gdb: add names to unwinders, add debug messages when looking for unwinder

I wrote this while debugging a problem where the expected unwinder for a
frame wasn't used.  It adds messages to show which unwinders are
considered for a frame, why they are not selected (if an exception is
thrown), and finally which unwinder is selected in the end.

To be able to show a meaningful, human-readable name for the unwinders,
add a "name" field to struct frame_unwind, and update all instances to
include a name.

Here's an example of the output:

    [frame] frame_unwind_find_by_frame: this_frame=0
    [frame] frame_unwind_try_unwinder: trying unwinder "dummy"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "dwarf2 tailcall"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "inline"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "jit"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "python"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "amd64 epilogue"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "i386 epilogue"
    [frame] frame_unwind_try_unwinder: no
    [frame] frame_unwind_try_unwinder: trying unwinder "dwarf2"
    [frame] frame_unwind_try_unwinder: yes

gdb/ChangeLog:

	* frame-unwind.h (struct frame_unwind) <name>: New.  Update
	instances everywhere to include this field.
	* frame-unwind.c (frame_unwind_try_unwinder,
	frame_unwind_find_by_frame): Add debug messages.

Change-Id: I813f17777422425f0d08b22499817b23922e8ddb

1 files changed, 10 insertions, 1 deletions

diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
index b19e95d..0fef2c1 100644
--- a/gdb/frame-unwind.c
+++ b/gdb/frame-unwind.c
@@ -127,10 +127,13 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
 
   try
     {
+      frame_debug_printf ("trying unwinder \"%s\"", unwinder->name);
       res = unwinder->sniffer (unwinder, this_frame, this_cache);
     }
   catch (const gdb_exception &ex)
     {
+      frame_debug_printf ("caught exception: %s", ex.message->c_str ());
+
       /* Catch all exceptions, caused by either interrupt or error.
 	 Reset *THIS_CACHE, unless something reinitialized the frame
 	 cache meanwhile, in which case THIS_FRAME/THIS_CACHE are now
@@ -153,9 +156,13 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
     }
 
   if (res)
-    return 1;
+    {
+      frame_debug_printf ("yes");
+      return 1;
+    }
   else
     {
+      frame_debug_printf ("no");
       /* Don't set *THIS_CACHE to NULL here, because sniffer has to do
 	 so.  */
       frame_cleanup_after_sniffer (this_frame);
@@ -171,6 +178,8 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
 void
 frame_unwind_find_by_frame (struct frame_info *this_frame, void **this_cache)
 {
+  frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
+
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   struct frame_unwind_table *table
     = (struct frame_unwind_table *) gdbarch_data (gdbarch, frame_unwind_data);