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 #include "defs.h"
  22 #include "bfd.h"
  23 #include "libbfd.h"             /* For bfd_elf_find_section */
  24 #include "libelf.h"
  25 #include "symtab.h"
  26 #include "symfile.h"
  27 #include "objfiles.h"
  28 #include "buildsym.h"
  29 #include "gdb-stabs.h"
  30 #include "complaints.h"
  31 #include <string.h>
  32 #include "demangle.h"
  33
  34 /* The struct elfinfo is available only during ELF symbol table and
  35    psymtab reading.  It is destroyed at the complation of psymtab-reading.
  36    It's local to elf_symfile_read.  */
  37
  38 struct elfinfo {
  39   file_ptr dboffset;            /* Offset to dwarf debug section */
  40   unsigned int dbsize;          /* Size of dwarf debug section */
  41   file_ptr lnoffset;            /* Offset to dwarf line number section */
  42   unsigned int lnsize;          /* Size of dwarf line number section */
  43   asection *stabsect;           /* Section pointer for .stab section */
  44   asection *stabindexsect;      /* Section pointer for .stab.index section */
  45 };
  46
  47 /* Various things we might complain about... */
  48
  49 struct complaint section_info_complaint =
  50   {"elf/stab section information %s without a preceding file symbol", 0, 0};
  51
  52 struct complaint section_info_dup_complaint =
  53   {"duplicated elf/stab section information for %s", 0, 0};
  54
  55 struct complaint stab_info_mismatch_complaint =
  56   {"elf/stab section information missing for %s", 0, 0};
  57
  58 struct complaint stab_info_questionable_complaint =
  59   {"elf/stab section information questionable for %s", 0, 0};
  60
  61 static void
  62 elf_symfile_init PARAMS ((struct objfile *));
  63
  64 static void
  65 elf_new_init PARAMS ((struct objfile *));
  66
  67 static void
  68 elf_symfile_read PARAMS ((struct objfile *, struct section_offsets *, int));
  69
  70 static void
  71 elf_symfile_finish PARAMS ((struct objfile *));
  72
  73 static void
  74 elf_symtab_read PARAMS ((bfd *,  CORE_ADDR, struct objfile *));
  75
  76 static void
  77 free_elfinfo PARAMS ((PTR));
  78
  79 static struct section_offsets *
  80 elf_symfile_offsets PARAMS ((struct objfile *, CORE_ADDR));
  81
  82 static void
  83 record_minimal_symbol_and_info PARAMS ((char *, CORE_ADDR,
  84                                         enum minimal_symbol_type, char *,
  85                                         struct objfile *));
  86
  87 static void
  88 elf_locate_sections PARAMS ((bfd *, asection *, PTR));
  89
  90 /* We are called once per section from elf_symfile_read.  We
  91    need to examine each section we are passed, check to see
  92    if it is something we are interested in processing, and
  93    if so, stash away some access information for the section.
  94
  95    For now we recognize the dwarf debug information sections and
  96    line number sections from matching their section names.  The
  97    ELF definition is no real help here since it has no direct
  98    knowledge of DWARF (by design, so any debugging format can be
  99    used).
 100
 101    We also recognize the ".stab" sections used by the Sun compilers
 102    released with Solaris 2.
