1 \chapter{Data Representation}
2 \label{datarep:datarepresentation}
4 This section describes the binary representation of the
5 debugging information entry itself, of the attribute types
6 and of other fundamental elements described above.
9 \section{Vendor Extensibility}
10 \label{datarep:vendorextensibility}
11 \addtoindexx{vendor extensibility}
12 \addtoindexx{vendor specific extensions|see{vendor extensibility}}
15 \addtoindexx{extensibility|see{vendor extensibility}}
16 reserve a portion of the DWARF name space and ranges of
17 enumeration values for use for vendor specific extensions,
18 special labels are reserved for tag names, attribute names,
19 base type encodings, location operations, language names,
20 calling conventions and call frame instructions.
22 The labels denoting the beginning and end of the reserved
23 value range for vendor specific extensions consist of the
24 appropriate prefix (DW\_TAG, DW\_AT, DW\_END, DW\_ATE, DW\_OP,
25 DW\_LANG, DW\_LNE, DW\_CC or DW\_CFA respectively) followed by
26 \hypertarget{chap:DWXXXlohiuser}{}
27 \_lo\_user or \_hi\_user.
28 \textit{For example, for entry tags, the special
29 labels are DW\_TAG\_lo\_user and DW\_TAG\_hi\_user.}
30 Values in the range between \textit{prefix}\_lo\_user
31 and \textit{prefix}\_hi\_user inclusive,
32 are reserved for vendor specific extensions. Vendors may
33 use values in this range without conflicting with current or
34 future system\dash defined values. All other values are reserved
35 for use by the system.
37 \textit{There may also be codes for vendor specific extensions
38 between the number of standard line number opcodes and
39 the first special line number opcode. However, since the
40 number of standard opcodes varies with the DWARF version,
41 the range for extensions is also version dependent. Thus,
42 \livetarg{chap:DWLNSlouser}{DW\_LNS\_lo\_user} and
43 \livetarg{chap:DWLNShiuser}{DW\_LNS\_hi\_user} symbols are not defined.
46 Vendor defined tags, attributes, base type encodings, location
47 atoms, language names, line number actions, calling conventions
48 and call frame instructions, conventionally use the form
49 \text{prefix\_vendor\_id\_name}, where
50 \textit{vendor\_id}\addtoindexx{vendor id} is some identifying
51 character sequence chosen so as to avoid conflicts with
54 To ensure that extensions added by one vendor may be safely
55 ignored by consumers that do not understand those extensions,
56 the following rules should be followed:
57 \begin{enumerate}[1. ]
59 \item New attributes should be added in such a way that a
60 debugger may recognize the format of a new attribute value
61 without knowing the content of that attribute value.
63 \item The semantics of any new attributes should not alter
64 the semantics of previously existing attributes.
66 \item The semantics of any new tags should not conflict with
67 the semantics of previously existing tags.
69 \item Do not add any new forms of attribute value.
74 \section{Reserved Values}
75 \label{datarep:reservedvalues}
76 \subsection{Error Values}
77 \label{datarep:errorvalues}
78 \addtoindexx{reserved values!error}
81 \addtoindexx{error value}
82 a convenience for consumers of DWARF information, the value
83 0 is reserved in the encodings for attribute names, attribute
84 forms, base type encodings, location operations, languages,
85 line number program opcodes, macro information entries and tag
86 names to represent an error condition or unknown value. DWARF
87 does not specify names for these reserved values, since they
88 do not represent valid encodings for the given type and should
89 not appear in DWARF debugging information.
92 \subsection{Initial Length Values}
93 \label{datarep:initiallengthvalues}
94 \addtoindexx{reserved values!initial length}
96 An \livetarg{datarep:initiallengthvalues}{initial length field} is one of the length fields that occur
98 of those DWARF sections that
104 \dotdebugpubnames{}, and
105 \dotdebugpubtypes{}) or the length field
106 that occurs at the beginning of the CIE and FDE structures
107 in the \dotdebugframe{} section.
109 In an \addtoindex{initial length field}, the values \wfffffffzero through
110 \wffffffff are reserved by DWARF to indicate some form of
111 extension relative to \addtoindex{DWARF Version 2}; such values must not
112 be interpreted as a length field. The use of one such value,
113 \xffffffff, is defined below
114 (see Section \refersec{datarep:32bitand64bitdwarfformats});
116 the other values is reserved for possible future extensions.
120 \section{Executable Objects and Shared Objects}
121 \label{datarep:executableobjectsandsharedobjects}
123 The relocated addresses in the debugging information for an
124 executable object are virtual addresses and the relocated
125 addresses in the debugging information for a shared object
126 are offsets relative to the start of the lowest region of
127 memory loaded from that shared object.
129 \textit{This requirement makes the debugging information for
130 shared objects position independent. Virtual addresses in a
131 shared object may be calculated by adding the offset to the
132 base address at which the object was attached. This offset
133 is available in the run\dash time linker\textquoteright s data structures.}
137 \section{32-Bit and 64-Bit DWARF Formats}
138 \label{datarep:32bitand64bitdwarfformats}
139 \hypertarget{datarep:xxbitdwffmt}{}
140 \addtoindexx{32-bit DWARF format}
141 \addtoindexx{64-bit DWARF format}
142 There are two closely related file formats. In the 32\dash bit DWARF
143 format, all values that represent lengths of DWARF sections
144 and offsets relative to the beginning of DWARF sections are
145 represented using 32\dash bits. In the 64\dash bit DWARF format, all
146 values that represent lengths of DWARF sections and offsets
147 relative to the beginning of DWARF sections are represented
148 using 64\dash bits. A special convention applies to the initial
149 length field of certain DWARF sections, as well as the CIE and
150 FDE structures, so that the 32\dash bit and 64\dash bit DWARF formats
151 can coexist and be distinguished within a single linked object.
153 The differences between the 32\dash\ and 64\dash bit
155 detailed in the following:
156 \begin{enumerate}[1. ]
158 \item In the 32\dash bit DWARF format, an
159 \addtoindex{initial length field}
161 \addtoindexx{initial length field!encoding}
162 Section \refersec{datarep:initiallengthvalues})
163 is an unsigned 32\dash bit integer (which
164 must be less than \xfffffffzero); in the 64\dash bit DWARF format,
165 an \addtoindex{initial length field} is 96 bits in size,
168 \item The first 32\dash bits have the value \xffffffff.
170 \item The following 64\dash bits contain the actual length
171 represented as an unsigned 64\dash bit integer.
174 \textit{This representation allows a DWARF consumer to dynamically
175 detect that a DWARF section contribution is using the 64\dash bit
176 format and to adapt its processing accordingly.}
178 \item Section offset and section length
179 \hypertarget{datarep:sectionoffsetlength}{}
180 \addtoindexx{section length!use in headers}
182 \addtoindexx{section offset!use in headers}
183 in the headers of DWARF sections (other
184 \addtoindexx{initial length field}
186 \addtoindex{initial length}
187 fields) are listed following. In the 32\dash bit DWARF format these
188 are 32\dash bit unsigned integer values; in the 64\dash bit DWARF format,
190 \addtoindexx{section length!in .debug\_aranges header}
192 \addtoindexx{section length!in .debug\_pubnames header}
194 \addtoindexx{section length!in .debug\_pubtypes header}
195 unsigned integer values.
199 Section &Name & Role \\ \hline
200 \dotdebugaranges{} & \addtoindex{debug\_info\_offset} & offset in \dotdebuginfo{} \\
201 \dotdebugframe{}/CIE & \addtoindex{CIE\_id} & CIE distinguished value \\
202 \dotdebugframe{}/FDE & \addtoindex{CIE\_pointer} & offset in \dotdebugframe{} \\
203 \dotdebuginfo{} & \addtoindex{debug\_abbrev\_offset} & offset in \dotdebugabbrev{} \\
204 \dotdebugline{} & \addtoindex{header\_length} & length of header itself \\
205 \dotdebugpubnames{} & \addtoindex{debug\_info\_offset} & offset in \dotdebuginfo{} \\
206 & \addtoindex{debug\_info\_length} & length of \dotdebuginfo{} \\
208 \dotdebugpubtypes{} & \addtoindex{debug\_info\_offset} & offset in \dotdebuginfo{} \\
209 & \addtoindex{debug\_info\_length} & length of \dotdebuginfo{} \\
211 \dotdebugtypes{} & \addtoindex{debug\_abbrev\_offset} & offset in \dotdebugabbrev{} \\
212 & \addtoindex{type\_offset} & offset in \dotdebugtypes{} \\
217 The \texttt{CIE\_id} field in a CIE structure must be 64 bits because
218 it overlays the \texttt{CIE\_pointer} in a FDE structure; this implicit
219 union must be accessed to distinguish whether a CIE or FDE is
220 present, consequently, these two fields must exactly overlay
221 each other (both offset and size).
223 \item Within the body of the \dotdebuginfo{} or \dotdebugtypes{}
224 section, certain forms of attribute value depend on the choice
225 of DWARF format as follows. For the 32\dash bit DWARF format,
226 the value is a 32\dash bit unsigned integer; for the 64\dash bit DWARF
227 format, the value is a 64\dash bit unsigned integer.
230 Form & Role \\ \hline
231 \livelink{chap:DWFORMrefaddr}{DW\_FORM\_ref\_addr}& offset in \dotdebuginfo{} \\
232 \livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}& offset in a section other than \\
233 &\dotdebuginfo{} or \dotdebugstr{} \\
234 \livelink{chap:DWFORMstrp}{DW\_FORM\_strp}&offset in \dotdebugstr{} \\
235 \livelink{chap:DWOPcallref}{DW\_OP\_call\_ref}&offset in \dotdebuginfo{} \\
239 \item Within the body of the \dotdebugpubnames{} and
241 sections, the representation of the first field
242 of each tuple (which represents an offset in the
244 section) depends on the DWARF format as follows: in the
245 32\dash bit DWARF format, this field is a 32\dash bit unsigned integer;
246 in the 64\dash bit DWARF format, it is a 64\dash bit unsigned integer.
251 The 32\dash bit and 64\dash bit DWARF format conventions must \emph{not} be
252 intermixed within a single compilation unit.
254 \textit{Attribute values and section header fields that represent
255 addresses in the target program are not affected by these
258 A DWARF consumer that supports the 64\dash bit DWARF format must
259 support executables in which some compilation units use the
260 32\dash bit format and others use the 64\dash bit format provided that
261 the combination links correctly (that is, provided that there
262 are no link\dash time errors due to truncation or overflow). (An
263 implementation is not required to guarantee detection and
264 reporting of all such errors.)
266 \textit{It is expected that DWARF producing compilers will \emph{not} use
267 the 64\dash bit format \emph{by default}. In most cases, the division of
268 even very large applications into a number of executable and
269 shared objects will suffice to assure that the DWARF sections
270 within each individual linked object are less than 4 GBytes
271 in size. However, for those cases where needed, the 64\dash bit
272 format allows the unusual case to be handled as well. Even
273 in this case, it is expected that only application supplied
274 objects will need to be compiled using the 64\dash bit format;
275 separate 32\dash bit format versions of system supplied shared
276 executable libraries can still be used.}
280 \section{Format of Debugging Information}
281 \label{datarep:formatofdebugginginformation}
283 For each compilation unit compiled with a DWARF producer,
284 a contribution is made to the \dotdebuginfo{} section of
285 the object file. Each such contribution consists of a
286 compilation unit header
287 (see Section \refersec{datarep:compilationunitheader})
289 single \livelink{chap:DWTAGcompileunit}{DW\_TAG\_compile\_unit} or
290 \livelink{chap:DWTAGpartialunit}{DW\_TAG\_partial\_unit} debugging
291 information entry, together with its children.
293 For each type defined in a compilation unit, a contribution may
294 be made to the \dotdebugtypes{}
295 section of the object file. Each
296 such contribution consists of a
297 \addtoindex{type unit} header
298 (see Section \refersec{datarep:typeunitheader})
299 followed by a \livelink{chap:DWTAGtypeunit}{DW\_TAG\_type\_unit} entry, together with
302 Each debugging information entry begins with a code that
303 represents an entry in a separate
304 \addtoindex{abbreviations table}. This
305 code is followed directly by a series of attribute values.
307 The appropriate entry in the
308 \addtoindex{abbreviations table} guides the
309 interpretation of the information contained directly in the
311 \dotdebugtypes{} section.
314 Multiple debugging information entries may share the same
315 abbreviation table entry. Each compilation unit is associated
316 with a particular abbreviation table, but multiple compilation
317 units may share the same table.
318 \subsection{Unit Headers}
319 \label{datarep:unitheaders}
321 \subsubsection{Compilation Unit Header}
322 \label{datarep:compilationunitheader}
323 \begin{enumerate}[1. ]
325 \item \texttt{unit\_length} (\livelink{datarep:initiallengthvalues}{initial length}) \\
326 \addttindexx{unit\_length}
327 A 4\dash byte or 12\dash byte
328 \addtoindexx{initial length}
329 unsigned integer representing the length
330 of the \dotdebuginfo{}
331 contribution for that compilation unit,
332 not including the length field itself. In the \thirtytwobitdwarfformat,
333 this is a 4\dash byte unsigned integer (which must be less
334 than \xfffffffzero); in the \sixtyfourbitdwarfformat, this consists
335 of the 4\dash byte value \wffffffff followed by an 8\dash byte unsigned
336 integer that gives the actual length
337 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
340 \item \texttt{version} (\addtoindex{uhalf}) \\
341 A 2\dash byte unsigned integer representing the version of the
342 DWARF information for the compilation unit \addtoindexx{version number!compilation unit}
343 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
344 The value in this field is 4.
346 \item \addttindex{debug\_abbrev\_offset} (\livelink{datarep:sectionoffsetlength}{section offset}) \\
348 \addtoindexx{section offset!in .debug\_info header}
349 4\dash byte or 8\dash byte unsigned offset into the
351 section. This offset associates the compilation unit with a
352 particular set of debugging information entry abbreviations. In
353 the \thirtytwobitdwarfformat, this is a 4\dash byte unsigned length;
354 in the \sixtyfourbitdwarfformat, this is an 8\dash byte unsigned length
355 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
357 \item \texttt{address\_size} (\addtoindex{ubyte}) \\
358 A 1\dash byte unsigned integer representing the size in bytes of
359 \addttindexx{address\_size}
360 an address on the target architecture. If the system uses
361 \addtoindexx{address space!segmented}
362 segmented addressing, this value represents the size of the
363 offset portion of an address.
368 \subsubsection{Type Unit Header}
369 \label{datarep:typeunitheader}
371 The header for the series of debugging information entries
372 contributing to the description of a type that has been
373 placed in its own \addtoindex{type unit}, within the
374 \dotdebugtypes{} section,
375 consists of the following information:
376 \begin{enumerate}[1. ]
378 \item \texttt{unit\_length} (\livelink{datarep:initiallengthvalues}{initial length}) \\
379 \addttindexx{unit\_length}
380 A 4\dash byte or 12\dash byte unsigned integer
381 \addtoindexx{initial length}
382 representing the length
383 of the \dotdebugtypes{} contribution for that compilation unit,
384 not including the length field itself. In the \thirtytwobitdwarfformat,
385 this is a 4\dash byte unsigned integer (which must be
386 less than \xfffffffzero); in the \sixtyfourbitdwarfformat, this
387 consists of the 4\dash byte value \wffffffff followed by an
388 8\dash byte unsigned integer that gives the actual length
389 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
392 \item \texttt{version} (\addtoindex{uhalf}) \\
393 A 2\dash byte unsigned integer representing the version of the
394 DWARF information for the
395 compilation unit\addtoindexx{version number!type unit}
396 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
397 The value in this field is 4.
399 \item \addttindex{debug\_abbrev\_offset} (\livelink{datarep:sectionoffsetlength}{section offset}) \\
401 \addtoindexx{section offset!in .debug\_types header}
402 4\dash byte or 8\dash byte unsigned offset into the
404 section. This offset associates the compilation unit with a
405 particular set of debugging information entry abbreviations. In
406 the \thirtytwobitdwarfformat, this is a 4\dash byte unsigned length;
407 in the \sixtyfourbitdwarfformat, this is an 8\dash byte unsigned length
408 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
410 \item \texttt{address\_size} (ubyte) \\
411 A 1\dash byte unsigned integer representing the size
412 \addtoindexx{size of an address}
414 \addttindexx{address\_size}
415 an address on the target architecture. If the system uses
416 \addtoindexx{address space!segmented}
417 segmented addressing, this value represents the size of the
418 offset portion of an address.
421 \item \texttt{type\_signature} (8\dash byte unsigned integer) \\
422 \addtoindexx{type signature}
424 \addttindexx{type\_signature}
425 64\dash bit unique signature (see Section
426 \refersec{datarep:typesignaturecomputation})
427 of the type described in this type
430 \textit{An attribute that refers (using
431 \livelink{chap:DWFORMrefsig8}{DW\_FORM\_ref\_sig8}) to
432 the primary type contained in this
433 \addtoindex{type unit} uses this value.}
436 \item \texttt{type\_offset} (\livelink{datarep:sectionoffsetlength}{section offset}) \\
437 \addttindexx{type\_offset}
438 A 4\dash byte or 8\dash byte unsigned offset
439 \addtoindexx{section offset!in .debug\_types header}
440 relative to the beginning
441 of the \addtoindex{type unit} header.
