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    SubjectRe: [PATCH 3.19 3/3] x86, mpx: Change the MPX enable/disable API to arch_prctl
    On Mon, Jan 5, 2015 at 8:04 PM, Andi Kleen <andi@firstfloor.org> wrote:
    >> We should avoid arch_prctl because glibc won't add a syscall stub that
    >> libgcc or whatever would want? My mind boggles.
    >
    > Please turn brain on before posting.

    Brain was on.

    >
    > Of course they would add it. But only in the next version. Which means
    > everyone using older glibc would be out of luck. So all the users
    > would be stuck using syscall(). Anything you may gain in the kernel
    > would be totally made up by that.
    >

    ISTM libmpx shouldn't link against glibc at all -- what if libmpx
    users want to use an alternate runtime (musl, Go, etc.)?

    But I decided to check whether libmpx links against glibc, and I can't
    find sources for it at all. Do they exist? Is there any code with
    source available that invokes this prctl?

    If not, I personally have very little sympathy for the argument that a
    binary buried in the depths of the Intel SDE would need to change if
    we switched to using arch_prctl. And I think that it should issue the
    syscall itself without using glibc, in which case the syscall wrapper
    issue is moot.

    --Andy

    > BTW I added arch_prctl, but in hindsight it wasn't good idea.
    >
    > -Andi



    --
    Andy Lutomirski
    AMA Capital Management, LLC


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