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1 | \input texinfo |
2 | @setfilename stabs.info | |
3 | ||
4 | @ifinfo | |
5 | @format | |
6 | START-INFO-DIR-ENTRY | |
612dbd4c | 7 | * Stabs: (stabs). The "stabs" debugging information format. |
e505224d PB |
8 | END-INFO-DIR-ENTRY |
9 | @end format | |
10 | @end ifinfo | |
11 | ||
12 | @ifinfo | |
612dbd4c | 13 | This document describes GNU stabs (debugging symbol tables) in a.out files. |
e505224d | 14 | |
612dbd4c | 15 | Copyright 1992 Free Software Foundation, Inc. |
e505224d PB |
16 | Contributed by Cygnus Support. Written by Julia Menapace. |
17 | ||
18 | Permission is granted to make and distribute verbatim copies of | |
19 | this manual provided the copyright notice and this permission notice | |
20 | are preserved on all copies. | |
21 | ||
22 | @ignore | |
23 | Permission is granted to process this file through Tex and print the | |
24 | results, provided the printed document carries copying permission | |
25 | notice identical to this one except for the removal of this paragraph | |
26 | (this paragraph not being relevant to the printed manual). | |
27 | ||
28 | @end ignore | |
29 | Permission is granted to copy or distribute modified versions of this | |
30 | manual under the terms of the GPL (for which purpose this text may be | |
31 | regarded as a program in the language TeX). | |
32 | @end ifinfo | |
33 | ||
34 | @setchapternewpage off | |
35 | @settitle STABS | |
36 | @titlepage | |
612dbd4c | 37 | @title{The "stabs" representation of debugging information.} |
e505224d PB |
38 | @author Julia Menapace |
39 | @author Cygnus Support | |
40 | @page | |
41 | @tex | |
42 | \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ | |
43 | \xdef\manvers{\$Revision$} % For use in headers, footers too | |
44 | {\parskip=0pt | |
45 | \hfill Cygnus Support\par | |
46 | \hfill \manvers\par | |
47 | \hfill \TeX{}info \texinfoversion\par | |
48 | } | |
49 | @end tex | |
50 | ||
51 | @vskip 0pt plus 1filll | |
899bafeb RP |
52 | Copyright @copyright{} 1992 Free Software Foundation, Inc. |
53 | Contributed by Cygnus Support. | |
e505224d PB |
54 | |
55 | Permission is granted to make and distribute verbatim copies of | |
56 | this manual provided the copyright notice and this permission notice | |
57 | are preserved on all copies. | |
58 | ||
59 | @end titlepage | |
60 | ||
899bafeb RP |
61 | @ifinfo |
62 | @node Top | |
63 | @top The "stabs" representation of debugging information | |
e505224d | 64 | |
612dbd4c | 65 | This document describes the GNU stabs debugging format in a.out files. |
e505224d PB |
66 | |
67 | @menu | |
612dbd4c JG |
68 | * Overview:: Overview of stabs |
69 | * Program structure:: Encoding of the structure of the program | |
e505224d | 70 | * Simple types:: |
612dbd4c | 71 | * Example:: A comprehensive example in C |
e505224d PB |
72 | * Variables:: |
73 | * Aggregate types:: | |
612dbd4c | 74 | * Symbol tables:: Symbol information in symbol tables |
e505224d PB |
75 | * GNU C++ stabs:: |
76 | ||
77 | Appendixes: | |
612dbd4c JG |
78 | * Example2.c:: Source code for extended example |
79 | * Example2.s:: Assembly code for extended example | |
80 | * Quick reference:: Various refernce tables | |
81 | * Expanded reference:: Reference information by stab type | |
82 | * Questions:: Questions and anomolies | |
83 | * xcoff-differences:: Differences between GNU stabs in a.out | |
84 | and GNU stabs in xcoff | |
85 | * Sun-differences:: Differences between GNU stabs and Sun | |
86 | native stabs | |
e505224d | 87 | @end menu |
899bafeb | 88 | @end ifinfo |
e505224d PB |
89 | |
90 | ||
899bafeb | 91 | @node Overview |
e505224d PB |
92 | @chapter Overview of stabs |
93 | ||
94 | @menu | |
95 | * Flow:: Overview of debugging information flow | |
96 | * Stabs format:: Overview of stab format | |
97 | * C example:: A simple example in C source | |
98 | * Assembly code:: The simple example at the assembly level | |
99 | @end menu | |
100 | ||
899bafeb | 101 | @node Flow |
e505224d PB |
102 | @section Overview of debugging information flow |
103 | ||
104 | GCC compiles C source in a .c file into assembly language in a .s | |
105 | file, which is translated by the assembler into a .o file, and then | |
106 | linked with other .o files and libraries to produce an executable | |
107 | file. | |
108 | ||
109 | When using the -g option, GCC puts additional debugging information in | |
110 | the .s file, which is slightly transformed by the assembler and | |
111 | linker, and carried through into the final executable. This debugging | |
112 | information describes features of the source file like line numbers, | |
113 | the types and scopes of variables, and functions, their parameters and | |
114 | their scopes. | |
115 | ||
116 | For some object file formats, the debugging information is | |
117 | encapsulated in pseudo-ops to the assembler known as `stab' (symbol | |
118 | table) directives, interspersed with the generated code. Stabs are | |
119 | the native format for debugging information in the a.out and xcoff | |
120 | object file formats. The GNU tools can also emit stabs in the coff | |
121 | and ecoff object file formats. | |
122 | ||
123 | The assembler adds the information from stabs to the symbol | |
124 | information it places by default in the symbol table and the string | |
125 | table of the .o file it is building. The linker consolidates the .o | |
126 | files into one executable file, with one symbol and one string table. | |
127 | Debuggers use the symbol and string tables in the executable as a | |
128 | source of debugging information about the program. | |
129 | ||
899bafeb | 130 | @node Stabs format |
e505224d PB |
131 | @section Overview of stab format |
132 | ||
133 | There are three overall formats for stab assembler directives | |
134 | differentiated by the first word of the stab. The first word | |
135 | describes what combination of four possible data fields will follow. | |
136 | It is either .stabs (string), .stabn (number), or .stabd (dot). | |
137 | ||
138 | The overall format of each class of stab is: | |
139 | ||
140 | @example | |
141 | .stabs "string",type,0,desc,value | |
142 | .stabn type,0,desc,value | |
143 | .stabd type,0,desc | |
144 | @end example | |
145 | ||
146 | In general, in .stabs the string field contains name and type | |
147 | information. For .stabd the value field is implicit and has the value | |
148 | of the current file location. Otherwise the value field often | |
149 | contains a relocatable address, frame pointer offset, or register | |
150 | number, that maps to the source code element described by the stab. | |
151 | ||
152 | The real key to decoding the meaning of a stab is the number in its | |
153 | type field. Each possible type number defines a different stab type. | |
154 | The stab type further defines the exact interpretation of, and | |
155 | possible values for, any remaining "string", desc, or value fields | |
156 | present in the stab. Table A lists in numeric order the possible type | |
157 | field values for stab directives. The reference section that follows | |
158 | Table A describes the meaning of the fields for each stab type in | |
159 | detail. The examples that follow this overview introduce the stab | |
160 | types in terms of the source code elements they describe. | |
161 | ||
162 | For .stabs the "string" field holds the meat of the debugging | |
163 | information. The generally unstructured nature of this field is what | |
164 | makes stabs extensible. For some stab types the string field contains | |
165 | only a name. For other stab types the contents can be a great deal | |
166 | more complex. | |
167 | ||
168 | The overall format is of the "string" field is: | |
169 | ||
170 | @example | |
171 | "name[:symbol_descriptor][type_number[=type_descriptor...]]" | |
172 | @end example | |
173 | ||
174 | name is the name of the symbol represented by the stab. | |
175 | ||
176 | The symbol_descriptor following the : is an alphabetic character that | |
177 | tells more specifically what kind of symbol the stab represents. If | |
178 | the symbol_descriptor is omitted, but type information follows, then | |
179 | the stab represents a local variable. See Table C for a list of | |
180 | symbol_descriptors. | |
181 | ||
182 | Type information it is either a type_number, or a type_number=. The | |
183 | type_number alone is a type reference, referring directly to a type | |
184 | that has already been defined. | |
185 | ||
186 | The type_number= is a type definition, where the number represents a | |
187 | new type which is about to be defined. The type definition may refer | |
188 | to other types by number, and those type numbers may be followed by = | |
189 | and nested definitions. | |
190 | ||
191 | In a type definition, if the character that follows the equals sign is | |
192 | non-numeric then it is a type_descriptor, and tells what kind of type | |
193 | is about to be defined. Any other values following the | |
194 | type_descriptor vary, depending on the type_descriptor. If a number | |
195 | follows the = then the number is a type_reference. This is described | |
196 | more thoroughly in the section on types. See Table D for a list of | |
197 | type_descriptors. | |
198 | ||
199 | All this can make the "string" field quite long. When the "string" | |
200 | part of a stab is more than 80 characters, we split the .stabs | |
201 | pseudo-op into two .stabs pseudo-ops, both stabs duplicate exactly all | |
202 | but the "string" field. The "string" field of the first stab contains | |
203 | the first part of the overlong string, marked as continued with a | |
204 | double-backslash at the end. The "string" field of the second stab | |
205 | holds the second half of the overlong string. | |
206 | ||
899bafeb | 207 | @node C example |
e505224d PB |
208 | @section A simple example in C source |
209 | ||
210 | To get the flavor of how stabs describe source information for a C | |
211 | program, let's look at the simple program: | |
212 | ||
213 | @example | |
214 | main() | |
215 | @{ | |
216 | printf("Hello world"); | |
217 | @} | |
218 | @end example | |
219 | ||
220 | When compiled with -g, the program above yields the following .s file. | |
221 | Line numbers have been added so it will be easier to refer to parts of | |
222 | the .s file in the description of the stabs that follows. | |
223 | ||
899bafeb | 224 | @node Assembly code |
e505224d PB |
225 | @section The simple example at the assembly level |
226 | ||
227 | @example | |
228 | 1 gcc2_compiled.: | |
229 | 2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 | |
230 | 3 .stabs "hello.c",100,0,0,Ltext0 | |
231 | 4 .text | |
232 | 5 Ltext0: | |
233 | 6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 | |
234 | 7 .stabs "char:t2=r2;0;127;",128,0,0,0 | |
235 | 8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0 | |
236 | 9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0 | |
237 | 10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0 | |
238 | 11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0 | |
239 | 12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0 | |
240 | 13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0 | |
241 | 14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0 | |
242 | 15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0 | |
243 | 16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0 | |
244 | 17 .stabs "float:t12=r1;4;0;",128,0,0,0 | |
245 | 18 .stabs "double:t13=r1;8;0;",128,0,0,0 | |
246 | 19 .stabs "long double:t14=r1;8;0;",128,0,0,0 | |
247 | 20 .stabs "void:t15=15",128,0,0,0 | |
248 | 21 .align 4 | |
249 | 22 LC0: | |
250 | 23 .ascii "Hello, world!\12\0" | |
251 | 24 .align 4 | |
252 | 25 .global _main | |
253 | 26 .proc 1 | |
254 | 27 _main: | |
255 | 28 .stabn 68,0,4,LM1 | |
256 | 29 LM1: | |
257 | 30 !#PROLOGUE# 0 | |
258 | 31 save %sp,-136,%sp | |
259 | 32 !#PROLOGUE# 1 | |
260 | 33 call ___main,0 | |
261 | 34 nop | |
262 | 35 .stabn 68,0,5,LM2 | |
263 | 36 LM2: | |
264 | 37 LBB2: | |
265 | 38 sethi %hi(LC0),%o1 | |
266 | 39 or %o1,%lo(LC0),%o0 | |
267 | 40 call _printf,0 | |
268 | 41 nop | |
269 | 42 .stabn 68,0,6,LM3 | |
270 | 43 LM3: | |
271 | 44 LBE2: | |
272 | 45 .stabn 68,0,6,LM4 | |
273 | 46 LM4: | |
274 | 47 L1: | |
275 | 48 ret | |
276 | 49 restore | |
277 | 50 .stabs "main:F1",36,0,0,_main | |
278 | 51 .stabn 192,0,0,LBB2 | |
279 | 52 .stabn 224,0,0,LBE2 | |
280 | @end example | |
281 | ||
282 | This simple hello world example, demonstrates several of the stab | |
283 | types used to describe C language source files. | |
284 | ||
899bafeb | 285 | @node Program structure |
e505224d PB |
286 | @chapter Encoding of the structure of the program |
287 | ||
288 | @menu | |
289 | * Source file:: The path and name of the source file | |
290 | * Line numbers:: | |
291 | * Procedures:: | |
292 | * Block structure:: | |
293 | @end menu | |
294 | ||
899bafeb | 295 | @node Source file |
e505224d PB |
296 | @section The path and name of the source file |
297 | ||
298 | @example | |
299 | .stabs, stab type N_SO | |
300 | @end example | |
301 | ||
302 | The first stabs in the .s file contain the name and path of the source | |
303 | file that was compiled to produce the .s file. This information is | |
304 | contained in two records of stab type N_SO (100). | |
305 | ||
306 | @example | |
307 | .stabs "path_name", N_SO, NIL, NIL, Code_address_of_program_start | |
308 | .stabs "file_name:", N_SO, NIL, NIL, Code_address_of_program_start | |
309 | @end example | |
310 | ||
311 | @example | |
312 | 2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 | |
313 | 3 .stabs "hello.c",100,0,0,Ltext0 | |
314 | 4 .text | |
315 | 5 Ltext0: | |
316 | @end example | |
317 | ||
899bafeb | 318 | @node Line numbers |
e505224d PB |
319 | @section Line Numbers |
320 | ||
321 | @example | |
322 | .stabn, stab type N_SLINE | |
323 | @end example | |
324 | ||
325 | The start of source lines is represented by the N_SLINE (68) stab | |
326 | type. | |
327 | ||
328 | @example | |
329 | .stabn N_SLINE, NIL, source_line_number, | |
330 | code_address_for_start_of_source_line | |
331 | @end example | |
332 | ||
333 | @example | |
334 | 27 _main: | |
335 | 28 .stabn 68,0,4,LM1 | |
336 | 29 LM1: | |
337 | 30 !#PROLOGUE# 0 | |
338 | @end example | |
339 | ||
899bafeb | 340 | @node Procedures |
e505224d PB |
341 | @section Procedures |
342 | ||
343 | @example | |
344 | .stabs, stab type N_FUN, | |
345 | symbol descriptors f (local), F (global) | |
346 | @end example | |
347 | ||
348 | Procedures are described by the N_FUN stab type. The symbol | |
349 | descriptor for a procedure is F if the proc is globally scoped and f | |
350 | if the procedure is static (locally scoped). | |
351 | ||
352 | The N_FUN stab representing a procedure is located immediatly | |
353 | following the code of the procedure. The N_FUN stab is in turn | |
354 | directly followed by a group of other stabs describing elements of the | |
355 | procedure. These other stabs describe the procedure's parameters, its | |
356 | block local variables and its block structure. | |
357 | ||
358 | @example | |
359 | 48 ret | |
360 | 49 restore | |
361 | @end example | |
362 | ||
363 | @example | |
364 | .stabs "procedure_name:symbol_desc(global proc)return_type_ref(int)", | |
365 | N_FUN, NIL, NIL, Code_address_of_procedure_start | |
366 | @end example | |
367 | ||
368 | @example | |
