Re: [patch/rfc] Add a sentinel frame

[Andrew Cagney <ac131313@redhat.com>]

> On Wed, Feb 19, 2003 at 08:32:32AM -0500, Andrew Cagney wrote:
> 
>> So I think it is one of these tests going awall:
>> 
>>   if (next_frame->level >= 0
>>       && !backtrace_below_main
>>       && inside_main_func (get_frame_pc (next_frame)))
>>     /* Don't unwind past main(), bug always unwind the sentinel frame.
>>        Note, this is done _before_ the frame has been marked as
>>        previously unwound.  That way if the user later decides to
>>        allow unwinds past main(), that just happens.  */
>>     return NULL;
>> 
>>   /* 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
>>      entry file is somewhat hokey.  */
>>   /* 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;
>> 
>> The second looks worrying (the dummy frame breakpoint lives in the entry 
>> file ...).  Perhaphs something like:
>> 
>> if (dummy_frame_p (get_frame_pc (next_frame) != NULL
>>     && inside_entry_file (get_frame_pc (next_frame))
>>   return NULL;
> 
> 
> Hrm, shouldn't we have already detected the dummy frame at this point? 

No.  GDB is trying to perform:

	pop_frame (get_current_frame())

with the assumption that it has a dummy frame and get_current_frame() 
will return it.

> That's what happens on i386 IIRC...

Chance has it inside_entry_file(entry-point) returns false.  Knowing 
that function, I'd not be suprized.

The `bug' is an unexpected interaction between get_prev_frame's 
end-of-frame test and the change to unwind from the sentinel frame. 
Previously the end-of-frame test wasn't applied to the current frame.

Andrew