phrase \doublequote{compilation unit}
90 is generally omitted, unless it is deemed needed for clarity
93 \subsection{Full and Partial Compilation Unit Entries}
94 \label{chap:fullandpartialcompilationunitentries}
95 A \addtoindex{full compilation unit}\addtoindexx{compilation unit!full}
96 is represented by a debugging information entry with the tag
97 \DWTAGcompileunitTARG.
98 A \addtoindex{partial compilation unit}\addtoindexx{compilation unit!partial}
99 is represented by a debugging information entry with the tag
100 \DWTAGpartialunitTARG.
103 In a simple compilation, a single compilation unit with
105 \DWTAGcompileunit{} represents a complete object file
107 \DWTAGpartialunit{} (as well as tag \DWTAGtypeunit) is not used.
109 employing the DWARF space compression and duplicate elimination
111 Appendix \refersec{app:usingcompilationunits},
112 multiple compilation units using
115 \DWTAGpartialunit{} and/or
117 are used to represent portions of an object file.
120 \textit{A full compilation unit typically represents the text and
121 data contributed to an executable by a single relocatable
122 object file. It may be derived from several source files,
123 including pre-processed header files.
124 A \addtoindex{partial compilation unit} typically represents a part
125 of the text and data of a relocatable object file, in a manner that
126 can potentially be shared with the results of other compilations
127 to save space. It may be derived from an \doublequote{include file,}
128 template instantiation, or other implementation-dependent
129 portion of a compilation. A full compilation unit can also
130 function in a manner similar to a partial compilation unit
132 See Appendix \refersec{app:dwarfcompressionandduplicateeliminationinformative}
133 for discussion of related compression techniques.}
135 A compilation unit entry owns debugging information
136 entries that represent all or part of the declarations
137 made in the corresponding compilation. In the case of a
138 partial compilation unit, the containing scope of its owned
139 declarations is indicated by imported unit entries in one
140 or more other compilation unit entries that refer to that
141 partial compilation unit (see
142 Section \refersec{chap:importedunitentries}).
144 Compilation unit entries may have the following
146 \begin{enumerate}[1. ]
147 \item Either a \DWATlowpc{} and
148 \DWAThighpc{} pair of
149 \addtoindexx{high PC attribute}
151 \addtoindexx{low PC attribute}
153 \addtoindexx{ranges attribute}
155 \DWATranges{} attribute
156 \addtoindexx{ranges attribute}
158 \addtoindexx{discontiguous address ranges|see{non-contiguous address ranges}}
160 non-contiguous address ranges, respectively,
161 of the machine instructions generated for the compilation
162 unit (see Section \refersec{chap:codeaddressesandranges}).
164 A \DWATlowpc{} attribute
165 may also be specified in combination
166 \addtoindexx{ranges attribute}
168 \DWATranges{} to specify the
169 \addtoindexx{ranges attribute}
170 default base address for use in
171 \addtoindexx{location list}
172 location lists (see Section
173 \refersec{chap:locationlists}) and range lists
174 \addtoindexx{range list}
175 (see Section \refersec{chap:noncontiguousaddressranges}).
177 \item \hypertarget{chap:DWATnamepathnameofcompilationsource}{}
178 A \DWATnameDEFN{} attribute \addtoindexx{name attribute}
179 whose value is a null-terminated string
180 containing the full or relative path name
181 (relative to the value of the \DWATcompdir{} attribute,
182 see below) of the primary
183 source file from which the compilation unit was derived.
185 \item \hypertarget{chap:DWATlanguageprogramminglanguage}{}
186 A \DWATlanguageDEFN{} attribute\addtoindexx{language attribute}
187 whose constant value is an integer code
188 indicating the source language of the compilation
189 unit. The set of language names and their meanings are given
190 in Table \refersec{tab:languagenames}.
193 \setlength{\extrarowheight}{0.1cm}
194 \begin{longtable}{l|l}
195 \caption{Language names} \label{tab:languagenames} \\
196 \hline \bfseries Language name & \bfseries Meaning \\ \hline
198 \bfseries Language name & \bfseries Meaning \\ \hline
200 \hline \emph{Continued on next page}
203 \addtoindexx{ISO-defined language names}
204 \DWLANGAdaeightythreeTARG{} \dag & ISO Ada:1983 \addtoindexx{Ada:1983 (ISO)} \\
205 \DWLANGAdaninetyfiveTARG{} \dag & ISO Ada:1995 \addtoindexx{Ada:1995 (ISO)} \\
206 \DWLANGCTARG & Non-standardized C, such as K\&R \addtoindexx{C!non-standard} \\*
207 \DWLANGCeightynineTARG & ISO C:1989 \addtoindexx{C:1989 (ISO)} \\*
208 \DWLANGCninetynineTARG & ISO C:1999 \addtoindexx{C:1999 (ISO)} \\*
209 \DWLANGCelevenTARG & ISO C:2011 \addtoindexx{C:2011 (ISO)} \\*
210 \DWLANGCplusplusTARG & ISO C++98 \addtoindexx{C++98 (ISO)} \\
211 \DWLANGCpluspluszerothreeTARG & ISO C++03 \addtoindexx{C++03 (ISO)} \\
212 \DWLANGCpluspluselevenTARG & ISO C++11 \addtoindexx{C++11 (ISO)} \\
213 \DWLANGCplusplusfourteenTARG & ISO C++14 \addtoindexx{C++14 (ISO)}
215 \DWLANGCobolseventyfourTARG & ISO COBOL:1974 \addtoindexx{COBOL:1974 (ISO)} \\
216 \DWLANGCoboleightyfiveTARG & ISO COBOL:1985 \addtoindexx{COBOL:1985 (ISO)} \\
217 \DWLANGDTARG{}~\dag & D \addtoindexx{D language} \\
218 \DWLANGDylanTARG~\dag & Dylan \addtoindexx{Dylan} \\
219 \DWLANGFortranseventysevenTARG & ISO FORTRAN:1977 \addtoindexx{FORTRAN:1977 (ISO)} \\
220 \DWLANGFortranninetyTARG & ISO Fortran:1990 \addtoindexx{Fortran:1990 (ISO)} \\
221 \DWLANGFortranninetyfiveTARG & ISO Fortran:1995 \addtoindexx{Fortran:1995 (ISO)} \\
222 \DWLANGFortranzerothreeTARG & ISO Fortran:2004 \addtoindexx{Fortran:2004 (ISO)} \\
223 \DWLANGFortranzeroeightTARG & ISO Fortran:2010 \addtoindexx{Fortran:2010 (ISO)} \\
224 \DWLANGGoTARG{}~\dag & \addtoindex{Go} \\
225 \DWLANGHaskellTARG{} \dag & \addtoindex{Haskell} \\
226 \DWLANGJavaTARG{} & \addtoindex{Java}\\
227 \DWLANGJuliaTARG{}~\dag & \addtoindex{Julia} \\
228 \DWLANGModulatwoTARG & ISO Modula\dash 2:1996 \addtoindexx{Modula-2:1996 (ISO)} \\
229 \DWLANGModulathreeTARG & \addtoindex{Modula-3} \\
230 \DWLANGObjCTARG{} & \addtoindex{Objective C} \\
231 \DWLANGObjCplusplusTARG{} & \addtoindex{Objective C++} \\
232 \DWLANGOCamlTARG{}~\dag & \addtoindex{OCaml}\index{Objective Caml|see{OCaml}} \\
233 \DWLANGOpenCLTARG{}~\dag & \addtoindex{OpenCL} \\
234 \DWLANGPascaleightythreeTARG & ISO Pascal:1983 \addtoindexx{Pascal:1983 (ISO)} \\
235 \DWLANGPLITARG{}~\dag & ANSI PL/I:1976 \addtoindexx{PL/I:1976 (ANSI)} \\
236 \DWLANGPythonTARG{}~\dag & \addtoindex{Python} \\
237 \DWLANGRenderScriptTARG~\dag & \addtoindex{RenderScript Kernal Language}
239 \DWLANGRustTARG{}~\dag & \addtoindex{Rust} \\
241 & \addtoindex{Swift} \\
242 \DWLANGUPCTARG{} & UPC (Unified Parallel C) \addtoindexx{UPC}
243 \index{Unified Parallel C|see{UPC}} \\
245 \dag \ \ \textit{Support for these languages is limited}& \\
250 \item \hypertarget{chap:DWATstmtlistlinenumberinformationforunit}{}
251 A \DWATstmtlistDEFN{}\addtoindexx{statement list attribute}
252 attribute whose value is a
253 \addtoindexx{section offset!in statement list attribute}
254 section offset to the line number information for this compilation
257 This information is placed in a separate object file
258 section from the debugging information entries themselves. The
259 value of the statement list attribute is the offset in the
260 \dotdebugline{} section of the first byte of the line number
261 information for this compilation unit
262 (see Section \refersec{chap:linenumberinformation}).
264 \item A \DWATmacrosDEFN{}\hypertarget{chap:DWATmacrosmacroinformation}{}
266 \addtoindexx{macro information attribute}
268 \addtoindexx{section offset!in macro information attribute}
269 section offset to the macro information for this compilation unit.
271 This information is placed in a separate object file section
272 from the debugging information entries themselves. The
273 value of the macro information attribute is the offset in
274 the \dotdebugmacro{} section of the first byte of the macro
275 information for this compilation unit
276 (see Section \refersec{chap:macroinformation}).
278 \textit{The \DWATmacrosNAME{} attribute is new in \DWARFVersionV,
280 \DWATmacroinfoDEFN{} attribute of earlier DWARF versions.
281 \livetarg{chap:DWATmacroinfomacroinformation}{}
282 While \DWATmacrosNAME{} and \DWATmacroinfoNAME{} attributes cannot both occur in the same
283 compilation unit, both may be found in the set of units that make up an executable
284 or shared object file. The two attributes have distinct encodings to facilitate such
288 \item \hypertarget{chap:DWATcompdircompilationdirectory}{}
289 A \DWATcompdirDEFN{} attribute\addtoindexx{compilation directory attribute}
291 null-terminated string containing the current working directory
292 of the compilation command that produced this compilation
293 unit in whatever form makes sense for the host system.
295 \item \hypertarget{chap:DWATproducercompileridentification}{}
296 A \DWATproducerDEFN{} attribute\addtoindexx{producer attribute}
297 whose value is a null-terminated string containing
298 information about the compiler that produced the compilation unit.
300 \textit{The actual contents of
301 the string will be specific to each producer, but should
302 begin with the name of the compiler vendor or some other
303 identifying character sequence that will avoid confusion
304 with other producer values.}
307 \item \hypertarget{chap:DWATidentifiercaseidentifiercaserule}{}
308 A \DWATidentifiercaseDEFN{} attribute
309 \addtoindexx{identifier case attribute} whose integer
310 constant value is a code describing the treatment
311 of identifiers within this compilation unit. The
312 set of identifier case codes is given in
313 Table \refersec{tab:identifiercasecodes}.
315 \begin{simplenametable}{Identifier case codes}{tab:identifiercasecodes}
316 \DWIDcasesensitive{} \\
319 \DWIDcaseinsensitive{} \\
320 \end{simplenametable}
322 \DWIDcasesensitiveTARG{} is the default for all compilation units
323 that do not have this attribute. It indicates that names given
324 as the values of \DWATname{} attributes
325 \addtoindexx{name attribute}
326 in debugging information
327 entries for the compilation unit reflect the names as they
328 appear in the source program.
330 \textit{A debugger should be sensitive
331 to the case of \addtoindex{identifier names} when doing identifier
335 \DWIDupcaseTARG{} means that the
336 producer of the debugging
337 information for this compilation unit converted all source
338 names to upper case. The values of the name attributes may not
339 reflect the names as they appear in the source program.
341 \textit{A debugger should convert all names to upper case
344 \DWIDdowncaseTARG{} means that the producer of the debugging
345 information for this compilation unit converted all source
346 names to lower case. The values of the name attributes may not
347 reflect the names as they appear in the source program.
349 \textit{A debugger should convert all names to lower case
353 \DWIDcaseinsensitiveTARG{} means that the values of the name
354 attributes reflect the names as they appear in the source
355 program but that case is not significant.
357 \textit{A debugger should ignore case when doing lookups.}
360 \item \hypertarget{chap:DWATbasetypesprimitivedatatypesofcompilationunit}{}
361 A \DWATbasetypesDEFN{} attribute\addtoindexx{base types attribute}
362 whose value is a \livelink{chap:classreference}{reference}.
