Re: [PATCH] selftests/vfio: avoid VLAs

[Vipin Sharma <vipinsh@google.com>]

On Fri, Jun 12, 2026 at 02:58:18PM -0700, Alex Mastro wrote:
> Allocate VFIO ioctl requests dynamically instead of using VLAs. GCC 11.5.0
> rejects initialized VLAs with:
> 
>   error: variable-sized object may not be initialized
> 
> The replaced stack u8 arrays also do not guarantee native struct alignment
> for the aliased pointers.
> 
> Fixes: 19faf6fd969c ("vfio: selftests: Add a helper library for VFIO selftests")
> Fixes: 20face8c75ff ("vfio: selftests: Add helper to set/override a vf_token")
> Signed-off-by: Alex Mastro <amastro@fb.com>
> Assisted-by: Codex:gpt-5.5-high
> ---
>  tools/testing/selftests/vfio/lib/vfio_pci_device.c | 28 +++++++++++++---------
>  1 file changed, 17 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> index 94dc5fcecbeb..0b437435cce1 100644
> --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> @@ -30,13 +30,12 @@
>  static void vfio_pci_irq_set(struct vfio_pci_device *device,
>  			     u32 index, u32 vector, u32 count, int *fds)
>  {
> -	u8 buf[sizeof(struct vfio_irq_set) + sizeof(int) * count];
> -	struct vfio_irq_set *irq = (void *)&buf;
> -	int *irq_fds = (void *)&irq->data;
> +	struct vfio_irq_set *irq;
> +	size_t irq_size = sizeof(*irq) + sizeof(int) * count;

Nit: Can you change it to Reverse Fir Tree style? Same for the other
change.

Other than that this looks good. Thanks!

Tested-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: Vipin Sharma <vipinsh@google.com>

index 0b437435cce1..c70636c214bc 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -31,8 +31,9 @@ static void vfio_pci_irq_set(struct vfio_pci_device *device,
                             u32 index, u32 vector, u32 count, int *fds)
 {
        struct vfio_irq_set *irq;
-       size_t irq_size = sizeof(*irq) + sizeof(int) * count;
+       size_t irq_size;

+       irq_size = sizeof(*irq) + sizeof(int) * count;
        irq = calloc(1, irq_size);
        VFIO_ASSERT_NOT_NULL(irq);
        irq->argsz = irq_size;
@@ -119,9 +120,10 @@ static int vfio_device_feature_ioctl(int fd, u32 flags, void *data,
                                     size_t data_size)
 {
        struct vfio_device_feature *feature;
-       size_t feature_size = sizeof(*feature) + data_size;
+       size_t feature_size;
        int ret;

+       feature_size = sizeof(*feature) + data_size;
        feature = calloc(1, feature_size);
        VFIO_ASSERT_NOT_NULL(feature);
        memcpy(feature->data, data, data_size);