gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2013 Free Software Foundation, Inc.
   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 3 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, see <http://www.gnu.org/licenses/>.  */
  19
  20 /* This file defines functions (and commands to exercise those
  21    functions) for reading debugging information from object files
  22    whose images are mapped directly into the inferior's memory.  For
  23    example, the Linux kernel maps a "syscall DSO" into each process's
  24    address space; this DSO provides kernel-specific code for some
  25    system calls.
  26
  27    At the moment, BFD only has functions for parsing object files from
  28    memory for the ELF format, even though the general idea isn't
  29    ELF-specific.  This means that BFD only provides the functions GDB
  30    needs when configured for ELF-based targets.  So these functions
  31    may only be compiled on ELF-based targets.
  32
  33    GDB has no idea whether it has been configured for an ELF-based
  34    target or not: it just tries to handle whatever files it is given.
  35    But this means there are no preprocessor symbols on which we could
  36    make these functions' compilation conditional.
  37
  38    So, for the time being, we put these functions alone in this file,
  39    and have .mt files reference them as appropriate.  In the future, I
  40    hope BFD will provide a format-independent bfd_from_remote_memory
  41    entry point.  */
  42
  43
  44 #include "defs.h"
  45 #include "symtab.h"
  46 #include "gdbcore.h"
  47 #include "objfiles.h"
  48 #include "exceptions.h"
  49 #include "gdbcmd.h"
  50 #include "target.h"
  51 #include "value.h"
  52 #include "symfile.h"
  53 #include "observer.h"
  54 #include "auxv.h"
  55 #include "elf/common.h"
  56 #include "gdb_bfd.h"
  57
  58 /* Verify parameters of target_read_memory_bfd and target_read_memory are
  59    compatible.  */
  60
  61 gdb_static_assert (sizeof (CORE_ADDR) == sizeof (bfd_vma));
  62 gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte));
  63 gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type));
  64
  65 /* Provide bfd/ compatible prototype for target_read_memory.  Casting would not
  66    be enough as LEN width may differ.  */
  67
  68 static int
  69 target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
  70 {
  71   /* MYADDR must be already allocated for the LEN size so it has to fit in
  72      ssize_t.  */
  73   gdb_assert ((ssize_t) len == len);
  74
  75   return target_read_memory (memaddr, myaddr, len);
  76 }
  77
  78 /* Read inferior memory at ADDR to find the header of a loaded object file
  79    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  80    representing the target's format.  NAME is the name to use for this
  81    symbol file in messages; it can be NULL or a malloc-allocated string
  82    which will be attached to the BFD.  */
  83 static struct objfile *
  84 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  85                              int from_tty)
  86 {
  87   struct objfile *objf;
  88   struct bfd *nbfd;
  89   struct bfd_section *sec;
  90   bfd_vma loadbase;
  91   struct section_addr_info *sai;
  92   unsigned int i;
  93   struct cleanup *cleanup;
  94
  95   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  96     error (_("add-symbol-file-from-memory not supported for this target"));
  97
  98   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
  99                                          target_read_memory_bfd);
 100   if (nbfd == NULL)
 101     error (_("Failed to read a valid object file image from memory."));
 102
 103   gdb_bfd_ref (nbfd);
 104   if (name == NULL)
 105     nbfd->filename = "shared object read from target memory";
 106   else
 107     {
 108       nbfd->filename = name;
 109       gdb_bfd_stash_filename (nbfd);
 110       xfree (name);
 111     }
 112
 113   cleanup = make_cleanup_bfd_unref (nbfd);
 114
 115   if (!bfd_check_format (nbfd, bfd_object))
 116     error (_("Got object file from memory but can't read symbols: %s."),
 117            bfd_errmsg (bfd_get_error ()));
 118
 119   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 120   make_cleanup (xfree, sai);
 121   i = 0;
 122   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 123     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 124       {
