linux-kernel - Re: [PATCH 40/46] x86/livepatch, lto: Disable live patching with gcc LTO

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Date:   Mon, 14 Nov 2022 11:07:42 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Martin Liska <mliska@...e.cz>, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH 40/46] x86/livepatch, lto: Disable live patching with gcc
 LTO

On Mon, Nov 14, 2022 at 12:43:38PM +0100, Jiri Slaby (SUSE) wrote:
> From: Andi Kleen <andi@...stfloor.org>
> 
> It is not supported by gcc 12 so far, so it causes compiler "sorry"
> messages.

What specifically is not supported by GCC 12?  What are the "sorry"
messages?

> Other than the compiler support, there shouldn't be any barriers for
> live patching LTOed kernels, although it might be more difficult to
> create patches for larger functions.

This seems to conflict with the documentation.

> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: Jiri Kosina <jikos@...nel.org>
> Cc: Miroslav Benes <mbenes@...e.cz>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: Joe Lawrence <joe.lawrence@...hat.com>
> Cc: live-patching@...r.kernel.org
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Martin Liska <mliska@...e.cz>
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> ---
>  kernel/livepatch/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/livepatch/Kconfig b/kernel/livepatch/Kconfig
> index 53d51ed619a3..22699adc39a6 100644
> --- a/kernel/livepatch/Kconfig
> +++ b/kernel/livepatch/Kconfig
> @@ -12,6 +12,7 @@ config LIVEPATCH
>  	depends on KALLSYMS_ALL
>  	depends on HAVE_LIVEPATCH
>  	depends on !TRIM_UNUSED_KSYMS
> +	depends on !LTO_GCC # not supported in gcc

The comment doesn't help.

-- 
Josh