gdb/elfread.c

   1 /* Read ELF (Executable and Linking Format) object files for GDB.
   2    Copyright (C) 1991 Free Software Foundation, Inc.
   3    Written by Fred Fish at Cygnus Support.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 /************************************************************************
  22  *                                                                      *
  23  *                              NOTICE                                  *
  24  *                                                                      *
  25  * This file is still under construction.  When it is complete, this    *
  26  * notice will be removed.  Until then, direct any questions or changes *
  27  * to Fred Fish at Cygnus Support (fnf@cygint)                          *
  28  *                                                                      *
  29  * FIXME        Still needs support for shared libraries.               *
  30  * FIXME        Still needs support for core files.                     *
  31  * FIXME        The ".debug" and ".line" section names are hardwired.   *
  32  * FIXME        Still needs support ELF symbol tables (as distinct      *
  33  *              from DWARF support).  Can use them to build the misc    *
  34  *              function vector at least.  This is fairly trivial once  *
  35  *              bfd is extended to handle ELF symbol tables.            *
  36  *                                                                      *
  37  ************************************************************************/
  38
  39 #include <stdio.h>
  40
  41 #include "defs.h"
  42 #include "elf/common.h"
  43 #include "elf/external.h"
  44 #include "elf/internal.h"
  45 #include "bfd.h"
  46 #include "symfile.h"
  47 #include "symtab.h"
  48 #include "ansidecl.h"
  49
  50 extern int EXFUN (strcmp, (CONST char *a, CONST char *b));
  51 extern int EXFUN (dwarf_build_psymtabs,
  52      (int desc, char *filename, CORE_ADDR addr, int mainline,
  53       unsigned int dbfoff, unsigned int dbsize, unsigned int lnoffset,
  54       unsigned int lnsize, struct objfile *objfile));
  55
  56 #define STREQ(a,b) (strcmp((a),(b))==0)
  57
  58 struct elfinfo {
  59   unsigned int dboffset;        /* Offset to dwarf debug section */
  60   unsigned int dbsize;          /* Size of dwarf debug section */
  61   unsigned int lnoffset;        /* Offset to dwarf line number section */
  62   unsigned int lnsize;          /* Size of dwarf line number section */
  63 };
  64
  65 /* We are called once per section from elf_symfile_read.  We
  66    need to examine each section we are passed, check to see
  67    if it is something we are interested in processing, and
  68    if so, stash away some access information for the section.
  69
  70    For now we recognize the dwarf debug information sections and
  71    line number sections from matching their section names.  The
  72    ELF definition is no real help here since it has no direct
  73    knowledge of DWARF (by design, so any debugging format can be
  74    used).
  75
  76    FIXME:  The section names should not be hardwired strings. */
  77
  78 static void
  79 DEFUN(elf_locate_sections, (abfd, sectp, ei),
  80       bfd *abfd AND
  81       asection *sectp AND
  82       struct elfinfo *ei)
  83 {
  84   if (STREQ (sectp -> name, ".debug"))
  85     {
  86       ei -> dboffset = sectp -> filepos;
  87       ei -> dbsize = bfd_get_section_size_before_reloc (sectp);
  88     }
  89   else if (STREQ (sectp -> name, ".line"))
  90     {
  91       ei -> lnoffset = sectp -> filepos;
  92       ei -> lnsize = bfd_get_section_size_before_reloc (sectp);
  93     }
  94 }
  95
  96 char *
  97 DEFUN(elf_interpreter, (abfd),
  98       bfd *abfd)
  99 {
 100   sec_ptr interp_sec;
 101   unsigned size;
 102   char *interp = NULL;
 103
 104   interp_sec = bfd_get_section_by_name (abfd, ".interp");
 105   if (interp_sec)
 106     {
 107       size = bfd_section_size (abfd, interp_sec);
 108       interp = alloca (size);
 109       if (bfd_get_section_contents (abfd, interp_sec, interp, (file_ptr)0,
 110                                     size))
 111         {
 112           interp = savestring (interp, size - 1);
 113         }
 114       else
 115         {
 116           interp = NULL;
 117         }
 118     }
 119   return (interp);
 120 }
 121
 122 /*
 123
 124 LOCAL FUNCTION
 125
 126         record_misc_function -- add entry to miscellaneous function vector
 127
 128 SYNOPSIS
 129
 130         static void record_misc_function (char *name, CORE_ADDR address)
 131
 132 DESCRIPTION
 133
 134         Given a pointer to the name of a symbol that should be added to the
 135         miscellaneous function vector, and the address associated with that
 136         symbol, records this information for later use in building the
 137         miscellaneous function vector.
