fix PR symtab/15597

This patch fixes gdb PR symtab/15597.

The bug is that the .gnu_debugaltlink section includes the build-id of
the alt file, but gdb does not use it.

This patch fixes the problem by changing gdb to do what it ought to
always have done: verify the build id of the file found using the
filename in .gnu_debugaltlink; and if that does not match, try to find
the correct debug file using the build-id and debug-file-directory.

This patch touches BFD.  Previously, gdb had its own code for parsing
.gnu_debugaltlink; I changed it to use the BFD functions after those
were introduced.  However, the BFD functions are incorrect -- they
assume that .gnu_debugaltlink is formatted like .gnu_debuglink.
However, it it is not.  Instead, it consists of a file name followed
by the build-id -- no alignment, and the build-id is not a CRC.

Fixing this properly is a bit of a pain.  But, because
separate_alt_debug_file_exists just has a FIXME for the build-id case,
I did not fix it properly.  Instead I introduced a hack.  This leaves
BFD working just as well as it did before my patch.

I'm willing to do something better here but I could use some guidance
as to what.  It seems that the build-id code in BFD is largely punted
on.

FWIW gdb is the only user of bfd_get_alt_debug_link_info outside of
BFD itself.

I moved the build-id logic out of elfread.c and into a new file.
This seemed cleanest to me.

Writing a test case was a bit of a pain.  I added a couple new
features to the DWARF assembler to handle this.

Built and regtested on x86-64 Fedora 18.

	* bfd-in2.h: Rebuild.
	* opncls.c (bfd_get_alt_debug_link_info): Add buildid_len
	parameter.  Change type of buildid_out.  Update.
	(get_alt_debug_link_info_shim): New function.
	(bfd_follow_gnu_debuglink): Use it.

	* Makefile.in (SFILES): Add build-id.c.
	(HFILES_NO_SRCDIR): Add build-id.h.
	* build-id.c: New file, largely from elfread.c.  Modified
	most functions.
	* build-id.h: New file.
	* dwarf2read.c (dwarf2_get_dwz_file): Update for change to
	bfd_get_alt_debug_link_info.  Verify dwz file's build-id.
	Search for dwz file using build-id.
	* elfread.c (build_id_bfd_get, build_id_verify)
	(build_id_to_debug_filename, find_separate_debug_file): Remove.

	* gdb.dwarf2/dwzbuildid.exp: New file.
	* lib/dwarf.exp (Dwarf::_section): Add "flags" and "type"
	parameters.
	(Dwarf::_defer_output): Change "section" parameter to
	"section_spec"; update.
	(Dwarf::gnu_debugaltlink, Dwarf::_note, Dwarf::build_id): New
	procs.

