linux-kernel - Re: [PATCH 00/46] gcc-LTO support for the kernel

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Date:   Mon, 14 Nov 2022 13:04:49 +0100
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Makhalov <amakhalov@...are.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Don Zickus <dzickus@...hat.com>, Hao Luo <haoluo@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        "H. Peter Anvin" <hpa@...or.com>, Huang Rui <ray.huang@....com>,
        Ingo Molnar <mingo@...hat.com>, Jan Hubicka <jh@...e.de>,
        Jason Baron <jbaron@...mai.com>,
        Jiri Kosina <jikos@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
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        Juri Lelli <juri.lelli@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Martin Liska <mliska@...e.cz>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Mel Gorman <mgorman@...e.de>, Miguel Ojeda <ojeda@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Miroslav Benes <mbenes@...e.cz>,
        Namhyung Kim <namhyung@...nel.org>,
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        Peter Zijlstra <peterz@...radead.org>,
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        "Rafael J. Wysocki" <rafael@...nel.org>,
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        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
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        Vincent Guittot <vincent.guittot@...aro.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH 00/46] gcc-LTO support for the kernel

On 14. 11. 22, 12:56, Ard Biesheuvel wrote:
> On Mon, 14 Nov 2022 at 12:44, Jiri Slaby (SUSE) <jirislaby@...nel.org> wrote:
>>
>> Hi,
>>
>> this is the first call for comments (and kbuild complaints) for this
>> support of gcc (full) LTO in the kernel. Most of the patches come from
>> Andi. Me and Martin rebased them to new kernels and fixed the to-use
>> known issues. Also I updated most of the commit logs and reordered the
>> patches to groups of patches with similar intent.
>>
>> The very first patch comes from Alexander and is pending on some x86
>> queue already (I believe). I am attaching it only for completeness.
>> Without that, the kernel does not boot (LTO reorders a lot).
>>
> 
> You didn't cc me on that patch so I will reply here: I don't think
> this is the right solution.
> On x86, there is a lot of stuff injected into .head.text that simply
> does not belong there, and getting rid of the __head annotation and
> dropping __HEAD from the Xen pvh head.S file would be a much better
> solution.

I think Alexander was working on that too. I'm not sure -- anyway, we 
still have the other fix. That is putting startup_64() to a special 
section and put that to the beginning of vmlinux using lds. (Until 
.head.text is completely gone for good -- same as on arm, you wrote 
somewhere.)

In any case, that patch was added only for reference, if anyone wants to 
give the series a try. Next time, I can attach the other workaround ;).

I don't expect anyone will take the series as is. There will be a lot of 
comments, I suppose. Hence many re-spins...

thanks,
-- 
js
suse labs