[PATCH] Introduce "set debug separate-debug-file"

Simon Marchi
2017-05-24T23:24:30Z

I helped someone figure out why their separate debug info (debug
link-based) was not found by gdb. It turns out that the debug file was
not named properly. It made me realize that it is quite difficult to
diagnose this kind of problems. This patch adds some debug output to
show where GDB looks for those files, so that it should be (more)
obvious to find what's wrong.

Here's an example of the result, first with an example of unsuccessful lookup,
and then a successful one.

(gdb) set debug separate-debug-file on
(gdb) file /usr/bin/gnome-calculator
Reading symbols from /usr/bin/gnome-calculator...
Looking for separate debug info (build-id) for /usr/bin/gnome-calculator
Trying /usr/local/lib/debug/.build-id/0d/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug

Looking for separate debug info (debug link) for /usr/bin/gnome-calculator
Trying /usr/bin/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug
Trying /usr/bin/.debug/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug
Trying /usr/local/lib/debug//usr/bin/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug
(no debugging symbols found)...done.
(gdb) set debug-file-directory /usr/lib/debug
(gdb) file /usr/bin/gnome-calculator
Reading symbols from /usr/bin/gnome-calculator...
Looking for separate debug info by build-id for /usr/bin/gnome-calculator
Trying /usr/lib/debug/.build-id/0d/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug
Reading symbols from /usr/lib/debug/.build-id/0d/5c5e8c86dbe4f4f95f7a13de04f91d377f3c6a.debug...done.
done.

Note: here, the debug link happens to be named like the build-id, but it
doesn't have to be this way. It puzzled me for a minute.

gdb/ChangeLog:

* symfile.h (separate_debug_file_debug): New global.
* symfile.c (separate_debug_file_debug): New global.
(separate_debug_file_exists, find_separate_debug_file): Add
debug output.
(_initialize_symfile): Add "set debug separate-debug-file"
command.
* build-id.c (build_id_to_debug_bfd,
find_separate_debug_file_by_buildid): Add debug output.
---
gdb/build-id.c | 7 +++++++
gdb/symfile.c | 19 +++++++++++++++++++
gdb/symfile.h | 5 +++++
3 files changed, 31 insertions(+)

diff --git a/gdb/build-id.c b/gdb/build-id.c
index 0f63223..2b7c046 100644
--- a/gdb/build-id.c
+++ b/gdb/build-id.c
@@ -112,6 +112,9 @@ build_id_to_debug_bfd (size_t build_id_len, const bfd_byte *build_id)
s += sprintf (s, "%02x", (unsigned) *data++);
strcpy (s, ".debug");

+ if (separate_debug_file_debug)
+ printf_unfiltered (" Trying %s\n", link);
+
/* lrealpath() is expensive even for the usually non-existent files. */
if (access (link, F_OK) == 0)
filename = lrealpath (link);
@@ -147,6 +150,10 @@ find_separate_debug_file_by_buildid (struct objfile *objfile)
build_id = build_id_bfd_get (objfile->obfd);
if (build_id != NULL)
{
+ if (separate_debug_file_debug)
+ printf_unfiltered ("\nLooking for separate debug info (build-id) for "
+ "%s\n", objfile_name (objfile));
+
gdb_bfd_ref_ptr abfd (build_id_to_debug_bfd (build_id->size,
build_id->data));
/* Prevent looping on a stripped .debug file. */
diff --git a/gdb/symfile.c b/gdb/symfile.c
index 846aabe..beda370 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1333,6 +1333,11 @@ symbol_file_clear (int from_tty)
printf_unfiltered (_("No symbol file now.\n"));
}

+/* See symfile.h. */
+
+int separate_debug_file_debug = 0;
+
+
static int
separate_debug_file_exists (const char *name, unsigned long crc,
struct objfile *parent_objfile)
@@ -1351,6 +1356,9 @@ separate_debug_file_exists (const char *name, unsigned long crc,
if (filename_cmp (name, objfile_name (parent_objfile)) == 0)
return 0;

+ if (separate_debug_file_debug)
+ printf_unfiltered (" Trying %s\n", name);
+
gdb_bfd_ref_ptr abfd (gdb_bfd_open (name, gnutarget, -1));

if (abfd == NULL)
@@ -1444,6 +1452,10 @@ find_separate_debug_file (const char *dir,
struct cleanup *back_to;
int ix;

+ if (separate_debug_file_debug)
+ printf_unfiltered ("\nLooking for separate debug info (debug link) for "
+ "%s\n", objfile_name (objfile));
+
/* Set I to std::max (strlen (canon_dir), strlen (dir)). */
i = strlen (dir);
if (canon_dir != NULL && strlen (canon_dir) > i)
@@ -3975,4 +3987,11 @@ full == print messages for the executable,\n\
NULL,
NULL,
&setprintlist, &showprintlist);
+
+ add_setshow_boolean_cmd ("separate-debug-file", no_class,
+ &separate_debug_file_debug, _("\
+Set printing of separate debug info file search debug."), _("\
+Show printing of separate debug info file search debug."), _("\
+When on, GDB will print the searched locations while looking for separate \
+debug info files."), NULL, NULL, &setdebuglist, &showdebuglist);
}
diff --git a/gdb/symfile.h b/gdb/symfile.h
index ab536e8..d05cb09 100644
--- a/gdb/symfile.h
+++ b/gdb/symfile.h
@@ -646,4 +646,9 @@ extern void elfmdebug_build_psymtabs (struct objfile *,

extern gdb_bfd_ref_ptr find_separate_debug_file_in_section (struct objfile *);

+
+/* True if we are printing debug output about separate debug info files. */
+
+extern int separate_debug_file_debug;
+
#endif /* !defined(SYMFILE_H) */
--
2.7.4