2 BFD tries to maintain as much symbol information as it can when
3 it moves information from file to file. BFD passes information
4 to applications though the @code{asymbol} structure. When the
5 application requests the symbol table, BFD reads the table in
6 the native form and translates parts of it into the internal
7 format. To maintain more than the information passed to
8 applications, some targets keep some information ``behind the
9 scenes'' in a structure only the particular back end knows
10 about. For example, the coff back end keeps the original
11 symbol table structure as well as the canonical structure when
12 a BFD is read in. On output, the coff back end can reconstruct
13 the output symbol table so that no information is lost, even
14 information unique to coff which BFD doesn't know or
15 understand. If a coff symbol table were read, but were written
16 through an a.out back end, all the coff specific information
17 would be lost. The symbol table of a BFD
18 is not necessarily read in until a canonicalize request is
19 made. Then the BFD back end fills in a table provided by the
20 application with pointers to the canonical information. To
21 output symbols, the application provides BFD with a table of
22 pointers to pointers to @code{asymbol}s. This allows applications
23 like the linker to output a symbol as it was read, since the ``behind
24 the scenes'' information will be still available.
30 * symbol handling functions::
33 @node Reading Symbols, Writing Symbols, Symbols, Symbols
34 @subsection Reading symbols
35 There are two stages to reading a symbol table from a BFD:
36 allocating storage, and the actual reading process. This is an
37 excerpt from an application which reads the symbol table:
41 asymbol **symbol_table;
42 long number_of_symbols;
45 storage_needed = bfd_get_symtab_upper_bound (abfd);
47 if (storage_needed < 0)
50 if (storage_needed == 0)
53 symbol_table = xmalloc (storage_needed);
56 bfd_canonicalize_symtab (abfd, symbol_table);
58 if (number_of_symbols < 0)
61 for (i = 0; i < number_of_symbols; i++)
62 process_symbol (symbol_table[i]);
65 All storage for the symbols themselves is in an objalloc
66 connected to the BFD; it is freed when the BFD is closed.
68 @node Writing Symbols, Mini Symbols, Reading Symbols, Symbols
69 @subsection Writing symbols
70 Writing of a symbol table is automatic when a BFD open for
71 writing is closed. The application attaches a vector of
72 pointers to pointers to symbols to the BFD being written, and
73 fills in the symbol count. The close and cleanup code reads
74 through the table provided and performs all the necessary
75 operations. The BFD output code must always be provided with an
76 ``owned'' symbol: one which has come from another BFD, or one
77 which has been created using @code{bfd_make_empty_symbol}. Here is an
78 example showing the creation of a symbol table with only one element:
88 abfd = bfd_openw ("foo","a.out-sunos-big");
89 bfd_set_format (abfd, bfd_object);
90 new = bfd_make_empty_symbol (abfd);
91 new->name = "dummy_symbol";
92 new->section = bfd_make_section_old_way (abfd, ".text");
93 new->flags = BSF_GLOBAL;
99 bfd_set_symtab (abfd, ptrs, 1);
106 00012345 A dummy_symbol
109 Many formats cannot represent arbitrary symbol information; for
110 instance, the @code{a.out} object format does not allow an
111 arbitrary number of sections. A symbol pointing to a section
112 which is not one of @code{.text}, @code{.data} or @code{.bss} cannot
115 @node Mini Symbols, typedef asymbol, Writing Symbols, Symbols
116 @subsection Mini Symbols
117 Mini symbols provide read-only access to the symbol table.
118 They use less memory space, but require more time to access.
119 They can be useful for tools like nm or objdump, which may
120 have to handle symbol tables of extremely large executables.
122 The @code{bfd_read_minisymbols} function will read the symbols
123 into memory in an internal form. It will return a @code{void *}
124 pointer to a block of memory, a symbol count, and the size of
125 each symbol. The pointer is allocated using @code{malloc}, and
126 should be freed by the caller when it is no longer needed.
128 The function @code{bfd_minisymbol_to_symbol} will take a pointer
129 to a minisymbol, and a pointer to a structure returned by
130 @code{bfd_make_empty_symbol}, and return a @code{asymbol} structure.
