Re: segfault using _Unwind_ForcedUnwind()

[Ian Lance Taylor <iant@xxxxxxxxxx>]

Andrew Haley <aph@xxxxxxxxxx> writes:

> On 03/30/2012 08:26 PM, Ian Lance Taylor wrote:
>> Oliver Kowalke <oliver.kowalke@xxxxxx> writes:
>> 
>>> Am 30.03.2012 17:08, schrieb Ian Lance Taylor:
>>>> "Oliver Kowalke"<oliver.kowalke@xxxxxx>  writes:
>>>>
>>>>> I get a segfault with following app - could you verify this?
>>>> This program works fine for me (gcc 4.4.3, glibc 2.11.1, Ubuntu Lucid)
>>>> in 64-bit mode.  But now I see that you are using 32-bit mode.  I can
>>>> confirm that the program crashes for me in that mode.
>>>>
>>>> Looking at the 32-bit implementation of makecontext in glibc, I can see
>>>> that the problem is that it doesn't set up correct unwind information
>>>> for the parameters pushed on the stack.  The effect is that the first
>>>> parameter on the stack appears to be a PC value.  I think this is a bug
>>>> in glibc.  It should be possible to arrange for unwind information which
>>>> skips %ebx words on the stack.
>>>
>>> I think the test app is not correct - on ppc32/linux it never returns.
>> 
>> Any application that tries to walk up the stack to the end is
>> unfortunately going to be tricky and non-portable.  If you want a
>> portable program you should always have some way to stop the stack
>> unwind yourself.  That is unfortunate but true.
>
> I'm not at all happy about that.  Any system that supports backtrace()
> should be able to get this right.  I've had to fix more than one
> system to make unwinding work right; if it doesn't, that can (and IMO
> should) be treated as a bug.

I suppose I can't argue with that.

As seen in my message quoted above, I think there is a bug in the 32-bit
x86 implementation of makecontext in glibc.

I have not looked into the PPC32 case.

Ian