 125         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 126         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 127         sai->other[i].sectindex = sec->index;
 128         ++i;
 129       }
 130   sai->num_sections = i;
 131
 132   objf = symbol_file_add_from_bfd (nbfd, from_tty ? SYMFILE_VERBOSE : 0,
 133                                    sai, OBJF_SHARED, NULL);
 134
 135   /* This might change our ideas about frames already looked at.  */
 136   reinit_frame_cache ();
 137
 138   do_cleanups (cleanup);
 139   return objf;
 140 }
 141
 142
 143 static void
 144 add_symbol_file_from_memory_command (char *args, int from_tty)
 145 {
 146   CORE_ADDR addr;
 147   struct bfd *templ;
 148
 149   if (args == NULL)
 150     error (_("add-symbol-file-from-memory requires an expression argument"));
 151
 152   addr = parse_and_eval_address (args);
 153
 154   /* We need some representative bfd to know the target we are looking at.  */
 155   if (symfile_objfile != NULL)
 156     templ = symfile_objfile->obfd;
 157   else
 158     templ = exec_bfd;
 159   if (templ == NULL)
 160     error (_("Must use symbol-file or exec-file "
 161              "before add-symbol-file-from-memory."));
 162
 163   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 164 }
 165
 166 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 167
 168 struct symbol_file_add_from_memory_args
 169 {
 170   struct bfd *bfd;
 171   CORE_ADDR sysinfo_ehdr;
 172   char *name;
 173   int from_tty;
 174 };
 175
 176 /* Wrapper function for symbol_file_add_from_memory, for
 177    catch_exceptions.  */
 178
 179 static int
 180 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 181 {
 182   struct symbol_file_add_from_memory_args *args = data;
 183
 184   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 185                                args->from_tty);
 186   return 0;
 187 }
 188
 189 /* Try to add the symbols for the vsyscall page, if there is one.
 190    This function is called via the inferior_created observer.  */
 191
 192 static void
 193 add_vsyscall_page (struct target_ops *target, int from_tty)
 194 {
 195   CORE_ADDR sysinfo_ehdr;
 196
 197   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 198       && sysinfo_ehdr != (CORE_ADDR) 0)
 199     {
 200       struct bfd *bfd;
 201       struct symbol_file_add_from_memory_args args;
 202
 203       if (core_bfd != NULL)
 204         bfd = core_bfd;
 205       else if (exec_bfd != NULL)
 206         bfd = exec_bfd;
 207       else
 208        /* FIXME: cagney/2004-05-06: Should not require an existing
 209           BFD when trying to create a run-time BFD of the VSYSCALL
 210           page in the inferior.  Unfortunately that's the current
 211           interface so for the moment bail.  Introducing a
 212           ``bfd_runtime'' (a BFD created using the loaded image) file
 213           format should fix this.  */
 214         {
 215           warning (_("Could not load vsyscall page "
 216                      "because no executable was specified\n"
 217                      "try using the \"file\" command first."));
 218           return;
 219         }
 220       args.bfd = bfd;
 221       args.sysinfo_ehdr = sysinfo_ehdr;
 222       args.name = xstrprintf ("system-supplied DSO at %s",
 223                               paddress (target_gdbarch (), sysinfo_ehdr));
 224       /* Pass zero for FROM_TTY, because the action of loading the
 225          vsyscall DSO was not triggered by the user, even if the user
 226          typed "run" at the TTY.  */
 227       args.from_tty = 0;
 228       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 229                         &args, RETURN_MASK_ALL);
 230     }
 231 }
 232
 233 \f
 234
 235 /* Provide a prototype to silence -Wmissing-prototypes.  */
 236 extern initialize_file_ftype _initialize_symfile_mem;
 237
 238 void
 239 _initialize_symfile_mem (void)
 240 {
 241   add_cmd ("add-symbol-file-from-memory", class_files,
 242            add_symbol_file_from_memory_command,
 243            _("Load the symbols out of memory from a "
 244              "dynamically loaded object file.\n"
 245              "Give an expression for the address "
 246              "of the file's shared object file header."),
 247            &cmdlist);
 248
 249   /* Want to know of each new inferior so that its vsyscall info can
 250      be extracted.  */
 251   observer_attach_inferior_created (add_vsyscall_page);
 252 }