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

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Date:   Thu, 3 Nov 2022 23:47:04 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>, 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 Thu, Nov 3, 2022 at 4:22 PM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> 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.
>


Can I see your LTO implementation somewhere in public?


I know Andy Kleen's GCC-LTO, the latest version is 5.13-ish.

https://github.com/andikleen/linux-misc.git





> thanks,
> --
> js
> suse labs
>


-- 
Best Regards
Masahiro Yamada