369 | 50 .stabs "main:F1",36,0,0,_main | |
370 | @end example | |
371 | ||
899bafeb | 372 | @node Block Structure |
e505224d PB |
373 | @section Block Structure |
374 | ||
375 | @example | |
376 | .stabn, stab types N_LBRAC, N_RRAC | |
377 | @end example | |
378 | ||
379 | The program's block structure is represented by the N_LBRAC (left | |
380 | brace) and the N_RBRAC (right brace) stab types. The following code | |
381 | range, which is the body of main, is labeled with LBB2: at the | |
382 | beginning and LBE2: at the end. | |
383 | ||
384 | @example | |
385 | 37 LBB2: | |
386 | 38 sethi %hi(LC0),%o1 | |
387 | 39 or %o1,%lo(LC0),%o0 | |
388 | 40 call _printf,0 | |
389 | 41 nop | |
390 | 42 .stabn 68,0,6,LM3 | |
391 | 43 LM3: | |
392 | 44 LBE2: | |
393 | @end example | |
394 | ||
395 | The N_LBRAC and N_RBRAC stabs that describe the block scope of the | |
396 | procedure are located after the N_FUNC stab that represents the | |
397 | procedure itself. The N_LBRAC uses the LBB2 label as the code address | |
398 | in its value field and the N_RBRAC uses the LBE2. | |
399 | ||
400 | @example | |
401 | 50 .stabs "main:F1",36,0,0,_main | |
402 | @end example | |
403 | ||
404 | @example | |
405 | .stabn N_LBRAC, NIL, NIL, Code_Address_for_left_brace | |
406 | .stabn N_RBRAC, NIL, NIL, Code_Address_for_right_brace | |
407 | @end example | |
408 | ||
409 | @example | |
410 | 51 .stabn 192,0,0,LBB2 | |
411 | 52 .stabn 224,0,0,LBE2 | |
412 | @end example | |
413 | ||
899bafeb | 414 | @node Simple types |
e505224d PB |
415 | @chapter Simple types |
416 | ||
417 | @menu | |
418 | * Basic types:: | |
419 | * Range types:: Range types defined by min and max value | |
420 | * Bit-ranges:: Range type defined by number of bits | |
421 | @end menu | |
422 | ||
899bafeb | 423 | @node Basic types |
e505224d PB |
424 | @section Basic type definitions |
425 | ||
426 | @example | |
427 | .stabs, stab type N_LSYM, | |
428 | symbol descriptor t | |
429 | @end example | |
430 | ||
431 | The basic types for the language are described using the N_LSYM stab | |
432 | type. They are boilerplate and are emited by the compiler for each | |
433 | compilation unit. Basic type definitions are not always a complete | |
434 | description of the type and are sometimes circular. The debugger | |
435 | recognizes the type anyway, and knows how to read bits as that type. | |
436 | ||
437 | Each language and compiler defines a slightly different set of basic | |
438 | types. In this example we are looking at the basic types for C emited | |
439 | by the GNU compiler targeting the Sun4. Here the basic types are | |
440 | mostly defined as range types. | |
441 | ||
442 | ||
899bafeb | 443 | @node Range types |
e505224d PB |
444 | @section Range types defined by min and max value |
445 | ||
446 | type descriptor r | |
447 | ||
448 | When defining a range type, if the number after the first semicolon is | |
449 | smaller than the number after the second one, then the two numbers | |
450 | represent the smallest and the largest values in the range. | |
451 | ||
452 | @example | |
453 | 4 .text | |
454 | 5 Ltext0: | |
455 | ||
456 | .stabs "name:sym_descriptor(type)type_def(1)=type_desc(range)type_ref(1);\ | |
457 | "low_bound;high_bound;",N_LSYM, NIL, NIL, NIL | |
458 | ||
459 | 6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 | |
460 | 7 .stabs "char:t2=r2;0;127;",128,0,0,0 | |
461 | @end example | |
462 | ||
463 | Here the integer type (1) is defined as a range of the integer type | |
464 | (1). Likewise char is a range of char. This part of the definition | |
465 | is circular, but at least the high and low bound values of the range | |
466 | hold more information about the type. | |
467 | ||
468 | Here short unsigned int is defined as type number 8 and described as a | |
469 | range of type int, with a minimum value of 0 and a maximum of 65535. | |
470 | ||
471 | @example | |
472 | 13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0 | |
473 | @end example | |
474 | ||
899bafeb | 475 | @node Bit-ranges |
e505224d PB |
476 | @section Range type defined by number of bits |
477 | ||
478 | type descriptor r | |
479 | ||
480 | In a range definition, if the number after the second semicolon is 0, | |
481 | then the number after the first semicolon is the number of bits needed | |
482 | to represent the type. | |
483 | ||
484 | @example | |
485 | .stabs "name:sym_desc(type)type_def(12)=type_desc(range)type_ref(int)\ | |
486 | ";number_of_bytes;0;", N_LSYM, NIL, NIL, NIL | |
487 | ||
488 | 17 .stabs "float:t12=r1;4;0;",128,0,0,0 | |
489 | 18 .stabs "double:t13=r1;8;0;",128,0,0,0 | |
490 | 19 .stabs "long double:t14=r1;8;0;",128,0,0,0 | |
491 | @end example | |
492 | ||
493 | Cosmically enough, the void type is defined directly in terms of | |
494 | itself. | |
495 | ||
496 | @example | |
497 | .stabs "name:symbol_desc(type)type_def(15)=type_ref(15)",N_LSYM,NIL,NIL,NIL | |
498 | @end example | |
499 | ||
500 | @example | |
501 | 20 .stabs "void:t15=15",128,0,0,0 | |
502 | @end example | |
503 | ||
504 | ||
899bafeb | 505 | @node Example |
e505224d PB |
506 | @chapter A Comprehensive Example in C |
507 | ||
508 | Now we'll examine a second program, example2, which builds on the | |
509 | first example to introduce the rest of the stab types, symbol | |
510 | descriptors, and type descriptors used in C. | |
511 | @xref{Example2.c} for the complete .c source, | |
899bafeb | 512 | and @pxref{Example2.s} for the .s assembly code. |
e505224d PB |
513 | This description includes parts of those files. |
514 | ||
515 | @section Flow of control and nested scopes | |
516 | ||
899bafeb | 517 | @code{.stabn}, stab types @code{N_SLINE}, @code{N_LBRAC}, @code{N_RBRAC} (cont.) |
e505224d | 518 | |
899bafeb RP |
519 | Consider the body of @code{main}, from @file{example2.c}. It shows more |
520 | about how @code{N_SLINE}, @code{N_RBRAC}, and @code{N_LBRAC} stabs are used. | |
e505224d PB |
521 | |
522 | @example | |
523 | 20 @{ | |
524 | 21 static float s_flap; | |
525 | 22 int times; | |
526 | 23 for (times=0; times < s_g_repeat; times++)@{ | |
527 | 24 int inner; | |
528 | 25 printf ("Hello world\n"); | |
529 | 26 @} | |
530 | 27 @}; | |
531 | @end example | |
532 | ||
899bafeb | 533 | Here we have a single source line, the @samp{for} line, that generates |
e505224d | 534 | non-linear flow of control, and non-contiguous code. In this case, an |
899bafeb | 535 | @code{N_SLINE} stab with the same line number proceeds each block of |
e505224d PB |
536 | non-contiguous code generated from the same source line. |
537 | ||
899bafeb | 538 | The example also shows nested scopes. The @code{N_LBRAC} and @code{N_LBRAC} stabs |
e505224d PB |
539 | that describe block structure are nested in the same order as the |
540 | corresponding code blocks, those of the for loop inside those for the | |
541 | body of main. | |
542 | ||
899bafeb RP |
543 | @example |
544 | @exdent Label for the @code{N_LBRAC} (left brace) stab marking the start of @code{main}. | |
e505224d PB |
545 | |
546 | 57 LBB2: | |
547 | ||
899bafeb RP |
548 | @exdent First code range for source line 23,`for' loop initialize and test |
549 | @exdent <68> N_SLINE - source line number associated with this code | |
550 | @exdent .stabn N_SLINE, NIL, line_number, code_address_of_line_start | |
e505224d | 551 | |
e505224d PB |
552 | 58 .stabn 68,0,23,LM2 |
553 | 59 LM2: | |
554 | 60 st %g0,[%fp-20] | |
555 | 61 L2: | |
556 | 62 sethi %hi(_s_g_repeat),%o0 | |
557 | 63 ld [%fp-20],%o1 | |
558 | 64 ld [%o0+%lo(_s_g_repeat)],%o0 | |
559 | 65 cmp %o1,%o0 | |
560 | 66 bge L3 | |
561 | 67 nop | |
e505224d | 562 | |
899bafeb | 563 | @exdent label for the N_LBRAC (start block) marking the start of `for' loop |
e505224d | 564 | |
e505224d PB |
565 | 68 LBB3: |
566 | 69 .stabn 68,0,25,LM3 | |
567 | 70 LM3: | |
568 | 71 sethi %hi(LC0),%o1 | |
569 | 72 or %o1,%lo(LC0),%o0 | |
570 | 73 call _printf,0 | |
571 | 74 nop | |
572 | 75 .stabn 68,0,26,LM4 | |
573 | 76 LM4: | |
e505224d | 574 | |
899bafeb | 575 | @exdent label for the N_RBRAC (end block) stab marking the end of the for loop |
e505224d | 576 | |
e505224d | 577 | 77 LBE3: |
e505224d | 578 | |
899bafeb | 579 | @exdent Second code range for source line 23, 'for' loop increment and return |
612dbd4c | 580 | |
899bafeb | 581 | @exdent <68> N_SLINE - source line number associated with this code |
612dbd4c | 582 | |
899bafeb | 583 | @exdent .stabn, SLINE, NIL, line_number, code_address_of_line_continuation. |
e505224d | 584 | |
e505224d PB |
585 | 78 .stabn 68,0,23,LM5 |
586 | 79 LM5: | |
587 | 80 L4: | |
588 | 81 ld [%fp-20],%o0 | |
589 | 82 add %o0,1,%o1 | |
590 | 83 st %o1,[%fp-20] | |
591 | 84 b,a L2 | |
592 | 85 L3: | |
593 | 86 .stabn 68,0,27,LM6 | |
594 | 87 LM6: | |
e505224d | 595 | |
899bafeb | 596 | @exdent label for the N_RBRAC (end block) stab marking the end of the for loop |
e505224d | 597 | |
e505224d PB |
598 | 88 LBE2: |
599 | 89 .stabn 68,0,27,LM7 | |
600 | 90 LM7: | |
601 | 91 L1: | |
602 | 92 ret | |
603 | 93 restore | |
604 | 94 .stabs "main:F1",36,0,0,_main | |
605 | 95 .stabs "argc:p1",160,0,0,68 | |
606 | 96 .stabs "argv:p20=*21=*2",160,0,0,72 | |
607 | 97 .stabs "s_flap:V12",40,0,0,_s_flap.0 | |
608 | 98 .stabs "times:1",128,0,0,-20 | |
609 | ||
899bafeb RP |
610 | @exdent stabs describing nested scopes, the stabs are nested like the scopes are. |
611 | @exdent <192> N_LBRAC - left brace, begin lexical block (scope) | |
612 | @exdent .stabn N_LBRAC,NIL,NIL,code_addr_of_block_start | |
e505224d PB |
613 | |
614 | 99 .stabn 192,0,0,LBB2 ## begin proc label | |
615 | 100 .stabs "inner:1",128,0,0,-24 | |
616 | 101 .stabn 192,0,0,LBB3 ## begin for label | |
617 | ||
899bafeb RP |
618 | @exdent <224> N_RBRAC - right brace, end lexical block (scope) |
619 | @exdent .stabn N_RBRAC,NIL,NIL,code_addr_of_block_end | |
e505224d PB |
620 | |
621 | 102 .stabn 224,0,0,LBE3 ## end for label | |
622 | 103 .stabn 224,0,0,LBE2 ## end proc label | |
623 | @end example | |
624 | ||
899bafeb | 625 | @node Variables |
e505224d PB |
626 | @chapter Variables |
627 | ||
628 | @menu | |
629 | * Automatic variables:: locally scoped | |
630 | * Global variables:: | |
631 | * Register variables:: | |
632 | * Initialized statics:: | |
633 | * Un-initialized statics:: | |
634 | * Parameters:: | |
635 | @end menu | |
636 | ||
899bafeb | 637 | @node Automatic variables |
e505224d PB |
638 | @section Locally scoped automatic variables |
639 | ||
640 | @example | |
641 | .stabs, stab type N_LSYM, | |
642 | symbol descriptor none | |
643 | @end example | |
644 | ||
645 | ||
646 | In addition to describing types, the N_LSYM stab type also describes | |
647 | locally scoped automatic variables. Refer again to the body of main | |
648 | in example2.c. It allocates two automatic variables, 'times' is | |
649 | scoped to the body of main and 'inner' is scoped to the body of the | |
650 | for loop. 's_flap' is locally scoped by not automatic and will be | |
651 | discussed later. | |
652 | ||
653 | @example | |
654 | 20 @{ | |
655 | 21 static float s_flap; | |
656 | 22 int times; | |
657 | 23 for (times=0; times < s_g_repeat; times++)@{ | |
658 | 24 int inner; | |
659 | 25 printf ("Hello world\n"); | |
660 | 26 @} | |
661 | 27 @}; | |
662 | @end example | |
663 | ||
664 | The N_LSYM stab for an automatic variable is located just before the | |
665 | N_LBRAC stab describing the open brace of the block to which it is | |
666 | scoped. | |
667 | ||
668 | @example | |
669 | <128> N_LSYM - automatic variable, scoped locally to main | |
670 | .stabs "name:type_ref(int)", N_LSYM, NIL, NIL, frame_pointer_offset | |
671 | ||
672 | 98 .stabs "times:1",128,0,0,-20 | |
673 | 99 .stabn 192,0,0,LBB2 ## begin `main' N_LBRAC | |
674 | ||
675 | <128> N_LSYM - automatic variable, scoped locally to the for loop | |
676 | .stabs "name:type_ref(int)", N_LSYM, NIL, NIL, frame_pointer_offset | |
677 | ||
678 | 100 .stabs "inner:1",128,0,0,-24 | |
679 | 101 .stabn 192,0,0,LBB3 ## begin `for' loop N_LBRAC | |
680 | @end example | |
681 | ||
682 | Since the character in the string field following the colon is not a | |
683 | letter, there is no symbol descriptor. This means that the stab | |
684 | describes a local variable, and that the number after the colon is a | |
685 | type reference. In this case it a a reference to the basic type int. | |
686 | Notice also that the frame pointer offset is negative number for | |
687 | automatic variables. | |
688 | ||
689 | ||
899bafeb | 690 | @node Global Variables |
e505224d PB |
691 | @section Global Variables |
692 | ||
693 | @example | |
694 | .stabs, stab type N_GSYM, | |
695 | symbol descriptor G | |
696 | @end example | |
697 | ||
698 | Global variables are represented by the N_GSYM stab type. The symbol | |
699 | descriptor, following the colon in the string field, is G. Following | |
700 | the G is a type reference or type definition. In this example it is a | |
701 | type reference to the basic C type, char. The first source line in | |
702 | example2.c | |
703 | ||
704 | @example | |
705 | 1 char g_foo = 'c'; | |
706 | @end example | |
707 | ||
708 | yields the following stab. The stab immediatly preceeds the code that | |
709 | allocates storage for the variable it describes. | |
710 | ||
711 | @example | |
712 | <32> N_GSYM - global symbol | |
713 | "name:sym_descriptor(Global)type_ref(char)", N_GSYM, NIL, NIL, NIL | |
714 | @end example | |
715 | ||
716 | @example | |
717 | 21 .stabs "g_foo:G2",32,0,0,0 | |
718 | 22 .global _g_foo | |
719 | 23 .data | |
720 | 24 _g_foo: | |
721 | 25 .byte 99 | |
722 | @end example | |
723 | ||
724 | The address of the variable represented by the N_GSYM is not contained | |
725 | in the N_GSYM stab. The debugger gets this information from the | |
726 | external symbol for the global variable. | |
727 | ||
899bafeb | 728 | @node Register variables |
e505224d PB |
729 | @section Register variables |
730 | ||
731 | @example | |
732 | .stabs, stab type N_RSYM, | |
733 | symbol descriptor r | |
734 | @end example | |
735 | ||
736 | The following source line defines a global variable, g_bar, which is | |
737 | allocated in global register %g5. | |
738 | ||
739 | @example | |
740 | 2 register int g_bar asm ("%g5"); | |
741 | @end example | |
742 | ||
743 | Register variables have their own stab type, N_RSYM, and their own | |
744 | symbol descriptor, r. The stab's value field contains the number of | |
745 | the register where the variable data will be stored. Since the | |
746 | variable was not initialized in this compilation unit, the stab is | |
747 | emited at the end of the object file, with the stabs for other | |
748 | uninitialized globals (bcc). | |
749 | ||
750 | @example | |
751 | <64> N_RSYM - register variable | |
752 | .stabs "name:sym_desc(reg_var)type_ref(int), N_RSYM, NIL, NIL, reg_num | |
753 | ||
754 | 133 .stabs "g_bar:r1",64,0,0,5 | |
755 | @end example | |
756 | ||
757 | ||
899bafeb | 758 | @node Initialized statics |
e505224d PB |
759 | @section Initialized static variables |
760 | ||
761 | @example | |
762 | .stabs, stab type N_STSYM, | |
763 | symbol descriptors S (file scope), V (procedure scope) | |
764 | @end example | |
765 | ||
766 | Initialized static variables are represented by the N_STSYM stab type. | |
767 | The symbol descriptor part of the string field shows if the variable | |
768 | is file scope static (S) or procedure scope static (V). The source | |
769 | line: | |
770 | ||
