2 \label{chap:typeentries}
3 This section presents the debugging information entries
4 that describe program types: base types, modified types and
5 user\dash defined types.
7 If the scope of the declaration of a named type begins after
8 \hypertarget{chap:DWATstartscopetypedeclaration}{}
9 the low pc value for the scope most closely enclosing the
10 declaration, the declaration may have a
12 attribute as described for objects in
13 Section \refersec{chap:dataobjectentries}.
15 \section{Base Type Entries}
16 \label{chap:basetypeentries}
18 \textit{A base type is a data type that is not defined in terms of
20 \addtoindexx{fundamental type|see{base type entry}}
21 Each programming language has a set of base
22 types that are considered to be built into that language.}
24 A base type is represented by a debugging information entry
28 A \addtoindex{base type entry}
29 has a \DWATname{} attribute
31 \addtoindexx{name attribute}
33 a null\dash terminated string containing the name of the base type
34 as recognized by the programming language of the compilation
35 unit containing the base type entry.
38 \addtoindexx{encoding attribute}
39 a \DWATencoding{} attribute describing
40 how the base type is encoded and is to be interpreted. The
41 value of this attribute is an
42 \livelink{chap:classconstant}{integer constant}. The set of
43 values and their meanings for the
44 \DWATencoding{} attribute
46 Table \refersec{tab:encodingattributevalues}
50 may have a \DWATendianity{} attribute
51 \addtoindexx{endianity attribute}
53 Section \refersec{chap:dataobjectentries}.
54 If omitted, the encoding assumes the representation that
55 is the default for the target architecture.
58 \hypertarget{chap:DWATbytesizedataobjectordatatypesize}{}
59 either a \DWATbytesize{} attribute
60 \hypertarget{chap:DWATbitsizebasetypebitsize}{}
61 or a \DWATbitsize{} attribute
62 \addtoindexx{bit size attribute}
63 whose \livelink{chap:classconstant}{integer constant} value
64 (see Section \refersec{chap:byteandbitsizes})
65 is the amount of storage needed to hold
69 \textit{For example, the
70 \addtoindex{C} type \texttt{int} on a machine that uses 32\dash bit
71 integers is represented by a base type entry with a name
72 attribute whose value is \doublequote{int}, an encoding attribute
73 whose value is \DWATEsigned{}
74 and a byte size attribute whose value is 4.}
76 If the value of an object of the given type does not fully
77 occupy the storage described by a byte size attribute,
78 \hypertarget{chap:DWATdatabitoffsetbasetypebitlocation}{}
79 the base type entry may also have
80 \addtoindexx{bit size attribute}
83 \DWATdatabitoffset{} attribute,
85 \addtoindexx{data bit offset attribute}
87 \livelink{chap:classconstant}{integer constant} values
88 (see Section \refersec{chap:staticanddynamicvaluesofattributes}).
90 attribute describes the actual size in bits used to represent
91 values of the given type. The data bit offset attribute is the
92 offset in bits from the beginning of the containing storage to
93 the beginning of the value. Bits that are part of the offset
94 are padding. The data bit offset uses the bit numbering and
95 direction conventions that are appropriate to the current
97 target system to locate the beginning of the storage and
98 value. If this attribute is omitted a default data bit offset
104 \addtoindexx{bit offset attribute}
106 \addtoindexx{data bit offset attribute}
108 \addtoindex{DWARF Version 4}, unchanged in \addtoindex{DWARF Version 5}, and
109 is also used for bit field members
110 (see Section \refersec{chap:datamemberentries}).
112 \hypertarget{chap:DWATbitoffsetbasetypebitlocation}{}
113 replaces the attribute
116 \addtoindexx{bit offset attribute (V3)}
117 types as defined in DWARF V3 and earlier.
119 is deprecated for use in base types in DWARF Version 4 and later.
120 See Section 5.1 in the DWARF Version 4
121 specification for a discussion of compatibility considerations.}
124 \caption{Encoding attribute values}
125 \label{tab:encodingattributevalues}
127 \begin{tabular}{l|p{8cm}}
129 Name&Meaning\\ \hline
130 \DWATEaddressTARG{} & linear machine address (for segmented\break
132 Section \refersec{chap:segmentedaddresses}) \\
133 \DWATEbooleanTARG& true or false \\
135 \DWATEcomplexfloatTARG& complex binary
136 floating\dash point number \\
137 \DWATEfloatTARG{} & binary floating\dash point number \\
138 \DWATEimaginaryfloatTARG& imaginary binary
139 floating\dash point number \\
140 \DWATEsignedTARG& signed binary integer \\
141 \DWATEsignedcharTARG& signed character \\
142 \DWATEunsignedTARG{} & unsigned binary integer \\
143 \DWATEunsignedcharTARG{} & unsigned character \\
144 \DWATEpackeddecimalTARG{} & packed decimal \\
145 \DWATEnumericstringTARG& numeric string \\
146 \DWATEeditedTARG{} & edited string \\
147 \DWATEsignedfixedTARG{} & signed fixed\dash point scaled integer \\
148 \DWATEunsignedfixedTARG& unsigned fixed\dash point scaled integer \\
149 \DWATEdecimalfloatTARG{} & decimal floating\dash point number \\
150 \DWATEUTFTARG{} & \addtoindex{Unicode} character \\
155 \textit{The \DWATEdecimalfloat{} encoding is intended for
156 floating\dash point representations that have a power\dash of\dash ten
157 exponent, such as that specified in IEEE 754R.}
159 \textit{The \DWATEUTF{} encoding is intended for \addtoindex{Unicode}
160 string encodings (see the Universal Character Set standard,
161 ISO/IEC 10646\dash 1:1993). For example, the
162 \addtoindex{C++} type char16\_t is
163 represented by a base type entry with a name attribute whose
164 value is \doublequote{char16\_t}, an encoding attribute whose value
165 is \DWATEUTF{} and a byte size attribute whose value is 2.}
168 \DWATEpackeddecimal{}
170 \DWATEnumericstring{}
172 represent packed and unpacked decimal string numeric data
173 types, respectively, either of which may be
175 \addtoindexx{decimal scale attribute}
177 \addtoindexx{decimal sign attribute}
179 \addtoindexx{digit count attribute}
181 \hypertarget{chap:DWATdecimalsigndecimalsignrepresentation}{}
183 \hypertarget{chap:DWATdigitcountdigitcountforpackeddecimalornumericstringtype}{}
184 base types are used in combination with
186 \DWATdigitcount{} and
191 A \DWATdecimalsign{} attribute
192 \addtoindexx{decimal sign attribute}
193 is an \livelink{chap:classconstant}{integer constant} that
194 conveys the representation of the sign of the decimal type
195 (see Table \refersec{tab:decimalsignattributevalues}).
196 Its \livelink{chap:classconstant}{integer constant} value is interpreted to
197 mean that the type has a leading overpunch, trailing overpunch,
198 leading separate or trailing separate sign representation or,
199 alternatively, no sign at all.
202 \caption{Decimal sign attribute values}
203 \label{tab:decimalsignattributevalues}
205 \begin{tabular}{l|p{9cm}}
209 \DWDSunsignedTARG{} & Unsigned \\
210 \DWDSleadingoverpunchTARG{} & Sign
211 is encoded in the most significant digit in a target\dash dependent manner \\
212 \DWDStrailingoverpunchTARG{} & Sign
213 is encoded in the least significant digit in a target\dash dependent manner \\
214 \DWDSleadingseparateTARG{}
215 & Decimal type: Sign is a \doublequote{+} or \doublequote{-} character
216 to the left of the most significant digit. \\
217 \DWDStrailingseparateTARG{}
218 & Decimal type: Sign is a \doublequote{+} or \doublequote{-} character
219 to the right of the least significant digit. \\
220 &Packed decimal type: Least significant nibble contains
221 a target\dash dependent value
222 indicating positive or negative. \\
230 \addtoindexx{digit count attribute}
231 is an \livelink{chap:classconstant}{integer constant}
232 value that represents the number of digits in an instance of
235 \hypertarget{chap:DWATdecimalscaledecimalscalefactor}{}
236 The \DWATdecimalscale{}
238 \addtoindexx{decimal scale attribute}
239 is an integer constant value
240 that represents the exponent of the base ten scale factor to
241 be applied to an instance of the type. A scale of zero puts the
242 decimal point immediately to the right of the least significant
243 digit. Positive scale moves the decimal point to the right
244 and implies that additional zero digits on the right are not
245 stored in an instance of the type. Negative scale moves the
246 decimal point to the left; if the absolute value of the scale
247 is larger than the digit count, this implies additional zero
248 digits on the left are not stored in an instance of the type.
252 \hypertarget{chap:DWATpicturestringpicturestringfornumericstringtype}{}
253 type is used to represent an edited
254 numeric or alphanumeric data type. It is used in combination
255 with a \DWATpicturestring{} attribute whose value is a
256 null\dash terminated string containing the target\dash dependent picture
257 string associated with the type.
259 If the edited base type entry describes an edited numeric
260 data type, the edited type entry has a \DWATdigitcount{} and a
261 \DWATdecimalscale{} attribute.
262 \addtoindexx{decimal scale attribute}
263 These attributes have the same
264 interpretation as described for the
265 \DWATEpackeddecimal{} and
266 \DWATEnumericstring{} base
267 types. If the edited type entry
268 describes an edited alphanumeric data type, the edited type
269 entry does not have these attributes.
272 \textit{The presence or absence of the \DWATdigitcount{} and
273 \DWATdecimalscale{} attributes
274 \addtoindexx{decimal scale attribute}
275 allows a debugger to easily
276 distinguish edited numeric from edited alphanumeric, although
277 in principle the digit count and scale are derivable by
278 interpreting the picture string.}
280 The \DWATEsignedfixed{} and \DWATEunsignedfixed{} entries
281 describe signed and unsigned fixed\dash point binary data types,
284 The fixed binary type entries have
285 \addtoindexx{digit count attribute}
288 attribute with the same interpretation as described for the
289 \DWATEpackeddecimal{} and \DWATEnumericstring{} base types.
292 For a data type with a decimal scale factor, the fixed binary
294 \DWATdecimalscale{} attribute
295 \addtoindexx{decimal scale attribute}
297 interpretation as described for the
298 \DWATEpackeddecimal{}
299 and \DWATEnumericstring{} base types.
301 \hypertarget{chap:DWATbinaryscalebinaryscalefactorforfixedpointtype}{}
302 For a data type with a binary scale factor, the fixed
303 \addtoindexx{binary scale attribute}
304 binary type entry has a
305 \DWATbinaryscale{} attribute.
