From: "H. Peter Anvin" <hpa@zytor.com>
Message-Id: <201703090437.v294b0RE021699@mail.zytor.com>
Date: Wed, 08 Mar 2017 20:36:30 -0800
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References: <20170303122712.13353-1-jslaby@suse.cz> <20170304130550.GT21222@n2100.armlinux.org.uk> <23e5808b-2a20-518d-b49a-4d95dd23cfde@landley.net>
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Subject: Re: [PATCH 1/3] futex: remove duplicated code
To: Rob Landley <rob@landley.net>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Jiri Slaby <jslaby@suse.cz>
CC: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        Richard Henderson <rth@twiddle.net>,
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        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, Richard Kuo <rkuo@codeaurora.org>,
        Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>,
        Michal Simek <monstr@monstr.eu>, Ralf Baechle <ralf@linux-mips.org>,
        Jonas Bonn <jonas@southpole.se>,
        Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
        Stafford Horne <shorne@gmail.com>,
        "James E.J. Bottomley" <jejb@parisc-linux.org>,
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<cmetcalf@mellanox.com>,Thomas Gleixner <tglx@linutronix.de>,Ingo Molnar <mingo@redhat.com>,Chris Zankel <chris@zankel.net>,Max Filippov <jcmvbkbc@gmail.com>,Arnd Bergmann <arnd@arndb.de>,x86@kernel.org,linux-alpha@vger.kernel.org,linux-snps-arc@lists.infradead.org,linux-arm-kernel@lists.infradead.org,linux-hexagon@vger.kernel.org,linux-ia64@vger.kernel.org,linux-mips@linux-mips.org,openrisc@lists.librecores.org,linux-parisc@vger.kernel.org,linuxppc-dev@lists.ozlabs.org,linux-s390@vger.kernel.org,linux-sh@vger.kernel.org,sparclinux@vger.kernel.org,linux-xtensa@linux-xtensa.org,linux-arch@vger.kernel.org
From: hpa@zytor.com
Message-ID: <83324528-AAA1-4BED-B0C7-48426ECBA261@zytor.com>

On March 8, 2017 8:16:49 PM PST, Rob Landley <rob@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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