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



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