307 \DWATbinaryscale{} attribute
308 is an \livelink{chap:classconstant}{integer constant} value
309 that represents the exponent of the base two scale factor to
310 be applied to an instance of the type. Zero scale puts the
311 binary point immediately to the right of the least significant
312 bit. Positive scale moves the binary point to the right and
313 implies that additional zero bits on the right are not stored
314 in an instance of the type. Negative scale moves the binary
315 point to the left; if the absolute value of the scale is
316 larger than the number of bits, this implies additional zero
317 bits on the left are not stored in an instance of the type.
320 \hypertarget{chap:DWATsmallscalefactorforfixedpointtype}{}
321 a data type with a non\dash decimal and non\dash binary scale factor,
322 the fixed binary type entry has a
323 \DWATsmall{} attribute which
324 \addtoindexx{small attribute}
326 \DWTAGconstant{} entry. The scale factor value
327 is interpreted in accordance with the value defined by the
328 \DWTAGconstant{} entry. The value represented is the product
329 of the integer value in memory and the associated constant
332 \textit{The \DWATsmall{} attribute
333 is defined with the \addtoindex{Ada} \texttt{small}
336 \section{Unspecified Type Entries}
337 \label{chap:unspecifiedtypeentries}
338 \addtoindexx{unspecified type entry}
339 \addtoindexx{void type|see{unspecified type entry}}
340 Some languages have constructs in which a type
341 may be left unspecified or the absence of a type
342 may be explicitly indicated.
344 An unspecified (implicit, unknown, ambiguous or nonexistent)
345 type is represented by a debugging information entry with
346 the tag \DWTAGunspecifiedtypeTARG.
347 If a name has been given
348 to the type, then the corresponding unspecified type entry
349 has a \DWATname{} attribute
350 \addtoindexx{name attribute}
352 a null\dash terminated
353 string containing the name as it appears in the source program.
355 The interpretation of this debugging information entry is
356 intentionally left flexible to allow it to be interpreted
357 appropriately in different languages. For example, in
358 \addtoindex{C} and \addtoindex{C++}
359 the language implementation can provide an unspecified type
360 entry with the name \doublequote{void} which can be referenced by the
361 type attribute of pointer types and typedef declarations for
363 Sections \refersec{chap:typemodifierentries} and
364 %The following reference was valid, so the following is probably correct.
365 Section \refersec{chap:typedefentries},
366 respectively). As another
367 example, in \addtoindex{Ada} such an unspecified type entry can be referred
368 to by the type attribute of an access type where the denoted
369 \addtoindexx{incomplete type (Ada)}
370 type is incomplete (the name is declared as a type but the
371 definition is deferred to a separate compilation unit).
373 \addtoindex{C++} permits using the
374 \addtoindexi{\texttt{auto}}{\texttt{auto return type}} specifier for the return
375 type of a member function declaration.
376 The actual return type is deduced based on the definition of the
377 function, so it may not be known when the function is declared. The language
378 implementation can provide an unspecified type entry with the name \texttt{auto} which
379 can be referenced by the return type attribute of a function declaration entry.
380 When the function is later defined, the \DWTAGsubprogram{} entry for the definition
381 includes a reference to the actual return type.
384 \section{Type Modifier Entries}
385 \label{chap:typemodifierentries}
386 \addtoindexx{type modifier entry}
387 \addtoindexx{type modifier|see{atomic type entry}}
388 \addtoindexx{type modifier|see{constant type entry}}
389 \addtoindexx{type modifier|see{reference type entry}}
390 \addtoindexx{type modifier|see{restricted type entry}}
391 \addtoindexx{type modifier|see{packed type entry}}
392 \addtoindexx{type modifier|see{pointer type entry}}
393 \addtoindexx{type modifier|see{shared type entry}}
394 \addtoindexx{type modifier|see{volatile type entry}}
395 A base or user\dash defined type may be modified in different ways
396 in different languages. A type modifier is represented in
397 DWARF by a debugging information entry with one of the tags
398 given in Table \refersec{tab:typemodifiertags}.
400 If a name has been given to the modified type in the source
401 program, then the corresponding modified type entry has
402 a \DWATname{} attribute
403 \addtoindexx{name attribute}
404 whose value is a null\dash terminated
405 string containing the modified type name as it appears in
408 Each of the type modifier entries has
409 \addtoindexx{type attribute}
411 \DWATtype{} attribute,
412 whose value is a \livelink{chap:classreference}{reference}
413 to a debugging information entry
414 describing a base type, a user-defined type or another type
417 A modified type entry describing a
418 \addtoindexx{pointer type entry}
419 pointer or \addtoindex{reference type}
420 (using \DWTAGpointertype,
421 \DWTAGreferencetype{} or
422 \DWTAGrvaluereferencetype)
423 % Another instance of no-good-place-to-put-index entry.
425 \addtoindexx{address class!attribute}
427 \hypertarget{chap:DWATadressclasspointerorreferencetypes}{}
430 attribute to describe how objects having the given pointer
431 or reference type ought to be dereferenced.
433 A modified type entry describing a \addtoindex{UPC} shared qualified type
434 (using \DWTAGsharedtype) may have a
435 \DWATcount{} attribute
436 \addtoindexx{count attribute}
437 whose value is a constant expressing the (explicit or implied) blocksize specified for the
438 type in the source. If no count attribute is present, then the \doublequote{infinite}
439 blocksize is assumed.
441 When multiple type modifiers are chained together to modify
442 a base or user-defined type, the tree ordering reflects the
444 \addtoindexx{reference type entry, lvalue|see{reference type entry}}
446 \addtoindexx{reference type entry, rvalue|see{rvalue reference type entry}}
448 \addtoindexx{parameter|see{macro formal parameter list}}
450 \addtoindexx{parameter|see{\textit{this} parameter}}
452 \addtoindexx{parameter|see{variable parameter attribute}}
454 \addtoindexx{parameter|see{optional parameter attribute}}
456 \addtoindexx{parameter|see{unspecified parameters entry}}
458 \addtoindexx{parameter|see{template value parameter entry}}
460 \addtoindexx{parameter|see{template type parameter entry}}
462 \addtoindexx{parameter|see{formal parameter entry}}
466 \caption{Type modifier tags}
467 \label{tab:typemodifiertags}
469 \begin{tabular}{l|p{9cm}}
471 Name&Meaning\\ \hline
472 \DWTAGatomictypeTARG{} & C \addtoindex{\_Atomic} qualified type \\
473 \DWTAGconsttypeTARG{} & C or C++ const qualified type
474 \addtoindexx{const qualified type entry} \addtoindexx{C} \addtoindexx{C++} \\
475 \DWTAGpackedtypeTARG& \addtoindex{Pascal} or Ada packed type\addtoindexx{packed type entry}
476 \addtoindexx{packed qualified type entry} \addtoindexx{Ada} \addtoindexx{Pascal} \\
477 \DWTAGpointertypeTARG{} & Pointer to an object of
478 the type being modified \addtoindexx{pointer qualified type entry} \\
479 \DWTAGreferencetypeTARG& C++ (lvalue) reference
480 to an object of the type
481 \addtoindexx{reference type entry}
482 \mbox{being} modified
483 \addtoindexx{reference qualified type entry} \\
484 \DWTAGrestricttypeTARG& \addtoindex{C}
486 \addtoindexx{restricted type entry}
488 \addtoindexx{restrict qualified type} \\
489 \DWTAGrvaluereferencetypeTARG{} & C++
490 \addtoindexx{rvalue reference type entry}
492 \addtoindexx{restricted type entry}
493 reference to an object of the type \mbox{being} modified
494 \addtoindexx{rvalue reference qualified type entry} \\
495 \DWTAGsharedtypeTARG&\addtoindex{UPC} shared qualified type
496 \addtoindexx{shared qualified type entry} \\
497 \DWTAGvolatiletypeTARG&C or C++ volatile qualified type
498 \addtoindexx{volatile qualified type entry} \\
504 \textit{As examples of how type modifiers are ordered, consider the following
505 \addtoindex{C} declarations:}
506 \begin{lstlisting}[numbers=none]
507 const unsigned char * volatile p;
509 \textit{which represents a volatile pointer to a constant
510 character. This is encoded in DWARF as:}
514 \DWTAGvariable(p) -->
515 \DWTAGvolatiletype -->
516 \DWTAGpointertype -->
518 \DWTAGbasetype(unsigned char)
523 \textit{On the other hand}
524 \begin{lstlisting}[numbers=none]
525 volatile unsigned char * const restrict p;
527 \textit{represents a restricted constant
528 pointer to a volatile character. This is encoded as:}
532 \DWTAGvariable(p) -->
533 \DWTAGrestricttype -->
535 \DWTAGpointertype -->
536 \DWTAGvolatiletype -->
537 \DWTAGbasetype(unsigned char)
541 \section{Typedef Entries}
542 \label{chap:typedefentries}
543 A named type that is defined in terms of another type
544 definition is represented by a debugging information entry with
545 \addtoindexx{typedef entry}
546 the tag \DWTAGtypedefTARG.
547 The typedef entry has a \DWATname{} attribute
548 \addtoindexx{name attribute}
549 whose value is a null\dash terminated string containing
550 the name of the typedef as it appears in the source program.
552 The typedef entry may also contain
553 \addtoindexx{type attribute}
555 \DWATtype{} attribute whose
556 value is a \livelink{chap:classreference}{reference}
557 to the type named by the typedef. If
558 the debugging information entry for a typedef represents
559 a declaration of the type that is not also a definition,
560 it does not contain a type attribute.
562 \textit{Depending on the language, a named type that is defined in
563 terms of another type may be called a type alias, a subtype,
564 a constrained type and other terms. A type name declared with
565 no defining details may be termed an
566 \addtoindexx{incomplete type}
567 incomplete, forward or hidden type.
568 While the DWARF \DWTAGtypedef{} entry was
569 originally inspired by the like named construct in
570 \addtoindex{C} and \addtoindex{C++},
571 it is broadly suitable for similar constructs (by whatever
572 source syntax) in other languages.}
574 \section{Array Type Entries}
575 \label{chap:arraytypeentries}
576 \label{chap:DWTAGgenericsubrange}
578 \textit{Many languages share the concept of an \doublequote{array,} which is
579 \addtoindexx{array type entry}
580 a table of components of identical type.}
582 An array type is represented by a debugging information entry
583 with the tag \DWTAGarraytypeTARG.
584 If a name has been given to
585 \addtoindexx{array!declaration of type}
586 the array type in the source program, then the corresponding
587 array type entry has a \DWATname{} attribute
588 \addtoindexx{name attribute}
590 null\dash terminated string containing the array type name as it
591 appears in the source program.
