[gdb/cli] Add maint info frame-unwinders

Add a new command "maint info frame-unwinders":
...
(gdb) help maint info frame-unwinders
List the frame unwinders currently in effect, starting with the highest \
  priority.
...

Output for i386:
...
$ gdb -q -batch -ex "set arch i386" -ex "maint info frame-unwinders"
The target architecture is set to "i386".
dummy                   DUMMY_FRAME
dwarf2 tailcall         TAILCALL_FRAME
inline                  INLINE_FRAME
i386 epilogue           NORMAL_FRAME
dwarf2                  NORMAL_FRAME
dwarf2 signal           SIGTRAMP_FRAME
i386 stack tramp        NORMAL_FRAME
i386 sigtramp           SIGTRAMP_FRAME
i386 prologue           NORMAL_FRAME
...

Output for x86_64:
...
$ gdb -q -batch -ex "set arch i386:x86-64" -ex "maint info frame-unwinders"
The target architecture is set to "i386:x86-64".
dummy                   DUMMY_FRAME
dwarf2 tailcall         TAILCALL_FRAME
inline                  INLINE_FRAME
python                  NORMAL_FRAME
amd64 epilogue          NORMAL_FRAME
i386 epilogue           NORMAL_FRAME
dwarf2                  NORMAL_FRAME
dwarf2 signal           SIGTRAMP_FRAME
amd64 sigtramp          SIGTRAMP_FRAME
amd64 prologue          NORMAL_FRAME
i386 stack tramp        NORMAL_FRAME
i386 sigtramp           SIGTRAMP_FRAME
i386 prologue           NORMAL_FRAME
...

Tested on x86_64-linux.

Reviewed-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Eli Zaretskii <eliz@gnu.org>

gdb/NEWS

@@ -52,6 +52,10 @@ maintenance print record-instruction [ N ]
   prints how GDB would undo the N-th previous instruction, and if N is
   positive, it prints how GDB will redo the N-th following instruction.
 
+maintenance info frame-unwinders
+  List the frame unwinders currently in effect, starting with the highest
+  priority.
+
 * MI changes
 
 ** mi now reports 'no-history' as a stop reason when hitting the end of the

gdb/doc/gdb.texinfo

@@ -40986,6 +40986,10 @@ with the DWARF frame unwinders enabled.
 If DWARF frame unwinders are not supported for a particular target
 architecture, then enabling this flag does not cause them to be used.
 
+@kindex maint info frame-unwinders
+@item maint info frame-unwinders
+List the frame unwinders currently in effect, starting with the highest priority.
+
 @kindex maint set worker-threads
 @kindex maint show worker-threads
 @item maint set worker-threads

gdb/frame-unwind.c

@@ -28,6 +28,7 @@
 #include "target.h"
 #include "gdbarch.h"
 #include "dwarf2/frame-tailcall.h"
+#include "cli/cli-cmds.h"
 
 struct frame_unwind_table_entry
 {
@@ -337,3 +338,34 @@ frame_unwind_got_address (frame_info_ptr frame, int regnum,
 	     register_type (gdbarch, regnum), addr);
   return reg_val;
 }
+
+/* Implement "maintenance info frame-unwinders" command.  */
+
+static void
+maintenance_info_frame_unwinders (const char *args, int from_tty)
+{
+  struct gdbarch *gdbarch = target_gdbarch ();
+  struct frame_unwind_table *table = get_frame_unwind_table (gdbarch);
+
+  for (struct frame_unwind_table_entry *entry = table->list; entry != NULL;
+       entry = entry->next)
+    {
+      const char *name = entry->unwinder->name;
+      const char *type = frame_type_str (entry->unwinder->type);
+
+      gdb_printf (gdb_stdout, "%-16s\t%-16s\n", name, type);
+    }
+}
+
+void _initialize_frame_unwind ();
+void
+_initialize_frame_unwind ()
+{
+  /* Add "maint info frame-unwinders".  */
+  add_cmd ("frame-unwinders",
+	   class_maintenance,
+	   maintenance_info_frame_unwinders,
+	   _("List the frame unwinders currently in effect, "
+	     "starting with the highest priority."),
+	   &maintenanceinfolist);
+}

gdb/frame.c

@@ -439,9 +439,9 @@ frame_id::to_string () const
   return res;
 }
 
-/* Return a string representation of TYPE.  */
+/* See frame.h.  */
 
-static const char *
+const char *
 frame_type_str (frame_type type)
 {
   switch (type)

gdb/frame.h

@@ -203,6 +203,10 @@ enum frame_type
   SENTINEL_FRAME
 };
 
+/* Return a string representation of TYPE.  */
+
+extern const char *frame_type_str (frame_type type);
+
 /* A wrapper for "frame_info *".  frame_info objects are invalidated
    whenever reinit_frame_cache is called.  This class arranges to
    invalidate the pointer when appropriate.  This is done to help