From: "H. Peter Anvin" <hpa@zytor.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
"H. Peter Anvin" <hpa@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs
Date: Wed, 8 Jun 2016 02:40:21 -0700 [thread overview]
Message-ID: <d1f14d3c-b4dc-bfbc-bae9-90ffc9282139@zytor.com> (raw)
In-Reply-To: <20160608092040.GA17389@gmail.com>
On 06/08/16 02:20, Ingo Molnar wrote:
>
> 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?
>
My big concern is doing a change to another architectures which I can't
test... and I will have to make assumptions about the properties of
asm() in that architecture.
Furthermore, if/when other architectures get support for =@cc or an
equivalent, they probably want to change their stuff.
>> 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?
Another reason to not hate on "bool" so much: I have personally gotten
bitten a few to many times by programmers who thought returning -1 or 2
for what was normally a 0/1 flag in some kind of exceptional case. If
the variable is bool you know that that can't happen.
One thing, though: we should NOT use bool as input to a system call,
because coming from userspace we cannot enforce the required invariant
that bits[7:1] == 0.
next prev parent reply other threads:[~2016-06-08 9:41 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-07 23:30 [PATCH 00/10] x86: use gcc 6+ asm flag output feature H. Peter Anvin
2016-06-07 23:31 ` [PATCH 01/10] x86, bitops: remove use of "sbb" to return CF H. Peter Anvin
2016-06-07 23:39 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 02/10] x86, asm: use bool for bitops and other assembly outputs H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 7:49 ` [PATCH 02/10] " Peter Zijlstra
2016-06-08 8:28 ` Ingo Molnar
2016-06-08 8:33 ` Ingo Molnar
2016-06-08 8:55 ` H. Peter Anvin
2016-06-08 9:01 ` Ingo Molnar
2016-06-08 9:12 ` H. Peter Anvin
2016-06-08 9:20 ` Ingo Molnar
2016-06-08 9:31 ` H. Peter Anvin
2016-06-08 9:39 ` Peter Zijlstra
2016-06-08 9:43 ` H. Peter Anvin
2016-06-08 9:40 ` H. Peter Anvin [this message]
2016-06-08 8:58 ` H. Peter Anvin
2016-06-08 9:06 ` Ingo Molnar
2016-06-07 23:31 ` [PATCH 03/10] x86, asm: change the GEN_*_RMWcc() macros to not quote the condition H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 04/10] x86, asm: define CC_SET() and CC_OUT() macros H. Peter Anvin
2016-06-07 23:40 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 5:09 ` [PATCH 04/10] " Andy Lutomirski
2016-06-08 19:29 ` H. Peter Anvin
2016-06-08 19:34 ` H. Peter Anvin
2016-06-08 19:35 ` Borislav Petkov
2016-06-07 23:31 ` [PATCH 05/10] x86, asm: change GEN_*_RMWcc() to use CC_SET()/CC_OUT() H. Peter Anvin
2016-06-07 23:41 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 06/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/bitops.h> H. Peter Anvin
2016-06-07 23:41 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 07/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/percpu.h> H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 08/10] x86, asm: Use CC_SET()/CC_OUT() in <asm/rwsem.h> H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-07 23:31 ` [PATCH 09/10] x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h H. Peter Anvin
2016-06-07 23:42 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 5:12 ` [PATCH 09/10] " Andy Lutomirski
2016-06-07 23:31 ` [PATCH 10/10] x86, asm, boot: Use CC_SET()/CC_OUT() in arch/x86/boot/boot.h H. Peter Anvin
2016-06-07 23:43 ` [tip:x86/asm] " tip-bot for H. Peter Anvin
2016-06-08 8:00 ` [PATCH 00/10] x86: use gcc 6+ asm flag output feature Peter Zijlstra
2016-06-08 8:56 ` H. Peter Anvin
2016-06-08 8:26 ` Ingo Molnar
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