Re: [PATCH v2] Add missing initialization for g_autofree variables

[Miroslav Rezanina]

On Mon, Mar 15, 2021 at 09:08:01AM +0100, Thomas Huth wrote:
> On 15/03/2021 09.00, mrezanin@redhat.com wrote:
> > From: Miroslav Rezanina <mrezanin@redhat.com>
> > 
> > When declaring g_autofree variable without inicialization, compiler
> > will raise "may be used uninitialized in this function" warning due
> > to automatic free handling.
> > 
> > This is mentioned in docs/devel/style.rst (quote from section
> > "Automatic memory deallocation"):
> > 
> >    * Variables declared with g_auto* MUST always be initialized,
> >      otherwise the cleanup function will use uninitialized stack memory
> > 
> > Add inicialization to NULL for these declaration to prevent this
> > warning.
> > 
> > Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
> > 
> > ---
> > * From v1:
> >    -- Removed fixes in hw/remote/memory.c and hw/remote/proxy.c
> >       fixed by patch sent by Zenghui Yu (multi-process: Initialize
> >       variables declared with g_auto*)
> > ---
> >   hw/s390x/s390-pci-vfio.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
> > index ead4f222d5..0ee7dc21f2 100644
> > --- a/hw/s390x/s390-pci-vfio.c
> > +++ b/hw/s390x/s390-pci-vfio.c
> > @@ -29,7 +29,7 @@
> >    */
> >   bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
> >   {
> > -    g_autofree struct vfio_iommu_type1_info *info;
> > +    g_autofree struct vfio_iommu_type1_info *info = NULL;
> >       uint32_t argsz;
> >       assert(avail);
> 
> I'd maybe rather rework the functions like this:
> 
> diff --git a/hw/s390x/s390-pci-vfio.c b/hw/s390x/s390-pci-vfio.c
> index ead4f222d5..1fe71fd93f 100644
> --- a/hw/s390x/s390-pci-vfio.c
> +++ b/hw/s390x/s390-pci-vfio.c
> @@ -29,14 +29,11 @@
>   */
>  bool s390_pci_update_dma_avail(int fd, unsigned int *avail)
>  {
> -    g_autofree struct vfio_iommu_type1_info *info;
> -    uint32_t argsz;
> +    uint32_t argsz = sizeof(struct vfio_iommu_type1_info);
> +    g_autofree struct vfio_iommu_type1_info *info = g_malloc0(argsz);
>      assert(avail);
> -    argsz = sizeof(struct vfio_iommu_type1_info);
> -    info = g_malloc0(argsz);
> -

Hi Thomas,

I thought about it but for some reason I miss-read the code and though
that avail is used for calculating argsz and didn't want to use it before
assert.

I'll send new version with this change.
>      /*
>       * If the specified argsz is not large enough to contain all capabilities
>       * it will be updated upon return from the ioctl.  Retry until we have
> 
> > @@ -230,7 +230,7 @@ static void s390_pci_read_pfip(S390PCIBusDevice *pbdev,
> >    */
> >   void s390_pci_get_clp_info(S390PCIBusDevice *pbdev)
> >   {
> > -    g_autofree struct vfio_device_info *info;
> > +    g_autofree struct vfio_device_info *info = NULL;
> >       VFIOPCIDevice *vfio_pci;
> >       uint32_t argsz;
> >       int fd;
> > 
> 
> Anyway,
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> 
>