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Date:   Mon, 14 Nov 2022 13:04:49 +0100
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To:     Ard Biesheuvel <ardb@kernel.org>, Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org,
        Alexander Potapenko <glider@google.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Alexei Starovoitov <ast@kernel.org>,
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        Ben Segall <bsegall@google.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Don Zickus <dzickus@redhat.com>, Hao Luo <haoluo@google.com>,
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        Ingo Molnar <mingo@redhat.com>, Jan Hubicka <jh@suse.de>,
        Jason Baron <jbaron@akamai.com>,
        Jiri Kosina <jikos@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        John Fastabend <john.fastabend@gmail.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        KP Singh <kpsingh@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Martin Liska <mliska@suse.cz>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Mel Gorman <mgorman@suse.de>, Miguel Ojeda <ojeda@kernel.org>,
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References: <20221114114344.18650-1-jirislaby@kernel.org>
 <CAMj1kXFqNvs2OvLJLi2CQYtPe4_BquHQg55F8J=oO76N9wRT9g@mail.gmail.com>
From:   Jiri Slaby <jirislaby@kernel.org>
Subject: Re: [PATCH 00/46] gcc-LTO support for the kernel
In-Reply-To: <CAMj1kXFqNvs2OvLJLi2CQYtPe4_BquHQg55F8J=oO76N9wRT9g@mail.gmail.com>
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On 14. 11. 22, 12:56, Ard Biesheuvel wrote:
> On Mon, 14 Nov 2022 at 12:44, Jiri Slaby (SUSE) <jirislaby@kernel.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