1/* Reading symbol files from memory.
2
3   Copyright (C) 1986, 1987, 1989, 1991, 1994, 1995, 1996, 1998, 2000, 2001,
4   2002, 2003, 2004, 2005, 2007 Free Software Foundation, Inc.
5
6   This file is part of GDB.
7
8   This program is free software; you can redistribute it and/or modify
9   it under the terms of the GNU General Public License as published by
10   the Free Software Foundation; either version 3 of the License, or
11   (at your option) any later version.
12
13   This program is distributed in the hope that it will be useful,
14   but WITHOUT ANY WARRANTY; without even the implied warranty of
15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16   GNU General Public License for more details.
17
18   You should have received a copy of the GNU General Public License
19   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
20
21/* This file defines functions (and commands to exercise those
22   functions) for reading debugging information from object files
23   whose images are mapped directly into the inferior's memory.  For
24   example, the Linux kernel maps a "syscall DSO" into each process's
25   address space; this DSO provides kernel-specific code for some
26   system calls.
27
28   At the moment, BFD only has functions for parsing object files from
29   memory for the ELF format, even though the general idea isn't
30   ELF-specific.  This means that BFD only provides the functions GDB
31   needs when configured for ELF-based targets.  So these functions
32   may only be compiled on ELF-based targets.
33
34   GDB has no idea whether it has been configured for an ELF-based
35   target or not: it just tries to handle whatever files it is given.
36   But this means there are no preprocessor symbols on which we could
37   make these functions' compilation conditional.
38
39   So, for the time being, we put these functions alone in this file,
40   and have .mt files reference them as appropriate.  In the future, I
41   hope BFD will provide a format-independent bfd_from_remote_memory
42   entry point.  */
43
44
45#include "defs.h"
46#include "symtab.h"
47#include "gdbcore.h"
48#include "objfiles.h"
49#include "exceptions.h"
50#include "gdbcmd.h"
51#include "target.h"
52#include "value.h"
53#include "symfile.h"
54#include "observer.h"
55#include "auxv.h"
56#include "elf/common.h"
57
58
59/* Read inferior memory at ADDR to find the header of a loaded object file
60   and read its in-core symbols out of inferior memory.  TEMPL is a bfd
61   representing the target's format.  NAME is the name to use for this
62   symbol file in messages; it can be NULL or a malloc-allocated string
63   which will be attached to the BFD.  */
64static struct objfile *
65symbol_file_add_from_memory (struct bfd *templ, CORE_ADDR addr, char *name,
66			     int from_tty)
67{
68  struct objfile *objf;
69  struct bfd *nbfd;
70  struct bfd_section *sec;
71  bfd_vma loadbase;
72  struct section_addr_info *sai;
73  unsigned int i;
74
75  if (bfd_get_flavour (templ) != bfd_target_elf_flavour)
76    error (_("add-symbol-file-from-memory not supported for this target"));
77
78  nbfd = bfd_elf_bfd_from_remote_memory (templ, addr, &loadbase,
79					 target_read_memory);
80  if (nbfd == NULL)
81    error (_("Failed to read a valid object file image from memory."));
82
83  if (name == NULL)
84    nbfd->filename = xstrdup ("shared object read from target memory");
85  else
86    nbfd->filename = name;
87
88  if (!bfd_check_format (nbfd, bfd_object))
89    {
90      /* FIXME: should be checking for errors from bfd_close (for one thing,
91         on error it does not free all the storage associated with the
92         bfd).  */
93      bfd_close (nbfd);
94      error (_("Got object file from memory but can't read symbols: %s."),
95	     bfd_errmsg (bfd_get_error ()));
96    }
97
98  sai = alloc_section_addr_info (bfd_count_sections (nbfd));
99  make_cleanup (xfree, sai);
100  i = 0;
