Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

H. Peter Anvin
2011-08-22T05:04:12Z

On 08/21/2011 09:26 PM, Al Viro wrote:
> On Sun, Aug 21, 2011 at 09:11:54PM -0700, H. Peter Anvin wrote:
>>> lack of point - the *only* CPU where it would matter would be K6-2, IIRC,
>>> and (again, IIRC) it had some differences in SYSCALL semantics compared to
>>> K7 (which supports SYSENTER as well). Bugger if I remember what those
>>> differences might've been... Some flag not cleared?
>>
>> The most likely reason for a binary to execute a stray SYSCALL is
>> because they read it out of the vdso. Totally daft, but we certainly
>> see a lot of stupid things as evidenced by the JIT thread earlier this
>> month.
>
> Um... What, blindly, no matter what surrounds it in there? What will
> happen to the same eager JIT when it steps on SYSENTER?

The JIT will have had to manage SYSENTER already. It's not a change,
whereas SYSCALL would be. We could just try it, and see if anything
breaks, of course.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.