[PATCH 1/3] futex: remove duplicated code

[H. Peter Anvin]

<cmetcalf at mellanox.com>,Thomas Gleixner <tglx at linutronix.de>,Ingo Molnar <mingo at redhat.com>,Chris Zankel <chris at zankel.net>,Max Filippov <jcmvbkbc at gmail.com>,Arnd Bergmann <arnd at arndb.de>,x86 at kernel.org,linux-alpha at vger.kernel.org,linux-snps-arc at lists.infradead.org,linux-arm-kernel at lists.infradead.org,linux-hexagon at vger.kernel.org,linux-ia64 at vger.kernel.org,linux-mips at linux-mips.org,openrisc at lists.librecores.org,linux-parisc at vger.kernel.org,linuxppc-dev at lists.ozlabs.org,linux-s390 at vger.kernel.org,linux-sh at vger.kernel.org,sparclinux at vger.kernel.org,linux-xtensa at linux-xtensa.org,linux-arch at vger.kernel.org
From: hpa at zytor.com
Message-ID: <83324528-AAA1-4BED-B0C7-48426ECBA261 at zytor.com>

On March 8, 2017 8:16:49 PM PST, Rob Landley <rob at landley.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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