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

[Thomas Huth <thuth@redhat.com>]

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);
-
      /*
       * 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>