gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2014 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.  SIZE, if
  80    non-zero, is the known size of the object.  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,
  86                              size_t size, char *name, 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, size, &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   xfree (bfd_get_filename (nbfd));
 106   if (name == NULL)
 107     nbfd->filename = xstrdup ("shared object read from target memory");
 108   else
 109     nbfd->filename = name;
 110
 111   cleanup = make_cleanup_bfd_unref (nbfd);
 112
 113   if (!bfd_check_format (nbfd, bfd_object))
 114     error (_("Got object file from memory but can't read symbols: %s."),
 115            bfd_errmsg (bfd_get_error ()));
 116
 117   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 118   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   sai->num_sections = i;
 129
 130   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 131                                    from_tty ? SYMFILE_VERBOSE : 0,
 132                                    sai, OBJF_SHARED, NULL);
 133
 134   /* This might change our ideas about frames already looked at.  */
 135   reinit_frame_cache ();
 136
 137   do_cleanups (cleanup);
 138   return objf;
 139 }
 140
 141
 142 static void
 143 add_symbol_file_from_memory_command (char *args, int from_tty)
 144 {
 145   CORE_ADDR addr;
 146   struct bfd *templ;
 147
 148   if (args == NULL)
 149     error (_("add-symbol-file-from-memory requires an expression argument"));
 150
 151   addr = parse_and_eval_address (args);
 152
 153   /* We need some representative bfd to know the target we are looking at.  */
 154   if (symfile_objfile != NULL)
 155     templ = symfile_objfile->obfd;
 156   else
 157     templ = exec_bfd;
 158   if (templ == NULL)
 159     error (_("Must use symbol-file or exec-file "
 160              "before add-symbol-file-from-memory."));
 161
 162   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 163 }
 164
 165 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 166
 167 struct symbol_file_add_from_memory_args
 168 {
 169   struct bfd *bfd;
 170   CORE_ADDR sysinfo_ehdr;
 171   size_t size;
 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->size,
 185                                args->name, args->from_tty);
 186   return 0;
 187 }
 188
 189 /* Rummage through mappings to find the vsyscall page size.  */
 190
 191 static int
 192 find_vdso_size (CORE_ADDR vaddr, unsigned long size,
 193                 int read, int write, int exec, int modified,
 194                 void *data)
 195 {
 196   struct symbol_file_add_from_memory_args *args = data;
 197
 198   if (vaddr == args->sysinfo_ehdr)
 199     {
 200       args->size = size;
 201       return 1;
 202     }
 203   return 0;
 204 }
 205
 206 /* Try to add the symbols for the vsyscall page, if there is one.
 207    This function is called via the inferior_created observer.  */
 208
 209 static void
 210 add_vsyscall_page (struct target_ops *target, int from_tty)
 211 {
 212   CORE_ADDR sysinfo_ehdr;
 213
 214   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 215       && sysinfo_ehdr != (CORE_ADDR) 0)
 216     {
 217       struct bfd *bfd;
 218       struct symbol_file_add_from_memory_args args;
 219
 220       if (core_bfd != NULL)
 221         bfd = core_bfd;
 222       else if (exec_bfd != NULL)
 223         bfd = exec_bfd;
 224       else
 225        /* FIXME: cagney/2004-05-06: Should not require an existing
 226           BFD when trying to create a run-time BFD of the VSYSCALL
 227           page in the inferior.  Unfortunately that's the current
 228           interface so for the moment bail.  Introducing a
 229           ``bfd_runtime'' (a BFD created using the loaded image) file
 230           format should fix this.  */
 231         {
 232           warning (_("Could not load vsyscall page "
 233                      "because no executable was specified\n"
 234                      "try using the \"file\" command first."));
 235           return;
 236         }
 237       args.bfd = bfd;
 238       args.sysinfo_ehdr = sysinfo_ehdr;
 239       args.size = 0;
 240       if (gdbarch_find_memory_regions_p (target_gdbarch ()))
 241         (void) gdbarch_find_memory_regions (target_gdbarch (),
 242                                             find_vdso_size, &args);
 243
 244       args.name = xstrprintf ("system-supplied DSO at %s",
 245                               paddress (target_gdbarch (), sysinfo_ehdr));
 246       /* Pass zero for FROM_TTY, because the action of loading the
 247          vsyscall DSO was not triggered by the user, even if the user
 248          typed "run" at the TTY.  */
 249       args.from_tty = 0;
 250       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 251                         &args, RETURN_MASK_ALL);
 252     }
 253 }
 254
 255 \f
 256
 257 /* Provide a prototype to silence -Wmissing-prototypes.  */
 258 extern initialize_file_ftype _initialize_symfile_mem;
 259
 260 void
 261 _initialize_symfile_mem (void)
 262 {
 263   add_cmd ("add-symbol-file-from-memory", class_files,
 264            add_symbol_file_from_memory_command,
 265            _("Load the symbols out of memory from a "
 266              "dynamically loaded object file.\n"
 267              "Give an expression for the address "
 268              "of the file's shared object file header."),
 269            &cmdlist);
 270
 271   /* Want to know of each new inferior so that its vsyscall info can
 272      be extracted.  */
 273   observer_attach_inferior_created (add_vsyscall_page);
 274 }