594 \hypertarget{chap:DWATorderingarrayrowcolumnordering}{}
595 array type entry describing a multidimensional array may
596 \addtoindexx{array!element ordering}
597 have a \DWATordering{} attribute whose
598 \livelink{chap:classconstant}{integer constant} value is
599 interpreted to mean either row-major or column-major ordering
600 of array elements. The set of values and their meanings
601 for the ordering attribute are listed in
602 Table \refersec{tab:arrayordering}.
604 ordering attribute is present, the default ordering for the
605 source language (which is indicated by the
608 \addtoindexx{language attribute}
609 of the enclosing compilation unit entry) is assumed.
611 \begin{simplenametable}[1.8in]{Array ordering}{tab:arrayordering}
612 \DWORDcolmajorTARG{} \\
613 \DWORDrowmajorTARG{} \\
614 \end{simplenametable}
616 The ordering attribute may optionally appear on one-dimensional
617 arrays; it will be ignored.
619 An array type entry has
620 \addtoindexx{type attribute}
621 a \DWATtype{} attribute
623 \addtoindexx{array!element type}
624 the type of each element of the array.
626 If the amount of storage allocated to hold each element of an
627 object of the given array type is different from the amount
628 \addtoindexx{stride attribute|see{bit stride attribute or byte stride attribute}}
629 of storage that is normally allocated to hold an individual
630 \hypertarget{chap:DWATbitstridearrayelementstrideofarraytype}{}
632 \hypertarget{chap:DWATbytestridearrayelementstrideofarraytype}{}
633 indicated element type, then the array type
634 \addtoindexx{bit stride attribute}
638 \addtoindexx{byte stride attribute}
641 \addtoindexx{bit stride attribute}
643 (see Section \refersec{chap:staticanddynamicvaluesofattributes})
645 element of the array.
647 The array type entry may have either a \DWATbytesize{} or a
648 \DWATbitsize{} attribute
649 (see Section \refersec{chap:byteandbitsizes}),
651 amount of storage needed to hold an instance of the array type.
653 \textit{If the size of the array can be determined statically at
654 compile time, this value can usually be computed by multiplying
655 the number of array elements by the size of each element.}
658 Each array dimension is described by a debugging information
659 entry with either the
660 \addtoindexx{subrange type entry!as array dimension}
661 tag \DWTAGsubrangetype{} or the
662 \addtoindexx{enumeration type entry!as array dimension}
664 \DWTAGenumerationtype. These entries are
666 array type entry and are ordered to reflect the appearance of
667 the dimensions in the source program (that is, leftmost dimension
668 first, next to leftmost second, and so on).
670 \textit{In languages that have no concept of a
671 \doublequote{multidimensional array} (for example,
672 \addtoindex{C}), an array of arrays may
673 be represented by a debugging information entry for a
674 multidimensional array.}
676 Alternatively, for an array with dynamic rank the array dimensions
677 are described by a debugging information entry with the tag
678 \DWTAGgenericsubrangeTARG.
679 This entry has the same attributes as a
680 \DWTAGsubrangetype{} entry; however,
681 there is just one \DWTAGgenericsubrangeNAME{} entry and it describes all of the
682 dimensions of the array.
683 If \DWTAGgenericsubrangeNAME{}
684 is used, the number of dimensions must be specified using a
685 \DWATrank{} attribute. See also Section
686 \refersec{chap:DWATrank}.
690 Other attributes especially applicable to arrays are
692 \DWATassociated{} and
694 which are described in
695 Section \refersec{chap:dynamictypeproperties}.
696 For relevant examples, see also Appendix \refersec{app:fortranarrayexample}.
698 \section{Coarray Type Entries}
699 \label{chap:coarraytypeentries}
700 \addtoindexx{coarray}
701 \textit{In Fortran, a \doublequote{coarray} is an array whose
702 elements are located in different processes rather than in the
703 memory of one process. The individual elements
704 of a coarray can be scalars or arrays.
705 Similar to arrays, coarrays have \doublequote{codimensions} that are
706 indexed using a \doublequote{coindex} or multiple \doublequote{coindices}.
707 \addtoindexx{codimension|see{coarray}}
708 \addtoindexx{coindex|see{coarray}}
711 A coarray type is represented by a debugging information entry
712 with the tag \DWTAGcoarraytypeTARG.
713 If a name has been given to the
714 coarray type in the source, then the corresponding coarray type
715 entry has a \DWATname{} attribute whose value is a null-terminated
716 string containing the array type name as it appears in the source
719 A coarray entry has one or more \DWTAGsubrangetype{} child entries,
720 one for each codimension. It also has a \DWATtype{} attribute
721 describing the type of each element of the coarray.
723 \textit{In a coarray application, the run-time number of processes in the application
724 is part of the coindex calculation. It is represented in the Fortran source by
725 a coindex which is declared with a \doublequote{*} as the upper bound. To express this
726 concept in DWARF, the \DWTAGsubrangetype{} child entry for that index has
727 only a lower bound and no upper bound.}
729 \textit{How coarray elements are located and how coindices are
730 converted to process specifications is processor-dependent.}
733 \section{Structure, Union, Class and Interface Type Entries}
734 \label{chap:structureunionclassandinterfacetypeentries}
736 \textit{The languages
738 \addtoindex{C++}, and
739 \addtoindex{Pascal}, among others, allow the
740 programmer to define types that are collections of related
741 \addtoindexx{structure type entry}
743 In \addtoindex{C} and \addtoindex{C++}, these collections are called
744 \doublequote{structures.}
745 In \addtoindex{Pascal}, they are called \doublequote{records.}
746 The components may be of different types. The components are
747 called \doublequote{members} in \addtoindex{C} and
748 \addtoindex{C++}, and \doublequote{fields} in \addtoindex{Pascal}.}
750 \textit{The components of these collections each exist in their
751 own space in computer memory. The components of a C or C++
752 \doublequote{union} all coexist in the same memory.}
754 \textit{\addtoindex{Pascal} and
755 other languages have a \doublequote{discriminated union,}
756 \addtoindexx{discriminated union|see {variant entry}}
757 also called a \doublequote{variant record.} Here, selection of a
758 number of alternative substructures (\doublequote{variants}) is based
759 on the value of a component that is not part of any of those
760 substructures (the \doublequote{discriminant}).}
762 \textit{\addtoindex{C++} and
763 \addtoindex{Java} have the notion of \doublequote{class,} which is in some
764 ways similar to a structure. A class may have \doublequote{member
765 functions} which are subroutines that are within the scope
766 of a class or structure.}
768 \textit{The \addtoindex{C++} notion of
769 structure is more general than in \addtoindex{C}, being
770 equivalent to a class with minor differences. Accordingly,
771 in the following discussion statements about
772 \addtoindex{C++} classes may
773 be understood to apply to \addtoindex{C++} structures as well.}
775 \subsection{Structure, Union and Class Type Entries}
776 \label{chap:structureunionandclasstypeentries}
779 Structure, union, and class types are represented by debugging
780 \addtoindexx{structure type entry}
782 \addtoindexx{union type entry}
784 \addtoindexx{class type entry}
786 \DWTAGstructuretypeTARG,
788 and \DWTAGclasstypeTARG,
789 respectively. If a name has been given to the structure,
790 union, or class in the source program, then the corresponding
791 structure type, union type, or class type entry has a
792 \DWATname{} attribute
793 \addtoindexx{name attribute}
794 whose value is a null\dash terminated string
795 containing the type name as it appears in the source program.
797 The members of a structure, union, or class are represented
798 by debugging information entries that are owned by the
799 corresponding structure type, union type, or class type entry
800 and appear in the same order as the corresponding declarations
801 in the source program.
803 A structure type, union type or class type entry may have
804 either a \DWATbytesize{} or a
805 \DWATbitsize{} attribute
806 \hypertarget{chap:DWATbitsizedatamemberbitsize}{}
807 (see Section \refersec{chap:byteandbitsizes}),
808 whose value is the amount of storage needed
809 to hold an instance of the structure, union or class type,
810 including any padding.
812 An incomplete structure, union or class type
813 \addtoindexx{incomplete structure/union/class}
815 \addtoindexx{incomplete type}
816 represented by a structure, union or class
817 entry that does not have a byte size attribute and that has
818 \addtoindexx{declaration attribute}
819 a \DWATdeclaration{} attribute.
821 If the complete declaration of a type has been placed in
822 \hypertarget{chap:DWATsignaturetypesignature}{}
823 a separate \addtoindex{type unit}
824 (see Section \refersec{chap:separatetypeunitentries}),
825 an incomplete declaration
826 \addtoindexx{incomplete type}
827 of that type in the compilation unit may provide
828 the unique 64\dash bit signature of the type using
829 \addtoindexx{type signature}
833 If a structure, union or class entry represents the definition
834 of a structure, union or class member corresponding to a prior
835 incomplete structure, union or class, the entry may have a
836 \DWATspecification{} attribute
837 \addtoindexx{specification attribute}
838 whose value is a \livelink{chap:classreference}{reference} to
839 the debugging information entry representing that incomplete
842 Structure, union and class entries containing the
843 \DWATspecification{} attribute
844 \addtoindexx{specification attribute}
845 do not need to duplicate
846 information provided by the declaration entry referenced by the
847 specification attribute. In particular, such entries do not
848 need to contain an attribute for the name of the structure,
849 union or class they represent if such information is already
850 provided in the declaration.
852 \textit{For \addtoindex{C} and \addtoindex{C++},
854 \addtoindexx{data member|see {member entry (data)}}
855 member declarations occurring within
856 the declaration of a structure, union or class type are
857 considered to be \doublequote{definitions} of those members, with
858 the exception of \doublequote{static} data members, whose definitions
859 appear outside of the declaration of the enclosing structure,
860 union or class type. Function member declarations appearing
861 within a structure, union or class type declaration are
862 definitions only if the body of the function also appears
863 within the type declaration.}
865 If the definition for a given member of the structure, union
866 or class does not appear within the body of the declaration,
867 that member also has a debugging information entry describing
868 its definition. That latter entry has a
869 \DWATspecification{} attribute
870 \addtoindexx{specification attribute}
871 referencing the debugging information entry
872 owned by the body of the structure, union or class entry and
873 representing a non\dash defining declaration of the data, function
874 or type member. The referenced entry will not have information
875 about the location of that member (low and high pc attributes
876 for function members, location descriptions for data members)
877 and will have a \DWATdeclaration{} attribute.
880 \textit{Consider a nested class whose
881 definition occurs outside of the containing class definition, as in:}
883 \begin{lstlisting}[numbers=none]
890 \textit{The two different structs can be described in
891 different compilation units to
892 facilitate DWARF space compression
893 (see Appendix \refersec{app:usingcompilationunits}).}
895 \subsection{Interface Type Entries}
896 \label{chap:interfacetypeentries}
898 \textit{The \addtoindex{Java} language defines \doublequote{interface} types.
