Introduce "set debug separate-debug-file"

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:

	* NEWS (Changes since GDB 8.0): Announce {set,show} debug
	separate-debug-file commands.
	* 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/doc/ChangeLog:

	* gdb.texinfo (Optional Messages about Internal Happenings):
	Document {set,show} debug separate-debug-file commands.

7 files changed, 59 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c48fb92..38a40e1 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,16 @@
+2017-06-11  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* NEWS (Changes since GDB 8.0): Announce {set,show} debug
+	separate-debug-file commands.
+	* 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.
+
 2017-06-10  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* gdbarch.sh (displaced_step_free_closure): Remove.
diff --git a/gdb/NEWS b/gdb/NEWS
index 8dab5d3..7c8a8f6 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -17,6 +17,12 @@
 QStartupWithShell
   Indicates whether the inferior must be started with a shell or not.
 
+* New commands
+
+set debug separate-debug-file
+show debug separate-debug-file
+  Control the display of debug output about separate debug file search.
+
 *** Changes in GDB 8.0
 
 * GDB now supports access to the PKU register on GNU/Linux. The register is
diff --git a/gdb/build-id.c b/gdb/build-id.c
index 0f63223..4b2b63e 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/doc/ChangeLog b/gdb/doc/ChangeLog
index 868cde9..aa4a9ce 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2017-06-11  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* gdb.texinfo (Optional Messages about Internal Happenings):
+	Document {set,show} debug separate-debug-file commands.
+
 2017-06-07  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* gdb.texinfo (Starting) <startup-with-shell>: Add @anchor.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 8d7a1c9..c167a86 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -23984,6 +23984,12 @@ the serial line to the remote machine.  The info is printed on the
 @value{GDBN} standard output stream. The default is off.
 @item show debug remote
 Displays the state of display of remote packets.
+
+@item set debug separate-debug-file
+Turns on or off display of debug output about separate debug file search.
+@item show debug separate-debug-file
+Displays the state of separate debug file search debug output.
+
 @item set debug serial
 Turns on or off display of @value{GDBN} serial debugging info. The
 default is off.
diff --git a/gdb/symfile.c b/gdb/symfile.c
index 846aabe..f936cf3 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1333,6 +1333,10 @@ 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 +1355,9 @@ 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 +1451,10 @@ 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 +3986,11 @@ 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 prints 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..bb47fdf 100644
--- a/gdb/symfile.h
+++ b/gdb/symfile.h
@@ -646,4 +646,8 @@ 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) */