[PATCH for-8.0 1/3] async: Suppress GCC13 false positive in aio_bh_poll()

[Cédric Le Goater]

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 an intermediate helper to
silent GCC. No functional change.

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, 12 insertions(+), 1 deletion(-)

diff --git a/util/async.c b/util/async.c
index 21016a1ac7..45be1ed218 100644
--- a/util/async.c
+++ b/util/async.c
@@ -155,6 +155,11 @@ void aio_bh_call(QEMUBH *bh)
     bh->cb(bh->opaque);
 }
 
+static void aio_bh_slice_insert(AioContext *ctx, BHListSlice *slice)
+{
+    QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, slice, next);
+}
+
 /* Multiple occurrences of aio_bh_poll cannot be called concurrently. */
 int aio_bh_poll(AioContext *ctx)
 {
@@ -164,7 +169,13 @@ 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);
-    QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
+
+    /*
+     * GCC13 [-Werror=dangling-pointer=] complains that the local variable
+     * 'slice' is being stored in a global list in 'ctx->bh_slice_list'.
+     * Use a helper to silent the compiler
+     */
+    aio_bh_slice_insert(ctx, &slice);
 
     while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) {
         QEMUBH *bh;
-- 
2.39.2