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

[Stefan Hajnoczi <stefanha@redhat.com>]

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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.

Stefan

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