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

H. Peter Anvin
2011-08-23T21:09:33Z

On 08/23/2011 10:33 AM, Linus Torvalds wrote:
>
> It would be *nice* if we did the swizzling automatically at setregs()
> time too, but we simply don't have enough information in the kernel to
> do that. Again, exactly because pt_regs doesn't have a "state"
> variable, when user-space does the SETREGS call, we simply don't know
> whether we are in "normal" code or in some system call entry or exit
> state. So the kernel does the swizzling at GETREGS time (by virtue of
> always having the registers in a "canonical" state for system call
> entry), but we fundamentally *cannot* to do the unswizzle, because we
> don't know what the SETREGS caller actually did.
>

Again, can we steal one of the padding fields to use for that state
variable? We have two 16-bit padding fields; one for cs and one for ss.

For UML, I agree, let's just not expose the vdso assuming that is
possible, but for other -- possibly future -- users.

-hpa