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Date: Mon, 6 Mar 2017 15:14:08 +0100 From: Geert Uytterhoeven <geert@...ux-m68k.org> To: Jiri Slaby <jslaby@...e.cz> Cc: Stafford Horne <shorne@...il.com>, "H. Peter Anvin" <hpa@...or.com>, Russell King - ARM Linux <linux@...linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, "linux-kernel@...r.kernel.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>, "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>, DavidS.Miller@...or.com Subject: Re: [PATCH 1/3] futex: remove duplicated code Hi Jiri, On Mon, Mar 6, 2017 at 9:46 AM, Jiri Slaby <jslaby@...e.cz> wrote: > futex: make the encoded_op decoding readable > > Decoding of encoded_op is a bit unreadable. It contains shifts to the > left and to the right by some constants. Make it clearly visible what > part of the bit mask is taken and shift the values only to the right > appropriately. And make sure sign extension takes place using > sign_extend32. > > Signed-off-by: Jiri Slaby <jslaby@...e.cz> > > diff --git a/kernel/futex.c b/kernel/futex.c > index 0ead0756a593..f90314bd42cb 100644 > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -1461,10 +1461,10 @@ futex_wake(u32 __user *uaddr, unsigned int > flags, int nr_wake, u32 bitset) > > static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr) > { > - int op = (encoded_op >> 28) & 7; > - int cmp = (encoded_op >> 24) & 15; At least for the two above (modulo 7 vs 15?), the old decoding code matched the flow of operation in FUTEX_OP(). > - 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; Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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