Re: [PATCH v5 0/3] bootconfig: Support embedding a bootconfig in kernel for non initrd boot

From: Masami Hiramatsu <mhiramat@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Padmanabha Srinivasaiah <treasure4paddy@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-doc@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
	Sami Tolvanen <samitolvanen@google.com>,
	Nathan Chancellor <nathan@kernel.org>,
	llvm@lists.linux.dev, Masahiro Yamada <masahiroy@kernel.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>
Subject: Re: [PATCH v5 0/3] bootconfig: Support embedding a bootconfig in kernel for non initrd boot
Date: Thu, 31 Mar 2022 10:45:31 +0900	[thread overview]
Message-ID: <20220331104531.81d0edf9a85a4f69020a9f13@kernel.org> (raw)
In-Reply-To: <CAKwvOdmAYQZtzGudBjmiRZNjT+VixTdNbJmYmxc7-gQNCsHfrA@mail.gmail.com>

Hi Nick,

On Wed, 30 Mar 2022 11:04:50 -0700
Nick Desaulniers <ndesaulniers@google.com> wrote:

> On Mon, Mar 28, 2022 at 7:29 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >
> > KNOWN ISSUE:
> >
> > According to the report from Padmanabha[3] and my analysis [4], the embedded
> > bootconfig data may not be updated if you do incremental build the kernel
> > with CONFIG_LTO_CLANG_THIN.
> >
> > [3] https://lore.kernel.org/all/20220321183500.GA4065@pswork/T/#u
> > [4] https://lore.kernel.org/all/20220327115526.cc4b0ff55fc53c97683c3e4d@kernel.org/
> >
> > This seems like clang's LTO Thin mode issue. It may not detect the inline
> > asm depends on external files.
> >
> > I think the possible workaround is to split the inline asm which includes
> > '.incbin' directive into an asm file. But this should be done in another
> > seires because there are other features which uses '.incbin'. (e.g.
> > /proc/config.gz)
> 
> Hi Masami,
> I saw Padmanabha's report (thanks for the report); sorry for not
> responding sooner, I've been traveling recently for a funeral.

Oh, sorry about that. I think this is not so hurry. 

> 
> Any chance we can use
> 
> CFLAGS_REMOVE_<file>.o := $(CC_FLAGS_LTO)
> 
> a la
> commit d2dcd3e37475 ("x86, cpu: disable LTO for cpu.c")

Hm, this looks good to me. Let me confirm that works.
(Does this mean the bootconfig.o will be compiled to elf binary?)

> 
> with a comment linking to
> https://github.com/ClangBuiltLinux/linux/issues/1618

Thanks for reporting!

> 
> for the Translation Units using .incbin, until we have had more time
> to triage+fix?

Yes. For this series, I can update with above one, but it doesn't cover the
other parts. And since this issue is independent from the bootconfig, 
I think we need a wider patch series to mitigate this issue on config.gz
(and other .incbin users) too.

Thank you,

> 
> -- 
> Thanks,
> ~Nick Desaulniers

-- 
Masami Hiramatsu <mhiramat@kernel.org>