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   /* Manage the new reference for the duration of this function.  */
 105   gdb_bfd_ref_ptr nbfd_holder = new_bfd_ref (nbfd);
 106
 107   xfree (bfd_get_filename (nbfd));
 108   if (name == NULL)
 109     nbfd->filename = xstrdup ("shared object read from target memory");
 110   else
 111     nbfd->filename = name;
 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   cleanup = 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   if (from_tty)
 131     add_flags |= SYMFILE_VERBOSE;
 132
 133   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 134                                    add_flags, sai, OBJF_SHARED, NULL);
 135
 136   add_target_sections_of_objfile (objf);
 137
 138   /* This might change our ideas about frames already looked at.  */
 139   reinit_frame_cache ();
 140
 141   do_cleanups (cleanup);
 142   return objf;
 143 }
 144
 145
 146 static void
 147 add_symbol_file_from_memory_command (const char *args, int from_tty)
 148 {
 149   CORE_ADDR addr;
 150   struct bfd *templ;
 151
 152   if (args == NULL)
 153     error (_("add-symbol-file-from-memory requires an expression argument"));
 154
 155   addr = parse_and_eval_address (args);
 156
 157   /* We need some representative bfd to know the target we are looking at.  */
 158   if (symfile_objfile != NULL)
 159     templ = symfile_objfile->obfd;
 160   else
 161     templ = exec_bfd;
 162   if (templ == NULL)
 163     error (_("Must use symbol-file or exec-file "
 164              "before add-symbol-file-from-memory."));
 165
 166   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 167 }
 168
 169 /* Try to add the symbols for the vsyscall page, if there is one.
 170    This function is called via the inferior_created observer.  */
 171
 172 static void
 173 add_vsyscall_page (struct target_ops *target, int from_tty)
 174 {
 175   struct mem_range vsyscall_range;
 176
 177   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 178     {
 179       struct bfd *bfd;
 180
 181       if (core_bfd != NULL)
 182         bfd = core_bfd;
 183       else if (exec_bfd != NULL)
 184         bfd = exec_bfd;
 185       else
 186        /* FIXME: cagney/2004-05-06: Should not require an existing
 187           BFD when trying to create a run-time BFD of the VSYSCALL
 188           page in the inferior.  Unfortunately that's the current
 189           interface so for the moment bail.  Introducing a
 190           ``bfd_runtime'' (a BFD created using the loaded image) file
 191           format should fix this.  */
 192         {
 193           warning (_("Could not load vsyscall page "
 194                      "because no executable was specified"));
 195           return;
 196         }
 197
 198       char *name = xstrprintf ("system-supplied DSO at %s",
 199                                paddress (target_gdbarch (), vsyscall_range.start));
 200       TRY
 201         {
 202           /* Pass zero for FROM_TTY, because the action of loading the
 203              vsyscall DSO was not triggered by the user, even if the
 204              user typed "run" at the TTY.  */
 205           symbol_file_add_from_memory (bfd,
 206                                        vsyscall_range.start,
 207                                        vsyscall_range.length,
 208                                        name,
 209                                        0 /* from_tty */);
 210         }
 211       CATCH (ex, RETURN_MASK_ALL)
 212         {
 213           exception_print (gdb_stderr, ex);
 214         }
 215       END_CATCH
 216     }
 217 }
 218
 219 void
 220 _initialize_symfile_mem (void)
 221 {
 222   add_cmd ("add-symbol-file-from-memory", class_files,
 223            add_symbol_file_from_memory_command,
 224            _("Load the symbols out of memory from a "
 225              "dynamically loaded object file.\n"
 226              "Give an expression for the address "
 227              "of the file's shared object file header."),
 228            &cmdlist);
 229
 230   /* Want to know of each new inferior so that its vsyscall info can
 231      be extracted.  */
 232   observer_attach_inferior_created (add_vsyscall_page);
 233 }