linux-kernel - Re: [PATCH v2] x86/alternative: fix undefined reference to __ibt_endbr_seal[

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Message-ID: <4b5f2d25-0cdf-132a-ae34-77e11611dbfc@huawei.com>
Date:   Tue, 11 Oct 2022 11:46:47 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>
CC:     <hpa@...or.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] x86/alternative: fix undefined reference to
 __ibt_endbr_seal[_end]

On 2022/10/11 19:38, Miaohe Lin wrote:
> Due to the explicit 'noinline' GCC-7.3 is not able to optimize away the
> argument setup of:
> 
> 	apply_ibt_endbr(__ibt_endbr_seal, __ibt_enbr_seal_end);
> 
> even when X86_KERNEL_IBT=n and the function is an empty stub which leads
> to link errors due to missing __ibt_endbr_seal* symbols like below:
> 
> 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'
> 
> Remove explicit 'noinline' to help gcc optimize them away.
> [Thanks Peter Zijlstra for tweaking the commit log.]
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Add cc Peter Zijlstra.

Change log for v2:
Tweak the commit log per Peter Zijlstra. Thanks!

I should have done this in previous thread. Sorry for make noise.

Thanks,
Miaohe Lin


> ---
>  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 */
>  
>