Re: [PATCH] migration/qemu-file: Fix maybe uninitialized on qemu_get_buffer_in_place()

[Dr. David Alan Gilbert]

* Philippe Mathieu-Daudé (philmd@redhat.com) wrote:
> On 1/28/21 6:16 PM, Dr. David Alan Gilbert wrote:
> > * Wainer dos Santos Moschetta (wainersm@redhat.com) wrote:
> >> Fixed error when compiling migration/qemu-file.c with 
> >> -Werror=maybe-uninitialized
> >> as shown here:
> >>
> >> ../migration/qemu-file.c: In function 'qemu_get_buffer_in_place':
> >> ../migration/qemu-file.c:604:18: error: 'src' may be used uninitialized in 
> >> this function [-Werror=maybe-uninitialized]
> >>   604 |             *buf = src;
> >>       |             ~~~~~^~~~~
> >> cc1: all warnings being treated as errors
> >>
> >> Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
> > 
> > Yes, I think I had a discussion with someone about this recently but
> > can't find it;
> 
> Maybe with Thomas, he reported that 2 years ago when building with -O3:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg599522.html

I've got this vague memory I've had a conversation much much more
recently; like in the last month or two but I can't find it.

Dave

> > the compiler is technically correct, but the only time
> > it's unitialised is the case where it's result doesn't matter.
> > 
> > Still, to shut the compiler up:
> > 
> > 
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > 
> >> ---
> >> Passed on CI: https://gitlab.com/wainersm/qemu/-/pipelines/247801576
> >>
> >>  migration/qemu-file.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> >> index be21518c57..d6e03dbc0e 100644
> >> --- a/migration/qemu-file.c
> >> +++ b/migration/qemu-file.c
> >> @@ -595,7 +595,7 @@ size_t qemu_get_buffer_in_place(QEMUFile *f, uint8_t 
> >> **buf, size_t size)
> >>  {
> >>      if (size < IO_BUF_SIZE) {
> >>          size_t res;
> >> -        uint8_t *src;
> >> +        uint8_t *src = NULL;
> >>  
> >>          res = qemu_peek_buffer(f, &src, size, 0);
> >>  
> >> -- 
> >> 2.28.0
> >>
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK