linux-kernel - Re: [PATCH] x86/asm: Use asm_inline() instead of asm() in amd_clear

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Message-ID: <96E2026E-CEF1-4A4C-B107-7FCE2CD9121F@alien8.de>
Date: Thu, 13 Mar 2025 20:26:28 +0100
From: Borislav Petkov <bp@...en8.de>
To: Uros Bizjak <ubizjak@...il.com>, x86@...nel.org, linux-kernel@...r.kernel.org
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/asm: Use asm_inline() instead of asm() in amd_clear_divider()

On March 13, 2025 8:18:09 PM GMT+01:00, Uros Bizjak <ubizjak@...il.com> wrote:
>Use asm_inline() to instruct the compiler that the size of asm()
>is the minimum size of one instruction, ignoring how many instructions
>the compiler thinks it is. ALTERNATIVE macro that expands to several
>pseudo directives causes instruction length estimate to count
>more than 20 instructions.
>
>bloat-o-meter reports no code size changes.
>
>Signed-off-by: Uros Bizjak <ubizjak@...il.com>
>Cc: Thomas Gleixner <tglx@...utronix.de>
>Cc: Ingo Molnar <mingo@...nel.org>
>Cc: Borislav Petkov <bp@...en8.de>
>Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>Cc: "H. Peter Anvin" <hpa@...or.com>
>---
> arch/x86/include/asm/processor.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
>index 5d2f7e5aff26..06e499ba4fe8 100644
>--- a/arch/x86/include/asm/processor.h
>+++ b/arch/x86/include/asm/processor.h
>@@ -707,7 +707,7 @@ static inline u32 per_cpu_l2c_id(unsigned int cpu)
>  */
> static __always_inline void amd_clear_divider(void)
> {
>-	asm volatile(ALTERNATIVE("", "div %2\n\t", X86_BUG_DIV0)
>+	asm_inline volatile(ALTERNATIVE("", "div %2", X86_BUG_DIV0)
> 		     :: "a" (0), "d" (0), "r" (1));
> }
> 

So there's no point for this one...
-- 
Sent from a small device: formatting sucks and brevity is inevitable.