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Date: Wed, 16 Feb 2022 12:01:20 -0800 From: Josh Poimboeuf <jpoimboe@...hat.com> To: Miroslav Benes <mbenes@...e.cz> Cc: Fāng-ruì Sòng <maskray@...gle.com>, Alexander Lobakin <alexandr.lobakin@...el.com>, linux-hardening@...r.kernel.org, x86@...nel.org, Borislav Petkov <bp@...en8.de>, Jesse Brandeburg <jesse.brandeburg@...el.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Kees Cook <keescook@...omium.org>, Miklos Szeredi <miklos@...redi.hu>, Ard Biesheuvel <ardb@...nel.org>, Tony Luck <tony.luck@...el.com>, Bruce Schlobohm <bruce.schlobohm@...el.com>, Jessica Yu <jeyu@...nel.org>, kernel test robot <lkp@...el.com>, Evgenii Shatokhin <eshatokhin@...tuozzo.com>, Jonathan Corbet <corbet@....net>, Masahiro Yamada <masahiroy@...nel.org>, Michal Marek <michal.lkml@...kovi.net>, Nick Desaulniers <ndesaulniers@...gle.com>, Herbert Xu <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>, Christoph Hellwig <hch@....de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Marios Pomonis <pomonis@...gle.com>, Sami Tolvanen <samitolvanen@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org, live-patching@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available On Wed, Feb 16, 2022 at 04:15:20PM +0100, Miroslav Benes wrote: > > > I subscribe to llvm@...ts.linux.dev 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@google.com > > > > > > 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@google.com/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
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