linux-kernel - Re: [PATCH] Fix the bool convert to int issue

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Message-ID: <20210918082020.GL4323@worktop.programming.kicks-ass.net>
Date:   Sat, 18 Sep 2021 10:20:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     cgel.zte@...il.com
Cc:     jpoimboe@...hat.com, jbaron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        linux-kernel@...r.kernel.org, Yang Guang <yang.guang5@....com.cn>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] Fix the bool convert to int issue

On Sat, Sep 18, 2021 at 07:30:37AM +0000, cgel.zte@...il.com wrote:
> From: Yang Guang <yang.guang5@....com.cn>
> 
> The int value which convert from bool true is 0xFFFFFFFF. Causing the
> __sc_insn return wrong type.

Aaah, this is where the insanity starts...

My copy of the C spec says:

  "When any scalar value is converted to _Bool, the result is 0 if the
   value compares equal to 0; otherwise, the result is 1."

What does yours say?

Also, did your kernel boot? If what you say is right it would've gone up
in flames a long time ago.

Please, learn C _before_ sending patches.

*plonk*

> 
> Signed-off-by: Yang Guang <yang.guang5@....com.cn>
> ---
>  arch/x86/kernel/static_call.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
> index ea028e736831..f608e6710300 100644
> --- a/arch/x86/kernel/static_call.c
> +++ b/arch/x86/kernel/static_call.c
> @@ -89,7 +89,7 @@ static inline enum insn_type __sc_insn(bool null, bool tail)
>  	 *	  1  |   0   |  JMP
>  	 *	  1  |   1   |  RET
>  	 */
> -	return 2*tail + null;
> +	return ((tail)?2:0) + ((null)?1:0);
>  }
>  
>  void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
> -- 
> 2.25.1
>