442 This offset refers to the debugging
443 information entry that describes the type. Because the type
444 may be nested inside a namespace or other structures, and may
445 contain references to other types that have not been placed in
446 separate type units, it is not necessarily either the first or
447 the only entry in the type unit. In the \thirtytwobitdwarfformat,
448 this is a 4\dash byte unsigned length; in the \sixtyfourbitdwarfformat,
449 this is an 8\dash byte unsigned length
450 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
454 \subsection{Debugging Information Entry}
455 \label{datarep:debugginginformationentry}
457 Each debugging information entry begins with an unsigned LEB128
458 number containing the abbreviation code for the entry. This
459 code represents an entry within the abbreviations table
460 associated with the compilation unit containing this entry. The
461 abbreviation code is followed by a series of attribute values.
463 On some architectures, there are alignment constraints on
464 section boundaries. To make it easier to pad debugging
465 information sections to satisfy such constraints, the
466 abbreviation code 0 is reserved. Debugging information entries
467 consisting of only the abbreviation code 0 are considered
470 \subsection{Abbreviations Tables}
471 \label{datarep:abbreviationstables}
473 The abbreviations tables for all compilation units
474 are contained in a separate object file section called
476 As mentioned before, multiple compilation
477 units may share the same abbreviations table.
479 The abbreviations table for a single compilation unit consists
480 of a series of abbreviation declarations. Each declaration
481 specifies the tag and attributes for a particular form of
482 debugging information entry. Each declaration begins with
483 an unsigned LEB128 number representing the abbreviation
484 code itself. It is this code that appears at the beginning
485 of a debugging information entry in the
488 section. As described above, the abbreviation
489 code 0 is reserved for null debugging information entries. The
490 abbreviation code is followed by another unsigned LEB128
491 number that encodes the entry\textquoteright s tag. The encodings for the
492 tag names are given in
493 Table \refersec{tab:tagencodings}.
496 \setlength{\extrarowheight}{0.1cm}
497 \begin{longtable}{l|l}
499 \caption{Tag encodings} \label{tab:tagencodings} \\
500 \hline \bfseries Tag name&\bfseries Value\\ \hline
502 \bfseries Tag name&\bfseries Value \\ \hline
504 \hline \emph{Continued on next page}
507 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
509 \livelink{chap:DWTAGarraytype}{DW\_TAG\_array\_type} &0x01 \\
510 \livelink{chap:DWTAGclasstype}{DW\_TAG\_class\_type}&0x02 \\
511 \livelink{chap:DWTAGentrypoint}{DW\_TAG\_entry\_point}&0x03 \\
512 \livelink{chap:DWTAGenumerationtype}{DW\_TAG\_enumeration\_type}&0x04 \\
513 \livelink{chap:DWTAGformalparameter}{DW\_TAG\_formal\_parameter}&0x05 \\
514 \livelink{chap:DWTAGimporteddeclaration}{DW\_TAG\_imported\_declaration}&0x08 \\
515 \livelink{chap:DWTAGlabel}{DW\_TAG\_label}&0x0a \\
516 \livelink{chap:DWTAGlexicalblock}{DW\_TAG\_lexical\_block}&0x0b \\
517 \livelink{chap:DWTAGmember}{DW\_TAG\_member}&0x0d \\
518 \livelink{chap:DWTAGpointertype}{DW\_TAG\_pointer\_type}&0x0f \\
519 \livelink{chap:DWTAGreferencetype}{DW\_TAG\_reference\_type}&0x10 \\
520 \livelink{chap:DWTAGcompileunit}{DW\_TAG\_compile\_unit}&0x11 \\
521 \livelink{chap:DWTAGstringtype}{DW\_TAG\_string\_type}&0x12 \\
522 \livelink{chap:DWTAGstructuretype}{DW\_TAG\_structure\_type}&0x13 \\
523 \livelink{chap:DWTAGsubroutinetype}{DW\_TAG\_subroutine\_type}&0x15 \\
524 \livelink{chap:DWTAGtypedef}{DW\_TAG\_typedef}&0x16 \\
525 \livelink{chap:DWTAGuniontype}{DW\_TAG\_union\_type}&0x17 \\
526 \livelink{chap:DWTAGunspecifiedparameters}{DW\_TAG\_unspecified\_parameters}&0x18 \\
527 \livelink{chap:DWTAGvariant}{DW\_TAG\_variant}&0x19 \\
528 \livelink{chap:DWTAGcommonblock}{DW\_TAG\_common\_block}&0x1a \\
529 \livelink{chap:DWTAGcommoninclusion}{DW\_TAG\_common\_inclusion}&0x1b \\
530 \livelink{chap:DWTAGinheritance}{DW\_TAG\_inheritance}&0x1c \\
531 \livelink{chap:DWTAGinlinedsubroutine}{DW\_TAG\_inlined\_subroutine}&0x1d \\
532 \livelink{chap:DWTAGmodule}{DW\_TAG\_module}&0x1e \\
533 \livelink{chap:DWTAGptrtomembertype}{DW\_TAG\_ptr\_to\_member\_type}&0x1f \\
534 \livelink{chap:DWTAGsettype}{DW\_TAG\_set\_type}&0x20 \\
535 \livelink{chap:DWTAGsubrangetype}{DW\_TAG\_subrange\_type}&0x21 \\
536 \livelink{chap:DWTAGwithstmt}{DW\_TAG\_with\_stmt}&0x22 \\
537 \livelink{chap:DWTAGaccessdeclaration}{DW\_TAG\_access\_declaration}&0x23 \\
538 \livelink{chap:DWTAGbasetype}{DW\_TAG\_base\_type}&0x24 \\
539 \livelink{chap:DWTAGcatchblock}{DW\_TAG\_catch\_block}&0x25 \\
540 \livelink{chap:DWTAGconsttype}{DW\_TAG\_const\_type}&0x26 \\
541 \livelink{chap:DWTAGconstant}{DW\_TAG\_constant}&0x27 \\
542 \livelink{chap:DWTAGenumerator}{DW\_TAG\_enumerator}&0x28 \\
543 \livelink{chap:DWTAGfiletype}{DW\_TAG\_file\_type}&0x29 \\
544 \livelink{chap:DWTAGfriend}{DW\_TAG\_friend}&0x2a \\
545 \livelink{chap:DWTAGnamelist}{DW\_TAG\_namelist}&0x2b \\
546 \livelink{chap:DWTAGnamelistitem}{DW\_TAG\_namelist\_item}&0x2c \\
547 \livelink{chap:DWTAGpackedtype}{DW\_TAG\_packed\_type}&0x2d \\
548 \livelink{chap:DWTAGsubprogram}{DW\_TAG\_subprogram}&0x2e \\
549 \livelink{chap:DWTAGtemplatetypeparameter}{DW\_TAG\_template\_type\_parameter}&0x2f \\
550 \livelink{chap:DWTAGtemplatevalueparameter}{DW\_TAG\_template\_value\_parameter}&0x30 \\
551 \livelink{chap:DWTAGthrowntype}{DW\_TAG\_thrown\_type}&0x31 \\
552 \livelink{chap:DWTAGtryblock}{DW\_TAG\_try\_block}&0x32 \\
553 \livelink{chap:DWTAGvariantpart}{DW\_TAG\_variant\_part}&0x33 \\
554 \livelink{chap:DWTAGvariable}{DW\_TAG\_variable}&0x34 \\
555 \livelink{chap:DWTAGvolatiletype}{DW\_TAG\_volatile\_type}&0x35 \\
556 \livelink{chap:DWTAGdwarfprocedure}{DW\_TAG\_dwarf\_procedure}&0x36 \\
557 \livelink{chap:DWTAGrestricttype}{DW\_TAG\_restrict\_type}&0x37 \\
558 \livelink{chap:DWTAGinterfacetype}{DW\_TAG\_interface\_type}&0x38 \\
559 \livelink{chap:DWTAGnamespace}{DW\_TAG\_namespace}&0x39 \\
560 \livelink{chap:DWTAGimportedmodule}{DW\_TAG\_imported\_module}&0x3a \\
561 \livelink{chap:DWTAGunspecifiedtype}{DW\_TAG\_unspecified\_type}&0x3b \\
562 \livelink{chap:DWTAGpartialunit}{DW\_TAG\_partial\_unit}&0x3c \\
563 \livelink{chap:DWTAGimportedunit}{DW\_TAG\_imported\_unit}&0x3d \\
564 \livelink{chap:DWTAGcondition}{DW\_TAG\_condition}&\xiiif \\
565 \livelink{chap:DWTAGsharedtype}{DW\_TAG\_shared\_type}&0x40 \\
566 \livelink{chap:DWTAGtypeunit}{DW\_TAG\_type\_unit} \ddag &0x41 \\
567 \livelink{chap:DWTAGrvaluereferencetype}{DW\_TAG\_rvalue\_reference\_type} \ddag &0x42 \\
568 \livelink{chap:DWTAGtemplatealias}{DW\_TAG\_template\_alias} \ddag &0x43 \\
569 \livelink{chap:DWXXXlohiuser}{DW\_TAG\_lo\_user}&0x4080 \\
570 \livelink{chap:DWXXXlohiuser}{DW\_TAG\_hi\_user}&\xffff \\
574 Following the tag encoding is a 1\dash byte value that determines
575 whether a debugging information entry using this abbreviation
576 has child entries or not. If the value is
577 \livetarg{chap:DWCHILDRENyes}{DW\_CHILDREN\_yes},
578 the next physically succeeding entry of any debugging
579 information entry using this abbreviation is the first
580 child of that entry. If the 1\dash byte value following the
581 abbreviation\textquoteright s tag encoding is
582 \livetarg{chap:DWCHILDRENno}{DW\_CHILDREN\_no}, the next
583 physically succeeding entry of any debugging information entry
584 using this abbreviation is a sibling of that entry. (Either
585 the first child or sibling entries may be null entries). The
586 encodings for the child determination byte are given in
587 Table \refersec{tab:childdeterminationencodings}
589 Section \refersec{chap:relationshipofdebugginginformationentries},
590 each chain of sibling entries is terminated by a null entry.)
594 \setlength{\extrarowheight}{0.1cm}
595 \begin{longtable}{l|l}
596 \caption{Child determination encodings}
597 \label{tab:childdeterminationencodings}
598 \addtoindexx{Child determination encodings} \\
599 \hline \bfseries Children determination name&\bfseries Value \\ \hline
601 \bfseries Children determination name&\bfseries Value \\ \hline
603 \hline \emph{Continued on next page}
607 \livelink{chap:DWCHILDRENno}{DW\_CHILDREN\_no}&0x00 \\
608 \livelink{chap:DWCHILDRENyes}{DW\_CHILDREN\_yes}&0x01 \\ \hline
613 Finally, the child encoding is followed by a series of
614 attribute specifications. Each attribute specification
615 consists of two parts. The first part is an unsigned LEB128
616 number representing the attribute\textquoteright s name. The second part
617 is an unsigned LEB128 number representing the attribute\textquoteright s
618 form. The series of attribute specifications ends with an
619 entry containing 0 for the name and 0 for the form.
622 \livetarg{chap:DWFORMindirect}{DW\_FORM\_indirect} is a special case. For
623 attributes with this form, the attribute value itself in the
626 section begins with an unsigned
627 LEB128 number that represents its form. This allows producers
628 to choose forms for particular attributes
629 \addtoindexx{abbreviations table!dynamic forms in}
631 without having to add a new entry to the abbreviations table.
633 The abbreviations for a given compilation unit end with an
634 entry consisting of a 0 byte for the abbreviation code.
637 Appendix \refersec{app:compilationunitsandabbreviationstableexample}
638 for a depiction of the organization of the
639 debugging information.}
642 \subsection{Attribute Encodings}
643 \label{datarep:attributeencodings}
645 The encodings for the attribute names are given in
646 Table \refersec{tab:attributeencodings}.
648 The attribute form governs how the value of the attribute is
649 encoded. There are nine classes of form, listed below. Each
650 class is a set of forms which have related representations
651 and which are given a common interpretation according to the
652 attribute in which the form is used.
654 Form \livetarg{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}
656 \addtoindexx{rangelistptr class}
658 \addtoindexx{macptr class}
660 \addtoindexx{loclistptr class}
662 \addtoindexx{lineptr class}
663 namely \livelink{chap:classlineptr}{lineptr},
664 \livelink{chap:classloclistptr}{loclistptr},
665 \livelink{chap:classmacptr}{macptr} or
666 \livelink{chap:classrangelistptr}{rangelistptr}; the list
667 of classes allowed by the applicable attribute in
668 Table \refersec{tab:attributeencodings}
669 determines the class of the form.
671 \textit{In DWARF V3 the forms \livelink{chap:DWFORMdata4}{DW\_FORM\_data4} and
672 \livelink{chap:DWFORMdata8}{DW\_FORM\_data8} were
673 \addtoindexx{lineptr class}
675 \addtoindexx{rangelistptr class}
677 \addtoindexx{macptr class}
679 \addtoindexx{loclistptr class}
680 class constant \addtoindexx{constant class}
681 or one of the classes
682 \livelink{chap:classlineptr}{lineptr},
683 \livelink{chap:classloclistptr}{loclistptr},
684 \livelink{chap:classmacptr}{macptr} or
685 \livelink{chap:classrangelistptr}{rangelistptr}, depending on context. In
687 \livelink{chap:DWFORMdata4}{DW\_FORM\_data4} and
688 \livelink{chap:DWFORMdata8}{DW\_FORM\_data8} are members of class
689 constant in all cases.
691 \livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset} replaces
692 their usage for the other classes.}
694 Each possible form belongs to one or more of the following classes:
697 \item \livelinki{chap:classaddress}{address}{address class} \\
698 \livetarg{datarep:classaddress}{}
699 Represented as an object of appropriate size to hold an
700 address on the target machine
701 (\livetarg{chap:DWFORMaddr}{DW\_FORM\_addr}).
703 encoded in the compilation unit header
704 (see Section \refersec{datarep:compilationunitheader}).
705 This address is relocatable in a relocatable object file and
706 is relocated in an executable file or shared object.
709 \item \livelink{chap:classblock}{block} \\
710 \livetarg{datarep:classblock}{}
711 Blocks come in four forms:
713 \begin{myindentpara}{1cm}
714 A 1\dash byte length followed by 0 to 255 contiguous information
715 bytes (\livetarg{chap:DWFORMblock1}{DW\_FORM\_block1}).
718 \begin{myindentpara}{1cm}
719 A 2\dash byte length followed by 0 to 65,535 contiguous information
720 bytes (\livetarg{chap:DWFORMblock2}{DW\_FORM\_block2}).
723 \begin{myindentpara}{1cm}
724 A 4\dash byte length followed by 0 to 4,294,967,295 contiguous
725 information bytes (\livetarg{chap:DWFORMblock4}{DW\_FORM\_block4}).
728 \begin{myindentpara}{1cm}
729 An unsigned LEB128 length followed by the number of bytes
730 specified by the length (\livetarg{chap:DWFORMblock}{DW\_FORM\_block}).
733 In all forms, the length is the number of information bytes
734 that follow. The information bytes may contain any mixture
735 of relocated (or relocatable) addresses, references to other
736 debugging information entries or data bytes.
738 \item \livelinki{chap:classconstant}{constant}{constant class} \\
739 \livetarg{datarep:classconstant}{}
740 There are six forms of constants. There are fixed length
741 constant data forms for one, two, four and eight byte values
743 \livetarg{chap:DWFORMdata1}{DW\_FORM\_data1},
744 \livetarg{chap:DWFORMdata2}{DW\_FORM\_data2},
745 \livetarg{chap:DWFORMdata4}{DW\_FORM\_data4},
746 and \livetarg{chap:DWFORMdata8}{DW\_FORM\_data8}).
747 There are also variable length constant
748 data forms encoded using LEB128 numbers (see below). Both
749 signed (\livetarg{chap:DWFORMsdata}{DW\_FORM\_sdata}) and unsigned
750 (\livetarg{chap:DWFORMudata}{DW\_FORM\_udata}) variable
751 length constants are available
753 The data in \livelink{chap:DWFORMdata1}{DW\_FORM\_data1},
754 \livelink{chap:DWFORMdata2}{DW\_FORM\_data2},
755 \livelink{chap:DWFORMdata4}{DW\_FORM\_data4} and
756 \livelink{chap:DWFORMdata8}{DW\_FORM\_data8}
757 can be anything. Depending on context, it may
758 be a signed integer, an unsigned integer, a floating\dash point
759 constant, or anything else. A consumer must use context to
760 know how to interpret the bits, which if they are target
761 machine data (such as an integer or floating point constant)
762 will be in target machine byte\dash order.
