gdb/elfread.c

   1 /* Read ELF (Executable and Linking Format) object files for GDB.
   2    Copyright 1991, 1992 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@cygnus.com)                      *
  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  *                                                                      *
  33  ************************************************************************/
  34
  35 #include "defs.h"
  36 #include "elf/common.h"
  37 #include "elf/external.h"
  38 #include "elf/internal.h"
  39 #include "bfd.h"
  40 #include "libbfd.h"             /* For bfd_elf_find_section */
  41 #include "symtab.h"
  42 #include "symfile.h"
  43 #include "objfiles.h"
  44 #include "buildsym.h"
  45
  46 #define STREQ(a,b) (strcmp((a),(b))==0)
  47
  48 struct elfinfo {
  49   unsigned int dboffset;        /* Offset to dwarf debug section */
  50   unsigned int dbsize;          /* Size of dwarf debug section */
  51   unsigned int lnoffset;        /* Offset to dwarf line number section */
  52   unsigned int lnsize;          /* Size of dwarf line number section */
  53   asection *stabsect;           /* Section pointer for .stab section */
  54   asection *stabindexsect;      /* Section pointer for .stab.index section */
  55 };
  56
  57 static void
  58 elf_symfile_init PARAMS ((struct objfile *));
  59
  60 static void
  61 elf_new_init PARAMS ((struct objfile *));
  62
  63 static void
  64 elf_symfile_read PARAMS ((struct objfile *, CORE_ADDR, int));
  65
  66 static void
  67 elf_symfile_finish PARAMS ((struct objfile *));
  68
  69 static void
  70 elf_symtab_read PARAMS ((bfd *,  CORE_ADDR, struct objfile *));
  71
  72 static void
  73 record_minimal_symbol PARAMS ((char *, CORE_ADDR, enum minimal_symbol_type,
  74                                struct objfile *));
  75
  76 static void
  77 elf_locate_sections PARAMS ((bfd *, asection *, PTR));
  78
  79 /* We are called once per section from elf_symfile_read.  We
  80    need to examine each section we are passed, check to see
  81    if it is something we are interested in processing, and
  82    if so, stash away some access information for the section.
  83
  84    For now we recognize the dwarf debug information sections and
  85    line number sections from matching their section names.  The
  86    ELF definition is no real help here since it has no direct
  87    knowledge of DWARF (by design, so any debugging format can be
  88    used).
  89
  90    We also recognize the ".stab" sections used by the Sun compilers
  91    released with Solaris 2.
  92
  93    FIXME:  The section names should not be hardwired strings. */
  94
  95 static void
  96 elf_locate_sections (ignore_abfd, sectp, eip)
  97      bfd *ignore_abfd;
  98      asection *sectp;
  99      PTR eip;
 100 {
 101   register struct elfinfo *ei;
 102
 103   ei = (struct elfinfo *) eip;
 104   if (STREQ (sectp -> name, ".debug"))
 105     {
 106       ei -> dboffset = sectp -> filepos;
 107       ei -> dbsize = bfd_get_section_size_before_reloc (sectp);
 108     }
 109   else if (STREQ (sectp -> name, ".line"))
 110     {
 111       ei -> lnoffset = sectp -> filepos;
 112       ei -> lnsize = bfd_get_section_size_before_reloc (sectp);
 113     }
 114   else if (STREQ (sectp -> name, ".stab"))
 115     {
 116       ei -> stabsect = sectp;
 117     }
 118   else if (STREQ (sectp -> name, ".stab.index"))
 119     {
 120       ei -> stabindexsect = sectp;
 121     }
 122 }
 123
 124 #if 0   /* Currently unused */
 125
 126 char *
 127 elf_interpreter (abfd)
 128      bfd *abfd;
 129 {
 130   sec_ptr interp_sec;
 131   unsigned size;
 132   char *interp = NULL;
 133
 134   interp_sec = bfd_get_section_by_name (abfd, ".interp");
 135   if (interp_sec)
 136     {
 137       size = bfd_section_size (abfd, interp_sec);
 138       interp = alloca (size);
 139       if (bfd_get_section_contents (abfd, interp_sec, interp, (file_ptr)0,
 140                                     size))
 141         {
 142           interp = savestring (interp, size - 1);
 143         }
 144       else
 145         {
 146           interp = NULL;
 147         }
 148     }
 149   return (interp);
 150 }
 151
 152 #endif
 153
 154 /*
 155
 156 LOCAL FUNCTION
 157
 158         record_minimal_symbol -- add entry to minimal symbol table
 159
 160 SYNOPSIS
 161
 162         static void record_minimal_symbol (char *name, CORE_ADDR address)
 163
 164 DESCRIPTION
 165
 166         Given a pointer to the name of a symbol that should be added to the
 167         minimal symbol table and the address associated with that symbol, records
 168         this information for later use in building the minimal symbol table.