771 | @example | |
772 | 3 static int s_g_repeat = 2; | |
773 | @end example | |
774 | ||
775 | yields the following code. The stab is located immediatly preceeding | |
776 | the storage for the variable it represents. Since the variable in | |
777 | this example is file scope static the symbol descriptor is S. | |
778 | ||
779 | @example | |
780 | <38> N_STSYM - initialized static variable (data seg w/internal linkage) | |
781 | .stabs "name:sym_desc(static_global)type_ref(int)",N_STSYM,NIL,NIL,var_addr | |
782 | @end example | |
783 | ||
784 | @example | |
785 | 26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat | |
786 | 27 .align 4 | |
787 | 28 _s_g_repeat: | |
788 | 29 .word 2 | |
789 | @end example | |
790 | ||
791 | ||
899bafeb | 792 | @node Un-initialized statics |
e505224d PB |
793 | @section Un-initialized static variables |
794 | ||
795 | @example | |
796 | .stabs, stab type N_LCSYM, | |
797 | symbol descriptors S (file scope), V (procedure scope) | |
798 | @end example | |
799 | ||
800 | Un-initilized static variables are represeted by the N_LCSYM stab | |
801 | type. The symbol descriptor part of the string shows if the variable | |
802 | is file scope static (S) or procedure scope static (V). In this | |
803 | example it is procedure scope static. The source line allocating | |
804 | s_flap immediatly follows the open brace for the procedure main. | |
805 | ||
806 | @example | |
807 | 20 @{ | |
808 | 21 static float s_flap; | |
809 | @end example | |
810 | ||
811 | ||
812 | The code that reserves storage for the variable s_flap preceeds the | |
813 | body of body of main. | |
814 | ||
815 | @example | |
816 | 39 .reserve _s_flap.0,4,"bss",4 | |
817 | @end example | |
818 | ||
819 | But since s_flap is scoped locally to main, its stab is located with | |
820 | the other stabs representing symbols local to main. The stab for | |
821 | s_flap is located just before the N_LBRAC for main. | |
822 | ||
823 | @example | |
824 | <40> N_LCSYM - un-initialized static var (BSS seg w/internal linkage) | |
825 | .stabs "name:sym_desc(static_local)type_ref(float)", N_LCSYM, | |
826 | NIL, NIL, data_addr | |
827 | @end example | |
828 | ||
829 | @example | |
830 | 97 .stabs "s_flap:V12",40,0,0,_s_flap.0 | |
831 | 98 .stabs "times:1",128,0,0,-20 | |
832 | 99 .stabn 192,0,0,LBB2 # N_LBRAC for main. | |
833 | @end example | |
834 | ||
899bafeb | 835 | @node Parameters |
e505224d PB |
836 | @section Parameters |
837 | ||
838 | @example | |
839 | .stabs, stab type N_PSYM, | |
840 | symbol descriptor p | |
841 | @end example | |
842 | ||
843 | Procedure parameters are represented by the N_PSYM stab type. The | |
844 | following source lines show the parameters of the main routine. | |
845 | ||
846 | @example | |
847 | 17 main (argc, argv) | |
848 | 18 int argc; | |
849 | 19 char* argv[]; | |
850 | 20 @{ | |
851 | @end example | |
852 | ||
853 | The N_PSYM stabs describing parameters to a function directly follow | |
854 | the N_FUN stab that represents the procedure itself. The N_FUN stab | |
855 | immediatly follows the code of the procedure it describes. Following | |
856 | the N_PSYM parameter stabs are any N_LSYM stabs representing local | |
857 | variables. | |
858 | ||
e505224d | 859 | @example |
899bafeb RP |
860 | @exdent <36> N_FUN - describing the procedure main |
861 | ||
e505224d PB |
862 | 94 .stabs "main:F1",36,0,0,_main |
863 | ||
899bafeb RP |
864 | @exdent <160> N_PSYM - parameters |
865 | @exdent .stabs "name:sym_desc(value_param)type_ref(int)", N_PSYM, | |
866 | @exdent NIL, NIL, frame_ptr_offset | |
867 | ||
e505224d PB |
868 | 95 .stabs "argc:p1",160,0,0,68 |
869 | ||
899bafeb RP |
870 | @exdent <160> N_PSYM - parameter |
871 | @exdent .stabs "name:sym_desc(value_param)type_def(20)=ptr_to type_def(21)= | |
872 | @exdent ptr_to type_ref(char) | |
873 | ||
e505224d PB |
874 | 96 .stabs "argv:p20=*21=*2",160,0,0,72 |
875 | @end example | |
876 | ||
877 | The type definition of argv is interesting because it defines two new | |
878 | types in terms of an existing one. The array argv contains character | |
879 | pointers. The type of the array name is a pointer to the type the | |
880 | array holds. Thus the type of argv is ptr to ptr to char. The stab | |
881 | for argv contains nested type_definitions. Type 21 is ptr to type 2 | |
882 | (char) and argv (type 20) is ptr to type 21. | |
883 | ||
899bafeb | 884 | @node Aggregate Types |
e505224d PB |
885 | @chapter Aggregate Types |
886 | ||
612dbd4c | 887 | Now let's look at some variable definitions involving complex types. |
e505224d PB |
888 | This involves understanding better how types are described. In the |
889 | examples so far types have been described as references to previously | |
890 | defined types or defined in terms of subranges of or pointers to | |
891 | previously defined types. The section that follows will talk about | |
892 | the various other type descriptors that may follow the = sign in a | |
893 | type definition. | |
894 | ||
895 | @menu | |
896 | * Arrays:: | |
897 | * Enumerations:: | |
898 | * Structure tags:: | |
899 | * Typedefs:: | |
900 | * Unions:: | |
901 | * Function types:: | |
902 | @end menu | |
903 | ||
899bafeb RP |
904 | @node Arrays |
905 | @section Array types | |
e505224d PB |
906 | |
907 | .stabs, stab types N_GSYM, N_LSYM, | |
899bafeb | 908 | |
e505224d PB |
909 | symbol descriptor T, type descriptor ar |
910 | ||
911 | As an example of an array type consider the global variable below. | |
912 | ||
913 | @example | |
914 | 15 char char_vec[3] = @{'a','b','c'@}; | |
915 | @end example | |
916 | ||
917 | Since the array is a global variable, it is described by the N_GSYM | |
918 | stab type. The symbol descriptor G, following the colon in stab's | |
919 | string field, also says the array is a global variable. Following the | |
920 | G is a definition for type (19) as shown by the equals sign after the | |
921 | type number. | |
922 | ||
923 | After the equals sign is a type descriptor, ar, which says that the | |
924 | type being defined is an array. Following the type descriptor for an | |
925 | array is the type of the index, a null field, the upper bound of the | |
926 | array indexing, and the type of the array elements. | |
927 | ||
928 | The array definition above generates the assembly language that | |
929 | follows. | |
930 | ||
931 | @example | |
899bafeb RP |
932 | @exdent <32> N_GSYM - global variable |
933 | @exdent .stabs "name:sym_desc(global)type_def(19)=type_desc(array) | |
934 | @exdent index_type_ref(int);NIL;high_bound(2);element_type_ref(char)"; | |
935 | @exdent N_GSYM, NIL, NIL, NIL | |
e505224d PB |
936 | |
937 | 32 .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0 | |
938 | 33 .global _char_vec | |
939 | 34 .align 4 | |
940 | 35 _char_vec: | |
941 | 36 .byte 97 | |
942 | 37 .byte 98 | |
943 | 38 .byte 99 | |
944 | @end example | |
945 | ||
899bafeb | 946 | @node Enumerations |
e505224d PB |
947 | @section Enumerations |
948 | ||
899bafeb | 949 | @display |
e505224d PB |
950 | .stabs, stab type N_LSYM, |
951 | symbol descriptor T, type descriptor e | |
899bafeb | 952 | @end display |
e505224d PB |
953 | |
954 | The source line below declares an enumeration type. It is defined at | |
955 | file scope between the bodies of main and s_proc in example2.c. | |
956 | Because the N_LSYM is located after the N_RBRAC that marks the end of | |
957 | the previous procedure's block scope, and before the N_FUN that marks | |
958 | the beginning of the next procedure's block scope, the N_LSYM does not | |
959 | describe a block local symbol, but a file local one. The source line: | |
960 | ||
961 | @example | |
962 | 29 enum e_places @{first,second=3,last@}; | |
963 | @end example | |
964 | ||
899bafeb | 965 | @noindent |
e505224d PB |
966 | generates the following stab, located just after the N_RBRAC (close |
967 | brace stab) for main. The type definition is in an N_LSYM stab | |
968 | because type definitions are file scope not global scope. | |
969 | ||
899bafeb | 970 | @display |
e505224d PB |
971 | <128> N_LSYM - local symbol |
972 | .stab "name:sym_dec(type)type_def(22)=sym_desc(enum) | |
973 | enum_name:value(0),enum_name:value(3),enum_name:value(4),;", | |
974 | N_LSYM, NIL, NIL, NIL | |
899bafeb | 975 | @end display |
e505224d | 976 | |
899bafeb | 977 | @example |
e505224d | 978 | 104 .stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0 |
899bafeb | 979 | @end example |
e505224d PB |
980 | |
981 | The symbol descriptor (T) says that the stab describes a structure, | |
982 | enumeration, or type tag. The type descriptor e, following the 22= of | |
983 | the type definition narrows it down to an enumeration type. Following | |
984 | the e is a list of the elements of the enumeration. The format is | |
985 | name:value,. The list of elements ends with a ;. | |
986 | ||
899bafeb | 987 | @node Structure tags |
e505224d PB |
988 | @section Structure Tags |
989 | ||
899bafeb | 990 | @display |
e505224d PB |
991 | .stabs, stab type N_LSYM, |
992 | symbol descriptor T, type descriptor s | |
899bafeb | 993 | @end display |
e505224d PB |
994 | |
995 | The following source code declares a structure tag and defines an | |
996 | instance of the structure in global scope. Then a typedef equates the | |
997 | structure tag with a new type. A seperate stab is generated for the | |
998 | structure tag, the structure typedef, and the structure instance. The | |
999 | stabs for the tag and the typedef are emited when the definitions are | |
1000 | encountered. Since the structure elements are not initialized, the | |
1001 | stab and code for the structure variable itself is located at the end | |
1002 | of the program in .common. | |
1003 | ||
1004 | @example | |
1005 | 6 struct s_tag @{ | |
1006 | 7 int s_int; | |
1007 | 8 float s_float; | |
1008 | 9 char s_char_vec[8]; | |
1009 | 10 struct s_tag* s_next; | |
1010 | 11 @} g_an_s; | |
1011 | 12 | |
1012 | 13 typedef struct s_tag s_typedef; | |
1013 | @end example | |
1014 | ||
1015 | The structure tag is an N_LSYM stab type because, like the enum, the | |
1016 | symbol is file scope. Like the enum, the symbol descriptor is T, for | |
1017 | enumeration, struct or tag type. The symbol descriptor s following | |
1018 | the 16= of the type definition narrows the symbol type to struct. | |
1019 | ||
1020 | Following the struct symbol descriptor is the number of bytes the | |
1021 | struct occupies, followed by a description of each structure element. | |
1022 | The structure element descriptions are of the form name:type, bit | |
1023 | offset from the start of the struct, and number of bits in the | |
1024 | element. | |
1025 | ||
1026 | ||
612dbd4c | 1027 | @example |
e505224d PB |
1028 | <128> N_LSYM - type definition |
1029 | .stabs "name:sym_desc(struct tag) Type_def(16)=type_desc(struct type) | |
1030 | struct_bytes | |
1031 | elem_name:type_ref(int),bit_offset,field_bits; | |
1032 | elem_name:type_ref(float),bit_offset,field_bits; | |
1033 | elem_name:type_def(17)=type_desc(dynamic array) index_type(int);NIL; | |
1034 | high_bound(7);element_type(char),bit_offset,field_bits;;", | |
1035 | N_LSYM,NIL,NIL,NIL | |
1036 | ||
1037 | 30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32; | |
1038 | s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0 | |
612dbd4c | 1039 | @end example |
e505224d PB |
1040 | |
1041 | In this example, two of the structure elements are previously defined | |
1042 | types. For these, the type following the name: part of the element | |
1043 | description is a simple type reference. The other two structure | |
1044 | elements are new types. In this case there is a type definition | |
1045 | embedded after the name:. The type definition for the array element | |
1046 | looks just like a type definition for a standalone array. The s_next | |
1047 | field is a pointer to the same kind of structure that the field is an | |
1048 | element of. So the definition of structure type 16 contains an type | |
1049 | definition for an element which is a pointer to type 16. | |
1050 | ||
899bafeb | 1051 | @node Typedefs |
e505224d PB |
1052 | @section Typedefs |
1053 | ||
899bafeb | 1054 | @display |
e505224d PB |
1055 | .stabs, stab type N_LSYM, |
1056 | symbol descriptor t | |
899bafeb | 1057 | @end display |
e505224d PB |
1058 | |
1059 | Here is the stab for the typedef equating the structure tag with a | |
1060 | type. | |
1061 | ||
899bafeb | 1062 | @display |
e505224d PB |
1063 | <128> N_LSYM - type definition |
1064 | .stabs "name:sym_desc(type name)type_ref(struct_tag)",N_LSYM,NIL,NIL,NIL | |
899bafeb | 1065 | @end display |
e505224d | 1066 | |
899bafeb | 1067 | @example |
e505224d | 1068 | 31 .stabs "s_typedef:t16",128,0,0,0 |
899bafeb | 1069 | @end example |
e505224d PB |
1070 | |
1071 | And here is the code generated for the structure variable. | |
1072 | ||
899bafeb | 1073 | @display |
e505224d PB |
1074 | <32> N_GSYM - global symbol |
1075 | .stabs "name:sym_desc(global)type_ref(struct_tag)",N_GSYM,NIL,NIL,NIL | |
899bafeb | 1076 | @end display |
e505224d PB |
1077 | |
1078 | @example | |
1079 | 136 .stabs "g_an_s:G16",32,0,0,0 | |
1080 | 137 .common _g_an_s,20,"bss" | |
1081 | @end example | |
1082 | ||
1083 | Notice that the structure tag has the same type number as the typedef | |
1084 | for the structure tag. It is impossible to distinguish between a | |
1085 | variable of the struct type and one of its typedef by looking at the | |
1086 | debugging information. | |
1087 | ||
1088 | ||
899bafeb | 1089 | @node Unions |
e505224d PB |
1090 | @section Unions |
1091 | ||
899bafeb | 1092 | @display |
e505224d PB |
1093 | .stabs, stab type N_LSYM, |
1094 | symbol descriptor T, type descriptor u | |
899bafeb | 1095 | @end display |
e505224d | 1096 | |
612dbd4c | 1097 | Next let's look at unions. In example2 this union type is declared |
e505224d PB |
1098 | locally to a procedure and an instance of the union is defined. |
1099 | ||
1100 | @example | |
1101 | 36 union u_tag @{ | |
1102 | 37 int u_int; | |
1103 | 38 float u_float; | |
1104 | 39 char* u_char; | |
1105 | 40 @} an_u; | |
1106 | @end example | |
1107 | ||
1108 | This code generates a stab for the union tag and a stab for the union | |
1109 | variable. Both use the N_LSYM stab type. Since the union variable is | |
1110 | scoped locally to the procedure in which it is defined, its stab is | |
1111 | located immediatly preceeding the N_LBRAC for the procedure's block | |
1112 | start. | |
1113 | ||
1114 | The stab for the union tag, however is located preceeding the code for | |
1115 | the procedure in which it is defined. The stab type is N_LSYM. This | |
1116 | would seem to imply that the union type is file scope, like the struct | |
1117 | type s_tag. This is not true. The contents and position of the stab | |
1118 | for u_type do not convey any infomation about its procedure local | |
1119 | scope. | |
1120 | ||
899bafeb | 1121 | @display |
e505224d PB |
1122 | <128> N_LSYM - type |
1123 | .stabs "name:sym_desc(union tag)type_def(22)=type_desc(union) | |
1124 | byte_size(4) | |
1125 | elem_name:type_ref(int),bit_offset(0),bit_size(32); | |
1126 | elem_name:type_ref(float),bit_offset(0),bit_size(32); | |
1127 | elem_name:type_ref(ptr to char),bit_offset(0),bit_size(32);;" | |
1128 | N_LSYM, NIL, NIL, NIL | |
899bafeb | 1129 | @end display |
e505224d | 1130 | |
899bafeb | 1131 | @example |
