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, 0 deletions

diff --git a/gdb/corelow.c b/gdb/corelow.c
index fa1661e..bdbfae37 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -43,6 +43,7 @@
 #include "gdb_bfd.h"
 #include "completer.h"
 #include "gdbsupport/filestuff.h"
+#include "build-id.h"
 
 #ifndef O_LARGEFILE
 #define O_LARGEFILE 0
@@ -351,6 +352,27 @@ core_file_command (const char *filename, int from_tty)
     core_target_open (filename, from_tty);
 }
 
+/* Locate (and load) an executable file (and symbols) given the core file
+   BFD ABFD.  */
+
+static void
+locate_exec_from_corefile_build_id (bfd *abfd, int from_tty)
+{
+  const bfd_build_id *build_id = build_id_bfd_get (abfd);
+  if (build_id == nullptr)
+    return;
+
+  gdb_bfd_ref_ptr execbfd
+    = build_id_to_exec_bfd (build_id->size, build_id->data);
+
+  if (execbfd != nullptr)
+    {
+      exec_file_attach (bfd_get_filename (execbfd.get ()), from_tty);
+      symbol_file_add_main (bfd_get_filename (execbfd.get ()),
+			    symfile_add_flag (from_tty ? SYMFILE_VERBOSE : 0));
+    }
+}
+
 /* See gdbcore.h.  */
 
 void
@@ -456,6 +478,9 @@ core_target_open (const char *arg, int from_tty)
 	switch_to_thread (thread);
     }
 
+  if (exec_bfd == nullptr)
+    locate_exec_from_corefile_build_id (core_bfd, from_tty);
+
   post_create_inferior (target, from_tty);
 
   /* Now go through the target stack looking for threads since there