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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 09:22 AM, Borislav Petkov wrote:
    > On Tue, Aug 23, 2011 at 12:11:43PM -0400, Andrew Lutomirski wrote:
    >> In any case, this seems insanely overcomplicated. I'd be less afraid
    >> of something like my approach (which, I think, makes all of the
    >> SYSCALL weirdness pretty much transparent to ptrace users) or of just
    >> removing SYSCALL entirely from 32-bit code.
    > I don't think that removing SYSCALL from 32-bit code just so that UML
    > trapped syscalls work is something we'd like since SYSCALL is much
    > cheaper than INT $0x80:
    > "As a result, SYSCALL and SYSRET can take fewer than one-fourth the
    > number of internal clock cycles to complete than the legacy CALL and RET
    > instructions."
    >, p. 152.
    > I know, it is 32-bit syscall on 64-bit kernel which should be pretty
    > rare but still...

    Right, but if you had said the difference had disappeared on current AMD
    silicon it would be much less of an issue. That's why I wanted to find
    that bit out from you.


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