gdb bt gives many question marks

Christopher Faylor cgf-use-the-mailinglist-please@cygwin.com
Thu Mar 14 14:49:00 GMT 2013


On Thu, Mar 14, 2013 at 09:34:45AM -0400, Ryan Johnson wrote:
>On 14/03/2013 3:37 AM, Ken Huang wrote:
>> Hi all,
>>
>> I have a problem when using gdb to debug my program in cygwin, the 'bt' command
>> gives me many '??'.
>>
>> So I write a quite easy program named abort.c which just aborts. after
>> compiled with
>> "gcc -g abort.c -o abort" and run with " gdb abort", it aborts as
>> expected. At this time
>> I type "bt" in gdb to see the backtrace info, but it only gives the following:
><standard useless windows stack frames that have nothing to do with the 
>actual cygwin program under debug>
>
>My experience is that you're SOL once Windows has started its exception 
>handling. I dont' know if it's an alternate stack, a debug info problem, 
>or what; but the only reliable way I know to debug aborts is to `b 
>__abort' so that gdb gets there before of Windows (I think it's two 
>underscores, but it could be one or three).

The changes mentioned here should help:
http://cygwin.com/ml/cygwin/2013-03/msg00176.html

But you'll need a snapshot.

(And now that I've had a few days to mull over the change I can see that
I probably need to do more work on the stack frame)

cgf

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