363 This attribute points to a debugging information entry
364 representing another compilation unit. It may be used
365 to specify the compilation unit containing the base type
366 entries used by entries in the current compilation unit
367 (see Section \refersec{chap:basetypeentries}).
370 \textit{This attribute provides a consumer a way to find the definition
371 of base types for a compilation unit that does not itself
372 contain such definitions. This allows a consumer, for example,
373 to interpret a type conversion to a base type correctly.}
375 \item \hypertarget{chap:DWATuseUTF8compilationunitusesutf8strings}{}
376 A \DWATuseUTFeightDEFN{} attribute,
377 \addtoindexx{use UTF8 attribute}\addtoindexx{UTF-8}
378 which is a \livelink{chap:classflag}{flag} whose
379 presence indicates that all strings (such as the names of
380 declared entities in the source program, or filenames in the line number table)
381 are represented using the UTF-8 representation.
385 \hypertarget{chap:DWATmainsubprogramunitcontainingmainorstartingsubprogram}{}
386 A \DWATmainsubprogramDEFN{} attribute,\addtoindexx{main subprogram attribute}
387 which is a \livelink{chap:classflag}{flag},
388 whose presence indicates that the compilation unit contains a
389 subprogram that has been identified as the starting
390 subprogram of the program. If more than one compilation unit contains
391 this \nolink{flag}, any one of them may contain the starting
394 \textit{\addtoindex{Fortran} has a \addtoindex{PROGRAM statement}
396 to specify and provide a user-specified name for the main
397 subroutine of a program.
398 \addtoindex{C} uses the name \doublequote{main} to identify
399 the main subprogram of a program. Some other languages provide
400 similar or other means to identify the main subprogram of
401 a program. The \DWATmainsubprogram{} attribute may also be used to
402 identify such subprograms (see
403 Section \refersec{chap:generalsubroutineandentrypointinformation}).}
406 \hypertarget{chap:DWATentrypcofcompileunit}{}
407 \hypertarget{chap:DWATentrypcofpartialunit}{}
408 A \DWATentrypc{} attribute whose value is the address of the first
409 \addtoindexx{entry pc attribute}
410 executable instruction of the unit (see
411 Section \refersec{chap:entryaddress}).
414 \item \hypertarget{chap:DWATstroffsetbaseforindirectstringtable}{}
415 A \DWATstroffsetsbaseDEFN\addtoindexx{string offset base attribute}
416 attribute, whose value is of class \CLASSstroffsetsptr.
417 This attribute points to the first string
418 offset of the compilation unit's contribution to the
419 \dotdebugstroffsets{} (or \dotdebugstroffsetsdwo{}) section.
420 Indirect string references
421 (using \DWFORMstrx) within the compilation unit are
422 interpreted as indices relative to this base.
425 \item \hypertarget{chap:DWATaddrbaseforaddresstable}{}
426 A \DWATaddrbaseDEFN\addtoindexx{address table base attribute}
427 attribute, whose value is of class \CLASSaddrptr.
428 This attribute points to the beginning of the compilation
429 unit's contribution to the \dotdebugaddr{} section.
430 Indirect references (using \DWFORMaddrx, \DWOPaddrx,
431 \DWOPconstx, \DWLLEbaseaddressx{},
432 \DWLLEstartxendx{} or \DWLLEstartxlength)
433 within the compilation unit are interpreted as indices
434 relative to this base.
437 \item \hypertarget{chap:DWATrnglistsbaseforrnglists}{}
438 A \DWATrnglistsbaseDEFN\addtoindexx{ranges table base attribute}
439 attribute, whose value is of class \CLASSrnglistsptr.
440 This attribute points to the base of the compilation
441 unit's contribution to the \dotdebugrnglists{} section.
442 References to range lists (using \DWFORMrnglistx)
443 within the compilation unit are
444 interpreted relative to this base.
446 \item \hypertarget{chap:DWATloclistsbaseinlocationlist}{}
447 A \DWATloclistsbase{}\addtoindexx{location table base attribute}
448 attribute, whose value is of class \CLASSloclistsptr.
449 This attribute points to the base of the compilation
450 unit's contribution to the \dotdebugloclists{} section. References
451 to location lists (using \DWFORMloclistx) within the compilation
452 unit are interpreted relative to this base.
455 The base address of a compilation unit is defined as the
456 value of the \DWATlowpc{} attribute, if present; otherwise,
457 it is undefined. If the base address is undefined, then any
458 DWARF entry or structure defined in terms of the base address
459 of that compilation unit is not valid.
462 \subsection{Skeleton Compilation Unit Entries}
463 \label{chap:skeletoncompilationunitentries}
464 \addtoindexx{compilation unit!skeleton}
465 \addtoindexx{skeleton compilation unit}
466 When generating a \splitDWARFobjectfile{} (see
467 Section \refersec{datarep:splitdwarfobjectfiles}), the
468 compilation unit in the \dotdebuginfo{} section is a "skeleton"
469 compilation unit with the tag
470 \DWTAGskeletonunitTARG, which contains a
471 \DWATdwoname{} attribute as well as a subset of the
472 attributes of a full or partial compilation unit. In general,
473 it contains those attributes that are necessary for the consumer
474 to locate the object file where the split full compilation unit
475 can be found, and for the consumer to interpret references to
476 addresses in the program.
479 A skeleton compilation unit has no children.
481 A skeleton compilation unit has a \DWATdwoname{} attribute:
483 \begin{enumerate}[1. ]
485 \item \livetarg{chap:DWATdwonameforunit}{}
486 A \DWATdwonameDEFN{} attribute
487 \addtoindexx{split DWARF object file name attribute}
489 null-terminated string containing the full or relative
490 path name (relative to the value of the \DWATcompdir{} attribute,
491 see below) of the object file that contains the full
494 The value in the \HFNdwoid{} field of the unit header for
495 this unit is the same as the value in the \HFNdwoid{} field
496 of the unit header of the corresponding full compilation
497 unit (see Section \refersec{datarep:unitheaders}).
499 \textit{The means of determining a compilation unit ID does
500 not need to be similar or related to the means of
501 determining a \TUsignature. However, it should
502 be suitable for detecting file version skew or other
503 kinds of mismatched files and for looking up a full
504 split unit in a DWARF package file
505 (see Section \refersec{datarep:dwarfpackagefiles}).}
509 A skeleton compilation unit may have additional attributes,
510 which are the same as for conventional compilation unit entries
511 except as noted, from among the following:
512 \begin{enumerate}[1. ]
513 \addtocounter{enumi}{1}
514 \item Either a \DWATlowpc{} and \DWAThighpc{} pair of attributes
515 or a \DWATranges{} attribute.
516 \item A \DWATstmtlist{} attribute.
517 \item A \DWATcompdir{} attribute.
520 \item A \DWATuseUTFeight{} attribute.
522 \textit{This attribute applies to strings referred to by the skeleton
523 compilation unit entry itself, and strings in the associated line
525 The representation for strings in the object file referenced
526 by the \DWATdwoname{} attribute is determined by the presence
527 of a \DWATuseUTFeight{} attribute in the full compilation unit
528 (see Section \refersec{chap:splitfullcompilationunitentries}).}
530 \item A \DWATstroffsetsbase{} attribute, for indirect strings references
531 from the skeleton compilation unit.
532 \item A \DWATaddrbase{} attribute.
536 All other attributes of a compilation unit entry (described
537 in Section \refersec{chap:fullandpartialcompilationunitentries})
538 are placed in the split full compilation unit
539 (see \refersec{chap:splitfullcompilationunitentries}).
540 The attributes provided by the skeleton compilation
541 unit entry do not need to be repeated in the full compilation
544 \textit{The \DWATaddrbase{}
545 and \DWATstroffsetsbase{} attributes provide context that may be
546 necessary to interpret the contents
547 of the corresponding \splitDWARFobjectfile.}
549 \textit{The \DWATbasetypes{} attribute is not defined for a
550 skeleton compilation unit.}
553 \subsection{Split Full Compilation Unit Entries}
554 \label{chap:splitfullcompilationunitentries}
555 A \definition{split full compilation unit} is represented by a
556 debugging information entry with tag \DWTAGcompileunit.
557 It is very similar to a conventional full compilation unit but
558 is logically paired with a specific skeleton compilation unit while
559 being physically separate.
561 A split full compilation unit
562 may have the following attributes,
563 which are the same as for conventional compilation unit entries
565 \begin{enumerate}[1. ]
566 \item A \DWATname{} attribute.
567 \item A \DWATlanguage{} attribute.
568 \item A \DWATmacros{} attribute.
569 The value of this attribute is of class \CLASSmacptr{}, which is
570 an offset relative to the \dotdebugmacrodwo{} section.
572 \item A \DWATproducer{} attribute.
573 \item A \DWATidentifiercase{} attribute.
574 \item A \DWATmainsubprogram{} attribute.
575 \item A \DWATentrypc{} attribute.
576 \item A \DWATuseUTFeight{} attribute.
580 \textit{The following attributes are not part of a
581 split full compilation unit entry but instead are inherited
582 (if present) from the corresponding skeleton compilation unit:
583 \DWATlowpc, \DWAThighpc, \DWATranges, \DWATstmtlist, \DWATcompdir,
584 \DWATstroffsetsbase, \DWATaddrbase{} and
587 \textit{The \DWATbasetypes{} attribute is not defined for a
588 split full compilation unit.}
592 \subsection{Type Unit Entries}
593 \label{chap:typeunitentries}
594 \addtoindexx{type unit}
595 \addtoindexx{type unit|see{\textit{also} compilation unit}}
596 \addtoindexx{compilation unit!\textit{see also} type unit}
597 An object file may contain any number of separate type
598 unit entries, each representing a single complete type
600 Each \addtoindex{type unit} must be uniquely identified by
601 an 8-byte signature, stored as part of the type unit, which
602 can be used to reference the type definition from debugging
603 information entries in other compilation units and type units.
605 Conventional and split type units are identical except for
606 the sections in which they are represented
607 (see \refersec{datarep:splitdwarfobjectfiles} for details).
608 \addtoindexx{conventional type unit}
609 \addtoindexx{split type unit}
610 Moreover, the \DWATstroffsetsbase{} attribute (see below) is not
611 used in a split type unit.
613 A type unit is represented by a debugging information entry
614 with the tag \DWTAGtypeunitTARG.
615 A \addtoindex{type unit entry} owns debugging
616 information entries that represent the definition of a single
617 type, plus additional debugging information entries that may
618 be necessary to include as part of the definition of the type.
621 A type unit entry may have the following attributes:
622 \begin{enumerate}[1. ]
625 \DWATlanguage{} attribute,
627 \addtoindexx{language attribute}
628 constant value is an integer code indicating the source
629 language used to define the type. The set of language names
630 and their meanings are given in Table \refersec{tab:languagenames}.
633 \item A \DWATstmtlist{} attribute\addtoindexx{statement list attribute}
634 whose value of class \CLASSlineptr{} points to the line number
635 information for this type unit.
637 \textit{Because type units do not describe any code, they
638 do not actually need a line number table, but the line number
639 headers contain a list of directories and file names that
640 may be referenced by the \DWATdeclfile{} attribute of the
641 type or part of its description.}
643 \textit{In an object file with a conventional compilation
644 unit entry, the type unit entries may refer to (share) the
645 line number table used by the compilation unit. In a type
646 unit located in a split compilation unit, the
647 \DWATstmtlistNAME{} attribute refers to a \doublequote{specialized}
648 line number table in the \dotdebuglinedwo{} section, which
649 contains only the list of directories and file names.}
651 \textit{All type unit entries in a \splitDWARFobjectfile{} may
652 (but are not required to) refer to the same
653 \addtoindex{specialized line number table}.}
655 \item A \DWATuseUTFeight{} attribute, which is a flag
656 whose presence indicates that all strings referred to by this type
657 unit entry, its children, and its associated
658 \addtoindex{specialized line number table},
659 are represented using the UTF-8 representation.
662 \item A \DWATstroffsetsbase\addtoindexx{string offsets base attribute}
663 attribute, whose value is of class \CLASSstroffsetsptr.
664 This attribute points
665 to the first string offset of the type unit's contribution to
666 the \dotdebugstroffsets{} section. Indirect string references
667 (using \DWFORMstrx) within the type unit are interpreted
668 as indices relative to this base.
