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SubjectRe: [PATCH] Fix _IOC_TYPECHECK sparse error
On Fri, 09 May 2014 09:43:58 +0200 Hans Verkuil <hverkuil@xs4all.nl> wrote:

> Andrew, can you merge this for 3.15 or 3.16 (you decide)? While it fixes a sparse error
> for the media subsystem, it is not really appropriate to go through our media tree.
>
> Thanks,
>
> Hans
>
>
> When running sparse over drivers/media/v4l2-core/v4l2-ioctl.c I get these
> errors:
>
> drivers/media/v4l2-core/v4l2-ioctl.c:2043:9: error: bad integer constant expression
> drivers/media/v4l2-core/v4l2-ioctl.c:2044:9: error: bad integer constant expression
> drivers/media/v4l2-core/v4l2-ioctl.c:2045:9: error: bad integer constant expression
> drivers/media/v4l2-core/v4l2-ioctl.c:2046:9: error: bad integer constant expression
>
> etc.
>
> The root cause of that turns out to be in include/asm-generic/ioctl.h:
>
> #include <uapi/asm-generic/ioctl.h>
>
> /* provoke compile error for invalid uses of size argument */
> extern unsigned int __invalid_size_argument_for_IOC;
> #define _IOC_TYPECHECK(t) \
> ((sizeof(t) == sizeof(t[1]) && \
> sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
> sizeof(t) : __invalid_size_argument_for_IOC)
>
> If it is defined as this (as is already done if __KERNEL__ is not defined):
>
> #define _IOC_TYPECHECK(t) (sizeof(t))
>
> then all is well with the world.
>
> This patch allows sparse to work correctly.
>
> --- a/include/asm-generic/ioctl.h
> +++ b/include/asm-generic/ioctl.h
> @@ -3,10 +3,15 @@
>
> #include <uapi/asm-generic/ioctl.h>
>
> +#ifdef __CHECKER__
> +#define _IOC_TYPECHECK(t) (sizeof(t))
> +#else
> /* provoke compile error for invalid uses of size argument */
> extern unsigned int __invalid_size_argument_for_IOC;
> #define _IOC_TYPECHECK(t) \
> ((sizeof(t) == sizeof(t[1]) && \
> sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
> sizeof(t) : __invalid_size_argument_for_IOC)
> +#endif
> +
> #endif /* _ASM_GENERIC_IOCTL_H */

Can't we use BUILD_BUG_ON() here? That's neater, more standard and
BUILD_BUG_ON() already has sparse handling.


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