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Date:   Tue, 10 Oct 2023 12:57:21 -0700
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     David Kaplan <david.kaplan@amd.com>, x86@kernel.org,
        luto@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] Revert "x86/retpoline: Remove
 .text..__x86.return_thunk section"
Message-ID: <20231010195721.p5pb273kevg7ydxz@treble>
References: <20231010171020.462211-1-david.kaplan@amd.com>
 <20231010171020.462211-2-david.kaplan@amd.com>
 <20231010174833.GG14330@noisy.programming.kicks-ass.net>
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On Tue, Oct 10, 2023 at 07:48:33PM +0200, Peter Zijlstra wrote:
> 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.

Yes, please.

Also we could make objtool properly detect the non-relocated jump
target.  But this works for now.

-- 
Josh