xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Revert "fast_hash: avoid indirect function calls"

Browse Source 
This reverts commit e5a2c89995.

	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>
This commit is contained in:
Jay Vosburgh
2014-11-14 11:05:06 -08:00
committed by David S. Miller
parent 8cd4313aa7
commit a77f9c5dcd
6 changed files with 93 additions and 98 deletions
Download Patch File Download Diff File Expand all files Collapse all files

36
include/asm-generic/hash.h
View File

@@ -1,41 +1,9 @@
#ifndef __ASM_GENERIC_HASH_H
#define __ASM_GENERIC_HASH_H
#include <linux/jhash.h>
/**
* 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.
*/
static inline u32 arch_fast_hash(const void *data, u32 len, u32 seed)
struct fast_hash_ops;
static inline void setup_arch_fast_hash(struct fast_hash_ops *ops)
{
return jhash(data, len, 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.
*/
static inline u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
{
return jhash2(data, len, seed);
}
#endif /* __ASM_GENERIC_HASH_H */