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Date:   Tue, 10 Oct 2023 19:48:33 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Kaplan <david.kaplan@amd.com>
Cc:     x86@kernel.org, luto@kernel.org, linux-kernel@vger.kernel.org,
        Josh Poimboeuf <jpoimboe@kernel.org>
Subject: Re: [PATCH 1/3] Revert "x86/retpoline: Remove
 .text..__x86.return_thunk section"
Message-ID: <20231010174833.GG14330@noisy.programming.kicks-ass.net>
References: <20231010171020.462211-1-david.kaplan@amd.com>
 <20231010171020.462211-2-david.kaplan@amd.com>
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On Tue, Oct 10, 2023 at 12:10:18PM -0500, David Kaplan wrote:

>  arch/x86/kernel/vmlinux.lds.S | 3 +++
>  arch/x86/lib/retpoline.S      | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 9cdb1a7332c4..54a5596adaa6 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -132,7 +132,10 @@ SECTIONS
>  		LOCK_TEXT
>  		KPROBES_TEXT
>  		SOFTIRQENTRY_TEXT
> +#ifdef CONFIG_RETPOLINE
>  		*(.text..__x86.indirect_thunk)
> +		*(.text..__x86.return_thunk)
> +#endif
>  		STATIC_CALL_TEXT
>  
>  		ALIGN_ENTRY_TEXT_BEGIN
> diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
> index db813113e637..3da768a71cf9 100644
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -129,6 +129,8 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array)
>  
>  #ifdef CONFIG_RETHUNK

Perhaps elucidate the future reader with a comment here? Lest someone
tries removing it again.

>  
> +	.section .text..__x86.return_thunk
> +
>  #ifdef CONFIG_CPU_SRSO