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

[Stefan Weil]

Am 23.09.2010 20:53, schrieb Blue Swirl:
> On Thu, Sep 23, 2010 at 6:37 PM, Stefan Weil<address@hidden>  wrote:
>    
> > Adding the gcc format attribute detects a format bug
> > which is fixed here.
> >
> > Cc: Blue Swirl<address@hidden>
> > Cc: Kevin Wolf<address@hidden>
> > Signed-off-by: Stefan Weil<address@hidden>
> > ---
> >   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.