e505224d | 1132 | 105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",128,0,0,0 |
899bafeb | 1133 | @end example |
e505224d PB |
1134 | |
1135 | The symbol descriptor, T, following the name: means that the stab | |
1136 | describes an enumeration struct or type tag. The type descriptor u, | |
1137 | following the 23= of the type definition, narrows it down to a union | |
1138 | type definition. Following the u is the number of bytes in the union. | |
1139 | After that is a list of union element descriptions. Their format is | |
1140 | name:type, bit offset into the union, and number of bytes for the | |
1141 | element;. | |
1142 | ||
1143 | The stab for the union variable follows. Notice that the frame | |
1144 | pointer offset for local variables is negative. | |
1145 | ||
899bafeb | 1146 | @display |
e505224d PB |
1147 | <128> N_LSYM - local variable (with no symbol descriptor) |
1148 | .stabs "name:type_ref(u_tag)", N_LSYM, NIL, NIL, frame_ptr_offset | |
899bafeb | 1149 | @end display |
e505224d | 1150 | |
899bafeb | 1151 | @example |
e505224d | 1152 | 130 .stabs "an_u:23",128,0,0,-20 |
899bafeb | 1153 | @end example |
e505224d | 1154 | |
899bafeb | 1155 | @node Function types |
e505224d PB |
1156 | @section Function types |
1157 | ||
899bafeb | 1158 | @display |
e505224d | 1159 | type descriptor f |
899bafeb | 1160 | @end display |
e505224d PB |
1161 | |
1162 | The last type descriptor in C which remains to be described is used | |
1163 | for function types. Consider the following source line defining a | |
1164 | global function pointer. | |
1165 | ||
1166 | @example | |
1167 | 4 int (*g_pf)(); | |
1168 | @end example | |
1169 | ||
1170 | It generates the following code. Since the variable is not | |
1171 | initialized, the code is located in the common area at the end of the | |
1172 | file. | |
1173 | ||
899bafeb | 1174 | @display |
e505224d PB |
1175 | <32> N_GSYM - global variable |
1176 | .stabs "name:sym_desc(global)type_def(24)=ptr_to(25)= | |
1177 | type_def(func)type_ref(int) | |
899bafeb | 1178 | @end display |
e505224d | 1179 | |
899bafeb | 1180 | @example |
e505224d PB |
1181 | 134 .stabs "g_pf:G24=*25=f1",32,0,0,0 |
1182 | 135 .common _g_pf,4,"bss" | |
899bafeb | 1183 | @end example |
e505224d PB |
1184 | |
1185 | Since the variable is global, the stab type is N_GSYM and the symbol | |
1186 | descriptor is G. The variable defines a new type, 24, which is a | |
1187 | pointer to another new type, 25, which is defined as a function | |
1188 | returning int. | |
1189 | ||
899bafeb | 1190 | @node Symbol tables |
e505224d PB |
1191 | @chapter Symbol information in symbol tables |
1192 | ||
1193 | This section examines more closely the format of symbol table entries | |
1194 | and how stab assembler directives map to them. It also describes what | |
1195 | transformations the assembler and linker make on data from stabs. | |
1196 | ||
1197 | Each time the assembler encounters a stab in its input file it puts | |
1198 | each field of the stab into corresponding fields in a symbol table | |
1199 | entry of its output file. If the stab contains a string field, the | |
1200 | symbol table entry for that stab points to a string table entry | |
1201 | containing the string data from the stab. Assembler labels become | |
1202 | relocatable addresses. Symbol table entries in a.out have the format: | |
1203 | ||
1204 | @example | |
1205 | struct internal_nlist @{ | |
1206 | unsigned long n_strx; /* index into string table of name */ | |
1207 | unsigned char n_type; /* type of symbol */ | |
1208 | unsigned char n_other; /* misc info (usually empty) */ | |
1209 | unsigned short n_desc; /* description field */ | |
1210 | bfd_vma n_value; /* value of symbol */ | |
1211 | @}; | |
1212 | @end example | |
1213 | ||
1214 | For .stabs directives, the n_strx field holds the character offset | |
1215 | from the start of the string table to the string table entry | |
1216 | containing the "string" field. For other classes of stabs (.stabn and | |
1217 | .stabd) this field is null. | |
1218 | ||
1219 | Symbol table entries with n_type fields containing a value greater or | |
1220 | equal to 0x20 originated as stabs generated by the compiler (with one | |
1221 | random exception). Those with n_type values less than 0x20 were | |
1222 | placed in the symbol table of the executable by the assembler or the | |
1223 | linker. | |
1224 | ||
1225 | The linker concatenates object files and does fixups of externally | |
1226 | defined symbols. You can see the transformations made on stab data by | |
1227 | the assembler and linker by examining the symbol table after each pass | |
1228 | of the build, first the assemble and then the link. | |
1229 | ||
1230 | To do this use nm with the -ap options. This dumps the symbol table, | |
1231 | including debugging information, unsorted. For stab entries the | |
1232 | columns are: value, other, desc, type, string. For assembler and | |
1233 | linker symbols, the columns are: value, type, string. | |
1234 | ||
1235 | There are a few important things to notice about symbol tables. Where | |
1236 | the value field of a stab contains a frame pointer offset, or a | |
1237 | register number, that value is unchanged by the rest of the build. | |
1238 | ||
1239 | Where the value field of a stab contains an assembly language label, | |
1240 | it is transformed by each build step. The assembler turns it into a | |
1241 | relocatable address and the linker turns it into an absolute address. | |
1242 | This source line defines a static variable at file scope: | |
1243 | ||
899bafeb | 1244 | @example |
e505224d | 1245 | 3 static int s_g_repeat |
899bafeb | 1246 | @end example |
e505224d | 1247 | |
899bafeb | 1248 | @noindent |
e505224d PB |
1249 | The following stab describes the symbol. |
1250 | ||
899bafeb | 1251 | @example |
e505224d | 1252 | 26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat |
899bafeb | 1253 | @end example |
e505224d | 1254 | |
899bafeb | 1255 | @noindent |
e505224d | 1256 | The assembler transforms the stab into this symbol table entry in the |
899bafeb | 1257 | @file{.o} file. The location is expressed as a data segment offset. |
e505224d | 1258 | |
899bafeb | 1259 | @example |
e505224d | 1260 | 21 00000084 - 00 0000 STSYM s_g_repeat:S1 |
899bafeb | 1261 | @end example |
e505224d | 1262 | |
899bafeb | 1263 | @noindent |
e505224d PB |
1264 | in the symbol table entry from the executable, the linker has made the |
1265 | relocatable address absolute. | |
1266 | ||
899bafeb | 1267 | @example |
e505224d | 1268 | 22 0000e00c - 00 0000 STSYM s_g_repeat:S1 |
899bafeb | 1269 | @end example |
e505224d PB |
1270 | |
1271 | Stabs for global variables do not contain location information. In | |
1272 | this case the debugger finds location information in the assembler or | |
1273 | linker symbol table entry describing the variable. The source line: | |
1274 | ||
899bafeb | 1275 | @example |
e505224d | 1276 | 1 char g_foo = 'c'; |
899bafeb | 1277 | @end example |
e505224d | 1278 | |
899bafeb | 1279 | @noindent |
e505224d PB |
1280 | generates the stab: |
1281 | ||
899bafeb | 1282 | @example |
e505224d | 1283 | 21 .stabs "g_foo:G2",32,0,0,0 |
899bafeb | 1284 | @end example |
e505224d PB |
1285 | |
1286 | The variable is represented by the following two symbol table entries | |
1287 | in the object file. The first one originated as a stab. The second | |
1288 | one is an external symbol. The upper case D signifies that the n_type | |
1289 | field of the symbol table contains 7, N_DATA with local linkage (see | |
1290 | Table B). The value field following the file's line number is empty | |
1291 | for the stab entry. For the linker symbol it contains the | |
1292 | rellocatable address corresponding to the variable. | |
1293 | ||
899bafeb | 1294 | @example |
e505224d PB |
1295 | 19 00000000 - 00 0000 GSYM g_foo:G2 |
1296 | 20 00000080 D _g_foo | |
899bafeb | 1297 | @end example |
e505224d | 1298 | |
899bafeb | 1299 | @noindent |
e505224d PB |
1300 | These entries as transformed by the linker. The linker symbol table |
1301 | entry now holds an absolute address. | |
1302 | ||
899bafeb | 1303 | @example |
e505224d | 1304 | 21 00000000 - 00 0000 GSYM g_foo:G2 |
899bafeb | 1305 | @dots{} |
e505224d | 1306 | 215 0000e008 D _g_foo |
899bafeb | 1307 | @end example |
e505224d | 1308 | |
899bafeb | 1309 | @node GNU C++ stabs |
612dbd4c | 1310 | @chapter GNU C++ stabs |
e505224d PB |
1311 | |
1312 | @menu | |
1313 | * Basic C++ types:: | |
1314 | * Simple classes:: | |
1315 | * Class instance:: | |
1316 | * Methods:: Method definition | |
1317 | * Protections:: | |
1318 | * Method Modifiers:: (const, volatile, const volatile) | |
1319 | * Virtual Methods:: | |
1320 | * Inheritence:: | |
1321 | * Virtual Base Classes:: | |
1322 | * Static Members:: | |
1323 | @end menu | |
1324 | ||
1325 | ||
1326 | @subsection Symbol descriptors added for C++ descriptions: | |
1327 | ||
899bafeb | 1328 | @display |
e505224d | 1329 | P - register parameter. |
899bafeb | 1330 | @end display |
e505224d PB |
1331 | |
1332 | @subsection type descriptors added for C++ descriptions | |
1333 | ||
1334 | @table @code | |
1335 | @item # | |
1336 | method type (two ## if minimal debug) | |
1337 | ||
1338 | @item xs | |
1339 | cross-reference | |
1340 | @end table | |
1341 | ||
1342 | ||
899bafeb | 1343 | @node Basic C++ types |
e505224d PB |
1344 | @section Basic types for C++ |
1345 | ||
1346 | << the examples that follow are based on a01.C >> | |
1347 | ||
1348 | ||
1349 | C++ adds two more builtin types to the set defined for C. These are | |
1350 | the unknown type and the vtable record type. The unknown type, type | |
1351 | 16, is defined in terms of itself like the void type. | |
1352 | ||
1353 | The vtable record type, type 17, is defined as a structure type and | |
1354 | then as a structure tag. The structure has four fields, delta, index, | |
1355 | pfn, and delta2. pfn is the function pointer. | |
1356 | ||
1357 | << In boilerplate $vtbl_ptr_type, what are the fields delta, | |
1358 | index, and delta2 used for? >> | |
1359 | ||
1360 | This basic type is present in all C++ programs even if there are no | |
1361 | virtual methods defined. | |
1362 | ||
899bafeb | 1363 | @display |
e505224d PB |
1364 | .stabs "struct_name:sym_desc(type)type_def(17)=type_desc(struct)struct_bytes(8) |
1365 | elem_name(delta):type_ref(short int),bit_offset(0),field_bits(16); | |
1366 | elem_name(index):type_ref(short int),bit_offset(16),field_bits(16); | |
1367 | elem_name(pfn):type_def(18)=type_desc(ptr to)type_ref(void), | |
1368 | bit_offset(32),field_bits(32); | |
1369 | elem_name(delta2):type_def(short int);bit_offset(32),field_bits(16);;" | |
1370 | N_LSYM, NIL, NIL | |
899bafeb | 1371 | @end display |
e505224d | 1372 | |
899bafeb | 1373 | @smallexample |
e505224d PB |
1374 | .stabs "$vtbl_ptr_type:t17=s8 |
1375 | delta:6,0,16;index:6,16,16;pfn:18=*15,32,32;delta2:6,32,16;;" | |
1376 | ,128,0,0,0 | |
899bafeb | 1377 | @end smallexample |
e505224d | 1378 | |
899bafeb | 1379 | @display |
e505224d | 1380 | .stabs "name:sym_dec(struct tag)type_ref($vtbl_ptr_type)",N_LSYM,NIL,NIL,NIL |
899bafeb | 1381 | @end display |
e505224d | 1382 | |
899bafeb | 1383 | @example |
e505224d | 1384 | .stabs "$vtbl_ptr_type:T17",128,0,0,0 |
899bafeb | 1385 | @end example |
e505224d | 1386 | |
899bafeb | 1387 | @node Simple classes |
e505224d PB |
1388 | @section Simple class definition |
1389 | ||
1390 | The stabs describing C++ language features are an extension of the | |
1391 | stabs describing C. Stabs representing C++ class types elaborate | |
1392 | extensively on the stab format used to describe structure types in C. | |
1393 | Stabs representing class type variables look just like stabs | |
1394 | representing C language variables. | |
1395 | ||
1396 | Consider the following very simple class definition. | |
1397 | ||
1398 | @example | |
1399 | class baseA @{ | |
1400 | public: | |
1401 | int Adat; | |
1402 | int Ameth(int in, char other); | |
1403 | @}; | |
1404 | @end example | |
1405 | ||
1406 | The class baseA is represented by two stabs. The first stab describes | |
1407 | the class as a structure type. The second stab describes a structure | |
1408 | tag of the class type. Both stabs are of stab type N_LSYM. Since the | |
1409 | stab is not located between an N_FUN and a N_LBRAC stab this indicates | |
1410 | that the class is defined at file scope. If it were, then the N_LSYM | |
1411 | would signify a local variable. | |
1412 | ||
1413 | A stab describing a C++ class type is similar in format to a stab | |
1414 | describing a C struct, with each class member shown as a field in the | |
1415 | structure. The part of the struct format describing fields is | |
1416 | expanded to include extra information relevent to C++ class members. | |
1417 | In addition, if the class has multiple base classes or virtual | |
1418 | functions the struct format outside of the field parts is also | |
1419 | augmented. | |
1420 | ||
1421 | In this simple example the field part of the C++ class stab | |
1422 | representing member data looks just like the field part of a C struct | |
1423 | stab. The section on protections describes how its format is | |
1424 | sometimes extended for member data. | |
1425 | ||
1426 | The field part of a C++ class stab representing a member function | |
1427 | differs substantially from the field part of a C struct stab. It | |
1428 | still begins with `name:' but then goes on to define a new type number | |
1429 | for the member function, describe its return type, its argument types, | |
1430 | its protection level, any qualifiers applied to the method definition, | |
1431 | and whether the method is virtual or not. If the method is virtual | |
1432 | then the method description goes on to give the vtable index of the | |
1433 | method, and the type number of the first base class defining the | |
1434 | method. | |
1435 | ||
1436 | When the field name is a method name it is followed by two colons | |
1437 | rather than one. This is followed by a new type definition for the | |
1438 | method. This is a number followed by an equal sign and then the | |
1439 | symbol descriptor `##', indicating a method type. This is followed by | |
1440 | a type reference showing the return type of the method and a | |
1441 | semi-colon. | |
1442 | ||
1443 | The format of an overloaded operator method name differs from that | |
1444 | of other methods. It is "op$::XXXX." where XXXX is the operator name | |
612dbd4c JG |
1445 | such as + or +=. The name ends with a period, and any characters except |
1446 | the period can occur in the XXXX string. | |
e505224d PB |
1447 | |
1448 | The next part of the method description represents the arguments to | |
1449 | the method, preceeded by a colon and ending with a semi-colon. The | |
1450 | types of the arguments are expressed in the same way argument types | |
1451 | are expressed in C++ name mangling. In this example an int and a char | |
1452 | map to `ic'. | |
1453 | ||
1454 | This is followed by a number, a letter, and an asterisk or period, | |
1455 | followed by another semicolon. The number indicates the protections | |
1456 | that apply to the member function. Here the 2 means public. The | |
1457 | letter encodes any qualifier applied to the method definition. In | |
1458 | this case A means that it is a normal function definition. The dot | |
1459 | shows that the method is not virtual. The sections that follow | |
