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Date: Tue, 23 Aug 2011 01:07:05 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Andrew Lutomirski <luto@mit.edu>,
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Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re:
 [RFC] weird crap with vdso on uml/i386)
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On Tue, Aug 23, 2011 at 01:03:14AM +0100, Al Viro wrote:
> On Mon, Aug 22, 2011 at 04:27:51PM -0700, Linus Torvalds wrote:
> 
> > So I think the "let's fix the vdso case for sysenter" + "let's remove
> > the 32-bit syscall vdso" is the right solution. If somebody has
> > hardcoded syscall instructions, or generates them dynamically with
> > some JIT, that's their problem. We'll continue to support it as well
> > as we ever have (read: "almost nobody will ever notice").
> 
> Umm...  Maybe, but I really wonder if it would be better to do this:
> 	* check if %ecx is the right one for vdso32 entry.  If it isn't,
> act as we act now (and possibly warn).  If it is, increment it by 4.
> 	* slap 0x90, 0x90, 0xcd, 0x80 right after that syscall insn -
> i.e. nop/nop/int 0x80.  Followed by what we currently do there.
> 
> 	Those who do syscall insn in 32bit mode outside of vdso will get
> what they currently get.  __kernel_vsyscall() will keep working and do
> that without restart problems.  And the price is comparison + branch not
> taken + addition for that path...

s/whine/set your "don't restart that one" flag/, even...