Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 6 Mar 2017 15:14:08 +0100 | Subject | Re: [PATCH 1/3] futex: remove duplicated code |
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Hi Jiri,
On Mon, Mar 6, 2017 at 9:46 AM, Jiri Slaby <jslaby@suse.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@suse.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@linux-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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