1460 | elaborate further on these fields and describe the additional | |
1461 | information present for virtual methods. | |
1462 | ||
1463 | ||
899bafeb | 1464 | @display |
e505224d PB |
1465 | .stabs "class_name:sym_desc(type)type_def(20)=type_desc(struct)struct_bytes(4) |
1466 | field_name(Adat):type(int),bit_offset(0),field_bits(32); | |
1467 | ||
1468 | method_name(Ameth)::type_def(21)=type_desc(method)return_type(int); | |
1469 | :arg_types(int char); | |
1470 | protection(public)qualifier(normal)virtual(no);;" | |
1471 | N_LSYM,NIL,NIL,NIL | |
899bafeb | 1472 | @end display |
e505224d | 1473 | |
899bafeb | 1474 | @smallexample |
e505224d PB |
1475 | .stabs "baseA:t20=s4Adat:1,0,32;Ameth::21=##1;:ic;2A.;;",128,0,0,0 |
1476 | ||
1477 | .stabs "class_name:sym_desc(struct tag)",N_LSYM,NIL,NIL,NIL | |
1478 | ||
1479 | .stabs "baseA:T20",128,0,0,0 | |
899bafeb | 1480 | @end smallexample |
e505224d | 1481 | |
899bafeb | 1482 | @node Class instance |
e505224d PB |
1483 | @section Class instance |
1484 | ||
1485 | As shown above, describing even a simple C++ class definition is | |
1486 | accomplished by massively extending the stab format used in C to | |
1487 | describe structure types. However, once the class is defined, C stabs | |
1488 | with no modifications can be used to describe class instances. The | |
1489 | following source: | |
1490 | ||
1491 | @example | |
1492 | main () @{ | |
1493 | baseA AbaseA; | |
1494 | @} | |
1495 | @end example | |
1496 | ||
899bafeb RP |
1497 | @noindent |
1498 | yields the following stab describing the class instance. It looks no | |
e505224d PB |
1499 | different from a standard C stab describing a local variable. |
1500 | ||
899bafeb | 1501 | @display |
e505224d | 1502 | .stabs "name:type_ref(baseA)", N_LSYM, NIL, NIL, frame_ptr_offset |
899bafeb | 1503 | @end display |
e505224d | 1504 | |
899bafeb | 1505 | @example |
e505224d | 1506 | .stabs "AbaseA:20",128,0,0,-20 |
899bafeb | 1507 | @end example |
e505224d | 1508 | |
899bafeb | 1509 | @node Methods |
e505224d PB |
1510 | @section Method defintion |
1511 | ||
1512 | The class definition shown above declares Ameth. The C++ source below | |
1513 | defines Ameth: | |
1514 | ||
1515 | @example | |
1516 | int | |
1517 | baseA::Ameth(int in, char other) | |
1518 | @{ | |
1519 | return in; | |
1520 | @}; | |
1521 | @end example | |
1522 | ||
1523 | ||
1524 | This method definition yields three stabs following the code of the | |
1525 | method. One stab describes the method itself and following two | |
1526 | describe its parameters. Although there is only one formal argument | |
1527 | all methods have an implicit argument which is the `this' pointer. | |
1528 | The `this' pointer is a pointer to the object on which the method was | |
1529 | called. Note that the method name is mangled to encode the class name | |
1530 | and argument types. << Name mangling is not described by this | |
1531 | document - Is there already such a doc? >> | |
1532 | ||
612dbd4c | 1533 | @example |
e505224d PB |
1534 | .stabs "name:symbol_desriptor(global function)return_type(int)", |
1535 | N_FUN, NIL, NIL, code_addr_of_method_start | |
1536 | ||
1537 | .stabs "Ameth__5baseAic:F1",36,0,0,_Ameth__5baseAic | |
612dbd4c | 1538 | @end example |
e505224d PB |
1539 | |
1540 | Here is the stab for the `this' pointer implicit argument. The name | |
1541 | of the `this' pointer is always $t. Type 19, the `this' pointer is | |
1542 | defined as a pointer to type 20, baseA, but a stab defining baseA has | |
1543 | not yet been emited. Since the compiler knows it will be emited | |
1544 | shortly, here it just outputs a cross reference to the undefined | |
1545 | symbol, by prefixing the symbol name with xs. | |
1546 | ||
612dbd4c | 1547 | @example |
e505224d PB |
1548 | .stabs "name:sym_desc(register param)type_def(19)= |
1549 | type_desc(ptr to)type_ref(baseA)= | |
1550 | type_desc(cross-reference to)baseA:",N_RSYM,NIL,NIL,register_number | |
1551 | ||
1552 | .stabs "$t:P19=*20=xsbaseA:",64,0,0,8 | |
612dbd4c | 1553 | @end example |
e505224d PB |
1554 | |
1555 | The stab for the explicit integer argument looks just like a parameter | |
1556 | to a C function. The last field of the stab is the offset from the | |
1557 | argument pointer, which in most systems is the same as the frame | |
1558 | pointer. | |
1559 | ||
612dbd4c | 1560 | @example |
e505224d PB |
1561 | .stabs "name:sym_desc(value parameter)type_ref(int)", |
1562 | N_PSYM,NIL,NIL,offset_from_arg_ptr | |
1563 | ||
1564 | .stabs "in:p1",160,0,0,72 | |
612dbd4c | 1565 | @end example |
e505224d PB |
1566 | |
1567 | << The examples that follow are based on A1.C >> | |
1568 | ||
899bafeb | 1569 | @node Protections |
e505224d PB |
1570 | @section Protections |
1571 | ||
1572 | ||
1573 | In the simple class definition shown above all member data and | |
1574 | functions were publicly accessable. The example that follows | |
1575 | contrasts public, protected and privately accessable fields and shows | |
1576 | how these protections are encoded in C++ stabs. | |
1577 | ||
1578 | Protections for class member data are signified by two characters | |
1579 | embeded in the stab defining the class type. These characters are | |
1580 | located after the name: part of the string. /0 means private, /1 | |
1581 | means protected, and /2 means public. If these characters are omited | |
1582 | this means that the member is public. The following C++ source: | |
1583 | ||
1584 | @example | |
1585 | class all_data @{ | |
1586 | private: | |
1587 | int priv_dat; | |
1588 | protected: | |
1589 | char prot_dat; | |
1590 | public: | |
1591 | float pub_dat; | |
1592 | @}; | |
1593 | @end example | |
1594 | ||
899bafeb | 1595 | @noindent |
e505224d PB |
1596 | generates the following stab to describe the class type all_data. |
1597 | ||
899bafeb | 1598 | @display |
e505224d PB |
1599 | .stabs "class_name:sym_desc(type)type_def(19)=type_desc(struct)struct_bytes |
1600 | data_name:/protection(private)type_ref(int),bit_offset,num_bits; | |
1601 | data_name:/protection(protected)type_ref(char),bit_offset,num_bits; | |
1602 | data_name:(/num omited, private)type_ref(float),bit_offset,num_bits;;" | |
1603 | N_LSYM,NIL,NIL,NIL | |
899bafeb | 1604 | @end display |
e505224d | 1605 | |
899bafeb | 1606 | @smallexample |
e505224d PB |
1607 | .stabs "all_data:t19=s12 |
1608 | priv_dat:/01,0,32;prot_dat:/12,32,8;pub_dat:12,64,32;;",128,0,0,0 | |
899bafeb | 1609 | @end smallexample |
e505224d PB |
1610 | |
1611 | Protections for member functions are signified by one digit embeded in | |
1612 | the field part of the stab describing the method. The digit is 0 if | |
1613 | private, 1 if protected and 2 if public. Consider the C++ class | |
1614 | definition below: | |
1615 | ||
1616 | @example | |
1617 | class all_methods @{ | |
1618 | private: | |
1619 | int priv_meth(int in)@{return in;@}; | |
1620 | protected: | |
1621 | char protMeth(char in)@{return in;@}; | |
1622 | public: | |
1623 | float pubMeth(float in)@{return in;@}; | |
1624 | @}; | |
1625 | @end example | |
1626 | ||
1627 | It generates the following stab. The digit in question is to the left | |
1628 | of an `A' in each case. Notice also that in this case two symbol | |
1629 | descriptors apply to the class name struct tag and struct type. | |
1630 | ||
899bafeb | 1631 | @display |
e505224d PB |
1632 | .stabs "class_name:sym_desc(struct tag&type)type_def(21)= |
1633 | sym_desc(struct)struct_bytes(1) | |
1634 | meth_name::type_def(22)=sym_desc(method)returning(int); | |
1635 | :args(int);protection(private)modifier(normal)virtual(no); | |
1636 | meth_name::type_def(23)=sym_desc(method)returning(char); | |
1637 | :args(char);protection(protected)modifier(normal)virual(no); | |
1638 | meth_name::type_def(24)=sym_desc(method)returning(float); | |
1639 | :args(float);protection(public)modifier(normal)virtual(no);;", | |
1640 | N_LSYM,NIL,NIL,NIL | |
899bafeb | 1641 | @end display |
e505224d | 1642 | |
899bafeb | 1643 | @smallexample |
e505224d PB |
1644 | .stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.; |
1645 | pubMeth::24=##12;:f;2A.;;",128,0,0,0 | |
899bafeb | 1646 | @end smallexample |
e505224d | 1647 | |
899bafeb RP |
1648 | @node Method Modifiers |
1649 | @section Method Modifiers (const, volatile, const volatile) | |
e505224d PB |
1650 | |
1651 | << based on a6.C >> | |
1652 | ||
1653 | In the class example described above all the methods have the normal | |
1654 | modifier. This method modifier information is located just after the | |
1655 | protection information for the method. This field has four possible | |
1656 | character values. Normal methods use A, const methods use B, volatile | |
1657 | methods use C, and const volatile methods use D. Consider the class | |
1658 | definition below: | |
1659 | ||
1660 | @example | |
1661 | class A @{ | |
1662 | public: | |
1663 | int ConstMeth (int arg) const @{ return arg; @}; | |
1664 | char VolatileMeth (char arg) volatile @{ return arg; @}; | |
1665 | float ConstVolMeth (float arg) const volatile @{return arg; @}; | |
1666 | @}; | |
1667 | @end example | |
1668 | ||
1669 | This class is described by the following stab: | |
1670 | ||
899bafeb | 1671 | @display |
e505224d PB |
1672 | .stabs "class(A):sym_desc(struct)type_def(20)=type_desc(struct)struct_bytes(1) |
1673 | meth_name(ConstMeth)::type_def(21)sym_desc(method) | |
1674 | returning(int);:arg(int);protection(public)modifier(const)virtual(no); | |
1675 | meth_name(VolatileMeth)::type_def(22)=sym_desc(method) | |
1676 | returning(char);:arg(char);protection(public)modifier(volatile)virt(no) | |
1677 | meth_name(ConstVolMeth)::type_def(23)=sym_desc(method) | |
1678 | returning(float);:arg(float);protection(public)modifer(const volatile) | |
899bafeb RP |
1679 | virtual(no);;", @dots{} |
1680 | @end display | |
e505224d | 1681 | |
899bafeb | 1682 | @example |
e505224d PB |
1683 | .stabs "A:T20=s1ConstMeth::21=##1;:i;2B.;VolatileMeth::22=##2;:c;2C.; |
1684 | ConstVolMeth::23=##12;:f;2D.;;",128,0,0,0 | |
612dbd4c | 1685 | @end example |
e505224d | 1686 | |
899bafeb | 1687 | @node Virtual Methods |
e505224d PB |
1688 | @section Virtual Methods |
1689 | ||
1690 | << The following examples are based on a4.C >> | |
1691 | ||
1692 | The presence of virtual methods in a class definition adds additional | |
1693 | data to the class description. The extra data is appended to the | |
1694 | description of the virtual method and to the end of the class | |
1695 | description. Consider the class definition below: | |
1696 | ||
1697 | @example | |
1698 | class A @{ | |
1699 | public: | |
1700 | int Adat; | |
1701 | virtual int A_virt (int arg) @{ return arg; @}; | |
1702 | @}; | |
1703 | @end example | |
1704 | ||
1705 | This results in the stab below describing class A. It defines a new | |
1706 | type (20) which is an 8 byte structure. The first field of the class | |
1707 | struct is Adat, an integer, starting at structure offset 0 and | |
1708 | occupying 32 bits. | |
1709 | ||
1710 | The second field in the class struct is not explicitly defined by the | |
1711 | C++ class definition but is implied by the fact that the class | |
1712 | contains a virtual method. This field is the vtable pointer. The | |
1713 | name of the vtable pointer field starts with $vf and continues with a | |
1714 | type reference to the class it is part of. In this example the type | |
1715 | reference for class A is 20 so the name of its vtable pointer field is | |
1716 | $vf20, followed by the usual colon. | |
1717 | ||
1718 | Next there is a type definition for the vtable pointer type (21). | |
1719 | This is in turn defined as a pointer to another new type (22). | |
1720 | ||
1721 | Type 22 is the vtable itself, which is defined as an array, indexed by | |
1722 | integers, with a high bound of 1, and elements of type 17. Type 17 | |
1723 | was the vtable record type defined by the boilerplate C++ type | |
1724 | definitions, as shown earlier. | |
1725 | ||
1726 | The bit offset of the vtable pointer field is 32. The number of bits | |
1727 | in the field are not specified when the field is a vtable pointer. | |
1728 | ||
1729 | Next is the method definition for the virtual member function A_virt. | |
1730 | Its description starts out using the same format as the non-virtual | |
1731 | member functions described above, except instead of a dot after the | |
1732 | `A' there is an asterisk, indicating that the function is virtual. | |
1733 | Since is is virtual some addition information is appended to the end | |
1734 | of the method description. | |
1735 | ||
1736 | The first number represents the vtable index of the method. This is a | |
1737 | 32 bit unsigned number with the high bit set, followed by a | |
1738 | semi-colon. | |
1739 | ||
1740 | The second number is a type reference to the first base class in the | |
1741 | inheritence hierarchy defining the virtual member function. In this | |
1742 | case the class stab describes a base class so the virtual function is | |
1743 | not overriding any other definition of the method. Therefore the | |
1744 | reference is to the type number of the class that the stab is | |
1745 | describing (20). | |
1746 | ||
1747 | This is followed by three semi-colons. One marks the end of the | |
1748 | current sub-section, one marks the end of the method field, and the | |
1749 | third marks the end of the struct definition. | |
1750 | ||
1751 | For classes containing virtual functions the very last section of the | |
1752 | string part of the stab holds a type reference to the first base | |
1753 | class. This is preceeded by `~%' and followed by a final semi-colon. | |
1754 | ||
899bafeb | 1755 | @display |
e505224d PB |
1756 | .stabs "class_name(A):type_def(20)=sym_desc(struct)struct_bytes(8) |
1757 | field_name(Adat):type_ref(int),bit_offset(0),field_bits(32); | |
1758 | field_name(A virt func ptr):type_def(21)=type_desc(ptr to)type_def(22)= | |
1759 | sym_desc(array)index_type_ref(int);NIL;elem_type_ref(vtbl elem type); | |
1760 | bit_offset(32); | |
1761 | meth_name(A_virt)::typedef(23)=sym_desc(method)returning(int); | |
1762 | :arg_type(int),protection(public)normal(yes)virtual(yes) | |
1763 | vtable_index(1);class_first_defining(A);;;~%first_base(A);", | |
1764 | N_LSYM,NIL,NIL,NIL | |
899bafeb | 1765 | @end display |
e505224d | 1766 | |
899bafeb | 1767 | @example |
e505224d | 1768 | .stabs "A:t20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0 |
612dbd4c | 1769 | @end example |
e505224d | 1770 | |
899bafeb | 1771 | @node Inheritence |
e505224d PB |
1772 | @section Inheritence |
1773 | ||
1774 | Stabs describing C++ derived classes include additional sections that | |
1775 | describe the inheritence hierarchy of the class. A derived class stab | |
1776 | also encodes the number of base classes. For each base class it tells | |
1777 | if the base class is virtual or not, and if the inheritence is private | |
1778 | or public. It also gives the offset into the object of the portion of | |
1779 | the object corresponding to each base class. | |
1780 | ||
1781 | This additional information is embeded in the class stab following the | |
1782 | number of bytes in the struct. First the number of base classes | |
1783 | appears bracketed by an exclamation point and a comma. | |
1784 | ||
1785 | Then for each base type there repeats a series: two digits, a number, | |
1786 | a comma, another number, and a semi-colon. | |
