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   struct target_section *sections, *sections_end, *tsec;
  96
  97   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  98     error (_("add-symbol-file-from-memory not supported for this target"));
  99
 100   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
 101                                          target_read_memory_bfd);
 102   if (nbfd == NULL)
 103     error (_("Failed to read a valid object file image from memory."));
 104
 105   gdb_bfd_ref (nbfd);
 106   xfree (bfd_get_filename (nbfd));
 107   if (name == NULL)
 108     nbfd->filename = xstrdup ("shared object read from target memory");
 109   else
 110     nbfd->filename = name;
 111
 112   cleanup = make_cleanup_bfd_unref (nbfd);
 113
 114   if (!bfd_check_format (nbfd, bfd_object))
 115     error (_("Got object file from memory but can't read symbols: %s."),
 116            bfd_errmsg (bfd_get_error ()));
 117
 118   sai = alloc_section_addr_info (bfd_count_sections (nbfd));
 119   make_cleanup (xfree, sai);
 120   i = 0;
 121   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 122     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 123       {
 124         sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
 125         sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
 126         sai->other[i].sectindex = sec->index;
 127         ++i;
 128       }
 129   sai->num_sections = i;
 130
 131   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 132                                    from_tty ? SYMFILE_VERBOSE : 0,
 133                                    sai, OBJF_SHARED, NULL);
 134
 135   sections = NULL;
 136   sections_end = NULL;
 137
 138   if (build_section_table (nbfd, &sections, &sections_end) == 0)
 139     {
 140       make_cleanup (xfree, sections);
 141
 142       /* Adjust the target section addresses by the load address.  */
 143       for (tsec = sections; tsec != sections_end; ++tsec)
 144         {
 145           tsec->addr += loadbase;
 146           tsec->endaddr += loadbase;
 147         }
 148
 149       add_target_sections (&nbfd, sections, sections_end);
 150     }
 151
 152   /* This might change our ideas about frames already looked at.  */
 153   reinit_frame_cache ();
 154
 155   do_cleanups (cleanup);
 156   return objf;
 157 }
 158
 159
 160 static void
 161 add_symbol_file_from_memory_command (char *args, int from_tty)
 162 {
 163   CORE_ADDR addr;
 164   struct bfd *templ;
 165
 166   if (args == NULL)
 167     error (_("add-symbol-file-from-memory requires an expression argument"));
 168
 169   addr = parse_and_eval_address (args);
 170
 171   /* We need some representative bfd to know the target we are looking at.  */
 172   if (symfile_objfile != NULL)
 173     templ = symfile_objfile->obfd;
 174   else
 175     templ = exec_bfd;
 176   if (templ == NULL)
 177     error (_("Must use symbol-file or exec-file "
 178              "before add-symbol-file-from-memory."));
 179
 180   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 181 }
 182
 183 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 184
 185 struct symbol_file_add_from_memory_args
 186 {
 187   struct bfd *bfd;
 188   CORE_ADDR sysinfo_ehdr;
 189   size_t size;
 190   char *name;
 191   int from_tty;
 192 };
 193
 194 /* Wrapper function for symbol_file_add_from_memory, for
 195    catch_exceptions.  */
 196
 197 static int
 198 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 199 {
 200   struct symbol_file_add_from_memory_args *args = data;
 201
 202   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->size,
 203                                args->name, args->from_tty);
 204   return 0;
 205 }
 206
 207 /* Rummage through mappings to find the vsyscall page size.  */
 208
 209 static int
 210 find_vdso_size (CORE_ADDR vaddr, unsigned long size,
 211                 int read, int write, int exec, int modified,
 212                 void *data)
 213 {
 214   struct symbol_file_add_from_memory_args *args = data;
 215
 216   if (vaddr == args->sysinfo_ehdr)
 217     {
 218       args->size = size;
 219       return 1;
 220     }
 221   return 0;
 222 }
 223
 224 /* Try to add the symbols for the vsyscall page, if there is one.
 225    This function is called via the inferior_created observer.  */
 226
 227 static void
 228 add_vsyscall_page (struct target_ops *target, int from_tty)
 229 {
 230   CORE_ADDR sysinfo_ehdr;
 231
 232   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 233       && sysinfo_ehdr != (CORE_ADDR) 0)
 234     {
 235       struct bfd *bfd;
 236       struct symbol_file_add_from_memory_args args;
 237
 238       if (core_bfd != NULL)
 239         bfd = core_bfd;
 240       else if (exec_bfd != NULL)
 241         bfd = exec_bfd;
 242       else
 243        /* FIXME: cagney/2004-05-06: Should not require an existing
 244           BFD when trying to create a run-time BFD of the VSYSCALL
 245           page in the inferior.  Unfortunately that's the current
 246           interface so for the moment bail.  Introducing a
 247           ``bfd_runtime'' (a BFD created using the loaded image) file
 248           format should fix this.  */
 249         {
 250           warning (_("Could not load vsyscall page "
 251                      "because no executable was specified\n"
 252                      "try using the \"file\" command first."));
 253           return;
 254         }
 255       args.bfd = bfd;
 256       args.sysinfo_ehdr = sysinfo_ehdr;
 257       args.size = 0;
 258       if (gdbarch_find_memory_regions_p (target_gdbarch ()))
 259         (void) gdbarch_find_memory_regions (target_gdbarch (),
 260                                             find_vdso_size, &args);
 261
 262       args.name = xstrprintf ("system-supplied DSO at %s",
 263                               paddress (target_gdbarch (), sysinfo_ehdr));
 264       /* Pass zero for FROM_TTY, because the action of loading the
 265          vsyscall DSO was not triggered by the user, even if the user
 266          typed "run" at the TTY.  */
 267       args.from_tty = 0;
 268       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 269                         &args, RETURN_MASK_ALL);
 270     }
 271 }
 272
 273 \f
 274
 275 /* Provide a prototype to silence -Wmissing-prototypes.  */
 276 extern initialize_file_ftype _initialize_symfile_mem;
 277
 278 void
 279 _initialize_symfile_mem (void)
 280 {
 281   add_cmd ("add-symbol-file-from-memory", class_files,
 282            add_symbol_file_from_memory_command,
 283            _("Load the symbols out of memory from a "
 284              "dynamically loaded object file.\n"
 285              "Give an expression for the address "
 286              "of the file's shared object file header."),
 287            &cmdlist);
 288
 289   /* Want to know of each new inferior so that its vsyscall info can
 290      be extracted.  */
 291   observer_attach_inferior_created (add_vsyscall_page);
 292 }