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    SubjectRe: [RFC 0/4] arm64: add livepatch support
    On Thu, May 28, 2015 at 07:08:42AM +0100, Li Bin wrote:
    > On 2015/4/24 17:27, Jiri Kosina wrote:
    > > On Fri, 24 Apr 2015, AKASHI Takahiro wrote:
    > >
    > >> This patchset enables livepatch support on arm64.
    > >>
    > >> Livepatch was merged in v4.0, and allows replacying a function dynamically
    > >> based on ftrace framework, but it also requires -mfentry option of gcc.
    > >> Currently arm64 gcc doesn't support it, but by adding a helper function to
    > >> ftrace, we will be able to support livepatch on arch's which don't support
    > >> this option.
    > >>
    > >> I submit this patchset as RFC since I'm not quite sure that I'm doing
    > >> in the right way, or we should definitely support -fentry instead.
    > >
    > > I don't have arm64 cross-compiler handy, could you please copy/paste how
    > > does function prologue, generated by gcc -pg on arm64 look like?
    > >
    >
    > The function prologue on arm64 with gcc -pg look like as following:
    > func:
    > stp x29, x30, [sp, -48]!
    > add x29, sp, 0
    > mov x1, x30
    > str w0, [x29,28]
    > mov x0, x1
    > bl _mcount

    Just for the avoidance of confusion, this looks like a function with
    a live parameter in x0, which explains the str to the stack and the
    juggling of x30 into x0. I don't think there's necessarily a golden
    template for the prologue code.

    Will


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