672 A \addtoindex{type unit} entry for a given type T owns a debugging
673 information entry that represents a defining declaration
674 of type T. If the type is nested within enclosing types or
675 namespaces, the debugging information entry for T is nested
676 within debugging information entries describing its containers;
677 otherwise, T is a direct child of the type unit entry.
679 A type unit entry may also own additional debugging information
680 entries that represent declarations of additional types that
681 are referenced by type T and have not themselves been placed in
682 separate type units. Like T, if an additional type U is nested
683 within enclosing types or namespaces, the debugging information
684 entry for U is nested within entries describing its containers;
685 otherwise, U is a direct child of the type unit entry.
687 The containing entries for types T and U are declarations,
688 and the outermost containing entry for any given type T or
689 U is a direct child of the type unit entry. The containing
690 entries may be shared among the additional types and between
691 T and the additional types.
693 \textit{Examples of these kinds of relationships are found in
694 Section \refersec{app:signaturecomputationexample} and
695 Section \refersec{app:declarationscompletingnondefiningdeclarations}.}
698 \textit{Types are not required to be placed in type units. In general,
699 only large types such as structure, class, enumeration, and
700 union types included from header files should be considered
701 for separate type units. Base types and other small types
702 are not usually worth the overhead of placement in separate
703 type units. Types that are unlikely to be replicated, such
704 as those defined in the main source file, are also better
705 left in the main compilation unit.}
707 \section{Module, Namespace and Importing Entries}
708 \textit{Modules and namespaces provide a means to collect related
709 entities into a single entity and to manage the names of
713 \subsection{Module Entries}
714 \label{chap:moduleentries}
715 \textit{Several languages have the concept of a \doublequote{module.}
716 \addtoindexx{Modula-2}
717 A Modula\dash 2 definition module
718 \addtoindexx{Modula-2!definition module}
719 may be represented by a module
721 \addtoindex{declaration attribute}
722 (\DWATdeclaration). A
723 \addtoindex{Fortran 90} module
724 \addtoindexx{Fortran!module (Fortran 90)}
725 may also be represented by a module entry
726 (but no declaration attribute is warranted because \addtoindex{Fortran}
727 has no concept of a corresponding module body).}
729 A module is represented by a debugging information entry
731 tag \DWTAGmoduleTARG.
732 Module entries may own other
733 debugging information entries describing program entities
734 whose declaration scopes end at the end of the module itself.
736 If the module has a name, the module entry has a
737 \DWATname{} attribute
738 \addtoindexx{name attribute}
739 whose value is a null\dash terminated string containing
742 The \addtoindex{module entry} may have either a
746 \addtoindexx{high PC attribute}
748 \addtoindexx{low PC attribute}
750 \DWATranges{} attribute
751 \addtoindexx{ranges attribute}
752 whose values encode the contiguous or non-contiguous address
753 ranges, respectively, of the machine instructions generated for
754 the module initialization
755 code\hypertarget{chap:DWATentrypcentryaddressofmoduleinitialization}{}
756 (see Section \refersec{chap:codeaddressesandranges}).
758 \addtoindexx{entry PC attribute!for module initialization}
759 \DWATentrypc{} attribute whose value is the address of
760 the first executable instruction of that initialization code
761 (see Section \refersec{chap:entryaddress}).
764 If\hypertarget{chap:DWATprioritymodulepriority}{}
765 the module has been assigned a priority, it may have a
766 \addtoindexx{priority attribute}
767 \DWATpriorityDEFN{} attribute.
768 The value of this attribute is a
769 reference to another debugging information entry describing
770 a variable with a constant value. The value of this variable
771 is the actual constant value of the module\textquoteright s priority,
772 represented as it would be on the target architecture.
774 \subsection{Namespace Entries}
775 \label{chap:namespaceentries}
776 \textit{\addtoindex{C++} has the notion of a namespace, which provides a way to
777 \addtoindexx{namespace (C++)}
778 implement name hiding, so that names of unrelated things
779 do not accidentally clash in the
780 \addtoindex{global namespace} when an
781 application is linked together.}
783 A namespace is represented by a debugging information entry
784 with the tag \DWTAGnamespaceTARG. A namespace extension
785 is\hypertarget{chap:DWATextensionpreviousnamespaceextensionororiginalnamespace}{}
786 represented by a \DWTAGnamespaceNAME{} entry with a
787 \DWATextensionDEFN{}\addtoindexx{extension attribute}
788 attribute referring to the previous extension, or if there
789 is no previous extension, to the original
790 \DWTAGnamespaceNAME{}
791 entry. A namespace extension entry does not need to duplicate
792 information in a previous extension entry of the namespace
793 nor need it duplicate information in the original namespace
794 entry. (Thus, for a namespace with a name,
795 a \DWATname{} attribute
796 \addtoindexx{name attribute}
797 need only be attached directly to the original
798 \DWTAGnamespaceNAME{} entry.)
801 Namespace and namespace extension entries may own
802 \addtoindexx{namespace extension entry}
804 \addtoindexx{namespace declaration entry}
805 debugging information entries describing program entities
806 whose declarations occur in the namespace.
808 A namespace may have a
809 \DWATexportsymbolsDEFN{}\livetarg{chap:DWATexportsymbolsofnamespace}{}
810 attribute\addtoindexx{export symbols attribute}
811 \addtoindexx{inline namespace|see{\textit{also} export symbols attribute}}
812 which is a \CLASSflag{} which
813 indicates that all member names defined within the
814 namespace may be referenced as if they were defined within
815 the containing namespace.
817 \textit{This may be used to describe an \addtoindex{inline namespace} in \addtoindex{C++}}.
819 If a type, variable, or function declared in a namespace is
820 defined outside of the body of the namespace declaration,
821 that type, variable, or function definition entry has a
822 \DWATspecification{} attribute
823 \addtoindexx{specification attribute}
824 whose value is a \livelink{chap:classreference}{reference} to the
825 debugging information entry representing the declaration of
826 the type, variable or function. Type, variable, or function
828 \DWATspecification{} attribute
829 \addtoindexx{specification attribute}
831 to duplicate information provided by the declaration entry
832 referenced by the specification attribute.
834 \textit{The \addtoindex{C++} \addtoindex{global namespace}
836 \addtoindexx{global namespace|see{namespace (C++), global}}
838 \addtoindexx{namespace (C++)!global}
840 \texttt{::f}, for example) is not explicitly represented in
841 DWARF with a namespace entry (thus mirroring the situation
842 in \addtoindex{C++} source).
843 Global items may be simply declared with no
844 reference to a namespace.}
846 \textit{The \addtoindex{C++}
847 compilation unit specific \doublequote{unnamed namespace} may
848 \addtoindexx{namespace (C++)!unnamed}
849 \addtoindexx{unnamed namespace|see {namespace (C++), unnamed}}
850 be represented by a namespace entry with no name attribute in
851 the original namespace declaration entry (and therefore no name
852 attribute in any namespace extension entry of this namespace).
853 C++ states that declarations in the unnamed namespace are
854 implicitly available in the containing scope; a producer
855 should make this effect explicit with the \DWATexportsymbols{}
856 attribute, or by using a \DWTAGimportedmodule{} that is a
857 sibling of the namespace entry and references it.}
859 \textit{A compiler emitting namespace information may choose to
860 explicitly represent namespace extensions, or to represent the
861 final namespace declaration of a compilation unit; this is a
862 quality-of-implementation issue and no specific requirements
863 are given here. If only the final namespace is represented,
864 \addtoindexx{namespace (C++)!using declaration}
865 it is impossible for a debugger to interpret using declaration
866 references in exactly the manner defined by the
867 \addtoindex{C++} language.}
869 \textit{For \addtoindex{C++} namespace examples,
870 see Appendix \refersec{app:namespaceexamples}.}
874 \subsection{Imported (or Renamed) Declaration Entries}
875 \label{chap:importedorrenameddeclarationentries}
877 \textit{Some languages support the concept of importing into or
878 making accessible in a given unit certain declarations that occur
879 in a different module or scope. An imported declaration may
880 sometimes be given another name.}
883 An imported declaration is represented by one or
884 \addtoindexx{imported declaration entry}
885 more debugging information entries with the
886 tag \DWTAGimporteddeclarationTARG.
887 When\hypertarget{chap:DWATimportimporteddeclaration}{}
888 an overloaded entity is imported, there is one imported
889 declaration entry for each overloading.
890 Each imported declaration entry has a
891 \DWATimportDEFN{} attribute,\addtoindexx{import attribute}
892 whose value is a \livelink{chap:classreference}{reference} to the
893 debugging information entry representing the declaration that
896 An imported declaration may also have a \DWATname{}
897 attribute\addtoindexx{name attribute}
898 whose value is a null-terminated string containing the
900 imported entity is to be known in the context of the imported
901 declaration entry (which may be different than the name of
902 the entity being imported). If no name is present, then the
903 name by which the entity is to be known is the same as the
904 name of the entity being imported.
906 An imported declaration entry with a name attribute may be
907 used as a general means to rename or provide an alias for
908 \addtoindexx{alias declaration|see{imported declaration entry}}
909 an entity, regardless of the context in which the importing
910 declaration or the imported entity occurs.
912 \textit{A \addtoindex{C++}
913 namespace alias\hypertarget{chap:DWATimportnamespacealias}{}
914 may be represented by an imported declaration entry
915 \addtoindexx{namespace (C++)!alias}
916 with a name attribute whose value is
917 a null-terminated string containing the alias name
918 and a \DWATimportDEFN{} attribute
919 whose value is a \livelink{chap:classreference}{reference} to the
920 applicable original namespace or namespace extension entry.}
922 \textit{A \addtoindex{C++} using declaration may be represented
924 imported\hypertarget{chap:DWATimportnamespaceusingdeclaration}{}
925 \addtoindexx{namespace (C++)!using declaration}
926 declaration entries. When the using declaration
927 refers to an overloaded function, there is one imported
928 declaration entry corresponding to each overloading. Each
929 imported declaration entry has no name attribute but it does
930 have a \DWATimportDEFN{} attribute that refers to the entry for the
931 entity being imported. (\addtoindex{C++}
932 provides no means to \doublequote{rename}
933 an imported entity, other than a namespace).}
936 \textit{A \addtoindex{Fortran} use statement
937 \addtoindexx{Fortran!use statement}
938 \addtoindexx{use statement|see {Fortran, use statement}}
939 with an \doublequote{only list} may be
940 represented by a series of imported declaration entries,
941 one (or more) for each entity that is imported. An entity
942 \addtoindexx{renamed declaration|see{imported declaration entry}}
943 that is renamed in the importing context may be represented
944 by an imported declaration entry with a name attribute that
945 specifies the new local name.
948 \subsection{Imported Module Entries}
949 \label{chap:importedmoduleentries}
951 \textit{Some languages support the concept of importing into or making
952 accessible in a given unit all of the declarations contained
953 within a separate module or namespace.
956 An imported module declaration is represented by a debugging
957 information entry with
958 \addtoindexx{imported module attribute}
960 \addtoindexx{imported module entry}
961 tag \DWTAGimportedmoduleTARG.
963 imported module entry contains a
964 \DWATimport{} attribute
965 \addtoindexx{import attribute}
966 whose value is a \livelink{chap:classreference}{reference}
967 to the module or namespace entry
968 containing the definition and/or declaration entries for
969 the entities that are to be imported into the context of the
970 imported module entry.
972 An imported module declaration may own a set of imported
973 declaration entries, each of which refers to an entry in the
974 module whose corresponding entity is to be known in the context
975 of the imported module declaration by a name other than its
976 name in that module. Any entity in the module that is not
977 renamed in this way is known in the context of the imported
978 module entry by the same name as it is declared in the module.
980 \textit{A \addtoindex{C++} using directive
981 \addtoindexx{namespace (C++)!using directive}
982 \addtoindexx{using directive|see {namespace (C++), using directive}}
983 may be represented by an imported
984 module\hypertarget{chap:DWATimportnamespaceusingdirective}{}
985 entry, with a \DWATimportDEFN{} attribute referring to the namespace
986 entry of the appropriate extension of the namespace (which
987 might be the original namespace entry) and no owned entries.
990 \textit{A \addtoindex{Fortran} use statement
991 \addtoindexx{Fortran!use statement}
992 with a \doublequote{rename list} may be
993 represented by an imported module entry with an import
994 attribute referring to the module and owned entries
995 corresponding to those entities that are renamed as part of
999 \textit{A \addtoindex{Fortran} use statement
1000 \addtoindexx{Fortran!use statement}
1001 with neither a \doublequote{rename list} nor
1002 an \doublequote{only list} may be represented by an imported module
1003 entry with an import attribute referring to the module and
1004 no owned child entries.