 138
 139 NOTES
 140
 141         FIXME:  For now we just use mf_unknown as the type.  This should be
 142         fixed.
 143  */
 144
 145 static void
 146 DEFUN(record_misc_function, (name, address, mf_type),
 147       char *name AND CORE_ADDR address AND enum misc_function_type mf_type)
 148 {
 149   prim_record_misc_function (obsavestring (name, strlen (name)), address,
 150                              mf_type);
 151 }
 152
 153 /*
 154
 155 LOCAL FUNCTION
 156
 157         elf_symtab_read -- read the symbol table of an ELF file
 158
 159 SYNOPSIS
 160
 161         void elf_symtab_read (bfd *abfd, CORE_ADDR addr, int mainline)
 162
 163 DESCRIPTION
 164
 165         Given an open bfd, a base address to relocate symbols to, and a
 166         flag that specifies whether or not this bfd is for an executable
 167         or not (may be shared library for example), add all the global
 168         function and data symbols to the miscellaneous function vector.
 169
 170 */
 171
 172 static void
 173 DEFUN (elf_symtab_read, (abfd, addr, mainline),
 174        bfd *abfd AND
 175        CORE_ADDR addr AND
 176        int mainline)
 177 {
 178   unsigned int storage_needed;
 179   asymbol *sym;
 180   asymbol **symbol_table;
 181   unsigned int number_of_symbols;
 182   unsigned int i;
 183   struct cleanup *back_to;
 184   CORE_ADDR symaddr;
 185   enum misc_function_type mf_type;
 186
 187   storage_needed = get_symtab_upper_bound (abfd);
 188
 189   if (storage_needed > 0)
 190     {
 191       symbol_table = (asymbol **) bfd_xmalloc (storage_needed);
 192       back_to = make_cleanup (free, symbol_table);
 193       number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
 194
 195       for (i = 0; i < number_of_symbols; i++)
 196         {
 197           sym = *symbol_table++;
 198           /* Select global symbols that are defined in a specific section
 199              or are absolute. */
 200           if (sym -> flags & BSF_GLOBAL
 201               && (sym -> section == &bfd_abs_section))
 202             {
 203               symaddr = sym -> value;
 204               if (!mainline)
 205                 {
 206                   /* Relocate all symbols by base address */
 207                   symaddr += addr;
 208                 }
 209               /* For non-absolute symbols, use the type of the section
 210                  they are relative to, to intuit text/data.  Bfd provides
 211                  no way of figuring this out for absolute symbols. */
 212               if (sym -> section && (sym -> section -> flags & SEC_CODE))
 213                 {
 214                   mf_type = mf_text;
 215                 }
 216               else if (sym -> section && (sym -> section -> flags & SEC_DATA))
 217                 {
 218                   mf_type = mf_data;
 219                 }
 220               else
 221                 {
 222                   mf_type = mf_unknown;
 223                 }
 224               record_misc_function ((char *) sym -> name, symaddr, mf_type);
 225             }
 226         }
 227       do_cleanups (back_to);
 228     }
 229 }
 230
 231 /* Scan and build partial symbols for a symbol file.
 232    We have been initialized by a call to elf_symfile_init, which
 233    currently does nothing.
 234
 235    ADDR is the address relative to which the symbols in it are (e.g.
 236    the base address of the text segment).
 237
 238    MAINLINE is true if we are reading the main symbol
 239    table (as opposed to a shared lib or dynamically loaded file).
 240
 241    This function only does the minimum work necessary for letting the
 242    user "name" things symbolically; it does not read the entire symtab.
 243    Instead, it reads the external and static symbols and puts them in partial
 244    symbol tables.  When more extensive information is requested of a
 245    file, the corresponding partial symbol table is mutated into a full
 246    fledged symbol table by going back and reading the symbols
 247    for real.  The function dwarf_psymtab_to_symtab() is the function that
 248    does this for DWARF symbols.