900 \addtoindexx{interface type entry}
901 in \addtoindex{Java} is similar to a \addtoindex{C++} or
902 \addtoindex{Java} class with only abstract
903 methods and constant data members.}
906 \addtoindexx{interface type entry}
907 are represented by debugging information
909 tag \DWTAGinterfacetypeTARG.
911 An interface type entry has
912 a \DWATname{} attribute,
913 \addtoindexx{name attribute}
915 value is a null\dash terminated string containing the type name
916 as it appears in the source program.
918 The members of an interface are represented by debugging
919 information entries that are owned by the interface type
920 entry and that appear in the same order as the corresponding
921 declarations in the source program.
923 \subsection{Derived or Extended Structs, Classes and Interfaces}
924 \label{chap:derivedorextendedstructsclasesandinterfaces}
926 \textit{In \addtoindex{C++}, a class (or struct)
928 \addtoindexx{derived type (C++)|see{inheritance entry}}
929 be \doublequote{derived from} or be a
930 \doublequote{subclass of} another class.
931 In \addtoindex{Java}, an interface may \doublequote{extend}
932 \addtoindexx{extended type (Java)|see{inheritance entry}}
934 \addtoindexx{implementing type (Java)|see{inheritance entry}}
935 or more other interfaces, and a class may \doublequote{extend} another
936 class and/or \doublequote{implement} one or more interfaces. All of these
937 relationships may be described using the following. Note that
938 in \addtoindex{Java},
939 the distinction between extends and implements is
940 implied by the entities at the two ends of the relationship.}
942 A class type or interface type entry that describes a
943 derived, extended or implementing class or interface owns
944 \addtoindexx{implementing type (Java)|see{inheritance entry}}
945 debugging information entries describing each of the classes
946 or interfaces it is derived from, extending or implementing,
947 respectively, ordered as they were in the source program. Each
949 \addtoindexx{inheritance entry}
951 tag \DWTAGinheritanceTARG.
954 \addtoindexx{type attribute}
956 \addtoindexx{inheritance entry}
958 \DWATtype{} attribute whose value is
959 a reference to the debugging information entry describing the
960 class or interface from which the parent class or structure
961 of the inheritance entry is derived, extended or implementing.
964 \addtoindexx{inheritance entry}
965 for a class that derives from or extends
966 \hypertarget{chap:DWATdatamemberlocationinheritedmemberlocation}{}
967 another class or struct also has
968 \addtoindexx{data member location attribute}
970 \DWATdatamemberlocation{}
971 attribute, whose value describes the location of the beginning
972 of the inherited type relative to the beginning address of the
973 instance of the derived class. If that value is a constant, it is the offset
974 in bytes from the beginning of the class to the beginning of
975 the instance of the inherited type. Otherwise, the value must be a location
976 description. In this latter case, the beginning address of
977 the instance of the derived class is pushed on the expression stack before
978 the \addtoindex{location description}
979 is evaluated and the result of the
980 evaluation is the location of the instance of the inherited type.
982 \textit{The interpretation of the value of this attribute for
983 inherited types is the same as the interpretation for data
985 (see Section \referfol{chap:datamemberentries}). }
988 \addtoindexx{inheritance entry}
990 \hypertarget{chap:DWATaccessibilitycppinheritedmembers}{}
992 \addtoindexx{accessibility attribute}
996 If no accessibility attribute
997 is present, private access is assumed for an entry of a class
998 and public access is assumed for an entry of an interface,
1002 \hypertarget{chap:DWATvirtualityvirtualityofbaseclass}{}
1003 the class referenced by the
1004 \addtoindexx{inheritance entry}
1005 inheritance entry serves
1006 as a \addtoindex{C++} virtual base class, the inheritance entry has a
1007 \DWATvirtuality{} attribute.
1009 \textit{For a \addtoindex{C++} virtual base, the
1010 \addtoindex{data member location attribute}
1011 will usually consist of a non-trivial
1012 \addtoindex{location description}.}
1014 \subsection{Access Declarations}
1015 \label{chap:accessdeclarations}
1017 \textit{In \addtoindex{C++}, a derived class may contain access declarations that
1018 \addtoindexx{access declaration entry}
1019 change the accessibility of individual class members from the
1020 overall accessibility specified by the inheritance declaration.
1021 A single access declaration may refer to a set of overloaded
1024 If a derived class or structure contains access declarations,
1025 each such declaration may be represented by a debugging
1026 information entry with the tag
1027 \DWTAGaccessdeclarationTARG.
1029 such entry is a child of the class or structure type entry.
1031 An access declaration entry has
1032 a \DWATname{} attribute,
1033 \addtoindexx{name attribute}
1035 value is a null\dash terminated string representing the name used
1036 in the declaration in the source program, including any class
1037 or structure qualifiers.
1039 An access declaration entry
1040 \hypertarget{chap:DWATaccessibilitycppbaseclasses}{}
1043 \DWATaccessibility{}
1044 attribute describing the declared accessibility of the named
1049 \subsection{Friends}
1050 \label{chap:friends}
1052 Each \doublequote{friend}
1053 \addtoindexx{friend entry}
1054 declared by a structure, union or class
1055 \hypertarget{chap:DWATfriendfriendrelationship}{}
1056 type may be represented by a debugging information entry
1057 that is a child of the structure, union or class type entry;
1058 the friend entry has the
1059 tag \DWTAGfriendTARG.
1062 \addtoindexx{friend attribute}
1063 a \DWATfriend{} attribute, whose value is
1064 a reference to the debugging information entry describing
1065 the declaration of the friend.
1068 \subsection{Data Member Entries}
1069 \label{chap:datamemberentries}
1071 A data member (as opposed to a member function) is
1072 represented by a debugging information entry with the
1073 tag \DWTAGmemberTARG.
1075 \addtoindexx{member entry (data)}
1076 member entry for a named member has
1077 a \DWATname{} attribute
1078 \addtoindexx{name attribute}
1079 whose value is a null\dash terminated
1080 string containing the member name as it appears in the source
1081 program. If the member entry describes an
1082 \addtoindex{anonymous union},
1083 the name attribute is omitted or the value of the attribute
1084 consists of a single zero byte.
1086 The data member entry has
1087 \addtoindexx{type attribute}
1089 \DWATtype{} attribute to denote
1090 \addtoindexx{member entry (data)}
1091 the type of that member.
1093 A data member entry may
1094 \addtoindexx{accessibility attribute}
1096 \DWATaccessibility{}
1097 attribute. If no accessibility attribute is present, private
1098 access is assumed for an entry of a class and public access
1099 is assumed for an entry of a structure, union, or interface.
1102 \hypertarget{chap:DWATmutablemutablepropertyofmemberdata}{}
1104 \addtoindexx{member entry (data)}
1106 \addtoindexx{mutable attribute}
1107 have a \DWATmutable{} attribute,
1108 which is a \livelink{chap:classflag}{flag}.
1109 This attribute indicates whether the data
1110 member was declared with the mutable storage class specifier.
1112 The beginning of a data member
1113 \addtoindexx{beginning of a data member}
1114 is described relative to
1115 \addtoindexx{beginning of an object}
1116 the beginning of the object in which it is immediately
1117 contained. In general, the beginning is characterized by
1118 both an address and a bit offset within the byte at that
1119 address. When the storage for an entity includes all of
1120 the bits in the beginning byte, the beginning bit offset is
1123 Bit offsets in DWARF use the bit numbering and direction
1124 conventions that are appropriate to the current language on
1128 \addtoindexx{member entry (data)}
1129 corresponding to a data member that is
1130 \hypertarget{chap:DWATdatabitoffsetdatamemberbitlocation}{}
1132 \hypertarget{chap:DWATdatamemberlocationdatamemberlocation}{}
1133 in a structure, union or class may have either
1134 \addtoindexx{data member location attribute}
1136 \DWATdatamemberlocation{} attribute or a
1137 \DWATdatabitoffset{}
1138 attribute. If the beginning of the data member is the same as
1139 the beginning of the containing entity then neither attribute
1143 For a \DWATdatamemberlocation{} attribute
1144 \addtoindexx{data member location attribute}
1145 there are two cases:
1146 \begin{enumerate}[1. ]
1147 \item If the value is an \livelink{chap:classconstant}{integer constant},
1149 in bytes from the beginning of the containing entity. If
1150 the beginning of the containing entity has a non-zero bit
1151 offset then the beginning of the member entry has that same
1154 \item Otherwise, the value must be a \addtoindex{location description}.
1156 this case, the beginning of the containing entity must be byte
1157 aligned. The beginning address is pushed on the DWARF stack
1158 before the \addtoindex{location} description is evaluated; the result of
1159 the evaluation is the base address of the member entry.
1161 \textit{The push on the DWARF expression stack of the base address of
1162 the containing construct is equivalent to execution of the
1163 \DWOPpushobjectaddress{} operation
1164 (see Section \refersec{chap:stackoperations});
1165 \DWOPpushobjectaddress{} therefore
1166 is not needed at the
1167 beginning of a \addtoindex{location description} for a data member.
1169 result of the evaluation is a location---either an address or
1170 the name of a register, not an offset to the member.}
1172 \textit{A \DWATdatamemberlocation{}
1174 \addtoindexx{data member location attribute}
1175 that has the form of a
1176 \addtoindex{location description} is not valid for a data member contained
1177 in an entity that is not byte aligned because DWARF operations
1178 do not allow for manipulating or computing bit offsets.}
1182 For a \DWATdatabitoffset{} attribute,
1183 the value is an \livelink{chap:classconstant}{integer constant}
1184 (see Section \refersec{chap:staticanddynamicvaluesofattributes})
1185 that specifies the number of bits
1186 from the beginning of the containing entity to the beginning
1187 of the data member. This value must be greater than or equal
1188 to zero, but is not limited to less than the number of bits
1191 If the size of a data member is not the same as the size
1192 of the type given for the data member, the data member has
1193 \addtoindexx{bit size attribute}
1194 either a \DWATbytesize{}
1195 or a \DWATbitsize{} attribute whose
1196 \livelink{chap:classconstant}{integer constant} value
1197 (see Section \refersec{chap:staticanddynamicvaluesofattributes})
1199 of storage needed to hold the value of the data member.