764 \textit{If one of the \livetarg{chap:DWFORMdata}{DW\_FORM\_data}\textless n\textgreater
765 forms is used to represent a
766 signed or unsigned integer, it can be hard for a consumer
767 to discover the context necessary to determine which
768 interpretation is intended. Producers are therefore strongly
769 encouraged to use \livelink{chap:DWFORMsdata}{DW\_FORM\_sdata} or
770 \livelink{chap:DWFORMudata}{DW\_FORM\_udata} for signed and
771 unsigned integers respectively, rather than
772 \livelink{chap:DWFORMdata}{DW\_FORM\_data}\textless n\textgreater.}
775 \item \livelinki{chap:classexprloc}{exprloc}{exprloc class} \\
776 \livetarg{datarep:classexprloc}{}
777 This is an unsigned LEB128 length followed by the
778 number of information bytes specified by the length
779 (\livetarg{chap:DWFORMexprloc}{DW\_FORM\_exprloc}).
780 The information bytes contain a DWARF expression
781 (see Section \refersec{chap:dwarfexpressions})
782 or location description
783 (see Section \refersec{chap:locationdescriptions}).
785 \item \livelinki{chap:classflag}{flag}{flag class} \\
786 \livetarg{datarep:classflag}{}
787 A flag \addtoindexx{flag class}
788 is represented explicitly as a single byte of data
789 (\livetarg{chap:DWFORMflag}{DW\_FORM\_flag}) or
790 implicitly (\livetarg{chap:DWFORMflagpresent}{DW\_FORM\_flag\_present}).
792 first case, if the \nolink{flag} has value zero, it indicates the
793 absence of the attribute; if the \nolink{flag} has a non\dash zero value,
794 it indicates the presence of the attribute. In the second
795 case, the attribute is implicitly indicated as present, and
796 no value is encoded in the debugging information entry itself.
798 \item \livelinki{chap:classlineptr}{lineptr}{lineptr class} \\
799 \livetarg{datarep:classlineptr}{}
800 This is an offset into
801 \addtoindexx{section offset!in class lineptr value}
803 \dotdebugline{} section
804 (\livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}).
805 It consists of an offset from the beginning of the
807 section to the first byte of
808 the data making up the line number list for the compilation
810 It is relocatable in a relocatable object file, and
811 relocated in an executable or shared object. In the
812 \thirtytwobitdwarfformat, this offset is a 4\dash byte unsigned value;
813 in the \sixtyfourbitdwarfformat, it is an 8\dash byte unsigned value
814 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
817 \item \livelinki{chap:classloclistptr}{loclistptr}{loclistptr class} \\
818 \livetarg{datarep:classloclistptr}{}
819 This is an offset into the
822 (\livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}).
823 It consists of an offset from the
824 \addtoindexx{section offset!in class loclistptr value}
827 section to the first byte of
828 the data making up the
829 \addtoindex{location list} for the compilation unit.
830 It is relocatable in a relocatable object file, and
831 relocated in an executable or shared object. In the
832 \thirtytwobitdwarfformat, this offset is a 4\dash byte unsigned value;
833 in the \sixtyfourbitdwarfformat, it is an 8\dash byte unsigned value
834 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
837 \item \livelinki{chap:classmacptr}{macptr}{macptr class} \\
838 \livetarg{datarep:classmacptr}{}
840 \addtoindexx{section offset!in class macptr value}
842 \dotdebugmacinfo{} section
843 (\livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}).
844 It consists of an offset from the
845 beginning of the \dotdebugmacinfo{}
846 section to the first byte of
847 the data making up the macro information list for the compilation
849 It is relocatable in a relocatable object file, and
850 relocated in an executable or shared object. In the
851 \thirtytwobitdwarfformat, this offset is a 4\dash byte unsigned value;
852 in the \sixtyfourbitdwarfformat, it is an 8\dash byte unsigned value
853 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
856 \item \livelinki{chap:classrangelistptr}{rangelistptr}{rangelistptr class} \\
857 \livetarg{datarep:classrangelistptr}{}
859 \addtoindexx{section offset!in class rangelistptr value}
860 offset into the \dotdebugranges{} section
861 (\livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset}).
863 offset from the beginning of the
864 \dotdebugranges{} section
865 to the beginning of the non\dash contiguous address ranges
866 information for the referencing entity.
868 a relocatable object file, and relocated in an executable or
869 shared object. In the \thirtytwobitdwarfformat, this offset
870 is a 4\dash byte unsigned value; in the 64\dash bit DWARF
871 format, it is an 8\dash byte unsigned value (see Section
872 \refersec{datarep:32bitand64bitdwarfformats}).
875 \textit{Because classes \livelink{chap:classlineptr}{lineptr},
876 \livelink{chap:classloclistptr}{loclistptr},
877 \livelink{chap:classmacptr}{macptr} and
878 \livelink{chap:classrangelistptr}{rangelistptr}
879 share a common representation, it is not possible for an
880 attribute to allow more than one of these classes}
884 \item \livelinki{chap:classreference}{reference}{reference class} \\
885 \livetarg{datarep:classreference}{}
886 There are three types of reference.
889 \addtoindexx{reference class}
890 first type of reference can identify any debugging
891 information entry within the containing unit.
894 \addtoindexx{section offset!in class reference value}
895 offset from the first byte of the compilation
896 header for the compilation unit containing the reference. There
897 are five forms for this type of reference. There are fixed
898 length forms for one, two, four and eight byte offsets
899 (respectively, \livetarg{chap:DWFORMref1}{DW\_FORM\_ref1},
900 \livetarg{chap:DWFORMref2}{DW\_FORM\_ref2},
901 \livetarg{chap:DWFORMref4}{DW\_FORM\_ref4},
902 and \livetarg{chap:DWFORMref8}{DW\_FORM\_ref8}).
903 There is also an unsigned variable
904 length offset encoded form that uses unsigned LEB128 numbers
905 (\livetarg{chap:DWFORMrefudata}{DW\_FORM\_ref\_udata}).
906 Because this type of reference is within
907 the containing compilation unit no relocation of the value
910 The second type of reference can identify any debugging
911 information entry within a
912 \dotdebuginfo{} section; in particular,
913 it may refer to an entry in a different compilation unit
914 from the unit containing the reference, and may refer to an
915 entry in a different shared object. This type of reference
916 (\livetarg{chap:DWFORMrefaddr}{DW\_FORM\_ref\_addr})
917 is an offset from the beginning of the
919 section of the target executable or shared object;
920 it is relocatable in a relocatable object file and frequently
921 relocated in an executable file or shared object. For
922 references from one shared object or static executable file
923 to another, the relocation and identification of the target
924 object must be performed by the consumer. In the
925 \thirtytwobitdwarfformat, this offset is a 4\dash byte unsigned value;
926 in the \sixtyfourbitdwarfformat, it is an 8\dash byte
928 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
930 \textit{A debugging information entry that may be referenced by
931 another compilation unit using
932 \livelink{chap:DWFORMrefaddr}{DW\_FORM\_ref\_addr} must have a
933 global symbolic name.}
935 \textit{For a reference from one executable or shared object to
936 another, the reference is resolved by the debugger to identify
937 the shared object or executable and the offset into that
938 object\textquoteright s \dotdebuginfo{}
939 section in the same fashion as the run
940 time loader, either when the debug information is first read,
941 or when the reference is used.}
943 The third type of reference can identify any debugging
944 information type entry that has been placed in its own
945 \addtoindex{type unit}. This type of
946 reference (\livetarg{chap:DWFORMrefsig8}{DW\_FORM\_ref\_sig8}) is the
947 \addtoindexx{type signature}
948 64\dash bit type signature
949 (see Section \refersec{datarep:typesignaturecomputation})
953 \textit{The use of compilation unit relative references will reduce the
954 number of link\dash time relocations and so speed up linking. The
955 use of the second and third type of reference allows for the
956 sharing of information, such as types, across compilation
959 \textit{A reference to any kind of compilation unit identifies the
960 debugging information entry for that unit, not the preceding
963 \item \livelinki{chap:classstring}{string}{string class} \\
964 \livetarg{datarep:classstring}{}
965 A string is a sequence of contiguous non\dash null bytes followed by
967 \addtoindexx{string class}
968 A string may be represented immediately in the
969 debugging information entry itself
970 (\livetarg{chap:DWFORMstring}{DW\_FORM\_string}), or may
972 \addtoindexx{section offset!in class string value}
973 offset into a string table contained in
974 the \dotdebugstr{} section of the object file
975 (\livetarg{chap:DWFORMstrp}{DW\_FORM\_strp}). In
976 the \thirtytwobitdwarfformat, the representation of a
977 \livelink{chap:DWFORMstrp}{DW\_FORM\_strp}
978 value is a 4\dash byte unsigned offset; in the \sixtyfourbitdwarfformat,
979 it is an 8\dash byte unsigned offset
980 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
982 If the \livelink{chap:DWATuseUTF8}{DW\_AT\_use\_UTF8}
983 \addtoindexx{use UTF8 attribute}\addtoindexx{UTF-8} attribute is specified for the
984 compilation unit entry, string values are encoded using the
985 UTF\dash 8 (\addtoindex{Unicode} Transformation Format\dash 8) from the Universal
986 Character Set standard (ISO/IEC 10646\dash 1:1993). Otherwise,
987 the string representation is unspecified.
989 \textit{The \addtoindex{Unicode} Standard Version 3 is fully compatible with
990 ISO/IEC 10646\dash 1:1993. It contains all the same characters
991 and encoding points as ISO/IEC 10646, as well as additional
992 information about the characters and their use.}
994 \textit{Earlier versions of DWARF did not specify the representation
995 of strings; for compatibility, this version also does
996 not. However, the UTF\dash 8 representation is strongly recommended.}
1000 In no case does an attribute use
1001 \addtoindexx{rangelistptr class}
1003 \addtoindexx{loclistptr class}
1005 \addtoindexx{lineptr class}
1007 \addtoindexx{macptr class}
1008 classes \livelink{chap:classlineptr}{lineptr},
1009 \livelink{chap:classloclistptr}{loclistptr}, \livelink{chap:classmacptr}{macptr} or
1010 \livelink{chap:classrangelistptr}{rangelistptr} to point into either the
1011 \dotdebuginfo{} or \dotdebugstr{} section.
1013 The form encodings are listed in
1014 Table \refersec{tab:attributeformencodings}.
1018 \setlength{\extrarowheight}{0.1cm}
1019 \begin{longtable}{l|l|l}
1020 \caption{Attribute encodings}
1021 \label{tab:attributeencodings}
1022 \addtoindexx{attribute encodings} \\
1023 \hline \bfseries Attribute name&\bfseries Value &\bfseries Classes \\ \hline
1025 \bfseries Attribute name&\bfseries Value &\bfseries Classes\\ \hline
1027 \hline \emph{Continued on next page}
1030 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
1032 \livelink{chap:DWATsibling}{DW\_AT\_sibling}&0x01&\livelink{chap:classreference}{reference}
1033 \addtoindexx{sibling attribute!encoding} \\
1034 \livelink{chap:DWATlocation}{DW\_AT\_location}&0x02&\livelink{chap:classexprloc}{exprloc},
1035 \livelink{chap:classloclistptr}{loclistptr}\addtoindexx{location attribute!encoding} \\
1036 \livelink{chap:DWATname}{DW\_AT\_name}&0x03&\livelink{chap:classstring}{string}
1037 \addtoindexx{name attribute!encoding} \\
1038 \livelink{chap:DWATordering}{DW\_AT\_ordering}&0x09&\livelink{chap:classconstant}{constant}
1039 \addtoindexx{ordering attribute!encoding} \\
1040 \livelink{chap:DWATbytesize}{DW\_AT\_byte\_size}&0x0b&\livelink{chap:classconstant}{constant}, \livelink{chap:classexprloc}{exprloc},
1041 \livelink{chap:classreference}{reference} \addtoindexx{byte size attribute!encoding} \\
1042 \livelink{chap:DWATbitoffset}{DW\_AT\_bit\_offset}&0x0c&\livelink{chap:classconstant}{constant},
1043 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference} \addtoindexx{bit offset attribute!encoding} \\
1044 \livelink{chap:DWATbitsize}{DW\_AT\_bit\_size}&0x0d&\livelink{chap:classconstant}{constant},
1045 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference} \addtoindexx{bit size attribute!encoding} \\
1046 \livelink{chap:DWATstmtlist}{DW\_AT\_stmt\_list}&0x10&\livelink{chap:classlineptr}{lineptr}
1047 \addtoindexx{statement list attribute!encoding} \\
1048 \livelink{chap:DWATlowpc}{DW\_AT\_low\_pc}&0x11&\livelink{chap:classaddress}{address}
1049 \addtoindexx{low PC attribute!encoding} \\
1050 \livelink{chap:DWAThighpc}{DW\_AT\_high\_pc}&0x12&\livelink{chap:classaddress}{address}, \livelink{chap:classconstant}{constant}
1051 \addtoindexx{high PC attribute!encoding} \\
1052 \livelink{chap:DWATlanguage}{DW\_AT\_language}&0x13&\livelink{chap:classconstant}{constant}
1053 \addtoindexx{language attribute!encoding} \\
1054 \livelink{chap:DWATdiscr}{DW\_AT\_discr}&0x15&\livelink{chap:classreference}{reference}
1055 \addtoindexx{discriminant attribute!encoding} \\
1056 \livelink{chap:DWATdiscrvalue}{DW\_AT\_discr\_value}&0x16&\livelink{chap:classconstant}{constant}
1057 \addtoindexx{discriminant value attribute!encoding} \\
1058 \livelink{chap:DWATvisibility}{DW\_AT\_visibility}&0x17&\livelink{chap:classconstant}{constant}
1059 \addtoindexx{visibility attribute!encoding} \\
1060 \livelink{chap:DWATimport}{DW\_AT\_import}&0x18&\livelink{chap:classreference}{reference}
1061 \addtoindexx{import attribute!encoding} \\
1062 \livelink{chap:DWATstringlength}{DW\_AT\_string\_length}&0x19&\livelink{chap:classexprloc}{exprloc},
1063 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{string length attribute!encoding} \\
1064 \livelink{chap:DWATcommonreference}{DW\_AT\_common\_reference}&0x1a&\livelink{chap:classreference}{reference}
1065 \addtoindexx{common reference attribute!encoding} \\
1066 \livelink{chap:DWATcompdir}{DW\_AT\_comp\_dir}&0x1b&\livelink{chap:classstring}{string}
1067 \addtoindexx{compilation directory attribute!encoding} \\
1068 \livelink{chap:DWATconstvalue}{DW\_AT\_const\_value}&0x1c&\livelink{chap:classblock}{block}, \livelink{chap:classconstant}{constant}, \livelink{chap:classstring}{string}
1069 \addtoindexx{constant value attribute!encoding} \\
1070 \livelink{chap:DWATcontainingtype}{DW\_AT\_containing\_type}&0x1d&\livelink{chap:classreference}{reference}
1071 \addtoindexx{containing type attribute!encoding} \\
1072 \livelink{chap:DWATdefaultvalue}{DW\_AT\_default\_value}&0x1e&\livelink{chap:classreference}{reference}
1073 \addtoindexx{default value attribute!encoding} \\
1074 \livelink{chap:DWATinline}{DW\_AT\_inline}&0x20&\livelink{chap:classconstant}{constant}
1075 \addtoindexx{inline attribute!encoding} \\
1076 \livelink{chap:DWATisoptional}{DW\_AT\_is\_optional}&0x21&\livelink{chap:classflag}{flag}
1077 \addtoindexx{is optional attribute!encoding} \\
1078 \livelink{chap:DWATlowerbound}{DW\_AT\_lower\_bound}&0x22&\livelink{chap:classconstant}{constant},
1079 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference} \addtoindexx{lower bound attribute!encoding} \\
1080 \livelink{chap:DWATproducer}{DW\_AT\_producer}&0x25&\livelink{chap:classstring}{string} \addtoindexx{producer attribute!encoding} \\
1081 \livelink{chap:DWATprototyped}{DW\_AT\_prototyped}&0x27&\livelink{chap:classflag}{flag}
1082 \addtoindexx{prototyped attribute!encoding} \\
1083 \livelink{chap:DWATreturnaddr}{DW\_AT\_return\_addr}&0x2a&\livelink{chap:classexprloc}{exprloc},
1084 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{return address attribute!encoding} \\