1 files changed, 168 insertions, 0 deletions

diff --git a/gdb/build-id.c b/gdb/build-id.c
new file mode 100644
index 0000000..330ed18
--- /dev/null
+++ b/gdb/build-id.c
@@ -0,0 +1,168 @@
+/* build-id-related functions.
+
+   Copyright (C) 1991-2013 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "defs.h"
+#include "bfd.h"
+#include "elf-bfd.h"
+#include "gdb_bfd.h"
+#include "build-id.h"
+#include "gdb_string.h"
+#include "gdb_vecs.h"
+#include "symfile.h"
+#include "objfiles.h"
+#include "filenames.h"
+
+/* Locate NT_GNU_BUILD_ID from ABFD and return its content.  */
+
+static const struct elf_build_id *
+build_id_bfd_get (bfd *abfd)
+{
+  if (!bfd_check_format (abfd, bfd_object)
+      || bfd_get_flavour (abfd) != bfd_target_elf_flavour
+      /* Although this is ELF_specific, it is safe to do in generic
+	 code because it does not rely on any ELF-specific symbols at
+	 link time, and if the ELF code is not available in BFD, then
+	 ABFD will not have the ELF flavour.  */
+      || elf_tdata (abfd)->build_id == NULL)
+    return NULL;
+
+  return elf_tdata (abfd)->build_id;
+}
+
+/* See build-id.h.  */
+
+int
+build_id_verify (bfd *abfd, size_t check_len, const bfd_byte *check)
+{
+  const struct elf_build_id *found;
+  int retval = 0;
+
+  found = build_id_bfd_get (abfd);
+
+  if (found == NULL)
+    warning (_("File \"%s\" has no build-id, file skipped"),
+	     bfd_get_filename (abfd));
+  else if (found->size != check_len
+           || memcmp (found->data, check, found->size) != 0)
+    warning (_("File \"%s\" has a different build-id, file skipped"),
+	     bfd_get_filename (abfd));
+  else
+    retval = 1;
+
+  return retval;
+}
+
+/* See build-id.h.  */
+
+bfd *
+build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
+{
+  char *link, *debugdir;
+  VEC (char_ptr) *debugdir_vec;
+  struct cleanup *back_to;
+  int ix;
+  bfd *abfd = NULL;
+
+  /* DEBUG_FILE_DIRECTORY/.build-id/ab/cdef */
+  link = alloca (strlen (debug_file_directory) + (sizeof "/.build-id/" - 1) + 1
+		 + 2 * build_id_len + (sizeof ".debug" - 1) + 1);
+
+  /* Keep backward compatibility so that DEBUG_FILE_DIRECTORY being "" will
+     cause "/.build-id/..." lookups.  */
+
+  debugdir_vec = dirnames_to_char_ptr_vec (debug_file_directory);
+  back_to = make_cleanup_free_char_ptr_vec (debugdir_vec);
+
+  for (ix = 0; VEC_iterate (char_ptr, debugdir_vec, ix, debugdir); ++ix)
+    {
+      size_t debugdir_len = strlen (debugdir);
+      const gdb_byte *data = build_id;
+      size_t size = build_id_len;
+      char *s;
+      char *filename = NULL;
+
+      memcpy (link, debugdir, debugdir_len);
+      s = &link[debugdir_len];
+      s += sprintf (s, "/.build-id/");
+      if (size > 0)
+	{
+	  size--;
+	  s += sprintf (s, "%02x", (unsigned) *data++);
+	}
+      if (size > 0)
+	*s++ = '/';
+      while (size-- > 0)
+	s += sprintf (s, "%02x", (unsigned) *data++);
+      strcpy (s, ".debug");
+
+      /* lrealpath() is expensive even for the usually non-existent files.  */
+      if (access (link, F_OK) == 0)
+	filename = lrealpath (link);
+
+      if (filename == NULL)
+	continue;
+
+      /* We expect to be silent on the non-existing files.  */
+      abfd = gdb_bfd_open_maybe_remote (filename);
+      if (abfd == NULL)
+	continue;
+
+      if (build_id_verify (abfd, build_id_len, build_id))
+	break;
+
+      gdb_bfd_unref (abfd);
+      abfd = NULL;
+    }
+
+  do_cleanups (back_to);
+  return abfd;
+}
+
+/* See build-id.h.  */
+
+char *
+find_separate_debug_file_by_buildid (struct objfile *objfile)
+{
+  const struct elf_build_id *build_id;
+
+  build_id = build_id_bfd_get (objfile->obfd);
+  if (build_id != NULL)
+    {
+      bfd *abfd;
+
+      abfd = build_id_to_debug_bfd (build_id->size, build_id->data);
+      /* Prevent looping on a stripped .debug file.  */
+      if (abfd != NULL
+	  && filename_cmp (bfd_get_filename (abfd),
+			   objfile_name (objfile)) == 0)
+        {
+	  warning (_("\"%s\": separate debug info file has no debug info"),
+		   bfd_get_filename (abfd));
+	  gdb_bfd_unref (abfd);
+	}
+      else if (abfd != NULL)
+	{
+	  char *result = xstrdup (bfd_get_filename (abfd));
+
+	  gdb_bfd_unref (abfd);
+	  return result;
+	}
+    }
+  return NULL;
+}