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.  */
  82 static struct objfile *
  83 symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr,
  84                              size_t size, const char *name, int from_tty)
  85 {
  86   struct objfile *objf;
  87   struct bfd *nbfd;
  88   struct bfd_section *sec;
  89   bfd_vma loadbase;
  90   symfile_add_flags add_flags = 0;
  91
  92   if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
  93     error (_("add-symbol-file-from-memory not supported for this target"));
  94
  95   nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, size, &loadbase,
  96                                          target_read_memory_bfd);
  97   if (nbfd == NULL)
  98     error (_("Failed to read a valid object file image from memory."));
  99
 100   /* Manage the new reference for the duration of this function.  */
 101   gdb_bfd_ref_ptr nbfd_holder = gdb_bfd_ref_ptr::new_reference (nbfd);
 102
 103   if (name == NULL)
 104     name = "shared object read from target memory";
 105   bfd_set_filename (nbfd, name);
 106
 107   if (!bfd_check_format (nbfd, bfd_object))
 108     error (_("Got object file from memory but can't read symbols: %s."),
 109            bfd_errmsg (bfd_get_error ()));
 110
 111   section_addr_info sai;
 112   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 113     if ((bfd_section_flags (sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 114       sai.emplace_back (bfd_section_vma (sec) + loadbase,
 115                         bfd_section_name (sec),
 116                         sec->index);
 117
 118   if (from_tty)
 119     add_flags |= SYMFILE_VERBOSE;
 120
 121   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 122                                    add_flags, &sai, OBJF_SHARED, NULL);
 123
 124   add_target_sections_of_objfile (objf);
 125
 126   /* This might change our ideas about frames already looked at.  */
 127   reinit_frame_cache ();
 128
 129   return objf;
 130 }
 131
 132
 133 static void
 134 add_symbol_file_from_memory_command (const char *args, int from_tty)
 135 {
 136   CORE_ADDR addr;
 137   struct bfd *templ;
 138
 139   if (args == NULL)
 140     error (_("add-symbol-file-from-memory requires an expression argument"));
 141
 142   addr = parse_and_eval_address (args);
 143
 144   /* We need some representative bfd to know the target we are looking at.  */
 145   if (symfile_objfile != NULL)
 146     templ = symfile_objfile->obfd;
 147   else
 148     templ = exec_bfd;
 149   if (templ == NULL)
 150     error (_("Must use symbol-file or exec-file "
 151              "before add-symbol-file-from-memory."));
 152
 153   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 154 }
 155
 156 /* Try to add the symbols for the vsyscall page, if there is one.
 157    This function is called via the inferior_created observer.  */
 158
 159 static void
 160 add_vsyscall_page (struct target_ops *target, int from_tty)
 161 {
 162   struct mem_range vsyscall_range;
 163
 164   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 165     {
 166       struct bfd *bfd;
 167
 168       if (core_bfd != NULL)
 169         bfd = core_bfd;
 170       else if (exec_bfd != NULL)
 171         bfd = exec_bfd;
 172       else
 173        /* FIXME: cagney/2004-05-06: Should not require an existing
 174           BFD when trying to create a run-time BFD of the VSYSCALL
 175           page in the inferior.  Unfortunately that's the current
 176           interface so for the moment bail.  Introducing a
 177           ``bfd_runtime'' (a BFD created using the loaded image) file
 178           format should fix this.  */
 179         {
 180           warning (_("Could not load vsyscall page "
 181                      "because no executable was specified"));
 182           return;
 183         }
 184
 185       std::string name = string_printf ("system-supplied DSO at %s",
 186                                         paddress (target_gdbarch (),
 187                                                   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.c_str (),
 197                                        0 /* from_tty */);
 198         }
 199       catch (const gdb_exception &ex)
 200         {
 201           exception_print (gdb_stderr, ex);
 202         }
 203     }
 204 }
 205
 206 void _initialize_symfile_mem ();
 207 void
 208 _initialize_symfile_mem ()
 209 {
 210   add_cmd ("add-symbol-file-from-memory", class_files,
 211            add_symbol_file_from_memory_command,
 212            _("Load the symbols out of memory from a "
 213              "dynamically loaded object file.\n"
 214              "Give an expression for the address "
 215              "of the file's shared object file header."),
 216            &cmdlist);
 217
 218   /* Want to know of each new inferior so that its vsyscall info can
 219      be extracted.  */
 220   gdb::observers::inferior_created.attach (add_vsyscall_page);
 221 }