 249
 250    Note that ELF files have a "minimal" symbol table, which looks a lot
 251    like a COFF symbol table, but has only the minimal information necessary
 252    for linking.  We process this also, and just use the information to
 253    add to the misc function vector.  This gives us some minimal debugging
 254    capability even for files compiled without -g.
 255  */
 256
 257 static void
 258 DEFUN(elf_symfile_read, (sf, addr, mainline),
 259       struct sym_fns *sf AND
 260       CORE_ADDR addr AND
 261       int mainline)
 262 {
 263   bfd *abfd = sf->objfile->obfd;
 264   struct elfinfo ei;
 265   struct cleanup *back_to;
 266
 267   init_misc_bunches ();
 268   back_to = make_cleanup (discard_misc_bunches, 0);
 269
 270   /* Process the normal ELF symbol table first. */
 271
 272   elf_symtab_read (abfd, addr, mainline);
 273
 274   /* Now process the DWARF debugging information, which is contained in
 275      special ELF sections.  We first have to find them... */
 276
 277   (void) memset ((char *) &ei, 0, sizeof (ei));
 278   bfd_map_over_sections (abfd, elf_locate_sections, &ei);
 279   if (ei.dboffset && ei.lnoffset)
 280     {
 281       dwarf_build_psymtabs (fileno ((FILE *)(abfd -> iostream)),
 282                             bfd_get_filename (abfd),
 283                             addr, mainline,
 284                             ei.dboffset, ei.dbsize,
 285                             ei.lnoffset, ei.lnsize, sf->objfile);
 286     }
 287
 288   if (!partial_symtab_list)
 289     {
 290       wrap_here ("");
 291       printf_filtered ("(no debugging symbols found)...");
 292       wrap_here ("");
 293     }
 294
 295   /* Go over the miscellaneous functions and install them in the
 296      miscellaneous function vector. */
 297
 298   condense_misc_bunches (!mainline);
 299   do_cleanups (back_to);
 300 }
 301
 302 /* Initialize anything that needs initializing when a completely new symbol
 303    file is specified (not just adding some symbols from another file, e.g. a
 304    shared library).
 305
 306    For now at least, we have nothing in particular to do, so this function is
 307    just a stub. */
 308
 309 static void
 310 DEFUN_VOID (elf_new_init)
 311 {
 312 }
 313
 314 /* ELF specific initialization routine for reading symbols.
 315
 316    It is passed a pointer to a struct sym_fns which contains, among other
 317    things, the BFD for the file whose symbols are being read, and a slot for
 318    a pointer to "private data" which we can fill with goodies.
 319
 320    For now at least, we have nothing in particular to do, so this function is
 321    just a stub. */
 322
 323 static void
 324 DEFUN(elf_symfile_init, (sf),
 325       struct sym_fns *sf)
 326 {
 327 }
 328
 329 \f
 330 /*  Register that we are able to handle ELF object file formats and DWARF
 331     debugging formats.
 332
 333     Unlike other object file formats, where the debugging information format
 334     is implied by the object file format, the ELF object file format and the
 335     DWARF debugging information format are two distinct, and potentially
 336     separate entities.  I.E. it is perfectly possible to have ELF objects
 337     with debugging formats other than DWARF.  And it is conceivable that the
 338     DWARF debugging format might be used with another object file format,
 339     like COFF, by simply using COFF's custom section feature.
 340
 341     GDB, and to a lesser extent BFD, should support the notion of separate
 342     object file formats and debugging information formats.  For now, we just
 343     use "elf" in the same sense as "a.out" or "coff", to imply both the ELF
 344     object file format and the DWARF debugging format. */
 345
 346 static struct sym_fns elf_sym_fns = {
 347   "elf",                /* sym_name: name or name prefix of BFD target type */
 348   3,                    /* sym_namelen: number of significant sym_name chars */
 349   elf_new_init,         /* sym_new_init: init anything gbl to entire symtab */
 350   elf_symfile_init,     /* sym_init: read initial info, setup for sym_read() */
 351   elf_symfile_read,     /* sym_read: read a symbol file into symtab */
 352   NULL,                 /* sym_bfd: accessor for symbol file being read */
 353   NULL,                 /* sym_private: sym_init & sym_read shared info */
 354   NULL                  /* next: pointer to next struct sym_fns */
 355 };
 356
 357 void
 358 DEFUN_VOID (_initialize_elfread)
 359 {
 360   add_symtab_fns (&elf_sym_fns);
 361 }