gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2020 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 "observable.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   symfile_add_flags add_flags = 0;
  92
  93   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  94     error (_("add-symbol-file-from-memory not supported for this target"));
  95
  96   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
  97                                          target_read_memory_bfd);
  98   if (nbfd == NULL)
  99     error (_("Failed to read a valid object file image from memory."));
 100
 101   /* Manage the new reference for the duration of this function.  */
 102   gdb_bfd_ref_ptr nbfd_holder = gdb_bfd_ref_ptr::new_reference (nbfd);
 103
 104   if (name == NULL)
 105     name = xstrdup ("shared object read from target memory");
 106   bfd_set_filename (nbfd, name);
 107
 108   if (!bfd_check_format (nbfd, bfd_object))
 109     error (_("Got object file from memory but can't read symbols: %s."),
 110            bfd_errmsg (bfd_get_error ()));
 111
 112   section_addr_info sai;
 113   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 114     if ((bfd_section_flags (sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 115       sai.emplace_back (bfd_section_vma (sec) + loadbase,
 116                         bfd_section_name (sec),
 117                         sec->index);
 118
 119   if (from_tty)
 120     add_flags |= SYMFILE_VERBOSE;
 121
 122   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 123                                    add_flags, &sai, OBJF_SHARED, NULL);
 124
 125   add_target_sections_of_objfile (objf);
 126
 127   /* This might change our ideas about frames already looked at.  */
 128   reinit_frame_cache ();
 129
 130   return objf;
 131 }
 132
 133
 134 static void
 135 add_symbol_file_from_memory_command (const char *args, int from_tty)
 136 {
 137   CORE_ADDR addr;
 138   struct bfd *templ;
 139
 140   if (args == NULL)
 141     error (_("add-symbol-file-from-memory requires an expression argument"));
 142
 143   addr = parse_and_eval_address (args);
 144
 145   /* We need some representative bfd to know the target we are looking at.  */
 146   if (symfile_objfile != NULL)
 147     templ = symfile_objfile->obfd;
 148   else
 149     templ = exec_bfd;
 150   if (templ == NULL)
 151     error (_("Must use symbol-file or exec-file "
 152              "before add-symbol-file-from-memory."));
 153
 154   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 155 }
 156
 157 /* Try to add the symbols for the vsyscall page, if there is one.
 158    This function is called via the inferior_created observer.  */
 159
 160 static void
 161 add_vsyscall_page (struct target_ops *target, int from_tty)
 162 {
 163   struct mem_range vsyscall_range;
 164
 165   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 166     {
 167       struct bfd *bfd;
 168
 169       if (core_bfd != NULL)
 170         bfd = core_bfd;
 171       else if (exec_bfd != NULL)
 172         bfd = exec_bfd;
 173       else
 174        /* FIXME: cagney/2004-05-06: Should not require an existing
 175           BFD when trying to create a run-time BFD of the VSYSCALL
 176           page in the inferior.  Unfortunately that's the current
 177           interface so for the moment bail.  Introducing a
 178           ``bfd_runtime'' (a BFD created using the loaded image) file
 179           format should fix this.  */
 180         {
 181           warning (_("Could not load vsyscall page "
 182                      "because no executable was specified"));
 183           return;
 184         }
 185
 186       char *name = xstrprintf ("system-supplied DSO at %s",
 187                                paddress (target_gdbarch (), vsyscall_range.start));
 188       try
 189         {
 190           /* Pass zero for FROM_TTY, because the action of loading the
 191              vsyscall DSO was not triggered by the user, even if the
 192              user typed "run" at the TTY.  */
 193           symbol_file_add_from_memory (bfd,
 194                                        vsyscall_range.start,
 195                                        vsyscall_range.length,
 196                                        name,
 197                                        0 /* from_tty */);
 198         }
 199       catch (const gdb_exception &ex)
 200         {
 201           exception_print (gdb_stderr, ex);
 202         }
 203     }
 204 }
 205
 206 void
 207 _initialize_symfile_mem (void)
 208 {
 209   add_cmd ("add-symbol-file-from-memory", class_files,
 210            add_symbol_file_from_memory_command,
 211            _("Load the symbols out of memory from a "
 212              "dynamically loaded object file.\n"
 213              "Give an expression for the address "
 214              "of the file's shared object file header."),
 215            &cmdlist);
 216
 217   /* Want to know of each new inferior so that its vsyscall info can
 218      be extracted.  */
 219   gdb::observers::inferior_created.attach (add_vsyscall_page);
 220 }