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

[H. Peter Anvin]

On 08/23/2011 09:48 AM, Al Viro wrote:
> 
> Um...  How would it know which syscall variant had that been, to start
> with?  For int 0x80 it would need to use registers as-is.  For SYSENTER
> it also could use them as-is - ebp will differ from what we put there
> when entering the sucker, but not critically so; on the way out of
> syscall we'll overwrite it anyway immediately (either by pop or mov).
> For SYSCALL... we don't really care about ecx contents prior to entering
> the kernel (and it'll be blown out anyway), and ebp one could be found in
> regs.ecx.  So yes, we can do it that way, but... how to tell what variant
> had been triggered?  Examining two bytes prior to user eip?  Sounds bloody
> brittle...

We could drop that information in a metaregister.  It's not backward
compatible, but at least it will be obvious when that information is
available and not.

	-hpa
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