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authorJay Vosburgh <jay.vosburgh@canonical.com>2014-11-14 11:05:06 -0800
committerDavid S. Miller <davem@davemloft.net>2014-11-14 16:36:25 -0500
commita77f9c5dcdf8480a93332792c336fa2bf9d31229 (patch)
tree003964de0cc772f361d254385406fa75f3fcbff2 /include/linux/hash.h
parent8cd4313aa775537f724486d5b7503b4d46c9f012 (diff)
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 <jesse@nicira.com>. Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/hash.h')
-rw-r--r--include/linux/hash.h34
1 files changed, 34 insertions, 0 deletions
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 */