Re: [PATCH liburing] examples/ucontext-cp.c: cope with variable SIGSTKSZ

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/22/21 3:22 PM, Stefano Garzarella wrote:
> +Cc: io-uring@vger.kernel.org
> +Cc: Pavel Begunkov <asml.silence@gmail.com>
> 
> Original message: https://www.spinics.net/lists/linux-block/msg67077.html
> 
> On Thu, Apr 22, 2021 at 10:59:42AM +0100, Stefan Hajnoczi wrote:
>> On Mon, Apr 19, 2021 at 11:38:07AM -0700, H.J. Lu wrote:
>>> On Mon, Apr 19, 2021 at 7:35 AM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>>> >
>>> > On Tue, Apr 13, 2021 at 04:03:19PM +0100, Stefan Hajnoczi wrote:
>>> > > The size of C arrays at file scope must be constant. The following
>>> > > compiler error occurs with recent upstream glibc (2.33.9000):
>>> > >
>>> > >   CC ucontext-cp
>>> > >   ucontext-cp.c:31:23: error: variably modified ‘stack_buf’ at file scope
>>> > >   31 |         unsigned char stack_buf[SIGSTKSZ];
>>> > >      |                       ^~~~~~~~~
>>> > >   make[1]: *** [Makefile:26: ucontext-cp] Error 1
>>> > >
>>> > > The following glibc commit changed SIGSTKSZ from a constant value to a
>>> > > variable:
>>> > >
>>> > >   commit 6c57d320484988e87e446e2e60ce42816bf51d53
>>> > >   Author: H.J. Lu <hjl.tools@gmail.com>
>>> > >   Date:   Mon Feb 1 11:00:38 2021 -0800
>>> > >
>>> > >     sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305]
>>> > >   ...
>>> > >   +# define SIGSTKSZ sysconf (_SC_SIGSTKSZ)
>>> > >
>>> > > Allocate the stack buffer explicitly to avoid declaring an array at file
>>> > > scope.
>>> > >
>>> > > Cc: H.J. Lu <hjl.tools@gmail.com>
>>> > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> > > ---
>>> > > Perhaps the glibc change needs to be revised before releasing glibc 2.34
>>> > > since it might break applications. That's up to the glibc folks. It
>>> > > doesn't hurt for liburing to take a safer approach that copes with the
>>> > > SIGSTKSZ change in any case.
>>> >
>>> > glibc folks, please take a look. The commit referenced above broke
>>> > compilation of liburing's tests. It's possible that applications will
>>> > hit similar issues. Can you check whether the SIGSTKSZ change needs to
>>> > be reverted/fixed before releasing glibc 2.34?
>>> >
>>>
>>> It won't be changed for glibc 2.34.
>>
>> Thanks for the response, H.J. and Paul.
>>
>> In that case liburing needs this patch.
>>
> 
> I think so:
> 
> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Right, and there are already people complaining
https://github.com/axboe/liburing/issues/320


-- 
Pavel Begunkov