Re: 3.15: kernel BUG at kernel/auditsc.c:1525!

Andy Lutomirski
2014-06-16T22:01:18Z

On Mon, Jun 16, 2014 at 2:58 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> For 64-bit, I want to do this instead:
>>
>> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/seccomp-fastpath&id=a5ec2d7af2c54b55fc7201fa662138b53fbbda39
>>
>> I see no reason why the 64-bit badsys code needs its own code path at
>> all. I haven't sent it yet because AFAICT it doesn't fix any bug, and
>> the series it's a part of isn't ready.
>>
>> I'm also contemplating rewriting the 64-bit syscall entry work path in C.
>>
>
> Cute... although it still leaves an extra branch for the badsys. It
> might perform better than a cmov, but it might not.

I bet that the branch is faster in most cases -- I'd be somewhat
surprised if CPUs can speculate through a cmov, and that value is
needed for control flow almost immediately.

--Andy