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

From: Nick Desaulniers <ndesaulniers@google.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
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: Wed, 30 Mar 2022 11:04:50 -0700	[thread overview]
Message-ID: <CAKwvOdmAYQZtzGudBjmiRZNjT+VixTdNbJmYmxc7-gQNCsHfrA@mail.gmail.com> (raw)
In-Reply-To: <164847778869.3060675.8115416881394543419.stgit@devnote2>

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.

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