 169
 170  */
 171
 172 static void
 173 record_minimal_symbol (name, address, ms_type, objfile)
 174      char *name;
 175      CORE_ADDR address;
 176      enum minimal_symbol_type ms_type;
 177      struct objfile *objfile;
 178 {
 179   name = obsavestring (name, strlen (name), &objfile -> symbol_obstack);
 180   prim_record_minimal_symbol (name, address, ms_type);
 181 }
 182
 183 static void
 184 record_minimal_symbol_and_info (name, address, ms_type, info, objfile)
 185      char *name;
 186      CORE_ADDR address;
 187      enum minimal_symbol_type ms_type;
 188      char *info;                /* FIXME, is this really char *? */
 189      struct objfile *objfile;
 190 {
 191   name = obsavestring (name, strlen (name), &objfile -> symbol_obstack);
 192   prim_record_minimal_symbol_and_info (name, address, ms_type, info);
 193 }
 194
 195 /*
 196
 197 LOCAL FUNCTION
 198
 199         elf_symtab_read -- read the symbol table of an ELF file
 200
 201 SYNOPSIS
 202
 203         void elf_symtab_read (bfd *abfd, CORE_ADDR addr,
 204                               struct objfile *objfile)
 205
 206 DESCRIPTION
 207
 208         Given an open bfd, a base address to relocate symbols to, and a
 209         flag that specifies whether or not this bfd is for an executable
 210         or not (may be shared library for example), add all the global
 211         function and data symbols to the minimal symbol table.
 212
 213 */
 214
 215 static void
 216 elf_symtab_read (abfd, addr, objfile)
 217      bfd *abfd;
 218      CORE_ADDR addr;
 219      struct objfile *objfile;
 220 {
 221   unsigned int storage_needed;
 222   asymbol *sym;
 223   asymbol **symbol_table;
 224   unsigned int number_of_symbols;
 225   unsigned int i;
 226   struct cleanup *back_to;
 227   CORE_ADDR symaddr;
 228   enum minimal_symbol_type ms_type;
 229
 230   storage_needed = get_symtab_upper_bound (abfd);
 231
 232   if (storage_needed > 0)
 233     {
 234       symbol_table = (asymbol **) xmalloc (storage_needed);
 235       back_to = make_cleanup (free, symbol_table);
 236       number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
 237
 238       for (i = 0; i < number_of_symbols; i++)
 239         {
 240           sym = *symbol_table++;
 241           /* Select global/weak symbols that are defined in a specific section.
 242              Note that bfd now puts abs symbols in their own section, so
 243              all symbols we are interested in will have a section. */
 244           if ((sym -> flags & (BSF_GLOBAL | BSF_WEAK))
 245               && (sym -> section != NULL))
 246             {
 247               symaddr = sym -> value;
 248               /* Relocate all non-absolute symbols by base address.  */
 249               if (sym -> section != &bfd_abs_section)
 250                 {
 251                   symaddr += addr;
 252                 }
 253               /* For non-absolute symbols, use the type of the section
 254                  they are relative to, to intuit text/data.  Bfd provides
 255                  no way of figuring this out for absolute symbols. */
 256               if (sym -> section -> flags & SEC_CODE)
 257                 {
 258                   ms_type = mst_text;
 259                 }
 260               else if (sym -> section -> flags & SEC_DATA)
 261                 {
 262                   ms_type = mst_data;
 263                 }
 264               else
 265                 {
 266                   ms_type = mst_unknown;
 267                 }
 268               /* Pass symbol size field in via BFD.  FIXME!!!  */
 269               record_minimal_symbol_and_info ((char *) sym -> name,
 270                          symaddr, ms_type, sym->udata, objfile);
 271             }
 272         }
 273       do_cleanups (back_to);
 274     }
 275 }
 276
 277 /* Scan and build partial symbols for a symbol file.
