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

Richard Weinberger
2011-08-23T16:58:28Z

Am 23.08.2011 18:53, schrieb Al Viro:
> On Tue, Aug 23, 2011 at 09:29:29AM -0700, Linus Torvalds wrote:
>
>> Oh yes.
>>
>> System call performance is *important*. And x86 is *important*.
>>
>> UML? In comparison, not that important.
>>
>> So quite frankly, if this is purely an UML issue (and unless we're
>> missing something else, that's what it looks like, despite all the
>> confusion we've had so far), then if we have a choice between "remove
>> syscall instruction" and "remove UML", then ...
>
> Agreed. Note, BTW, that UML has perfectly usable workaround for 99% of
> that - don't tell the binaries it has *any* vdso in such cases. And
> "remove UML" turns into "remove support under UML for 32bit binaries
> that go out of their way to do SYSCALL directly, which wouldn't work
> on native 32bit", which is really a no-brainer.

What about this hack/solution?
While booting UML can check whether the host's vDSO contains
a SYSCALL instruction.
If so, UML will not make the host's vDSO available to it's
processes...

Thanks,
//richard