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    SubjectRe: [PATCH] Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled"
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    On 20/07/20 9:05 am, Joe Lawrence wrote:
    > On 7/17/20 2:29 PM, Josh Poimboeuf wrote:
    >> Use of the new -flive-patching flag was introduced with the following
    >> commit:
    >>
    >>    43bd3a95c98e ("kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled")
    >>
    >> This flag has several drawbacks:
    >>
    >> [ ... snip ... ]
    >>
    >> - While there *is* a distro which relies on this flag for their distro
    >>    livepatch module builds, there's not a publicly documented way to
    >>    create safe livepatch modules with it.  Its use seems to be based on
    >>    tribal knowledge.  It serves no benefit to those who don't know how to
    >>    use it.
    >>
    >>    (In fact, I believe the current livepatch documentation and samples
    >>    are misleading and dangerous, and should be corrected.  Or at least
    >>    amended with a disclaimer.  But I don't feel qualified to make such
    >>    changes.)
    >
    > FWIW, I'm not exactly qualified to document source-based creation either, however I have written a few of the samples and obviously the kselftest modules.
    >
    > The samples should certainly include a disclaimer (ie, they are only for API demonstration purposes!) and eventually it would be great if the kselftest modules could guarantee their safety as well.  I don't know quite yet how we can automate that, but perhaps some kind of post-build sanity check could verify that they are in fact patching what they intend to patch.
    >
    > As for a more general, long-form warning about optimizations, I grabbed Miroslav's LPC slides from a few years back and poked around at some IPA-optimized disassembly... Here are my notes that attempt to capture some common cases:
    >
    > http://file.bos.redhat.com/~jolawren/klp-compiler-notes/livepatch/compiler-considerations.html

    Hi Joe,

    The notes link you shared is not accessible.

    Regards,

    --
    Kamalesh

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