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    SubjectRe: [patch 17/26] Xen-paravirt_ops: Add nosegneg capability to the vsyscall page notes
    Roland McGrath wrote:
    > This should be:
    >
    > NOTE_KERNELCAP_BEGIN(1, 1)
    > NOTE_KERNELCAP(0, "nosegneg")
    > NOTE_KERNELCAP_END
    >
    > i.e. 1->0 in the "bit" member. (Note the ld.so.conf.d file must have the
    > matching bit number for ldconfig-based lookups to do the right thing.)
    > Or else:
    >
    > NOTE_KERNELCAP_BEGIN(1, 2)
    > NOTE_KERNELCAP(0, "nosegneg")
    > NOTE_KERNELCAP_END
    >
    > i.e. 1->2 in the "mask" member. (The mask value should be 1<<bit.)
    >

    Thanks Roland. I've never really understood this stuff, and I just
    copied this cargo-cultishly.

    I'm not quite sure what you're suggesting here though. Do you mean one of:

    NOTE_KERNELCAP_BEGIN(1, 1)
    NOTE_KERNELCAP(0, "nosegneg")
    NOTE_KERNELCAP_END

    or

    NOTE_KERNELCAP_BEGIN(1, 2)
    NOTE_KERNELCAP(1, "nosegneg")
    NOTE_KERNELCAP_END

    is the correct thing to use?

    > Some pre-release glibc's (before 2.4) had a bug in the code that parses
    > this, and would crash parsing the correct note. Using the wrong bit value
    > with nonmatching mask worked around this. IIRC, no glibc release ever
    > included the buggy version of the code. In nonbuggy glibc, the mismatched
    > value causes the "nosegneg" to be omitted from the directory search (under
    > LD_LIBRARY_PATH and default directories), though ldconfig-based lookups
    > will work (the most common case).
    >

    Are you saying that one of the corrected forms might cause old glibcs to
    crash, or just ignore nosegneg?

    J

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