Re: [PATCH] linux-2.5.43_vsyscall_A0

Andrea Arcangeli
2002-10-20T14:53:13Z

On Sun, Oct 20, 2002 at 03:19:32PM +0200, Andreas Jaeger wrote:
> Andi Kleen <ak@muc.de> writes:
>
> > [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 ?
>
> Create a new AT_ constant, and pass it via the auxiliary vector and we
> can use it in glibc.

will it be a pointer to function?

Andrea