1007 \textit{A use statement with an \doublequote{only list} is represented by a
1008 series of individual imported declaration entries as described
1009 in Section \refersec{chap:importedorrenameddeclarationentries}.
1013 \textit{A \addtoindex{Fortran} use statement for an entity in a module that is
1014 \addtoindexx{Fortran!use statement}
1015 itself imported by a use statement without an explicit mention
1016 may be represented by an imported declaration entry that refers
1017 to the original debugging information entry. For example, given
1034 \textit{the imported declaration entry for Q within module C refers
1035 directly to the variable declaration entry for X in module A
1036 because there is no explicit representation for X in module B.
1039 \textit{A similar situation arises for a \addtoindex{C++} using declaration
1040 \addtoindexx{namespace (C++)!using declaration}
1041 \addtoindexx{using declaration|see {namespace (C++), using declaration}}
1042 that imports an entity in terms of a namespace alias. See
1043 Appendix \refersec{app:namespaceexamples}
1047 \subsection{Imported Unit Entries}
1048 \label{chap:importedunitentries}
1049 \hypertarget{chap:DWATimportimportedunit}{}
1050 The place where a normal or partial compilation unit is imported is
1051 represented by a debugging information entry with the
1052 \addtoindexx{imported unit entry}
1053 tag \DWTAGimportedunitTARG.
1054 An imported unit entry contains a
1055 \DWATimportDEFN{} attribute\addtoindexx{import attribute}
1056 whose value is a \livelink{chap:classreference}{reference} to the
1057 normal or partial compilation unit whose declarations logically
1058 belong at the place of the imported unit entry.
1060 \textit{An imported unit entry does not necessarily correspond to
1061 any entity or construct in the source program. It is merely
1062 \doublequote{glue} used to relate a partial unit, or a compilation
1063 unit used as a partial unit, to a place in some other
1066 \section{Subroutine and Entry Point Entries}
1067 \label{chap:subroutineandentrypointentries}
1069 The following tags exist to describe
1070 debugging information entries
1071 \addtoindexx{function entry|see{subroutine entry}}
1073 \addtoindexx{subroutine entry}
1075 \addtoindexx{subprogram entry}
1077 % FIXME: is entry point entry the right index 'entry'?
1078 \addtoindexx{entry point entry}
1081 \begin{tabular}{lp{9.0cm}}
1082 \DWTAGsubprogramTARG{} & A subroutine or function \\
1083 \DWTAGinlinedsubroutine{} & A particular inlined
1084 \addtoindexx{inlined subprogram entry}
1085 instance of a subroutine or function \\
1086 \DWTAGentrypointTARG{} & An alternate entry point \\
1091 \subsection{General Subroutine and Entry Point Information}
1092 \label{chap:generalsubroutineandentrypointinformation}
1093 The subroutine or entry point entry has a \DWATname{}
1094 attribute whose value is a null-terminated string containing the
1095 subroutine or entry point name.
1096 It may also have a \DWATlinkagename{} attribute as
1097 described in Section \refersec{chap:linkagenames}.
1099 If the name of the subroutine described by an entry with the
1100 \addtoindexx{subprogram entry}
1101 tag \DWTAGsubprogram{}\hypertarget{chap:DWATexternalexternalsubroutine}{}
1102 is visible outside of its containing
1103 compilation unit, that entry has a
1104 \DWATexternalDEFN{} attribute,\addtoindexx{external attribute}
1105 which is a \livelink{chap:classflag}{flag}.
1107 \textit{Additional attributes for functions that are members of a
1108 class or structure are described in
1109 Section \refersec{chap:memberfunctionentries}.
1112 A\hypertarget{chap:DWATmainsubprogrammainorstartingsubprogram}{}
1113 subroutine entry may contain a
1114 \DWATmainsubprogramDEFN{} attribute
1115 \addtoindexx{main subprogram attribute}
1117 a \CLASSflag{} whose presence indicates that the
1118 subroutine has been identified as the starting function of
1119 the program. If more than one subprogram contains this
1121 any one of them may be the starting subroutine of the program.
1123 \textit{See also Section \refersec{chap:unitentries}) regarding the
1124 related use of this attribute to indicate that a compilation
1125 unit contains the main subroutine of a program.}
1127 \subsubsection{Calling Convention Information}
1128 \hypertarget{chap:DWATcallingconventionforsubprograms}{}
1129 A subroutine entry may contain a
1130 \DWATcallingconventionDEFN{}
1131 \addtoindexx{calling convention attribute!for subprogram}
1132 attribute, whose value is an
1133 \livelink{chap:classconstant}{integer constant}. The set of
1134 \addtoindexi{calling convention codes for subroutines}{calling convention codes!for subroutines}
1135 is given in Table \refersec{tab:callingconventioncodesforsubroutines}.
1137 \begin{simplenametable}[1.4in]{Calling convention codes for subroutines}{tab:callingconventioncodesforsubroutines}
1141 \end{simplenametable}
1143 If this attribute is not present, or its value is the constant
1144 \DWCCnormalTARG, then the subroutine may be safely called by
1145 obeying the \doublequote{standard} calling conventions of the target
1146 architecture. If the value of the calling convention attribute
1147 is the constant \DWCCnocallTARG, the subroutine does not obey
1148 standard calling conventions, and it may not be safe for the
1149 debugger to call this subroutine.
1151 \textit{Note that \DWCCnormal{} is also used as a calling convention
1152 code for certain types
1153 (see Table \refersec{tab:callingconventioncodesfortypes}).}
1155 If the semantics of the language of the compilation unit
1156 containing the subroutine entry distinguishes between ordinary
1157 subroutines and subroutines that can serve as the \doublequote{main
1158 program,} that is, subroutines that cannot be called
1159 directly according to the ordinary calling conventions,
1160 then the debugging information entry for such a subroutine
1161 may have a calling convention attribute whose value is the
1162 constant \DWCCprogramTARG.
1164 \textit{A common debugger feature is to allow the debugger user to call
1165 a subroutine within the subject program. In certain cases,
1166 however, the generated code for a subroutine will not obey
1167 the standard calling conventions for the target architecture
1168 and will therefore not be safe to call from within a debugger.}
1170 \textit{The \DWCCprogram{}
1171 value is intended to support \addtoindex{Fortran} main
1172 \addtoindexx{Fortran!main program}
1173 programs which in some implementations may not be callable
1174 or which must be invoked in a special way. It is not intended
1175 as a way of finding the entry address for the program.}
1178 \subsubsection{Miscellaneous Subprogram Properties}
1179 \textit{In \addtoindex{C}
1180 there is a difference between the types of functions
1181 declared using function prototype style declarations and
1182 those declared using non-prototype declarations.}
1184 A subroutine entry declared with a function prototype style
1185 declaration may have a
1186 \addtoindexx{prototyped attribute}
1187 \DWATprototypedDEFN{} attribute, which is
1189 The attribute indicates whether a subroutine entry point corresponds
1190 to a function declaration that includes parameter prototype information.
1192 A subprogram entry may have
1193 a\hypertarget{chap:DWATelementalelementalpropertyofasubroutine}{}
1194 \DWATelementalDEFN{} attribute,\addtoindexx{elemental attribute}
1195 which is a \livelink{chap:classflag}{flag}.
1196 The attribute indicates whether the subroutine
1197 or entry point was declared with the \doublequote{elemental} keyword
1200 A\hypertarget{chap:DWATpurepurepropertyofasubroutine}{}
1201 subprogram entry may have a
1202 \addtoindexx{pure attribute}
1203 \DWATpureDEFN{} attribute, which is
1204 a \livelink{chap:classflag}{flag}.
1205 The attribute indicates whether the subroutine was
1206 declared with the \doublequote{pure} keyword or property.
1208 A\hypertarget{chap:DWATrecursiverecursivepropertyofasubroutine}{}
1209 subprogram entry may have a
1210 \addtoindexx{recursive attribute}
1211 \DWATrecursiveDEFN{} attribute, which
1212 is a \livelink{chap:classflag}{flag}.
1213 The attribute indicates whether the subroutine
1214 or entry point was declared with the \doublequote{recursive} keyword
1217 A subprogram entry may have a
1219 \livetargi{chap:DWATnoreturnofsubprogram}{attribute}{noreturn attribute},
1220 which is a \CLASSflag. The attribute
1221 indicates whether the subprogram was declared with the \doublequote{noreturn} keyword or property
1222 indicating that the subprogram can be called, but will never return to its caller.
1225 \textit{The \addtoindex{Fortran}
1226 language allows the keywords \texttt{elemental}, \texttt{pure}
1227 and \texttt{recursive} to be included as part of the declaration of
1228 a subroutine; these attributes reflect that usage. These
1229 attributes are not relevant for languages that do not support
1230 similar keywords or syntax. In particular, the \DWATrecursiveNAME{}
1231 attribute is neither needed nor appropriate in languages such
1232 as \addtoindex{C} where functions support recursion by default.}
1235 \subsubsection{Call Site-Related Attributes}
1236 \textit{While subprogram attributes in the previous section provide
1237 information about the subprogram and its entry point(s) as a whole,
1238 the following attributes provide summary information about the calls
1239 that occur within a subprogram.}
1241 A subroutine entry may have \DWATcallalltailcalls,
1242 \DWATcallallcalls{} and/or \DWATcallallsourcecalls{}
1243 attributes, each of which is a \CLASSflag.
1244 \addtoindexx{call site summary information}
1245 \addtoindexx{subroutine call site summary attributes}
1246 These flags indicate the completeness of the call site
1247 information provided by call site entries (see
1248 Section \refersec{chap:callsiteentries}) within the subprogram.
1250 The \DWATcallalltailcallsDEFN{}
1251 \livetargi{chap:DWATcallalltailcallsofasubprogram}{attribute}{all tail calls summary attribute}
1252 indicates that every tail call
1253 that occurs in the code for the subprogram is described by a
1254 \DWTAGcallsite{} entry.
1255 (There may or may not be other non-tail calls to some of the same
1256 target subprograms.)
1258 The \DWATcallallcallsDEFN{}
1259 \livetargi{chap:DWATcallallcallsofasubprogram}{attribute}{all calls summary attribute}
1260 indicates that every non-inlined call
1261 (either a tail call or a normal call) that occurs in the code for the subprogram
1262 is described by a \DWTAGcallsite{} entry.
1264 The \DWATcallallsourcecallsDEFN{}
1265 \livetargi{chap:DWATcallallsourcecallsofasubprogram}{attribute}{all source calls summary attribute}
1266 indicates that every call that occurs in the
1267 code for the subprogram, including every call inlined into it, is described by either a
1268 \DWTAGcallsite{} entry or a \DWTAGinlinedsubroutine{} entry; further, any call
1269 that is optimized out is nonetheless also described using a \DWTAGcallsite{} entry
1270 that has neither a \DWATcallpc{} nor \DWATcallreturnpc{} attribute.
1272 \textit{The \DWATcallallsourcecallsNAME{} attribute is intended for debugging
1273 information format consumers that analyze call graphs.}
1275 If the the \DWATcallallsourcecalls{} attribute is present then the
1276 \DWATcallallcalls{} and \DWATcallalltailcalls{} attributes are
1277 also implicitly present. Similarly, if the
1278 \DWATcallallcalls{} attribute is present then the \DWATcallalltailcalls{}
1279 attribute is implicitly present.
1282 \subsection{Subroutine and Entry Point Return Types}
1283 \label{chap:subroutineandentrypointreturntypes}
1285 If\hypertarget{chap:DWATtypetypeofsubroutinereturn}{}
1286 the subroutine or entry point
1287 \addtoindexx{return type of subroutine}
1288 is a function that returns a
1289 value, then its debugging information entry has
1290 \addtoindexx{type attribute}
1291 a \DWATtypeDEFN{} attribute
1292 to denote the type returned by that function.