 278    We have been initialized by a call to elf_symfile_init, which
 279    currently does nothing.
 280
 281    ADDR is the address relative to which the symbols in it are (e.g.
 282    the base address of the text segment).
 283
 284    MAINLINE is true if we are reading the main symbol
 285    table (as opposed to a shared lib or dynamically loaded file).
 286
 287    This function only does the minimum work necessary for letting the
 288    user "name" things symbolically; it does not read the entire symtab.
 289    Instead, it reads the external and static symbols and puts them in partial
 290    symbol tables.  When more extensive information is requested of a
 291    file, the corresponding partial symbol table is mutated into a full
 292    fledged symbol table by going back and reading the symbols
 293    for real.
 294
 295    We look for sections with specific names, to tell us what debug
 296    format to look for:  FIXME!!!
 297
 298    dwarf_build_psymtabs() builds psymtabs for DWARF symbols;
 299    elfstab_build_psymtabs() handles STABS symbols.
 300
 301    Note that ELF files have a "minimal" symbol table, which looks a lot
 302    like a COFF symbol table, but has only the minimal information necessary
 303    for linking.  We process this also, and use the information to
 304    build gdb's minimal symbol table.  This gives us some minimal debugging
 305    capability even for files compiled without -g.  */
 306
 307 static void
 308 elf_symfile_read (objfile, addr, mainline)
 309      struct objfile *objfile;
 310      CORE_ADDR addr;
 311      int mainline;
 312 {
 313   bfd *abfd = objfile->obfd;
 314   struct elfinfo ei;
 315   struct cleanup *back_to;
 316   asection *text_sect;
 317   CORE_ADDR offset;
 318
 319   init_minimal_symbol_collection ();
 320   back_to = make_cleanup (discard_minimal_symbols, 0);
 321
 322   /* Compute the amount to relocate all symbols by.  The value passed in
 323      as ADDR is typically either the actual address of the text section,
 324      or a user specified address.  By subtracting off the actual address
 325      of the text section, we can compute the relocation amount. */
 326
 327   text_sect = bfd_get_section_by_name (objfile -> obfd, ".text");
 328   offset = addr - bfd_section_vma (objfile -> obfd, text_sect);
 329
 330   /* Process the normal ELF symbol table first. */
 331
 332   elf_symtab_read (abfd, offset, objfile);
 333
 334   /* Now process debugging information, which is contained in
 335      special ELF sections.  We first have to find them... */
 336
 337   (void) memset ((char *) &ei, 0, sizeof (ei));
 338   bfd_map_over_sections (abfd, elf_locate_sections, (PTR) &ei);
 339   if (ei.dboffset && ei.lnoffset)
 340     {
 341       /* DWARF sections */
 342       dwarf_build_psymtabs (fileno ((FILE *)(abfd -> iostream)),
 343                             bfd_get_filename (abfd),
 344                             offset, mainline,
 345                             ei.dboffset, ei.dbsize,
 346                             ei.lnoffset, ei.lnsize, objfile);
 347     }
 348   if (ei.stabsect)
 349     {
 350       /* STABS sections */
 351
 352       /* FIXME:  Sun didn't really know how to implement this well.
