Re: [PATCH v4 08/10] vfio: selftests: Add mlx5 driver - HW init and command interface

[David Matlack <dmatlack@google.com>]

On 2026-08-12 08:32 PM, Jason Gunthorpe wrote:
> On Wed, Aug 12, 2026 at 09:41:28PM +0000, David Matlack wrote:
> > On 2026-08-12 11:59 AM, Jason Gunthorpe wrote:
> > > @@ -0,0 +1,108 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
> > > +/*
> > > + * mlx5 VFIO selftest driver - HW definitions
> > > + *
> > > + * Typed wrappers, constants, and helpers for programming mlx5 hardware
> > > + * via the VFIO selftest framework.  Most HW constants and all MLX5_SET/GET
> > > + * macros come from the kernel headers (mlx5_ifc.h, mlx5_ifc_macros.h).
> > > + */
> > > +#ifndef SELFTESTS_VFIO_MLX5_HW_H
> > > +#define SELFTESTS_VFIO_MLX5_HW_H
> > > +
> > > +#include <linux/io.h>
> > > +#include <linux/build_bug.h>
> > > +#include <vdso/bits.h>
> > > +
> > > +#include "mlx5_ifc.h"
> > > +#include "mlx5_ifc_macros.h"
> > 
> > I'm getting a compiler warning here when building with clang which is
> > getting upgraded to error from -Werror.
> 
> I don't get that. My builds have -Wno-gnu-variable-sized-type-not-at-end
> which comes from here:
> 
> tools/testing/selftests/lib.mk:
> 
> # gcc defaults to silence (off) for the following warnings, but clang defaults
> # to the opposite. The warnings are not useful for the kernel itself, which is
> # why they have remained disabled in gcc for the main kernel build. And it is
> # only due to including kernel data structures in the selftests, that we get the
> # warnings from clang. Therefore, disable the warnings for clang builds.
> CFLAGS += -Wno-address-of-packed-member
> CFLAGS += -Wno-gnu-variable-sized-type-not-at-end
> 
> Why doesn't yours? Are you building it correctly?

Ah I see the problem. I was building with this command:

  make CC=clang -C tools/testing/selftests/vfio

But the correct way to build selftests with clang is to use:

  make LLVM=1 -C tools/testing/selftests/vfio

LLVM=1 triggers the conditional logic to add
-Wno-gnu-variable-sized-type-not-at-end to CFLAGS and the build works.