Add patch to fix build with rawhide glibc 2.33.9000

See the patch for information on why examples/ucontext-cp.c does not
build with rawhide's glibc 2.33.9000. I sent this patch upstream to
liburing and notified glibc of a potential incompatible change.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

0003-examples-ucontext-cp.c-cope-with-variable-SIGSTKSZ.patch

@@ -0,0 +1,82 @@
+From 595b858eb0576d70884337a61ace3d98a411b949 Mon Sep 17 00:00:00 2001
+From: Stefan Hajnoczi <stefanha@redhat.com>
+Date: Tue, 13 Apr 2021 15:45:52 +0100
+Subject: [PATCH] examples/ucontext-cp.c: cope with variable SIGSTKSZ
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+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.
+---
+ examples/ucontext-cp.c | 12 +++++++++---
+ 1 file changed, 9 insertions(+), 3 deletions(-)
+
+diff --git a/examples/ucontext-cp.c b/examples/ucontext-cp.c
+index 0b2a6b5..ea0c934 100644
+--- a/examples/ucontext-cp.c
++++ b/examples/ucontext-cp.c
+@@ -28,7 +28,7 @@
+ 
+ typedef struct {
+ 	struct io_uring *ring;
+-	unsigned char stack_buf[SIGSTKSZ];
++	unsigned char *stack_buf;
+ 	ucontext_t ctx_main, ctx_fnew;
+ } async_context;
+ 
+@@ -115,8 +115,13 @@ static int setup_context(async_context *pctx, struct io_uring *ring)
+ 		perror("getcontext");
+ 		return -1;
+ 	}
+-	pctx->ctx_fnew.uc_stack.ss_sp = &pctx->stack_buf;
+-	pctx->ctx_fnew.uc_stack.ss_size = sizeof(pctx->stack_buf);
++	pctx->stack_buf = malloc(SIGSTKSZ);
++	if (!pctx->stack_buf) {
++		perror("malloc");
++		return -1;
++	}
++	pctx->ctx_fnew.uc_stack.ss_sp = pctx->stack_buf;
++	pctx->ctx_fnew.uc_stack.ss_size = SIGSTKSZ;
+ 	pctx->ctx_fnew.uc_link = &pctx->ctx_main;
+ 
+ 	return 0;
+@@ -174,6 +179,7 @@ static void copy_file_wrapper(arguments_bundle *pbundle)
+ 	free(iov.iov_base);
+ 	close(pbundle->infd);
+ 	close(pbundle->outfd);
++	free(pbundle->pctx->stack_buf);
+ 	free(pbundle->pctx);
+ 	free(pbundle);
+ 
+-- 
+2.30.2
+

liburing.spec

@@ -10,6 +10,7 @@ BuildRequires: gcc
 BuildRequires: make
 Patch1: 0001-spec-bump-version-to-2.0.patch
 Patch2: 0002-spec-add-explicit-build-dependency-on-make.patch
+Patch3: 0003-examples-ucontext-cp.c-cope-with-variable-SIGSTKSZ.patch
 
 %description
 Provides native async IO for the Linux kernel, in a fast and efficient