1787 | ||
1788 | The first of the two digits is 1 if the base class is virtual and 0 if | |
1789 | not. The second digit is 2 if the derivation is public and 0 if not. | |
1790 | ||
1791 | The number following the first two digits is the offset from the start | |
1792 | of the object to the part of the object pertaining to the base class. | |
1793 | ||
1794 | After the comma, the second number is a type_descriptor for the base | |
1795 | type. Finally a semi-colon ends the series, which repeats for each | |
1796 | base class. | |
1797 | ||
1798 | The source below defines three base classes A, B, and C and the | |
1799 | derived class D. | |
1800 | ||
1801 | ||
1802 | @example | |
1803 | class A @{ | |
1804 | public: | |
1805 | int Adat; | |
1806 | virtual int A_virt (int arg) @{ return arg; @}; | |
1807 | @}; | |
1808 | ||
1809 | class B @{ | |
1810 | public: | |
1811 | int B_dat; | |
1812 | virtual int B_virt (int arg) @{return arg; @}; | |
1813 | @}; | |
1814 | ||
1815 | class C @{ | |
1816 | public: | |
1817 | int Cdat; | |
1818 | virtual int C_virt (int arg) @{return arg; @}; | |
1819 | @}; | |
1820 | ||
1821 | class D : A, virtual B, public C @{ | |
1822 | public: | |
1823 | int Ddat; | |
1824 | virtual int A_virt (int arg ) @{ return arg+1; @}; | |
1825 | virtual int B_virt (int arg) @{ return arg+2; @}; | |
1826 | virtual int C_virt (int arg) @{ return arg+3; @}; | |
1827 | virtual int D_virt (int arg) @{ return arg; @}; | |
1828 | @}; | |
1829 | @end example | |
1830 | ||
1831 | Class stabs similar to the ones described earlier are generated for | |
1832 | each base class. | |
1833 | ||
899bafeb | 1834 | @smallexample |
e505224d PB |
1835 | .stabs "A:T20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0 |
1836 | ||
1837 | .stabs "B:Tt25=s8Bdat:1,0,32;$vf25:21,32;B_virt::26=##1;:i;2A*-2147483647;25;;;~%25;",128,0,0,0 | |
1838 | ||
1839 | .stabs "C:Tt28=s8Cdat:1,0,32;$vf28:21,32;C_virt::29=##1;:i;2A*-2147483647;28;;;~%28;",128,0,0,0 | |
899bafeb | 1840 | @end smallexample |
e505224d PB |
1841 | |
1842 | In the stab describing derived class D below, the information about | |
1843 | the derivation of this class is encoded as follows. | |
1844 | ||
899bafeb | 1845 | @display |
e505224d PB |
1846 | .stabs "derived_class_name:symbol_descriptors(struct tag&type)= |
1847 | type_descriptor(struct)struct_bytes(32)!num_bases(3), | |
1848 | base_virtual(no)inheritence_public(no)base_offset(0), | |
1849 | base_class_type_ref(A); | |
1850 | base_virtual(yes)inheritence_public(no)base_offset(NIL), | |
1851 | base_class_type_ref(B); | |
1852 | base_virtual(no)inheritence_public(yes)base_offset(64), | |
899bafeb RP |
1853 | base_class_type_ref(C); @dots{} |
1854 | @end display | |
e505224d | 1855 | |
899bafeb | 1856 | @smallexample |
e505224d | 1857 | .stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1,160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i;2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0 |
899bafeb | 1858 | @end smallexample |
e505224d | 1859 | |
899bafeb | 1860 | @node Virtual Base Classes |
e505224d PB |
1861 | @section Virtual Base Classes |
1862 | ||
1863 | A derived class object consists of a concatination in memory of the | |
1864 | data areas defined by each base class, starting with the leftmost and | |
1865 | ending with the rightmost in the list of base classes. The exception | |
1866 | to this rule is for virtual inheritence. In the example above, class | |
1867 | D inherits virtually from base class B. This means that an instance | |
1868 | of a D object will not contain it's own B part but merely a pointer to | |
1869 | a B part, known as a virtual base pointer. | |
1870 | ||
1871 | In a derived class stab, the base offset part of the derivation | |
1872 | information, described above, shows how the base class parts are | |
1873 | ordered. The base offset for a virtual base class is always given as | |
1874 | 0. Notice that the base offset for B is given as 0 even though B is | |
1875 | not the first base class. The first base class A starts at offset 0. | |
1876 | ||
1877 | The field information part of the stab for class D describes the field | |
1878 | which is the pointer to the virtual base class B. The vbase pointer | |
1879 | name is $vb followed by a type reference to the virtual base class. | |
1880 | Since the type id for B in this example is 25, the vbase pointer name | |
1881 | is $vb25. | |
1882 | ||
899bafeb | 1883 | @smallexample |
e505224d | 1884 | .stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1,160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i;2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0 |
899bafeb | 1885 | @end smallexample |
e505224d PB |
1886 | |
1887 | Following the name and a semicolon is a type reference describing the | |
1888 | type of the virtual base class pointer, in this case 24. Type 24 was | |
1889 | defined earlier as the type of the B class `this` pointer, $t. The | |
1890 | `this' pointer for a class is a pointer to the class type. | |
1891 | ||
899bafeb | 1892 | @example |
e505224d | 1893 | .stabs "$t:P24=*25=xsB:",64,0,0,8 |
899bafeb | 1894 | @end example |
e505224d PB |
1895 | |
1896 | Finally the field offset part of the vbase pointer field description | |
1897 | shows that the vbase pointer is the first field in the D object, | |
1898 | before any data fields defined by the class. The layout of a D class | |
1899 | object is a follows, Adat at 0, the vtable pointer for A at 32, Cdat | |
1900 | at 64, the vtable pointer for C at 96, the virtual ase pointer for B | |
1901 | at 128, and Ddat at 160. | |
1902 | ||
1903 | ||
899bafeb | 1904 | @node Static Members |
e505224d PB |
1905 | @section Static Members |
1906 | ||
1907 | The data area for a class is a concatination of the space used by the | |
1908 | data members of the class. If the class has virtual methods a vtable | |
1909 | pointer follows the class data. The field offset part of each field | |
1910 | description in the class stab shows this ordering. | |
1911 | ||
1912 | << how is this reflected in stabs? >> | |
1913 | ||
899bafeb | 1914 | @node Example2.c |
e505224d PB |
1915 | @appendix Example2.c - source code for extended example |
1916 | ||
1917 | @example | |
1918 | 1 char g_foo = 'c'; | |
1919 | 2 register int g_bar asm ("%g5"); | |
1920 | 3 static int s_g_repeat = 2; | |
1921 | 4 int (*g_pf)(); | |
1922 | 5 | |
1923 | 6 struct s_tag @{ | |
1924 | 7 int s_int; | |
1925 | 8 float s_float; | |
1926 | 9 char s_char_vec[8]; | |
1927 | 10 struct s_tag* s_next; | |
1928 | 11 @} g_an_s; | |
1929 | 12 | |
1930 | 13 typedef struct s_tag s_typedef; | |
1931 | 14 | |
1932 | 15 char char_vec[3] = @{'a','b','c'@}; | |
1933 | 16 | |
1934 | 17 main (argc, argv) | |
1935 | 18 int argc; | |
1936 | 19 char* argv[]; | |
1937 | 20 @{ | |
1938 | 21 static float s_flap; | |
1939 | 22 int times; | |
1940 | 23 for (times=0; times < s_g_repeat; times++)@{ | |
1941 | 24 int inner; | |
1942 | 25 printf ("Hello world\n"); | |
1943 | 26 @} | |
1944 | 27 @}; | |
1945 | 28 | |
1946 | 29 enum e_places @{first,second=3,last@}; | |
1947 | 30 | |
1948 | 31 static s_proc (s_arg, s_ptr_arg, char_vec) | |
1949 | 32 s_typedef s_arg; | |
1950 | 33 s_typedef* s_ptr_arg; | |
1951 | 34 char* char_vec; | |
1952 | 35 @{ | |
1953 | 36 union u_tag @{ | |
1954 | 37 int u_int; | |
1955 | 38 float u_float; | |
1956 | 39 char* u_char; | |
1957 | 40 @} an_u; | |
1958 | 41 @} | |
1959 | 42 | |
1960 | 43 | |
1961 | @end example | |
1962 | ||
899bafeb | 1963 | @node Example2.s |
e505224d PB |
1964 | @appendix Example2.s - assembly code for extended example |
1965 | ||
1966 | @example | |
1967 | 1 gcc2_compiled.: | |
1968 | 2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0 | |
1969 | 3 .stabs "example2.c",100,0,0,Ltext0 | |
1970 | 4 .text | |
1971 | 5 Ltext0: | |
1972 | 6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0 | |
1973 | 7 .stabs "char:t2=r2;0;127;",128,0,0,0 | |
1974 | 8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0 | |
1975 | 9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0 | |
1976 | 10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0 | |
1977 | 11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0 | |
1978 | 12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0 | |
1979 | 13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0 | |
1980 | 14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0 | |
1981 | 15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0 | |
1982 | 16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0 | |
1983 | 17 .stabs "float:t12=r1;4;0;",128,0,0,0 | |
1984 | 18 .stabs "double:t13=r1;8;0;",128,0,0,0 | |
1985 | 19 .stabs "long double:t14=r1;8;0;",128,0,0,0 | |
1986 | 20 .stabs "void:t15=15",128,0,0,0 | |
1987 | 21 .stabs "g_foo:G2",32,0,0,0 | |
1988 | 22 .global _g_foo | |
1989 | 23 .data | |
1990 | 24 _g_foo: | |
1991 | 25 .byte 99 | |
1992 | 26 .stabs "s_g_repeat:S1",38,0,0,_s_g_repeat | |
1993 | 27 .align 4 | |
1994 | 28 _s_g_repeat: | |
1995 | 29 .word 2 | |
1996 | 30 .stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0 | |
1997 | 31 .stabs "s_typedef:t16",128,0,0,0 | |
1998 | 32 .stabs "char_vec:G19=ar1;0;2;2",32,0,0,0 | |
1999 | 33 .global _char_vec | |
2000 | 34 .align 4 | |
2001 | 35 _char_vec: | |
2002 | 36 .byte 97 | |
2003 | 37 .byte 98 | |
2004 | 38 .byte 99 | |
2005 | 39 .reserve _s_flap.0,4,"bss",4 | |
2006 | 40 .text | |
2007 | 41 .align 4 | |
2008 | 42 LC0: | |
2009 | 43 .ascii "Hello world\12\0" | |
2010 | 44 .align 4 | |
2011 | 45 .global _main | |
2012 | 46 .proc 1 | |
2013 | 47 _main: | |
2014 | 48 .stabn 68,0,20,LM1 | |
2015 | 49 LM1: | |
2016 | 50 !#PROLOGUE# 0 | |
2017 | 51 save %sp,-144,%sp | |
2018 | 52 !#PROLOGUE# 1 | |
2019 | 53 st %i0,[%fp+68] | |
2020 | 54 st %i1,[%fp+72] | |
2021 | 55 call ___main,0 | |
2022 | 56 nop | |
2023 | 57 LBB2: | |
2024 | 58 .stabn 68,0,23,LM2 | |
2025 | 59 LM2: | |
2026 | 60 st %g0,[%fp-20] | |
2027 | 61 L2: | |
2028 | 62 sethi %hi(_s_g_repeat),%o0 | |
2029 | 63 ld [%fp-20],%o1 | |
2030 | 64 ld [%o0+%lo(_s_g_repeat)],%o0 | |
2031 | 65 cmp %o1,%o0 | |
2032 | 66 bge L3 | |
2033 | 67 nop | |
2034 | 68 LBB3: | |
2035 | 69 .stabn 68,0,25,LM3 | |
2036 | 70 LM3: | |
2037 | 71 sethi %hi(LC0),%o1 | |
2038 | 72 or %o1,%lo(LC0),%o0 | |
2039 | 73 call _printf,0 | |
2040 | 74 nop | |
2041 | 75 .stabn 68,0,26,LM4 | |
2042 | 76 LM4: | |
2043 | 77 LBE3: | |
2044 | 78 .stabn 68,0,23,LM5 | |
2045 | 79 LM5: | |
2046 | 80 L4: | |
2047 | 81 ld [%fp-20],%o0 | |
2048 | 82 add %o0,1,%o1 | |
2049 | 83 st %o1,[%fp-20] | |
2050 | 84 b,a L2 | |
2051 | 85 L3: | |
2052 | 86 .stabn 68,0,27,LM6 | |
2053 | 87 LM6: | |
2054 | 88 LBE2: | |
2055 | 89 .stabn 68,0,27,LM7 | |
2056 | 90 LM7: | |
2057 | 91 L1: | |
2058 | 92 ret | |
2059 | 93 restore | |
2060 | 94 .stabs "main:F1",36,0,0,_main | |
2061 | 95 .stabs "argc:p1",160,0,0,68 | |
2062 | 96 .stabs "argv:p20=*21=*2",160,0,0,72 | |
2063 | 97 .stabs "s_flap:V12",40,0,0,_s_flap.0 | |
2064 | 98 .stabs "times:1",128,0,0,-20 | |
2065 | 99 .stabn 192,0,0,LBB2 | |
2066 | 100 .stabs "inner:1",128,0,0,-24 | |
2067 | 101 .stabn 192,0,0,LBB3 | |
2068 | 102 .stabn 224,0,0,LBE3 | |
2069 | 103 .stabn 224,0,0,LBE2 | |
2070 | 104 .stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0 | |
2071 | 105 .stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",128,0,0,0 | |
2072 | 106 .align 4 | |
2073 | 107 .proc 1 | |
2074 | 108 _s_proc: | |
2075 | 109 .stabn 68,0,35,LM8 | |
2076 | 110 LM8: | |
2077 | 111 !#PROLOGUE# 0 | |
2078 | 112 save %sp,-120,%sp | |
2079 | 113 !#PROLOGUE# 1 | |
2080 | 114 mov %i0,%o0 | |
2081 | 115 st %i1,[%fp+72] | |
2082 | 116 st %i2,[%fp+76] | |
2083 | 117 LBB4: | |
2084 | 118 .stabn 68,0,41,LM9 | |
2085 | 119 LM9: | |
2086 | 120 LBE4: | |
2087 | 121 .stabn 68,0,41,LM10 | |
2088 | 122 LM10: | |
2089 | 123 L5: | |
2090 | 124 ret | |
2091 | 125 restore | |
2092 | 126 .stabs "s_proc:f1",36,0,0,_s_proc | |
2093 | 127 .stabs "s_arg:p16",160,0,0,0 | |
2094 | 128 .stabs "s_ptr_arg:p18",160,0,0,72 | |
2095 | 129 .stabs "char_vec:p21",160,0,0,76 | |
2096 | 130 .stabs "an_u:23",128,0,0,-20 | |
2097 | 131 .stabn 192,0,0,LBB4 | |
2098 | 132 .stabn 224,0,0,LBE4 | |
2099 | 133 .stabs "g_bar:r1",64,0,0,5 | |
2100 | 134 .stabs "g_pf:G24=*25=f1",32,0,0,0 | |
2101 | 135 .common _g_pf,4,"bss" | |
2102 | 136 .stabs "g_an_s:G16",32,0,0,0 | |
2103 | 137 .common _g_an_s,20,"bss" | |
2104 | @end example | |
2105 | ||
2106 | ||
899bafeb | 2107 | @node Quick reference |
e505224d PB |
2108 | @appendix Quick reference |
2109 | ||
2110 | @menu | |
2111 | * Stab types:: Table A: Symbol types from stabs | |
2112 | * Assembler types:: Table B: Symbol types from assembler and linker | |
2113 | * Symbol descriptors:: Table C | |
2114 | * Type Descriptors:: Table D | |
2115 | @end menu | |
2116 | ||
899bafeb | 2117 | @node Stab types |
e505224d PB |
2118 | @section Table A: Symbol types from stabs |
2119 | ||
2120 | Table A lists stab types sorted by type number. Stab type numbers are | |
2121 | 32 and greater. This is the full list of stab numbers, including stab | |
2122 | types that are used in languages other than C. | |
2123 | ||
2124 | The #define names for these stab types are defined in: | |
2125 | devo/include/aout/stab.def | |
2126 | ||
899bafeb | 2127 | @smallexample |
e505224d PB |
2128 | type type #define used to describe |
2129 | dec hex name source program feature | |
2130 | ------------------------------------------------------------------------------- | |
2131 | 32 0x20 N_GYSM global symbol | |
2132 | 34 0X22 N_FNAME function name (for BSD Fortran) | |
2133 | 36 0x24 N_FUN function name or text segment variable for C | |
2134 | 38 0x26 N_STSYM static symbol (data segment w/internal linkage) | |
2135 | 40 0x28 N_LCSYM .lcomm symbol(BSS-seg variable w/internal linkage) | |
2136 | 42 0x2a N_MAIN Name of main routine (not used in C) | |
2137 | 48 0x30 N_PC global symbol (for Pascal) | |
2138 | 50 0x32 N_NSYMS number of symbols (according to Ultrix V4.0) | |
2139 | 52 0x34 N_NOMAP no DST map for sym (according to Ultrix V4.0) | |
2140 | 64 0x40 N_RSYM register variable | |
2141 | 66 0x42 N_M2C Modula-2 compilation unit | |
2142 | 68 0x44 N_SLINE line number in text segment | |
2143 | 70 0x46 N_DSLINE line number in data segment | |
2144 | ||
2145 | 72 0x48 N_BSLINE line number in bss segment | |
2146 | 72 0x48 N_BROWS Sun source code browser, path to .cb file | |
2147 | ||
612dbd4c | 2148 | 74 0x4a N_DEFD GNU Modula2 definition module dependency |
e505224d | 2149 | |
612dbd4c | 2150 | 80 0x50 N_EHDECL GNU C++ exception variable |
e505224d PB |
2151 | 80 0x50 N_MOD2 Modula2 info "for imc" (according to Ultrix V4.0) |
2152 | ||
612dbd4c | 2153 | 84 0x54 N_CATCH GNU C++ "catch" clause |
e505224d PB |
2154 | 96 0x60 N_SSYM structure of union element |
2155 | 100 0x64 N_SO path and name of source file | |
2156 | 128 0x80 N_LSYM automatic var in the stack (also used for type desc.) | |
2157 | 130 0x82 N_BINCL beginning of an include file (Sun only) | |
2158 | 132 0x84 N_SOL Name of sub-source (#include) file. | |
2159 | 160 0xa0 N_PSYM parameter variable | |
2160 | 162 0xa2 N_EINCL end of an include file | |
2161 | 164 0xa4 N_ENTRY alternate entry point | |
2162 | 192 0xc0 N_LBRAC beginning of a lexical block | |
2163 | 194 0xc2 N_EXCL place holder for a deleted include file | |
2164 | 196 0xc4 N_SCOPE modula2 scope information (Sun linker) | |
2165 | 224 0xe0 N_RBRAC end of a lexical block | |