 103
 104    FIXME:  The section names should not be hardwired strings. */
 105
 106 static void
 107 elf_locate_sections (ignore_abfd, sectp, eip)
 108      bfd *ignore_abfd;
 109      asection *sectp;
 110      PTR eip;
 111 {
 112   register struct elfinfo *ei;
 113
 114   ei = (struct elfinfo *) eip;
 115   if (STREQ (sectp -> name, ".debug"))
 116     {
 117       ei -> dboffset = sectp -> filepos;
 118       ei -> dbsize = bfd_get_section_size_before_reloc (sectp);
 119     }
 120   else if (STREQ (sectp -> name, ".line"))
 121     {
 122       ei -> lnoffset = sectp -> filepos;
 123       ei -> lnsize = bfd_get_section_size_before_reloc (sectp);
 124     }
 125   else if (STREQ (sectp -> name, ".stab"))
 126     {
 127       ei -> stabsect = sectp;
 128     }
 129   else if (STREQ (sectp -> name, ".stab.index"))
 130     {
 131       ei -> stabindexsect = sectp;
 132     }
 133 }
 134
 135 #if 0   /* Currently unused */
 136
 137 char *
 138 elf_interpreter (abfd)
 139      bfd *abfd;
 140 {
 141   sec_ptr interp_sec;
 142   unsigned size;
 143   char *interp = NULL;
 144
 145   interp_sec = bfd_get_section_by_name (abfd, ".interp");
 146   if (interp_sec)
 147     {
 148       size = bfd_section_size (abfd, interp_sec);
 149       interp = alloca (size);
 150       if (bfd_get_section_contents (abfd, interp_sec, interp, (file_ptr)0,
 151                                     size))
 152         {
 153           interp = savestring (interp, size - 1);
 154         }
 155       else
 156         {
 157           interp = NULL;
 158         }
 159     }
 160   return (interp);
 161 }
 162
 163 #endif
 164
 165 static void
 166 record_minimal_symbol_and_info (name, address, ms_type, info, objfile)
 167      char *name;
 168      CORE_ADDR address;
 169      enum minimal_symbol_type ms_type;
 170      char *info;                /* FIXME, is this really char *? */
 171      struct objfile *objfile;
 172 {
 173   name = obsavestring (name, strlen (name), &objfile -> symbol_obstack);
 174   prim_record_minimal_symbol_and_info (name, address, ms_type, info, -1);
 175 }
 176
 177 /*
 178
 179 LOCAL FUNCTION
 180
 181         elf_symtab_read -- read the symbol table of an ELF file
 182
 183 SYNOPSIS
 184
 185         void elf_symtab_read (bfd *abfd, CORE_ADDR addr,
 186                               struct objfile *objfile)
 187
 188 DESCRIPTION
 189
 190         Given an open bfd, a base address to relocate symbols to, and a
 191         flag that specifies whether or not this bfd is for an executable
 192         or not (may be shared library for example), add all the global
 193         function and data symbols to the minimal symbol table.
 194
 195         In stabs-in-ELF, as implemented by Sun, there are some local symbols
 196         defined in the ELF symbol table, which can be used to locate
 197         the beginnings of sections from each ".o" file that was linked to
 198         form the executable objfile.  We gather any such info and record it
 199         in data structures hung off the objfile's private data.
 200
 201 */
 202
 203 static void
 204 elf_symtab_read (abfd, addr, objfile)
 205      bfd *abfd;
 206      CORE_ADDR addr;
 207      struct objfile *objfile;
 208 {
 209   unsigned int storage_needed;
 210   asymbol *sym;
 211   asymbol **symbol_table;
 212   unsigned int number_of_symbols;
 213   unsigned int i;
 214   int index;
 215   struct cleanup *back_to;
 216   CORE_ADDR symaddr;
 217   enum minimal_symbol_type ms_type;
 218   /* If sectinfo is nonzero, it contains section info that should end up
 219      filed in the objfile.  */
 220   struct stab_section_info *sectinfo = 0;
 221   /* If filesym is nonzero, it points to a file symbol, but we haven't
 222      seen any section info for it yet.  */
 223   asymbol *filesym = 0;
 224   struct dbx_symfile_info *dbx = (struct dbx_symfile_info *)
 225                                  objfile->sym_private;
 226
 227   storage_needed = get_symtab_upper_bound (abfd);
 228
 229   if (storage_needed > 0)
 230     {
 231       symbol_table = (asymbol **) xmalloc (storage_needed);
 232       back_to = make_cleanup (free, symbol_table);
 233       number_of_symbols = bfd_canonicalize_symtab (abfd, symbol_table);
 234
 235       for (i = 0; i < number_of_symbols; i++)
 236         {
 237           sym = symbol_table[i];
 238           /* Select global/weak symbols that are defined in a specific section.
