From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tim Northover <t.p.northover@gmail.com>,
Ramkumar Ramachandra <artagnon@gmail.com>,
Jeremy Fitzhardinge <jeremy@goop.org>,
Andi Kleen <ak@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
LLVMdev <llvmdev@cs.uiuc.edu>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [LLVMdev] [PATCH] x86/asm: avoid mnemonics without type suffix
Date: Mon, 15 Jul 2013 11:40:04 -0700 [thread overview]
Message-ID: <51E44204.4000802@zytor.com> (raw)
In-Reply-To: <CA+55aFwcxWR-SFD=QFXAb38sPnN-hcOBF-W+NuRBSMx-n+RnxQ@mail.gmail.com>
On 07/14/2013 12:49 PM, Linus Torvalds wrote:
> On Sun, Jul 14, 2013 at 12:30 PM, Tim Northover <t.p.northover@gmail.com> wrote:
>>
>> I don't think you've actually tested that, have you? (x86-64)
>
> Oh, you're right, for constants > 5 bits you have that other thing
> going on. I didn't think about the fact that the constant changed in
> the middle of the thread (it started out as 1).
>
> We use the gcc constraint "I" (0-31) in the kernel for this reason.
>
> Linus
This is also why the Intel manuals point out that "some assemblers" can
take things like:
bt[l] $63,(%rsi)
... and turn it into:
btl $31,4(%rsi)
This is definitely the friendly thing to do toward the human programmer.
Unfortunately gas doesn't, nor does e.g. NASM.
-hpa
next prev parent reply other threads:[~2013-07-15 18:44 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-14 12:56 [PATCH] x86/asm: avoid mnemonics without type suffix Ramkumar Ramachandra
2013-07-14 17:19 ` Linus Torvalds
2013-07-14 18:26 ` Ramkumar Ramachandra
2013-07-14 18:34 ` Linus Torvalds
2013-07-14 18:49 ` Ramkumar Ramachandra
2013-07-14 18:35 ` [LLVMdev] " Tim Northover
2013-07-14 19:09 ` Linus Torvalds
2013-07-14 19:30 ` Tim Northover
2013-07-14 19:41 ` Jeremy Fitzhardinge
2013-07-14 19:49 ` Linus Torvalds
2013-07-15 18:40 ` H. Peter Anvin [this message]
2013-07-15 18:56 ` Linus Torvalds
2013-07-15 19:00 ` H. Peter Anvin
2013-07-15 19:00 ` Linus Torvalds
2013-07-14 19:23 ` Jeremy Fitzhardinge
2013-07-14 19:29 ` Linus Torvalds
2013-07-15 18:40 ` H. Peter Anvin
2013-07-14 19:23 ` Jeremy Fitzhardinge
2013-07-14 21:14 ` Andi Kleen
2013-07-15 18:42 ` H. Peter Anvin
2013-07-15 18:47 ` H. Peter Anvin
2013-07-15 18:58 ` Linus Torvalds
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