1294 \textit{Debugging information entries for
1295 \addtoindex{C} void functions should
1296 not have an attribute for the return type. }
1298 \textit{Debugging information entries for declarations of \addtoindex{C++}
1299 member functions with an
1300 \autoreturntype{} specifier should use an unspecified type entry (see
1301 Section \refersec{chap:unspecifiedtypeentries}).
1302 The debugging information entry for the corresponding definition
1303 should provide the deduced return type. This practice causes the description of
1304 the containing class to be consistent across compilation units, allowing the class
1305 declaration to be placed into a separate type unit if desired.}
1308 \subsection{Subroutine and Entry Point Locations}
1309 \label{chap:subroutineandentrypointlocations}
1311 A subroutine entry may have either a \DWATlowpc{} and
1312 \DWAThighpc{} pair of attributes or a \DWATranges{} attribute
1313 \addtoindexx{ranges attribute}
1315 \addtoindexx{high PC attribute}
1317 \addtoindexx{low PC attribute}
1318 encode the contiguous or non-contiguous address
1319 ranges, respectively, of the machine instructions generated
1320 for the subroutine (see
1321 Section \refersec{chap:codeaddressesandranges}).
1323 A\hypertarget{chap:DWATentrypcentryaddressofsubprogram}{}
1324 subroutine entry may also have a
1325 \addtoindexx{entry PC attribute!for subroutine}
1326 \DWATentrypc{} attribute
1327 whose value is the address of the first executable instruction
1328 of the subroutine (see
1329 Section \refersec{chap:entryaddress}).
1331 An entry point has a \DWATlowpc{} attribute whose value is the
1332 relocated address of the first machine instruction generated
1333 for the entry point.
1336 %\textit{While the \DWATentrypc{} attribute
1337 %\addtoindexx{entry pc attribute!for subroutine}
1338 %might also seem appropriate for this purpose, historically the
1339 %\DWATlowpc{} attribute was used before the
1340 %\DWATentrypc{} was introduced (in
1341 %\addtoindex{DWARF Version 3}).
1342 %There is insufficient reason to change this.}
1344 Subroutines and entry points may also have
1345 \DWATsegment{}\hypertarget{chap:DWATaddressclasssubroutineorsubroutinetype}{}
1346 \addtoindexx{segment attribute} and
1347 \DWATaddressclassDEFN{}\addtoindexx{address class attribute}
1348 attributes, as appropriate, to specify
1349 which segments the code for the subroutine resides in and
1350 the addressing mode to be used in calling that subroutine.
1352 A subroutine entry representing a subroutine declaration
1353 that is not also a definition does not have code address or
1357 \subsection{Declarations Owned by Subroutines and Entry Points}
1358 \label{chap:declarationsownedbysubroutinesandentrypoints}
1359 \addtoindexx{subroutine formal parameters}
1360 The declarations enclosed by a subroutine or entry point are
1361 represented by debugging information entries that are owned
1362 by the subroutine or entry point entry. Entries representing
1363 \addtoindexx{formal parameter}
1364 the formal parameters of the subroutine or entry point appear
1365 in the same order as the corresponding declarations in the
1369 \textit{There is no ordering requirement for entries for declarations
1370 other than formal parameters. The formal parameter
1371 entries may be interspersed with other entries used by formal
1372 parameter entries, such as type entries.}
1374 The unspecified (sometimes called \doublequote{varying})
1375 parameters of a subroutine parameter list are
1376 represented by a debugging information
1377 entry\addtoindexx{unspecified parameters entry}
1378 with the tag \DWTAGunspecifiedparametersTARG.
1381 The entry for a subroutine that includes a
1382 \addtoindex{Fortran}
1383 \addtoindexx{Fortran!common block}
1384 \livelink{chap:fortrancommonblock}{common}
1385 \livelink{chap:commonblockentry}{block}
1386 \addtoindexx{common block|see{Fortran common block}}
1387 has a child entry with the
1388 tag \DWTAGcommoninclusionTARG.
1389 The\hypertarget{chap:commonreferencecommonblockusage}{}
1390 common inclusion entry has a
1391 \DWATcommonreferenceDEFN{} attribute
1392 \addtoindexx{common block reference attribute}
1393 whose value is a \livelink{chap:classreference}{reference}
1394 to the debugging information entry
1395 for the common \nolink{block} being included
1396 (see Section \refersec{chap:commonblockentries}).
1398 \subsection{Low-Level Information}
1399 \label{chap:lowlevelinformation}
1401 A\hypertarget{chap:DWATreturnaddrsubroutinereturnaddresssavelocation}{}
1402 subroutine or entry point entry may have a
1403 \addtoindexx{return address attribute}
1404 \DWATreturnaddrDEFN{}
1405 attribute, whose value is a location description. The location
1406 specified is the place where the return address for the
1407 subroutine or entry point is stored.
1409 A\hypertarget{chap:DWATframebasesubroutineframebaseaddress}{}
1410 subroutine or entry point entry may also have a
1411 \addtoindexx{frame base attribute}
1412 \DWATframebaseDEFN{} attribute, whose value is a location
1413 description that describes the \doublequote{frame base} for the
1414 subroutine or entry point. If the location description is
1415 a simple register location description, the given register
1416 contains the frame base address. If the location description is
1417 a DWARF expression, the result of evaluating that expression
1418 is the frame base address. Finally, for a
1419 \addtoindex{location list},
1420 this interpretation applies to each location description
1421 contained in the list of \addtoindex{location list} entries.
1423 \textit{The use of one of the \DWOPregn{}
1424 operations in this context is equivalent to using
1425 \DWOPbregn(0) but more
1426 compact. However, these are not equivalent in general.}
1429 \textit{The frame base for a subprogram is typically an address
1430 relative to the first unit of storage allocated for the
1431 subprogram\textquoteright s stack frame. The \DWATframebase{} attribute
1432 can be used in several ways:}
1433 \begin{enumerate}[1. ]
1434 \item \textit{In subprograms that need
1435 \addtoindexx{location list}
1436 location lists to locate local
1437 variables, the \DWATframebase{} can hold the needed location
1438 list, while all variables\textquoteright\ location descriptions can be
1439 simpler ones involving the frame base.}
1441 \item \textit{It can be used in resolving \doublequote{up\dash level} addressing
1442 within nested routines.
1443 (See also \DWATstaticlink, below)}
1447 \textit{Some languages support nested subroutines. In such languages,
1448 it is possible to reference the local variables of an
1449 outer subroutine from within an inner subroutine. The
1450 \DWATstaticlink{} and \DWATframebase{} attributes allow
1451 debuggers to support this same kind of referencing.}
1453 If\hypertarget{chap:DWATstaticlinklocationofuplevelframe}{}
1454 a subroutine or entry point is nested, it may have a
1455 \addtoindexx{address!uplevel|see {static link attribute}}
1456 \addtoindexx{uplevel address|see {static link attribute}}
1457 \DWATstaticlinkDEFN{} attribute, whose value is a location
1458 description that computes the frame base of the relevant
1459 instance of the subroutine that immediately encloses the
1460 subroutine or entry point.
1462 In the context of supporting nested subroutines, the
1463 \DWATframebase{} attribute value obeys the following constraints:
1465 \begin{enumerate}[1. ]
1467 It computes a value that does not change during the
1468 life of the subprogram, and
1470 \item The computed value is unique among instances of
1471 the same subroutine.
1473 \textit{For typical \DWATframebase{} use, this
1474 means that a recursive subroutine\textquoteright s stack frame must have
1479 \textit{If a debugger is attempting to resolve an up\dash level reference
1480 to a variable, it uses the nesting structure of DWARF to
1481 determine which subroutine is the lexical parent and the
1482 \DWATstaticlink{} value to identify the appropriate active
1483 frame of the parent. It can then attempt to find the reference
1484 within the context of the parent.}
1488 \subsection{Types Thrown by Exceptions}
1489 \label{chap:typesthrownbyexceptions}
1491 \textit{In \addtoindex{C++} a subroutine may declare a set of types which
1492 it may validly throw.}
1494 If a subroutine explicitly declares that it may throw
1495 \addtoindexx{exception thrown|see{thrown type entry}}
1497 \addtoindexx{thrown exception|see{thrown type entry}}
1498 exception of one or more types, each such type is
1499 represented by a debugging information entry with
1500 \addtoindexx{thrown type entry}
1502 \DWTAGthrowntypeTARG.
1503 Each such entry is a child of the entry
1504 representing the subroutine that may throw this type. Each
1505 thrown type entry contains
1506 \addtoindexx{type attribute}
1507 a \DWATtype{} attribute, whose
1508 value is a \livelink{chap:classreference}{reference}
1509 to an entry describing the type of the
1510 exception that may be thrown.
1512 \subsection{Function Template Instantiations}
1513 \label{chap:functiontemplateinstantiations}
1515 \textit{In \addtoindex{C++}, a function template is a generic definition of
1516 a function that is instantiated differently for calls with
1517 values of different types. DWARF does not represent the generic
1518 template definition, but does represent each instantiation.}
1521 A \addtoindex{function template instantiation}\addtoindexx{template instantiation!function}
1522 is represented by a debugging information entry with the
1523 \addtoindexx{subprogram entry!use for template instantiation}
1524 tag \DWTAGsubprogram.
1526 exceptions, such an entry will contain the same attributes and
1527 will have the same types of child entries as would an entry
1528 for a subroutine defined explicitly using the instantiation
1529 types and values. The exceptions are:
1531 \begin{enumerate}[1. ]
1532 \item Template parameters are described and referenced as specified in
1533 Section \refersec{chap:templateparameters}.
1536 \item If the compiler has generated a separate compilation unit
1537 to hold the template instantiation and that compilation unit
1538 has a different name from the compilation unit containing
1539 the template definition, the name attribute for the debugging
1540 information entry representing that compilation unit is empty
1543 \item If the subprogram entry representing the template
1544 instantiation or any of its child entries contain declaration
1545 coordinate attributes, those attributes refer to the source
1546 for the template definition, not to any source generated
1547 artificially by the compiler for this instantiation.
1552 \subsection{Inlinable and Inlined Subroutines}
1553 \label{chap:inlinedsubroutines}
1554 A declaration or a definition of an inlinable subroutine
1555 is represented by a debugging information entry with the
1556 tag \DWTAGsubprogram.
1557 The entry for a subroutine
1558 \addtoindexx{subprogram entry!use in inlined subprogram}
1559 that is\hypertarget{chap:DWATinlineinlinedsubroutine}{}
1560 explicitly declared to be available for inline expansion or
1561 that was expanded inline implicitly by the compiler has a
1562 \addtoindexx{inline attribute}
1563 \DWATinlineDEFN{} attribute whose value is an
1564 \livelink{chap:classconstant}{integer constant}. The
1565 set of values for the \DWATinline{} attribute is given in
1566 Table \refersec{tab:inlinecodes}.
1570 \caption{Inline codes}
1571 \label{tab:inlinecodes}
1572 \begin{tabular}{l|P{8cm}}
1574 Name&Meaning\\ \hline
1575 \DWINLnotinlinedTARG{} & Not declared inline nor inlined by the
1576 \mbox{compiler} (equivalent to the absence of the
1577 containing \DWATinline{} attribute) \\
1578 \DWINLinlinedTARG{} & Not declared inline but inlined by the \mbox{compiler} \\
1579 \DWINLdeclarednotinlinedTARG{} & Declared inline but
1580 not inlined by the \mbox{compiler} \\
1581 \DWINLdeclaredinlinedTARG{} & Declared inline and inlined by the
1587 \textit{In \addtoindex{C++}, a function or a constructor declared with
1588 \addttindex{constexpr} is implicitly declared inline. The abstract
1589 instance (see Section \refersec{chap:abstractinstances})
1590 is represented by a debugging information
1591 entry with the tag \DWTAGsubprogram. Such an entry has a
1592 \DWATinline{} attribute whose value is \DWINLinlined.}
1595 \subsubsection{Abstract Instances}
1596 \label{chap:abstractinstances}
1597 Any subroutine entry that contains a
1598 \DWATinlineDEFN{} attribute\addtoindexx{inline attribute}
1599 whose value is other than
1601 is known as an \definition{abstract instance root}.
1602 \addtoindexx{abstract instance!root}
1603 \hypertarget{chap:DWATinlineabstracttinstance}{}
1604 Any debugging information entry that is owned (either
1605 directly or indirectly) by an abstract instance root
1607 \definition{abstract instance entry.}\addtoindexx{abstract instance!entry}
1608 Any set of abstract instance entries that are all
1609 children (either directly or indirectly) of some abstract
1610 instance root, together with the root itself, is known as an
1611 \definition{abstract instance tree.}\addtoindexx{abstract instance!tree}
1612 However, in the case where an abstract instance tree is
1613 nested within another abstract instance tree, the entries in the
1614 \addtoindex{nested abstract instance}
1615 tree are not considered to be entries in the outer abstract
1619 Each abstract instance root is either part of a larger
1620 \addtoindexx{abstract instance!root}
1621 tree (which gives a context for the root) or
1622 \addtoindexx{specification attribute}
1624 \DWATspecification{}
1625 to refer to the declaration in context.
