gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2017 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   symfile_add_flags add_flags = 0;
  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   /* Manage the new reference for the duration of this function.  */
 106   gdb_bfd_ref_ptr nbfd_holder (nbfd);
 107
 108   xfree (bfd_get_filename (nbfd));
 109   if (name == NULL)
 110     nbfd->filename = xstrdup ("shared object read from target memory");
 111   else
 112     nbfd->filename = name;
 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   cleanup = 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   if (from_tty)
 132     add_flags |= SYMFILE_VERBOSE;
 133
 134   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 135                                    add_flags, sai, OBJF_SHARED, NULL);
 136
 137   add_target_sections_of_objfile (objf);
 138
 139   /* This might change our ideas about frames already looked at.  */
 140   reinit_frame_cache ();
 141
 142   do_cleanups (cleanup);
 143   return objf;
 144 }
 145
 146
 147 static void
 148 add_symbol_file_from_memory_command (const char *args, int from_tty)
 149 {
 150   CORE_ADDR addr;
 151   struct bfd *templ;
 152
 153   if (args == NULL)
 154     error (_("add-symbol-file-from-memory requires an expression argument"));
 155
 156   addr = parse_and_eval_address (args);
 157
 158   /* We need some representative bfd to know the target we are looking at.  */
 159   if (symfile_objfile != NULL)
 160     templ = symfile_objfile->obfd;
 161   else
 162     templ = exec_bfd;
 163   if (templ == NULL)
 164     error (_("Must use symbol-file or exec-file "
 165              "before add-symbol-file-from-memory."));
 166
 167   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 168 }
 169
 170 /* Try to add the symbols for the vsyscall page, if there is one.
 171    This function is called via the inferior_created observer.  */
 172
 173 static void
 174 add_vsyscall_page (struct target_ops *target, int from_tty)
 175 {
 176   struct mem_range vsyscall_range;
 177
 178   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 179     {
 180       struct bfd *bfd;
 181
 182       if (core_bfd != NULL)
 183         bfd = core_bfd;
 184       else if (exec_bfd != NULL)
 185         bfd = exec_bfd;
 186       else
 187        /* FIXME: cagney/2004-05-06: Should not require an existing
 188           BFD when trying to create a run-time BFD of the VSYSCALL
 189           page in the inferior.  Unfortunately that's the current
 190           interface so for the moment bail.  Introducing a
 191           ``bfd_runtime'' (a BFD created using the loaded image) file
 192           format should fix this.  */
 193         {
 194           warning (_("Could not load vsyscall page "
 195                      "because no executable was specified"));
 196           return;
 197         }
 198
 199       char *name = xstrprintf ("system-supplied DSO at %s",
 200                                paddress (target_gdbarch (), vsyscall_range.start));
 201       TRY
 202         {
 203           /* Pass zero for FROM_TTY, because the action of loading the
 204              vsyscall DSO was not triggered by the user, even if the
 205              user typed "run" at the TTY.  */
 206           symbol_file_add_from_memory (bfd,
 207                                        vsyscall_range.start,
 208                                        vsyscall_range.length,
 209                                        name,
 210                                        0 /* from_tty */);
 211         }
 212       CATCH (ex, RETURN_MASK_ALL)
 213         {
 214           exception_print (gdb_stderr, ex);
 215         }
 216       END_CATCH
 217     }
 218 }
 219
 220 void
 221 _initialize_symfile_mem (void)
 222 {
 223   add_cmd ("add-symbol-file-from-memory", class_files,
 224            add_symbol_file_from_memory_command,
 225            _("Load the symbols out of memory from a "
 226              "dynamically loaded object file.\n"
 227              "Give an expression for the address "
 228              "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 }