1085 % FIXME: lower case , not Constant
1086 \livelink{chap:DWATstartscope}{DW\_AT\_start\_scope}&0x2c&\livelink{chap:classconstant}{constant},
1087 \livelink{chap:classrangelistptr}{rangelistptr} \addtoindexx{start scope attribute!encoding} \\
1088 \livelink{chap:DWATbitstride}{DW\_AT\_bit\_stride}&0x2e&\livelink{chap:classconstant}{constant},
1089 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference} \addtoindexx{bit stride attribute!encoding} \\
1090 \livelink{chap:DWATupperbound}{DW\_AT\_upper\_bound}&0x2f&\livelink{chap:classconstant}{constant},
1091 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference} \addtoindexx{upper bound attribute!encoding} \\
1092 \livelink{chap:DWATabstractorigin}{DW\_AT\_abstract\_origin}&0x31&\livelink{chap:classreference}{reference}
1093 \addtoindexx{abstract origin attribute!encoding} \\
1094 \livelink{chap:DWATaccessibility}{DW\_AT\_accessibility}&0x32&\livelink{chap:classconstant}{constant}
1095 \addtoindexx{accessibility attribute!encoding} \\
1096 \livelink{chap:DWATaddressclass}{DW\_AT\_address\_class}&0x33&\livelink{chap:classconstant}{constant}
1097 \addtoindexx{address class attribute!encoding} \\
1098 \livelink{chap:DWATartificial}{DW\_AT\_artificial}&0x34&\livelink{chap:classflag}{flag}
1099 \addtoindexx{artificial attribute!encoding} \\
1100 \livelink{chap:DWATbasetypes}{DW\_AT\_base\_types}&0x35&\livelink{chap:classreference}{reference}
1101 \addtoindexx{base types attribute!encoding} \\
1102 \livelink{chap:DWATcallingconvention}{DW\_AT\_calling\_convention}&0x36&\livelink{chap:classconstant}{constant}
1103 \addtoindexx{calling convention attribute!encoding} \\
1104 \livelink{chap:DWATcount}{DW\_AT\_count}&0x37&\livelink{chap:classconstant}{constant}, \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classreference}{reference}
1105 \addtoindexx{count attribute!encoding} \\
1106 \livelink{chap:DWATdatamemberlocation}{DW\_AT\_data\_member\_location}&0x38&\livelink{chap:classconstant}{constant},
1107 \livelink{chap:classexprloc}{exprloc}, \livelink{chap:classloclistptr}{loclistptr}
1108 \addtoindexx{data member attribute!encoding} \\
1109 \livelink{chap:DWATdeclcolumn}{DW\_AT\_decl\_column}&0x39&\livelink{chap:classconstant}{constant}
1110 \addtoindexx{declaration column attribute!encoding} \\
1111 \livelink{chap:DWATdeclfile}{DW\_AT\_decl\_file}&0x3a&\livelink{chap:classconstant}{constant}
1112 \addtoindexx{declaration file attribute!encoding} \\
1113 \livelink{chap:DWATdeclline}{DW\_AT\_decl\_line}&0x3b&\livelink{chap:classconstant}{constant}
1114 \addtoindexx{declaration line attribute!encoding} \\
1115 \livelink{chap:DWATdeclaration}{DW\_AT\_declaration}&0x3c&\livelink{chap:classflag}{flag}
1116 \addtoindexx{declaration attribute!encoding} \\
1117 \livelink{chap:DWATdiscrlist}{DW\_AT\_discr\_list}&0x3d&\livelink{chap:classblock}{block}
1118 \addtoindexx{discriminant list attribute!encoding} \\
1119 \livelink{chap:DWATencoding}{DW\_AT\_encoding}&0x3e&\livelink{chap:classconstant}{constant}
1120 \addtoindexx{encoding attribute!encoding} \\
1121 \livelink{chap:DWATexternal}{DW\_AT\_external}&\xiiif&\livelink{chap:classflag}{flag}
1122 \addtoindexx{external attribute!encoding} \\
1123 \livelink{chap:DWATframebase}{DW\_AT\_frame\_base}&0x40&\livelink{chap:classexprloc}{exprloc},
1124 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{frame base attribute!encoding} \\
1125 \livelink{chap:DWATfriend}{DW\_AT\_friend}&0x41&\livelink{chap:classreference}{reference}
1126 \addtoindexx{friend attribute!encoding} \\
1127 \livelink{chap:DWATidentifiercase}{DW\_AT\_identifier\_case}&0x42&\livelink{chap:classconstant}{constant}
1128 \addtoindexx{identifier case attribute!encoding} \\
1129 \livelink{chap:DWATmacroinfo}{DW\_AT\_macro\_info}&0x43&\livelink{chap:classmacptr}{macptr}
1130 \addtoindexx{macro information attribute!encoding} \\
1131 \livelink{chap:DWATnamelistitem}{DW\_AT\_namelist\_item}&0x44&\livelink{chap:classreference}{reference}
1132 \addtoindexx{name list item attribute!encoding} \\
1133 \livelink{chap:DWATpriority}{DW\_AT\_priority}&0x45&\livelink{chap:classreference}{reference}
1134 \addtoindexx{priority attribute!encoding} \\
1135 \livelink{chap:DWATsegment}{DW\_AT\_segment}&0x46&\livelink{chap:classexprloc}{exprloc},
1136 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{segment attribute!encoding} \\
1137 \livelink{chap:DWATspecification}{DW\_AT\_specification}&0x47&\livelink{chap:classreference}{reference}
1138 \addtoindexx{specification attribute!encoding} \\
1139 \livelink{chap:DWATstaticlink}{DW\_AT\_static\_link}&0x48&\livelink{chap:classexprloc}{exprloc},
1140 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{static link attribute!encoding} \\
1141 \livelink{chap:DWATtype}{DW\_AT\_type}&0x49&\livelink{chap:classreference}{reference}
1142 \addtoindexx{type attribute!encoding} \\
1143 \livelink{chap:DWATuselocation}{DW\_AT\_use\_location}&0x4a&\livelink{chap:classexprloc}{exprloc},
1144 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{location list attribute!encoding} \\
1145 \livelink{chap:DWATvariableparameter}{DW\_AT\_variable\_parameter}&0x4b&\livelink{chap:classflag}{flag}
1146 \addtoindexx{variable parameter attribute!encoding} \\
1147 \livelink{chap:DWATvirtuality}{DW\_AT\_virtuality}&0x4c&\livelink{chap:classconstant}{constant}
1148 \addtoindexx{virtuality attribute!encoding} \\
1149 \livelink{chap:DWATvtableelemlocation}{DW\_AT\_vtable\_elem\_location}&0x4d&\livelink{chap:classexprloc}{exprloc},
1150 \livelink{chap:classloclistptr}{loclistptr} \addtoindexx{vtable element location attribute!encoding} \\
1151 \livelink{chap:DWATallocated}{DW\_AT\_allocated}&0x4e&\livelink{chap:classconstant}{constant}, \livelink{chap:classexprloc}{exprloc},
1152 \livelink{chap:classreference}{reference} \addtoindexx{allocated attribute!encoding} \\
1153 \livelink{chap:DWATassociated}{DW\_AT\_associated}&0x4f&\livelink{chap:classconstant}{constant}, \livelink{chap:classexprloc}{exprloc},
1154 \livelink{chap:classreference}{reference} \addtoindexx{associated attribute!encoding} \\
1155 \livelink{chap:DWATdatalocation}{DW\_AT\_data\_location}&0x50&\livelink{chap:classexprloc}{exprloc}
1156 \addtoindexx{data location attribute!encoding} \\
1157 \livelink{chap:DWATbytestride}{DW\_AT\_byte\_stride}&0x51&\livelink{chap:classconstant}{constant}, \livelink{chap:classexprloc}{exprloc},
1158 \livelink{chap:classreference}{reference} \addtoindexx{byte stride attribute!encoding} \\
1159 \livelink{chap:DWATentrypc}{DW\_AT\_entry\_pc}&0x52&\livelink{chap:classaddress}{address}
1160 \addtoindexx{entry pc attribute!encoding} \\
1161 \livelink{chap:DWATuseUTF8}{DW\_AT\_use\_UTF8}&0x53&\livelink{chap:classflag}{flag}
1162 \addtoindexx{use UTF8 attribute!encoding}\addtoindexx{UTF-8} \\
1163 \livelink{chap:DWATextension}{DW\_AT\_extension}&0x54&\livelink{chap:classreference}{reference}
1164 \addtoindexx{extension attribute!encoding} \\
1165 \livelink{chap:DWATranges}{DW\_AT\_ranges}&0x55&\livelink{chap:classrangelistptr}{rangelistptr}
1166 \addtoindexx{ranges attribute!encoding} \\
1167 \livelink{chap:DWATtrampoline}{DW\_AT\_trampoline}&0x56&\livelink{chap:classaddress}{address}, \livelink{chap:classflag}{flag},
1168 \livelink{chap:classreference}{reference}, \livelink{chap:classstring}{string} \addtoindexx{trampoline attribute!encoding} \\
1169 \livelink{chap:DWATcallcolumn}{DW\_AT\_call\_column}&0x57&\livelink{chap:classconstant}{constant}
1170 \addtoindexx{call column attribute!encoding} \\
1171 \livelink{chap:DWATcallfile}{DW\_AT\_call\_file}&0x58&\livelink{chap:classconstant}{constant}
1172 \addtoindexx{call file attribute!encoding} \\
1173 \livelink{chap:DWATcallline}{DW\_AT\_call\_line}&0x59&\livelink{chap:classconstant}{constant}
1174 \addtoindexx{call line attribute!encoding} \\
1175 \livelink{chap:DWATdescription}{DW\_AT\_description}&0x5a&\livelink{chap:classstring}{string}
1176 \addtoindexx{description attribute!encoding} \\
1177 \livelink{chap:DWATbinaryscale}{DW\_AT\_binary\_scale}&0x5b&\livelink{chap:classconstant}{constant}
1178 \addtoindexx{binary scale attribute!encoding} \\
1179 \livelink{chap:DWATdecimalscale}{DW\_AT\_decimal\_scale}&0x5c&\livelink{chap:classconstant}{constant}
1180 \addtoindexx{decimal scale attribute!encoding} \\
1181 \livelink{chap:DWATsmall}{DW\_AT\_small} &0x5d&\livelink{chap:classreference}{reference}
1182 \addtoindexx{small attribute!encoding} \\
1183 \livelink{chap:DWATdecimalsign}{DW\_AT\_decimal\_sign}&0x5e&\livelink{chap:classconstant}{constant}
1184 \addtoindexx{decimal scale attribute!encoding} \\
1185 \livelink{chap:DWATdigitcount}{DW\_AT\_digit\_count}&0x5f&\livelink{chap:classconstant}{constant}
1186 \addtoindexx{digit count attribute!encoding} \\
1187 \livelink{chap:DWATpicturestring}{DW\_AT\_picture\_string}&0x60&\livelink{chap:classstring}{string}
1188 \addtoindexx{picture string attribute!encoding} \\
1189 \livelink{chap:DWATmutable}{DW\_AT\_mutable}&0x61&\livelink{chap:classflag}{flag}
1190 \addtoindexx{mutable attribute!encoding} \\
1191 \livelink{chap:DWATthreadsscaled}{DW\_AT\_threads\_scaled}&0x62&\livelink{chap:classflag}{flag}
1192 \addtoindexx{thread scaled attribute!encoding} \\
1193 \livelink{chap:DWATexplicit}{DW\_AT\_explicit}&0x63&\livelink{chap:classflag}{flag}
1194 \addtoindexx{explicit attribute!encoding} \\
1195 \livelink{chap:DWATobjectpointer}{DW\_AT\_object\_pointer}&0x64&\livelink{chap:classreference}{reference}
1196 \addtoindexx{object pointer attribute!encoding} \\
1197 \livelink{chap:DWATendianity}{DW\_AT\_endianity}&0x65&\livelink{chap:classconstant}{constant}
1198 \addtoindexx{endianity attribute!encoding} \\
1199 \livelink{chap:DWATelemental}{DW\_AT\_elemental}&0x66&\livelink{chap:classflag}{flag}
1200 \addtoindexx{elemental attribute!encoding} \\
1201 \livelink{chap:DWATpure}{DW\_AT\_pure}&0x67&\livelink{chap:classflag}{flag}
1202 \addtoindexx{pure attribute!encoding} \\
1203 \livelink{chap:DWATrecursive}{DW\_AT\_recursive}&0x68&\livelink{chap:classflag}{flag}
1204 \addtoindexx{recursive attribute!encoding} \\
1205 \livelink{chap:DWATsignature}{DW\_AT\_signature} \ddag &0x69&\livelink{chap:classreference}{reference}
1206 \addtoindexx{signature attribute!encoding} \\
1207 \livelink{chap:DWATmainsubprogram}{DW\_AT\_main\_subprogram} \ddag &0x6a&\livelink{chap:classflag}{flag}
1208 \addtoindexx{main subprogram attribute!encoding} \\
1209 \livelink{chap:DWATdatabitoffset}{DW\_AT\_data\_bit\_offset} \ddag &0x6b&\livelink{chap:classconstant}{constant}
1210 \addtoindexx{data bit offset attribute!encoding} \\
1211 \livelink{chap:DWATconstexpr}{DW\_AT\_const\_expr} \ddag &0x6c&\livelink{chap:classflag}{flag}
1212 \addtoindexx{constant expression attribute!encoding} \\
1213 \livelink{chap:DWATenumclass}{DW\_AT\_enum\_class} \ddag &0x6d&\livelink{chap:classflag}{flag}
1214 \addtoindexx{enumeration class attribute!encoding} \\
1215 \livelink{chap:DWATlinkagename}{DW\_AT\_linkage\_name} \ddag &0x6e&\livelink{chap:classstring}{string}
1216 \addtoindexx{linkage name attribute!encoding} \\
1217 \livelink{chap:DWXXXlohiuser}{DW\_AT\_lo\_user}&0x2000 & --- \addtoindexx{low user attribute encoding} \\
1218 \livelink{chap:DWXXXlohiuser}{DW\_AT\_hi\_user}&\xiiifff& --- \addtoindexx{high user attribute encoding} \\
1224 \setlength{\extrarowheight}{0.1cm}
1225 \begin{longtable}{l|l|l}
1226 \caption{Attribute form encodings} \label{tab:attributeformencodings} \\
1227 \hline \bfseries Form name&\bfseries Value &\bfseries Classes \\ \hline
1229 \bfseries Form name&\bfseries Value &\bfseries Classes\\ \hline
1231 \hline \emph{Continued on next page}
1234 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
1236 \livelink{chap:DWFORMaddr}{DW\_FORM\_addr}&0x01&\livelink{chap:classaddress}{address} \\
1237 \livelink{chap:DWFORMblock2}{DW\_FORM\_block2}&0x03&\livelink{chap:classblock}{block} \\
1238 \livelink{chap:DWFORMblock4}{DW\_FORM\_block4}&0x04&\livelink{chap:classblock}{block} \\
1239 \livelink{chap:DWFORMdata2}{DW\_FORM\_data2}&0x05&\livelink{chap:classconstant}{constant} \\
1240 \livelink{chap:DWFORMdata4}{DW\_FORM\_data4}&0x06&\livelink{chap:classconstant}{constant} \\
1241 \livelink{chap:DWFORMdata8}{DW\_FORM\_data8}&0x07&\livelink{chap:classconstant}{constant} \\
1242 \livelink{chap:DWFORMstring}{DW\_FORM\_string}&0x08&\livelink{chap:classstring}{string} \\
1243 \livelink{chap:DWFORMblock}{DW\_FORM\_block}&0x09&\livelink{chap:classblock}{block} \\
1244 \livelink{chap:DWFORMblock1}{DW\_FORM\_block1}&0x0a&\livelink{chap:classblock}{block} \\
1245 \livelink{chap:DWFORMdata1}{DW\_FORM\_data1}&0x0b&\livelink{chap:classconstant}{constant} \\
1246 \livelink{chap:DWFORMflag}{DW\_FORM\_flag}&0x0c&\livelink{chap:classflag}{flag} \\
1247 \livelink{chap:DWFORMsdata}{DW\_FORM\_sdata}&0x0d&\livelink{chap:classconstant}{constant} \\
1248 \livelink{chap:DWFORMstrp}{DW\_FORM\_strp}&0x0e&\livelink{chap:classstring}{string} \\
1249 \livelink{chap:DWFORMudata}{DW\_FORM\_udata}&0x0f&\livelink{chap:classconstant}{constant} \\
1250 \livelink{chap:DWFORMrefaddr}{DW\_FORM\_ref\_addr}&0x10&\livelink{chap:classreference}{reference} \\
1251 \livelink{chap:DWFORMref1}{DW\_FORM\_ref1}&0x11&\livelink{chap:classreference}{reference} \\
1252 \livelink{chap:DWFORMref2}{DW\_FORM\_ref2}&0x12&\livelink{chap:classreference}{reference} \\
1253 \livelink{chap:DWFORMref4}{DW\_FORM\_ref4}&0x13&\livelink{chap:classreference}{reference} \\
1254 \livelink{chap:DWFORMref8}{DW\_FORM\_ref8}&0x14&\livelink{chap:classreference}{reference} \\
1255 \livelink{chap:DWFORMrefudata}{DW\_FORM\_ref\_udata}&0x15&\livelink{chap:classreference}{reference} \\
1256 \livelink{chap:DWFORMindirect}{DW\_FORM\_indirect}&0x16&(see Section \refersec{datarep:abbreviationstables}) \\
1257 \livelink{chap:DWFORMsecoffset}{DW\_FORM\_sec\_offset} \ddag &0x17&\livelink{chap:classlineptr}{lineptr}, \livelink{chap:classloclistptr}{loclistptr}, \livelink{chap:classmacptr}{macptr}, \livelink{chap:classrangelistptr}{rangelistptr} \\
1258 \livelink{chap:DWFORMexprloc}{DW\_FORM\_exprloc} \ddag &0x18&\livelink{chap:classexprloc}{exprloc} \\
1259 \livelink{chap:DWFORMflagpresent}{DW\_FORM\_flag\_present} \ddag &0x19&\livelink{chap:classflag}{flag} \\
1260 \livelink{chap:DWFORMrefsig8}{DW\_FORM\_ref\_sig8} \ddag &0x20&\livelink{chap:classreference}{reference} \\
1267 \section{Variable Length Data}
1268 \label{datarep:variablelengthdata}
1269 \addtoindexx{variable length data|see {LEB128}}
1271 \addtoindexx{Little Endian Base 128|see{LEB128}}
1272 encoded using \doublequote{Little Endian Base 128}
1273 \addtoindexx{little-endian encoding|see{endian attribute}}
1275 \addtoindexx{LEB128}
1276 LEB128 is a scheme for encoding integers
1277 densely that exploits the assumption that most integers are
1280 \textit{This encoding is equally suitable whether the target machine
1281 architecture represents data in big\dash\ endian or little\dash endian
1282 order. It is \doublequote{little\dash endian} only in the sense that it
1283 avoids using space to represent the \doublequote{big} end of an
1284 unsigned integer, when the big end is all zeroes or sign
1287 Unsigned LEB128 (ULEB128) numbers are encoded as follows:
1288 \addtoindexx{LEB128!unsigned, encoding as}
1289 start at the low order end of an unsigned integer and chop
1290 it into 7\dash bit chunks. Place each chunk into the low order 7
1291 bits of a byte. Typically, several of the high order bytes
1292 will be zero; discard them. Emit the remaining bytes in a
1293 stream, starting with the low order byte; set the high order
1294 bit on each byte except the last emitted byte. The high bit
1295 of zero on the last byte indicates to the decoder that it
1296 has encountered the last byte.
