vfs: make word-at-a-time accesses handle a non-existing page

[pandora-kernel.git] / arch / x86 / include / asm / word-at-a-time.h

diff --git a/arch/x86/include/asm/word-at-a-time.h b/arch/x86/include/asm/word-at-a-time.h
index 6fe6767..e58f03b 100644 (file)
--- a/arch/x86/include/asm/word-at-a-time.h
+++ b/arch/x86/include/asm/word-at-a-time.h
@@ -43,4 +43,37 @@ static inline unsigned long has_zero(unsigned long a)
        return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
 }
 
+/*
+ * Load an unaligned word from kernel space.
+ *
+ * In the (very unlikely) case of the word being a page-crosser
+ * and the next page not being mapped, take the exception and
+ * return zeroes in the non-existing part.
+ */
+static inline unsigned long load_unaligned_zeropad(const void *addr)
+{
+       unsigned long ret, dummy;
+
+       asm(
+               "1:\tmov %2,%0\n"
+               "2:\n"
+               ".section .fixup,\"ax\"\n"
+               "3:\t"
+               "lea %2,%1\n\t"
+               "and %3,%1\n\t"
+               "mov (%1),%0\n\t"
+               "leal %2,%%ecx\n\t"
+               "andl %4,%%ecx\n\t"
+               "shll $3,%%ecx\n\t"
+               "shr %%cl,%0\n\t"
+               "jmp 2b\n"
+               ".previous\n"
+               _ASM_EXTABLE(1b, 3b)
+               :"=&r" (ret),"=&c" (dummy)
+               :"m" (*(unsigned long *)addr),
+                "i" (-sizeof(unsigned long)),
+                "i" (sizeof(unsigned long)-1));
+       return ret;
+}
+
 #endif /* _ASM_WORD_AT_A_TIME_H */