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

Al Viro
2011-08-23T00:07:41Z

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...