1298 The integer zero is a special case, consisting of a single
1301 Table \refersec{tab:examplesofunsignedleb128encodings}
1302 gives some examples of unsigned LEB128 numbers. The
1303 0x80 in each case is the high order bit of the byte, indicating
1304 that an additional byte follows.
1307 The encoding for signed, two\textquoteright s complement LEB128 (SLEB128)
1308 \addtoindexx{LEB128!signed, encoding as}
1309 numbers is similar, except that the criterion for discarding
1310 high order bytes is not whether they are zero, but whether
1311 they consist entirely of sign extension bits. Consider the
1312 32\dash bit integer -2. The three high level bytes of the number
1313 are sign extension, thus LEB128 would represent it as a single
1314 byte containing the low order 7 bits, with the high order
1315 bit cleared to indicate the end of the byte stream. Note
1316 that there is nothing within the LEB128 representation that
1317 indicates whether an encoded number is signed or unsigned. The
1318 decoder must know what type of number to expect.
1319 Table \refersec{tab:examplesofunsignedleb128encodings}
1320 gives some examples of unsigned LEB128 numbers and
1321 Table \refersec{tab:examplesofsignedleb128encodings}
1322 gives some examples of signed LEB128
1325 \textit{Appendix \refersec{app:variablelengthdataencodingdecodinginformative}
1326 \addtoindexx{LEB128!examples}
1327 gives algorithms for encoding and decoding these forms.}
1331 \setlength{\extrarowheight}{0.1cm}
1332 \begin{longtable}{l|l|l}
1333 \caption{Examples of unsigned LEB128 encodings}
1334 \label{tab:examplesofunsignedleb128encodings}
1335 \addtoindexx{LEB128 encoding!examples} \\
1336 \hline \bfseries Number&\bfseries First byte &\bfseries Second byte \\ \hline
1338 \bfseries Number&\bfseries First Byte &\bfseries Second byte\\ \hline
1340 \hline \emph{Continued on next page}
1346 128& 0 + 0x80 & 1 \\
1347 129& 1 + 0x80 & 1 \\
1348 130& 2 + 0x80 & 1 \\
1349 12857& 57 + 0x80 & 100 \\
1356 \setlength{\extrarowheight}{0.1cm}
1357 \begin{longtable}{l|l|l}
1358 \caption{Examples of signed LEB128 encodings} \label{tab:examplesofsignedleb128encodings} \\
1359 \hline \bfseries Number&\bfseries First byte &\bfseries Second byte \\ \hline
1361 \bfseries Number&\bfseries First Byte &\bfseries Second byte\\ \hline
1363 \hline \emph{Continued on next page}
1369 127& 127 + 0x80 & 0 \\
1370 -127& 1 + 0x80 & 0x7f \\
1371 128& 0 + 0x80 & 1 \\
1372 -128& 0 + 0x80 & 0x7f \\
1373 129& 1 + 0x80 & 1 \\
1374 -129& 0x7f + 0x80 & 0x7e \\
1381 \section{DWARF Expressions and Location Descriptions}
1382 \label{datarep:dwarfexpressionsandlocationdescriptions}
1383 \subsection{DWARF Expressions}
1384 \label{datarep:dwarfexpressions}
1387 \addtoindexx{DWARF Expression!operator encoding}
1388 DWARF expression is stored in a \nolink{block} of contiguous
1389 bytes. The bytes form a sequence of operations. Each operation
1390 is a 1\dash byte code that identifies that operation, followed by
1391 zero or more bytes of additional data. The encodings for the
1392 operations are described in
1393 Table \refersec{tab:dwarfoperationencodings}.
1396 \setlength{\extrarowheight}{0.1cm}
1397 \begin{longtable}{l|l|c|l}
1398 \caption{DWARF operation encodings} \label{tab:dwarfoperationencodings} \\
1399 \hline & &\bfseries No. of &\\
1400 \bfseries Operation&\bfseries Code &\bfseries Operands &\bfseries Notes\\ \hline
1402 & &\bfseries No. of &\\
1403 \bfseries Operation&\bfseries Code &\bfseries Operands &\bfseries Notes\\ \hline
1405 \hline \emph{Continued on next page}
1408 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
1411 \livelink{chap:DWOPaddr}{DW\_OP\_addr}&0x03&1 & constant address \\
1412 & & &(size target specific) \\
1414 \livelink{chap:DWOPderef}{DW\_OP\_deref}&0x06&0 & \\
1417 \livelink{chap:DWOPconst1u}{DW\_OP\_const1u}&0x08&1&1\dash byte constant \\
1418 \livelink{chap:DWOPconst1s}{DW\_OP\_const1s}&0x09&1&1\dash byte constant \\
1419 \livelink{chap:DWOPconst2u}{DW\_OP\_const2u}&0x0a&1&2\dash byte constant \\
1420 \livelink{chap:DWOPconst2s}{DW\_OP\_const2s}&0x0b&1&2\dash byte constant \\
1421 \livelink{chap:DWOPconst4u}{DW\_OP\_const4u}&0x0c&1&4\dash byte constant \\
1422 \livelink{chap:DWOPconst4s}{DW\_OP\_const4s}&0x0d&1&4\dash byte constant \\
1423 \livelink{chap:DWOPconst8u}{DW\_OP\_const8u}&0x0e&1&8\dash byte constant \\
1424 \livelink{chap:DWOPconst8s}{DW\_OP\_const8s}&0x0f&1&8\dash byte constant \\
1425 \livelink{chap:DWOPconstu}{DW\_OP\_constu}&0x10&1&ULEB128 constant \\
1426 \livelink{chap:DWOPconsts}{DW\_OP\_consts}&0x11&1&SLEB128 constant \\
1427 \livelink{chap:DWOPdup}{DW\_OP\_dup}&0x12&0 & \\
1428 \livelink{chap:DWOPdrop}{DW\_OP\_drop}&0x13&0 & \\
1429 \livelink{chap:DWOPover}{DW\_OP\_over}&0x14&0 & \\
1430 \livelink{chap:DWOPpick}{DW\_OP\_pick}&0x15&1&1\dash byte stack index \\
1431 \livelink{chap:DWOPswap}{DW\_OP\_swap}&0x16&0 & \\
1432 \livelink{chap:DWOProt}{DW\_OP\_rot}&0x17&0 & \\
1433 \livelink{chap:DWOPxderef}{DW\_OP\_xderef}&0x18&0 & \\
1434 \livelink{chap:DWOPabs}{DW\_OP\_abs}&0x19&0 & \\
1435 \livelink{chap:DWOPand}{DW\_OP\_and}&0x1a&0 & \\
1436 \livelink{chap:DWOPdiv}{DW\_OP\_div}&0x1b&0 & \\
1440 \livelink{chap:DWOPminus}{DW\_OP\_minus}&0x1c&0 & \\
1441 \livelink{chap:DWOPmod}{DW\_OP\_mod}&0x1d&0 & \\
1442 \livelink{chap:DWOPmul}{DW\_OP\_mul}&0x1e&0 & \\
1443 \livelink{chap:DWOPneg}{DW\_OP\_neg}&0x1f&0 & \\
1444 \livelink{chap:DWOPnot}{DW\_OP\_not}&0x20&0 & \\
1445 \livelink{chap:DWOPor}{DW\_OP\_or}&0x21&0 & \\
1446 \livelink{chap:DWOPplus}{DW\_OP\_plus}&0x22&0 & \\
1447 \livelink{chap:DWOPplusuconst}{DW\_OP\_plus\_uconst}&0x23&1&ULEB128 addend \\
1448 \livelink{chap:DWOPshl}{DW\_OP\_shl}&0x24&0 & \\
1449 \livelink{chap:DWOPshr}{DW\_OP\_shr}&0x25&0 & \\
1450 \livelink{chap:DWOPshra}{DW\_OP\_shra}&0x26&0 & \\
1451 \livelink{chap:DWOPxor}{DW\_OP\_xor}&0x27&0 & \\
1453 \livelink{chap:DWOPbra}{DW\_OP\_bra}&0x28&1 & signed 2\dash byte constant \\
1454 \livelink{chap:DWOPeq}{DW\_OP\_eq}&0x29&0 & \\
1455 \livelink{chap:DWOPge}{DW\_OP\_ge}&0x2a&0 & \\
1456 \livelink{chap:DWOPgt}{DW\_OP\_gt}&0x2b&0 & \\
1457 \livelink{chap:DWOPle}{DW\_OP\_le}&0x2c&0 & \\
1458 \livelink{chap:DWOPlt}{DW\_OP\_lt}&0x2d&0 & \\
1459 \livelink{chap:DWOPne}{DW\_OP\_ne}&0x2e&0 & \\
1460 \livelink{chap:DWOPskip}{DW\_OP\_skip}&0x2f&1&signed 2\dash byte constant \\ \hline
1462 \livelink{chap:DWOPlit0}{DW\_OP\_lit0}&0x30 & 0 & \\
1463 \livelink{chap:DWOPlit1}{DW\_OP\_lit1}&0x31 & 0& literals 0 .. 31 = \\
1464 \ldots & & &\hspace{0.5cm}(\livelink{chap:DWOPlit0}{DW\_OP\_lit0} + literal) \\
1465 \livelink{chap:DWOPlit31}{DW\_OP\_lit31}&0x4f & 0 & \\ \hline
1467 \livelink{chap:DWOPreg0}{DW\_OP\_reg0} & 0x50 & 0 & \\
1468 \livelink{chap:DWOPreg1}{DW\_OP\_reg1} & 0x51 & 0® 0 .. 31 = \\
1469 \ldots & & &\hspace{0.5cm}(\livelink{chap:DWOPreg0}{DW\_OP\_reg0} + regnum) \\
1470 \livelink{chap:DWOPreg31}{DW\_OP\_reg31} & 0x6f & 0 & \\ \hline
1472 \livelink{chap:DWOPbreg0}{DW\_OP\_breg0} & 0x70 &1 & SLEB128 offset \\
1473 \livelink{chap:DWOPbreg1}{DW\_OP\_breg1} & 0x71 & 1 &base register 0 .. 31 = \\
1474 ... & & &\hspace{0.5cm}(\livelink{chap:DWOPbreg0}{DW\_OP\_breg0} + regnum) \\
1475 \livelink{chap:DWOPbreg31}{DW\_OP\_breg31} & 0x8f & 1 & \\ \hline
1477 \livelink{chap:DWOPregx}{DW\_OP\_regx} & 0x90 &1&ULEB128 register \\
1478 \livelink{chap:DWOPfbreg}{DW\_OP\_fbreg} & 0x91&1&SLEB128 offset \\
1479 \livelink{chap:DWOPbregx}{DW\_OP\_bregx} & 0x92&2 &ULEB128 register followed \\
1480 & & & by SLEB128 offset \\
1481 \livelink{chap:DWOPpiece}{DW\_OP\_piece} & 0x93 &1& ULEB128 size of piece addressed \\
1482 \livelink{chap:DWOPderefsize}{DW\_OP\_deref\_size} & 0x94 &1& 1-byte size of data retrieved \\
1483 \livelink{chap:DWOPxderefsize}{DW\_OP\_xderef\_size} & 0x95&1&1-byte size of data retrieved \\
1484 \livelink{chap:DWOPnop}{DW\_OP\_nop} & 0x96 &0& \\
1487 \livelink{chap:DWOPpushobjectaddress}{DW\_OP\_push\_object\_address}&0x97&0 & \\
1488 \livelink{chap:DWOPcall2}{DW\_OP\_call2}&0x98&1& 2\dash byte offset of DIE \\
1489 \livelink{chap:DWOPcall4}{DW\_OP\_call4}&0x99&1& 4\dash byte offset of DIE \\
1490 \livelink{chap:DWOPcallref}{DW\_OP\_call\_ref}&0x9a&1& 4\dash\ or 8\dash byte\\
1491 &&& offset of DIE \\
1492 \livelink{chap:DWOPformtlsaddress}{DW\_OP\_form\_tls\_address}&0x9b &0& \\
1493 \livelink{chap:DWOPcallframecfa}{DW\_OP\_call\_frame\_cfa} &0x9c &0& \\
1494 \livelink{chap:DWOPbitpiece}{DW\_OP\_bit\_piece}&0x9d &2&ULEB128 size followed by \\
1496 \livelink{chap:DWOPimplicitvalue}{DW\_OP\_implicit\_value} \ddag &0x9e &2&ULEB128 size followed by \\
1497 &&&\nolink{block} of that size\\
1498 \livelink{chap:DWOPstackvalue}{DW\_OP\_stack\_value} \ddag &0x9f &0& \\
1499 \livelink{chap:DWXXXlohiuser}{DW\_OP\_lo\_user} &0xe0 && \\
1500 \livelink{chap:DWXXXlohiuser}{DW\_OP\_hi\_user} &\xff && \\
1506 \subsection{Location Descriptions}
1507 \label{datarep:locationdescriptions}
1509 A location description is used to compute the
1510 location of a variable or other entity.
1512 \subsection{Location Lists}
1513 \label{datarep:locationlists}
1515 Each entry in a \addtoindex{location list} is either a location list entry,
1516 a base address selection entry, or an
1517 \addtoindexx{end of list entry!in location list}
1520 A \addtoindex{location list} entry consists of two address offsets followed
1521 by a 2\dash byte length, followed by a block of contiguous bytes
1522 that contains a DWARF location description. The length
1523 specifies the number of bytes in that block. The two offsets
1524 are the same size as an address on the target machine.
1527 A base address selection entry and an
1528 \addtoindexx{end of list entry!in location list}
1529 end of list entry each
1530 consist of two (constant or relocated) address offsets. The two
1531 offsets are the same size as an address on the target machine.
1533 For a \addtoindex{location list} to be specified, the base address of
1534 \addtoindexx{base address selection entry!in location list}
1535 the corresponding compilation unit must be defined
1536 (see Section \refersec{chap:normalandpartialcompilationunitentries}).
