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

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Message-ID: <4E53DC2A.3020004@nod.at>
Date:	Tue, 23 Aug 2011 18:58:18 +0200
From:	Richard Weinberger <richard@....at>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...64.org>,
	Andrew Lutomirski <luto@....edu>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>
Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re:
 [RFC] weird crap with vdso on uml/i386)

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
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