linux-kernel - Re: [PATCH 1/2] x86/bootflag: Change some static functions to bool

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Message-ID: <ef6e2925-f005-41e9-bc24-b9adc3922706@kernel.org>
Date: Mon, 24 Feb 2025 08:48:22 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] x86/bootflag: Change some static functions to bool

On 24. 02. 25, 8:39, Uros Bizjak wrote:
> The internal compiler representation of the following testcase:
> 
> _Bool foo (int x) { return x; }
> 
> is:
> 
> --cut here--
> _Bool foo (int x)
> {
>   _Bool _2;
> 
>   <bb 2> [local count: 1073741824]:
>   _2 = x_1(D) != 0;
>   return _2;

Yes, exactly as dictated by the C99 standard.

> }
> --cut here--
> 
> For me, !!x in the source means that the change of types was
> intentional. Surely, the compiler can do it by itself, so at the end
> of the day, it is just a matter of personal taste.

I've just learnt, that we even have that in CodingStyle:
===
> 17) Using bool
> --------------
> 
> The Linux kernel bool type is an alias for the C99 _Bool type. bool values can
> only evaluate to 0 or 1, and implicit or explicit conversion to bool
> automatically converts the value to true or false. When using bool types the
> !! construction is not needed, which eliminates a class of bugs.
===

> FYI, the whole function will soon be removed and replaced with a
> generic parity8() function.

Yeah, your post in that thread brought me here, in fact. Though, I 
didn't realize it actually removes this very function in full.

thanks,
-- 
js
suse labs