1538 \section{Base Type Attribute Encodings}
1539 \label{datarep:basetypeattributeencodings}
1541 The encodings of the
1542 \hypertarget{chap:DWATencodingencodingofbasetype}
1544 \addtoindexx{encoding attribute!encoding}
1546 \livelink{chap:DWATencoding}{DW\_AT\_encoding}
1547 attribute are given in
1548 Table \refersec{tab:basetypeencodingvalues}
1551 \setlength{\extrarowheight}{0.1cm}
1552 \begin{longtable}{l|c}
1553 \caption{Base type encoding values} \label{tab:basetypeencodingvalues} \\
1554 \hline \bfseries Base type encoding code name&\bfseries Value \\ \hline
1556 \bfseries Base type encoding code name&\bfseries Value\\ \hline
1558 \hline \emph{Continued on next page}
1561 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
1564 \livelink{chap:DWATEaddress}{DW\_ATE\_address}&0x01 \\
1565 \livelink{chap:DWATEboolean}{DW\_ATE\_boolean}&0x02 \\
1566 \livelink{chap:DWATEcomplexfloat}{DW\_ATE\_complex\_float}&0x03 \\
1567 \livelink{chap:DWATEfloat}{DW\_ATE\_float}&0x04 \\
1568 \livelink{chap:DWATEsigned}{DW\_ATE\_signed}&0x05 \\
1569 \livelink{chap:DWATEsignedchar}{DW\_ATE\_signed\_char}&0x06 \\
1570 \livelink{chap:DWATEunsigned}{DW\_ATE\_unsigned}&0x07 \\
1571 \livelink{chap:DWATEunsignedchar}{DW\_ATE\_unsigned\_char}&0x08 \\
1572 \livelink{chap:DWATEimaginaryfloat}{DW\_ATE\_imaginary\_float}&0x09 \\
1573 \livelink{chap:DWATEpackeddecimal}{DW\_ATE\_packed\_decimal}&0x0a \\
1574 \livelink{chap:DWATEnumericstring}{DW\_ATE\_numeric\_string}&0x0b \\
1575 \livelink{chap:DWATEedited}{DW\_ATE\_edited}&0x0c \\
1576 \livelink{chap:DWATEsignedfixed}{DW\_ATE\_signed\_fixed}&0x0d \\
1577 \livelink{chap:DWATEunsignedfixed}{DW\_ATE\_unsigned\_fixed}&0x0e \\
1578 \livelink{chap:DWATEdecimalfloat}{DW\_ATE\_decimal\_float} & 0x0f \\
1579 \livelink{chap:DWATEUTF}{DW\_ATE\_UTF} \ddag & 0x10 \\
1580 \livelink{chap:DWXXXlohiuser}{DW\_ATE\_lo\_user} & 0x80 \\
1581 \livelink{chap:DWXXXlohiuser}{DW\_ATE\_hi\_user} & \xff \\
1587 The encodings of the constants used in the
1588 \livelink{chap:DWATdecimalsign}{DW\_AT\_decimal\_sign} attribute
1590 Table \refersec{tab:decimalsignencodings}.
1594 \setlength{\extrarowheight}{0.1cm}
1595 \begin{longtable}{l|c}
1596 \caption{Decimal sign encodings} \label{tab:decimalsignencodings} \\
1597 \hline \bfseries Decimal sign code name&\bfseries Value \\ \hline
1599 \bfseries Decimal sign code name&\bfseries Value\\ \hline
1601 \hline \emph{Continued on next page}
1606 \livelink{chap:DWDSunsigned}{DW\_DS\_unsigned} & 0x01 \\
1607 \livelink{chap:DWDSleadingoverpunch}{DW\_DS\_leading\_overpunch} & 0x02 \\
1608 \livelink{chap:DWDStrailingoverpunch}{DW\_DS\_trailing\_overpunch} & 0x03 \\
1609 \livelink{chap:DWDSleadingseparate}{DW\_DS\_leading\_separate} & 0x04 \\
1610 \livelink{chap:DWDStrailingseparate}{DW\_DS\_trailing\_separate} & 0x05 \\
1615 The encodings of the constants used in the
1616 \livelink{chap:DWATendianity}{DW\_AT\_endianity} attribute are given in
1617 Table \refersec{tab:endianityencodings}.
1620 \setlength{\extrarowheight}{0.1cm}
1621 \begin{longtable}{l|c}
1622 \caption{Endianity encodings} \label{tab:endianityencodings}\\
1623 \hline \bfseries Endian code name&\bfseries Value \\ \hline
1625 \bfseries Endian code name&\bfseries Value\\ \hline
1627 \hline \emph{Continued on next page}
1632 \livelink{chap:DWENDdefault}{DW\_END\_default} & 0x00 \\
1633 \livelink{chap:DWENDbig}{DW\_END\_big} & 0x01 \\
1634 \livelink{chap:DWENDlittle}{DW\_END\_little} & 0x02 \\
1635 \livelink{chap:DWXXXlohiuser}{DW\_END\_lo\_user} & 0x40 \\
1636 \livelink{chap:DWXXXlohiuser}{DW\_END\_hi\_user} & \xff \\
1641 \section{Accessibility Codes}
1642 \label{datarep:accessibilitycodes}
1643 The encodings of the constants used in the
1644 \livelink{chap:DWATaccessibility}{DW\_AT\_accessibility}
1646 \addtoindexx{accessibility attribute!encoding}
1648 Table \refersec{tab:accessibilityencodings}.
1651 \setlength{\extrarowheight}{0.1cm}
1652 \begin{longtable}{l|c}
1653 \caption{Accessibility encodings} \label{tab:accessibilityencodings}\\
1654 \hline \bfseries Accessibility code name&\bfseries Value \\ \hline
1656 \bfseries Accessibility code name&\bfseries Value\\ \hline
1658 \hline \emph{Continued on next page}
1663 \livelink{chap:DWACCESSpublic}{DW\_ACCESS\_public}&0x01 \\
1664 \livelink{chap:DWACCESSprotected}{DW\_ACCESS\_protected}&0x02 \\
1665 \livelink{chap:DWACCESSprivate}{DW\_ACCESS\_private}&0x03 \\
1671 \section{Visibility Codes}
1672 \label{datarep:visibilitycodes}
1673 The encodings of the constants used in the
1674 \livelink{chap:DWATvisibility}{DW\_AT\_visibility} attribute are given in
1675 Table \refersec{tab:visibilityencodings}.
1678 \setlength{\extrarowheight}{0.1cm}
1679 \begin{longtable}{l|c}
1680 \caption{Visibility encodings} \label{tab:visibilityencodings}\\
1681 \hline \bfseries Visiibility code name&\bfseries Value \\ \hline
1683 \bfseries Visibility code name&\bfseries Value\\ \hline
1685 \hline \emph{Continued on next page}
1690 \livelink{chap:DWVISlocal}{DW\_VIS\_local}&0x01 \\
1691 \livelink{chap:DWVISexported}{DW\_VIS\_exported}&0x02 \\
1692 \livelink{chap:DWVISqualified}{DW\_VIS\_qualified}&0x03 \\
1697 \section{Virtuality Codes}
1698 \label{datarep:vitualitycodes}
1700 The encodings of the constants used in the
1701 \livelink{chap:DWATvirtuality}{DW\_AT\_virtuality} attribute are given in
1702 Table \refersec{tab:virtualityencodings}.
1705 \setlength{\extrarowheight}{0.1cm}
1706 \begin{longtable}{l|c}
1707 \caption{Virtuality encodings} \label{tab:virtualityencodings}\\
1708 \hline \bfseries Virtuality code name&\bfseries Value \\ \hline
1710 \bfseries Virtuality code name&\bfseries Value\\ \hline
1712 \hline \emph{Continued on next page}
1717 \livelink{chap:DWVIRTUALITYnone}{DW\_VIRTUALITY\_none}&0x00 \\
1718 \livelink{chap:DWVIRTUALITYvirtual}{DW\_VIRTUALITY\_virtual}&0x01 \\
1719 \livelink{chap:DWVIRTUALITYpurevirtual}{DW\_VIRTUALITY\_pure\_virtual}&0x02 \\
1727 \livelink{chap:DWVIRTUALITYnone}{DW\_VIRTUALITY\_none} is equivalent to the absence of the
1728 \livelink{chap:DWATvirtuality}{DW\_AT\_virtuality}
1731 \section{Source Languages}
1732 \label{datarep:sourcelanguages}
1734 The encodings of the constants used
1735 \addtoindexx{language attribute, encoding}
1737 \addtoindexx{language name encoding}
1739 \livelink{chap:DWATlanguage}{DW\_AT\_language}
1740 attribute are given in
1741 Table \refersec{tab:languageencodings}.
1743 % If we don't force a following space it looks odd
1745 and their associated values are reserved, but the
1746 languages they represent are not well supported.
1747 Table \refersec{tab:languageencodings}
1749 \addtoindexx{lower bound attribute!default}
1750 default lower bound, if any, assumed for
1751 an omitted \livelink{chap:DWATlowerbound}{DW\_AT\_lower\_bound} attribute in the context of a
1752 \livelink{chap:DWTAGsubrangetype}{DW\_TAG\_subrange\_type} debugging information entry for each
1756 \setlength{\extrarowheight}{0.1cm}
1757 \begin{longtable}{l|c|c}
1758 \caption{Language encodings} \label{tab:languageencodings}\\
1759 \hline \bfseries Language name&\bfseries Value &\bfseries Default Lower Bound \\ \hline
1761 \bfseries Language name&\bfseries Value &\bfseries Default Lower Bound\\ \hline
1763 \hline \emph{Continued on next page}
1766 \dag \ \textit{See text}
1769 \livelink{chap:DWLANGC89}{DW\_LANG\_C89}&0x0001&0 \\
1770 \livelink{chap:DWLANGC}{DW\_LANG\_C}&0x0002&0 \\
1771 \livelink{chap:DWLANGAda83}{DW\_LANG\_Ada83} \dag &0x0003&1 \addtoindexx{Ada} \\
1772 \livelink{chap:DWLANGCplusplus}{DW\_LANG\_C\_plus\_plus} &0x0004&0 \\
1773 \livelink{chap:DWLANGCobol74}{DW\_LANG\_Cobol74} \dag &0x0005&1 \\
1774 \livelink{chap:DWLANGCobol85}{DW\_LANG\_Cobol85} \dag &0x0006&1 \\
1775 \livelink{chap:DWLANGFortran77}{DW\_LANG\_Fortran77}&0x0007&1 \\
1776 \livelink{chap:DWLANGFortran90}{DW\_LANG\_Fortran90}&0x0008&1 \\
1777 \livelink{chap:DWLANGPascal83}{DW\_LANG\_Pascal83}&0x0009&1 \\
1778 \livelink{chap:DWLANGModula2}{DW\_LANG\_Modula2}&0x000a&1 \\
1779 \livelink{chap:DWLANGJava}{DW\_LANG\_Java}&0x000b&0 \\
1780 \livelink{chap:DWLANGC99}{DW\_LANG\_C99}&0x000c&0 \\
1781 \livelink{chap:DWLANGAda95}{DW\_LANG\_Ada95} \dag &0x000d&1 \addtoindexx{Ada} \\
1782 \livelink{chap:DWLANGFortran95}{DW\_LANG\_Fortran95} &0x000e&1 \\
1783 \livelink{chap:DWLANGPLI}{DW\_LANG\_PLI} \dag &0x000f&1 \\
1784 \livelink{chap:DWLANGObjC}{DW\_LANG\_ObjC}&0x0010&0 \\
1785 \livelink{chap:DWLANGObjCplusplus}{DW\_LANG\_ObjC\_plus\_plus}&0x0011&0 \\
1786 \livelink{chap:DWLANGUPC}{DW\_LANG\_UPC}&0x0012&0 \\
1787 \livelink{chap:DWLANGD}{DW\_LANG\_D}&0x0013&0 \\
1788 \livelink{chap:DWLANGPython}{DW\_LANG\_Python} \dag &0x0014&0 \\
1789 \livelink{chap:DWXXXlohiuser}{DW\_LANG\_lo\_user}&0x8000 & \\
1790 \livelink{chap:DWXXXlohiuser}{DW\_LANG\_hi\_user}&\xffff & \\
1795 \section{Address Class Encodings}
1796 \label{datarep:addressclassencodings}
1798 The value of the common
1799 \addtoindexi{address}{address class!attribute encoding}
1801 \livelink{chap:DWADDRnone}{DW\_ADDR\_none} is 0.
1804 \section{Identifier Case}
1805 \label{datarep:identifiercase}
1807 The encodings of the constants used in the
1808 \livelink{chap:DWATidentifiercase}{DW\_AT\_identifier\_case} attribute are given in
1809 Table \refersec{tab:identifiercaseencodings}.
1812 \setlength{\extrarowheight}{0.1cm}
1813 \begin{longtable}{l|c}
1814 \caption{Identifier case encodings} \label{tab:identifiercaseencodings}\\
1815 \hline \bfseries Identifier case name&\bfseries Value \\ \hline
1817 \bfseries Identifier case name&\bfseries Value\\ \hline
1819 \hline \emph{Continued on next page}
1823 \livelink{chap:DWIDcasesensitive}{DW\_ID\_case\_sensitive}&0x00 \\
1824 \livelink{chap:DWIDupcase}{DW\_ID\_up\_case}&0x01 \\
1825 \livelink{chap:DWIDdowncase}{DW\_ID\_down\_case}&0x02 \\
1826 \livelink{chap:DWIDcaseinsensitive}{DW\_ID\_case\_insensitive}&0x03 \\
1830 \section{Calling Convention Encodings}
1831 \label{datarep:callingconventionencodings}
1832 The encodings of the constants used in the
1833 \livelink{chap:DWATcallingconvention}{DW\_AT\_calling\_convention} attribute are given in
1834 Table \refersec{tab:callingconventionencodings}.
1837 \setlength{\extrarowheight}{0.1cm}
1838 \begin{longtable}{l|c}
1839 \caption{Calling convention encodings} \label{tab:callingconventionencodings}\\
1840 \hline \bfseries Calling Convention name&\bfseries Value \\ \hline
1842 \bfseries Calling Convention name&\bfseries Value\\ \hline
1844 \hline \emph{Continued on next page}
1849 \livelink{chap:DWCCnormal}{DW\_CC\_normal}&0x01 \\
1850 \livelink{chap:DWCCprogram}{DW\_CC\_program}&0x02 \\
1851 \livelink{chap:DWCCnocall}{DW\_CC\_nocall}&0x03 \\
1852 \livelink{chap:DWXXXlohiuser}{DW\_CC\_lo\_user}&0x40 \\
1853 \livelink{chap:DWXXXlohiuser}{DW\_CC\_hi\_user}&\xff \\
1858 \section{Inline Codes}
1859 \label{datarep:inlinecodes}
1861 The encodings of the constants used in
1862 \addtoindexx{inline attribute!encoding}
1864 \livelink{chap:DWATinline}{DW\_AT\_inline} attribute are given in
1865 Table \refersec{tab:inlineencodings}.
1869 \setlength{\extrarowheight}{0.1cm}
1870 \begin{longtable}{l|c}
1871 \caption{Inline encodings} \label{tab:inlineencodings}\\
1872 \hline \bfseries Inline Code name&\bfseries Value \\ \hline
1874 \bfseries Inline Code name&\bfseries Value\\ \hline
1876 \hline \emph{Continued on next page}
1881 \livelink{chap:DWINLnotinlined}{DW\_INL\_not\_inlined}&0x00 \\
1882 \livelink{chap:DWINLinlined}{DW\_INL\_inlined}&0x01 \\
1883 \livelink{chap:DWINLdeclarednotinlined}{DW\_INL\_declared\_not\_inlined}&0x02 \\
1884 \livelink{chap:DWINLdeclaredinlined}{DW\_INL\_declared\_inlined}&0x03 \\
1889 % this clearpage is ugly, but the following table came
1890 % out oddly without it.
1892 \section{Array Ordering}
1893 \label{datarep:arrayordering}
1895 The encodings of the constants used in the
1896 \livelink{chap:DWATordering}{DW\_AT\_ordering} attribute are given in
1897 Table \refersec{tab:orderingencodings}.
1901 \setlength{\extrarowheight}{0.1cm}
1902 \begin{longtable}{l|c}
1903 \caption{Ordering encodings} \label{tab:orderingencodings}\\
1904 \hline \bfseries Ordering name&\bfseries Value \\ \hline
1906 \bfseries Ordering name&\bfseries Value\\ \hline
1908 \hline \emph{Continued on next page}
1913 \livelink{chap:DWORDrowmajor}{DW\_ORD\_row\_major}&0x00 \\
1914 \livelink{chap:DWORDcolmajor}{DW\_ORD\_col\_major}&0x01 \\
1920 \section{Discriminant Lists}
1921 \label{datarep:discriminantlists}
1923 The descriptors used in
1924 \addtoindexx{discriminant list attribute!encoding}
1926 \livelink{chap:DWATdiscrlist}{DW\_AT\_discr\_list} attribute are
1927 encoded as 1\dash byte constants. The
1928 defined values are given in
1929 Table \refersec{tab:discriminantdescriptorencodings}.
1931 % Odd that the 'Name' field capitalized here, it is not caps elsewhere.
1933 \setlength{\extrarowheight}{0.1cm}
1934 \begin{longtable}{l|c}
1935 \caption{Discriminant descriptor encodings} \label{tab:discriminantdescriptorencodings}\\
1936 \hline \bfseries Descriptor Name&\bfseries Value \\ \hline
1938 \bfseries Descriptor Name&\bfseries Value\\ \hline
1940 \hline \emph{Continued on next page}
1945 \livelink{chap:DWDSClabel}{DW\_DSC\_label}&0x00 \\
1946 \livelink{chap:DWDSCrange}{DW\_DSC\_range}&0x01 \\
1952 \section{Name Lookup Tables}
1953 \label{datarep:namelookuptables}
1955 Each set of entries in the table of global names contained
1956 in the \dotdebugpubnames{} and
1957 \dotdebugpubtypes{} sections begins
1958 with a header consisting of:
1959 \begin{enumerate}[1. ]
1961 \item \texttt{unit\_length} (\livelink{datarep:initiallengthvalues}{initial length}) \\
1962 \addttindexx{unit\_length}
1963 A 4\dash byte or 12\dash byte unsigned integer
1964 \addtoindexx{initial length}
1965 representing the length
1966 of the \dotdebuginfo{}
1967 contribution for that compilation unit,
1968 not including the length field itself. In the
1969 \thirtytwobitdwarfformat, this is a 4\dash byte unsigned integer (which must be less
1970 than \xfffffffzero); in the \sixtyfourbitdwarfformat, this consists
1971 of the 4\dash byte value \wffffffff followed by an 8\dash byte unsigned
1972 integer that gives the actual length
1973 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
1975 \item version (\addtoindex{uhalf}) \\
1976 A 2\dash byte unsigned integer representing the version of the
1977 DWARF information for the name lookup table
1978 \addtoindexx{version number!name lookup table}
1979 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
1980 The value in this field is 2.
1983 \item \addtoindex{debug\_info\_offset} (section offset) \\
1985 \addtoindexx{section offset!in name lookup table set of entries}
1986 4\dash byte or 8\dash byte
1989 section of the compilation unit header.
