[RFA] Use TRY/CATCH in remove_prev_frame

[RFA] Use TRY/CATCH in remove_prev_frame

[Tom Tromey]

This changes remove_prev_frame to use TRY/CATCH instead of a cleanup.
TRY/CATCH seemed appropriate here because the cleanup is only needed
in the case where an exception is thrown.

Tested by the buildbot.

ChangeLog
2018-05-24  Tom Tromey  <tom@tromey.com>

	* frame.c (remove_prev_frame): Remove.
	(get_prev_frame_if_no_cycle): Use TRY/CATCH.
---
 gdb/ChangeLog |  5 +++++
 gdb/frame.c   | 58 +++++++++++++++++++++++++---------------------------------
 2 files changed, 30 insertions(+), 33 deletions(-)

diff --git a/gdb/frame.c b/gdb/frame.c
index 1d0eb72514..e55b4e1630 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -1871,22 +1871,6 @@ frame_register_unwind_location (struct frame_info *this_frame, int regnum,
     }
 }
 
-/* Called during frame unwinding to remove a previous frame pointer from a
-   frame passed in ARG.  */
-
-static void
-remove_prev_frame (void *arg)
-{
-  struct frame_info *this_frame, *prev_frame;
-
-  this_frame = (struct frame_info *) arg;
-  prev_frame = this_frame->prev;
-  gdb_assert (prev_frame != NULL);
-
-  prev_frame->next = NULL;
-  this_frame->prev = NULL;
-}
-
 /* Get the previous raw frame, and check that it is not identical to
    same other frame frame already in the chain.  If it is, there is
    most likely a stack cycle, so we discard it, and mark THIS_FRAME as
@@ -1899,7 +1883,6 @@ static struct frame_info *
 get_prev_frame_if_no_cycle (struct frame_info *this_frame)
 {
   struct frame_info *prev_frame;
-  struct cleanup *prev_frame_cleanup;
 
   prev_frame = get_prev_frame_raw (this_frame);
 
@@ -1915,29 +1898,38 @@ get_prev_frame_if_no_cycle (struct frame_info *this_frame)
   if (prev_frame->level == 0)
     return prev_frame;
 
-  /* The cleanup will remove the previous frame that get_prev_frame_raw
-     linked onto THIS_FRAME.  */
-  prev_frame_cleanup = make_cleanup (remove_prev_frame, this_frame);
-
-  compute_frame_id (prev_frame);
-  if (!frame_stash_add (prev_frame))
+  TRY
     {
-      /* Another frame with the same id was already in the stash.  We just
-	 detected a cycle.  */
-      if (frame_debug)
+      compute_frame_id (prev_frame);
+      if (!frame_stash_add (prev_frame))
 	{
-	  fprintf_unfiltered (gdb_stdlog, "-> ");
-	  fprint_frame (gdb_stdlog, NULL);
-	  fprintf_unfiltered (gdb_stdlog, " // this frame has same ID }\n");
+	  /* Another frame with the same id was already in the stash.  We just
+	     detected a cycle.  */
+	  if (frame_debug)
+	    {
+	      fprintf_unfiltered (gdb_stdlog, "-> ");
+	      fprint_frame (gdb_stdlog, NULL);
+	      fprintf_unfiltered (gdb_stdlog, " // this frame has same ID }\n");
+	    }
+	  this_frame->stop_reason = UNWIND_SAME_ID;
+	  /* Unlink.  */
+	  prev_frame->next = NULL;
+	  this_frame->prev = NULL;
+	  prev_frame = NULL;
 	}
-      this_frame->stop_reason = UNWIND_SAME_ID;
-      /* Unlink.  */
+    }
+  CATCH (ex, RETURN_MASK_ERROR)
+    {
+      prev_frame = this_frame->prev;
+      gdb_assert (prev_frame != NULL);
+
       prev_frame->next = NULL;
       this_frame->prev = NULL;
-      prev_frame = NULL;
+
+      throw_exception (ex);
     }
+  END_CATCH
 
-  discard_cleanups (prev_frame_cleanup);
   return prev_frame;
 }
 
-- 
2.13.6

Re: [RFA] Use TRY/CATCH in remove_prev_frame

[Pedro Alves]

Quoting a "git diff -w" version of the patch, for easier context.