2166 | 226 0xe2 N_BCOMM begin named common block | |
2167 | 228 0xe4 N_ECOMM end named common block | |
2168 | 232 0xe8 N_ECOML end common (local name) | |
2169 | ||
2170 | << used on Gould systems for non-base registers syms >> | |
2171 | 240 0xf0 N_NBTEXT ?? | |
2172 | 242 0xf2 N_NBDATA ?? | |
2173 | 244 0xf4 N_NBBSS ?? | |
2174 | 246 0xf6 N_NBSTS ?? | |
2175 | 248 0xf8 N_NBLCS ?? | |
899bafeb | 2176 | @end smallexample |
e505224d | 2177 | |
899bafeb | 2178 | @node Assembler types |
e505224d PB |
2179 | @section Table B: Symbol types from assembler and linker |
2180 | ||
2181 | Table B shows the types of symbol table entries that hold assembler | |
2182 | and linker symbols. | |
2183 | ||
2184 | The #define names for these n_types values are defined in | |
2185 | /include/aout/aout64.h | |
2186 | ||
899bafeb | 2187 | @smallexample |
e505224d PB |
2188 | dec hex #define |
2189 | n_type n_type name used to describe | |
2190 | ----------------------------------------------------------------------------- | |
2191 | 1 0x0 N_UNDF undefined symbol | |
2192 | 2 0x2 N_ABS absolute symbol -- defined at a particular address | |
2193 | 3 0x3 extern " (vs. file scope) | |
2194 | 4 0x4 N_TEXT text symbol -- defined at offset in text segment | |
2195 | 5 0x5 extern " (vs. file scope) | |
2196 | 6 0x6 N_DATA data symbol -- defined at offset in data segment | |
2197 | 7 0x7 extern " (vs. file scope) | |
2198 | 8 0x8 N_BSS BSS symbol -- defined at offset in zero'd segment | |
2199 | 9 extern " (vs. file scope) | |
2200 | ||
2201 | 12 0x0C N_FN_SEQ func name for Sequent compilers (stab exception) | |
2202 | ||
2203 | 49 0x12 N_COMM common sym -- visable after shared lib dynamic link | |
2204 | 31 0x1f N_FN file name of a .o file | |
899bafeb | 2205 | @end smallexample |
e505224d | 2206 | |
899bafeb | 2207 | @node Symbol descriptors |
e505224d PB |
2208 | @section Table C: Symbol descriptors |
2209 | ||
2210 | @example | |
2211 | descriptor meaning | |
2212 | ------------------------------------------------- | |
2213 | (empty) local variable | |
2214 | f local function | |
2215 | F global function | |
2216 | G global variable | |
2217 | p value parameter | |
2218 | r register variable | |
2219 | S static global variable | |
2220 | t type name | |
2221 | T enumeration, struct or type tag | |
2222 | V static local variable | |
2223 | @end example | |
2224 | ||
899bafeb | 2225 | @node Type Descriptors |
e505224d PB |
2226 | @section Table D: Type Descriptors |
2227 | ||
2228 | @example | |
2229 | descriptor meaning | |
2230 | ------------------------------------- | |
2231 | (empty) type reference | |
2232 | a array type | |
2233 | e enumeration type | |
2234 | f function type | |
2235 | r range type | |
2236 | s structure type | |
2237 | u union specifications | |
2238 | * pointer type | |
2239 | @end example | |
2240 | ||
2241 | ||
899bafeb | 2242 | @node Expanded reference |
e505224d PB |
2243 | @appendix Expanded reference by stab type. |
2244 | ||
2245 | Format of an entry: | |
2246 | ||
2247 | The first line is the symbol type expressed in decimal, hexadecimal, | |
2248 | and as a #define (see devo/include/aout/stab.def). | |
2249 | ||
2250 | The second line describes the language constructs the symbol type | |
2251 | represents. | |
2252 | ||
2253 | The third line is the stab format with the significant stab fields | |
2254 | named and the rest NIL. | |
2255 | ||
2256 | Subsequent lines expand upon the meaning and possible values for each | |
2257 | significant stab field. # stands in for the type descriptor. | |
2258 | ||
2259 | Finally, any further information. | |
2260 | ||
899bafeb RP |
2261 | @menu |
2262 | * N_GSYM:: Global variable | |
2263 | * N_FNAME:: Function name (BSD Fortran) | |
2264 | * N_FUN:: C Function name or text segment variable | |
2265 | * N_STSYM:: Initialized static symbol | |
2266 | * N_LCSYM:: Uninitialized static symbol | |
2267 | * N_MAIN:: Name of main routine (not for C) | |
2268 | * N_PC:: Pascal global symbol | |
2269 | * N_NSYMS:: Number of symbols | |
2270 | * N_NOMAP:: No DST map | |
2271 | * N_RSYM:: Register variable | |
2272 | * N_M2C:: Modula-2 compilation unit | |
2273 | * N_SLINE:: Line number in text segment | |
2274 | * N_DSLINE:: Line number in data segment | |
2275 | * N_BSLINE:: Line number in bss segment | |
2276 | * N_BROWS:: Path to .cb file for Sun source code browser | |
2277 | * N_DEFD:: GNU Modula2 definition module dependency | |
2278 | * N_EHDECL:: GNU C++ exception variable | |
2279 | * N_MOD2:: Modula2 information "for imc" | |
2280 | * N_CATCH:: GNU C++ "catch" clause | |
2281 | * N_SSYM:: Structure or union element | |
2282 | * N_SO:: Source file containing main | |
2283 | * N_LSYM:: Automatic variable | |
2284 | * N_BINCL:: Beginning of include file (Sun only) | |
2285 | * N_SOL:: Name of include file | |
2286 | * N_PSYM:: Parameter variable | |
2287 | * N_EINCL:: End of include file | |
2288 | * N_ENTRY:: Alternate entry point | |
2289 | * N_LBRAC:: Beginning of lexical block | |
2290 | * N_EXCL:: Deleted include file | |
2291 | * N_SCOPE:: Modula2 scope information (Sun only) | |
2292 | * N_RBRAC:: End of lexical block | |
2293 | * N_BCOMM:: Begin named common block | |
2294 | * N_ECOMM:: End named common block | |
2295 | * N_ECOML:: End common | |
2296 | * Gould:: non-base register symbols used on Gould systems | |
2297 | * N_LENG:: Length of preceding entry | |
2298 | @end menu | |
2299 | ||
2300 | @node N_GSYM | |
2301 | @section 32 - 0x20 - N_GYSM | |
2302 | ||
2303 | @display | |
e505224d PB |
2304 | Global variable. |
2305 | ||
2306 | .stabs "name", N_GSYM, NIL, NIL, NIL | |
899bafeb | 2307 | @end display |
e505224d | 2308 | |
899bafeb | 2309 | @example |
e505224d PB |
2310 | "name" -> "symbol_name:#type" |
2311 | # -> G | |
899bafeb | 2312 | @end example |
e505224d PB |
2313 | |
2314 | Only the "name" field is significant. the location of the variable is | |
2315 | obtained from the corresponding external symbol. | |
2316 | ||
899bafeb RP |
2317 | @node N_FNAME |
2318 | @section 34 - 0x22 - N_FNAME | |
e505224d PB |
2319 | Function name (for BSD Fortran) |
2320 | ||
899bafeb | 2321 | @display |
e505224d | 2322 | .stabs "name", N_FNAME, NIL, NIL, NIL |
899bafeb | 2323 | @end display |
e505224d | 2324 | |
899bafeb | 2325 | @example |
e505224d | 2326 | "name" -> "function_name" |
899bafeb | 2327 | @end example |
e505224d PB |
2328 | |
2329 | Only the "name" field is significant. The location of the symbol is | |
2330 | obtained from the corresponding extern symbol. | |
2331 | ||
899bafeb RP |
2332 | @node N_FUN |
2333 | @section 36 - 0x24 - N_FUN | |
e505224d PB |
2334 | Function name or text segment variable for C. |
2335 | ||
899bafeb | 2336 | @display |
e505224d | 2337 | .stabs "name", N_FUN, NIL, desc, value |
899bafeb | 2338 | @end display |
e505224d | 2339 | |
899bafeb RP |
2340 | @example |
2341 | @exdent @emph{For functions:} | |
e505224d PB |
2342 | "name" -> "proc_name:#return_type" |
2343 | # -> F (global function) | |
2344 | f (local function) | |
2345 | desc -> line num for proc start. (GCC doesn't set and DBX doesn't miss it.) | |
2346 | value -> Code address of proc start. | |
2347 | ||
899bafeb | 2348 | @exdent @emph{For text segment variables:} |
e505224d | 2349 | <<How to create one?>> |
899bafeb | 2350 | @end example |
e505224d | 2351 | |
899bafeb RP |
2352 | @node N_STSYM |
2353 | @section 38 - 0x26 - N_STSYM | |
e505224d PB |
2354 | Initialized static symbol (data segment w/internal linkage). |
2355 | ||
899bafeb | 2356 | @display |
e505224d | 2357 | .stabs "name", N_STSYM, NIL, NIL, value |
899bafeb | 2358 | @end display |
e505224d | 2359 | |
899bafeb | 2360 | @example |
e505224d PB |
2361 | "name" -> "symbol_name#type" |
2362 | # -> S (scope global to compilation unit) | |
2363 | -> V (scope local to a procedure) | |
2364 | value -> Data Address | |
899bafeb | 2365 | @end example |
e505224d | 2366 | |
899bafeb RP |
2367 | @node N_LCSYM |
2368 | @section 40 - 0x28 - N_LCSYM | |
e505224d PB |
2369 | Unitialized static (.lcomm) symbol(BSS segment w/internal linkage). |
2370 | ||
899bafeb | 2371 | @display |
e505224d | 2372 | .stabs "name", N_LCLSYM, NIL, NIL, value |
899bafeb | 2373 | @end display |
e505224d | 2374 | |
899bafeb | 2375 | @example |
e505224d PB |
2376 | "name" -> "symbol_name#type" |
2377 | # -> S (scope global to compilation unit) | |
2378 | -> V (scope local to procedure) | |
2379 | value -> BSS Address | |
899bafeb | 2380 | @end example |
e505224d | 2381 | |
899bafeb RP |
2382 | @node N_MAIN |
2383 | @section 42 - 0x2a - N_MAIN | |
e505224d PB |
2384 | Name of main routine (not used in C) |
2385 | ||
899bafeb | 2386 | @display |
e505224d | 2387 | .stabs "name", N_MAIN, NIL, NIL, NIL |
899bafeb | 2388 | @end display |
e505224d | 2389 | |
899bafeb | 2390 | @example |
e505224d | 2391 | "name" -> "name_of_main_routine" |
899bafeb | 2392 | @end example |
e505224d | 2393 | |
899bafeb RP |
2394 | @node N_PC |
2395 | @section 48 - 0x30 - N_PC | |
e505224d PB |
2396 | Global symbol (for Pascal) |
2397 | ||
899bafeb | 2398 | @display |
e505224d | 2399 | .stabs "name", N_PC, NIL, NIL, value |
899bafeb | 2400 | @end display |
e505224d | 2401 | |
899bafeb | 2402 | @example |
e505224d PB |
2403 | "name" -> "symbol_name" <<?>> |
2404 | value -> supposedly the line number (stab.def is skeptical) | |
899bafeb | 2405 | @end example |
e505224d | 2406 | |
899bafeb | 2407 | @display |
e505224d PB |
2408 | stabdump.c says: |
2409 | ||
2410 | global pascal symbol: name,,0,subtype,line | |
2411 | << subtype? >> | |
899bafeb | 2412 | @end display |
e505224d | 2413 | |
899bafeb RP |
2414 | @node N_NSYMS |
2415 | @section 50 - 0x32 - N_NSYMS | |
e505224d PB |
2416 | Number of symbols (according to Ultrix V4.0) |
2417 | ||
899bafeb | 2418 | @display |
e505224d | 2419 | 0, files,,funcs,lines (stab.def) |
899bafeb | 2420 | @end display |
e505224d | 2421 | |
899bafeb RP |
2422 | @node N_NOMAP |
2423 | @section 52 - 0x34 - N_NOMAP | |
e505224d PB |
2424 | no DST map for sym (according to Ultrix V4.0) |
2425 | ||
899bafeb | 2426 | @display |
e505224d | 2427 | name, ,0,type,ignored (stab.def) |
899bafeb RP |
2428 | @end display |
2429 | ||
2430 | @node N_RSYM | |
2431 | @section 64 - 0x40 - N_RSYM | |
e505224d PB |
2432 | register variable |
2433 | ||
899bafeb | 2434 | @display |
e505224d | 2435 | .stabs "name:type",N_RSYM,0,RegSize,RegNumber (Sun doc) |
899bafeb | 2436 | @end display |
e505224d | 2437 | |
899bafeb RP |
2438 | @node N_M2C |
2439 | @section 66 - 0x42 - N_M2C | |
e505224d PB |
2440 | Modula-2 compilation unit |
2441 | ||
899bafeb | 2442 | @display |
e505224d | 2443 | .stabs "name", N_M2C, 0, desc, value |
899bafeb | 2444 | @end display |
e505224d | 2445 | |
899bafeb | 2446 | @example |
e505224d PB |
2447 | "name" -> "unit_name,unit_time_stamp[,code_time_stamp] |
2448 | desc -> unit_number | |
2449 | value -> 0 (main unit) | |
2450 | 1 (any other unit) | |
899bafeb | 2451 | @end example |
e505224d | 2452 | |
899bafeb RP |
2453 | @node N_SLINE |
2454 | @section 68 - 0x44 - N_SLINE | |
e505224d PB |
2455 | Line number in text segment |
2456 | ||
899bafeb | 2457 | @display |
e505224d | 2458 | .stabn N_SLINE, 0, desc, value |
899bafeb | 2459 | @end display |
e505224d | 2460 | |
899bafeb | 2461 | @example |
e505224d PB |
2462 | desc -> line_number |
2463 | value -> code_address (relocatable addr where the corresponding code starts) | |
899bafeb | 2464 | @end example |
e505224d PB |
2465 | |
2466 | For single source lines that generate discontiguous code, such as flow | |
2467 | of control statements, there may be more than one N_SLINE stab for the | |
2468 | same source line. In this case there is a stab at the start of each | |
2469 | code range, each with the same line number. | |
2470 | ||
899bafeb RP |
2471 | @node N_DSLINE |
2472 | @section 70 - 0x46 - N_DSLINE | |
e505224d PB |
2473 | Line number in data segment |
2474 | ||
899bafeb | 2475 | @display |
e505224d | 2476 | .stabn N_DSLINE, 0, desc, value |
899bafeb | 2477 | @end display |
e505224d | 2478 | |
899bafeb | 2479 | @example |
e505224d | 2480 | desc -> line_number |
899bafeb RP |
2481 | value -> data_address (relocatable addr where the corresponding code |
2482 | starts) | |
2483 | @end example | |
e505224d PB |
2484 | |
2485 | See comment for N_SLINE above. | |
2486 | ||
899bafeb RP |
2487 | @node N_BSLINE |
2488 | @section 72 - 0x48 - N_BSLINE | |
e505224d PB |
2489 | Line number in bss segment |
2490 | ||
899bafeb | 2491 | @display |
e505224d | 2492 | .stabn N_BSLINE, 0, desc, value |
899bafeb | 2493 | @end display |
e505224d | 2494 | |
899bafeb | 2495 | @example |
e505224d | 2496 | desc -> line_number |
899bafeb RP |
2497 | value -> bss_address (relocatable addr where the corresponding code |
2498 | starts) | |
2499 | @end example | |
e505224d PB |
2500 | |
2501 | See comment for N_SLINE above. | |
2502 | ||
899bafeb RP |
2503 | @node N_BROWS |
2504 | @section 72 - 0x48 - N_BROWS | |
e505224d PB |
2505 | Sun source code browser, path to .cb file |
2506 | ||
2507 | <<?>> | |
2508 | "path to associated .cb file" | |
2509 | ||
2510 | Note: type field value overlaps with N_BSLINE | |
2511 | ||
899bafeb RP |
2512 | @node N_DEFD |
2513 | @section 74 - 0x4a - N_DEFD | |
612dbd4c | 2514 | GNU Modula2 definition module dependency |
e505224d PB |
2515 | |
2516 | GNU Modula-2 definition module dependency. Value is the modification | |
2517 | time of the definition file. Other is non-zero if it is imported with | |
2518 | the GNU M2 keyword %INITIALIZE. Perhaps N_M2C can be used if there | |
2519 | are enough empty fields? | |
2520 | ||
899bafeb RP |
2521 | @node N_EHDECL |
2522 | @section 80 - 0x50 - N_EHDECL | |
612dbd4c | 2523 | GNU C++ exception variable <<?>> |
e505224d PB |
2524 | |
2525 | "name is variable name" | |
2526 | ||
2527 | Note: conflicts with N_MOD2. | |
2528 | ||
899bafeb RP |
2529 | @node N_MOD2 |
2530 | @section 80 - 0x50 - N_MOD2 | |
2531 | Modula2 info "for imc" (according to Ultrix V4.0) | |
e505224d PB |
2532 | |
2533 | Note: conflicts with N_EHDECL <<?>> | |
2534 | ||
899bafeb RP |
2535 | @node N_CATCH |
2536 | @section 84 - 0x54 - N_CATCH | |
2537 | GNU C++ "catch" clause | |
e505224d PB |
2538 | |
2539 | GNU C++ `catch' clause. Value is its address. Desc is nonzero if | |
2540 | this entry is immediately followed by a CAUGHT stab saying what | |
2541 | exception was caught. Multiple CAUGHT stabs means that multiple | |
2542 | exceptions can be caught here. If Desc is 0, it means all exceptions | |
2543 | are caught here. | |
2544 | ||
899bafeb RP |
2545 | @node N_SSYM |
2546 | @section 96 - 0x60 - N_SSYM | |
e505224d PB |
2547 | Structure or union element |
2548 | ||
899bafeb RP |
2549 | Value is offset in the structure. |
2550 | ||
2551 | <<?looking at structs and unions in C I didn't see these>> | |
e505224d | 2552 | |
899bafeb RP |
2553 | @node N_SO |
2554 | @section 100 - 0x64 - N_SO | |
e505224d PB |
2555 | Path and name of source file containing main routine |
2556 | ||
899bafeb | 2557 | @display |
e505224d | 2558 | .stabs "name", N_SO, NIL, NIL, value |
899bafeb | 2559 | @end display |
e505224d | 2560 | |
899bafeb | 2561 | @example |
e505224d PB |
2562 | "name" -> /path/to/source/file |
2563 | -> source_file_terminal_name | |
2564 | ||
2565 | value -> the starting text address of the compilation. | |
899bafeb | 2566 | @end example |
e505224d PB |
2567 | |
2568 | These are found two in a row. The name field of the first N_SO | |