1201 \textit{Bit fields in \addtoindex{C} and \addtoindex{C++}
1203 \addtoindexx{bit fields}
1205 \addtoindexx{data bit offset}
1207 \addtoindexx{data bit size}
1209 \DWATdatabitoffset{} and
1210 \DWATbitsize{} attributes.}
1213 \textit{This Standard uses the following bit numbering and direction
1214 conventions in examples. These conventions are for illustrative
1215 purposes and other conventions may apply on particular
1218 \item \textit{For big\dash endian architectures, bit offsets are
1219 counted from high-order to low\dash order bits within a byte (or
1220 larger storage unit); in this case, the bit offset identifies
1221 the high\dash order bit of the object.}
1223 \item \textit{For little\dash endian architectures, bit offsets are
1224 counted from low\dash order to high\dash order bits within a byte (or
1225 larger storage unit); in this case, the bit offset identifies
1226 the low\dash order bit of the object.}
1230 \textit{In either case, the bit so identified is defined as the
1231 \addtoindexx{beginning of an object}
1232 beginning of the object.}
1235 \textit{For example, take one possible representation of the following
1236 \addtoindex{C} structure definition
1237 in both big\dash and little\dash endian byte orders:}
1248 \textit{Figures \referfol{fig:bigendiandatabitoffsets} and
1249 \refersec{fig:littleendiandatabitoffsets}
1250 show the structure layout
1251 and data bit offsets for example big\dash\ and little\dash endian
1252 architectures, respectively. Both diagrams show a structure
1253 that begins at address A and whose size is four bytes. Also,
1254 high order bits are to the left and low order bits are to
1266 Addresses increase ->
1267 | A | A + 1 | A + 2 | A + 3 |
1269 Data bit offsets increase ->
1270 +---------------+---------------+---------------+---------------+
1271 |0 4|5 10|11 15|16 23|24 31|
1272 | j | k | m | n | <pad> |
1274 +---------------------------------------------------------------+
1278 \caption{Big-endian data bit offsets}
1279 \label{fig:bigendiandatabitoffsets}
1290 <- Addresses increase
1291 | A + 3 | A + 2 | A + 1 | A |
1293 <- Data bit offsets increase
1294 +---------------+---------------+---------------+---------------+
1295 |31 24|23 16|15 11|10 5|4 0|
1296 | <pad> | n | m | k | j |
1298 +---------------------------------------------------------------+
1302 \caption{Little-endian data bit offsets}
1303 \label{fig:littleendiandatabitoffsets}
1306 \textit{Note that data member bit offsets in this example are the
1307 same for both big\dash\ and little\dash endian architectures even
1308 though the fields are allocated in different directions
1309 (high\dash order to low-order versus low\dash order to high\dash order);
1310 the bit naming conventions for memory and/or registers of
1311 the target architecture may or may not make this seem natural.}
1313 \textit{For a more extensive example showing nested and packed records
1315 Appendix \refersec{app:pascalexample}.}
1317 \textit{Attribute \DWATdatabitoffset{}
1319 \addtoindex{DWARF Version 4}, unchanged in \addtoindex{DWARF Version 5},
1320 and is also used for base types
1322 \refersec{chap:basetypeentries}).
1324 \livetarg{chap:DWATbitoffsetdatamemberbitlocation}{}
1325 attributes \DWATbitoffset{} and
1326 \DWATbytesize{} when used to
1327 identify the beginning of bit field data members as defined
1328 in DWARF V3 and earlier. The \DWATbytesize,
1331 attribute combination is deprecated for data members in DWARF
1332 Version 4 and later. See Section 5.6.6 in the DWARF Version 4
1333 specification for a discussion of compatibility considerations.}
1335 \subsection{Member Function Entries}
1336 \label{chap:memberfunctionentries}
1338 A member function is represented by a
1339 \addtoindexx{member function entry}
1340 debugging information entry
1342 \addtoindexx{subprogram entry!as member function}
1343 tag \DWTAGsubprogram.
1344 The member function entry
1345 may contain the same attributes and follows the same rules
1346 as non\dash member global subroutine entries
1347 (see Section \refersec{chap:subroutineandentrypointentries}).
1349 \textit{In particular, if the member function entry is an
1350 instantiation of a member function template, it follows the
1351 same rules as function template instantiations (see Section
1352 \refersec{chap:functiontemplateinstantiations}).
1356 \addtoindexx{accessibility attribute}
1357 member function entry may have a
1358 \DWATaccessibility{}
1359 attribute. If no accessibility attribute is present, private
1360 access is assumed for an entry of a class and public access
1361 is assumed for an entry of a structure, union or interface.
1364 \hypertarget{chap:DWATvirtualityvirtualityoffunction}{}
1365 the member function entry describes a virtual function,
1366 then that entry has a
1367 \DWATvirtuality{} attribute.
1370 \hypertarget{chap:DWATexplicitexplicitpropertyofmemberfunction}{}
1371 the member function entry describes an explicit member
1372 function, then that entry has
1373 \addtoindexx{explicit attribute}
1375 \DWATexplicit{} attribute.
1378 \hypertarget{chap:DWATvtableelemlocationvirtualfunctiontablevtableslot}{}
1379 entry for a virtual function also has a
1380 \DWATvtableelemlocation{}
1381 \addtoindexi{attribute}{vtable element location attribute} whose value contains
1382 a \addtoindex{location description}
1383 yielding the address of the slot
1384 for the function within the virtual function table for the
1385 enclosing class. The address of an object of the enclosing
1386 type is pushed onto the expression stack before the location
1387 description is evaluated.
1390 \hypertarget{chap:DWATobjectpointerobjectthisselfpointerofmemberfunction}{}
1391 the member function entry describes a non\dash static member
1392 \addtoindexx{this pointer attribute|see{object pointer attribute}}
1393 function, then that entry
1394 \addtoindexx{self pointer attribute|see{object pointer attribute}}
1396 \addtoindexx{object pointer attribute}
1397 a \DWATobjectpointer{}
1399 whose value is a \livelink{chap:classreference}{reference}
1400 to the formal parameter entry
1401 that corresponds to the object for which the function is
1402 called. The name attribute of that formal parameter is defined
1403 by the current language (for example,
1404 \texttt{this} for \addtoindex{C++} or \texttt{self}
1405 for \addtoindex{Objective C}
1406 and some other languages). That parameter
1407 also has a \DWATartificial{} attribute whose value is true.
1409 Conversely, if the member function entry describes a static
1410 member function, the entry does not have
1411 \addtoindexx{object pointer attribute}
1413 \DWATobjectpointer{}
1416 \textit{In \addtoindex{C++}, non-static member functions can have const-volatile
1417 qualifiers, which affect the type of the first formal parameter (the
1418 \doublequote{\texttt{this}}-pointer).}
1420 If the member function entry describes a non\dash static member
1421 function that has a const\dash volatile qualification, then
1422 the entry describes a non\dash static member function whose
1423 object formal parameter has a type that has an equivalent
1424 const\dash volatile qualification.
1426 \textit{In \addtoindex{C++11}, non-static member functions can also have one of the
1427 ref-qualifiers, \& and \&\&. They do not change the type of the
1428 \doublequote{\texttt{this}}-pointer, but they affect the types of object values the
1429 function can be invoked on.}
1431 The member function entry may have an \DWATreferenceNAME{} attribute
1432 \livetarg{chap:DWATreferenceofnonstaticmember}{}
1433 to indicate a non-static member function that can only be called on
1434 l-value objects, or the \DWATrvaluereferenceNAME{} attribute
1435 \livetarg{chap:DWATrvaluereferenceofnonstaticmember}{}
1436 to indicate that it can only be called on pr-values and x-values.
1438 If a subroutine entry represents the defining declaration
1439 of a member function and that definition appears outside of
1440 the body of the enclosing class declaration, the subroutine
1442 \DWATspecification{} attribute,
1443 \addtoindexx{specification attribute}
1445 a reference to the debugging information entry representing
1446 the declaration of this function member. The referenced entry
1447 will be a child of some class (or structure) type entry.
1449 Subroutine entries containing the
1450 \DWATspecification{} attribute
1451 \addtoindexx{specification attribute}
1452 do not need to duplicate information provided
1453 by the declaration entry referenced by the specification
1454 attribute. In particular, such entries do not need to contain
1455 a name attribute giving the name of the function member whose
1456 definition they represent.
1457 Similarly, such entries do not need to contain a return type attribute,
1458 unless the return type on the declaration was unspecified (for example, the
1459 declaration used the \addtoindex{C++} \addtoindex{\texttt{auto} return type} specifier).
1462 \subsection{Class Template Instantiations}
1463 \label{chap:classtemplateinstantiations}
1465 \textit{In \addtoindex{C++} a class template is a generic definition of a class
1466 type that may be instantiated when an instance of the class
1467 is declared or defined. The generic description of the class may include
1468 parameterized types, parameterized compile-time constant
1469 values, and/or parameterized run-time constant addresses.
1470 DWARF does not represent the generic template
1471 definition, but does represent each instantiation.}
1473 A class template instantiation is represented by a
1474 debugging information entry with the tag \DWTAGclasstype,
1475 \DWTAGstructuretype{} or
1476 \DWTAGuniontype. With the following
1477 exceptions, such an entry will contain the same attributes
1478 and have the same types of child entries as would an entry
1479 for a class type defined explicitly using the instantiation
1480 types and values. The exceptions are:
1482 \begin{enumerate}[1. ]
1483 \item Template parameters are described and referenced as
1484 specified in Section \refersec{chap:templateparameters}.
1487 \item If the compiler has generated a special compilation unit to
1489 \addtoindexx{template instantiation!and special compilation unit}
1490 template instantiation and that special compilation
1491 unit has a different name from the compilation unit containing
1492 the template definition, the name attribute for the debugging
1493 information entry representing the special compilation unit
1494 should be empty or omitted.
1497 \item If the class type entry representing the template
1498 instantiation or any of its child entries contains declaration
1499 coordinate attributes, those attributes should refer to
1500 the source for the template definition, not to any source
1501 generated artificially by the compiler.
1505 \subsection{Variant Entries}
1506 \label{chap:variantentries}
1508 A variant part of a structure is represented by a debugging
1509 information entry\addtoindexx{variant part entry} with the
1510 tag \DWTAGvariantpartTARG{} and is
1511 owned by the corresponding structure type entry.
1513 If the variant part has a discriminant, the discriminant is
1514 \hypertarget{chap:DWATdiscrdiscriminantofvariantpart}{}
1516 \addtoindexx{discriminant (entry)}
1517 separate debugging information entry which
1518 is a child of the variant part entry. This entry has the form
1520 \addtoindexx{member entry (data)!as discriminant}
1521 structure data member entry. The variant part entry will
1522 \addtoindexx{discriminant attribute}
1524 \DWATdiscr{} attribute
1525 whose value is a \livelink{chap:classreference}{reference} to
1526 the member entry for the discriminant.