 239              Note that bfd now puts abs symbols in their own section, so
 240              all symbols we are interested in will have a section. */
 241           if ((sym -> flags & (BSF_GLOBAL | BSF_WEAK))
 242               && (sym -> section != NULL))
 243             {
 244               /* Bfd symbols are section relative. */
 245               symaddr = sym -> value + sym -> section -> vma;
 246               /* Relocate all non-absolute symbols by base address.  */
 247               if (sym -> section != &bfd_abs_section)
 248                 symaddr += addr;
 249
 250               /* For non-absolute symbols, use the type of the section
 251                  they are relative to, to intuit text/data.  Bfd provides
 252                  no way of figuring this out for absolute symbols. */
 253               if (sym -> section -> flags & SEC_CODE)
 254                 {
 255                   ms_type = mst_text;
 256                 }
 257               else if (sym -> section -> flags & SEC_DATA)
 258                 {
 259                   ms_type = mst_data;
 260                 }
 261               else
 262                 {
 263                   /* FIXME:  Solaris2 shared libraries include lots of
 264                      odd "absolute" and "undefined" symbols, that play
 265                      hob with actions like finding what function the PC
 266                      is in.  Ignore them if they aren't text or data.  */
 267                   /* ms_type = mst_unknown; */
 268                   continue;             /* Skip this symbol. */
 269                 }
 270               /* Pass symbol size field in via BFD.  FIXME!!!  */
 271               {
 272                 elf32_symbol_type *esym = (elf32_symbol_type *) sym;
 273                 unsigned long size = esym->internal_elf_sym.st_size;
 274                 record_minimal_symbol_and_info ((char *) sym -> name, symaddr,
 275                                                 ms_type, (PTR) size, objfile);
 276               }
 277             }
 278
 279           /* See if this is a debugging symbol that helps Solaris
 280              stabs-in-elf debugging.  */
 281
 282           else if (sym->flags & BSF_FILE)
 283             {
 284               /* Chain any old one onto the objfile; remember new sym.  */
 285               if (sectinfo)
 286                 {
 287                     sectinfo->next = dbx->stab_section_info;
 288                     dbx->stab_section_info = sectinfo;
 289                     sectinfo = 0;
 290                 }
 291               filesym = sym;
 292             }
 293           else if ((sym->flags & BSF_LOCAL) &&
 294                    (sym->section) &&
 295                    (sym->section->flags & SEC_DATA) &&
 296                    (sym->name))
 297             {
 298               /* Named Local variable in a Data section.  Check its name.  */
 299               index = -1;
 300               switch (sym->name[1])
 301                 {
 302                   case 'b':
 303                         if (STREQ ("Bbss.bss", sym->name))
 304                           index = SECT_OFF_BSS;
 305                         break;
 306                   case 'd':
 307                         if (STREQ ("Ddata.data", sym->name))
 308                           index = SECT_OFF_DATA;
 309                         break;
 310                   case 'r':
 311                         if (STREQ ("Drodata.rodata", sym->name))
 312                           index = SECT_OFF_RODATA;
 313                         break;
 314                 }
 315               if (index > 0)
 316                 {
 317                   /* We have some new info.  Allocate a sectinfo, if
 318                      needed, and fill it in.  */
 319                   if (!sectinfo)
 320                     {
 321                       sectinfo = (struct stab_section_info *)
 322                                  xmmalloc (objfile -> md,
 323                                            sizeof (*sectinfo));
 324                       memset ((PTR) sectinfo, 0, sizeof (*sectinfo));
 325                       if (!filesym)
 326                         complain (&section_info_complaint, sym->name);
 327                       else
 328                         sectinfo->filename = (char *)filesym->name;
 329                     }
 330                   if (sectinfo->sections[index])
 331                     complain (&section_info_dup_complaint, sectinfo->filename);
 332
 333                   /* Bfd symbols are section relative. */
 334                   symaddr = sym -> value + sym -> section -> vma;
 335                   /* Relocate all non-absolute symbols by base address.  */
 336                   if (sym -> section != &bfd_abs_section)
 337                       symaddr += addr;
 338                   sectinfo->sections[index] = symaddr;
 339                 }
 340             }
 341         }
 342       do_cleanups (back_to);
 343     }
 344 }
 345
 346 /* Scan and build partial symbols for a symbol file.