On 05/25/2018 04:36 AM, Tom Tromey wrote:

> diff --git a/gdb/frame.c b/gdb/frame.c
> index 1d0eb725145..e55b4e16305 100644
> --- a/gdb/frame.c
> +++ b/gdb/frame.c
> @@ -1871,22 +1871,6 @@ frame_register_unwind_location (struct frame_info *this_frame, int regnum,
>      }
>  }
>  
> -/* Called during frame unwinding to remove a previous frame pointer from a
> -   frame passed in ARG.  */
> -
> -static void
> -remove_prev_frame (void *arg)
> -{
> -  struct frame_info *this_frame, *prev_frame;
> -
> -  this_frame = (struct frame_info *) arg;
> -  prev_frame = this_frame->prev;
> -  gdb_assert (prev_frame != NULL);
> -
> -  prev_frame->next = NULL;
> -  this_frame->prev = NULL;
> -}
> -
>  /* Get the previous raw frame, and check that it is not identical to
>     same other frame frame already in the chain.  If it is, there is
>     most likely a stack cycle, so we discard it, and mark THIS_FRAME as
> @@ -1899,7 +1883,6 @@ static struct frame_info *
>  get_prev_frame_if_no_cycle (struct frame_info *this_frame)
>  {
>    struct frame_info *prev_frame;
> -  struct cleanup *prev_frame_cleanup;
>  
>    prev_frame = get_prev_frame_raw (this_frame);
>  
> @@ -1915,10 +1898,8 @@ get_prev_frame_if_no_cycle (struct frame_info *this_frame)
>    if (prev_frame->level == 0)
>      return prev_frame;
>  
> -  /* The cleanup will remove the previous frame that get_prev_frame_raw
> -     linked onto THIS_FRAME.  */
> -  prev_frame_cleanup = make_cleanup (remove_prev_frame, this_frame);
> -
> +  TRY
> +    {
>        compute_frame_id (prev_frame);
>        if (!frame_stash_add (prev_frame))
>  	{
> @@ -1936,8 +1917,19 @@ get_prev_frame_if_no_cycle (struct frame_info *this_frame)
>  	  this_frame->prev = NULL;
>  	  prev_frame = NULL;
>  	}
> +    }
> +  CATCH (ex, RETURN_MASK_ERROR)

Use RETURN_MASK_ALL.

> +    {
> +      prev_frame = this_frame->prev;
> +      gdb_assert (prev_frame != NULL);

I think these two lines aren't necessary?  It seems like
they existed in remove_prev_frame because that needs to
find the prev_frame from its passed-in argument, which is
just this_frame.  But here we already have prev_frame handy.

OK with those changes.

> +
> +      prev_frame->next = NULL;
> +      this_frame->prev = NULL;
> +
> +      throw_exception (ex);
> +    }
> +  END_CATCH
>  
> -  discard_cleanups (prev_frame_cleanup);
>    return prev_frame;
>  }
>  
> 

Re: [RFA] Use TRY/CATCH in remove_prev_frame

[Tom Tromey]

>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

>> +  CATCH (ex, RETURN_MASK_ERROR)

Pedro> Use RETURN_MASK_ALL.

I made this change but someone may want to audit the other uses of
TRY/CATCH in frame.c.  They all use RETURN_MASK_ERROR.  Or I could just
convert them all.

Tom

Re: [RFA] Use TRY/CATCH in remove_prev_frame

[Tom Tromey]

>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

Pedro> The other uses are all correct.

Thanks, I see.

Tom

Re: [RFA] Use TRY/CATCH in remove_prev_frame

[Pedro Alves]

On 05/25/2018 03:58 PM, Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
>>> +  CATCH (ex, RETURN_MASK_ERROR)
> 
> Pedro> Use RETURN_MASK_ALL.
> 
> I made this change but someone may want to audit the other uses of
> TRY/CATCH in frame.c.  They all use RETURN_MASK_ERROR.  Or I could just
> convert them all.

The other uses are all correct.  They want to handle specific
types of exceptions, like:

  CATCH (ex, RETURN_MASK_ERROR)
    {
      if (ex.error == MEMORY_ERROR)

  CATCH (ex, RETURN_MASK_ERROR)
    {
      if (ex.error == NOT_AVAILABLE_ERROR)

All other types of exception are rethrown.  So it would be
useless to use RETURN_MASK_ALL for those, because it would
mean we would catch Ctrl-C just to rethrow it again
immediately.

Thanks,
Pedro Alves