linux-kernel - Re: [RFC PATCH] kbuild: pass objects instead of archives to linker

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Message-ID: <9fe8615c-fe31-ebf7-09bd-453fae189666@kernel.org>
Date:   Thu, 3 Nov 2022 08:22:44 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, Michael Matz <matz@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [RFC PATCH] kbuild: pass objects instead of archives to linker

On 02. 11. 22, 10:44, Masahiro Yamada wrote:
> Jiri Slaby reported that the (not-upstreamed) GCC-LTO tree got broken
> due to 321648455061 ("kbuild: use obj-y instead extra-y for objects
> placed at the head")
> 
> https://lore.kernel.org/linux-kbuild/ea468b86-abb7-bb2b-1e0a-4c8959d23f1c@kernel.org/
> 
> 
> I am not pretty sure because I did not check the downstream code.
> 
> 
> If I understood his report correctly, the reason for the breakage is
> because I put all objects into the thin archive, expecting
> the linker would preserve the object order in the archive.
> 
> By specifying the object order directly in the command line,
> GCC-LTO should get back working again.

...

> I think my patch is unneeded (hence RFC), but I just wanted to know
> if linkers (gnu ld and lld) see any difference.

Yes, including your patch (instead of vmlinux.S and /compressed/* 
changes) also fixes the issue. So the linker (gcc-ld) indeed respects 
command line, but not order of objects in .a.

thanks,
-- 
js
suse labs