 347    We have been initialized by a call to elf_symfile_init, which
 348    currently does nothing.
 349
 350    SECTION_OFFSETS is a set of offsets to apply to relocate the symbols
 351    in each section.  We simplify it down to a single offset for all
 352    symbols.  FIXME.
 353
 354    MAINLINE is true if we are reading the main symbol
 355    table (as opposed to a shared lib or dynamically loaded file).
 356
 357    This function only does the minimum work necessary for letting the
 358    user "name" things symbolically; it does not read the entire symtab.
 359    Instead, it reads the external and static symbols and puts them in partial
 360    symbol tables.  When more extensive information is requested of a
 361    file, the corresponding partial symbol table is mutated into a full
 362    fledged symbol table by going back and reading the symbols
 363    for real.
 364
 365    We look for sections with specific names, to tell us what debug
 366    format to look for:  FIXME!!!
 367
 368    dwarf_build_psymtabs() builds psymtabs for DWARF symbols;
 369    elfstab_build_psymtabs() handles STABS symbols.
 370
 371    Note that ELF files have a "minimal" symbol table, which looks a lot
 372    like a COFF symbol table, but has only the minimal information necessary
 373    for linking.  We process this also, and use the information to
 374    build gdb's minimal symbol table.  This gives us some minimal debugging
 375    capability even for files compiled without -g.  */
 376
 377 static void
 378 elf_symfile_read (objfile, section_offsets, mainline)
 379      struct objfile *objfile;
 380      struct section_offsets *section_offsets;
 381      int mainline;
 382 {
 383   bfd *abfd = objfile->obfd;
 384   struct elfinfo ei;
 385   struct cleanup *back_to;
 386   CORE_ADDR offset;
 387
 388   init_minimal_symbol_collection ();
 389   back_to = make_cleanup (discard_minimal_symbols, 0);
 390
 391   memset ((char *) &ei, 0, sizeof (ei));
 392
 393   /* Allocate struct to keep track of the symfile */
 394   objfile->sym_private = (PTR)
 395     xmmalloc (objfile -> md, sizeof (struct dbx_symfile_info));
 396   memset ((char *) objfile->sym_private, 0, sizeof (struct dbx_symfile_info));
 397   make_cleanup (free_elfinfo, (PTR) objfile);
 398
 399   /* Process the normal ELF symbol table first.  This may write some
 400      chain of info into the dbx_symfile_info in objfile->sym_private,
 401      which can later be used by elfstab_offset_sections.  */
 402
 403   /* FIXME, should take a section_offsets param, not just an offset.  */
 404   offset = ANOFFSET (section_offsets, 0);
 405   elf_symtab_read (abfd, offset, objfile);
 406
 407   /* Now process debugging information, which is contained in
 408      special ELF sections.  We first have to find them... */
 409
 410   bfd_map_over_sections (abfd, elf_locate_sections, (PTR) &ei);
 411   if (ei.dboffset && ei.lnoffset)
 412     {
 413       /* DWARF sections */
 414       dwarf_build_psymtabs (objfile,
 415                             section_offsets, mainline,
 416                             ei.dboffset, ei.dbsize,
 417                             ei.lnoffset, ei.lnsize);
 418     }
 419   if (ei.stabsect)
 420     {
 421       /* STABS sections */
 422
 423       /* FIXME:  Sun didn't really know how to implement this well.
