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

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Date:   Wed, 30 Mar 2022 11:04:50 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
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

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.

Any chance we can use

CFLAGS_REMOVE_<file>.o := $(CC_FLAGS_LTO)

a la
commit d2dcd3e37475 ("x86, cpu: disable LTO for cpu.c")

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

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

-- 
Thanks,
~Nick Desaulniers