[PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames

[PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames

[Markus Metzger]

Patch 7eb895307f53 Skip unwritable frames in command "finish"
skips non-writable frames in addition to tailcall frames.

If skip_tailcall_frames already returns NULL, skip_unwritable_frames
will be called with a NULL frame and crash in get_frame_arch.  This is
caught by gdb.btrace/tailcall-only.exp.

Further, if we ever end up with a mixture of tailcall and non-writable
frames, we may not skip all of them, as intended.

Loop over skip_tailcall_frames and skip_unwritable_frames as long as at least
one of them makes progress.

2016-05-31  Markus Metzger  <markus.t.metzger@intel.com>

	* infcmd.c (skip_finish_frames): New.
	(finish_command): Call skip_finish_frames.
---
 gdb/infcmd.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 14d51fd..ca8655a 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1927,6 +1927,28 @@ finish_forward (struct finish_command_fsm *sm, struct frame_info *frame)
   proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
 }
 
+/* Skip frames for "finish".  */
+
+static struct frame_info *
+skip_finish_frames (struct frame_info *frame)
+{
+  struct frame_info *start;
+
+  do {
+    start = frame;
+
+    frame = skip_tailcall_frames (frame);
+    if (frame == NULL)
+      break;
+
+    frame = skip_unwritable_frames (frame);
+    if (frame == NULL)
+      break;
+  } while (start != frame);
+
+  return frame;
+}
+
 /* "finish": Set a temporary breakpoint at the place the selected
    frame will return to, then continue.  */
 
@@ -2025,11 +2047,7 @@ finish_command (char *arg, int from_tty)
     finish_backward (sm);
   else
     {
-      /* Ignore TAILCALL_FRAME type frames, they were executed already before
-	 entering THISFRAME.  */
-      frame = skip_tailcall_frames (frame);
-
-      frame = skip_unwritable_frames (frame);
+      frame = skip_finish_frames (frame);
 
       if (frame == NULL)
 	error (_("Cannot find the caller frame."));
-- 
1.8.3.1

Re: [PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames

[Yao Qi]

Markus Metzger <markus.t.metzger@intel.com> writes:

Patch is good to me, nits on code format,

> +  do {

"{" should be in the new line.

> +    start = frame;
> +
> +    frame = skip_tailcall_frames (frame);
> +    if (frame == NULL)
> +      break;
> +
> +    frame = skip_unwritable_frames (frame);
> +    if (frame == NULL)
> +      break;
> +  } while (start != frame);

"while" should be in the new line too.  The format is documented in
https://www.gnu.org/prep/standards/standards.html#Writing-C

-- 
Yao (齐尧)

RE: [PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames

[Metzger, Markus T]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="utf-8", Size: 768 bytes --]

> -----Original Message-----
> From: Yao Qi [mailto:qiyaoltc@gmail.com]
> Sent: Wednesday, June 1, 2016 10:51 AM
> To: Metzger, Markus T <markus.t.metzger@intel.com>
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH] infcmd, btrace: fix crash in 'finish' for tailcall-only frames
> 
> Markus Metzger <markus.t.metzger@intel.com> writes:
> 
> Patch is good to me, nits on code format,

Thanks,
Markus.

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