 424          They made .stab sections that don't point to the .stabstr
 425          section with the sh_link field.  BFD doesn't make string table
 426          sections visible to the caller.  So we have to search the
 427          ELF section table, not the BFD section table, for the string
 428          table.  */
 429       struct elf32_internal_shdr *elf_sect;
 430
 431       elf_sect = bfd_elf_find_section (abfd, ".stabstr");
 432       if (elf_sect)
 433         elfstab_build_psymtabs (objfile,
 434           section_offsets,
 435           mainline,
 436           ei.stabsect->filepos,                         /* .stab offset */
 437           bfd_get_section_size_before_reloc (ei.stabsect),/* .stab size */
 438           (file_ptr) elf_sect->sh_offset,               /* .stabstr offset */
 439           elf_sect->sh_size);                           /* .stabstr size */
 440     }
 441
 442   if (!have_partial_symbols ())
 443     {
 444       wrap_here ("");
 445       printf_filtered ("(no debugging symbols found)...");
 446       wrap_here ("");
 447     }
 448
 449   /* Install any minimal symbols that have been collected as the current
 450      minimal symbols for this objfile. */
 451
 452   install_minimal_symbols (objfile);
 453
 454   do_cleanups (back_to);
 455 }
 456
 457 /* This cleans up the objfile's sym_private pointer, and the chain of
 458    stab_section_info's, that might be dangling from it.  */
 459
 460 static void
 461 free_elfinfo (objp)
 462      PTR objp;
 463 {
 464   struct objfile *objfile = (struct objfile *)objp;
 465   struct dbx_symfile_info *dbxinfo = (struct dbx_symfile_info *)
 466                                      objfile->sym_private;
 467   struct stab_section_info *ssi, *nssi;
 468
 469   ssi = dbxinfo->stab_section_info;
 470   while (ssi)
 471     {
 472       nssi = ssi->next;
 473       mfree (objfile->md, ssi);
 474       ssi = nssi;
 475     }
 476
 477   dbxinfo->stab_section_info = 0;       /* Just say No mo info about this.  */
 478 }
 479
 480
 481 /* Initialize anything that needs initializing when a completely new symbol
 482    file is specified (not just adding some symbols from another file, e.g. a
 483    shared library).
 484
 485    We reinitialize buildsym, since we may be reading stabs from an ELF file.  */
 486
 487 static void
 488 elf_new_init (ignore)
 489      struct objfile *ignore;
 490 {
 491   stabsread_new_init ();
 492   buildsym_new_init ();
 493 }
 494
 495 /* Perform any local cleanups required when we are done with a particular
 496    objfile.  I.E, we are in the process of discarding all symbol information
 497    for an objfile, freeing up all memory held for it, and unlinking the
 498    objfile struct from the global list of known objfiles. */
 499
 500 static void
 501 elf_symfile_finish (objfile)
 502      struct objfile *objfile;
 503 {
 504   if (objfile -> sym_private != NULL)
 505     {
 506       mfree (objfile -> md, objfile -> sym_private);
 507     }
 508 }
 509
 510 /* ELF specific initialization routine for reading symbols.
 511
 512    It is passed a pointer to a struct sym_fns which contains, among other
 513    things, the BFD for the file whose symbols are being read, and a slot for
 514    a pointer to "private data" which we can fill with goodies.
 515
 516    For now at least, we have nothing in particular to do, so this function is
 517    just a stub. */
 518
 519 static void
 520 elf_symfile_init (ignore)
 521      struct objfile *ignore;
 522 {
 523 }
 524
 525 /* ELF specific parsing routine for section offsets.
 526
 527    Plain and simple for now.  */
 528
 529 static
 530 struct section_offsets *
 531 elf_symfile_offsets (objfile, addr)
 532      struct objfile *objfile;
 533      CORE_ADDR addr;
 534 {
 535   struct section_offsets *section_offsets;
 536   int i;
 537
 538   section_offsets = (struct section_offsets *)
 539     obstack_alloc (&objfile -> psymbol_obstack,
 540                    sizeof (struct section_offsets) +
 541                           sizeof (section_offsets->offsets) * (SECT_OFF_MAX-1));
 542
 543   for (i = 0; i < SECT_OFF_MAX; i++)
 544     ANOFFSET (section_offsets, i) = addr;
 545
 546   return section_offsets;
 547 }
 548 \f
 549 /* When handling an ELF file that contains Sun STABS debug info,
 550    some of the debug info is relative to the particular chunk of the
 551    section that was generated in its individual .o file.  E.g.
