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 = (asymbol **) 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]);
66 All storage for the symbols themselves is in an objalloc
67 connected to the BFD; it is freed when the BFD is closed.
69 @node Writing Symbols, Mini Symbols, Reading Symbols, Symbols
70 @subsection Writing symbols
71 Writing of a symbol table is automatic when a BFD open for
72 writing is closed. The application attaches a vector of
73 pointers to pointers to symbols to the BFD being written, and
74 fills in the symbol count. The close and cleanup code reads
75 through the table provided and performs all the necessary
76 operations. The BFD output code must always be provided with an
77 ``owned'' symbol: one which has come from another BFD, or one
78 which has been created using @code{bfd_make_empty_symbol}. Here is an
79 example showing the creation of a symbol table with only one element:
89 abfd = bfd_openw("foo","a.out-sunos-big");
90 bfd_set_format(abfd, bfd_object);
91 new = bfd_make_empty_symbol(abfd);
92 new->name = "dummy_symbol";
93 new->section = bfd_make_section_old_way(abfd, ".text");
94 new->flags = BSF_GLOBAL;
98 ptrs[1] = (asymbol *)0;
100 bfd_set_symtab(abfd, ptrs, 1);
106 00012345 A dummy_symbol
109 Many formats cannot represent arbitary symbol information; for
110 instance, the @code{a.out} object format does not allow an
111 arbitary 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 symbol_cache_entry
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 0x01
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 0x02
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_FORT_COMM}, @code{BSF_UNDEFINED} or
181 @code{BSF_GLOBAL}. */
183 /* The symbol is a debugging record. The value has an arbitary
184 meaning, unless BSF_DEBUGGING_RELOC is also set. */
185 #define BSF_DEBUGGING 0x08
187 /* The symbol denotes a function entry point. Used in ELF,
188 perhaps others someday. */
189 #define BSF_FUNCTION 0x10
191 /* Used by the linker. */
192 #define BSF_KEEP 0x20
193 #define BSF_KEEP_G 0x40
195 /* A weak global symbol, overridable without warnings by
196 a regular global symbol of the same name. */
197 #define BSF_WEAK 0x80
199 /* This symbol was created to point to a section, e.g. ELF's
200 STT_SECTION symbols. */
201 #define BSF_SECTION_SYM 0x100
203 /* The symbol used to be a common symbol, but now it is
205 #define BSF_OLD_COMMON 0x200
207 /* The default value for common data. */
208 #define BFD_FORT_COMM_DEFAULT_VALUE 0
210 /* In some files the type of a symbol sometimes alters its
211 location in an output file - ie in coff a @code{ISFCN} symbol
212 which is also @code{C_EXT} symbol appears where it was
213 declared and not at the end of a section. This bit is set
214 by the target BFD part to convey this information. */
215 #define BSF_NOT_AT_END 0x400
217 /* Signal that the symbol is the label of constructor section. */
218 #define BSF_CONSTRUCTOR 0x800
220 /* Signal that the symbol is a warning symbol. The name is a
221 warning. The name of the next symbol is the one to warn about;
222 if a reference is made to a symbol with the same name as the next
223 symbol, a warning is issued by the linker. */
224 #define BSF_WARNING 0x1000
226 /* Signal that the symbol is indirect. This symbol is an indirect
227 pointer to the symbol with the same name as the next symbol. */
228 #define BSF_INDIRECT 0x2000
230 /* BSF_FILE marks symbols that contain a file name. This is used
231 for ELF STT_FILE symbols. */
232 #define BSF_FILE 0x4000
234 /* Symbol is from dynamic linking information. */
235 #define BSF_DYNAMIC 0x8000
237 /* The symbol denotes a data object. Used in ELF, and perhaps
239 #define BSF_OBJECT 0x10000
241 /* This symbol is a debugging symbol. The value is the offset
242 into the section of the data. BSF_DEBUGGING should be set
244 #define BSF_DEBUGGING_RELOC 0x20000
248 /* A pointer to the section to which this symbol is
249 relative. This will always be non NULL, there are special
250 sections for undefined and absolute symbols. */
253 /* Back end special data. */
265 @node symbol handling functions, , typedef asymbol, Symbols
266 @subsection Symbol handling functions
269 @findex bfd_get_symtab_upper_bound
270 @subsubsection @code{bfd_get_symtab_upper_bound}
271 @strong{Description}@*
272 Return the number of bytes required to store a vector of pointers
273 to @code{asymbols} for all the symbols in the BFD @var{abfd},
274 including a terminal NULL pointer. If there are no symbols in
275 the BFD, then return 0. If an error occurs, return -1.
277 #define bfd_get_symtab_upper_bound(abfd) \
278 BFD_SEND (abfd, _bfd_get_symtab_upper_bound, (abfd))
282 @findex bfd_is_local_label
283 @subsubsection @code{bfd_is_local_label}
286 boolean bfd_is_local_label(bfd *abfd, asymbol *sym);
288 @strong{Description}@*
289 Return true if the given symbol @var{sym} in the BFD @var{abfd} is
290 a compiler generated local label, else return false.
