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

Ingo Molnar
2011-08-22T09:56:02Z

* H. Peter Anvin <hpa@zytor.com> wrote:

> Borislav,
>
> We're tracking down an issue with the way system call arguments are
> handled on 32 bits. We have a solution for SYSENTER but not
> SYSCALL; fixing SYSCALL "properly" appears to be very difficult at
> best.
>
> So the question is: how much overhead would it be to simply fall
> back to int $0x80 or some other legacy-style domain crossing
> instruction for 32-bit system calls on AMD64 processors? We don't
> ever use SYSCALL in legacy mode, so native i386 kernels are
> unaffected.

Last i measured INT80 and SYSCALL costs they were pretty close to
each other on AMD CPUs - closer than on Intel.

Also, most installations are either pure 32-bit or dominantly 64-bit,
the significantly mixed-mode case is dwindling.

Unifying some more in this area would definitely simplify things ...

Thanks,

Ingo