 353          They made .stab sections that don't point to the .stabstr
 354          section with the sh_link field.  BFD doesn't make string table
 355          sections visible to the caller.  So we have to search the
 356          ELF section table, not the BFD section table, for the string
 357          table.  */
 358       struct elf_internal_shdr *elf_sect;
 359
 360       elf_sect = bfd_elf_find_section (abfd, ".stabstr");
 361       if (elf_sect)
 362         elfstab_build_psymtabs (objfile,
 363           addr, /* We really pass the text seg addr, not the offset, here. */
 364           mainline,
 365           ei.stabsect->filepos,                         /* .stab offset */
 366           bfd_get_section_size_before_reloc (ei.stabsect),/* .stab size */
 367           elf_sect->sh_offset,                          /* .stabstr offset */
 368           elf_sect->sh_size);                           /* .stabstr size */
 369     }
 370
 371   if (!have_partial_symbols ())
 372     {
 373       wrap_here ("");
 374       printf_filtered ("(no debugging symbols found)...");
 375       wrap_here ("");
 376     }
 377
 378   /* Install any minimal symbols that have been collected as the current
 379      minimal symbols for this objfile. */
 380
 381   install_minimal_symbols (objfile);
 382
 383   do_cleanups (back_to);
 384 }
 385
 386 /* Initialize anything that needs initializing when a completely new symbol
 387    file is specified (not just adding some symbols from another file, e.g. a
 388    shared library).
 389
 390    We reinitialize buildsym, since we may be reading stabs from an ELF file.  */
 391
 392 static void
 393 elf_new_init (ignore)
 394      struct objfile *ignore;
 395 {
 396   buildsym_new_init ();
 397 }
 398
 399 /* Perform any local cleanups required when we are done with a particular
 400    objfile.  I.E, we are in the process of discarding all symbol information
 401    for an objfile, freeing up all memory held for it, and unlinking the
 402    objfile struct from the global list of known objfiles. */
 403
 404 static void
 405 elf_symfile_finish (objfile)
 406      struct objfile *objfile;
 407 {
 408   if (objfile -> sym_private != NULL)
 409     {
 410       mfree (objfile -> md, objfile -> sym_private);
 411     }
 412 }
 413
 414 /* ELF specific initialization routine for reading symbols.
 415
 416    It is passed a pointer to a struct sym_fns which contains, among other
 417    things, the BFD for the file whose symbols are being read, and a slot for
 418    a pointer to "private data" which we can fill with goodies.
 419
 420    For now at least, we have nothing in particular to do, so this function is
 421    just a stub. */
 422
 423 static void
 424 elf_symfile_init (ignore)
 425      struct objfile *ignore;
 426 {
 427 }
 428
 429 \f
 430 /*  Register that we are able to handle ELF object file formats and DWARF
 431     debugging formats.
 432
 433     Unlike other object file formats, where the debugging information format
 434     is implied by the object file format, the ELF object file format and the
 435     DWARF debugging information format are two distinct, and potentially
 436     separate entities.  I.E. it is perfectly possible to have ELF objects
 437     with debugging formats other than DWARF.  And it is conceivable that the
 438     DWARF debugging format might be used with another object file format,
 439     like COFF, by simply using COFF's custom section feature.
 440
 441     GDB, and to a lesser extent BFD, should support the notion of separate
 442     object file formats and debugging information formats.  For now, we just
 443     use "elf" in the same sense as "a.out" or "coff", to imply both the ELF
 444     object file format and the DWARF debugging format. */
 445
 446 static struct sym_fns elf_sym_fns =
 447 {
 448   "elf",                /* sym_name: name or name prefix of BFD target type */
 449   3,                    /* sym_namelen: number of significant sym_name chars */
 450   elf_new_init,         /* sym_new_init: init anything gbl to entire symtab */
 451   elf_symfile_init,     /* sym_init: read initial info, setup for sym_read() */
 452   elf_symfile_read,     /* sym_read: read a symbol file into symtab */
 453   elf_symfile_finish,   /* sym_finish: finished with file, cleanup */
 454   NULL                  /* next: pointer to next struct sym_fns */
 455 };
 456
 457 void
 458 _initialize_elfread ()
 459 {
 460   add_symtab_fns (&elf_sym_fns);
 461 }