From: Florian Weimer <fweimer@redhat.com>
To: Andrew Haley <aph@redhat.com>
Cc: "gcc-help@gcc.gnu.org" <gcc-help@gcc.gnu.org>
Subject: Re: Incorrect asm constraints or GCC bug?
Date: Mon, 19 Nov 2012 11:56:00 -0000 [thread overview]
Message-ID: <50AA1E6A.3070009@redhat.com> (raw)
In-Reply-To: <50AA1B81.4070602@redhat.com>
On 11/19/2012 12:44 PM, Andrew Haley wrote:
> On 11/19/2012 11:28 AM, Florian Weimer wrote:
>> Note how %0 and %3 are assigned the same register. Changing "=r" to
>> "+r" fixes this. If an output-only operand must be modified last, the
>> original register assignment would be correct, but the Extended Asm
>> documentation does not require such a thing.
>
> It does.
>
> "Unless an output operand has the `&' constraint modifier, GCC may
> allocate it in the same register as an unrelated input operand, on the
> assumption the inputs are consumed before the outputs are produced."
Oh, thanks, that settles it. I've submitted a fix for OpenSSL. (This
was a recent regression on their part.)
--
Florian Weimer / Red Hat Product Security Team
prev parent reply other threads:[~2012-11-19 11:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-19 11:28 Florian Weimer
2012-11-19 11:44 ` Andrew Haley
2012-11-19 11:56 ` Florian Weimer [this message]
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