[ovs-discuss] [PATCH net-next] Revert "fast_hash: avoid indirect function calls"
Hannes Frederic Sowa
hannes at stressinduktion.org
Fri Nov 14 21:43:02 UTC 2014
On Fr, 2014-11-14 at 11:05 -0800, Jay Vosburgh wrote:
> 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
> 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
> This commit was suggested as the source of the problem by Jesse
> Gross <jesse at nicira.com>.
> Signed-off-by: Jay Vosburgh <jay.vosburgh at canonical.com>
I am totally fine to revert this and try to come up with a better
Acked-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
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