On Tue, 17 Mar 2026 10:44:02 +0530
<[email protected]> wrote:
> From: Manish Honap <[email protected]>
>
> C does not permit an initialiser expression on a variable-length array
> (C99 Section 6.7.9 constraint: "The type of the entity to be initialized
> shall not be a variable length array type").
>
> vfio_pci_irq_set() declared:
>
> u8 buf[sizeof(struct vfio_irq_set) + sizeof(int) * count] = {};
>
> where `count` is a runtime function parameter, making `buf` a VLA.
>
> GCC rejects this with (tried with GCC-9.4.0):
>
> error: variable-sized object may not be initialized
>
> Fix by removing the `= {}` initialiser and inserting an explicit
> memset() immediately after the declaration. memset() on a VLA is
> perfectly legal and achieves the same zero-initialisation on all
> conforming C implementations.
>
> Fixes: 19faf6fd969c ("vfio: selftests: Add a helper library for VFIO
> selftests")
> Cc: [email protected]
> Reviewed-by: Dave Jiang <[email protected]>
> Reviewed-by: David Matlack <[email protected]>
> Signed-off-by: Manish Honap <[email protected]>
> ---
>
> This fix is self-contained: it touches only the existing vfio selftest
> helper library and carries no dependency on any other patch. It was
> originally included as PATCH 20/20 in the CXL Type-2 VFIO passthrough
> RFC series [1] but belongs on the vfio list independently, as noted by
> Dave Jiang.
>
> [1] https://lore.kernel.org/all/[email protected]/
>
> tools/testing/selftests/vfio/lib/vfio_pci_device.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> index fac4c0ecadef..3258e814f450 100644
> --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
> @@ -26,8 +26,10 @@
> 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] = {};
> + u8 buf[sizeof(struct vfio_irq_set) + sizeof(int) * count];
> struct vfio_irq_set *irq = (void *)&buf;
> +
> + memset(buf, 0, sizeof(buf));
> int *irq_fds = (void *)&irq->data;
>
> irq->argsz = sizeof(buf);
> --
> 2.25.1
>
This unnecessarily split the declaration block. Without objection,
I'll commit this with the following change:
diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
index d306ab81123a..fc75e04ef010 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c
@@ -32,9 +32,9 @@ static void vfio_pci_irq_set(struct vfio_pci_device *device,
{
u8 buf[sizeof(struct vfio_irq_set) + sizeof(int) * count];
struct vfio_irq_set *irq = (void *)&buf;
+ int *irq_fds = (void *)&irq->data;
memset(buf, 0, sizeof(buf));
- int *irq_fds = (void *)&irq->data;
irq->argsz = sizeof(buf);
irq->flags = VFIO_IRQ_SET_ACTION_TRIGGER;
Thanks,
Alex
