[Qemu-devel] Re: [PATCH] block: Use GCC_FMT_ATTR and fix a format error

[Stefan Weil <weil@mail.berlios.de>]

Am 23.09.2010 20:53, schrieb Blue Swirl:
> On Thu, Sep 23, 2010 at 6:37 PM, Stefan Weil<weil@mail.berlios.de>  wrote:
>    
>> Adding the gcc format attribute detects a format bug
>> which is fixed here.
>>
>> Cc: Blue Swirl<blauwirbel@gmail.com>
>> Cc: Kevin Wolf<kwolf@redhat.com>
>> Signed-off-by: Stefan Weil<weil@mail.berlios.de>
>> ---
>>   block/blkverify.c |    5 +++--
>>   1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/blkverify.c b/block/blkverify.c
>> index 8083464..b39fb67 100644
>> --- a/block/blkverify.c
>> +++ b/block/blkverify.c
>> @@ -53,7 +53,8 @@ static AIOPool blkverify_aio_pool = {
>>      .cancel             = blkverify_aio_cancel,
>>   };
>>
>> -static void blkverify_err(BlkverifyAIOCB *acb, const char *fmt, ...)
>> +static void GCC_FMT_ATTR(2, 3) blkverify_err(BlkverifyAIOCB *acb,
>> +                                             const char *fmt, ...)
>>   {
>>      va_list ap;
>>
>> @@ -300,7 +301,7 @@ static void blkverify_verify_readv(BlkverifyAIOCB *acb)
>>      ssize_t offset = blkverify_iovec_compare(acb->qiov,&acb->raw_qiov);
>>      if (offset != -1) {
>>          blkverify_err(acb, "contents mismatch in sector %ld",
>> -                      acb->sector_num + (offset / BDRV_SECTOR_SIZE));
>> +                      (long)(acb->sector_num + (offset / BDRV_SECTOR_SIZE)));
>>      
> sector_num is int64_t, so the correct fix is to change '%ld' to '%" PRId64'.
>
>    

I noticed that, too. But offset is ssize_t.
Can you always be sure that (int64_t + ssize_t) results in a int64_t?
I don't think it's so easy.