From: "Jan Beulich" <JBeulich@suse.com>
To: Tim Deegan <tim@xen.org>
Cc: Ian Campbell <Ian.Campbell@eu.citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [PATCH 2/2] arm64: fix fls()
Date: Thu, 22 Jan 2015 14:05:12 +0000 [thread overview]
Message-ID: <54C111A802000078000582E3@mail.emea.novell.com> (raw)
In-Reply-To: <20150122140115.GF97314@deinos.phlegethon.org>
>>> On 22.01.15 at 15:01, <tim@xen.org> wrote:
> At 13:38 +0000 on 22 Jan (1421930334), Jan Beulich wrote:
>> It using CLZ on a 64-bit register while specifying the input operand as
>> only 32 bits wide is wrong: An operand intentionally shrunk down to 32
>> bits at the source level doesn't imply respective zero extension also
>> happens at the machine instruction level, and hence the wrong result
>> could get returned.
>>
>> Add suitable inline assembly abstraction so that the function can
>> remain shared between arm32 and arm64.
>
> Would casting the asm arguments to unsigned long DTRT withuot
> needing #ifdefs?
The input one - yes, I think so. But it wouldn't be me to introduce
such (suspicious) casts, and I also think it is better to use 32-bit
instruction variants where possible (which quite certainly won't
perform worse than the 64-bit ones, but may perform better).
Jan
next prev parent reply other threads:[~2015-01-22 14:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-22 13:26 [PATCH 0/2] fls() / ffs() adjustments Jan Beulich
2015-01-22 13:38 ` [PATCH 1/2] make fls() and ffs() consistent across architectures Jan Beulich
2015-01-23 14:38 ` Andrew Cooper
2015-01-23 14:53 ` Jan Beulich
2015-01-22 13:38 ` [PATCH 2/2] arm64: fix fls() Jan Beulich
2015-01-22 14:01 ` Tim Deegan
2015-01-22 14:05 ` Jan Beulich [this message]
2015-01-22 14:29 ` Tim Deegan
2015-01-22 14:59 ` [PATCH 0/2] fls() / ffs() adjustments Ian Campbell
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