linux-kernel - Re: [PATCH 1/3] futex: remove duplicated code

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Date:   Wed, 08 Mar 2017 20:36:30 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Rob Landley <rob@...dley.net>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.cz>
CC:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Richard Kuo <rkuo@...eaurora.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Michal Simek <monstr@...str.eu>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>, Chris.Metcalf@...or.com
Subject: Re: [PATCH 1/3] futex: remove duplicated code

<cmetcalf@...lanox.com>,Thomas Gleixner <tglx@...utronix.de>,Ingo Molnar <mingo@...hat.com>,Chris Zankel <chris@...kel.net>,Max Filippov <jcmvbkbc@...il.com>,Arnd Bergmann <arnd@...db.de>,x86@...nel.org,linux-alpha@...r.kernel.org,linux-snps-arc@...ts.infradead.org,linux-arm-kernel@...ts.infradead.org,linux-hexagon@...r.kernel.org,linux-ia64@...r.kernel.org,linux-mips@...ux-mips.org,openrisc@...ts.librecores.org,linux-parisc@...r.kernel.org,linuxppc-dev@...ts.ozlabs.org,linux-s390@...r.kernel.org,linux-sh@...r.kernel.org,sparclinux@...r.kernel.org,linux-xtensa@...ux-xtensa.org,linux-arch@...r.kernel.org
From: hpa@...or.com
Message-ID: <83324528-AAA1-4BED-B0C7-48426ECBA261@...or.com>

On March 8, 2017 8:16:49 PM PST, Rob Landley <rob@...dley.net> wrote:
>On 03/04/2017 07:05 AM, Russell King - ARM Linux wrote:
>> On Fri, Mar 03, 2017 at 01:27:10PM +0100, Jiri Slaby wrote:
>>> diff --git a/kernel/futex.c b/kernel/futex.c
>>> index b687cb22301c..c5ff9850952f 100644
>>> --- a/kernel/futex.c
>>> +++ b/kernel/futex.c
>>> @@ -1457,6 +1457,42 @@ futex_wake(u32 __user *uaddr, unsigned int
>flags, int nr_wake, u32 bitset)
>>>  	return ret;
>>>  }
>>>  
>>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user
>*uaddr)
>>> +{
>>> +	int op = (encoded_op >> 28) & 7;
>>> +	int cmp = (encoded_op >> 24) & 15;
>>> +	int oparg = (encoded_op << 8) >> 20;
>>> +	int cmparg = (encoded_op << 20) >> 20;
>> 
>> Hmm.  oparg and cmparg look like they're doing these shifts to get
>sign
>> extension of the 12-bit values by assuming that "int" is 32-bit -
>> probably worth a comment, or for safety, they should be "s32" so it's
>> not dependent on the bit-width of "int".
>
>I thought Linux depended on the LP64 standard for all architectures?
>
>Standard: http://www.unix.org/whitepapers/64bit.html
>Rationale: http://www.unix.org/version2/whatsnew/lp64_wp.html
>
>So int has a defined bit width (32) on linux?
>
>Rob

Linux is ILP32 on 32-bit architectures and LP64 on 64-bit architectures, but that doesn't inherently make this stuff clear.
-- 
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