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, 20 insertions, 12 deletions

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 5e2ace7..4cb66db 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -69,6 +69,7 @@
 #include "f-lang.h"
 #include "source.h"
 #include "filestuff.h"
+#include "build-id.h"
 
 #include <fcntl.h>
 #include "gdb_string.h"
@@ -2364,14 +2365,15 @@ dwarf2_get_dwz_file (void)
   struct cleanup *cleanup;
   const char *filename;
   struct dwz_file *result;
-  unsigned long buildid;
+  size_t buildid_len;
+  bfd_byte *buildid;
 
   if (dwarf2_per_objfile->dwz_file != NULL)
     return dwarf2_per_objfile->dwz_file;
 
   bfd_set_error (bfd_error_no_error);
   data = bfd_get_alt_debug_link_info (dwarf2_per_objfile->objfile->obfd,
-				      &buildid);
+				      &buildid_len, &buildid);
   if (data == NULL)
     {
       if (bfd_get_error () == bfd_error_no_error)
@@ -2380,6 +2382,7 @@ dwarf2_get_dwz_file (void)
 	     bfd_errmsg (bfd_get_error ()));
     }
   cleanup = make_cleanup (xfree, data);
+  make_cleanup (xfree, buildid);
 
   filename = (const char *) data;
   if (!IS_ABSOLUTE_PATH (filename))
@@ -2396,20 +2399,25 @@ dwarf2_get_dwz_file (void)
       filename = rel;
     }
 
-  /* The format is just a NUL-terminated file name, followed by the
-     build-id.  For now, though, we ignore the build-id.  */
+  /* First try the file name given in the section.  If that doesn't
+     work, try to use the build-id instead.  */
   dwz_bfd = gdb_bfd_open (filename, gnutarget, -1);
-  if (dwz_bfd == NULL)
-    error (_("could not read '%s': %s"), filename,
-	   bfd_errmsg (bfd_get_error ()));
-
-  if (!bfd_check_format (dwz_bfd, bfd_object))
+  if (dwz_bfd != NULL)
     {
-      gdb_bfd_unref (dwz_bfd);
-      error (_("file '%s' was not usable: %s"), filename,
-	     bfd_errmsg (bfd_get_error ()));
+      if (!build_id_verify (dwz_bfd, buildid_len, buildid))
+	{
+	  gdb_bfd_unref (dwz_bfd);
+	  dwz_bfd = NULL;
+	}
     }
 
+  if (dwz_bfd == NULL)
+    dwz_bfd = build_id_to_debug_bfd (buildid_len, buildid);
+
+  if (dwz_bfd == NULL)
+    error (_("could not find '.gnu_debugaltlink' file for %s"),
+	   objfile_name (dwarf2_per_objfile->objfile));
+
   result = OBSTACK_ZALLOC (&dwarf2_per_objfile->objfile->objfile_obstack,
 			   struct dwz_file);
   result->dwz_bfd = dwz_bfd;