131 The return value may or may not be the same as the value from
132 @code{bfd_make_empty_symbol} which was passed in.
135 @node typedef asymbol, symbol handling functions, Mini Symbols, Symbols
136 @subsection typedef asymbol
137 An @code{asymbol} has the form:
142 typedef struct bfd_symbol
144 /* A pointer to the BFD which owns the symbol. This information
145 is necessary so that a back end can work out what additional
146 information (invisible to the application writer) is carried
149 This field is *almost* redundant, since you can use section->owner
150 instead, except that some symbols point to the global sections
151 bfd_@{abs,com,und@}_section. This could be fixed by making
152 these globals be per-bfd (or per-target-flavor). FIXME. */
153 struct bfd *the_bfd; /* Use bfd_asymbol_bfd(sym) to access this field. */
155 /* The text of the symbol. The name is left alone, and not copied; the
156 application may not alter it. */
159 /* The value of the symbol. This really should be a union of a
160 numeric value with a pointer, since some flags indicate that
161 a pointer to another symbol is stored here. */
164 /* Attributes of a symbol. */
165 #define BSF_NO_FLAGS 0x00
167 /* The symbol has local scope; @code{static} in @code{C}. The value
168 is the offset into the section of the data. */
169 #define BSF_LOCAL (1 << 0)
171 /* The symbol has global scope; initialized data in @code{C}. The
172 value is the offset into the section of the data. */
173 #define BSF_GLOBAL (1 << 1)
175 /* The symbol has global scope and is exported. The value is
176 the offset into the section of the data. */
177 #define BSF_EXPORT BSF_GLOBAL /* No real difference. */
179 /* A normal C symbol would be one of:
180 @code{BSF_LOCAL}, @code{BSF_COMMON}, @code{BSF_UNDEFINED} or
181 @code{BSF_GLOBAL}. */
183 /* The symbol is a debugging record. The value has an arbitrary
184 meaning, unless BSF_DEBUGGING_RELOC is also set. */
185 #define BSF_DEBUGGING (1 << 2)
187 /* The symbol denotes a function entry point. Used in ELF,
188 perhaps others someday. */
189 #define BSF_FUNCTION (1 << 3)
191 /* Used by the linker. */
192 #define BSF_KEEP (1 << 5)
193 #define BSF_KEEP_G (1 << 6)
195 /* A weak global symbol, overridable without warnings by
196 a regular global symbol of the same name. */
197 #define BSF_WEAK (1 << 7)
199 /* This symbol was created to point to a section, e.g. ELF's
200 STT_SECTION symbols. */
201 #define BSF_SECTION_SYM (1 << 8)
203 /* The symbol used to be a common symbol, but now it is
205 #define BSF_OLD_COMMON (1 << 9)
207 /* In some files the type of a symbol sometimes alters its
208 location in an output file - ie in coff a @code{ISFCN} symbol
209 which is also @code{C_EXT} symbol appears where it was
210 declared and not at the end of a section. This bit is set
211 by the target BFD part to convey this information. */
212 #define BSF_NOT_AT_END (1 << 10)
214 /* Signal that the symbol is the label of constructor section. */
215 #define BSF_CONSTRUCTOR (1 << 11)
217 /* Signal that the symbol is a warning symbol. The name is a
218 warning. The name of the next symbol is the one to warn about;
219 if a reference is made to a symbol with the same name as the next
220 symbol, a warning is issued by the linker. */
221 #define BSF_WARNING (1 << 12)
223 /* Signal that the symbol is indirect. This symbol is an indirect
224 pointer to the symbol with the same name as the next symbol. */
225 #define BSF_INDIRECT (1 << 13)
227 /* BSF_FILE marks symbols that contain a file name. This is used
228 for ELF STT_FILE symbols. */
229 #define BSF_FILE (1 << 14)
231 /* Symbol is from dynamic linking information. */
232 #define BSF_DYNAMIC (1 << 15)
234 /* The symbol denotes a data object. Used in ELF, and perhaps
236 #define BSF_OBJECT (1 << 16)
238 /* This symbol is a debugging symbol. The value is the offset
239 into the section of the data. BSF_DEBUGGING should be set
241 #define BSF_DEBUGGING_RELOC (1 << 17)
243 /* This symbol is thread local. Used in ELF. */
244 #define BSF_THREAD_LOCAL (1 << 18)
246 /* This symbol represents a complex relocation expression,
247 with the expression tree serialized in the symbol name. */
248 #define BSF_RELC (1 << 19)
250 /* This symbol represents a signed complex relocation expression,
251 with the expression tree serialized in the symbol name. */
252 #define BSF_SRELC (1 << 20)
254 /* This symbol was created by bfd_get_synthetic_symtab. */
255 #define BSF_SYNTHETIC (1 << 21)
257 /* This symbol is an indirect code object. Unrelated to BSF_INDIRECT.
