Revert "fast_hash: avoid indirect function calls"
authorJay Vosburgh <jay.vosburgh@canonical.com>
Fri, 14 Nov 2014 19:05:06 +0000 (11:05 -0800)
committerDavid S. Miller <davem@davemloft.net>
Fri, 14 Nov 2014 21:36:25 +0000 (16:36 -0500)
commita77f9c5dcdf8480a93332792c336fa2bf9d31229
tree003964de0cc772f361d254385406fa75f3fcbff2
parent8cd4313aa775537f724486d5b7503b4d46c9f012
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>
arch/x86/include/asm/hash.h
arch/x86/lib/hash.c
include/asm-generic/hash.h
include/linux/hash.h
lib/Makefile
lib/hash.c [new file with mode: 0644]