linux-kernel - Re: [PATCH] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases as _

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Date:   Fri, 25 Jan 2019 11:46:35 +0100
From:   Laura Abbott <labbott@...hat.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Martin Sebor <msebor@....gnu.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases
 as __pure

On 1/24/19 7:44 AM, Miguel Ojeda 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@...il.com>
> ---
> 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.
> 


Tested-by: Laura Abbott <labbott@...hat.com>