Re: [patch/rfc] Add a sentinel frame

[Andrew Cagney <ac131313@redhat.com>]

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Michael, try the attached patch.

Andrew

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> Hello,
> 
> This improves the checks in get_prev_frame() that look for stuff like the top-of-stack or a corrupt stack.
> 
> d10v (which uses this) showed no regressions, neither did i386.
> 
> I'll commit `tomorrow'.
> 
> Andrew

With patch....


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2003-02-24  Andrew Cagney  <cagney@redhat.com>

	* frame.c (get_prev_frame): Add comment on check for
	inside_entry_func. Only check for inside_entry_file when not a
	dummy and not a sentinel.  Check that the new frame is not inner
	to the old frame.

Index: frame.c
===================================================================
RCS file: /cvs/src/src/gdb/frame.c,v
retrieving revision 1.67
diff -u -r1.67 frame.c
--- frame.c	20 Feb 2003 16:35:51 -0000	1.67
+++ frame.c	25 Feb 2003 03:51:35 -0000
@@ -1230,7 +1230,6 @@
     return next_frame->prev;
   next_frame->prev_p = 1;
 
-  /* If we're inside the entry file, it isn't valid.  */
   /* NOTE: drow/2002-12-25: should there be a way to disable this
      check?  It assumes a single small entry file, and the way some
      debug readers (e.g.  dbxread) figure out which object is the
@@ -1238,8 +1237,26 @@
   /* NOTE: cagney/2003-01-10: If there is a way of disabling this test
      then it should probably be moved to before the ->prev_p test,
      above.  */
-  if (inside_entry_file (get_frame_pc (next_frame)))
-      return NULL;
+  /* If we're inside the entry file, it isn't valid.  Don't apply this
+     test to a dummy frame - dummy frame PC's typically land in the
+     entry file.  Don't apply this test to the sentinel frame.
+     Sentinel frames should always be allowed to unwind.  */
+  if (next_frame->type != DUMMY_FRAME && next_frame->level >= 0
+      && inside_entry_file (get_frame_pc (next_frame)))
+    return NULL;
+
+#if 0
+  /* NOTE: cagney/2003-02-25: Don't enable until someone has found
+     evidence that this is needed.  */
+  /* If we're already inside the entry function for the main objfile,
+     then it isn't valid.  Don't apply this test to a dummy frame -
+     dummy frame PC's typically land in the entry func.  Don't apply
+     this test to the sentinel frame.  Sentinel frames should always
+     be allowed to unwind.  */
+  if (next_frame->type != DUMMY_FRAME && next_frame->level >= 0
+      && inside_entry_func (get_frame_pc (fi)))
+    return 0;
+#endif
 
   /* If any of the old frame initialization methods are around, use
      the legacy get_prev_frame method.  Just don't try to unwind a
@@ -1301,6 +1318,16 @@
     struct frame_id id = frame_id_unwind (next_frame);
     if (!frame_id_p (id))
       return NULL;
+    /* Check that the new frame isn't inner to (younger, below, next)
+       the old frame - we've not gone backwards.  Ignore the sentinel
+       frame where weird things happen.  */
+    if (next_frame->level >= 0
+	&& frame_id_inner (id, get_frame_id (next_frame)))
+      error ("Unwound frame inner to selected frame (corrupt stack?)");
+    /* Note that, due to frameless functions, the stronger test of the
+       new frame being outer to the old frame can't be used -
+       frameless functions differ by only their PC value.  Ignore the
+       sentinel frame where weird things happen.  */
     prev_frame->frame = id.base;
   }