2569 | contains the path to the source file. The name field of the second | |
2570 | N_SO contains the terminal name of the source file itself. | |
2571 | ||
899bafeb RP |
2572 | @node N_LSYM |
2573 | @section 128 - 0x80 - N_LSYM | |
e505224d PB |
2574 | Automatic var in the stack (also used for type descriptors.) |
2575 | ||
899bafeb | 2576 | @display |
e505224d | 2577 | .stabs "name" N_LSYM, NIL, NIL, value |
899bafeb | 2578 | @end display |
e505224d | 2579 | |
899bafeb RP |
2580 | @example |
2581 | @exdent @emph{For stack based local variables:} | |
e505224d PB |
2582 | |
2583 | "name" -> name of the variable | |
2584 | value -> offset from frame pointer (negative) | |
2585 | ||
899bafeb | 2586 | @exdent @emph{For type descriptors:} |
e505224d PB |
2587 | |
2588 | "name" -> "name_of_the_type:#type" | |
2589 | # -> t | |
2590 | ||
2591 | type -> type_ref (or) type_def | |
2592 | ||
2593 | type_ref -> type_number | |
2594 | type_def -> type_number=type_desc etc. | |
899bafeb | 2595 | @end example |
e505224d PB |
2596 | |
2597 | Type may be either a type reference or a type definition. A type | |
2598 | reference is a number that refers to a previously defined type. A | |
2599 | type definition is the number that will refer to this type, followed | |
2600 | by an equals sign, a type descriptor and the additional data that | |
2601 | defines the type. See the Table D for type descriptors and the | |
2602 | section on types for what data follows each type descriptor. | |
2603 | ||
899bafeb RP |
2604 | @node N_BINCL |
2605 | @section 130 - 0x82 - N_BINCL | |
e505224d PB |
2606 | |
2607 | Beginning of an include file (Sun only) | |
2608 | ||
2609 | Beginning of an include file. Only Sun uses this. In an object file, | |
2610 | only the name is significant. The Sun linker puts data into some of | |
2611 | the other fields. | |
2612 | ||
899bafeb RP |
2613 | @node N_SOL |
2614 | @section 132 - 0x84 - N_SOL | |
e505224d PB |
2615 | |
2616 | Name of a sub-source file (#include file). Value is starting address | |
2617 | of the compilation. | |
2618 | <<?>> | |
2619 | ||
899bafeb RP |
2620 | @node N_PSYM |
2621 | @section 160 - 0xa0 - N_PSYM | |
e505224d PB |
2622 | |
2623 | Parameter variable | |
2624 | ||
899bafeb | 2625 | @display |
e505224d | 2626 | stabs. "name", N_PSYM, NIL, NIL, value |
899bafeb | 2627 | @end display |
e505224d | 2628 | |
899bafeb | 2629 | @example |
e505224d PB |
2630 | "name" -> "param_name:#type" |
2631 | # -> p (value parameter) | |
2632 | -> i (value parameter by reference, indirect access) | |
2633 | -> v (variable parameter by reference) | |
2634 | -> C ( read-only parameter, conformant array bound) | |
2635 | -> x (confomant array value parameter) | |
2636 | -> pP (<<??>>) | |
2637 | -> pF (<<??>>) | |
2638 | -> X (function result variable) | |
2639 | -> b (based variable) | |
2640 | ||
2641 | value -> offset from the argument pointer (positive). | |
899bafeb | 2642 | @end example |
e505224d PB |
2643 | |
2644 | On most machines the argument pointer is the same as the frame | |
2645 | pointer. | |
2646 | ||
899bafeb RP |
2647 | @node N_EINCL |
2648 | @section 162 - 0xa2 - N_EINCL | |
e505224d PB |
2649 | |
2650 | End of an include file. This and N_BINCL act as brackets around the | |
2651 | file's output. In an ojbect file, there is no significant data in | |
899bafeb | 2652 | this entry. The Sun linker puts data into some of the fields. |
e505224d PB |
2653 | <<?>> |
2654 | ||
899bafeb RP |
2655 | @node N_ENTRY |
2656 | @section 164 - 0xa4 - N_ENTRY | |
e505224d PB |
2657 | |
2658 | Alternate entry point. | |
2659 | Value is its address. | |
2660 | <<?>> | |
2661 | ||
899bafeb RP |
2662 | @node N_LBRAC |
2663 | @section 192 - 0xc0 - N_LBRAC | |
e505224d PB |
2664 | |
2665 | Beginning of a lexical block (left brace). The variable defined | |
2666 | inside the block precede the N_LBRAC symbol. Or can they follow as | |
2667 | well as long as a new N_FUNC was not encountered. <<?>> | |
2668 | ||
899bafeb | 2669 | @display |
e505224d | 2670 | .stabn N_LBRAC, NIL, NIL, value |
899bafeb | 2671 | @end display |
e505224d | 2672 | |
899bafeb | 2673 | @example |
e505224d | 2674 | value -> code address of block start. |
899bafeb | 2675 | @end example |
e505224d | 2676 | |
899bafeb RP |
2677 | @node N_EXCL |
2678 | @section 194 - 0xc2 - N_EXCL | |
e505224d PB |
2679 | |
2680 | Place holder for a deleted include file. Replaces a N_BINCL and | |
2681 | everything up to the corresponding N_EINCL. The Sun linker generates | |
2682 | these when it finds multiple indentical copies of the symbols from an | |
2683 | included file. This appears only in output from the Sun linker. | |
2684 | <<?>> | |
2685 | ||
899bafeb RP |
2686 | @node N_SCOPE |
2687 | @section 196 - 0xc4 - N_SCOPE | |
e505224d PB |
2688 | |
2689 | Modula2 scope information (Sun linker) | |
2690 | <<?>> | |
2691 | ||
899bafeb RP |
2692 | @node N_RBRAC |
2693 | @section 224 - 0xe0 - N_RBRAC | |
e505224d PB |
2694 | |
2695 | End of a lexical block (right brace) | |
2696 | ||
899bafeb | 2697 | @display |
e505224d | 2698 | .stabn N_RBRAC, NIL, NIL, value |
899bafeb | 2699 | @end display |
e505224d | 2700 | |
899bafeb | 2701 | @example |
e505224d | 2702 | value -> code address of the end of the block. |
899bafeb | 2703 | @end example |
e505224d | 2704 | |
899bafeb RP |
2705 | @node N_BCOMM |
2706 | @section 226 - 0xe2 - N_BCOMM | |
e505224d PB |
2707 | |
2708 | Begin named common block. | |
2709 | ||
2710 | Only the name is significant. | |
2711 | <<?>> | |
2712 | ||
899bafeb RP |
2713 | @node N_ECOMM |
2714 | @section 228 - 0xe4 - N_ECOMM | |
e505224d PB |
2715 | |
2716 | End named common block. | |
2717 | ||
2718 | Only the name is significant and it should match the N_BCOMM | |
2719 | <<?>> | |
2720 | ||
899bafeb RP |
2721 | @node N_ECOML |
2722 | @section 232 - 0xe8 - N_ECOML | |
e505224d PB |
2723 | |
2724 | End common (local name) | |
2725 | ||
2726 | value is address. | |
2727 | <<?>> | |
2728 | ||
899bafeb RP |
2729 | @node Gould |
2730 | @section Non-base registers on Gould systems | |
e505224d PB |
2731 | << used on Gould systems for non-base registers syms, values assigned |
2732 | at random, need real info from Gould. >> | |
2733 | <<?>> | |
2734 | ||
899bafeb | 2735 | @example |
e505224d PB |
2736 | 240 0xf0 N_NBTEXT ?? |
2737 | 242 0xf2 N_NBDATA ?? | |
2738 | 244 0xf4 N_NBBSS ?? | |
2739 | 246 0xf6 N_NBSTS ?? | |
2740 | 248 0xf8 N_NBLCS ?? | |
899bafeb | 2741 | @end example |
e505224d | 2742 | |
899bafeb RP |
2743 | @node N_LENG |
2744 | @section - 0xfe - N_LENG | |
e505224d PB |
2745 | |
2746 | Second symbol entry containing a length-value for the preceding entry. | |
2747 | The value is the length. | |
2748 | ||
899bafeb RP |
2749 | @node Questions |
2750 | @appendix Questions and anomalies | |
e505224d PB |
2751 | |
2752 | @itemize @bullet | |
2753 | @item | |
2754 | For GNU C stabs defining local and global variables (N_LSYM and | |
2755 | N_GSYM), the desc field is supposed to contain the source line number | |
2756 | on which the variable is defined. In reality the desc field is always | |
2757 | 0. (This behavour is defined in dbxout.c and putting a line number in | |
2758 | desc is controlled by #ifdef WINNING_GDB which defaults to false). Gdb | |
2759 | supposedly uses this information if you say 'list var'. In reality | |
2760 | var can be a variable defined in the program and gdb says `function | |
2761 | var not defined' | |
2762 | ||
2763 | @item | |
612dbd4c | 2764 | In GNU C stabs there seems to be no way to differentiate tag types: |
e505224d PB |
2765 | structures, unions, and enums (symbol descriptor T) and typedefs |
2766 | (symbol descriptor t) defined at file scope from types defined locally | |
2767 | to a procedure or other more local scope. They all use the N_LSYM | |
2768 | stab type. Types defined at procedure scope are emited after the | |
2769 | N_RBRAC of the preceeding function and before the code of the | |
2770 | procedure in which they are defined. This is exactly the same as | |
2771 | types defined in the source file between the two procedure bodies. | |
2772 | GDB overcompensates by placing all types in block #1 the block for | |
2773 | symbols of file scope. This is true for default, -ansi and | |
2774 | -traditional compiler options. (p0001063-gcc, p0001066-gdb) | |
2775 | ||
2776 | @item | |
2777 | What ends the procedure scope? Is it the proc block's N_RBRAC or the | |
2778 | next N_FUN? (I believe its the first.) | |
2779 | ||
2780 | @item | |
2781 | The comment in xcoff.h says DBX_STATIC_CONST_VAR_CODE is used for | |
2782 | static const variables. DBX_STATIC_CONST_VAR_CODE is set to N_FUN by | |
2783 | default, in dbxout.c. If included, xcoff.h redefines it to N_STSYM. | |
2784 | But testing the default behaviour, my Sun4 native example shows | |
2785 | N_STSYM not N_FUN is used to describe file static initialized | |
2786 | variables. (the code tests for TREE_READONLY(decl) && | |
2787 | !TREE_THIS_VOLATILE(decl) and if true uses DBX_STATIC_CONST_VAR_CODE). | |
2788 | ||
2789 | @item | |
2790 | Global variable stabs don't have location information. This comes | |
2791 | from the external symbol for the same variable. The external symbol | |
2792 | has a leading underbar on the _name of the variable and the stab does | |
2793 | not. How do we know these two symbol table entries are talking about | |
2794 | the same symbol when their names are different? | |
2795 | ||
2796 | @item | |
2797 | Can gcc be configured to output stabs the way the Sun compiler | |
2798 | does, so that their native debugging tools work? <NO?> It doesn't by | |
2799 | default. GDB reads either format of stab. (gcc or SunC). How about | |
2800 | dbx? | |
2801 | @end itemize | |
2802 | ||
899bafeb | 2803 | @node xcoff-differences |
e505224d PB |
2804 | @appendix Differences between GNU stabs in a.out and GNU stabs in xcoff |
2805 | ||
2806 | (The AIX/RS6000 native object file format is xcoff with stabs) | |
2807 | ||
2808 | @itemize @bullet | |
2809 | @item | |
2810 | Instead of .stabs, xcoff uses .stabx. | |
2811 | ||
2812 | @item | |
2813 | The data fields of an xcoff .stabx are in a different order than an | |
2814 | a.out .stabs. The order is: string, value, type. The desc and null | |
2815 | fields present in a.out stabs are missing in xcoff stabs. For N_GSYM | |
2816 | the value field is the name of the symbol. | |
2817 | ||
2818 | @item | |
2819 | BSD a.out stab types map to AIX xcoff storage classes. In general the | |
2820 | mapping is N_STABTYPE becomes C_STABTYPE. Some stab types in a.out | |
2821 | are not supported in xcoff. See Table E. for full mappings. | |
2822 | ||
2823 | exception: | |
2824 | initialised static N_STSYM and un-initialized static N_LCSYM both map | |
2825 | to the C_STSYM storage class. But the destinction is preserved | |
2826 | because in xcoff N_STSYM and N_LCSYM must be emited in a named static | |
2827 | block. Begin the block with .bs s[RW] data_section_name for N_STSYM | |
2828 | or .bs s bss_section_name for N_LCSYM. End the block with .es | |
2829 | ||
2830 | @item | |
2831 | xcoff stabs describing tags and typedefs use the N_DECL (0x8c)instead | |
2832 | of N_LSYM stab type. | |
2833 | ||
2834 | @item | |
2835 | xcoff uses N_RPSYM (0x8e) instead of the N_RSYM stab type for register | |
2836 | variables. If the register variable is also a value parameter, then | |
2837 | use R instead of P for the symbol descriptor. | |
2838 | ||
2839 | 6. | |
2840 | xcoff uses negative numbers as type references to the basic types. | |
2841 | There are no boilerplate type definitions emited for these basic | |
2842 | types. << make table of basic types and type numbers for C >> | |
2843 | ||
2844 | @item | |
2845 | xcoff .stabx sometimes don't have the name part of the string field. | |
2846 | ||
2847 | @item | |
2848 | xcoff uses a .file stab type to represent the source file name. There | |
2849 | is no stab for the path to the source file. | |
2850 | ||
2851 | @item | |
2852 | xcoff uses a .line stab type to represent source lines. The format | |
2853 | is: .line line_number. | |
2854 | ||
2855 | @item | |
2856 | xcoff emits line numbers relative to the start of the current | |
2857 | function. The start of a function is marked by .bf. If a function | |
2858 | includes lines from a seperate file, then those line numbers are | |
2859 | absolute line numbers in the <<sub-?>> file being compiled. | |
2860 | ||
2861 | @item | |
2862 | The start of current include file is marked with: .bi "filename" and | |
2863 | the end marked with .ei "filename" | |
2864 | ||
2865 | @item | |
2866 | If the xcoff stab is a N_FUN (C_FUN) then follow the string field with | |
2867 | ,. instead of just , | |
2868 | ||
2869 | @item | |
2870 | The symbol descriptor for register parameters is P for a.out and R for | |
2871 | xcoff. | |
2872 | @end itemize | |
2873 | ||
2874 | ||
2875 | (I think that's it for .s file differences. They could stand to be | |
2876 | better presented. This is just a list of what I have noticed so far. | |
2877 | There are a *lot* of differences in the information in the symbol | |
2878 | tables of the executable and object files.) | |
2879 | ||
2880 | Table E: mapping a.out stab types to xcoff storage classes | |
2881 | ||
2882 | @example | |
2883 | stab type storage class | |
2884 | ------------------------------- | |
2885 | N_GSYM C_GSYM | |
2886 | N_FNAME unknown | |
2887 | N_FUN C_FUN | |
2888 | N_STSYM C_STSYM | |
2889 | N_LCSYM C_STSYM | |
2890 | N_MAIN unkown | |
2891 | N_PC unknown | |
2892 | N_RSYM C_RSYM | |
2893 | N_RPSYM (0x8e) C_RPSYM | |
2894 | N_M2C unknown | |
2895 | N_SLINE unknown | |
2896 | N_DSLINE unknown | |
2897 | N_BSLINE unknown | |
2898 | N_BROWSE unchanged | |
2899 | N_CATCH unknown | |
2900 | N_SSYM unknown | |
2901 | N_SO unknown | |
2902 | N_LSYM C_LSYM | |
2903 | N_DECL (0x8c) C_DECL | |
2904 | N_BINCL unknown | |
2905 | N_SOL unknown | |
2906 | N_PSYM C_PSYM | |
2907 | N_EINCL unknown | |
2908 | N_ENTRY C_ENTRY | |
2909 | N_LBRAC unknown | |
2910 | N_EXCL unknown | |
2911 | N_SCOPE unknown | |
2912 | N_RBRAC unknown | |
2913 | N_BCOMM C_BCOMM | |
2914 | N_ECOMM C_ECOMM | |
2915 | N_ECOML C_ECOML | |
2916 | ||
2917 | N_LENG unknown | |
2918 | @end example | |
2919 | ||
899bafeb | 2920 | @node Sun-differences |
e505224d PB |
2921 | @appendix Differences between GNU stabs and Sun native stabs. |
2922 | ||
2923 | @itemize @bullet | |
2924 | @item | |
612dbd4c | 2925 | GNU C stabs define *all* types, file or procedure scope, as |
e505224d PB |
2926 | N_LSYM. Sun doc talks about using N_GSYM too. |
2927 | ||
2928 | @item | |
612dbd4c | 2929 | GNU C stabs use `ar' as type descriptor when defining arrays vs. just |
e505224d PB |
2930 | `a' in Sun doc. |
2931 | ||
2932 | @item | |
2933 | Stabs describing block scopes, N_LBRAC and N_RBRAC are supposed to | |
2934 | contain the nesting level of the block in the desc field, re Sun doc. | |
2935 | GNU stabs always have 0 in that field. | |
2936 | ||
2937 | @item | |
2938 | Sun C stabs use type number pairs in the format (a,b) where a is a | |
2939 | number starting with 1 and incremented for each sub-source file in the | |
2940 | compilation. b is a number starting with 1 and incremented for each | |
612dbd4c | 2941 | new type defined in the compilation. GNU C stabs use the type number |
e505224d PB |
2942 | alone, with no source file number. |
2943 | @end itemize | |
2944 | ||
2945 | @contents | |
2946 | @bye |