On 21/03/2023 17.16, Cédric Le Goater wrote:
From: Cédric Le Goater <clg@redhat.com>
GCC13 reports an error :
../util/async.c: In function ‘aio_bh_poll’:
include/qemu/queue.h:303:22: error: storing the address of local variable
‘slice’ in ‘*ctx.bh_slice_list.sqh_last’ [-Werror=dangling-pointer=]
303 | (head)->sqh_last = &(elm)->field.sqe_next;
\
| ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
../util/async.c:169:5: note: in expansion of macro ‘QSIMPLEQ_INSERT_TAIL’
169 | QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
| ^~~~~~~~~~~~~~~~~~~~
../util/async.c:161:17: note: ‘slice’ declared here
161 | BHListSlice slice;
| ^~~~~
../util/async.c:161:17: note: ‘ctx’ declared here
But the local variable 'slice' is removed from the global context list
in following loop of the same routine. Add a pragma to silent GCC.
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
---
util/async.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/util/async.c b/util/async.c
index 21016a1ac7..de9b431236 100644
--- a/util/async.c
+++ b/util/async.c
@@ -164,7 +164,20 @@ int aio_bh_poll(AioContext *ctx)
/* Synchronizes with QSLIST_INSERT_HEAD_ATOMIC in aio_bh_enqueue(). */
QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list);
+
+ /*
+ * GCC13 [-Werror=dangling-pointer=] complains that the local variable
+ * 'slice' is being stored in the global 'ctx->bh_slice_list' but the
+ * list is emptied before this function returns.
+ */
+#if !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdangling-pointer="
That warning parameter looks like a new one in GCC 13 ?
... so you have to check whether it's available before disabling
it, otherwise this will fail with older versions of GCC. I just
gave it a try with my GCC 8.5 and got this:
../../devel/qemu/util/async.c: In function ‘aio_bh_poll’:
../../devel/qemu/util/async.c:175:32: error: unknown option after ‘#pragma GCC
diagnostic’ kind [-Werror=pragmas]
#pragma GCC diagnostic ignored "-Wdangling-pointer="
^~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
Thomas
What about reworking the code like this:
diff --git a/util/async.c b/util/async.c
index 21016a1ac7..b236bdfbd8 100644
--- a/util/async.c
+++ b/util/async.c
@@ -156,15 +156,14 @@ void aio_bh_call(QEMUBH *bh)
}
/* Multiple occurrences of aio_bh_poll cannot be called concurrently. */
-int aio_bh_poll(AioContext *ctx)
+static int aio_bh_poll_slice(AioContext *ctx, BHListSlice *slice)
{
- BHListSlice slice;
BHListSlice *s;
int ret = 0;
/* Synchronizes with QSLIST_INSERT_HEAD_ATOMIC in aio_bh_enqueue(). */
- QSLIST_MOVE_ATOMIC(&slice.bh_list, &ctx->bh_list);
- QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
+ QSLIST_MOVE_ATOMIC(&slice->bh_list, &ctx->bh_list);
+ QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, slice, next);
while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) {
QEMUBH *bh;
@@ -191,6 +190,13 @@ int aio_bh_poll(AioContext *ctx)
return ret;
}
+int aio_bh_poll(AioContext *ctx)
+{
+ BHListSlice slice;
+
+ return aio_bh_poll_slice(ctx, &slice);
+}
+
void qemu_bh_schedule_idle(QEMUBH *bh)
{
aio_bh_enqueue(bh, BH_SCHEDULED | BH_IDLE);
Would that work with GCC 13 and be acceptable?