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Re: [PATCH 3/3] futex: make the encoded_op decoding readable

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On 03/03/2017, 01:27 PM, Jiri Slaby wrote:
> 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
> appropriatelly.
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> ---
>  kernel/futex.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index c09424406560..5834df248f09 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1459,10 +1459,10 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
>  
>  static int futex_atomic_op_inuser(unsigned 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 = (encoded_op & 0x00fff000) >> 12;
> +	int cmparg = encoded_op & 0x00000fff;

And it turned out that this one is actually invalid as it doesn't
preserve signedness on oparg and cmdarg. So please avoid applying this one.

thanks,
-- 
js
suse labs

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[PATCH 1/3] futex: remove duplicated code Jiri Slaby <jslaby@suse.cz> - 2017-03-03 13:40 +0100
  [PATCH 2/3] futex: fix decoding of operation Jiri Slaby <jslaby@suse.cz> - 2017-03-03 19:30 +0100
  [PATCH 3/3] futex: make the encoded_op decoding readable Jiri Slaby <jslaby@suse.cz> - 2017-03-03 19:30 +0100
    Re: [PATCH 3/3] futex: make the encoded_op decoding readable Jiri Slaby <jslaby@suse.cz> - 2017-03-05 09:00 +0100
  Re: [PATCH 1/3] futex: remove duplicated code Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-03-03 21:10 +0100
  Re: [PATCH 1/3] futex: remove duplicated code Michael Ellerman <mpe@ellerman.id.au> - 2017-03-04 14:00 +0100
  Re: [PATCH 1/3] futex: remove duplicated code Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-04 14:20 +0100
    Re: [PATCH 1/3] futex: remove duplicated code "H. Peter Anvin" <hpa@zytor.com> - 2017-03-04 20:30 +0100
      Re: [PATCH 1/3] futex: remove duplicated code Stafford Horne <shorne@gmail.com> - 2017-03-04 22:40 +0100
        Re: [PATCH 1/3] futex: remove duplicated code "H. Peter Anvin" <hpa@zytor.com> - 2017-03-05 00:20 +0100
          Re: [PATCH 1/3] futex: remove duplicated code Stafford Horne <shorne@gmail.com> - 2017-03-05 00:40 +0100
            Re: [PATCH 1/3] futex: remove duplicated code Jiri Slaby <jslaby@suse.cz> - 2017-03-06 09:50 +0100
              Re: [PATCH 1/3] futex: remove duplicated code "H. Peter Anvin" <hpa@zytor.com> - 2017-03-06 10:20 +0100
              Re: [PATCH 1/3] futex: remove duplicated code Geert Uytterhoeven <geert@linux-m68k.org> - 2017-03-06 15:20 +0100
        Re: [PATCH 1/3] futex: remove duplicated code "H. Peter Anvin" <hpa@zytor.com> - 2017-03-05 00:20 +0100
    Re: [PATCH 1/3] futex: remove duplicated code Rob Landley <rob@landley.net> - 2017-03-09 05:20 +0100
      Re: [PATCH 1/3] futex: remove duplicated code "H. Peter Anvin" <hpa@zytor.com> - 2017-03-09 06:10 +0100
        Re: [PATCH 1/3] futex: remove duplicated code Rich Felker <dalias@libc.org> - 2017-03-09 23:50 +0100
  Re: [PATCH 1/3] futex: remove duplicated code Rich Felker <dalias@libc.org> - 2017-03-06 03:20 +0100
  Re: [PATCH 1/3] futex: remove duplicated code Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-03-09 23:50 +0100

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