Re: [PATCH] linux-2.5.43_vsyscall_A0

Andi Kleen
2002-10-19T03:57:12Z

[full quote for context]

On Sat, Oct 19, 2002 at 06:49:59AM +0200, Jeff Dike wrote:
> ak@muc.de said:
> > Guess you'll have some problems then with UML on x86-64, which always
> > uses vgettimeofday. But it's only used for gettimeofday() currently,
> > perhaps it's not that bad when the UML child runs with the host's
> > time.
>
> It's not horrible, but it's still broken. There are people who depend
> on UML being able to keep its own time separately from the host.
>
> > I guess it would be possible to add some support for UML to map own
> > code over the vsyscall reserved locations. UML would need to use the
> > syscalls then. But it'll be likely ugly.
>
> Yeah, it would be.
>
> My preferred solution would be for libc to ask the kernel where the vsyscall
> area is. That's reasonably clean and virtualizable. Andrea doesn't like it
> because it adds a few instructions to the vsyscall address calculation.

I would have no problems with adding that to the x86-64 kernel. It could
be passed in by the ELF environment vector and added to the ABI.
Overhead should be negligible, it just needs a single table lookup.
Andreas, what do you think ?

-Andi