gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-1987, 1989, 1991, 1994-1996, 1998, 2000-2005,
   4    2007-2012 Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 /* This file defines functions (and commands to exercise those
  22    functions) for reading debugging information from object files
  23    whose images are mapped directly into the inferior's memory.  For
  24    example, the Linux kernel maps a "syscall DSO" into each process's
  25    address space; this DSO provides kernel-specific code for some
  26    system calls.
  27
  28    At the moment, BFD only has functions for parsing object files from
  29    memory for the ELF format, even though the general idea isn't
  30    ELF-specific.  This means that BFD only provides the functions GDB
  31    needs when configured for ELF-based targets.  So these functions
  32    may only be compiled on ELF-based targets.
  33
  34    GDB has no idea whether it has been configured for an ELF-based
  35    target or not: it just tries to handle whatever files it is given.
  36    But this means there are no preprocessor symbols on which we could
  37    make these functions' compilation conditional.
  38
  39    So, for the time being, we put these functions alone in this file,
  40    and have .mt files reference them as appropriate.  In the future, I
  41    hope BFD will provide a format-independent bfd_from_remote_memory
  42    entry point.  */
  43
  44
  45 #include "defs.h"
  46 #include "symtab.h"
  47 #include "gdbcore.h"
  48 #include "objfiles.h"
  49 #include "exceptions.h"
  50 #include "gdbcmd.h"
  51 #include "target.h"
  52 #include "value.h"
  53 #include "symfile.h"
  54 #include "observer.h"
  55 #include "auxv.h"
  56 #include "elf/common.h"
  57
  58
  59 /* Read inferior memory at ADDR to find the header of a loaded object file
  60    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  61    representing the target's format.  NAME is the name to use for this
  62    symbol file in messages; it can be NULL or a malloc-allocated string
  63    which will be attached to the BFD.  */
  64 static struct objfile *
  65 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  66                              int from_tty)
  67 {
  68   struct objfile *objf;
  69   struct bfd *nbfd;
  70   struct bfd_section *sec;
  71   bfd_vma loadbase;
  72   struct section_addr_info *sai;
  73   unsigned int i;
  74   struct cleanup *cleanup;
  75
  76   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  77     error (_("add-symbol-file-from-memory not supported for this target"));
  78
  79   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
  80                                          target_read_memory);
  81   if (nbfd == NULL)
  82     error (_("Failed to read a valid object file image from memory."));
  83
  84   if (name == NULL)
  85     nbfd->filename = xstrdup ("shared object read from target memory");
  86   else
  87     nbfd->filename = name;
  88
  89   if (!bfd_check_format (nbfd, bfd_object))
  90     {
  91       /* FIXME: should be checking for errors from bfd_close (for one thing,
  92          on error it does not free all the storage associated with the
  93          bfd).  */
  94       bfd_close (nbfd);
  95       error (_("Got object file from memory but can't read symbols: %s."),
  96              bfd_errmsg (bfd_get_error ()));
  97     }
  98
  99   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 100   cleanup = make_cleanup (xfree, sai);
 101   i = 0;
 102   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 103     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 104       {
 105         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 106         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 107         sai->other[i].sectindex = sec->index;
 108         ++i;
 109       }
 110
 111   objf = symbol_file_add_from_bfd (nbfd, from_tty ? SYMFILE_VERBOSE : 0,
 112                                    sai, OBJF_SHARED, NULL);
 113
 114   /* This might change our ideas about frames already looked at.  */
 115   reinit_frame_cache ();
 116
 117   do_cleanups (cleanup);
 118   return objf;
 119 }
 120
 121
 122 static void
 123 add_symbol_file_from_memory_command (char *args, int from_tty)
 124 {
 125   CORE_ADDR addr;
 126   struct bfd *templ;
 127
 128   if (args == NULL)
 129     error (_("add-symbol-file-from-memory requires an expression argument"));
 130
 131   addr = parse_and_eval_address (args);
 132
 133   /* We need some representative bfd to know the target we are looking at.  */
 134   if (symfile_objfile != NULL)
 135     templ = symfile_objfile->obfd;
 136   else
 137     templ = exec_bfd;
 138   if (templ == NULL)
 139     error (_("Must use symbol-file or exec-file "
 140              "before add-symbol-file-from-memory."));
 141
 142   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 143 }
 144
 145 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 146
 147 struct symbol_file_add_from_memory_args
 148 {
 149   struct bfd *bfd;
 150   CORE_ADDR sysinfo_ehdr;
 151   char *name;
 152   int from_tty;
 153 };
 154
 155 /* Wrapper function for symbol_file_add_from_memory, for
 156    catch_exceptions.  */
 157
 158 static int
 159 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 160 {
 161   struct symbol_file_add_from_memory_args *args = data;
 162
 163   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 164                                args->from_tty);
 165   return 0;
 166 }
 167
 168 /* Try to add the symbols for the vsyscall page, if there is one.
 169    This function is called via the inferior_created observer.  */
 170
 171 static void
 172 add_vsyscall_page (struct target_ops *target, int from_tty)
 173 {
 174   CORE_ADDR sysinfo_ehdr;
 175
 176   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 177       && sysinfo_ehdr != (CORE_ADDR) 0)
 178     {
 179       struct bfd *bfd;
 180       struct symbol_file_add_from_memory_args args;
 181
 182       if (core_bfd != NULL)
 183         bfd = core_bfd;
 184       else if (exec_bfd != NULL)
 185         bfd = exec_bfd;
 186       else
 187        /* FIXME: cagney/2004-05-06: Should not require an existing
 188           BFD when trying to create a run-time BFD of the VSYSCALL
 189           page in the inferior.  Unfortunately that's the current
 190           interface so for the moment bail.  Introducing a
 191           ``bfd_runtime'' (a BFD created using the loaded image) file
 192           format should fix this.  */
 193         {
 194           warning (_("Could not load vsyscall page "
 195                      "because no executable was specified\n"
 196                      "try using the \"file\" command first."));
 197           return;
 198         }
 199       args.bfd = bfd;
 200       args.sysinfo_ehdr = sysinfo_ehdr;
 201       args.name = xstrprintf ("system-supplied DSO at %s",
 202                               paddress (target_gdbarch, sysinfo_ehdr));
 203       /* Pass zero for FROM_TTY, because the action of loading the
 204          vsyscall DSO was not triggered by the user, even if the user
 205          typed "run" at the TTY.  */
 206       args.from_tty = 0;
 207       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 208                         &args, RETURN_MASK_ALL);
 209     }
 210 }
 211
 212 \f
 213
 214 /* Provide a prototype to silence -Wmissing-prototypes.  */
 215 extern initialize_file_ftype _initialize_symfile_mem;
 216
 217 void
 218 _initialize_symfile_mem (void)
 219 {
 220   add_cmd ("add-symbol-file-from-memory", class_files,
 221            add_symbol_file_from_memory_command,
 222            _("Load the symbols out of memory from a "
 223              "dynamically loaded object file.\n"
 224              "Give an expression for the address "
 225              "of the file's shared object file header."),
 226            &cmdlist);
 227
 228   /* Want to know of each new inferior so that its vsyscall info can
 229      be extracted.  */
 230   observer_attach_inferior_created (add_vsyscall_page);
 231 }