Re: RFC: one approach to fixing PR 14100

[Tom Tromey <tromey@redhat.com>]

>>>>> "Tom" == Tom Tromey <tromey@redhat.com> writes:

Tom> Then we need a cleanup instead.
Tom> I'll look at it on Monday.

Here it is.
I regression-tested it on x86-64 Fedora 16.

Tom

    	* dwarf2-frame.c (clear_pointer_cleanup): New function.
    	(dwarf2_frame_cache): Use it.
    	* frame-unwind.h (frame_sniffer_ftype): Document prologue
    	cache initialization constraint.

diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index 741a103..986aaea 100644
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -994,10 +994,20 @@ struct dwarf2_frame_cache
   void *tailcall_cache;
 };
 
+/* A cleanup that sets a pointer to NULL.  */
+
+static void
+clear_pointer_cleanup (void *arg)
+{
+  void **ptr = arg;
+
+  *ptr = NULL;
+}
+
 static struct dwarf2_frame_cache *
 dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
 {
-  struct cleanup *old_chain;
+  struct cleanup *reset_cache_cleanup, *old_chain;
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   const int num_regs = gdbarch_num_regs (gdbarch)
 		       + gdbarch_num_pseudo_regs (gdbarch);
@@ -1017,6 +1027,7 @@ 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);
 
   /* Allocate and initialize the frame state.  */
   fs = XZALLOC (struct dwarf2_frame_state);
@@ -1111,6 +1122,7 @@ dwarf2_frame_cache (struct frame_info *this_frame, void **this_cache)
 	{
 	  cache->unavailable_retaddr = 1;
 	  do_cleanups (old_chain);
+	  discard_cleanups (reset_cache_cleanup);
 	  return cache;
 	}
 
@@ -1226,6 +1238,7 @@ incomplete CFI data; unspecified registers (e.g., %s) at %s"),
 				 (entry_cfa_sp_offset_p
 				  ? &entry_cfa_sp_offset : NULL));
 
+  discard_cleanups (reset_cache_cleanup);
   return cache;
 }
 
diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
index f82d763..aa58640 100644
--- a/gdb/frame-unwind.h
+++ b/gdb/frame-unwind.h
@@ -44,7 +44,9 @@ struct value;
 
 /* Given THIS frame, take a whiff of its registers (namely
    the PC and attributes) and if SELF is the applicable unwinder,
-   return non-zero.  Possibly also initialize THIS_PROLOGUE_CACHE.  */
+   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.  */
 
 typedef int (frame_sniffer_ftype) (const struct frame_unwind *self,
 				   struct frame_info *this_frame,