Core file build-id support

This patch uses new BFD support for detecting build-ids in core
files.

After this patch, it is possible to run gdb with only the
core file, and gdb will automatically load the executable and
debug info [example from tests]:

$ gdb -nx -q
(gdb) core-file corefile-buildid.core
[New LWP 29471]
Reading symbols from gdb.base/corefile-buildid/debugdir-exec/.build-id/36/fe5722c5a7ca3ac746a84e223c6a2a69193a24...
Core was generated by `outputs/gdb.base/coref'.
Program terminated with signal SIGABRT, Aborted.
(gdb)

This work is based on functionality available in Fedora originally
written by Jan Kratochvil.

Regression tested on buildbot.

gdb/ChangeLog:
2019-12-07  Keith Seitz  <keiths@redhat.com>

	* build-id.c (build_id_bfd_get): Permit bfd_core, too.
	(build_id_to_debug_bfd): Make static, rewriting to use
	build_id_to_bfd_suffix.
	(build_id_to_bfd_suffix): Copy of build_id_to_debug_bfd,
	adding `suffix' parameter. Append SUFFIX to file names
	when searching for matching files.
	(build_id_to_debug_bfd): Use build_id_to_bfd_suffix.
	(build_id_to_exec_bfd): Likewise.
	* build-id.h (build_id_to_debug_bfd): Clarify that function
	searches for BFD of debug info file.
	(build_id_to_exec_bfd): Declare.
	* corelow.c: Include build-id.h.
	(locate_exec_from_corefile_build_id): New function.
	(core_target_open): If no executable BFD is found,
	search for a core file BFD using build-id.

gdb/testsuite/ChangeLog:
2019-12-07  Keith Seitz  <keiths@redhat.com>

	* gdb.base/corefile-buildid-shlib-shr.c: New file.
	* gdb.base/corefile-buildid-shlib.c: New file.
	* gdb.base/corefile-buildid.c: New file.
	* gdb.base/corefile-buildid.exp: New file.

Change-Id: I15e9e8e58f10c68b5cae55e2eba58df1e8aef529

1 files changed, 25 insertions, 5 deletions

diff --git a/gdb/build-id.c b/gdb/build-id.c
index 048da2a..e8d77bb 100644
--- a/gdb/build-id.c
+++ b/gdb/build-id.c
@@ -32,7 +32,8 @@
 const struct bfd_build_id *
 build_id_bfd_get (bfd *abfd)
 {
-  if (!bfd_check_format (abfd, bfd_object))
+  if (!bfd_check_format (abfd, bfd_object)
+      && !bfd_check_format (abfd, bfd_core))
     return NULL;
 
   if (abfd->build_id != NULL)
@@ -117,10 +118,13 @@ build_id_to_debug_bfd_1 (const std::string &link, size_t build_id_len,
   return debug_bfd;
 }
 
-/* See build-id.h.  */
+/* Common code for finding BFDs of a given build-id.  This function
+   works with both debuginfo files (SUFFIX == ".debug") and executable
+   files (SUFFIX == "").  */
 
-gdb_bfd_ref_ptr
-build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
+static gdb_bfd_ref_ptr
+build_id_to_bfd_suffix (size_t build_id_len, const bfd_byte *build_id,
+			const char *suffix)
 {
   /* Keep backward compatibility so that DEBUG_FILE_DIRECTORY being "" will
      cause "/.build-id/..." lookups.  */
@@ -149,7 +153,7 @@ build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
       while (size-- > 0)
 	string_appendf (link, "%02x", (unsigned) *data++);
 
-      link += ".debug";
+      link += suffix;
 
       gdb_bfd_ref_ptr debug_bfd
 	= build_id_to_debug_bfd_1 (link, build_id_len, build_id);
@@ -177,6 +181,22 @@ build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
 
 /* See build-id.h.  */
 
+gdb_bfd_ref_ptr
+build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
+{
+  return build_id_to_bfd_suffix (build_id_len, build_id, ".debug");
+}
+
+/* See build-id.h.  */
+
+gdb_bfd_ref_ptr
+build_id_to_exec_bfd (size_t build_id_len, const bfd_byte *build_id)
+{
+  return build_id_to_bfd_suffix (build_id_len, build_id, "");
+}
+
+/* See build-id.h.  */
+
 std::string
 find_separate_debug_file_by_buildid (struct objfile *objfile)
 {