Re: [PATCH] [v3] vduse: fix compat handling for VDUSE_IOTLB_GET_FD/VDUSE_VQ_GET_INFO

[Michael S. Tsirkin]

On Wed, Jun 10, 2026 at 08:54:59AM +0200, Arnd Bergmann wrote:
> On Wed, Jun 10, 2026, at 07:26, Michael S. Tsirkin wrote:
> > On Fri, Feb 13, 2026 at 04:40:46PM +0100, Arnd Bergmann wrote:
> >> +	};
> >> +	__u8 ready;
> >> +	__u8 padding[3];
> >> +} __uapi_arch_align;
> >
> > what is this __uapi_arch_align supposed to be doing?
> >
> > It compiles by luck because gcc thinks it's a global variable.
> 
> Sorry, that should not have been part of this patch, it is
> part of the series of changes I was testing when I noticed
> the problem here, but that other series is unfortunately
> still not ready for merging.
> 
> The background here is that I'm adding -Werror=padded to
> the UAPI checks in usr/include/Makefile, in order to find
> any instances of data structures with implied padding,
> and then instead add explicit padding using architecture
> specific macros. In vduse_vq_info, this includes a final
> 32 bit of padding on architectures with naturally
> aligned __u64 but no padding when __u64 has a smaller
> alignment.
> 
> The __uapi_arch_align macro in turn is what I add to
> structures with optional padding, in order to be able
> to reduce the alignment of a structure when building the
> kernel with a higher default alignment than userspace
> (e.g. on m68k with -malign-int).
> 
> Removing the __uapi_arch_align is the correct fix for the
> moment. Let me know if you would like me to send a
> replacement patch without it, a fixup patch on top, or if
> you will fix it up yourself.
> 
>      Arnd

I fixed it, thanks.