linux/lib/hash.c
Jay Vosburgh a77f9c5dcd Revert "fast_hash: avoid indirect function calls"
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>
2014-11-14 16:36:25 -05:00

40 lines
1.0 KiB
C

/* General purpose hashing library
*
* That's a start of a kernel hashing library, which can be extended
* with further algorithms in future. arch_fast_hash{2,}() will
* eventually resolve to an architecture optimized implementation.
*
* Copyright 2013 Francesco Fusco <ffusco@redhat.com>
* Copyright 2013 Daniel Borkmann <dborkman@redhat.com>
* Copyright 2013 Thomas Graf <tgraf@redhat.com>
* Licensed under the GNU General Public License, version 2.0 (GPLv2)
*/
#include <linux/jhash.h>
#include <linux/hash.h>
#include <linux/cache.h>
static struct fast_hash_ops arch_hash_ops __read_mostly = {
.hash = jhash,
.hash2 = jhash2,
};
u32 arch_fast_hash(const void *data, u32 len, u32 seed)
{
return arch_hash_ops.hash(data, len, seed);
}
EXPORT_SYMBOL_GPL(arch_fast_hash);
u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
{
return arch_hash_ops.hash2(data, len, seed);
}
EXPORT_SYMBOL_GPL(arch_fast_hash2);
static int __init hashlib_init(void)
{
setup_arch_fast_hash(&arch_hash_ops);
return 0;
}
early_initcall(hashlib_init);