Re: [PATCH liburing] examples/ucontext-cp.c: cope with variable SIGSTKSZ
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: 2021-04-19 14:35:16
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 [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? Thanks, Stefan
quoted hunk ↗ jump to hunk
--- 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
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