From a77f9c5dcdf8480a93332792c336fa2bf9d31229 Mon Sep 17 00:00:00 2001 From: Jay Vosburgh Date: Fri, 14 Nov 2014 11:05:06 -0800 Subject: Revert "fast_hash: avoid indirect function calls" This reverts commit e5a2c899957659cd1a9f789bc462f9c0b35f5150. Commit e5a2c899 introduced an alternative_call, arch_fast_hash2, that selects between __jhash2 and __intel_crc4_2_hash based on the X86_FEATURE_XMM4_2. Unfortunately, the alternative_call system does not appear to be suitable for use with C functions, as register usage is not handled properly for the called functions. The __jhash2 function in particular clobbers registers that are not preserved when called via alternative_call, resulting in a panic for direct callers of arch_fast_hash2 on older CPUs lacking sse4_2. It is possible that __intel_crc4_2_hash works merely by chance because it uses fewer registers. This commit was suggested as the source of the problem by Jesse Gross . Signed-off-by: Jay Vosburgh Signed-off-by: David S. Miller --- include/linux/hash.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) (limited to 'include/linux/hash.h') diff --git a/include/linux/hash.h b/include/linux/hash.h index 6e8fb028848c..d0494c399392 100644 --- a/include/linux/hash.h +++ b/include/linux/hash.h @@ -84,4 +84,38 @@ static inline u32 hash32_ptr(const void *ptr) return (u32)val; } +struct fast_hash_ops { + u32 (*hash)(const void *data, u32 len, u32 seed); + u32 (*hash2)(const u32 *data, u32 len, u32 seed); +}; + +/** + * arch_fast_hash - Caclulates a hash over a given buffer that can have + * arbitrary size. This function will eventually use an + * architecture-optimized hashing implementation if + * available, and trades off distribution for speed. + * + * @data: buffer to hash + * @len: length of buffer in bytes + * @seed: start seed + * + * Returns 32bit hash. + */ +extern u32 arch_fast_hash(const void *data, u32 len, u32 seed); + +/** + * arch_fast_hash2 - Caclulates a hash over a given buffer that has a + * size that is of a multiple of 32bit words. This + * function will eventually use an architecture- + * optimized hashing implementation if available, + * and trades off distribution for speed. + * + * @data: buffer to hash (must be 32bit padded) + * @len: number of 32bit words + * @seed: start seed + * + * Returns 32bit hash. + */ +extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed); + #endif /* _LINUX_HASH_H */ -- cgit v1.2.3-70-g09d2