linux-kernel - Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs

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Message-ID: <20160608092040.GA17389@gmail.com>
Date:	Wed, 8 Jun 2016 11:20:40 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly
 outputs


* H. Peter Anvin <hpa@...or.com> wrote:

> On 06/08/16 02:01, Ingo Molnar wrote:
> > 
> > That's a divergence with an underlying reason - but not harmonizing the return 
> > code is an unforced error AFAICS and can be fixed.
> >
> 
> Perhaps.  It is also no real question that "bool" is the right return
> type for a single bit.  Changing that in all architectures at one time
> is a major undertaking, however, and it seems to me that it would be
> better to leave that to the respective architecture maintainers.

Yeah, so extrapolating from past performance in most cases that is really a 
shorthand for 'it will never happen' :-/

Also, unless I'm missing something it's not really 'hard' or dangerous per se to 
do that change for every architecture, just incredibly boring! ;-)

I'm not sure how much it matters though, given other asymmetries in the bitops API 
signatures - does anyone have any preferences?

> Perhaps I'm wrong, but I'd really like to avoid the upcasting to "int"
> which isn't needed, because in my testing I find that it definitely
> encourages gcc to generate poor code.

Yeah, absolutely. I hate 'bool' with a vengence but if 'int' generates worse code 
with modern compilers then I'm not going to argue for worse code. Would a 'char' 
return type be very weird?

Thanks,

	Ingo