258 The dynamic linker will compute the value of this symbol by
259 calling the function that it points to. BSF_FUNCTION must
261 #define BSF_GNU_INDIRECT_FUNCTION (1 << 22)
262 /* This symbol is a globally unique data object. The dynamic linker
263 will make sure that in the entire process there is just one symbol
264 with this name and type in use. BSF_OBJECT must also be set. */
265 #define BSF_GNU_UNIQUE (1 << 23)
269 /* A pointer to the section to which this symbol is
270 relative. This will always be non NULL, there are special
271 sections for undefined and absolute symbols. */
272 struct bfd_section *section;
274 /* Back end special data. */
286 @node symbol handling functions, , typedef asymbol, Symbols
287 @subsection Symbol handling functions
290 @findex bfd_get_symtab_upper_bound
291 @subsubsection @code{bfd_get_symtab_upper_bound}
292 @strong{Description}@*
293 Return the number of bytes required to store a vector of pointers
294 to @code{asymbols} for all the symbols in the BFD @var{abfd},
295 including a terminal NULL pointer. If there are no symbols in
296 the BFD, then return 0. If an error occurs, return -1.
298 #define bfd_get_symtab_upper_bound(abfd) \
299 BFD_SEND (abfd, _bfd_get_symtab_upper_bound, (abfd))
303 @findex bfd_is_local_label
304 @subsubsection @code{bfd_is_local_label}
307 bfd_boolean bfd_is_local_label (bfd *abfd, asymbol *sym);
309 @strong{Description}@*
310 Return TRUE if the given symbol @var{sym} in the BFD @var{abfd} is
311 a compiler generated local label, else return FALSE.
313 @findex bfd_is_local_label_name
314 @subsubsection @code{bfd_is_local_label_name}
317 bfd_boolean bfd_is_local_label_name (bfd *abfd, const char *name);
319 @strong{Description}@*
320 Return TRUE if a symbol with the name @var{name} in the BFD
321 @var{abfd} is a compiler generated local label, else return
322 FALSE. This just checks whether the name has the form of a
325 #define bfd_is_local_label_name(abfd, name) \
326 BFD_SEND (abfd, _bfd_is_local_label_name, (abfd, name))
330 @findex bfd_is_target_special_symbol
331 @subsubsection @code{bfd_is_target_special_symbol}
334 bfd_boolean bfd_is_target_special_symbol (bfd *abfd, asymbol *sym);
336 @strong{Description}@*
337 Return TRUE iff a symbol @var{sym} in the BFD @var{abfd} is something
338 special to the particular target represented by the BFD. Such symbols
339 should normally not be mentioned to the user.
