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 #include "gdb_bfd.h"
  58
  59 /* Verify parameters of target_read_memory_bfd and target_read_memory are
  60    compatible.  */
  61
  62 gdb_static_assert (sizeof (CORE_ADDR) == sizeof (bfd_vma));
  63 gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte));
  64 gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type));
  65
  66 /* Provide bfd/ compatible prototype for target_read_memory.  Casting would not
  67    be enough as LEN width may differ.  */
  68
  69 static int
  70 target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
  71 {
  72   /* MYADDR must be already allocated for the LEN size so it has to fit in
  73      ssize_t.  */
  74   gdb_assert ((ssize_t) len == len);
  75
  76   return target_read_memory (memaddr, myaddr, len);
  77 }
  78
  79 /* Read inferior memory at ADDR to find the header of a loaded object file
  80    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  81    representing the target's format.  NAME is the name to use for this
  82    symbol file in messages; it can be NULL or a malloc-allocated string
  83    which will be attached to the BFD.  */
  84 static struct objfile *
  85 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  86                              int from_tty)
  87 {
  88   struct objfile *objf;
  89   struct bfd *nbfd;
  90   struct bfd_section *sec;
  91   bfd_vma loadbase;
  92   struct section_addr_info *sai;
  93   unsigned int i;
  94   struct cleanup *cleanup;
  95
  96   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  97     error (_("add-symbol-file-from-memory not supported for this target"));
  98
  99   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
 100                                          target_read_memory_bfd);
 101   if (nbfd == NULL)
 102     error (_("Failed to read a valid object file image from memory."));
 103
 104   gdb_bfd_ref (nbfd);
 105   if (name == NULL)
 106     nbfd->filename = xstrdup ("shared object read from target memory");
 107   else
 108     nbfd->filename = name;
 109
 110   if (!bfd_check_format (nbfd, bfd_object))
 111     {
 112       make_cleanup_bfd_close (nbfd);
 113       error (_("Got object file from memory but can't read symbols: %s."),
 114              bfd_errmsg (bfd_get_error ()));
 115     }
 116
 117   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 118   cleanup = make_cleanup (xfree, sai);
 119   i = 0;
 120   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 121     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 122       {
 123         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 124         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 125         sai->other[i].sectindex = sec->index;
 126         ++i;
 127       }
 128
 129   objf = symbol_file_add_from_bfd (nbfd, from_tty ? SYMFILE_VERBOSE : 0,
 130                                    sai, OBJF_SHARED, NULL);
 131
 132   /* This might change our ideas about frames already looked at.  */
 133   reinit_frame_cache ();
 134
 135   do_cleanups (cleanup);
 136   return objf;
 137 }
 138
 139
 140 static void
 141 add_symbol_file_from_memory_command (char *args, int from_tty)
 142 {
 143   CORE_ADDR addr;
 144   struct bfd *templ;
 145
 146   if (args == NULL)
 147     error (_("add-symbol-file-from-memory requires an expression argument"));
 148
 149   addr = parse_and_eval_address (args);
 150
 151   /* We need some representative bfd to know the target we are looking at.  */
 152   if (symfile_objfile != NULL)
 153     templ = symfile_objfile->obfd;
 154   else
 155     templ = exec_bfd;
 156   if (templ == NULL)
 157     error (_("Must use symbol-file or exec-file "
 158              "before add-symbol-file-from-memory."));
 159
 160   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 161 }
 162
 163 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 164
 165 struct symbol_file_add_from_memory_args
 166 {
 167   struct bfd *bfd;
 168   CORE_ADDR sysinfo_ehdr;
 169   char *name;
 170   int from_tty;
 171 };
 172
 173 /* Wrapper function for symbol_file_add_from_memory, for
 174    catch_exceptions.  */
 175
 176 static int
 177 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 178 {
 179   struct symbol_file_add_from_memory_args *args = data;
 180
 181   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 182                                args->from_tty);
 183   return 0;
 184 }
 185
 186 /* Try to add the symbols for the vsyscall page, if there is one.
 187    This function is called via the inferior_created observer.  */
 188
 189 static void
 190 add_vsyscall_page (struct target_ops *target, int from_tty)
 191 {
 192   CORE_ADDR sysinfo_ehdr;
 193
 194   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 195       && sysinfo_ehdr != (CORE_ADDR) 0)
 196     {
 197       struct bfd *bfd;
 198       struct symbol_file_add_from_memory_args args;
 199
 200       if (core_bfd != NULL)
 201         bfd = core_bfd;
 202       else if (exec_bfd != NULL)
 203         bfd = exec_bfd;
 204       else
 205        /* FIXME: cagney/2004-05-06: Should not require an existing
 206           BFD when trying to create a run-time BFD of the VSYSCALL
 207           page in the inferior.  Unfortunately that's the current
 208           interface so for the moment bail.  Introducing a
 209           ``bfd_runtime'' (a BFD created using the loaded image) file
 210           format should fix this.  */
 211         {
 212           warning (_("Could not load vsyscall page "
 213                      "because no executable was specified\n"
 214                      "try using the \"file\" command first."));
 215           return;
 216         }
 217       args.bfd = bfd;
 218       args.sysinfo_ehdr = sysinfo_ehdr;
 219       args.name = xstrprintf ("system-supplied DSO at %s",
 220                               paddress (target_gdbarch, sysinfo_ehdr));
 221       /* Pass zero for FROM_TTY, because the action of loading the
 222          vsyscall DSO was not triggered by the user, even if the user
 223          typed "run" at the TTY.  */
 224       args.from_tty = 0;
 225       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 226                         &args, RETURN_MASK_ALL);
 227     }
 228 }
 229
 230 \f
 231
 232 /* Provide a prototype to silence -Wmissing-prototypes.  */
 233 extern initialize_file_ftype _initialize_symfile_mem;
 234
 235 void
 236 _initialize_symfile_mem (void)
 237 {
 238   add_cmd ("add-symbol-file-from-memory", class_files,
 239            add_symbol_file_from_memory_command,
 240            _("Load the symbols out of memory from a "
 241              "dynamically loaded object file.\n"
 242              "Give an expression for the address "
 243              "of the file's shared object file header."),
 244            &cmdlist);
 245
 246   /* Want to know of each new inferior so that its vsyscall info can
 247      be extracted.  */
 248   observer_attach_inferior_created (add_vsyscall_page);
 249 }