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

[AKASHI Takahiro]

On 05/28/2015 05:58 PM, Will Deacon wrote:
> 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.

We just started the discussion about gcc, -mfentry vs. a more generic option
that I mentioned in:
  http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/346632.html
on gcc's devel ML.

-Takahiro AKASHI

> Will
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/