Re: [RFC 0/4] arm64: add livepatch support

[Will Deacon]

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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