1627 \textit{For example, in \addtoindex{C++} the context might be a namespace
1628 declaration or a class declaration.}
1630 \textit{Abstract instance trees are defined so that no entry is part
1631 of more than one abstract instance tree.}
1633 Attributes and children in an abstract instance are shared
1634 by all concrete instances (see Section \refersec{chap:concreteinstances}).
1636 A debugging information entry that is a member of an abstract
1637 instance tree may not contain any attributes which describe
1638 aspects of the subroutine which vary between distinct inlined
1639 expansions or distinct out-of-line expansions.
1641 \textit{For example,
1642 \addtoindexx{entry pc attribute!and abstract instance}
1643 the \DWATlowpc,\addtoindexx{low PC attribute!and abstract instance}
1644 \DWAThighpc,\addtoindexx{high PC attribute!and abstract instance}
1645 \DWATranges,\addtoindexx{ranges attribute!and abstract instance}
1646 \DWATentrypc,\addtoindexx{entry PC attribute!and abstract instance}
1647 \DWATlocation,\addtoindexx{location attribute!and abstract instance}
1648 \DWATreturnaddr,\addtoindexx{return address attribute!and abstract instance}
1649 \DWATstartscope,\addtoindexx{start scope attribute!and abstract instance}
1651 \DWATsegment{}\addtoindexx{segment attribute!and abstract instance}
1652 attributes typically should be omitted; however, this list is not
1656 \textit{It would not make sense normally to put these attributes into
1657 abstract instance entries since such entries do not represent
1658 actual (concrete) instances and thus do not actually exist at
1659 run\dash time. However,
1660 see Appendix \refersec{app:inlineouteronenormalinner}
1661 for a contrary example.}
1663 The rules for the relative location of entries belonging to
1664 abstract instance trees are exactly the same as for other
1665 similar types of entries that are not abstract. Specifically,
1666 the rule that requires that an entry representing a declaration
1667 be a direct child of the entry representing the scope of the
1668 declaration applies equally to both abstract and non-abstract
1669 entries. Also, the ordering rules for formal parameter entries,
1670 member entries, and so on, all apply regardless of whether
1671 or not a given entry is abstract.
1674 \subsubsection{Concrete Instances}
1675 \label{chap:concreteinstances}
1677 Each inline expansion of a subroutine is represented
1678 by a debugging information entry with the
1679 tag \DWTAGinlinedsubroutineTARG. Each such entry is a direct
1680 child of the entry that represents the scope within which
1681 the inlining occurs.
1684 Each inlined subroutine entry may have either a
1686 and \DWAThighpc{} pair of attributes
1687 \addtoindexx{high PC attribute}
1688 \addtoindexx{low PC attribute}
1689 or a \DWATranges{}\addtoindexx{ranges attribute}
1690 attribute whose values encode the contiguous or non-contiguous
1691 address ranges, respectively, of the machine instructions
1692 generated for the inlined subroutine (see
1693 Section \referfol{chap:codeaddressesandranges}).
1694 An\hypertarget{chap:DWATentrypcentryaddressofinlinedsubprogram}{}
1695 inlined subroutine entry may
1696 \addtoindexx{inlined subprogram entry!in concrete instance}
1698 \addtoindexx{inlined subprogram entry}
1700 \addtoindexx{entry PC attribute!for inlined subprogram}
1703 attribute, representing the first executable instruction of
1704 the inline expansion (see
1705 Section \refersec{chap:entryaddress}).
1707 % Positions of the 3 targets here is a bit arbitrary.
1708 An inlined\hypertarget{chap:DWATcalllinelinenumberofinlinedsubroutinecall}{}
1709 subroutine\hypertarget{chap:DWATcallcolumncolumnpositionofinlinedsubroutinecall}{}
1710 entry\hypertarget{chap:DWATcallfilefilecontaininginlinedsubroutinecall}{}
1711 may also have \DWATcallfileDEFN,
1712 \DWATcalllineDEFN{} and \DWATcallcolumnDEFN{} attributes,
1713 \addtoindexx{inlined call location attributes}
1715 value is an \livelink{chap:classconstant}{integer constant}.
1716 These attributes represent the
1717 source file, source line number, and source column number,
1718 respectively, of the first character of the statement or
1719 expression that caused the inline expansion. The call file,
1720 call line, and call column attributes are interpreted in
1721 the same way as the declaration file, declaration line, and
1722 declaration column attributes, respectively (see
1723 Section \refersec{chap:declarationcoordinates}).
1725 \textit{The call file, call line and call column coordinates do not
1726 describe the coordinates of the subroutine declaration that
1727 was inlined, rather they describe the coordinates of the call.
1730 An inlined subroutine entry may have
1731 a\hypertarget{chap:DWATconstexprcompiletimeconstantfunction}{}
1732 \DWATconstexprDEFN{} attribute,\addtoindexx{constant expression attribute}
1733 which is a \livelink{chap:classflag}{flag}
1734 whose presence indicates that the
1735 subroutine has been evaluated as a compile\dash time constant. Such
1736 an entry may also have a \DWATconstvalue{} attribute,
1737 whose value may be of any form that is appropriate for the
1738 representation of the subroutine's return value. The value of
1739 this attribute is the actual return value of the subroutine,
1740 represented as it would be on the target architecture.
1742 \textit{In \addtoindex{C++}, if a function or a constructor declared with
1743 \addttindex{constexpr}
1744 is called with constant expressions, then the corresponding
1745 concrete inlined instance has a
1746 \DWATconstexpr{} attribute,
1747 as well as a \DWATconstvalue{} attribute whose value represents
1748 the actual return value of the concrete inlined instance.}
1751 Any debugging information entry that is owned (either
1752 directly or indirectly) by a debugging information entry
1753 with the tag \DWTAGinlinedsubroutine{} is referred to as a
1754 \doublequote{concrete inlined instance entry.} Any entry that has
1756 \DWTAGinlinedsubroutine{}
1757 is known as a \doublequote{concrete inlined instance root.}
1758 Any set of concrete inlined instance
1759 entries that are all children (either directly or indirectly)
1760 of some concrete inlined instance root, together with the root
1761 itself, is known as a \doublequote{concrete inlined instance tree.}
1762 However, in the case where a concrete inlined instance tree
1763 is nested within another concrete instance tree, the entries
1764 in the \addtoindex{nested concrete inline instance} tree
1765 are not considered to
1766 be entries in the outer concrete instance tree.
1769 \textit{Concrete inlined instance trees are defined so that no entry
1770 is part of more than one concrete inlined instance tree. This
1771 simplifies later descriptions.}
1773 Each concrete inlined instance tree is uniquely associated
1774 with one (and only one) abstract instance tree.
1776 \textit{Note, however, that the reverse is not true. Any given abstract
1777 instance tree may be associated with several different concrete
1778 inlined instance trees, or may even be associated with zero
1779 concrete inlined instance trees.}
1781 Concrete inlined instance entries may omit attributes that
1782 are not specific to the concrete instance (but present in
1783 the abstract instance) and need include only attributes that
1784 are specific to the concrete instance (but omitted in the
1785 abstract instance). In place of these omitted attributes,
1786 each\hypertarget{chap:DWATabstractorigininlineinstance}{}
1787 concrete inlined instance entry has a
1788 \addtoindexx{abstract origin attribute}
1789 \DWATabstractoriginDEFN{}
1790 attribute that may be used to obtain the missing information
1791 (indirectly) from the associated abstract instance entry. The
1792 value of the abstract origin attribute is a reference to the
1793 associated abstract instance entry.
1795 If an entry within a concrete inlined instance tree contains
1796 attributes describing the
1797 \addtoindexx{declaration coordinates!in concrete instance}
1798 \livelink{chap:declarationcoordinates}{declaration coordinates}
1799 of that entry, then those attributes refer to the file, line
1800 and column of the original declaration of the subroutine,
1801 not to the point at which it was inlined. As a consequence,
1802 they may usually be omitted from any entry that has an abstract
1806 For each pair of entries that are associated via a
1807 \addtoindexx{abstract origin attribute}
1808 \DWATabstractorigin{} attribute, both members of the pair
1809 have the same tag. So, for example, an entry with the tag
1810 \DWTAGvariable{} can only be associated with another entry
1811 that also has the tag \DWTAGvariable. The only exception
1812 to this rule is that the root of a concrete instance tree
1813 (which must always have the tag \DWTAGinlinedsubroutine)
1814 can only be associated with the root of its associated abstract
1815 instance tree (which must have the tag \DWTAGsubprogram).
1818 In general, the structure and content of any given concrete
1819 inlined instance tree will be closely analogous to the
1820 structure and content of its associated abstract instance
1821 tree. There are a few exceptions:
1823 \begin{enumerate}[1. ]
1824 \item An entry in the concrete instance tree may be omitted if
1826 \addtoindexx{abstract origin attribute}
1827 \DWATabstractorigin{} attribute and either
1828 has no children, or its children are omitted. Such entries
1829 would provide no useful information. In C\dash like languages,
1830 such entries frequently include types, including structure,
1831 union, class, and interface types; and members of types. If any
1832 entry within a concrete inlined instance tree needs to refer
1833 to an entity declared within the scope of the relevant inlined
1834 subroutine and for which no concrete instance entry exists,
1835 the reference refers to the abstract instance entry.
1838 \item Entries in the concrete instance tree which are associated
1839 with entries in the abstract instance tree such that neither
1840 has a \DWATname{} attribute,
1841 \addtoindexx{name attribute}
1842 and neither is referenced by
1843 any other debugging information entry, may be omitted. This
1844 may happen for debugging information entries in the abstract
1845 instance trees that became unnecessary in the concrete instance
1846 tree because of additional information available there. For
1847 example, an anonymous variable might have been created and
1848 described in the abstract instance tree, but because of
1849 the actual parameters for a particular inlined expansion,
1850 it could be described as a constant value without the need
1851 for that separate debugging information entry.
1854 \item A concrete instance tree may contain entries which do
1855 not correspond to entries in the abstract instance tree
1856 to describe new entities that are specific to a particular
1857 inlined expansion. In that case, they will not have associated
1858 entries in the abstract instance tree, do not contain
1859 \addtoindexx{abstract origin attribute}
1860 \DWATabstractorigin{} attributes, and must contain all their
1861 own attributes directly. This allows an abstract instance tree
1862 to omit debugging information entries for anonymous entities
1863 that are unlikely to be needed in most inlined expansions. In
1864 any expansion which deviates from that expectation, the
1865 entries can be described in its concrete inlined instance tree.
1869 \subsubsection{Out-of-Line Instances of Inlined Subroutines}
1870 \label{chap:outoflineinstancesofinlinedsubroutines}
1871 Under some conditions, compilers may need to generate concrete
1872 executable instances of inlined subroutines other than at
1873 points where those subroutines are actually called. Such
1874 concrete instances of inlined subroutines are referred to as
1875 \doublequote{concrete out\dash of\dash line instances.}
1877 \textit{In \addtoindex{C++}, for example,
1878 taking the address of a function declared
1879 to be inline can necessitate the generation of a concrete
1880 out\dash of\dash line instance of the given function.}
1882 The DWARF representation of a concrete out-of-line instance
1883 of an inlined subroutine is essentially the same as for a
1884 concrete inlined instance of that subroutine (as described in
1885 the preceding section). The representation of such a concrete
1886 % It is critical that the hypertarget and livelink be
1887 % separated to avoid problems with latex.
1889 \addtoindexx{abstract origin attribute}
1891 \hypertarget{chap:DWATabstractoriginoutoflineinstance}{}
1893 \DWATabstractoriginDEFN{}
1894 attributes in exactly the same way as they are used for
1895 a concrete inlined instance (that is, as references to
1896 corresponding entries within the associated abstract instance
1899 The differences between the DWARF representation of a
1900 concrete out\dash of\dash line instance of a given subroutine and the
1901 representation of a concrete inlined instance of that same
1902 subroutine are as follows:
1903 \begin{enumerate}[1. ]
1904 \item The root entry for a concrete out\dash of\dash line instance
1905 of a given inlined subroutine has the same tag as does its
1906 associated (abstract) inlined subroutine entry (that is, tag
1907 \DWTAGsubprogram{} rather than \DWTAGinlinedsubroutine).
