Re: [PATCH] async: Suppress GCC13 false positive in aio_bh_poll()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

On 4/20/23 18:07, Daniel Henrique Barboza wrote:
> 
> 
> On 4/20/23 17:29, 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>
>> ---
> 
> 
> Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> 
> 
> If no one opposes I'll queue this patch, and the following 2 already reviewed
> patches, in ppc-next:
> 
> [PATCH for-8.0 v2 3/3] target/ppc: Fix helper_pminsn() prototype
> [PATCH for-8.0 v2 2/3] target/s390x: Fix float_comp_to_cc() prototype


Nevermind, these 2 patches are already applied. We're missing just this one.



Daniel

> 
> 
> The reason is that I updated to Fedora 38 too soon and became aggravated by
> these GCC13 false positives.
> 
> 
> 
> Thanks,
> 
> 
> Daniel
> 
> 
> 
>>   util/async.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/util/async.c b/util/async.c
>> index 21016a1ac7..856e1a8a33 100644
>> --- a/util/async.c
>> +++ b/util/async.c
>> @@ -164,7 +164,21 @@ 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 "-Wpragmas"
>> +#pragma GCC diagnostic ignored "-Wdangling-pointer="
>> +#endif
>>       QSIMPLEQ_INSERT_TAIL(&ctx->bh_slice_list, &slice, next);
>> +#if !defined(__clang__)
>> +#pragma GCC diagnostic pop
>> +#endif
>>       while ((s = QSIMPLEQ_FIRST(&ctx->bh_slice_list))) {
>>           QEMUBH *bh;