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

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Message-Id: <20220331104531.81d0edf9a85a4f69020a9f13@kernel.org>
Date:   Thu, 31 Mar 2022 10:45:31 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Padmanabha Srinivasaiah <treasure4paddy@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Randy Dunlap <rdunlap@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v5 0/3] bootconfig: Support embedding a bootconfig in
 kernel for non initrd boot

Hi Nick,

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

> On Mon, Mar 28, 2022 at 7:29 AM Masami Hiramatsu <mhiramat@...nel.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@...nel.org>