1909 \item The root entry for a concrete out\dash of\dash line instance tree
1910 is normally owned by the same parent entry that also owns
1911 the root entry of the associated abstract instance. However,
1912 it is not required that the abstract and out\dash of\dash line instance
1913 trees be owned by the same parent entry.
1917 \subsubsection{Nested Inlined Subroutines}
1918 \label{nestedinlinedsubroutines}
1919 Some languages and compilers may permit the logical nesting of
1920 a subroutine within another subroutine, and may permit either
1921 the outer or the nested subroutine, or both, to be inlined.
1923 For a non-inlined subroutine nested within an inlined
1924 subroutine, the nested subroutine is described normally in
1925 both the abstract and concrete inlined instance trees for
1926 the outer subroutine. All rules pertaining to the abstract
1927 and concrete instance trees for the outer subroutine apply
1928 also to the abstract and concrete instance entries for the
1932 For an inlined subroutine nested within another inlined
1933 subroutine, the following rules apply to their abstract and
1934 \addtoindexx{abstract instance!nested}
1935 \addtoindexx{concrete instance!nested}
1936 concrete instance trees:
1938 \begin{enumerate}[1. ]
1939 \item The abstract instance tree for the nested subroutine is
1940 described within the abstract instance tree for the outer
1941 subroutine according to the rules in
1942 Section \refersec{chap:abstractinstances}, and
1943 without regard to the fact that it is within an outer abstract
1946 \item Any abstract instance tree for a nested subroutine is
1947 always omitted within the concrete instance tree for an
1950 \item A concrete instance tree for a nested subroutine is
1951 always omitted within the abstract instance tree for an
1954 \item The concrete instance tree for any inlined or
1955 \addtoindexx{out-of-line instance}
1957 \addtoindexx{out-of-line instance|see{\textit{also} concrete out-of-line instance}}
1958 expansion of the nested subroutine is described within a
1959 concrete instance tree for the outer subroutine according
1961 Sections \refersec{chap:concreteinstances} or
1962 \referfol{chap:outoflineinstancesofinlinedsubroutines}
1964 and without regard to the fact that it is within an outer
1965 concrete instance tree.
1968 \textit{See Appendix \refersec{app:inliningexamples}
1969 for discussion and examples.}
1971 \subsection{Trampolines}
1972 \label{chap:trampolines}
1974 \textit{A trampoline is a compiler\dash generated subroutine that serves
1975 as\hypertarget{chap:DWATtrampolinetargetsubroutine}{}
1976 an intermediary in making a call to another subroutine. It may
1977 adjust parameters and/or the result (if any) as appropriate
1978 to the combined calling and called execution contexts.}
1980 A trampoline is represented by a debugging information entry
1981 \addtoindexx{trampoline (subprogram) entry}
1982 with the tag \DWTAGsubprogram{} or \DWTAGinlinedsubroutine{}
1984 \addtoindexx{trampoline attribute}
1985 a \DWATtrampolineDEFN{} attribute.
1987 attribute indicates the target subroutine of the trampoline,
1988 that is, the subroutine to which the trampoline passes
1989 control. (A trampoline entry may but need not also have a
1990 \DWATartificial{} attribute.)
1993 The value of the trampoline attribute may be represented
1994 using any of the following forms:
1997 \item If the value is of class \CLASSreference{}, then the value
1998 specifies the debugging information entry of the target
2001 \item If the value is of class \CLASSaddress{}, then the value is
2002 the relocated address of the target subprogram.
2005 \item If the value is of class \CLASSstring{}, then the value is the
2006 (possibly mangled) \addtoindexx{mangled names}
2007 name of the target subprogram.
2009 \item If the value is of class \CLASSflag, then the value true
2010 indicates that the containing subroutine is a trampoline but
2011 that the target subroutine is not known.
2015 The target subprogram may itself be a trampoline. (A sequence
2016 of trampolines necessarily ends with a non-trampoline
2019 \textit{In \addtoindex{C++}, trampolines may be used to implement
2020 derived virtual member functions; such trampolines typically
2022 \texttt{this} parameter\index{this parameter@\texttt{this} parameter}
2023 in the course of passing control.
2024 Other languages and environments may use trampolines in a manner
2025 sometimes known as transfer functions or transfer vectors.}
2027 \textit{Trampolines may sometimes pass control to the target
2028 subprogram using a branch or jump instruction instead of a
2029 call instruction, thereby leaving no trace of their existence
2030 in the subsequent execution context. }
2032 \textit{This attribute helps make it feasible for a debugger to arrange
2033 that stepping into a trampoline or setting a breakpoint in
2034 a trampoline will result in stepping into or setting the
2035 breakpoint in the target subroutine instead. This helps to
2036 hide the compiler generated subprogram from the user. }
2038 \section{Call Site Entries and Parameters}
2039 \label{chap:callsiteentriesandparameters}
2041 A call site entry describes a call from one subprogram to another in the
2042 source program. It provides information about the actual parameters of
2043 the call so that they may be more easily accessed by a debugger. When
2044 used together with call frame information
2045 (see Section \refersec{chap:callframeinformation}),
2046 call site entries can be useful for computing the value of an actual parameter
2047 passed by a caller, even when the location description for the callee's
2048 corresponding formal parameter does not provide a current location for
2049 the formal parameter.}
2051 \textit{The DWARF expression for computing the value of an actual parameter at
2052 a call site may refer to registers or memory locations. The expression
2053 assumes these contain the values they would have at the point where the
2054 call is executed. After the called subprogram has been entered, these
2055 registers and memory locations might have been modified. In order to
2056 recover the values that existed at the point of the call (to allow
2057 evaluation of the DWARF expression for the actual parameter), a debugger
2058 may virtually unwind the subprogram activation
2059 (see Section \refersec{chap:callframeinformation}). Any
2060 register or memory location that cannot be recovered is referred to as
2061 "clobbered by the call."}
2063 A source call can be compiled into different types of machine code:
2066 A \textit{normal call} uses a call-like instruction which transfers
2067 control to the start of some subprogram and preserves the call site
2068 location for use by the callee.
2071 A \textit{tail call} uses a jump-like instruction which
2072 transfers control to the start of some subprogram, but
2073 there is no call site location address to preserve
2074 (and thus none is available using the
2075 virtual unwind information).
2078 A \textit{tail recursion call} is a call
2079 to the current subroutine which is compiled as a jump
2080 to the current subroutine.
2084 An \textit{inline (or inlined) call} is a call to an inlined subprogram,
2085 where at least one instruction has the location of the inlined subprogram
2086 or any of its blocks or inlined subprograms.
2090 There are also different types of \doublequote{optimized out} calls:
2093 An \textit{optimized out (normal) call} is a call that is in unreachable code that
2094 has not been emitted (such as, for example, the call to \texttt{foo} in
2095 \texttt{if (0) foo();}).
2097 An \textit{optimized out inline call}
2098 is a call to an inlined subprogram which either did not expand to any instructions
2099 or only parts of instructions belong to it and for debug information purposes those
2100 instructions are given a location in the caller.
2103 \DWTAGcallsite{} entries describe normal and tail calls but not tail recursion calls,
2104 while \DWTAGinlinedsubroutine{} entries describe inlined calls
2105 (see Section \refersec{chap:inlinedsubroutines}).
2106 Call site entries cannot describe tail recursion or optimized out calls.
2108 \subsection{Call Site Entries}
2109 \label{chap:callsiteentries}
2110 A call site is represented by a debugging information entry with the tag
2111 \DWTAGcallsiteTARG{}\addtoindexx{call site entry}.
2112 The entry for a call site is owned by the innermost
2113 debugging information entry representing the scope within which the
2114 call is present in the source program.
2117 \textit{A scope entry (for example, a lexical block) that would not
2118 otherwise be present in the debugging information of a subroutine
2119 need not be introduced solely to represent the immediately containing scope
2122 The call site entry may have a
2123 \DWATcallreturnpcDEFN{}\addtoindexx{call site return pc attribute}
2124 \livetargi{chap:DWATcallreturnpcofcallsite}{attribute}{call return pc attribute}
2125 which is the return address after the call.
2126 The value of this attribute corresponds to the return address
2127 computed by call frame information in the called subprogram
2128 (see Section \refersec{datarep:callframeinformation}).
2130 \textit{On many architectures the return address is the
2131 address immediately following the call instruction, but
2132 on architectures with delay slots it might
2133 be an address after the delay slot of the call.}
2135 The call site entry may have a
2136 \DWATcallpcDEFN{}\addtoindexx{call pc attribute}
2137 \livetargi{chap:DWATcallpcofcallsite}{attribute}{call pc attribute}
2138 which is the address of the
2139 call-like instruction for a normal call or the jump-like
2140 instruction for a tail call.
2142 If the call site entry corresponds to a tail call, it has the
2143 \DWATcalltailcallDEFN{}\addtoindexx{call tail call attribute}
2144 \livetargi{chap:DWATcalltailcallofcallsite}{attribute}{call tail call attribute},
2145 which is a \CLASSflag.
2147 The call site entry may have a
2148 \DWATcalloriginDEFN{}\addtoindexx{call origin attribute}
2149 \livetargi{chap:DWATcalloriginofcallsite}{attribute}{call origin attribute}
2150 which is a \CLASSreference. For direct calls or jumps where the called
2151 subprogram is known it is a reference to the called subprogram's debugging
2152 information entry. For indirect calls it may be a reference to a
2153 \DWTAGvariable{}, \DWTAGformalparameter{} or \DWTAGmember{} entry representing
2154 the subroutine pointer that is called.
2157 The call site may have a
2158 \DWATcalltargetDEFN{}\addtoindexx{call target attribute}
2159 \livetargi{chap:DWATcalltargetofcallsite}{attribute}{call target attribute} which is
2160 a DWARF expression. For indirect calls or jumps where it is unknown at
2161 compile time which subprogram will be called the expression computes the
2162 address of the subprogram that will be called.
2164 \textit{The DWARF expression should
2165 not use register or memory locations that might be clobbered by the call.}
2168 The call site entry may have a
2169 \DWATcalltargetclobberedDEFN{}\addtoindexx{call target clobbered attribute}
2170 \livetargi{chap:DWATcalltargetclobberedofcallsite}{attribute}{call target clobbered attribute}
2171 which is a DWARF expression. For indirect calls or jumps where the
2172 address is not computable without use of registers or memory locations that
2173 might be clobbered by the call the \DWATcalltargetclobberedNAME{}
2174 attribute is used instead of the \DWATcalltarget{} attribute.
2176 \textit{The expression of a call target clobbered attribute may only be
2177 valid at the time the call or call-like transfer of control is executed.}
2179 The call site entry may have a \DWATtypeDEFN{}\addtoindexx{call type attribute}
2180 \livetargi{chap:DWATtypeofcallsite}{attribute}{type attribute!of call site entry}
2181 referencing a debugging information entry for the type of the called function.
2183 \textit{When \DWATcallorigin{} is present, \DWATtypeNAME{} is usually omitted.}
2185 The call site entry may have
2186 \DWATcallfileDEFN{}\addtoindexx{call file attribute},
2187 \DWATcalllineDEFN{}\addtoindexx{call line attribute} and
2188 \DWATcallcolumnDEFN{}\addtoindexx{call column attribute}
2189 \livetargi{chap:DWATcallfileofcallsite}{attributes,}{call file attribute!of call site entry}
2190 \livetargi{chap:DWATcalllineofcallsite}{}{call line attribute!of call site entry}
2191 \livetargi{chap:DWATcallcolumnofcallsite}{}{call column attribute!of call site entry}
2192 each of whose value is an integer constant.
2193 These attributes represent the source file, source line number, and source
2194 column number, respectively, of the first character of the call statement or
2195 expression. The call file, call line, and call column attributes are
2196 interpreted in the same way as the declaration file, declaration
2197 line, and declaration column attributes, respectively
2198 (see Section \refersec{chap:declarationcoordinates}).
2200 \textit{The call file, call line and call column coordinates do
2201 not describe the coordinates of the subroutine declaration that
2202 was called, rather they describe the coordinates of the call.}
2205 \subsection{Call Site Parameters}
2206 \label{chap:callsiteparameters}
2207 The call site entry may own
2208 \DWTAGcallsiteparameterTARG{}\index{call site parameter entry}
2209 debugging information entries representing the parameters passed
2211 Call site parameter entries occur in the same order as the
2212 corresponding parameters in the source.
