From: Andreas Schwab <schwab@linux-m68k.org>
To: Brad Boyer <flar@allandria.com>
Cc: gcc-help@gcc.gnu.org, linuxppc-dev@ozlabs.org,
linux-kernel@vger.kernel.org,
kernel mailz <kernelmailz@googlemail.com>
Subject: Re: Inline assembly queries [2]
Date: Fri, 03 Jul 2009 22:57:12 +0200 [thread overview]
Message-ID: <m23a9deb87.fsf@igel.home> (raw)
In-Reply-To: <20090703174031.GA12410@cynthia.pants.nu> (Brad Boyer's message of "Fri, 3 Jul 2009 10:40:31 -0700")
Brad Boyer <flar@allandria.com> writes:
> On Fri, Jul 03, 2009 at 12:14:41PM +0530, kernel mailz wrote:
>> b. using m or Z with a memory address. I tried replacing m/Z but no change
>> Is there some guideline ?
>> gcc documentation says Z is obsolete. Is m/Z replaceable ?
>
> No idea. I don't remember ever seeing 'Z' used in anything. Maybe somebody
> else remembers what it used to mean.
The 'Z' constraint is required for a memory operand for insns that don't
have an update form (which would be selected by the %U modifier). It
should only be used together with the %y operand modifier, which makes
sure that the first register is never 0. If the 'm' constraint were
used the operand could contain a pre-in/decrement operation, and without
%U the side effect would be lost.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
next prev parent reply other threads:[~2009-07-03 21:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-03 6:44 Inline assembly queries [2] kernel mailz
2009-07-03 17:40 ` Brad Boyer
2009-07-03 20:05 ` kernel mailz
2009-07-03 21:19 ` Andreas Schwab
2009-07-03 20:57 ` Andreas Schwab [this message]
2009-07-06 6:56 ` Gabriel Paubert
2009-07-07 12:40 ` Andreas Schwab
2009-07-07 13:46 ` Gabriel Paubert
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