1528 If the variant part does not have a discriminant (tag field),
1529 the variant part entry has
1530 \addtoindexx{type attribute}
1532 \DWATtype{} attribute to represent
1535 Each variant of a particular variant part is represented by
1536 \hypertarget{chap:DWATdiscrvaluediscriminantvalue}{}
1537 a debugging information entry\addtoindexx{variant entry} with the
1538 tag \DWTAGvariantTARG{}
1539 and is a child of the variant part entry. The value that
1540 selects a given variant may be represented in one of three
1541 ways. The variant entry may have a
1542 \DWATdiscrvalue{} attribute
1543 whose value represents a single case label. The value of this
1544 attribute is encoded as an LEB128 number. The number is signed
1545 if the tag type for the variant part containing this variant
1546 is a signed type. The number is unsigned if the tag type is
1551 \hypertarget{chap:DWATdiscrlistlistofdiscriminantvalues}{}
1552 the variant entry may contain
1553 \addtoindexx{discriminant list attribute}
1556 attribute, whose value represents a list of discriminant
1557 values. This list is represented by any of the
1558 \livelink{chap:classblock}{block} forms and
1559 may contain a mixture of case labels and label ranges. Each
1560 item on the list is prefixed with a discriminant value
1561 descriptor that determines whether the list item represents
1562 a single label or a label range. A single case label is
1563 represented as an LEB128 number as defined above for
1564 \addtoindexx{discriminant value attribute}
1567 attribute. A label range is represented by
1568 two LEB128 numbers, the low value of the range followed by the
1569 high value. Both values follow the rules for signedness just
1570 described. The discriminant value descriptor is an integer
1571 constant that may have one of the values given in
1572 Table \refersec{tab:discriminantdescriptorvalues}.
1574 \begin{simplenametable}[1.4in]{Discriminant descriptor values}{tab:discriminantdescriptorvalues}
1575 \DWDSClabelTARG{} \\
1576 \DWDSCrangeTARG{} \\
1577 \end{simplenametable}
1579 If a variant entry has neither a \DWATdiscrvalue{}
1580 attribute nor a \DWATdiscrlist{} attribute, or if it has
1581 a \DWATdiscrlist{} attribute with 0 size, the variant is a
1584 The components selected by a particular variant are represented
1585 by debugging information entries owned by the corresponding
1586 variant entry and appear in the same order as the corresponding
1587 declarations in the source program.
1590 \section{Condition Entries}
1591 \label{chap:conditionentries}
1593 \textit{COBOL has the notion of
1594 \addtoindexx{level-88 condition, COBOL}
1595 a \doublequote{level\dash 88 condition} that
1596 associates a data item, called the conditional variable, with
1597 a set of one or more constant values and/or value ranges.
1598 % Note: the {} after \textquoteright (twice) is necessary to assure a following space separator
1599 Semantically, the condition is \textquoteleft true\textquoteright{}
1601 variable's value matches any of the described constants,
1602 and the condition is \textquoteleft false\textquoteright{} otherwise.}
1604 The \DWTAGconditionTARG{}
1605 debugging information entry\addtoindexx{condition entry}
1607 logical condition that tests whether a given data item\textquoteright s
1608 value matches one of a set of constant values. If a name
1609 has been given to the condition, the condition entry has a
1610 \DWATname{} attribute
1611 \addtoindexx{name attribute}
1612 whose value is a null\dash terminated string
1613 giving the condition name as it appears in the source program.
1615 The condition entry's parent entry describes the conditional
1616 variable; normally this will be a \DWTAGvariable,
1618 \DWTAGformalparameter{} entry.
1620 \addtoindexx{formal parameter entry}
1622 entry has an array type, the condition can test any individual
1623 element, but not the array as a whole. The condition entry
1624 implicitly specifies a \doublequote{comparison type} that is the
1625 type of an array element if the parent has an array type;
1626 otherwise it is the type of the parent entry.
1629 The condition entry owns \DWTAGconstant{} and/or
1630 \DWTAGsubrangetype{} entries that describe the constant
1631 values associated with the condition. If any child entry
1632 \addtoindexx{type attribute}
1634 a \DWATtype{} attribute,
1635 that attribute should describe a type
1636 compatible with the comparison type (according to the source
1637 language); otherwise the child\textquoteright s type is the same as the
1640 \textit{For conditional variables with alphanumeric types, COBOL
1641 permits a source program to provide ranges of alphanumeric
1642 constants in the condition. Normally a subrange type entry
1643 does not describe ranges of strings; however, this can be
1644 represented using bounds attributes that are references to
1645 constant entries describing strings. A subrange type entry may
1646 refer to constant entries that are siblings of the subrange
1650 \section{Enumeration Type Entries}
1651 \label{chap:enumerationtypeentries}
1653 \textit{An \doublequote{enumeration type} is a scalar that can assume one of
1654 a fixed number of symbolic values.}
1656 An enumeration type is represented by a debugging information
1658 \DWTAGenumerationtypeTARG.
1660 If a name has been given to the enumeration type in the source
1661 program, then the corresponding enumeration type entry has
1662 a \DWATname{} attribute
1663 \addtoindexx{name attribute}
1664 whose value is a null\dash terminated
1665 string containing the enumeration type name as it appears
1666 in the source program. This entry also has a
1668 attribute whose \livelink{chap:classconstant}{integer constant}
1669 value is the number of bytes
1670 required to hold an instance of the enumeration.
1672 The \addtoindex{enumeration type entry}
1674 \addtoindexx{type attribute}
1675 a \DWATtype{} attribute
1676 which refers to the underlying data type used to implement
1679 If an enumeration type has type safe
1680 \addtoindexx{type safe enumeration types}
1683 \begin{enumerate}[1. ]
1684 \item Enumerators are contained in the scope of the enumeration type, and/or
1686 \item Enumerators are not implicitly converted to another type
1689 then the \addtoindex{enumeration type entry} may
1690 \addtoindexx{enum class|see{type-safe enumeration}}
1691 have a \DWATenumclass{}
1692 attribute, which is a \livelink{chap:classflag}{flag}.
1693 In a language that offers only
1694 one kind of enumeration declaration, this attribute is not
1697 \textit{In \addtoindex{C} or \addtoindex{C++},
1698 the underlying type will be the appropriate
1699 integral type determined by the compiler from the properties of
1700 \hypertarget{chap:DWATenumclasstypesafeenumerationdefinition}{}
1701 the enumeration literal values.
1702 A \addtoindex{C++} type declaration written
1703 using enum class declares a strongly typed enumeration and
1704 is represented using \DWTAGenumerationtype{}
1705 in combination with \DWATenumclass.}
1707 Each enumeration literal is represented by a debugging
1708 \addtoindexx{enumeration literal|see{enumeration entry}}
1709 information entry with the
1710 tag \DWTAGenumeratorTARG.
1712 such entry is a child of the
1713 \addtoindex{enumeration type entry}, and the
1714 enumerator entries appear in the same order as the declarations
1715 of the enumeration literals in the source program.
1717 Each \addtoindex{enumerator entry} has a
1718 \DWATname{} attribute, whose
1719 \addtoindexx{name attribute}
1720 value is a null\dash terminated string containing the name of the
1721 \hypertarget{chap:DWATconstvalueenumerationliteralvalue}{}
1722 enumeration literal as it appears in the source program.
1723 Each enumerator entry also has a
1724 \DWATconstvalue{} attribute,
1725 whose value is the actual numeric value of the enumerator as
1726 represented on the target system.
1729 If the enumeration type occurs as the description of a
1730 \addtoindexx{enumeration type endry!as array dimension}
1731 dimension of an array type, and the stride for that dimension
1732 \hypertarget{chap:DWATbytestrideenumerationstridedimensionofarraytype}{}
1733 is different than what would otherwise be determined, then
1734 \hypertarget{chap:DWATbitstrideenumerationstridedimensionofarraytype}{}
1735 the enumeration type entry has either a
1737 or \DWATbitstride{} attribute
1738 \addtoindexx{bit stride attribute}
1739 which specifies the separation
1740 between successive elements along the dimension as described
1742 Section \refersec{chap:staticanddynamicvaluesofattributes}.
1744 \DWATbitstride{} attribute
1745 \addtoindexx{bit stride attribute}
1746 is interpreted as bits and the value of
1747 \addtoindexx{byte stride attribute}
1750 attribute is interpreted as bytes.
1753 \section{Subroutine Type Entries}
1754 \label{chap:subroutinetypeentries}
1756 \textit{It is possible in \addtoindex{C}
1757 to declare pointers to subroutines
1758 that return a value of a specific type. In both
1759 \addtoindex{C} and \addtoindex{C++},
1760 it is possible to declare pointers to subroutines that not
1761 only return a value of a specific type, but accept only
1762 arguments of specific types. The type of such pointers would
1763 be described with a \doublequote{pointer to} modifier applied to a
1764 user\dash defined type.}
1766 A subroutine type is represented by a debugging information
1768 \addtoindexx{subroutine type entry}
1769 tag \DWTAGsubroutinetypeTARG.
1771 been given to the subroutine type in the source program,
1772 then the corresponding subroutine type entry has
1773 a \DWATname{} attribute
1774 \addtoindexx{name attribute}
1775 whose value is a null\dash terminated string containing
1776 the subroutine type name as it appears in the source program.
1778 If the subroutine type describes a function that returns
1779 a value, then the subroutine type entry has
1780 \addtoindexx{type attribute}
1782 attribute to denote the type returned by the subroutine. If
1783 the types of the arguments are necessary to describe the
1784 subroutine type, then the corresponding subroutine type
1785 entry owns debugging information entries that describe the
1786 arguments. These debugging information entries appear in the
1787 order that the corresponding argument types appear in the
1790 \textit{In \addtoindex{C} there
1791 is a difference between the types of functions
1792 declared using function prototype style declarations and
1793 those declared using non\dash prototype declarations.}
1796 \hypertarget{chap:DWATprototypedsubroutineprototype}{}
1797 subroutine entry declared with a function prototype style
1798 declaration may have
1799 \addtoindexx{prototyped attribute}
1801 \DWATprototyped{} attribute, which is
1802 a \livelink{chap:classflag}{flag}.
1804 Each debugging information entry owned by a subroutine
1805 type entry corresponds to either a formal parameter or the sequence of
1806 unspecified parameters of the subprogram type:
1808 \begin{enumerate}[1. ]
1809 \item A formal parameter of a parameter list (that has a
1810 specific type) is represented by a debugging information entry
1811 with the tag \DWTAGformalparameter.
1812 Each formal parameter
1814 \addtoindexx{type attribute}
1815 a \DWATtype{} attribute that refers to the type of
1816 the formal parameter.
1818 \item The unspecified parameters of a variable parameter list
1819 \addtoindexx{unspecified parameters entry}
1821 \addtoindexx{\texttt{...} parameters|see{unspecified parameters entry}}
1822 represented by a debugging information entry with the
1823 tag \DWTAGunspecifiedparameters.
