Re: [PATCH v5 1/2] arm64/neon: add workaround for ambiguous C99 stdint.h types

[Will Deacon <will.deacon@arm.com>]

On Wed, Nov 28, 2018 at 09:09:00AM +0800, Jackie Liu wrote:
> In a way similar to ARM commit 09096f6a0ee2 ("ARM: 7822/1: add workaround
> for ambiguous C99 stdint.h types"), this patch redefines the macros that
> are used in stdint.h so its definitions of uint64_t and int64_t are
> compatible with those of the kernel.
> 
> This patch comes from: https://patchwork.kernel.org/patch/3540001/
> Wrote by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> 
> We mark this file as a private file and don't have to override asm/types.h
> 
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
> ---
>  arch/arm64/include/asm/neon-intrinsics.h | 34 ++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>  create mode 100644 arch/arm64/include/asm/neon-intrinsics.h
> 
> diff --git a/arch/arm64/include/asm/neon-intrinsics.h b/arch/arm64/include/asm/neon-intrinsics.h
> new file mode 100644
> index 0000000..e378766
> --- /dev/null
> +++ b/arch/arm64/include/asm/neon-intrinsics.h
> @@ -0,0 +1,34 @@
> +#ifndef _NEON_INTRINSICS_H
> +#define _NEON_INTRINSICS_H

We tend to name these with an __ASM_ prefix, so it should be:

#ifndef __ASM_NEON_INTRINSICS_H

That said, I notice that the commit you refer to for arch/arm/ actually
places this stuff under uapi/. Is that needed?

> +#include <asm-generic/int-ll64.h>
> +
> +/*
> + * For Aarch64, there is some ambiguity in the definition of the types below
> + * between the kernel and GCC itself. This is usually not a big deal, but it
> + * causes trouble when including GCC's version of 'stdint.h' (this is the file
> + * that gets included when you #include <stdint.h> on a -ffreestanding build).
> + * As this file also gets included implicitly when including 'arm_neon.h' (the
> + * NEON intrinsics support header), we need the following to work around the
> + * issue if we want to use NEON intrinsics in the kernel.
> + */

Could you elaborate on what the ambiguities / conflicts in the types are
please? I think you can also remove the sentence about directly including
stdint on a freestanding build, since it doesn't seem relevant to the
kernel afaict (we only pull it in via arm_neon.h).

> +
> +#ifdef __INT64_TYPE__
> +#undef __INT64_TYPE__
> +#define __INT64_TYPE__		__signed__ long long

Do we need this __signed__ part?

Will