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   add_target_sections_of_objfile (objf);
 135
 136   /* This might change our ideas about frames already looked at.  */
 137   reinit_frame_cache ();
 138
 139   do_cleanups (cleanup);
 140   return objf;
 141 }
 142
 143
 144 static void
 145 add_symbol_file_from_memory_command (char *args, int from_tty)
 146 {
 147   CORE_ADDR addr;
 148   struct bfd *templ;
 149
 150   if (args == NULL)
 151     error (_("add-symbol-file-from-memory requires an expression argument"));
 152
 153   addr = parse_and_eval_address (args);
 154
 155   /* We need some representative bfd to know the target we are looking at.  */
 156   if (symfile_objfile != NULL)
 157     templ = symfile_objfile->obfd;
 158   else
 159     templ = exec_bfd;
 160   if (templ == NULL)
 161     error (_("Must use symbol-file or exec-file "
 162              "before add-symbol-file-from-memory."));
 163
 164   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 165 }
 166
 167 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 168
 169 struct symbol_file_add_from_memory_args
 170 {
 171   struct bfd *bfd;
 172   CORE_ADDR sysinfo_ehdr;
 173   size_t size;
 174   char *name;
 175   int from_tty;
 176 };
 177
 178 /* Wrapper function for symbol_file_add_from_memory, for
 179    catch_exceptions.  */
 180
 181 static int
 182 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 183 {
 184   struct symbol_file_add_from_memory_args *args = data;
 185
 186   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->size,
 187                                args->name, args->from_tty);
 188   return 0;
 189 }
 190
 191 /* Rummage through mappings to find the vsyscall page size.  */
 192
 193 static int
 194 find_vdso_size (CORE_ADDR vaddr, unsigned long size,
 195                 int read, int write, int exec, int modified,
 196                 void *data)
 197 {
 198   struct symbol_file_add_from_memory_args *args = data;
 199
 200   if (vaddr == args->sysinfo_ehdr)
 201     {
 202       args->size = size;
 203       return 1;
 204     }
 205   return 0;
 206 }
 207
 208 /* Try to add the symbols for the vsyscall page, if there is one.
 209    This function is called via the inferior_created observer.  */
 210
 211 static void
 212 add_vsyscall_page (struct target_ops *target, int from_tty)
 213 {
 214   CORE_ADDR sysinfo_ehdr;
 215
 216   if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
 217       && sysinfo_ehdr != (CORE_ADDR) 0)
 218     {
 219       struct bfd *bfd;
 220       struct symbol_file_add_from_memory_args args;
 221
 222       if (core_bfd != NULL)
 223         bfd = core_bfd;
 224       else if (exec_bfd != NULL)
 225         bfd = exec_bfd;
 226       else
 227        /* FIXME: cagney/2004-05-06: Should not require an existing
 228           BFD when trying to create a run-time BFD of the VSYSCALL
 229           page in the inferior.  Unfortunately that's the current
 230           interface so for the moment bail.  Introducing a
 231           ``bfd_runtime'' (a BFD created using the loaded image) file
 232           format should fix this.  */
 233         {
 234           warning (_("Could not load vsyscall page "
 235                      "because no executable was specified\n"
 236                      "try using the \"file\" command first."));
 237           return;
 238         }
 239       args.bfd = bfd;
 240       args.sysinfo_ehdr = sysinfo_ehdr;
 241       args.size = 0;
 242       if (gdbarch_find_memory_regions_p (target_gdbarch ()))
 243         (void) gdbarch_find_memory_regions (target_gdbarch (),
 244                                             find_vdso_size, &args);
 245
 246       args.name = xstrprintf ("system-supplied DSO at %s",
 247                               paddress (target_gdbarch (), sysinfo_ehdr));
 248       /* Pass zero for FROM_TTY, because the action of loading the
 249          vsyscall DSO was not triggered by the user, even if the user
 250          typed "run" at the TTY.  */
 251       args.from_tty = 0;
 252       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 253                         &args, RETURN_MASK_ALL);
 254     }
 255 }
 256
 257 \f
 258
 259 /* Provide a prototype to silence -Wmissing-prototypes.  */
 260 extern initialize_file_ftype _initialize_symfile_mem;
 261
 262 void
 263 _initialize_symfile_mem (void)
 264 {
 265   add_cmd ("add-symbol-file-from-memory", class_files,
 266            add_symbol_file_from_memory_command,
 267            _("Load the symbols out of memory from a "
 268              "dynamically loaded object file.\n"
 269              "Give an expression for the address "
 270              "of the file's shared object file header."),
 271            &cmdlist);
 272
 273   /* Want to know of each new inferior so that its vsyscall info can
 274      be extracted.  */
 275   observer_attach_inferior_created (add_vsyscall_page);
 276 }