Re: [PATCH 1/3] futex: remove duplicated code

2017-03-04 Thread H. Peter Anvin 
,Chris Metcalf ,Thomas Gleixner 
,Ingo Molnar ,Chris Zankel 
,Max Filippov ,Arnd Bergmann 
,x...@kernel.org,linux-alpha@vger.kernel.org,linux-snps-...@lists.infradead.org,linux-arm-ker...@lists.infradead.org,linux-hexa...@vger.kernel.org,linux-i...@vger.kernel.org,linux-m...@linux-mips.org,openr...@lists.librecores.org,linux-par...@vger.kernel.org,linuxppc-...@lists.ozlabs.org,linux-s...@vger.kernel.org,linux...@vger.kernel.org,sparcli...@vger.kernel.org,linux-xte...@linux-xtensa.org,linux-a...@vger.kernel.org
From: h...@zytor.com
Message-ID: 

On March 4, 2017 1:38:05 PM PST, Stafford Horne  wrote:
>On Sat, Mar 04, 2017 at 11:15:17AM -0800, H. Peter Anvin wrote:
>> On 03/04/17 05:05, Russell King - ARM Linux 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;
>> > 
>> > 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".
>> > 
>> 
>> For readability, perhaps we should make sign- and zero-extension an
>> explicit facility?
>
>There is some of this in already here, 32 and 64 bit versions:
>
>  include/linux/bitops.h
>
>Do we really need zero extension? It seems the same.
>
>Example implementation from bitops.h
>
>static inline __s32 sign_extend32(__u32 value, int index)
>{
>__u8 shift = 31 - index;
>return (__s32)(value << shift) >> shift;
>}
>
>> /*
>>  * Truncate an integer x to n bits, using sign- or
>>  * zero-extension, respectively.
>>  */
>> static inline __const_func__ s32 sex32(s32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ s64 sex64(s64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define sex(x,y) \
>>  ((__typeof__(x))\
>>   (((__builtin_constant_p(y) && ((y) <= 32)) ||  \
>> (sizeof(x) <= sizeof(s32)))  \
>>? sex32((x),(y)) : sex64((x),(y
>> 
>> static inline __const_func__ u32 zex32(u32 x, int n)
>> {
>>   return (x << (32-n)) >> (32-n);
>> }
>> 
>> static inline __const_func__ u64 zex64(u64 x, int n)
>> {
>>   return (x << (64-n)) >> (64-n);
>> }
>> 
>> #define zex(x,y) \
>>  ((__typeof__(x))\
>>   (((__builtin_constant_p(y) && ((y) <= 32)) ||  \
>> (sizeof(x) <= sizeof(u32)))  \
>>? zex32((x),(y)) : zex64((x),(y
>> 

Also, i strongly believe that making it syntactically cumbersome encodes people 
to open-code it which is bad...
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.
--
To unsubscribe from this list: send the line "unsubscribe linux-alpha" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH 1/3] futex: remove duplicated code

2017-03-04 Thread Michael Ellerman 
Jiri Slaby  writes:

> There is code duplicated over all architecture's headers for
> futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> and comparison of the result.
>
> Remove this duplication and leave up to the arches only the needed
> assembly which is now in arch_futex_atomic_op_inuser.

Looks OK and boots on powerpc. But I don't think anything's actually
calling those futex ops. Is there a test suite I should run?

Acked-by: Michael Ellerman  (powerpc)

cheers
--
To unsubscribe from this list: send the line "unsubscribe linux-alpha" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html