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, 5 insertions, 3 deletions

diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 6b8927a..2aa8134 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -717,7 +717,7 @@ SFILES = ada-exp.y ada-lang.c ada-typeprint.c ada-valprint.c ada-tasks.c \
 	bfd-target.c \
 	block.c blockframe.c \
 	breakpoint.c break-catch-sig.c break-catch-throw.c \
-	buildsym.c \
+	build-id.c buildsym.c \
 	c-exp.y c-lang.c c-typeprint.c c-valprint.c \
 	charset.c cleanups.c cli-out.c coffread.c coff-pe-read.c \
 	complaints.c completer.c continuations.c corefile.c corelow.c \
@@ -814,7 +814,8 @@ tui/tui-file.h tui/tui-command.h tui/tui-disasm.h tui/tui-wingeneral.h \
 tui/tui-windata.h tui/tui-data.h tui/tui-win.h tui/tui-stack.h \
 tui/tui-winsource.h tui/tui-regs.h tui/tui-io.h tui/tui-layout.h \
 tui/tui-source.h sol2-tdep.h gregset.h sh-tdep.h sh64-tdep.h \
-expression.h score-tdep.h gdb_select.h ser-tcp.h buildsym.h valprint.h \
+expression.h score-tdep.h gdb_select.h ser-tcp.h \
+build-id.h buildsym.h valprint.h \
 typeprint.h mi/mi-getopt.h mi/mi-parse.h mi/mi-console.h \
 mi/mi-out.h mi/mi-main.h mi/mi-common.h mi/mi-cmds.h linux-nat.h \
 complaints.h gdb_proc_service.h gdb_regex.h xtensa-tdep.h inf-loop.h \
@@ -911,7 +912,8 @@ COMMON_OBS = $(DEPFILES) $(CONFIG_OBS) $(YYOBJ) \
 	event-loop.o event-top.o inf-loop.o completer.o \
 	gdbarch.o arch-utils.o gdbtypes.o gdb_bfd.o gdb_obstack.o \
 	osabi.o copying.o \
-	memattr.o mem-break.o target.o parse.o language.o buildsym.o \
+	memattr.o mem-break.o target.o parse.o language.o \
+	build-id.o buildsym.o \
 	findcmd.o \
 	std-regs.o \
 	signals.o \