linux-kernel - Re: [PATCH 1/5] x86/alternative: simplify DUMP

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Date:   Tue, 05 Apr 2022 18:36:53 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexey Dobriyan <adobriyan@...il.com>, x86@...nel.org
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, linux-kernel@...r.kernel.org, adobriyan@...il.com
Subject: Re: [PATCH 1/5] x86/alternative: simplify DUMP_BYTES macro

On Fri, Mar 11 2022 at 17:43, Alexey Dobriyan wrote:
> Avoid zero length check with clever whitespace placement in the format
> string.
>
> Signed-off-by: Alexey Dobriyan (CloudLinux) <adobriyan@...il.com>
> ---
>  arch/x86/kernel/alternative.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 5007c3ffe96f..6c9758ee6810 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -66,13 +66,10 @@ do {									\
>  	if (unlikely(debug_alternative)) {				\
>  		int j;							\
>  									\
> -		if (!(len))						\
> -			break;						\
> -									\

How does that clever whitespace placement prevent this being printed in
the len == 0 case, which is a legit case?

>  		printk(KERN_DEBUG pr_fmt(fmt), ##args);			\

This is debug muck. So why does it have to be "optimized"?

Thanks,

        tglx