341 #define bfd_is_target_special_symbol(abfd, sym) \
342 BFD_SEND (abfd, _bfd_is_target_special_symbol, (abfd, sym))
346 @findex bfd_canonicalize_symtab
347 @subsubsection @code{bfd_canonicalize_symtab}
348 @strong{Description}@*
349 Read the symbols from the BFD @var{abfd}, and fills in
350 the vector @var{location} with pointers to the symbols and
352 Return the actual number of symbol pointers, not
355 #define bfd_canonicalize_symtab(abfd, location) \
356 BFD_SEND (abfd, _bfd_canonicalize_symtab, (abfd, location))
360 @findex bfd_set_symtab
361 @subsubsection @code{bfd_set_symtab}
364 bfd_boolean bfd_set_symtab
365 (bfd *abfd, asymbol **location, unsigned int count);
367 @strong{Description}@*
368 Arrange that when the output BFD @var{abfd} is closed,
369 the table @var{location} of @var{count} pointers to symbols
372 @findex bfd_print_symbol_vandf
373 @subsubsection @code{bfd_print_symbol_vandf}
376 void bfd_print_symbol_vandf (bfd *abfd, void *file, asymbol *symbol);
378 @strong{Description}@*
379 Print the value and flags of the @var{symbol} supplied to the
382 @findex bfd_make_empty_symbol
383 @subsubsection @code{bfd_make_empty_symbol}
384 @strong{Description}@*
385 Create a new @code{asymbol} structure for the BFD @var{abfd}
386 and return a pointer to it.
388 This routine is necessary because each back end has private
389 information surrounding the @code{asymbol}. Building your own
390 @code{asymbol} and pointing to it will not create the private
391 information, and will cause problems later on.
393 #define bfd_make_empty_symbol(abfd) \
394 BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
398 @findex _bfd_generic_make_empty_symbol
399 @subsubsection @code{_bfd_generic_make_empty_symbol}
402 asymbol *_bfd_generic_make_empty_symbol (bfd *);
404 @strong{Description}@*
405 Create a new @code{asymbol} structure for the BFD @var{abfd}
406 and return a pointer to it. Used by core file routines,
407 binary back-end and anywhere else where no private info
410 @findex bfd_make_debug_symbol
411 @subsubsection @code{bfd_make_debug_symbol}
412 @strong{Description}@*
413 Create a new @code{asymbol} structure for the BFD @var{abfd},
414 to be used as a debugging symbol. Further details of its use have
415 yet to be worked out.
417 #define bfd_make_debug_symbol(abfd,ptr,size) \
418 BFD_SEND (abfd, _bfd_make_debug_symbol, (abfd, ptr, size))
422 @findex bfd_decode_symclass
423 @subsubsection @code{bfd_decode_symclass}
424 @strong{Description}@*
425 Return a character corresponding to the symbol
426 class of @var{symbol}, or '?' for an unknown class.
430 int bfd_decode_symclass (asymbol *symbol);
432 @findex bfd_is_undefined_symclass
433 @subsubsection @code{bfd_is_undefined_symclass}
434 @strong{Description}@*
435 Returns non-zero if the class symbol returned by
436 bfd_decode_symclass represents an undefined symbol.
437 Returns zero otherwise.
441 bfd_boolean bfd_is_undefined_symclass (int symclass);
443 @findex bfd_symbol_info
444 @subsubsection @code{bfd_symbol_info}
445 @strong{Description}@*
446 Fill in the basic info about symbol that nm needs.
447 Additional info may be added by the back-ends after
448 calling this function.
452 void bfd_symbol_info (asymbol *symbol, symbol_info *ret);
454 @findex bfd_copy_private_symbol_data
455 @subsubsection @code{bfd_copy_private_symbol_data}
458 bfd_boolean bfd_copy_private_symbol_data
459 (bfd *ibfd, asymbol *isym, bfd *obfd, asymbol *osym);
461 @strong{Description}@*
462 Copy private symbol information from @var{isym} in the BFD
463 @var{ibfd} to the symbol @var{osym} in the BFD @var{obfd}.
464 Return @code{TRUE} on success, @code{FALSE} on error. Possible error
470 @code{bfd_error_no_memory} -
471 Not enough memory exists to create private data for @var{osec}.
474 #define bfd_copy_private_symbol_data(ibfd, isymbol, obfd, osymbol) \
475 BFD_SEND (obfd, _bfd_copy_private_symbol_data, \
476 (ibfd, isymbol, obfd, osymbol))