Re: [patch/rfc] Add a sentinel frame

Andrew Cagney
2003-02-25T19:43:03Z

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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;
}