1826 \textit{\addtoindex{C++} const-volatile qualifiers are encoded as
1827 part of the type of the
1828 \doublequote{\texttt{this}}-pointer.
1829 \addtoindex{C++11} reference and rvalue-reference qualifiers are encoded using
1830 the \DWATreference{} and \DWATrvaluereference{} attributes, respectively.
1831 See also Section \refersec{chap:memberfunctionentries}.}
1833 A subroutine type entry may have the \DWATreference{} or
1834 \DWATrvaluereference{} attribute to indicate that it describes the
1835 type of a member function with reference or rvalue-reference
1836 semantics, respectively.
1839 \section{String Type Entries}
1840 \label{chap:stringtypeentries}
1842 \textit{A \doublequote{string} is a sequence of characters that have specific
1843 \addtoindexx{string type entry}
1844 semantics and operations that distinguish them from arrays of
1846 \addtoindex{Fortran} is one of the languages that has a string
1847 type. Note that \doublequote{string} in this context refers to a target
1848 machine concept, not the class string as used in this document
1849 (except for the name attribute).}
1851 A string type is represented by a debugging information entry
1852 with the tag \DWTAGstringtypeTARG.
1853 If a name has been given to
1854 the string type in the source program, then the corresponding
1855 string type entry has a
1856 \DWATname{} attribute
1857 \addtoindexx{name attribute}
1859 a null\dash terminated string containing the string type name as
1860 it appears in the source program.
1863 The string type entry may have a
1864 \DWATbytesize{} attribute or
1866 attribute, whose value
1867 (see Section \refersec{chap:byteandbitsizes})
1869 storage needed to hold a value of the string type.
1872 \hypertarget{chap:DWATstringlengthstringlengthofstringtype}{}
1873 string type entry may also have a
1874 \DWATstringlength{} attribute
1876 \addtoindexx{string length attribute}
1878 \addtoindex{location description} yielding the location
1879 where the length of the string is stored in the program.
1880 If the \DWATstringlength{} attribute is not present, the size
1881 of the string is assumed to be the amount of storage that is
1882 allocated for the string (as specified by the \DWATbytesize{}
1883 or \DWATbitsize{} attribute).
1885 The string type entry may also have a
1886 \DWATstringlengthbytesizeNAME{}
1888 \DWATstringlengthbitsizeNAME{} attribute,
1889 \addtoindexx{string length attribute!size of length data}
1890 whose value (see Section \refersec{chap:byteandbitsizes})
1891 is the size of the data to be retrieved from the location
1892 referenced by the string length attribute. If no (byte or bit)
1893 size attribute is present, the size of the data to be retrieved
1895 \addtoindex{size of an address} on the target machine.
1897 \addtoindexx{DWARF Version 5} % Avoid italics
1898 \textit{Prior to DWARF Version 5, the meaning of a
1899 \DWATbytesize{} attribute depends on the presence of the
1900 \DWATstringlength{} attribute:
1902 \item If \DWATstringlength{} is present, \DWATbytesize{}
1903 specifies the size of the length data to be retrieved
1904 from the location specified by the \DWATstringlength{} attribute.
1905 \item If \DWATstringlength{} is not present, \DWATbytesize{}
1906 specifies the amount of storage allocated for objects
1909 In DWARF Version 5, \DWATbytesize{} always specifies the amount of storage
1910 allocated for objects of the string type.}
1913 \section{Set Type Entries}
1914 \label{chap:settypeentries}
1916 \textit{\addtoindex{Pascal} provides the concept of a \doublequote{set,} which represents
1917 a group of values of ordinal type.}
1919 A set is represented by a debugging information entry with
1920 the tag \DWTAGsettypeTARG.
1921 \addtoindexx{set type entry}
1922 If a name has been given to the
1923 set type, then the set type entry has
1924 a \DWATname{} attribute
1925 \addtoindexx{name attribute}
1926 whose value is a null\dash terminated string containing the
1927 set type name as it appears in the source program.
1929 The set type entry has
1930 \addtoindexx{type attribute}
1931 a \DWATtype{} attribute to denote the
1932 type of an element of the set.
1935 If the amount of storage allocated to hold each element of an
1936 object of the given set type is different from the amount of
1937 storage that is normally allocated to hold an individual object
1938 of the indicated element type, then the set type entry has
1939 either a \DWATbytesize{} attribute, or
1940 \DWATbitsize{} attribute
1941 whose value (see Section \refersec{chap:byteandbitsizes}) is
1942 the amount of storage needed to hold a value of the set type.
1945 \section{Subrange Type Entries}
1946 \label{chap:subrangetypeentries}
1948 \textit{Several languages support the concept of a \doublequote{subrange}
1949 type object. These objects can represent a subset of the
1950 values that an object of the basis type for the subrange can
1952 Subrange type entries may also be used to represent
1953 the bounds of array dimensions.}
1955 A subrange type is represented by a debugging information
1957 \addtoindexx{subrange type entry}
1958 tag \DWTAGsubrangetypeTARG.
1960 given to the subrange type, then the subrange type entry
1961 has a \DWATname{} attribute
1962 \addtoindexx{name attribute}
1963 whose value is a null\dash terminated
1964 string containing the subrange type name as it appears in
1967 The tag \DWTAGgenericsubrange{} is
1968 used to describe arrays with a dynamic rank. See Section
1969 \refersec{chap:DWTAGgenericsubrange}.
1971 The subrange entry may have
1972 \addtoindexx{type attribute}
1973 a \DWATtype{} attribute to describe
1974 the type of object, called the basis type, of whose values
1975 this subrange is a subset.
1977 If the amount of storage allocated to hold each element of an
1978 object of the given subrange type is different from the amount
1979 of storage that is normally allocated to hold an individual
1980 object of the indicated element type, then the subrange
1982 \DWATbytesize{} attribute or
1984 attribute, whose value
1985 (see Section \refersec{chap:staticanddynamicvaluesofattributes})
1987 storage needed to hold a value of the subrange type.
1990 \hypertarget{chap:DWATthreadsscaledupcarrayboundthreadsscalfactor}{}
1991 subrange entry may have
1992 \addtoindexx{threads scaled attribute}
1994 \DWATthreadsscaled{} attribute,
1995 which is a \livelink{chap:classflag}{flag}.
1996 If present, this attribute indicates whether
1997 this subrange represents a \addtoindex{UPC} array bound which is scaled
1998 by the runtime THREADS value (the number of UPC threads in
1999 this execution of the program).
2001 \textit{This allows the representation of a \addtoindex{UPC} shared array such as}
2003 \begin{lstlisting}[numbers=none]
2004 int shared foo[34*THREADS][10][20];
2008 \hypertarget{chap:DWATlowerboundlowerboundofsubrange}{}
2010 \hypertarget{chap:DWATupperboundupperboundofsubrange}{}
2011 entry may have the attributes
2013 \addtoindexx{lower bound attribute}
2014 and \DWATupperbound{}
2015 \addtoindexx{upper bound attribute} to specify, respectively, the lower
2016 and upper bound values of the subrange. The
2019 \hypertarget{chap:DWATcountelementsofsubrangetype}{}
2021 % FIXME: The following matches DWARF4: odd as there is no default count.
2022 \addtoindexx{count attribute!default}
2024 \addtoindexx{count attribute}
2026 \DWATcount{} attribute,
2028 value describes the number of elements in the subrange rather
2029 than the value of the last element. The value of each of
2030 these attributes is determined as described in
2031 Section \refersec{chap:staticanddynamicvaluesofattributes}.
2033 If the lower bound value is missing, the value is assumed to
2034 be a language\dash dependent default constant.
2035 \addtoindexx{lower bound attribute!default}
2036 The default lower bound is 0 for
2041 \addtoindex{Haskell},
2043 \addtoindex{Objective C},
2044 \addtoindex{Objective C++},
2045 \addtoindex{OpenCL},
2046 \addtoindex{Python},
2047 \addtoindex{Rust}, and
2049 The default lower bound is 1 for
2052 \addtoindex{Fortran},
2053 \addtoindex{Modula-2},
2054 \addtoindex{Modula-3},
2055 \addtoindex{Pascal} and
2058 \textit{No other default lower bound values are currently defined.}
2060 If the upper bound and count are missing, then the upper bound value is
2061 \textit{unknown}.\addtoindexx{upper bound attribute!default unknown}
2063 If the subrange entry has no type attribute describing the
2064 basis type, the basis type is determined as follows:
2065 \begin{enumerate}[1. ]
2067 If there is a lower bound attribute that references an object,
2068 the basis type is assumed to be the same as the type of that object.
2070 Otherwise, if there is an upper bound or count attribute that references
2071 an object, the basis type is assumed to be the same as the type of that object.
2073 Otherwise, the type is
2074 assumed to be the same type, in the source language of the
2075 compilation unit containing the subrange entry, as a signed
2076 integer with the same size as an address on the target machine.
2079 If the subrange type occurs as the description of a dimension
2080 of an array type, and the stride for that dimension is
2081 \hypertarget{chap:DWATbytestridesubrangestridedimensionofarraytype}{}
2082 different than what would otherwise be determined, then
2083 \hypertarget{chap:DWATbitstridesubrangestridedimensionofarraytype}{}
2084 the subrange type entry has either
2085 \addtoindexx{byte stride attribute}
2087 \DWATbytestride{} or
2088 \DWATbitstride{} attribute
2089 \addtoindexx{bit stride attribute}
2090 which specifies the separation
2091 between successive elements along the dimension as described
2093 Section \refersec{chap:byteandbitsizes}.
2095 \textit{Note that the stride can be negative.}
2097 \section{Pointer to Member Type Entries}
2098 \label{chap:pointertomembertypeentries}
2100 \textit{In \addtoindex{C++}, a
2101 pointer to a data or function member of a class or
2102 structure is a unique type.}
2104 A debugging information entry representing the type of an
2105 object that is a pointer to a structure or class member has
2106 the tag \DWTAGptrtomembertypeTARG.
2108 If the \addtoindex{pointer to member type} has a name, the
2109 \addtoindexx{pointer to member type entry}
2110 pointer to member entry has a
2111 \DWATname{} attribute,
2112 \addtoindexx{name attribute}
2114 null\dash terminated string containing the type name as it appears
2115 in the source program.
2117 The \addtoindex{pointer to member} entry
2119 \addtoindexx{type attribute}
2120 a \DWATtype{} attribute to
2121 describe the type of the class or structure member to which
2122 objects of this type may point.
2124 The \addtoindexx{pointer to member} entry also
2125 \hypertarget{chap:DWATcontainingtypecontainingtypeofpointertomembertype}{}
2127 \DWATcontainingtype{}
2128 attribute, whose value is a \livelink{chap:classreference}{reference} to a debugging
2129 information entry for the class or structure to whose members
2130 objects of this type may point.
