Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221102091308.11568-1-masahiroy@kernel.org> <CAMj1kXGzFEnUGkoD_JV6=mrKQ+eXLo=SYU8823mPezHZfY_FRQ@mail.gmail.com>
 <CAK7LNASjBm=WWpkSaL1+QuLokhnepUucvhYyP3CCeZYx6nOTHA@mail.gmail.com> <9fe8615c-fe31-ebf7-09bd-453fae189666@kernel.org>
In-Reply-To: <9fe8615c-fe31-ebf7-09bd-453fae189666@kernel.org>
From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 3 Nov 2022 23:47:04 +0900
Message-ID: <CAK7LNATBuERrR4QvLzDNOw1TVmMP+2J=sJviihBdy8gF=CfA=w@mail.gmail.com>
Subject: Re: [RFC PATCH] kbuild: pass objects instead of archives to linker
To:     Jiri Slaby <jirislaby@kernel.org>
Cc:     Ard Biesheuvel <ardb@kernel.org>, linux-kbuild@vger.kernel.org,
        Michael Matz <matz@suse.de>, Kees Cook <keescook@chromium.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        Fangrui Song <maskray@google.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Nov 3, 2022 at 4:22 PM Jiri Slaby <jirislaby@kernel.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