gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright 1986, 1987, 1989, 1991, 1994, 1995, 1996, 1998, 2000,
   4    2001, 2002, 2003, 2004 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 2 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, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330,
  21    Boston, MA 02111-1307, USA.  */
  22
  23 /* This file defines functions (and commands to exercise those
  24    functions) for reading debugging information from object files
  25    whose images are mapped directly into the inferior's memory.  For
  26    example, the Linux kernel maps a "syscall DSO" into each process's
  27    address space; this DSO provides kernel-specific code for some
  28    system calls.
  29
  30    At the moment, BFD only has functions for parsing object files from
  31    memory for the ELF format, even though the general idea isn't
  32    ELF-specific.  This means that BFD only provides the functions GDB
  33    needs when configured for ELF-based targets.  So these functions
  34    may only be compiled on ELF-based targets.
  35
  36    GDB has no idea whether it has been configured for an ELF-based
  37    target or not: it just tries to handle whatever files it is given.
  38    But this means there are no preprocessor symbols on which we could
  39    make these functions' compilation conditional.
  40
  41    So, for the time being, we put these functions alone in this file,
  42    and have .mt files reference them as appropriate.  In the future, I
  43    hope BFD will provide a format-independent bfd_from_remote_memory
  44    entry point.  */
  45
  46
  47 #include "defs.h"
  48 #include "symtab.h"
  49 #include "gdbcore.h"
  50 #include "objfiles.h"
  51 #include "exceptions.h"
  52 #include "gdbcmd.h"
  53 #include "target.h"
  54 #include "value.h"
  55 #include "symfile.h"
  56 #include "observer.h"
  57 #include "auxv.h"
  58 #include "elf/common.h"
  59
  60
  61 /* FIXME: cagney/2005-01-27: Should be a function with the signature:
  62    int (void *object, const bfd_byte *myaddr, int len).  */
  63
  64 static int
  65 do_target_read_memory (bfd_vma vma, char *myaddr, int len)
  66 {
  67   return target_read_memory (vma, myaddr, len);
  68 }
  69
  70 /* Read inferior memory at ADDR to find the header of a loaded object file
  71    and read its in-core symbols out of inferior memory.  TEMPL is a bfd
  72    representing the target's format.  NAME is the name to use for this
  73    symbol file in messages; it can be NULL or a malloc-allocated string
  74    which will be attached to the BFD.  */
  75 static struct objfile *
  76 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
  77                              int from_tty)
  78 {
  79   struct objfile *objf;
  80   struct bfd *nbfd;
  81   struct bfd_section *sec;
  82   bfd_vma loadbase;
  83   struct section_addr_info *sai;
  84   unsigned int i;
  85
  86   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  87     error (_("add-symbol-file-from-memory not supported for this target"));
  88
  89   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
  90                                          do_target_read_memory);
  91   if (nbfd == NULL)
  92     error (_("Failed to read a valid object file image from memory."));
  93
  94   if (name == NULL)
  95     nbfd->filename = xstrdup ("shared object read from target memory");
  96   else
  97     nbfd->filename = name;
  98
  99   if (!bfd_check_format (nbfd, bfd_object))
 100     {
 101       /* FIXME: should be checking for errors from bfd_close (for one thing,
 102          on error it does not free all the storage associated with the
 103          bfd).  */
 104       bfd_close (nbfd);
 105       error (_("Got object file from memory but can't read symbols: %s."),
 106              bfd_errmsg (bfd_get_error ()));
 107     }
 108
 109   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 110   make_cleanup (xfree, sai);
 111   i = 0;
 112   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 113     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 114       {
 115         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 116         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 117         sai->other[i].sectindex = sec->index;
 118         ++i;
 119       }
 120
 121   objf = symbol_file_add_from_bfd (nbfd, from_tty,
 122                                    sai, 0, OBJF_SHARED);
 123
 124   /* This might change our ideas about frames already looked at.  */
 125   reinit_frame_cache ();
 126
 127   return objf;
 128 }
 129
 130
 131 static void
 132 add_symbol_file_from_memory_command (char *args, int from_tty)
 133 {
 134   CORE_ADDR addr;
 135   struct bfd *templ;
 136
 137   if (args == NULL)
 138     error (_("add-symbol-file-from-memory requires an expression argument"));
 139
 140   addr = parse_and_eval_address (args);
 141
 142   /* We need some representative bfd to know the target we are looking at.  */
 143   if (symfile_objfile != NULL)
 144     templ = symfile_objfile->obfd;
 145   else
 146     templ = exec_bfd;
 147   if (templ == NULL)
 148     error (_("\
 149 Must use symbol-file or exec-file before add-symbol-file-from-memory."));
 150
 151   symbol_file_add_from_memory (templ, addr, NULL, from_tty);
 152 }
 153
 154 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 155
 156 struct symbol_file_add_from_memory_args
 157 {
 158   struct bfd *bfd;
 159   CORE_ADDR sysinfo_ehdr;
 160   char *name;
 161   int from_tty;
 162 };
 163
 164 /* Wrapper function for symbol_file_add_from_memory, for
 165    catch_exceptions.  */
 166
 167 static int
 168 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 169 {
 170   struct symbol_file_add_from_memory_args *args = data;
 171
 172   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
 173                                args->from_tty);
 174   return 0;
 175 }
 176
 177 /* Try to add the symbols for the vsyscall page, if there is one.  This function
 178    is called via the inferior_created observer.  */
 179
 180 static void
 181 add_vsyscall_page (struct target_ops *target, int from_tty)
 182 {
 183   CORE_ADDR sysinfo_ehdr;
 184
 185   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 186       && sysinfo_ehdr != (CORE_ADDR) 0)
 187     {
 188       struct bfd *bfd;
 189       struct symbol_file_add_from_memory_args args;
 190
 191       if (core_bfd != NULL)
 192         bfd = core_bfd;
 193       else if (exec_bfd != NULL)
 194         bfd = exec_bfd;
 195       else
 196        /* FIXME: cagney/2004-05-06: Should not require an existing
 197           BFD when trying to create a run-time BFD of the VSYSCALL
 198           page in the inferior.  Unfortunately that's the current
 199           interface so for the moment bail.  Introducing a
 200           ``bfd_runtime'' (a BFD created using the loaded image) file
 201           format should fix this.  */
 202         {
 203           warning (_("\
 204 Could not load vsyscall page because no executable was specified\n\
 205 try using the \"file\" command first."));
 206           return;
 207         }
 208       args.bfd = bfd;
 209       args.sysinfo_ehdr = sysinfo_ehdr;
 210       xasprintf (&args.name, "system-supplied DSO at 0x%s",
 211                  paddr_nz (sysinfo_ehdr));
 212       /* Pass zero for FROM_TTY, because the action of loading the
 213          vsyscall DSO was not triggered by the user, even if the user
 214          typed "run" at the TTY.  */
 215       args.from_tty = 0;
 216       catch_exceptions (uiout, symbol_file_add_from_memory_wrapper,
 217                         &args, RETURN_MASK_ALL);
 218     }
 219 }
 220
 221 \f
 222 void
 223 _initialize_symfile_mem (void)
 224 {
 225   add_cmd ("add-symbol-file-from-memory", class_files,
 226            add_symbol_file_from_memory_command, _("\
 227 Load the symbols out of memory from a dynamically loaded object file.\n\
 228 Give an expression for the address of the file's shared object file header."),
 229            &cmdlist);
 230
 231   /* Want to know of each new inferior so that its vsyscall info can
 232      be extracted.  */
 233   observer_attach_inferior_created (add_vsyscall_page);
 234 }