101  for (sec = nbfd->sections; sec != NULL; sec = sec->next)
102    if ((bfd_get_section_flags (nbfd, sec) & (SEC_ALLOC|SEC_LOAD)) != 0)
103      {
104	sai->other[i].addr = bfd_get_section_vma (nbfd, sec) + loadbase;
105	sai->other[i].name = (char *) bfd_get_section_name (nbfd, sec);
106	sai->other[i].sectindex = sec->index;
107	++i;
108      }
109
110  objf = symbol_file_add_from_bfd (nbfd, from_tty,
111                                   sai, 0, OBJF_SHARED);
112
113  /* This might change our ideas about frames already looked at.  */
114  reinit_frame_cache ();
115
116  return objf;
117}
118
119
120static void
121add_symbol_file_from_memory_command (char *args, int from_tty)
122{
123  CORE_ADDR addr;
124  struct bfd *templ;
125
126  if (args == NULL)
127    error (_("add-symbol-file-from-memory requires an expression argument"));
128
129  addr = parse_and_eval_address (args);
130
131  /* We need some representative bfd to know the target we are looking at.  */
132  if (symfile_objfile != NULL)
133    templ = symfile_objfile->obfd;
134  else
135    templ = exec_bfd;
136  if (templ == NULL)
137    error (_("\
138Must use symbol-file or exec-file before add-symbol-file-from-memory."));
139
140  symbol_file_add_from_memory (templ, addr, NULL, from_tty);
141}
142
143/* Arguments for symbol_file_add_from_memory_wrapper.  */
144
145struct symbol_file_add_from_memory_args
146{
147  struct bfd *bfd;
148  CORE_ADDR sysinfo_ehdr;
149  char *name;
150  int from_tty;
151};
152
153/* Wrapper function for symbol_file_add_from_memory, for
154   catch_exceptions.  */
155
156static int
157symbol_file_add_from_memory_wrapper (struct ui_out *uiout, void *data)
158{
159  struct symbol_file_add_from_memory_args *args = data;
160
161  symbol_file_add_from_memory (args->bfd, args->sysinfo_ehdr, args->name,
162			       args->from_tty);
163  return 0;
164}
165
166/* Try to add the symbols for the vsyscall page, if there is one.  This function
167   is called via the inferior_created observer.  */
168
169static void
170add_vsyscall_page (struct target_ops *target, int from_tty)
171{
172  CORE_ADDR sysinfo_ehdr;
173
174  if (target_auxv_search (target, AT_SYSINFO_EHDR, &sysinfo_ehdr) > 0
175      && sysinfo_ehdr != (CORE_ADDR) 0)
176    {
177      struct bfd *bfd;
178      struct symbol_file_add_from_memory_args args;
179
180      if (core_bfd != NULL)
181	bfd = core_bfd;
182      else if (exec_bfd != NULL)
183	bfd = exec_bfd;
184      else
185       /* FIXME: cagney/2004-05-06: Should not require an existing
186	  BFD when trying to create a run-time BFD of the VSYSCALL
187	  page in the inferior.  Unfortunately that's the current
188	  interface so for the moment bail.  Introducing a
189	  ``bfd_runtime'' (a BFD created using the loaded image) file
190	  format should fix this.  */
191	{
192	  warning (_("\
193Could not load vsyscall page because no executable was specified\n\
194try using the \"file\" command first."));
195	  return;
196	}
197      args.bfd = bfd;
198      args.sysinfo_ehdr = sysinfo_ehdr;
199      xasprintf (&args.name, "system-supplied DSO at 0x%s",
200		 paddr_nz (sysinfo_ehdr));
201      /* Pass zero for FROM_TTY, because the action of loading the
202	 vsyscall DSO was not triggered by the user, even if the user
203	 typed "run" at the TTY.  */
204      args.from_tty = 0;
205      catch_exceptions (uiout, symbol_file_add_from_memory_wrapper,
206			&args, RETURN_MASK_ALL);
207    }
208}
209
210
211void
212_initialize_symfile_mem (void)
213{
214  add_cmd ("add-symbol-file-from-memory", class_files,
215           add_symbol_file_from_memory_command, _("\
216Load the symbols out of memory from a dynamically loaded object file.\n\
217Give an expression for the address of the file's shared object file header."),
218           &cmdlist);
219
220  /* Want to know of each new inferior so that its vsyscall info can
221     be extracted.  */
222  observer_attach_inferior_created (add_vsyscall_page);
223}
224