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authorDavid S. Miller <davem@davemloft.net>2012-05-23 19:20:20 -0700
committerDavid S. Miller <davem@davemloft.net>2012-05-23 19:20:20 -0700
commit4efcac3a244de86593a82ca4ed945e839eb4c5af (patch)
tree7456cbb6d71b3f92385d94cab546e2b93dc19c6a /arch/sparc/lib
parentff06dffbc8abfc60d6a0332f058f1d1bb01abb31 (diff)
downloadlinux-4efcac3a244de86593a82ca4ed945e839eb4c5af.tar.gz
sparc: Optimize strncpy_from_user() zero byte search.
Compute a mask that will only have 0x80 in the bytes which had a zero in them. The formula is: ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f) In the inner word iteration, we have to compute the "x | 0x7f7f7f7f" part, so we can reuse that in the above calculation. Once we have this mask, we perform divide and conquer to find the highest 0x80 location. Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch/sparc/lib')
-rw-r--r--arch/sparc/lib/usercopy.c50
1 files changed, 21 insertions, 29 deletions
diff --git a/arch/sparc/lib/usercopy.c b/arch/sparc/lib/usercopy.c
index 851cb75ce189..87f96453403a 100644
--- a/arch/sparc/lib/usercopy.c
+++ b/arch/sparc/lib/usercopy.c
@@ -11,35 +11,20 @@ EXPORT_SYMBOL(copy_from_user_overflow);
#define REPEAT_BYTE(x) ((~0ul / 0xff) * (x))
-/* Return the high bit set in the first byte that is a zero */
-static inline unsigned long has_zero(unsigned long a)
-{
- return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
-}
-
-static inline long find_zero(unsigned long c)
+static inline long find_zero(unsigned long mask)
{
+ long byte = 0;
#ifdef CONFIG_64BIT
- if (!(c & 0xff00000000000000UL))
- return 0;
- if (!(c & 0x00ff000000000000UL))
- return 1;
- if (!(c & 0x0000ff0000000000UL))
- return 2;
- if (!(c & 0x000000ff00000000UL))
- return 3;
-#define __OFF 4
-#else
-#define __OFF 0
+ if (mask >> 32)
+ mask >>= 32;
+ else
+ byte = 4;
#endif
- if (!(c & 0xff000000))
- return __OFF + 0;
- if (!(c & 0x00ff0000))
- return __OFF + 1;
- if (!(c & 0x0000ff00))
- return __OFF + 2;
- return __OFF + 3;
-#undef __OFF
+ if (mask >> 16)
+ mask >>= 16;
+ else
+ byte += 2;
+ return (mask >> 8) ? byte : byte + 1;
}
/*
@@ -50,6 +35,8 @@ static inline long find_zero(unsigned long c)
*/
static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
{
+ const unsigned long high_bits = REPEAT_BYTE(0xfe) + 1;
+ const unsigned long low_bits = REPEAT_BYTE(0x7f);
long res = 0;
/*
@@ -63,14 +50,19 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src, long
goto byte_at_a_time;
while (max >= sizeof(unsigned long)) {
- unsigned long c;
+ unsigned long c, v, rhs;
/* Fall back to byte-at-a-time if we get a page fault */
if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
break;
+ rhs = c | low_bits;
+ v = (c + high_bits) & ~rhs;
*(unsigned long *)(dst+res) = c;
- if (has_zero(c))
- return res + find_zero(c);
+ if (v) {
+ v = (c & low_bits) + low_bits;;
+ v = ~(v | rhs);
+ return res + find_zero(v);
+ }
res += sizeof(unsigned long);
max -= sizeof(unsigned long);
}