2132 The \addtoindex{pointer to member entry}
2133 \hypertarget{chap:DWATuselocationmemberlocationforpointertomembertype}{}
2135 \DWATuselocation{} attribute
2136 \addtoindexx{use location attribute}
2138 \addtoindex{location description} that computes the
2139 address of the member of the class to which the pointer to
2140 member entry points.
2142 \textit{The method used to find the address of a given member of a
2143 class or structure is common to any instance of that class
2144 or structure and to any instance of the pointer or member
2145 type. The method is thus associated with the type entry,
2146 rather than with each instance of the type.}
2148 The \DWATuselocation{} description is used in conjunction
2149 with the location descriptions for a particular object of the
2150 given \addtoindex{pointer to member type} and for a particular structure or
2151 class instance. The \DWATuselocation{}
2152 attribute expects two values to be
2153 \addtoindexi{pushed}{address!implicit push for member operator}
2154 onto the DWARF expression stack before
2155 the \DWATuselocation{} description is evaluated.
2157 \addtoindexi{pushed}{address!implicit push for member operator}
2158 is the value of the \addtoindex{pointer to member} object
2159 itself. The second value
2160 \addtoindexi{pushed}{address!implicit push for member operator}
2161 is the base address of the
2162 entire structure or union instance containing the member
2163 whose address is being calculated.
2166 \textit{For an expression such as}
2168 \begin{lstlisting}[numbers=none]
2171 \textit{where \texttt{mbr\_ptr} has some \addtoindex{pointer to member type}, a debugger should:}
2172 \begin{enumerate}[1. ]
2173 \item \textit{Push the value of \texttt{mbr\_ptr} onto the DWARF expression stack.}
2174 \item \textit{Push the base address of \texttt{object} onto the DWARF expression stack.}
2175 \item \textit{Evaluate the \DWATuselocation{} description
2176 given in the type of \texttt{mbr\_ptr}.}
2180 \section{File Type Entries}
2181 \label{chap:filetypeentries}
2183 \textit{Some languages, such as \addtoindex{Pascal},
2184 provide a data type to represent
2187 A file type is represented by a debugging information entry
2189 \addtoindexx{file type entry}
2192 If the file type has a name,
2193 the file type entry has a \DWATname{} attribute,
2194 \addtoindexx{name attribute}
2196 is a null\dash terminated string containing the type name as it
2197 appears in the source program.
2199 The file type entry has
2200 \addtoindexx{type attribute}
2201 a \DWATtype{} attribute describing
2202 the type of the objects contained in the file.
2204 The file type entry also
2205 \addtoindexx{byte size}
2207 \addtoindexx{bit size}
2210 \DWATbitsize{} attribute, whose value
2211 (see Section \refersec{chap:staticanddynamicvaluesofattributes})
2212 is the amount of storage need to hold a value of the file type.
2214 \section{Dynamic Type Entries and Properties}
2216 \subsection{Dynamic Type Entries}
2217 \textit{Some languages such as
2218 \addtoindex{Fortran 90}, provide types whose values
2219 may be dynamically allocated or associated with a variable
2220 under explicit program control. However, unlike the related
2221 pointer type in \addtoindex{C} or
2222 \addtoindex{C++}, the indirection involved in accessing
2223 the value of the variable is generally implicit, that is, not
2224 indicated as part of program source.}
2226 A dynamic type entry is used to declare a dynamic type that is
2227 \doublequote{just like} another non-dynamic type without needing to
2228 replicate the full description of that other type.
2230 A dynamic type is represented by a debugging information entry
2231 with the tag \DWTAGdynamictypeTARG. If a name has been given to the
2232 dynamic type, then the dynamic type has a \DWATname{} attribute
2233 whose value is a null-terminated string containing the dynamic
2234 type name as it appears in the source.
2236 A dynamic type entry has a \DWATtype{} attribute whose value is a
2237 reference to the type of the entities that are dynamically allocated.
2239 A dynamic type entry also has a \DWATdatalocation, and may also
2240 have \DWATallocated{} and/or \DWATassociated{} attributes as
2241 described following (Section 5.15.1). The type referenced by the
2242 \DWATtype{} attribute must not have any of these attributes.
2244 \subsection{Dynamic Type Properties}
2245 \label{chap:dynamictypeproperties}
2247 The \DWATdatalocation, \DWATallocated{} and \DWATassociated{}
2248 attributes described in this section can be used for any type, not
2249 just dynamic types.}
2252 \subsubsection{Data Location}
2253 \label{chap:datalocation}
2255 \textit{Some languages may represent objects using descriptors to hold
2256 information, including a location and/or run\dash time parameters,
2257 about the data that represents the value for that object.}
2259 \hypertarget{chap:DWATdatalocationindirectiontoactualdata}{}
2260 The \DWATdatalocation{}
2261 attribute may be used with any
2262 \addtoindexx{data location attribute}
2263 type that provides one or more levels of
2264 \addtoindexx{hidden indirection|see{data location attribute}}
2266 and/or run\dash time parameters in its representation. Its value
2267 is a \addtoindex{location description}.
2268 The result of evaluating this
2269 description yields the location of the data for an object.
2270 When this attribute is omitted, the address of the data is
2271 the same as the address of the object.
2274 \textit{This location description will typically begin with
2275 \DWOPpushobjectaddress{}
2276 which loads the address of the
2277 object which can then serve as a descriptor in subsequent
2278 calculation. For an example using
2280 for a \addtoindex{Fortran 90 array}, see
2281 Appendix \refersec{app:fortranarrayexample}.}
2283 \subsubsection{Allocation and Association Status}
2284 \label{chap:allocationandassociationstatus}
2286 \textit{Some languages, such as \addtoindex{Fortran 90},
2287 provide types whose values
2288 may be dynamically allocated or associated with a variable
2289 under explicit program control.}
2291 \hypertarget{chap:DWATallocatedallocationstatusoftypes}{}
2295 \addtoindexx{allocated attribute}
2296 may optionally be used with any
2297 type for which objects of the type can be explicitly allocated
2298 and deallocated. The presence of the attribute indicates that
2299 objects of the type are allocatable and deallocatable. The
2300 integer value of the attribute (see below) specifies whether
2301 an object of the type is
2302 currently allocated or not.
2304 \hypertarget{chap:DWATassociatedassociationstatusoftypes}{}
2306 \DWATassociated{} attribute
2308 \addtoindexx{associated attribute}
2309 optionally be used with
2310 any type for which objects of the type can be dynamically
2311 associated with other objects. The presence of the attribute
2312 indicates that objects of the type can be associated. The
2313 integer value of the attribute (see below) indicates whether
2314 an object of the type is currently associated or not.
2316 \textit{While these attributes are defined specifically with
2317 \addtoindex{Fortran 90} ALLOCATABLE and POINTER types
2318 in mind, usage is not limited
2319 to just that language.}
2321 The value of these attributes is determined as described in
2322 Section \refersec{chap:staticanddynamicvaluesofattributes}.
2324 A non\dash zero value is interpreted as allocated or associated,
2325 and zero is interpreted as not allocated or not associated.
2327 \textit{For \addtoindex{Fortran 90},
2328 if the \DWATassociated{}
2329 attribute is present,
2330 the type has the POINTER property where either the parent
2331 variable is never associated with a dynamic object or the
2332 implementation does not track whether the associated object
2333 is static or dynamic. If the \DWATallocated{} attribute is
2334 present and the \DWATassociated{} attribute is not, the type
2335 has the ALLOCATABLE property. If both attributes are present,
2336 then the type should be assumed to have the POINTER property
2337 (and not ALLOCATABLE); the \DWATallocated{} attribute may then
2338 be used to indicate that the association status of the object
2339 resulted from execution of an ALLOCATE statement rather than
2340 pointer assignment.}
2342 \textit{For examples using
2343 \DWATallocated{} for \addtoindex{Ada} and
2344 \addtoindex{Fortran 90}
2346 see Appendix \refersec{app:aggregateexamples}.}
2348 \subsubsection{Array Rank}
2349 \label{chap:DWATrank}
2350 \addtoindexx{array!assumed-rank}
2351 \addtoindexx{assumed-rank array|see{array, assumed-rank}}
2352 \textit{The Fortran language supports \doublequote{assumed-rank arrays}. The
2353 rank (the number of dimensions) of an assumed-rank array is unknown
2354 at compile time. The Fortran runtime stores the rank in the array
2355 descriptor metadata.}
2358 \hypertarget{chap:DWATrankofdynamicarray}{\DWATrankINDX}
2359 attribute indicates that an array's rank
2360 (dimensionality) is dynamic, and therefore unknown at compile
2361 time. The value of the \DWATrankINDX{} attribute is either an integer constant
2362 or a location expression whose evaluation yields the dynamic rank.
2364 The bounds of an array with dynamic rank are described using the
2365 \DWTAGgenericsubrange{} tag, which
2366 is the dynamic rank array equivalent of
2367 \DWTAGsubrangetype. The
2368 difference is that a \DWTAGgenericsubrangeINDX{} contains generic
2369 lower/upper bound and stride expressions that need to be evaluated for
2370 each dimension: Before any expression contained in a
2371 \DWTAGgenericsubrangeINDX{} can be evaluated, the dimension for which the
2372 expression should be evaluated needs to be pushed onto the stack. The
2373 expression will use it to find the offset of the respective field in
2374 the array descriptor metadata.
2376 \textit{The Fortran compiler is free to choose any layout for the
2377 array descriptor. In particular, the upper and lower bounds and
2378 stride values do not need to be bundled into a structure or record,
2379 but could be laid end to end in the containing descriptor, pointed
2380 to by the descriptor, or even allocated independently of the
2383 Dimensions are enumerated $0$ to $\mathit{rank}-1$ in a left-to-right
2386 \textit{For an example in Fortran 2008, see
2387 Section~\refersec{app:assumedrankexample}.}
2390 \section{Template Alias Entries}
2391 \label{chap:templatealiasentries}
2394 In \addtoindex{C++}, a template alias is a form of typedef that has template
2395 parameters. DWARF does not represent the template alias definition
2396 but does represent instantiations of the alias.
2399 A type named using a template alias is represented
2400 by a debugging information entry
2401 \addtoindexx{template alias entry}
2403 \DWTAGtemplatealiasTARG.
2404 The template alias entry has a
2405 \DWATname{} attribute
2406 \addtoindexx{name attribute}
2407 whose value is a null\dash terminated string
2408 containing the name of the template alias as it appears in
2410 The template alias entry has child entries describing the template
2411 actual parameters (see Section \refersec{chap:templateparameters}).