Re: [PATCH] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases as __pure

[Ard Biesheuvel]

On Thu, 24 Jan 2019 at 16:44, Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> The upcoming GCC 9 release extends the -Wmissing-attributes warnings
> (enabled by -Wall) to C and aliases: it warns when particular function
> attributes are missing in the aliases but not in their target.
>
> In particular, it triggers here because crc32_le_base/__crc32c_le_base
> aren't __pure while their target crc32_le/__crc32c_le are.
>
> These aliases are used by architectures as a fallback in accelerated
> versions of CRC32. See commit 9784d82db3eb ("lib/crc32: make core crc32()
> routines weak so they can be overridden").
>
> Therefore, being fallbacks, it is likely that even if the aliases
> were called from C, there wouldn't be any optimizations possible.
> Currently, the only user is arm64, which calls this from asm.
>
> Still, marking the aliases as __pure makes sense and is a good idea
> for documentation purposes and possible future optimizations,
> which also silences the warning.
>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>

Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

> ---
> I am picking this up through the compiler-attributes tree
> and putting it into -next along with the other cleanup
> for -Wmissing-attributes (unless some other maintainer wants it).
>
>  lib/crc32.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/crc32.c b/lib/crc32.c
> index 45b1d67a1767..4a20455d1f61 100644
> --- a/lib/crc32.c
> +++ b/lib/crc32.c
> @@ -206,8 +206,8 @@ u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
>  EXPORT_SYMBOL(crc32_le);
>  EXPORT_SYMBOL(__crc32c_le);
>
> -u32 crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
> -u32 __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
> +u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
> +u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
>
>  /*
>   * This multiplies the polynomials x and y modulo the given modulus.
> --
> 2.17.1
>