292 @findex bfd_is_local_label_name
293 @subsubsection @code{bfd_is_local_label_name}
296 boolean bfd_is_local_label_name(bfd *abfd, const char *name);
298 @strong{Description}@*
299 Return true if a symbol with the name @var{name} in the BFD
300 @var{abfd} is a compiler generated local label, else return
301 false. This just checks whether the name has the form of a
304 #define bfd_is_local_label_name(abfd, name) \
305 BFD_SEND (abfd, _bfd_is_local_label_name, (abfd, name))
309 @findex bfd_canonicalize_symtab
310 @subsubsection @code{bfd_canonicalize_symtab}
311 @strong{Description}@*
312 Read the symbols from the BFD @var{abfd}, and fills in
313 the vector @var{location} with pointers to the symbols and
315 Return the actual number of symbol pointers, not
318 #define bfd_canonicalize_symtab(abfd, location) \
319 BFD_SEND (abfd, _bfd_canonicalize_symtab,\
324 @findex bfd_set_symtab
325 @subsubsection @code{bfd_set_symtab}
328 boolean bfd_set_symtab (bfd *abfd, asymbol **location, unsigned int count);
330 @strong{Description}@*
331 Arrange that when the output BFD @var{abfd} is closed,
332 the table @var{location} of @var{count} pointers to symbols
335 @findex bfd_print_symbol_vandf
336 @subsubsection @code{bfd_print_symbol_vandf}
339 void bfd_print_symbol_vandf(bfd *abfd, PTR file, asymbol *symbol);
341 @strong{Description}@*
342 Print the value and flags of the @var{symbol} supplied to the
345 @findex bfd_make_empty_symbol
346 @subsubsection @code{bfd_make_empty_symbol}
347 @strong{Description}@*
348 Create a new @code{asymbol} structure for the BFD @var{abfd}
349 and return a pointer to it.
351 This routine is necessary because each back end has private
352 information surrounding the @code{asymbol}. Building your own
353 @code{asymbol} and pointing to it will not create the private
354 information, and will cause problems later on.
356 #define bfd_make_empty_symbol(abfd) \
357 BFD_SEND (abfd, _bfd_make_empty_symbol, (abfd))
361 @findex _bfd_generic_make_empty_symbol
362 @subsubsection @code{_bfd_generic_make_empty_symbol}
365 asymbol *_bfd_generic_make_empty_symbol (bfd *);
367 @strong{Description}@*
368 Create a new @code{asymbol} structure for the BFD @var{abfd}
369 and return a pointer to it. Used by core file routines,
370 binary back-end and anywhere else where no private info
373 @findex bfd_make_debug_symbol
374 @subsubsection @code{bfd_make_debug_symbol}
375 @strong{Description}@*
376 Create a new @code{asymbol} structure for the BFD @var{abfd},
377 to be used as a debugging symbol. Further details of its use have
378 yet to be worked out.
380 #define bfd_make_debug_symbol(abfd,ptr,size) \
381 BFD_SEND (abfd, _bfd_make_debug_symbol, (abfd, ptr, size))
385 @findex bfd_decode_symclass
386 @subsubsection @code{bfd_decode_symclass}
387 @strong{Description}@*
388 Return a character corresponding to the symbol
389 class of @var{symbol}, or '?' for an unknown class.
393 int bfd_decode_symclass(asymbol *symbol);
395 @findex bfd_is_undefined_symclass
396 @subsubsection @code{bfd_is_undefined_symclass}
397 @strong{Description}@*
398 Returns non-zero if the class symbol returned by
399 bfd_decode_symclass represents an undefined symbol.
400 Returns zero otherwise.
404 boolean bfd_is_undefined_symclass (int symclass);
406 @findex bfd_symbol_info
407 @subsubsection @code{bfd_symbol_info}
408 @strong{Description}@*
409 Fill in the basic info about symbol that nm needs.
410 Additional info may be added by the back-ends after
411 calling this function.
415 void bfd_symbol_info(asymbol *symbol, symbol_info *ret);
417 @findex bfd_copy_private_symbol_data
418 @subsubsection @code{bfd_copy_private_symbol_data}
421 boolean bfd_copy_private_symbol_data(bfd *ibfd, asymbol *isym, bfd *obfd, asymbol *osym);
423 @strong{Description}@*
424 Copy private symbol information from @var{isym} in the BFD
425 @var{ibfd} to the symbol @var{osym} in the BFD @var{obfd}.
426 Return @code{true} on success, @code{false} on error. Possible error
432 @code{bfd_error_no_memory} -
433 Not enough memory exists to create private data for @var{osec}.
436 #define bfd_copy_private_symbol_data(ibfd, isymbol, obfd, osymbol) \
437 BFD_SEND (obfd, _bfd_copy_private_symbol_data, \
438 (ibfd, isymbol, obfd, osymbol))