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

From: Catalin Marinas <catalin.marinas@arm.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Kees Cook <keescook@chromium.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] arm64/alternatives: move length validation inside the subsection
Date: Fri, 31 Jul 2020 10:31:56 +0100	[thread overview]
Message-ID: <20200731093155.GA29569@gaia> (raw)
In-Reply-To: <20200731064915.GI1508201@kroah.com>

On Fri, Jul 31, 2020 at 08:49:15AM +0200, Greg Kroah-Hartman wrote:
> 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@arm.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@vger.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.

Good to know. Thanks for the clarification.

-- 
Catalin