linux-kernel - Re: [PATCH] arm64/alternatives: move length validation inside the subsection

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Message-ID: <20200731064915.GI1508201@kroah.com>
Date:   Fri, 31 Jul 2020 08:49:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] arm64/alternatives: move length validation inside the
 subsection

On Thu, Jul 30, 2020 at 04:23:31PM +0100, Catalin Marinas wrote:
> On Thu, Jul 30, 2020 at 08:13:05AM -0700, Sami Tolvanen wrote:
> > On Thu, Jul 30, 2020 at 5:22 AM Catalin Marinas <catalin.marinas@....com> wrote:
> > >
> > > On Wed, Jul 29, 2020 at 02:51:52PM -0700, Sami Tolvanen wrote:
> > > > Commit f7b93d42945c ("arm64/alternatives: use subsections for replacement
> > > > sequences") breaks LLVM's integrated assembler, because due to its
> > > > one-pass design, it cannot compute instruction sequence lengths before the
> > > > layout for the subsection has been finalized. This change fixes the build
> > > > by moving the .org directives inside the subsection, so they are processed
> > > > after the subsection layout is known.
> > > >
> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1078
> > > > Cc: <stable@...r.kernel.org> # 4.14+
> > >
> > > Commit f7b93d42945c went in 5.8-rc4. Why is this cc stable from 4.14? If
> > > Will picks it up for 5.8, it doesn't even need a cc stable.
> > 
> > Greg or Sasha can probably answer why, but this patch is in 4.14.189,
> > 4.19.134, 5.4.53, and 5.7.10, which ended up breaking some downstream
> > Android kernel builds.
> 
> I see but I don't think we need the explicit cc stable for 4.14. That's
> why the Fixes tag is important. If a patch was back-ported, the
> subsequent fixes should be picked by the stable maintainers as well.

If you know it ahead of time, the explict "# kernel.version" hint is
always nice to have as it ensures I will try to backport it that far,
and if I have problems, I will ask for help.

thanks,

greg k-h