Re: [PATCH] linux-2.5.43_vsyscall_A0

Andreas Jaeger
2002-10-20T13:13:31Z

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.

Andreas
--
Andreas Jaeger
SuSE Labs aj@suse.de
private aj@arthur.inka.de