gdb/symfile-mem.c

   1 /* Reading symbol files from memory.
   2
   3    Copyright (C) 1986-2019 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   xfree (bfd_get_filename (nbfd));
 105   if (name == NULL)
 106     nbfd->filename = xstrdup ("shared object read from target memory");
 107   else
 108     nbfd->filename = name;
 109
 110   if (!bfd_check_format (nbfd, bfd_object))
 111     error (_("Got object file from memory but can't read symbols: %s."),
 112            bfd_errmsg (bfd_get_error ()));
 113
 114   section_addr_info sai;
 115   for (sec = nbfd->sections; sec != NULL; sec = sec->next)
 116     if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
 117       sai.emplace_back (bfd_get_section_vma (nbfd, sec) + loadbase,
 118                         bfd_get_section_name (nbfd, sec),
 119                         sec->index);
 120
 121   if (from_tty)
 122     add_flags |= SYMFILE_VERBOSE;
 123
 124   objf = symbol_file_add_from_bfd (nbfd, bfd_get_filename (nbfd),
 125                                    add_flags, &sai, OBJF_SHARED, NULL);
 126
 127   add_target_sections_of_objfile (objf);
 128
 129   /* This might change our ideas about frames already looked at.  */
 130   reinit_frame_cache ();
 131
 132   return objf;
 133 }
 134
 135
 136 static void
 137 add_symbol_file_from_memory_command (const char *args, int from_tty)
 138 {
 139   CORE_ADDR addr;
 140   struct bfd *templ;
 141
 142   if (args == NULL)
 143     error (_("add-symbol-file-from-memory requires an expression argument"));
 144
 145   addr = parse_and_eval_address (args);
 146
 147   /* We need some representative bfd to know the target we are looking at.  */
 148   if (symfile_objfile != NULL)
 149     templ = symfile_objfile->obfd;
 150   else
 151     templ = exec_bfd;
 152   if (templ == NULL)
 153     error (_("Must use symbol-file or exec-file "
 154              "before add-symbol-file-from-memory."));
 155
 156   symbol_file_add_from_memory (templ, addr, 0, NULL, from_tty);
 157 }
 158
 159 /* Try to add the symbols for the vsyscall page, if there is one.
 160    This function is called via the inferior_created observer.  */
 161
 162 static void
 163 add_vsyscall_page (struct target_ops *target, int from_tty)
 164 {
 165   struct mem_range vsyscall_range;
 166
 167   if (gdbarch_vsyscall_range (target_gdbarch (), &vsyscall_range))
 168     {
 169       struct bfd *bfd;
 170
 171       if (core_bfd != NULL)
 172         bfd = core_bfd;
 173       else if (exec_bfd != NULL)
 174         bfd = exec_bfd;
 175       else
 176        /* FIXME: cagney/2004-05-06: Should not require an existing
 177           BFD when trying to create a run-time BFD of the VSYSCALL
 178           page in the inferior.  Unfortunately that's the current
 179           interface so for the moment bail.  Introducing a
 180           ``bfd_runtime'' (a BFD created using the loaded image) file
 181           format should fix this.  */
 182         {
 183           warning (_("Could not load vsyscall page "
 184                      "because no executable was specified"));
 185           return;
 186         }
 187
 188       char *name = xstrprintf ("system-supplied DSO at %s",
 189                                paddress (target_gdbarch (), vsyscall_range.start));
 190       try
 191         {
 192           /* Pass zero for FROM_TTY, because the action of loading the
 193              vsyscall DSO was not triggered by the user, even if the
 194              user typed "run" at the TTY.  */
 195           symbol_file_add_from_memory (bfd,
 196                                        vsyscall_range.start,
 197                                        vsyscall_range.length,
 198                                        name,
 199                                        0 /* from_tty */);
 200         }
 201       catch (const gdb_exception_RETURN_MASK_ALL &ex)
 202         {
 203           exception_print (gdb_stderr, ex);
 204         }
 205     }
 206 }
 207
 208 void
 209 _initialize_symfile_mem (void)
 210 {
 211   add_cmd ("add-symbol-file-from-memory", class_files,
 212            add_symbol_file_from_memory_command,
 213            _("Load the symbols out of memory from a "
 214              "dynamically loaded object file.\n"
 215              "Give an expression for the address "
 216              "of the file's shared object file header."),
 217            &cmdlist);
 218
 219   /* Want to know of each new inferior so that its vsyscall info can
 220      be extracted.  */
 221   gdb::observers::inferior_created.attach (add_vsyscall_page);
 222 }