linux-kernel - Re: [PATCH] x86/alternative: fix undefined reference to __ibt_endbr_seal[

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Message-ID: <Y0K+YbcwyLJg9Iwr@hirez.programming.kicks-ass.net>
Date:   Sun, 9 Oct 2022 14:28:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/alternative: fix undefined reference to
 __ibt_endbr_seal[_end]

On Sun, Oct 09, 2022 at 11:45:32PM +0800, Miaohe Lin wrote:
> When I compile the kernel bzImage, there are several compile errors:
> 
> ld: arch/x86/kernel/alternative.o: in function
> `alternative_instructions':
> alternative.c:(.init.text+0x15d): undefined reference to
> `__ibt_endbr_seal_end'
> ld: alternative.c:(.init.text+0x164): undefined reference to
> `__ibt_endbr_seal'
> 
> It's because __ibt_endbr_seal and __ibt_endbr_seal_end are not optimized
> away when CONFIG_X86_KERNEL_IBT isn't enabled. Remove noinline attribute
> to help gcc optimize them away.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kernel/alternative.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 5cadcea035e0..beaf9fc44e2f 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -624,7 +624,7 @@ void __init_or_module noinline apply_ibt_endbr(s32 *start, s32 *end)
>  
>  #else
>  
> -void __init_or_module noinline apply_ibt_endbr(s32 *start, s32 *end) { }
> +void __init_or_module apply_ibt_endbr(s32 *start, s32 *end) { }
>  
>  #endif /* CONFIG_X86_KERNEL_IBT */
>  

None of this makes any sense...