Subject: Re: [PATCH 1/3] futex: remove duplicated code
To: Jiri Slaby <jslaby@suse.cz>, Stafford Horne <shorne@gmail.com>
References: <20170303122712.13353-1-jslaby@suse.cz>
 <20170304130550.GT21222@n2100.armlinux.org.uk>
 <3994975e-89a5-d2b5-60be-a8633ddc3733@zytor.com>
 <20170304213805.GA2449@lianli.shorne-pla.net>
 <201703042308.v24N8wvh012716@mail.zytor.com>
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 <3662dd60-2467-f858-dc32-0b0fb6abb33b@suse.cz>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        Richard Henderson <rth@twiddle.net>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Matt Turner <mattst88@gmail.com>, Vineet Gupta <vgupta@synopsys.com>,
        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>,
        "James E.J. Bottomley" <jejb@parisc-linux.org>,
        Helge Deller <deller@gmx.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <29ec8cda-02bd-fe07-340b-2bb775c8446b@zytor.com>
Date: Mon, 6 Mar 2017 01:13:52 -0800
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On 03/06/17 00:46, Jiri Slaby wrote:
> 
>  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;
> +       int op =                  (encoded_op & 0x70000000) >> 28;
> +       int cmp =                 (encoded_op & 0x0f000000) >> 24;
> +       int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 12);
> +       int cmparg = sign_extend32(encoded_op & 0x00000fff, 12);
>         int oldval, ret;
> 

At least in the sign-extend case the mask is unnecessary.

This is why it would be nice to have both sign and zero extend for symmetry.

	-hpa