2213 Each such entry has a \DWATlocation{} attribute which is a location
2214 description. This location description
2215 describes where the parameter is passed
2216 (usually either some register, or a memory location expressible as
2217 the contents of the stack register plus some offset).
2220 Each \DWTAGcallsiteparameter{} entry may have a
2221 \DWATcallvalueDEFN{}\addtoindexx{call value attribute}
2222 \livetargi{chap:DWATcallvalueofcallparameter}{attribute}{call value attribute}
2223 which is a DWARF expression
2224 which when evaluated yields the value of the parameter at the time of the call.
2226 \textit{If it is not
2227 possible to avoid registers or memory locations that might be clobbered by
2228 the call in the expression, then the \DWATcallvalueNAME{} attribute should
2229 not be provided. The reason for the restriction is that the value of the parameter may be
2230 needed in the midst of the callee, where the call clobbered registers or
2231 memory might be already clobbered, and if the consumer is not assured by
2232 the producer it can safely use those values, the consumer can not safely
2233 use the values at all.}
2235 For parameters passed by reference, where the code passes a pointer to
2236 a location which contains the parameter, or for reference type parameters,
2237 the \DWTAGcallsiteparameter{} entry may also have a
2238 \DWATcalldatalocationDEFN{}\addtoindexx{call data location attribute}
2239 \livetargi{chap:DWATcalldatalocationofcallparameter}{attribute}{call data location attribute}
2240 whose value is a location description and a
2241 \DWATcalldatavalueDEFN{}\addtoindexx{call data value attribute}
2242 \livetargi{chap:DWATcalldatavalueofcallparameter}{attribute}{call data value attribute}
2243 whose value is a DWARF expression. The \DWATcalldatalocationNAME{} attribute
2244 \addtoindexx{call data location attribute}
2245 describes where the referenced value lives during the call. If it is just
2246 \DWOPpushobjectaddress{}, it may be left out. The
2247 \DWATcalldatavalueNAME{} attribute describes the value in that location.
2248 The expression should not use registers or memory
2249 locations that might be clobbered by the call, as it might be evaluated after
2250 virtually unwinding from the called function back to the caller.
2253 Each call site parameter entry may also have a
2254 \DWATcallparameterDEFN{}\addtoindexx{call parameter attribute}
2255 \livetargi{chap:DWATcallparameterofcallparameter}{attribute}{call parameter attribute}
2256 which contains a reference to a \DWTAGformalparameter{} entry,
2257 \DWATtype{} attribute referencing the type of the parameter or
2258 \DWATname{} attribute describing the parameter's name.
2260 \textit{Examples using call site entries and related attributes are
2261 found in Appendix \refersec{app:callsiteexamples}.}
2264 \section{Lexical Block Entries}
2265 \label{chap:lexicalblockentries}
2268 lexical \livetargi{chap:lexicalblock}{block}{lexical block}
2270 \addtoindexx{lexical block}
2271 a bracketed sequence of source statements
2272 that may contain any number of declarations. In some languages
2273 (including \addtoindex{C} and \addtoindex{C++}),
2274 \nolink{blocks} can be nested within other
2275 \nolink{blocks} to any depth.}
2277 % We do not need to link to the preceding paragraph.
2278 A lexical \nolink{block} is represented by a debugging information
2280 tag \DWTAGlexicalblockTARG.
2282 The lexical \livetargi{chap:lexicalblockentry}{block}{lexical block entry}
2284 either a \DWATlowpc{} and
2285 \DWAThighpc{} pair of
2287 \addtoindexx{high PC attribute}
2289 \addtoindexx{low PC attribute}
2291 \DWATranges{} attribute
2292 \addtoindexx{ranges attribute}
2293 whose values encode the contiguous or non-contiguous address
2294 ranges, respectively, of the machine instructions generated
2295 for the lexical \nolink{block}
2296 (see Section \refersec{chap:codeaddressesandranges}).
2298 A\hypertarget{chap:DWATentrypcoflexicalblock}{}
2299 lexical block entry may also have a
2300 \addtoindexx{entry PC attribute!for lexical block}
2301 \DWATentrypc{} attribute
2302 whose value is the address of the first executable instruction
2303 of the lexical block (see
2304 Section \refersec{chap:entryaddress}).
2306 If a name has been given to the lexical \nolink{block}
2307 in the source program, then the corresponding
2308 lexical \nolink{block} entry has a
2309 \DWATname{} attribute whose
2310 \addtoindexx{name attribute}
2311 value is a null-terminated string
2312 containing the name of the lexical \nolink{block}.
2314 \textit{This is not the same as a \addtoindex{C} or
2315 \addtoindex{C++} label (see Section \refersec{chap:labelentries}).}
2317 The lexical \nolink{block} entry owns debugging
2318 information entries that describe the declarations
2319 within that lexical \nolink{block}. There is
2320 one such debugging information entry for each local declaration
2321 of an identifier or inner lexical \nolink{block}.
2324 \section{Label Entries}
2325 \label{chap:labelentries}
2326 \textit{A label is a way of identifying a source location.
2327 A labeled statement is usually the target of one or more
2328 \doublequote{go to} statements.}
2331 A label is represented by a debugging information entry with
2332 \addtoindexx{label entry} the tag \DWTAGlabelTARG.
2333 The entry for a label is owned by
2334 the debugging information entry representing the scope within
2335 which the name of the label could be legally referenced within
2338 The label entry has a \DWATlowpc{} attribute whose value
2339 is the address of the first executable instruction for the
2340 location identified by the label in
2341 the source program. The label entry also has a
2342 \DWATname{} attribute
2343 \addtoindexx{name attribute}
2344 whose value is a null-terminated string containing
2345 the name of the label.
2348 \section{With Statement Entries}
2349 \label{chap:withstatemententries}
2351 \textit{Both \addtoindex{Pascal} and
2352 \addtoindexx{Modula-2}
2353 Modula-2 support the concept of a \doublequote{with}
2354 statement. The with statement specifies a sequence of
2355 executable statements within which the fields of a record
2356 variable may be referenced, unqualified by the name of the
2359 A with statement is represented by a
2360 \addtoindexi{debugging information entry}{with statement entry}
2361 with the tag \DWTAGwithstmtTARG.
2363 A with statement entry may have either a
2365 \DWAThighpc{} pair of attributes
2366 \addtoindexx{low PC attribute}
2367 \addtoindexx{high PC attribute}
2369 \DWATranges{} attribute
2370 \addtoindexx{ranges attribute}
2371 whose values encode the contiguous or non-contiguous address
2372 ranges, respectively, of the machine instructions generated
2373 for the with statement
2374 (see Section \refersec{chap:codeaddressesandranges}).
2376 A\hypertarget{chap:DWATentrypcofwithstmt}{}
2377 with statement entry may also have a
2378 \addtoindexx{entry PC attribute!for with statement}
2379 \DWATentrypc{} attribute
2380 whose value is the address of the first executable instruction
2381 of the with statement (see
2382 Section \refersec{chap:entryaddress}).
2385 The with statement entry has a
2386 \addtoindexx{type attribute}
2387 \DWATtype{} attribute, denoting
2388 the type of record whose fields may be referenced without full
2389 qualification within the body of the statement. It also has
2390 \addtoindexx{location attribute}
2391 a \DWATlocation{} attribute, describing how to find the base
2392 address of the record object referenced within the body of
2396 \section{Try and Catch Block Entries}
2397 \label{chap:tryandcatchblockentries}
2398 \livetarg{chap:tryandcatchblockentries}{}
2399 \textit{In \addtoindex{C++}, a \livelink{chap:lexicalblock}{lexical block} may be
2400 designated as a \doublequote{catch \nolink{block}.}
2401 A catch \nolink{block} is an exception handler that
2402 handles exceptions thrown by an immediately preceding
2403 \doublequote{try \nolink{block}.}
2404 A catch \nolink{block}
2405 designates the type of the exception that it can handle.}
2407 A \livetarg{chap:tryblock}{try block} is represented
2408 by a debugging information entry
2409 \addtoindexx{try block entry}
2410 with the tag \DWTAGtryblockTARG.
2411 A \livetarg{chap:catchblock}{catch block} is represented by
2412 a debugging information entry
2413 \addtoindexx{catch block entry}
2414 with the tag \DWTAGcatchblockTARG.
2416 Both try and catch \nolink{block} entries may have either a
2418 \DWAThighpc{} pair of attributes
2419 \addtoindexx{low PC attribute}
2420 \addtoindexx{high PC attribute}
2422 \DWATranges{} attribute
2423 \addtoindexx{ranges attribute}
2424 whose values encode the contiguous
2425 or non-contiguous address ranges, respectively, of the
2426 machine instructions generated for the \nolink{block}
2427 (see Section \refersec{chap:codeaddressesandranges}).
2429 A\hypertarget{chap:DWATentrypcoftryblock}{}
2430 try or catch\hypertarget{chap:DWATentrypcofcatchblock}{}
2431 block entry may also have a
2432 \addtoindexx{entry PC attribute!for try block}
2433 \addtoindexx{entry PC attribute!for catch block}
2434 \DWATentrypc{} attribute
2435 whose value is the address of the first executable instruction
2436 of the try or catch block
2437 (see Section \refersec{chap:entryaddress}).
2440 Catch \nolink{block} entries have at least one child entry,
2441 an entry representing the type of exception accepted by
2442 that catch \nolink{block}.
2443 This child entry has one of the tags
2444 \DWTAGformalparameter{}\addtoindexx{formal parameter entry!in catch block}
2446 \DWTAGunspecifiedparameters{},
2447 \addtoindexx{unspecified parameters entry!in catch block}
2448 and will have the same form as other parameter entries.
2450 The siblings immediately following a try \nolink{block}
2451 entry are its corresponding catch \nolink{block} entries.
2454 \section{Declarations with Reduced Scope}
2455 \label{declarationswithreducedscope}
2456 \hypertarget{chap:DWATstartscopeofdeclaration}{}
2457 Any debugging information entry for a declaration
2458 (including objects, subprograms, types and modules) whose scope
2459 has an address range that is a subset of the address range for
2460 the lexical scope most closely enclosing the declared entity
2462 \DWATstartscopeDEFN{}\addtoindexx{start scope attribute}
2463 attribute to specify that reduced range of addresses.
2465 There are two cases:
2466 \begin{enumerate}[1. ]
2467 \item If the address range for the scope of the entry
2468 includes all of addresses for the containing scope except
2469 for a contiguous sequence of bytes at the beginning of the
2470 address range for the containing scope, then the address is
2471 specified using a value of class \CLASSconstant.
2473 \begin{enumerate}[a) ]
2474 \item If the address
2475 range of the containing scope is contiguous, the value of
2476 this attribute is the offset in bytes of the beginning of
2477 the address range for the scope of the object from the low
2478 PC value of the debugging information entry that defines
2479 that containing scope.
2480 \item If the address range of the containing
2481 scope is non-contiguous
2482 (see \refersec{chap:noncontiguousaddressranges})
2483 the value of this attribute is the offset in bytes of the
2484 beginning of the address range for the scope of the entity
2485 from the beginning of the first \addtoindex{range list} entry
2486 for the containing scope that is not a base
2487 address entry, a default location
2488 entry or an end-of-list entry.
2492 \item Otherwise, the set of addresses for the scope of the
2493 entity is specified using a value of class \CLASSrnglistsptr{}.
2494 This value indicates the beginning of a \addtoindex{range list}
2495 (see Section \refersec{chap:noncontiguousaddressranges}).
2498 \textit{For example, the scope of a variable may begin somewhere
2499 in the midst of a lexical \livelink{chap:lexicalblock}{block} in a
2500 language that allows executable code in a
2501 \nolink{block} before a variable declaration, or where one declaration
2502 containing initialization code may change the scope of a
2503 subsequent declaration.}
2506 \textit{Consider the following example \addtoindex{C} code:}
2518 \textit{\addtoindex{C} scoping rules require that the value of the
2519 variable \texttt{x} assigned to the variable \texttt{f} in the
2520 initialization sequence is the value of the global variable \texttt{x},
2521 rather than the local \texttt{x}, because the scope of the local variable
2522 \texttt{x} only starts after the full declarator for the local \texttt{x}.}
2524 \textit{Due to optimization, the scope of an object may be
2525 non-contiguous and require use of a \addtoindex{range list} even when
2526 the containing scope is contiguous. Conversely, the scope of
2527 an object may not require its own \addtoindex{range list} even when the
2528 containing scope is non-contiguous.}