Reset *THIS_CACHE in frame_unwind_try_unwinder in case of exception

It is required that unwinder->sniffer should set *this_cache to NULL if
the unwinder is not applicable or exception is thrown, so
78ac5f8316 adds clear_pointer_cleanup to set
*this_cache to NULL in case of exception in order to fix PR 14100.
https://sourceware.org/ml/gdb-patches/2012-08/msg00075.html

This patch removes that clear_pointer_cleanup, and catch all exception in
the caller of unwinder->sniffer.  In case of exception, reset *this_case.

gdb:

2017-08-11  Yao Qi  <yao.qi@linaro.org>

	* dwarf2-frame.c (clear_pointer_cleanup): Remove.
	(dwarf2_frame_cache): Remove reset_cache_cleanup.
	(dwarf2_frame_cache):
	* frame-unwind.c (frame_unwind_try_unwinder): Catch
	RETURN_MASK_ALL and set *this_case to NULL.
	* frame-unwind.h: Update comments.

gdb/ChangeLog

@@ -1,3 +1,12 @@
+2017-08-11  Yao Qi  <yao.qi@linaro.org>
+
+	* dwarf2-frame.c (clear_pointer_cleanup): Remove.
+	(dwarf2_frame_cache): Remove reset_cache_cleanup.
+	(dwarf2_frame_cache):
+	* frame-unwind.c (frame_unwind_try_unwinder): Catch
+	RETURN_MASK_ALL and set *this_case to NULL.
+	* frame-unwind.h: Update comments.
+
 2017-08-11  Yao Qi  <yao.qi@linaro.org>
 
 	* dwarf2-frame.c (dwarf2_frame_state_alloc_regs): Remove.

gdb/dwarf2-frame.c

@@ -960,20 +960,9 @@ struct dwarf2_frame_cache
   int entry_cfa_sp_offset_p;
 };
 
-/* A cleanup that sets a pointer to NULL.  */
-
-static void
-clear_pointer_cleanup (void *arg)
-{
-  void **ptr = (void **) arg;
-
-  *ptr = NULL;
-}
-
 static struct dwarf2_frame_cache *
 dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
 {
-  struct cleanup *reset_cache_cleanup;
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   const int num_regs = gdbarch_num_regs (gdbarch)
 		       + gdbarch_num_pseudo_regs (gdbarch);
@@ -989,7 +978,6 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
   cache = FRAME_OBSTACK_ZALLOC (struct dwarf2_frame_cache);
   cache->reg = FRAME_OBSTACK_CALLOC (num_regs, struct dwarf2_frame_state_reg);
   *this_cache = cache;
-  reset_cache_cleanup = make_cleanup (clear_pointer_cleanup, this_cache);
 
   /* Unwind the PC.
 
@@ -1078,7 +1066,6 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
       if (ex.error == NOT_AVAILABLE_ERROR)
 	{
 	  cache->unavailable_retaddr = 1;
-	  discard_cleanups (reset_cache_cleanup);
 	  return cache;
 	}
 
@@ -1184,7 +1171,6 @@ incomplete CFI data; unspecified registers (e.g., %s) at %s"),
       && fs.regs.reg[fs.retaddr_column].how == DWARF2_FRAME_REG_UNDEFINED)
     cache->undefined_retaddr = 1;
 
-  discard_cleanups (reset_cache_cleanup);
   return cache;
 }
 

gdb/frame-unwind.c

@@ -106,8 +106,11 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
     {
       res = unwinder->sniffer (unwinder, this_frame, this_cache);
     }
-  CATCH (ex, RETURN_MASK_ERROR)
+  CATCH (ex, RETURN_MASK_ALL)
     {
+      /* Catch all exceptions, caused by either interrupt or error.
+	 Reset *THIS_CACHE.  */
+      *this_cache = NULL;
       if (ex.error == NOT_AVAILABLE_ERROR)
 	{
 	  /* This usually means that not even the PC is available,
@@ -128,6 +131,8 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
     }
   else
     {
+      /* Don't set *THIS_CACHE to NULL here, because sniffer has to do
+	 so.  */
       do_cleanups (old_cleanup);
       return 0;
     }

gdb/frame-unwind.h

@@ -46,7 +46,8 @@ struct value;
    the PC and attributes) and if SELF is the applicable unwinder,
    return non-zero.  Possibly also initialize THIS_PROLOGUE_CACHE; but
    only if returning 1.  Initializing THIS_PROLOGUE_CACHE in other
-   cases (0 return, or exception) is invalid.  */
+   cases (0 return) is invalid.  In case of exception, the caller has
+   to set *THIS_PROLOGUE_CACHE to NULL.  */
 
 typedef int (frame_sniffer_ftype) (const struct frame_unwind *self,
 				   struct frame_info *this_frame,