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

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Date:   Thu, 24 Jan 2019 16:44:20 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        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: [PATCH] lib/crc32.c: mark crc32_le_base/__crc32c_le_base aliases as
 __pure

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.
-- 
2.17.1