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   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   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 (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 /* Arguments for symbol_file_add_from_memory_wrapper.  */
 170
 171 struct symbol_file_add_from_memory_args
 172 {
 173   struct bfd *bfd;
 174   CORE_ADDR sysinfo_ehdr;
 175   size_t size;
 176   char *name;
 177   int from_tty;
 178 };
 179
 180 /* Wrapper function for symbol_file_add_from_memory, for
 181    catch_exceptions.  */
 182
 183 static int
 184 symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
 185 {
 186   struct symbol_file_add_from_memory_args *args
 187     = (struct symbol_file_add_from_memory_args *) data;
 188
 189   symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->size,
 190                                args->name, args->from_tty);
 191   return 0;
 192 }
 193
 194 /* Try to add the symbols for the vsyscall page, if there is one.
 195    This function is called via the inferior_created observer.  */
 196
 197 static void
 198 add_vsyscall_page (struct target_ops *target, int from_tty)
 199 {
 200   struct mem_range vsyscall_range;
 201
 202   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 203     {
 204       struct bfd *bfd;
 205       struct symbol_file_add_from_memory_args args;
 206
 207       if (core_bfd != NULL)
 208         bfd = core_bfd;
 209       else if (exec_bfd != NULL)
 210         bfd = exec_bfd;
 211       else
 212        /* FIXME: cagney/2004-05-06: Should not require an existing
 213           BFD when trying to create a run-time BFD of the VSYSCALL
 214           page in the inferior.  Unfortunately that's the current
 215           interface so for the moment bail.  Introducing a
 216           ``bfd_runtime'' (a BFD created using the loaded image) file
 217           format should fix this.  */
 218         {
 219           warning (_("Could not load vsyscall page "
 220                      "because no executable was specified"));
 221           return;
 222         }
 223       args.bfd = bfd;
 224       args.sysinfo_ehdr = vsyscall_range.start;
 225       args.size = vsyscall_range.length;
 226
 227       args.name = xstrprintf ("system-supplied DSO at %s",
 228                               paddress (target_gdbarch (), vsyscall_range.start));
 229       /* Pass zero for FROM_TTY, because the action of loading the
 230          vsyscall DSO was not triggered by the user, even if the user
 231          typed "run" at the TTY.  */
 232       args.from_tty = 0;
 233       catch_exceptions (current_uiout, symbol_file_add_from_memory_wrapper,
 234                         &args, RETURN_MASK_ALL);
 235     }
 236 }
 237
 238 \f
 239
 240 /* Provide a prototype to silence -Wmissing-prototypes.  */
 241 extern initialize_file_ftype _initialize_symfile_mem;
 242
 243 void
 244 _initialize_symfile_mem (void)
 245 {
 246   add_cmd ("add-symbol-file-from-memory", class_files,
 247            add_symbol_file_from_memory_command,
 248            _("Load the symbols out of memory from a "
 249              "dynamically loaded object file.\n"
 250              "Give an expression for the address "
 251              "of the file's shared object file header."),
 252            &cmdlist);
 253
 254   /* Want to know of each new inferior so that its vsyscall info can
 255      be extracted.  */
 256   observer_attach_inferior_created (add_vsyscall_page);
 257 }