On Mon, Apr 19, 2021 at 7:35 AM Stefan Hajnoczi [off-list ref] wrote:

On Tue, Apr 13, 2021 at 04:03:19PM +0100, Stefan Hajnoczi wrote:

quoted

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 [off-list ref]
  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 <redacted>
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.

-- 
H.J.