Re: [PATCH v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available

[Josh Poimboeuf]

On Wed, Feb 16, 2022 at 04:15:20PM +0100, Miroslav Benes wrote:
> > > I subscribe to llvm@xxxxxxxxxxxxxxx and happen to notice this message
> > > (can't keep up with the changes...)
> > > I am a bit concerned with this option and replied last time on
> > > https://lore.kernel.org/r/20220105032456.hs3od326sdl4zjv4@xxxxxxxxxx
> > > 
> > > My full reasoning is on
> > > https://maskray.me/blog/2020-11-15-explain-gnu-linker-options#z-unique-symbol
> > 
> > Ah, right.  Also discussed here:
> > 
> >   https://lore.kernel.org/all/20210123225928.z5hkmaw6qjs2gu5g@xxxxxxxxxx/T/#u
> >   https://lore.kernel.org/all/20210125172124.awabevkpvq4poqxf@treble/
> > 
> > I'm not qualified to comment on LTO/PGO stability issues, but it doesn't
> > sound good.  And we want to support livepatch for LTO kernels.
> 
> Hm, bear with me, because I am very likely missing something which is 
> clear to everyone else...
> 
> Is the stability really a problem for the live patching (and I am talking 
> about the live patching only here. It may be a problem elsewhere, but I am 
> just trying to understand.)? I understand that two different kernel builds 
> could have a different name mapping between the original symbols and their 
> unique renames. Not nice. But we can prepare two different live patches 
> for these two different kernels. Something one would like to avoid if 
> possible, but it is not impossible. Am I missing something?

Maybe Fāng-ruì can clarify, but my understanding was that the stability
issue affects the kernel in general (particularly if LTO or PGO is
enabled) and isn't necessarily specific to livepatch itself.

-- 
Josh