gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986, 1987, 1989, 1991, 1994, 1995, 1996, 1998, 2000, 2001,
   4    2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010, 2011
   5    Free Software Foundation, Inc.
   6
   7    This file is part of GDB.
   8
   9    This program is free software; you can redistribute it and/or modify
  10    it under the terms of the GNU General Public License as published by
  11    the Free Software Foundation; either version 3 of the License, or
  12    (at your option) any later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 /* This file defines functions (and commands to exercise those
  23    functions) for reading debugging information from object files
  24    whose images are mapped directly into the inferior's memory.  For
  25    example, the Linux kernel maps a "syscall DSO" into each process's
  26    address space; this DSO provides kernel-specific code for some
  27    system calls.
  28
  29    At the moment, BFD only has functions for parsing object files from
  30    memory for the ELF format, even though the general idea isn't
  31    ELF-specific.  This means that BFD only provides the functions GDB
  32    needs when configured for ELF-based targets.  So these functions
  33    may only be compiled on ELF-based targets.
  34
  35    GDB has no idea whether it has been configured for an ELF-based
  36    target or not: it just tries to handle whatever files it is given.
  37    But this means there are no preprocessor symbols on which we could
  38    make these functions' compilation conditional.
  39
  40    So, for the time being, we put these functions alone in this file,
  41    and have .mt files reference them as appropriate.  In the future, I
  42    hope BFD will provide a format-independent bfd_from_remote_memory
  43    entry point.  */
  44
  45
  46 #include "defs.h"
  47 #include "symtab.h"
  48 #include "gdbcore.h"
  49 #include "objfiles.h"
  50 #include "exceptions.h"
  51 #include "gdbcmd.h"
  52 #include "target.h"
  53 #include "value.h"
  54 #include "symfile.h"
  55 #include "observer.h"
  56 #include "auxv.h"
  57 #include "elf/common.h"
  58
  59
  60 /* Read inferior memory at ADDR to find the header of a loaded object file
  61    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  62    representing the target's format.  NAME is the name to use for this
  63    symbol file in messages; it can be NULL or a malloc-allocated string
  64    which will be attached to the BFD.  */
  65 static struct objfile *
  66 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  67                              int from_tty)
  68 {
  69   struct objfile *objf;
  70   struct bfd *nbfd;
  71   struct bfd_section *sec;
  72   bfd_vma loadbase;
  73   struct section_addr_info *sai;
  74   unsigned int i;
  75   struct cleanup *cleanup;
  76
  77   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  78     error (_("add-symbol-file-from-memory not supported for this target"));
  79
  80   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
  81                                          target_read_memory);
  82   if (nbfd == NULL)
  83     error (_("Failed to read a valid object file image from memory."));
  84
  85   if (name == NULL)
  86     nbfd->filename = xstrdup ("shared object read from target memory");
  87   else
  88     nbfd->filename = name;
  89
  90   if (!bfd_check_format (nbfd, bfd_object))
  91     {
  92       /* FIXME: should be checking for errors from bfd_close (for one thing,
  93          on error it does not free all the storage associated with the
  94          bfd).  */
  95       bfd_close (nbfd);
  96       error (_("Got object file from memory but can't read symbols: %s."),
  97              bfd_errmsg (bfd_get_error ()));
  98     }
  99
 100   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 101   cleanup = make_cleanup (xfree, sai);
 102   i = 0;
 103   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 104     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 105       {
 106         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 107         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 108         sai->other[i].sectindex = sec->index;
 109         ++i;
 110       }
 111
 112   objf = symbol_file_add_from_bfd (nbfd, from_tty ? SYMFILE_VERBOSE : 0,
 113                                    sai, OBJF_SHARED, NULL);
 114
 115   /* This might change our ideas about frames already looked at.  */
 116   reinit_frame_cache ();
 117
 118   do_cleanups (cleanup);
 119   return objf;
 120 }
 121
 122
 123 static void
 124 add_symbol_file_from_memory_command (char *args, int from_tty)
 125 {
 126   CORE_ADDR addr;
 127   struct bfd *templ;
 128
 129   if (args == NULL)
 130     error (_("add-symbol-file-from-memory requires an expression argument"));
 131
 132   addr = parse_and_eval_address (args);
 133
 134   /* We need some representative bfd to know the target we are looking at.  */
 135   if (symfile_objfile != NULL)
 136     templ = symfile_objfile->obfd;
 137   else
 138     templ = exec_bfd;
 139   if (templ == NULL)
 140     error (_("Must use symbol-file or exec-file "
 141              "before add-symbol-file-from-memory."));
 142
 143   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 144 }
 145
 146 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 147
 148 struct symbol_file_add_from_memory_args
 149 {
 150   struct bfd *bfd;
 151   CORE_ADDR sysinfo_ehdr;
 152   char *name;
 153   int from_tty;
 154 };
 155
 156 /* Wrapper function for symbol_file_add_from_memory, for
 157    catch_exceptions.  */
 158
 159 static int
 160 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 161 {
 162   struct symbol_file_add_from_memory_args *args = data;
 163
 164   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 165                                args->from_tty);
 166   return 0;
 167 }
 168
 169 /* Try to add the symbols for the vsyscall page, if there is one.
 170    This function is called via the inferior_created observer.  */
 171
 172 static void
 173 add_vsyscall_page (struct target_ops *target, int from_tty)
 174 {
 175   CORE_ADDR sysinfo_ehdr;
 176
 177   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 178       && sysinfo_ehdr != (CORE_ADDR) 0)
 179     {
 180       struct bfd *bfd;
 181       struct symbol_file_add_from_memory_args args;
 182
 183       if (core_bfd != NULL)
 184         bfd = core_bfd;
 185       else if (exec_bfd != NULL)
 186         bfd = exec_bfd;
 187       else
 188        /* FIXME: cagney/2004-05-06: Should not require an existing
 189           BFD when trying to create a run-time BFD of the VSYSCALL
 190           page in the inferior.  Unfortunately that's the current
 191           interface so for the moment bail.  Introducing a
 192           ``bfd_runtime'' (a BFD created using the loaded image) file
 193           format should fix this.  */
 194         {
 195           warning (_("Could not load vsyscall page "
 196                      "because no executable was specified\n"
 197                      "try using the \"file\" command first."));
 198           return;
 199         }
 200       args.bfd = bfd;
 201       args.sysinfo_ehdr = sysinfo_ehdr;
 202       args.name = xstrprintf ("system-supplied DSO at %s",
 203                               paddress (target_gdbarch, sysinfo_ehdr));
 204       /* Pass zero for FROM_TTY, because the action of loading the
 205          vsyscall DSO was not triggered by the user, even if the user
 206          typed "run" at the TTY.  */
 207       args.from_tty = 0;
 208       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 209                         &args, RETURN_MASK_ALL);
 210     }
 211 }
 212
 213 \f
 214
 215 /* Provide a prototype to silence -Wmissing-prototypes.  */
 216 extern initialize_file_ftype _initialize_symfile_mem;
 217
 218 void
 219 _initialize_symfile_mem (void)
 220 {
 221   add_cmd ("add-symbol-file-from-memory", class_files,
 222            add_symbol_file_from_memory_command,
 223            _("Load the symbols out of memory from a "
 224              "dynamically loaded object file.\n"
 225              "Give an expression for the address "
 226              "of the file's shared object file header."),
 227            &cmdlist);
 228
 229   /* Want to know of each new inferior so that its vsyscall info can
 230      be extracted.  */
 231   observer_attach_inferior_created (add_vsyscall_page);
 232 }