1990 In the \thirtytwobitdwarfformat, this is a 4\dash byte unsigned offset;
1991 in the \sixtyfourbitdwarfformat, this is an 8\dash byte unsigned offsets
1992 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
1994 \item \addtoindex{debug\_info\_length} (\livelink{datarep:sectionoffsetlength}{section length}) \\
1995 \addtoindexx{section length!in .debug\_pubnames header}
1997 \addtoindexx{section length!in .debug\_pubtypes header}
1998 4\dash byte or 8\dash byte length containing the size in bytes of the
1999 contents of the \dotdebuginfo{}
2000 section generated to represent
2001 this compilation unit. In the \thirtytwobitdwarfformat, this is
2002 a 4\dash byte unsigned length; in the \sixtyfourbitdwarfformat, this
2003 is an 8-byte unsigned length
2004 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
2009 This header is followed by a series of tuples. Each tuple
2010 consists of a 4\dash byte or 8\dash byte offset followed by a string
2011 of non\dash null bytes terminated by one null byte.
2013 DWARF format, this is a 4\dash byte offset; in the 64\dash bit DWARF
2014 format, it is an 8\dash byte offset.
2015 Each set is terminated by an
2016 offset containing the value 0.
2020 \section{Address Range Table}
2021 \label{datarep:addrssrangetable}
2023 Each set of entries in the table of address ranges contained
2024 in the \dotdebugaranges{}
2025 section begins with a header containing:
2026 \begin{enumerate}[1. ]
2027 % FIXME The unit length text is not fully consistent across
2030 \item \texttt{unit\_length} (\livelink{datarep:initiallengthvalues}{initial length}) \\
2031 \addttindexx{unit\_length}
2032 A 4-byte or 12-byte length containing the length of the
2033 \addtoindexx{initial length}
2034 set of entries for this compilation unit, not including the
2035 length field itself. In the \thirtytwobitdwarfformat, this is a
2036 4-byte unsigned integer (which must be less than \xfffffffzero);
2037 in the \sixtyfourbitdwarfformat, this consists of the 4-byte value
2038 \wffffffff followed by an 8-byte unsigned integer that gives
2040 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
2042 \item version (\addtoindex{uhalf}) \\
2043 A 2\dash byte version identifier representing the version of the
2044 DWARF information for the address range table
2045 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
2046 This value in this field \addtoindexx{version number!address range table} is 2.
2049 \item debug\_info\_offset (\livelink{datarep:sectionoffsetlength}{section offset}) \\
2051 \addtoindexx{section offset!in .debug\_aranges header}
2052 4\dash byte or 8\dash byte offset into the
2053 \dotdebuginfo{} section of
2054 the compilation unit header. In the \thirtytwobitdwarfformat,
2055 this is a 4\dash byte unsigned offset; in the \sixtyfourbitdwarfformat,
2056 this is an 8\dash byte unsigned offset
2057 (see Section \refersec{datarep:32bitand64bitdwarfformats}).
2059 \item address\_size (ubyte) \\
2060 A 1\dash byte unsigned integer containing the size in bytes of an
2061 \addtoindexx{address\_size}
2063 \addtoindexx{size of an address}
2064 (or the offset portion of an address for segmented
2065 \addtoindexx{address space!segmented}
2066 addressing) on the target system.
2068 \item segment\_size (ubyte) \\
2070 \addtoindexx{segment\_size}
2071 1\dash byte unsigned integer containing the size in bytes of a
2072 segment selector on the target system.
2076 This header is followed by a series of tuples. Each tuple
2077 consists of a segment, an address and a length.
2079 size is given by the \addtoindex{segment\_size} field of the header; the
2080 address and length size are each given by the address\_size
2081 field of the header.
2082 The first tuple following the header in
2083 each set begins at an offset that is a multiple of the size
2084 of a single tuple (that is, the size of a segment selector
2085 plus twice the \addtoindex{size of an address}).
2086 The header is padded, if
2087 necessary, to that boundary. Each set of tuples is terminated
2088 by a 0 for the segment, a 0 for the address and 0 for the
2089 length. If the \addtoindex{segment\_size} field in the header is zero,
2090 the segment selectors are omitted from all tuples, including
2091 the terminating tuple.
2094 \section{Line Number Information}
2095 \label{datarep:linenumberinformation}
2097 The \addtoindexi{version number}{version number!line number information}
2098 in the line number program header is 4
2099 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
2101 The boolean values \doublequote{true} and \doublequote{false}
2102 used by the line number information program are encoded
2103 as a single byte containing the value 0
2104 for \doublequote{false,} and a non-zero value for \doublequote{true.}
2106 The encodings for the standard opcodes are given in
2107 \addtoindexx{line number opcodes!standard opcode encoding}
2108 Table \refersec{tab:linenumberstandardopcodeencodings}.
2110 % Odd that the 'Name' field capitalized here, it is not caps elsewhere.
2112 \setlength{\extrarowheight}{0.1cm}
2113 \begin{longtable}{l|c}
2114 \caption{Line number standard opcode encodings} \label{tab:linenumberstandardopcodeencodings}\\
2115 \hline \bfseries Opcode name&\bfseries Value \\ \hline
2117 \bfseries Opcode name&\bfseries Value\\ \hline
2119 \hline \emph{Continued on next page}
2124 \livelink{chap:DWLNScopy}{DW\_LNS\_copy}&0x01 \\
2125 \livelink{chap:DWLNSadvancepc}{DW\_LNS\_advance\_pc}&0x02 \\
2126 \livelink{chap:DWLNSadvanceline}{DW\_LNS\_advance\_line}&0x03 \\
2127 \livelink{chap:DWLNSsetfile}{DW\_LNS\_set\_file}&0x04 \\
2128 \livelink{chap:DWLNSsetcolumn}{DW\_LNS\_set\_column}&0x05 \\
2129 \livelink{chap:DWLNSnegatestmt}{DW\_LNS\_negate\_stmt}&0x06 \\
2130 \livelink{chap:DWLNSsetbasicblock}{DW\_LNS\_set\_basic\_block}&0x07 \\
2131 \livelink{chap:DWLNSconstaddpc}{DW\_LNS\_const\_add\_pc}&0x08 \\
2132 \livelink{chap:DWLNSfixedadvancepc}{DW\_LNS\_fixed\_advance\_pc}&0x09 \\
2133 \livelink{chap:DWLNSsetprologueend}{DW\_LNS\_set\_prologue\_end}&0x0a \\
2134 \livelink{chap:DWLNSsetepiloguebegin}{DW\_LNS\_set\_epilogue\_begin}&0x0b \\
2135 \livelink{chap:DWLNSsetisa}{DW\_LNS\_set\_isa}&0x0c \\
2142 The encodings for the extended opcodes are given in
2143 \addtoindexx{line number opcodes!extended opcode encoding}
2144 Table \refersec{tab:linenumberextendedopcodeencodings}.
2147 \setlength{\extrarowheight}{0.1cm}
2148 \begin{longtable}{l|c}
2149 \caption{Line number extended opcode encodings} \label{tab:linenumberextendedopcodeencodings}\\
2150 \hline \bfseries Opcode name&\bfseries Value \\ \hline
2152 \bfseries Opcode name&\bfseries Value\\ \hline
2154 \hline \emph{Continued on next page}
2157 \ddag \ \textit{New in \addtoindex{DWARF Version 4}}
2160 \livelink{chap:DWLNEendsequence}{DW\_LNE\_end\_sequence}&0x01 \\
2161 \livelink{chap:DWLNEsetaddress}{DW\_LNE\_set\_address}&0x02\\
2162 \livelink{chap:DWLNEdefinefile}{DW\_LNE\_define\_file}&0x03\\
2163 \livelink{chap:DWLNEsetdiscriminator}{DW\_LNE\_set\_discriminator} \ddag &0x04 \\
2164 \livelink{chap:DWXXXlohiuser}{DW\_LNE\_lo\_user}&0x80 \\
2165 \livelink{chap:DWXXXlohiuser}{DW\_LNE\_hi\_user}&\xff \\
2170 \section{Macro Information}
2171 \label{datarep:macroinformation}
2173 The source line numbers and source file indices encoded in the
2174 macro information section are represented as unsigned LEB128
2175 numbers as are the constants in a
2176 \livelink{chap:DWMACINFOvendorext}{DW\_MACINFO\_vendor\_ext} entry.
2178 The macinfo type is encoded as a single byte.
2180 \addtoindexx{macinfo types!encoding}
2182 Table \refersec{tab:macinfotypeencodings}.
2186 \setlength{\extrarowheight}{0.1cm}
2187 \begin{longtable}{l|c}
2188 \caption{Macinfo type encodings} \label{tab:macinfotypeencodings}\\
2189 \hline \bfseries Macinfo Type Name&\bfseries Value \\ \hline
2191 \bfseries Macinfo Type Name&\bfseries Value\\ \hline
2193 \hline \emph{Continued on next page}
2198 \livelink{chap:DWMACINFOdefine}{DW\_MACINFO\_define}&0x01 \\
2199 \livelink{chap:DWMACINFOundef}{DW\_MACINFO\_undef}&0x02 \\
2200 \livelink{chap:DWMACINFOstartfile}{DW\_MACINFO\_start\_file}&0x03 \\
2201 \livelink{chap:DWMACINFOendfile}{DW\_MACINFO\_end\_file}&0x04 \\
2202 \livelink{chap:DWMACINFOvendorext}{DW\_MACINFO\_vendor\_ext}&\xff \\
2208 \section{Call Frame Information}
2209 \label{datarep:callframeinformation}
2211 In the \thirtytwobitdwarfformat, the value of the CIE id in the
2212 CIE header is \xffffffff; in the \sixtyfourbitdwarfformat, the
2213 value is \xffffffffffffffff.
2215 The value of the CIE \addtoindexi{version number}{version number!call frame information}
2216 is 4 (see Appendix \refersec{app:dwarfsectionversionnumbersinformative}).
2218 Call frame instructions are encoded in one or more bytes. The
2219 primary opcode is encoded in the high order two bits of
2220 the first byte (that is, opcode = byte $\gg$ 6). An operand
2221 or extended opcode may be encoded in the low order 6
2222 bits. Additional operands are encoded in subsequent bytes.
2223 The instructions and their encodings are presented in
2224 Table \refersec{tab:callframeinstructionencodings}.
2227 \setlength{\extrarowheight}{0.1cm}
2228 \begin{longtable}{l|c|c|l|l}
2229 \caption{Call frame instruction encodings} \label{tab:callframeinstructionencodings} \\
2230 \hline &\bfseries High 2 &\bfseries Low 6 & & \\
2231 \bfseries Instruction&\bfseries Bits &\bfseries Bits &\bfseries Operand 1 &\bfseries Operand 2\\ \hline
2233 & \bfseries High 2 &\bfseries Low 6 & &\\
2234 \bfseries Instruction&\bfseries Bits &\bfseries Bits &\bfseries Operand 1 &\bfseries Operand 2\\ \hline
2236 \hline \emph{Continued on next page}
2241 \livelink{chap:DWCFAadvanceloc}{DW\_CFA\_advance\_loc}&0x1&delta & \\
2242 \livelink{chap:DWCFAoffset}{DW\_CFA\_offset}&0x2®ister&ULEB128 offset \\
2243 \livelink{chap:DWCFArestore}{DW\_CFA\_restore}&0x3®ister & & \\
2244 \livelink{chap:DWCFAnop}{DW\_CFA\_nop}&0&0 & & \\
2245 \livelink{chap:DWCFAsetloc}{DW\_CFA\_set\_loc}&0&0x01&address & \\
2246 \livelink{chap:DWCFAadvanceloc1}{DW\_CFA\_advance\_loc1}&0&0x02&1\dash byte delta & \\
2247 \livelink{chap:DWCFAadvanceloc2}{DW\_CFA\_advance\_loc2}&0&0x03&2\dash byte delta & \\
2248 \livelink{chap:DWCFAadvanceloc4}{DW\_CFA\_advance\_loc4}&0&0x04&4\dash byte delta & \\
2249 \livelink{chap:DWCFAoffsetextended}{DW\_CFA\_offset\_extended}&0&0x05&ULEB128 register&ULEB128 offset \\
2250 \livelink{chap:DWCFArestoreextended}{DW\_CFA\_restore\_extended}&0&0x06&ULEB128 register & \\
2251 \livelink{chap:DWCFAundefined}{DW\_CFA\_undefined}&0&0x07&ULEB128 register & \\
2252 \livelink{chap:DWCFAsamevalue}{DW\_CFA\_same\_value}&0&0x08 &ULEB128 register & \\
2253 \livelink{chap:DWCFAregister}{DW\_CFA\_register}&0&0x09&ULEB128 register &ULEB128 offset \\
2254 \livelink{chap:DWCFArememberstate}{DW\_CFA\_remember\_state}&0&0x0a & & \\
2255 \livelink{chap:DWCFArestorestate}{DW\_CFA\_restore\_state}&0&0x0b & & \\
2256 \livelink{chap:DWCFAdefcfa}{DW\_CFA\_def\_cfa}&0&0x0c &ULEB128 register&ULEB128 offset \\
2257 \livelink{chap:DWCFAdefcfaregister}{DW\_CFA\_def\_cfa\_register}&0&0x0d&ULEB128 register & \\
2258 \livelink{chap:DWCFAdefcfaoffset}{DW\_CFA\_def\_cfa\_offset}&0&0x0e &ULEB128 offset & \\
2259 \livelink{chap:DWCFAdefcfaexpression}{DW\_CFA\_def\_cfa\_expression}&0&0x0f &BLOCK \\
2260 \livelink{chap:DWCFAexpression}{DW\_CFA\_expression}&0&0x10&ULEB128 register & BLOCK \\
2262 \livelink{chap:DWCFAoffsetextendedsf}{DW\_CFA\_offset\_extended\_sf}&0&0x11&ULEB128 register&SLEB128 offset \\
2263 \livelink{chap:DWCFAdefcfasf}{DW\_CFA\_def\_cfa\_sf}&0&0x12&ULEB128 register&SLEB128 offset \\
2264 \livelink{chap:DWCFAdefcfaoffsetsf}{DW\_CFA\_def\_cfa\_offset\_sf}&0&0x13&SLEB128 offset & \\
2265 \livelink{chap:DWCFAvaloffset}{DW\_CFA\_val\_offset}&0&0x14&ULEB128&ULEB128 \\
2266 \livelink{chap:DWCFAvaloffsetsf}{DW\_CFA\_val\_offset\_sf}&0&0x15&ULEB128&SLEB128 \\
2267 \livelink{chap:DWCFAvalexpression}{DW\_CFA\_val\_expression}&0&0x16&ULEB128&BLOCK \\
2268 \livelink{chap:DWXXXlohiuser}{DW\_CFA\_lo\_user}&0&0x1c & & \\
2269 \livelink{chap:DWXXXlohiuser}{DW\_CFA\_hi\_user}&0&\xiiif & & \\
2273 \section{Non-contiguous Address Ranges}
2274 \label{datarep:noncontiguousaddressranges}
2276 Each entry in a \addtoindex{range list}
2277 (see Section \refersec{chap:noncontiguousaddressranges})
2279 \addtoindexx{base address selection entry!in range list}
2281 \addtoindexx{range list}
2282 a base address selection entry, or an end
2285 A \addtoindex{range list} entry consists of two relative addresses. The
2286 addresses are the same size as addresses on the target machine.
2288 A base address selection entry and an
2289 \addtoindexx{end of list entry!in range list}
2290 end of list entry each
2291 \addtoindexx{base address selection entry!in range list}
2292 consist of two (constant or relocated) addresses. The two
2293 addresses are the same size as addresses on the target machine.
2295 For a \addtoindex{range list} to be specified, the base address of the
2296 \addtoindexx{base address selection entry!in range list}
2297 corresponding compilation unit must be defined
2298 (see Section \refersec{chap:normalandpartialcompilationunitentries}).
2301 \section{Dependencies and Constraints}
2302 \label{datarep:dependenciesandconstraints}
2304 The debugging information in this format is intended to
2306 \addtoindexx{DWARF section names!list of}
2308 the \dotdebugabbrev{},
2315 \dotdebugpubnames{},
2316 \dotdebugpubtypes{},
2321 sections of an object file, or equivalent
2322 separate file or database. The information is not
2323 word\dash aligned. Consequently:
2326 \item For the \thirtytwobitdwarfformat{} and a target architecture with
2327 32\dash bit addresses, an assembler or compiler must provide a way
2328 to produce 2\dash byte and 4\dash byte quantities without alignment
2329 restrictions, and the linker must be able to relocate a
2330 4\dash byte address or
2331 \addtoindexx{section offset!alignment of}
2332 section offset that occurs at an arbitrary
2335 \item For the \thirtytwobitdwarfformat{} and a target architecture with
2336 64\dash bit addresses, an assembler or compiler must provide a
2337 way to produce 2\dash byte, 4\dash byte and 8\dash byte quantities without
2338 alignment restrictions, and the linker must be able to relocate
2339 an 8\dash byte address or 4\dash byte
2340 \addtoindexx{section offset!alignment of}
2341 section offset that occurs at an
2342 arbitrary alignment.