 552    offsets to static variables are relative to the start of the data
 553    segment *for that module before linking*.  This information is
 554    painfully squirreled away in the ELF symbol table as local symbols
 555    with wierd names.  Go get 'em when needed.  */
 556
 557 void
 558 elfstab_offset_sections (objfile, pst)
 559      struct objfile *objfile;
 560      struct partial_symtab *pst;
 561 {
 562   char *filename = pst->filename;
 563   struct dbx_symfile_info *dbx = (struct dbx_symfile_info *)
 564                                  objfile->sym_private;
 565   struct stab_section_info *maybe = dbx->stab_section_info;
 566   struct stab_section_info *questionable = 0;
 567   int i;
 568   char *p;
 569
 570   /* The ELF symbol info doesn't include path names, so strip the path
 571      (if any) from the psymtab filename.  */
 572   while (0 != (p = strchr (filename, '/')))
 573     filename = p+1;
 574
 575   /* FIXME:  This linear search could speed up significantly
 576      if it was chained in the right order to match how we search it,
 577      and if we unchained when we found a match. */
 578   for (; maybe; maybe = maybe->next)
 579     {
 580       if (filename[0] == maybe->filename[0]
 581           && STREQ (filename, maybe->filename))
 582         {
 583           /* We found a match.  But there might be several source files
 584              (from different directories) with the same name.  */
 585           if (0 == maybe->found)
 586             break;
 587           questionable = maybe;         /* Might use it later.  */
 588         }
 589     }
 590
 591   if (maybe == 0 && questionable != 0)
 592     {
 593       complain (&stab_info_questionable_complaint, filename);
 594       maybe = questionable;
 595     }
 596
 597   if (maybe)
 598     {
 599       /* Found it!  Allocate a new psymtab struct, and fill it in.  */
 600       maybe->found++;
 601       pst->section_offsets = (struct section_offsets *)
 602         obstack_alloc (&objfile -> psymbol_obstack,
 603                        sizeof (struct section_offsets) +
 604                sizeof (pst->section_offsets->offsets) * (SECT_OFF_MAX-1));
 605
 606       for (i = 0; i < SECT_OFF_MAX; i++)
 607         ANOFFSET (pst->section_offsets, i) = maybe->sections[i];
 608       return;
 609     }
 610
 611   /* We were unable to find any offsets for this file.  Complain.  */
 612   if (dbx->stab_section_info)           /* If there *is* any info, */
 613     complain (&stab_info_mismatch_complaint, filename);
 614 }
 615 \f
 616 /*  Register that we are able to handle ELF object file formats and DWARF
 617     debugging formats.
 618
 619     Unlike other object file formats, where the debugging information format
 620     is implied by the object file format, the ELF object file format and the
 621     DWARF debugging information format are two distinct, and potentially
 622     separate entities.  I.E. it is perfectly possible to have ELF objects
 623     with debugging formats other than DWARF.  And it is conceivable that the
 624     DWARF debugging format might be used with another object file format,
 625     like COFF, by simply using COFF's custom section feature.
 626
 627     GDB, and to a lesser extent BFD, should support the notion of separate
 628     object file formats and debugging information formats.  For now, we just
 629     use "elf" in the same sense as "a.out" or "coff", to imply both the ELF
 630     object file format and the DWARF debugging format. */
 631
 632 static struct sym_fns elf_sym_fns =
 633 {
 634   "elf",                /* sym_name: name or name prefix of BFD target type */
 635   3,                    /* sym_namelen: number of significant sym_name chars */
 636   elf_new_init,         /* sym_new_init: init anything gbl to entire symtab */
 637   elf_symfile_init,     /* sym_init: read initial info, setup for sym_read() */
 638   elf_symfile_read,     /* sym_read: read a symbol file into symtab */
 639   elf_symfile_finish,   /* sym_finish: finished with file, cleanup */
 640   elf_symfile_offsets,  /* sym_offsets:  Translate ext. to int. relocation */
 641   NULL                  /* next: pointer to next struct sym_fns */
 642 };
 643
 644 void
 645 _initialize_elfread ()
 646 {
 647   add_symtab_fns (&elf_sym_fns);
 648 }