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
  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   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);
 113
 114   /* This might change our ideas about frames already looked at.  */
 115   reinit_frame_cache ();
 116
 117   return objf;
 118 }
 119
 120
 121 static void
 122 add_symbol_file_from_memory_command (char *args, int from_tty)
 123 {
 124   CORE_ADDR addr;
 125   struct bfd *templ;
 126
 127   if (args == NULL)
 128     error (_("add-symbol-file-from-memory requires an expression argument"));
 129
 130   addr = parse_and_eval_address (args);
 131
 132   /* We need some representative bfd to know the target we are looking at.  */
 133   if (symfile_objfile != NULL)
 134     templ = symfile_objfile->obfd;
 135   else
 136     templ = exec_bfd;
 137   if (templ == NULL)
 138     error (_("\
 139 Must use symbol-file or exec-file before add-symbol-file-from-memory."));
 140
 141   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 142 }
 143
 144 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 145
 146 struct symbol_file_add_from_memory_args
 147 {
 148   struct bfd *bfd;
 149   CORE_ADDR sysinfo_ehdr;
 150   char *name;
 151   int from_tty;
 152 };
 153
 154 /* Wrapper function for symbol_file_add_from_memory, for
 155    catch_exceptions.  */
 156
 157 static int
 158 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 159 {
 160   struct symbol_file_add_from_memory_args *args = data;
 161
 162   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 163                                args->from_tty);
 164   return 0;
 165 }
 166
 167 /* Try to add the symbols for the vsyscall page, if there is one.  This function
 168    is called via the inferior_created observer.  */
 169
 170 static void
 171 add_vsyscall_page (struct target_ops *target, int from_tty)
 172 {
 173   CORE_ADDR sysinfo_ehdr;
 174
 175   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 176       && sysinfo_ehdr != (CORE_ADDR) 0)
 177     {
 178       struct bfd *bfd;
 179       struct symbol_file_add_from_memory_args args;
 180
 181       if (core_bfd != NULL)
 182         bfd = core_bfd;
 183       else if (exec_bfd != NULL)
 184         bfd = exec_bfd;
 185       else
 186        /* FIXME: cagney/2004-05-06: Should not require an existing
 187           BFD when trying to create a run-time BFD of the VSYSCALL
 188           page in the inferior.  Unfortunately that's the current
 189           interface so for the moment bail.  Introducing a
 190           ``bfd_runtime'' (a BFD created using the loaded image) file
 191           format should fix this.  */
 192         {
 193           warning (_("\
 194 Could not load vsyscall page because no executable was specified\n\
 195 try using the \"file\" command first."));
 196           return;
 197         }
 198       args.bfd = bfd;
 199       args.sysinfo_ehdr = sysinfo_ehdr;
 200       args.name = xstrprintf ("system-supplied DSO at %s",
 201                               paddress (target_gdbarch, sysinfo_ehdr));
 202       /* Pass zero for FROM_TTY, because the action of loading the
 203          vsyscall DSO was not triggered by the user, even if the user
 204          typed "run" at the TTY.  */
 205       args.from_tty = 0;
 206       catch_exceptions (uiout, symbol_file_add_from_memory_wrapper,
 207                         &args, RETURN_MASK_ALL);
 208     }
 209 }
 210
 211 \f
 212
 213 /* Provide a prototype to silence -Wmissing-prototypes.  */
 214 extern initialize_file_ftype _initialize_symfile_mem;
 215
 216 void
 217 _initialize_symfile_mem (void)
 218 {
 219   add_cmd ("add-symbol-file-from-memory", class_files,
 220            add_symbol_file_from_memory_command, _("\
 221 Load the symbols out of memory from a dynamically loaded object file.\n\
 222 Give an expression for the address of the file's shared object file header."),
 223            &cmdlist);
 224
 225   /* Want to know of each new inferior so that its vsyscall info can
 226      be extracted.  */
 227   observer_attach_inferior_created (add_vsyscall_page);
 228 }