gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2015 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 "gdbcmd.h"
  49 #include "target.h"
  50 #include "value.h"
  51 #include "symfile.h"
  52 #include "observer.h"
  53 #include "auxv.h"
  54 #include "elf/common.h"
  55 #include "gdb_bfd.h"
  56
  57 /* Verify parameters of target_read_memory_bfd and target_read_memory are
  58    compatible.  */
  59
  60 gdb_static_assert (sizeof (CORE_ADDR) == sizeof (bfd_vma));
  61 gdb_static_assert (sizeof (gdb_byte) == sizeof (bfd_byte));
  62 gdb_static_assert (sizeof (ssize_t) <= sizeof (bfd_size_type));
  63
  64 /* Provide bfd/ compatible prototype for target_read_memory.  Casting would not
  65    be enough as LEN width may differ.  */
  66
  67 static int
  68 target_read_memory_bfd (bfd_vma memaddr, bfd_byte *myaddr, bfd_size_type len)
  69 {
  70   /* MYADDR must be already allocated for the LEN size so it has to fit in
  71      ssize_t.  */
  72   gdb_assert ((ssize_t) len == len);
  73
  74   return target_read_memory (memaddr, myaddr, len);
  75 }
  76
  77 /* Read inferior memory at ADDR to find the header of a loaded object file
  78    and read its in-core symbols out of inferior memory.  SIZE, if
  79    non-zero, is the known size of the object.  TEMPL is a bfd
  80    representing the target's format.  NAME is the name to use for this
  81    symbol file in messages; it can be NULL or a malloc-allocated string
  82    which will be attached to the BFD.  */
  83 static struct objfile *
  84 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr,
  85                              size_t size, char *name, int from_tty)
  86 {
  87   struct objfile *objf;
  88   struct bfd *nbfd;
  89   struct bfd_section *sec;
  90   bfd_vma loadbase;
  91   struct section_addr_info *sai;
  92   unsigned int i;
  93   struct cleanup *cleanup;
  94
  95   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  96     error (_("add-symbol-file-from-memory not supported for this target"));
  97
  98   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
  99                                          target_read_memory_bfd);
 100   if (nbfd == NULL)
 101     error (_("Failed to read a valid object file image from memory."));
 102
 103   gdb_bfd_ref (nbfd);
 104   xfree (bfd_get_filename (nbfd));
 105   if (name == NULL)
 106     nbfd->filename = xstrdup ("shared object read from target memory");
 107   else
 108     nbfd->filename = name;
 109
 110   cleanup = make_cleanup_bfd_unref (nbfd);
 111
 112   if (!bfd_check_format (nbfd, bfd_object))
 113     error (_("Got object file from memory but can't read symbols: %s."),
 114            bfd_errmsg (bfd_get_error ()));
 115
 116   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 117   make_cleanup (xfree, sai);
 118   i = 0;
 119   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 120     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 121       {
 122         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 123         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 124         sai->other[i].sectindex = sec->index;
 125         ++i;
 126       }
 127   sai->num_sections = i;
 128
 129   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 130                                    from_tty ? SYMFILE_VERBOSE : 0,
 131                                    sai, OBJF_SHARED, NULL);
 132
 133   add_target_sections_of_objfile (objf);
 134
 135   /* This might change our ideas about frames already looked at.  */
 136   reinit_frame_cache ();
 137
 138   do_cleanups (cleanup);
 139   return objf;
 140 }
 141
 142
 143 static void
 144 add_symbol_file_from_memory_command (char *args, int from_tty)
 145 {
 146   CORE_ADDR addr;
 147   struct bfd *templ;
 148
 149   if (args == NULL)
 150     error (_("add-symbol-file-from-memory requires an expression argument"));
 151
 152   addr = parse_and_eval_address (args);
 153
 154   /* We need some representative bfd to know the target we are looking at.  */
 155   if (symfile_objfile != NULL)
 156     templ = symfile_objfile->obfd;
 157   else
 158     templ = exec_bfd;
 159   if (templ == NULL)
 160     error (_("Must use symbol-file or exec-file "
 161              "before add-symbol-file-from-memory."));
 162
 163   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 164 }
 165
 166 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 167
 168 struct symbol_file_add_from_memory_args
 169 {
 170   struct bfd *bfd;
 171   CORE_ADDR sysinfo_ehdr;
 172   size_t size;
 173   char *name;
 174   int from_tty;
 175 };
 176
 177 /* Wrapper function for symbol_file_add_from_memory, for
 178    catch_exceptions.  */
 179
 180 static int
 181 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 182 {
 183   struct symbol_file_add_from_memory_args *args = data;
 184
 185   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->size,
 186                                args->name, args->from_tty);
 187   return 0;
 188 }
 189
 190 /* Try to add the symbols for the vsyscall page, if there is one.
 191    This function is called via the inferior_created observer.  */
 192
 193 static void
 194 add_vsyscall_page (struct target_ops *target, int from_tty)
 195 {
 196   struct mem_range vsyscall_range;
 197
 198   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 199     {
 200       struct bfd *bfd;
 201       struct symbol_file_add_from_memory_args args;
 202
 203       if (core_bfd != NULL)
 204         bfd = core_bfd;
 205       else if (exec_bfd != NULL)
 206         bfd = exec_bfd;
 207       else
 208        /* FIXME: cagney/2004-05-06: Should not require an existing
 209           BFD when trying to create a run-time BFD of the VSYSCALL
 210           page in the inferior.  Unfortunately that's the current
 211           interface so for the moment bail.  Introducing a
 212           ``bfd_runtime'' (a BFD created using the loaded image) file
 213           format should fix this.  */
 214         {
 215           warning (_("Could not load vsyscall page "
 216                      "because no executable was specified\n"
 217                      "try using the \"file\" command first."));
 218           return;
 219         }
 220       args.bfd = bfd;
 221       args.sysinfo_ehdr = vsyscall_range.start;
 222       args.size = vsyscall_range.length;
 223
 224       args.name = xstrprintf ("system-supplied DSO at %s",
 225                               paddress (target_gdbarch (), vsyscall_range.start));
 226       /* Pass zero for FROM_TTY, because the action of loading the
 227          vsyscall DSO was not triggered by the user, even if the user
 228          typed "run" at the TTY.  */
 229       args.from_tty = 0;
 230       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 231                         &args, RETURN_MASK_ALL);
 232     }
 233 }
 234
 235 \f
 236
 237 /* Provide a prototype to silence -Wmissing-prototypes.  */
 238 extern initialize_file_ftype _initialize_symfile_mem;
 239
 240 void
 241 _initialize_symfile_mem (void)
 242 {
 243   add_cmd ("add-symbol-file-from-memory", class_files,
 244            add_symbol_file_from_memory_command,
 245            _("Load the symbols out of memory from a "
 246              "dynamically loaded object file.\n"
 247              "Give an expression for the address "
 248              "of the file's shared object file header."),
 249            &cmdlist);
 250
 251   /* Want to know of each new inferior so that its vsyscall info can
 252      be extracted.  */
 253   observer_attach_inferior_created (add_vsyscall_page);
 254 }