2344 \item For the \sixtyfourbitdwarfformat{} and a target architecture with
2345 32\dash bit addresses, an assembler or compiler must provide a
2346 way to produce 2\dash byte, 4\dash byte and 8\dash byte quantities without
2347 alignment restrictions, and the linker must be able to relocate
2348 a 4\dash byte address or 8\dash byte
2349 \addtoindexx{section offset!alignment of}
2350 section offset that occurs at an
2351 arbitrary alignment.
2353 \textit{It is expected that this will be required only for very large
2354 32\dash bit programs or by those architectures which support
2355 a mix of 32\dash bit and 64\dash bit code and data within the same
2358 \item For the \sixtyfourbitdwarfformat{} and a target architecture with
2359 64\dash bit addresses, an assembler or compiler must provide a
2360 way to produce 2\dash byte, 4\dash byte and 8\dash byte quantities without
2361 alignment restrictions, and the linker must be able to
2362 relocate an 8\dash byte address or
2363 \addtoindexx{section offset!alignment of}
2364 section offset that occurs at
2365 an arbitrary alignment.
2368 \section{Integer Representation Names}
2369 \label{datarep:integerrepresentationnames}
2371 The sizes of the integers used in the lookup by name, lookup
2372 by address, line number and call frame information sections
2374 Table \ref{tab:integerrepresentationnames}.
2377 \setlength{\extrarowheight}{0.1cm}
2378 \begin{longtable}{c|l}
2379 \caption{Integer representation names} \label{tab:integerrepresentationnames}\\
2380 \hline \bfseries Representation name&\bfseries Representation \\ \hline
2382 \bfseries Representation name&\bfseries Representation\\ \hline
2384 \hline \emph{Continued on next page}
2389 \addtoindex{sbyte}& signed, 1\dash byte integer \\
2390 \addtoindex{ubyte}&unsigned, 1\dash byte integer \\
2391 \addtoindex{uhalf}&unsigned, 2\dash byte integer \\
2392 \addtoindex{uword}&unsigned, 4\dash byte integer \\
2398 \section{Type Signature Computation}
2399 \label{datarep:typesignaturecomputation}
2401 A type signature is computed only by the DWARF producer;
2402 \addtoindexx{type signature computation}
2403 it is used by a DWARF consumer to resolve type references to
2404 the type definitions that are contained in
2405 \addtoindexx{type unit}
2408 The type signature for a type T0 is formed from the
2409 \addtoindex{MD5 hash}
2410 of a flattened description of the type. The flattened
2411 description of the type is a byte sequence derived from the
2412 DWARF encoding of the type as follows:
2413 \begin{enumerate}[1. ]
2415 \item Start with an empty sequence S and a list V of visited
2416 types, where V is initialized to a list containing the type
2417 T0 as its single element. Elements in V are indexed from 1,
2420 \item If the debugging information entry represents a type that
2421 is nested inside another type or a namespace, append to S
2422 the type\textquoteright s context as follows: For each surrounding type
2423 or namespace, beginning with the outermost such construct,
2424 append the letter 'C', the DWARF tag of the construct, and
2425 the name (taken from
2426 \addtoindexx{name attribute}
2427 the \livelink{chap:DWATname}{DW\_AT\_name} attribute) of the type
2428 \addtoindexx{name attribute}
2429 or namespace (including its trailing null byte).
2431 \item Append to S the letter 'D', followed by the DWARF tag of
2432 the debugging information entry.
2434 \item For each of the attributes in
2435 Table \refersec{tab:attributesusedintypesignaturecomputation}
2437 the debugging information entry, in the order listed,
2438 append to S a marker letter (see below), the DWARF attribute
2439 code, and the attribute value.
2442 \caption{Attributes used in type signature computation}
2443 \label{tab:attributesusedintypesignaturecomputation}
2444 \simplerule[\textwidth]
2446 \autocols[0pt]{c}{2}{l}{
2447 \livelink{chap:DWATname}{DW\_AT\_name},
2448 \livelink{chap:DWATaccessibility}{DW\_AT\_accessibility},
2449 \livelink{chap:DWATaddressclass}{DW\_AT\_address\_class},
2450 \livelink{chap:DWATallocated}{DW\_AT\_allocated},
2451 \livelink{chap:DWATartificial}{DW\_AT\_artificial},
2452 \livelink{chap:DWATassociated}{DW\_AT\_associated},
2453 \livelink{chap:DWATbinaryscale}{DW\_AT\_binary\_scale},
2454 \livelink{chap:DWATbitoffset}{DW\_AT\_bit\_offset},
2455 \livelink{chap:DWATbitsize}{DW\_AT\_bit\_size},
2456 \livelink{chap:DWATbitstride}{DW\_AT\_bit\_stride},
2457 \livelink{chap:DWATbytesize}{DW\_AT\_byte\_size},
2458 \livelink{chap:DWATbytestride}{DW\_AT\_byte\_stride},
2459 \livelink{chap:DWATconstexpr}{DW\_AT\_const\_expr},
2460 \livelink{chap:DWATconstvalue}{DW\_AT\_const\_value},
2461 \livelink{chap:DWATcontainingtype}{DW\_AT\_containing\_type},
2462 \livelink{chap:DWATcount}{DW\_AT\_count},
2463 \livelink{chap:DWATdatabitoffset}{DW\_AT\_data\_bit\_offset},
2464 \livelink{chap:DWATdatalocation}{DW\_AT\_data\_location},
2465 \livelink{chap:DWATdatamemberlocation}{DW\_AT\_data\_member\_location},
2466 \livelink{chap:DWATdecimalscale}{DW\_AT\_decimal\_scale},
2467 \livelink{chap:DWATdecimalsign}{DW\_AT\_decimal\_sign},
2468 \livelink{chap:DWATdefaultvalue}{DW\_AT\_default\_value},
2469 \livelink{chap:DWATdigitcount}{DW\_AT\_digit\_count},
2470 \livelink{chap:DWATdiscr}{DW\_AT\_discr},
2471 \livelink{chap:DWATdiscrlist}{DW\_AT\_discr\_list},
2472 \livelink{chap:DWATdiscrvalue}{DW\_AT\_discr\_value},
2473 \livelink{chap:DWATencoding}{DW\_AT\_encoding},
2474 \livelink{chap:DWATenumclass}{DW\_AT\_enum\_class},
2475 \livelink{chap:DWATendianity}{DW\_AT\_endianity},
2476 \livelink{chap:DWATexplicit}{DW\_AT\_explicit},
2477 \livelink{chap:DWATisoptional}{DW\_AT\_is\_optional},
2478 \livelink{chap:DWATlocation}{DW\_AT\_location},
2479 \livelink{chap:DWATlowerbound}{DW\_AT\_lower\_bound},
2480 \livelink{chap:DWATmutable}{DW\_AT\_mutable},
2481 \livelink{chap:DWATordering}{DW\_AT\_ordering},
2482 \livelink{chap:DWATpicturestring}{DW\_AT\_picture\_string},
2483 \livelink{chap:DWATprototyped}{DW\_AT\_prototyped},
2484 \livelink{chap:DWATsmall}{DW\_AT\_small},
2485 \livelink{chap:DWATsegment}{DW\_AT\_segment},
2486 \livelink{chap:DWATstringlength}{DW\_AT\_string\_length},
2487 \livelink{chap:DWATthreadsscaled}{DW\_AT\_threads\_scaled},
2488 \livelink{chap:DWATupperbound}{DW\_AT\_upper\_bound},
2489 \livelink{chap:DWATuselocation}{DW\_AT\_use\_location},
2490 \livelink{chap:DWATuseUTF8}{DW\_AT\_use\_UTF8},
2491 \livelink{chap:DWATvariableparameter}{DW\_AT\_variable\_parameter},
2492 \livelink{chap:DWATvirtuality}{DW\_AT\_virtuality},
2493 \livelink{chap:DWATvisibility}{DW\_AT\_visibility},
2494 \livelink{chap:DWATvtableelemlocation}{DW\_AT\_vtable\_elem\_location}
2497 \simplerule[\textwidth]
2500 Note that except for the initial
2501 \livelink{chap:DWATname}{DW\_AT\_name} attribute,
2502 \addtoindexx{name attribute}
2503 attributes are appended in order according to the alphabetical
2504 spelling of their identifier.
2506 If an implementation defines any vendor-specific attributes,
2507 any such attributes that are essential to the definition of
2508 the type should also be included at the end of the above list,
2509 in their own alphabetical suborder.
2511 An attribute that refers to another type entry T is processed
2512 as follows: (a) If T is in the list V at some V[x], use the
2513 letter 'R' as the marker and use the unsigned LEB128 encoding
2514 of x as the attribute value; otherwise, (b) use the letter 'T'
2515 as the marker, process the type T recursively by performing
2516 Steps 2 through 7, and use the result as the attribute value.
2518 Other attribute values use the letter 'A' as the marker, and
2519 the value consists of the form code (encoded as an unsigned
2520 LEB128 value) followed by the encoding of the value according
2521 to the form code. To ensure reproducibility of the signature,
2522 the set of forms used in the signature computation is limited
2523 to the following: \livelink{chap:DWFORMsdata}{DW\_FORM\_sdata},
2524 \livelink{chap:DWFORMflag}{DW\_FORM\_flag},
2525 \livelink{chap:DWFORMstring}{DW\_FORM\_string},
2526 and \livelink{chap:DWFORMblock}{DW\_FORM\_block}.
2528 \item If the tag in Step 3 is one of \livelink{chap:DWTAGpointertype}{DW\_TAG\_pointer\_type},
2529 \livelink{chap:DWTAGreferencetype}{DW\_TAG\_reference\_type},
2530 \livelink{chap:DWTAGrvaluereferencetype}{DW\_TAG\_rvalue\_reference\_type},
2531 \livelink{chap:DWTAGptrtomembertype}{DW\_TAG\_ptr\_to\_member\_type},
2532 or \livelink{chap:DWTAGfriend}{DW\_TAG\_friend}, and the referenced
2533 type (via the \livelink{chap:DWATtype}{DW\_AT\_type} or
2534 \livelink{chap:DWATfriend}{DW\_AT\_friend} attribute) has a
2535 \livelink{chap:DWATname}{DW\_AT\_name} attribute, append to S the letter 'N', the DWARF
2536 attribute code (\livelink{chap:DWATtype}{DW\_AT\_type} or
2537 \livelink{chap:DWATfriend}{DW\_AT\_friend}), the context of
2538 the type (according to the method in Step 2), the letter 'E',
2539 and the name of the type. For \livelink{chap:DWTAGfriend}{DW\_TAG\_friend}, if the referenced
2540 entry is a \livelink{chap:DWTAGsubprogram}{DW\_TAG\_subprogram}, the context is omitted and the
2541 name to be used is the ABI-specific name of the subprogram
2542 (e.g., the mangled linker name).
2545 \item If the tag in Step 3 is not one of \livelink{chap:DWTAGpointertype}{DW\_TAG\_pointer\_type},
2546 \livelink{chap:DWTAGreferencetype}{DW\_TAG\_reference\_type},
2547 \livelink{chap:DWTAGrvaluereferencetype}{DW\_TAG\_rvalue\_reference\_type},
2548 \livelink{chap:DWTAGptrtomembertype}{DW\_TAG\_ptr\_to\_member\_type}, or
2549 \livelink{chap:DWTAGfriend}{DW\_TAG\_friend}, but has
2550 a \livelink{chap:DWATtype}{DW\_AT\_type} attribute, or if the referenced type (via
2551 the \livelink{chap:DWATtype}{DW\_AT\_type} or
2552 \livelink{chap:DWATfriend}{DW\_AT\_friend} attribute) does not have a
2553 \livelink{chap:DWATname}{DW\_AT\_name} attribute, the attribute is processed according to
2554 the method in Step 4 for an attribute that refers to another
2558 \item Visit each child C of the debugging information
2559 entry as follows: If C is a nested type entry or a member
2560 function entry, and has
2561 a \livelink{chap:DWATname}{DW\_AT\_name} attribute, append to
2562 \addtoindexx{name attribute}
2563 S the letter 'S', the tag of C, and its name; otherwise,
2564 process C recursively by performing Steps 3 through 7,
2565 appending the result to S. Following the last child (or if
2566 there are no children), append a zero byte.
2571 For the purposes of this algorithm, if a debugging information
2573 \livelink{chap:DWATspecification}{DW\_AT\_specification}
2574 attribute that refers to
2575 another entry D (which has a
2576 \livelink{chap:DWATdeclaration}{DW\_AT\_declaration}
2578 then S inherits the attributes and children of D, and S is
2579 processed as if those attributes and children were present in
2580 the entry S. Exception: if a particular attribute is found in
2581 both S and D, the attribute in S is used and the corresponding
2582 one in D is ignored.
2584 DWARF tag and attribute codes are appended to the sequence
2585 as unsigned LEB128 values, using the values defined earlier
2588 \textit{A grammar describing this computation may be found in
2589 Appendix \refersec{app:typesignaturecomputationgrammar}.
2592 \textit{An attribute that refers to another type entry should
2593 be recursively processed or replaced with the name of the
2594 referent (in Step 4, 5 or 6). If neither treatment applies to
2595 an attribute that references another type entry, the entry
2596 that contains that attribute should not be considered for a
2597 separate \addtoindex{type unit}.}
2599 \textit{If a debugging information entry contains an attribute from
2600 the list above that would require an unsupported form, that
2601 entry should not be considered for a separate
2602 \addtoindex{type unit}.}
2604 \textit{A type should be considered for a separate
2605 \addtoindex{type unit} only
2606 if all of the type entries that it contains or refers to in
2607 Steps 6 and 7 can themselves each be considered for a separate
2608 \addtoindex{type unit}.}
2611 Where the DWARF producer may reasonably choose two or more
2612 different forms for a given attribute, it should choose
2613 the simplest possible form in computing the signature. (For
2614 example, a constant value should be preferred to a location
2615 expression when possible.)
2617 Once the string S has been formed from the DWARF encoding,
2618 an \addtoindex{MD5 hash} is computed for the string and the lower 64 bits
2619 are taken as the type signature.
2621 \textit{The string S is intended to be a flattened representation of
2622 the type that uniquely identifies that type (i.e., a different
2623 type is highly unlikely to produce the same string).}
2625 \textit{A debugging information entry should not be placed in a
2626 separate \addtoindex{type unit}
2627 if any of the following apply:}
2631 \item \textit{The entry has an attribute whose value is a location
2632 expression, and the location expression contains a reference to
2633 another debugging information entry (e.g., a \livelink{chap:DWOPcallref}{DW\_OP\_call\_ref}
2634 operator), as it is unlikely that the entry will remain
2635 identical across compilation units.}
2637 \item \textit{The entry has an attribute whose value refers
2638 to a code location or a \addtoindex{location list}.}
2640 \item \textit{The entry has an attribute whose value refers
2641 to another debugging information entry that does not represent
2647 \textit{Certain attributes are not included in the type signature:}
2650 \item \textit{The \livelink{chap:DWATdeclaration}{DW\_AT\_declaration} attribute is not included because it
2651 indicates that the debugging information entry represents an
2652 incomplete declaration, and incomplete declarations should
2654 \addtoindexx{type unit}
2655 separate type units.}
2657 \item \textit{The \livelink{chap:DWATdescription}{DW\_AT\_description} attribute is not included because
2658 it does not provide any information unique to the defining
2659 declaration of the type.}
2661 \item \textit{The \livelink{chap:DWATdeclfile}{DW\_AT\_decl\_file},
2662 \livelink{chap:DWATdeclline}{DW\_AT\_decl\_line}, and
2663 \livelink{chap:DWATdeclcolumn}{DW\_AT\_decl\_column} attributes are not included because they
2664 may vary from one source file to the next, and would prevent
2665 two otherwise identical type declarations from producing the
2666 \addtoindexx{MD5 hash}
2669 \item \textit{The \livelink{chap:DWATobjectpointer}{DW\_AT\_object\_pointer} attribute is not included
2670 because the information it provides is not necessary for the
2671 computation of a unique type signature.}
2675 \textit{Nested types and some types referred to by a debugging
2676 information entry are encoded by name rather than by recursively
2677 encoding the type to allow for cases where a complete definition
2678 of the type might not be available in all compilation units.}
2680 \textit{If a type definition contains the definition of a member function,
2681 it cannot be moved as is into a type unit, because the member function
2682 contains attributes that are unique to that compilation unit.
2683 Such a type definition can be moved to a type unit by rewriting the DIE tree,
2684 moving the member function declaration into a separate declaration tree,
2685 and replacing the function definition in the type with a non-defining
2686 declaration of the function (as if the function had been defined out of
2689 An example that illustrates the computation of an MD5 hash may be found in
2690 Appendix \refersec{app:usingtypeunits}.