asm volatile()

in include/asm/uaccess.h [201:289]

• 84 lines of code
• 12 McCabe index (conditional complexity)

	asm volatile ("\n"						\
		"1:	"MOVES"."#s1"	(%2)+,%3\n"			\
		"	move."#s1"	%3,(%1)+\n"			\
		"	.ifnc	\""#s2"\",\"\"\n"			\
		"2:	"MOVES"."#s2"	(%2)+,%3\n"			\
		"	move."#s2"	%3,(%1)+\n"			\
		"	.ifnc	\""#s3"\",\"\"\n"			\
		"3:	"MOVES"."#s3"	(%2)+,%3\n"			\
		"	move."#s3"	%3,(%1)+\n"			\
		"	.endif\n"					\
		"	.endif\n"					\
		"4:\n"							\
		"	.section __ex_table,\"a\"\n"			\
		"	.align	4\n"					\
		"	.long	1b,10f\n"				\
		"	.ifnc	\""#s2"\",\"\"\n"			\
		"	.long	2b,20f\n"				\
		"	.ifnc	\""#s3"\",\"\"\n"			\
		"	.long	3b,30f\n"				\
		"	.endif\n"					\
		"	.endif\n"					\
		"	.previous\n"					\
		"\n"							\
		"	.section .fixup,\"ax\"\n"			\
		"	.even\n"					\
		"10:	addq.l #"#n1",%0\n"				\
		"	.ifnc	\""#s2"\",\"\"\n"			\
		"20:	addq.l #"#n2",%0\n"				\
		"	.ifnc	\""#s3"\",\"\"\n"			\
		"30:	addq.l #"#n3",%0\n"				\
		"	.endif\n"					\
		"	.endif\n"					\
		"	jra	4b\n"					\
		"	.previous\n"					\
		: "+d" (res), "+&a" (to), "+a" (from), "=&d" (tmp)	\
		: : "memory")

#define ___constant_copy_from_user_asm(res, to, from, tmp, n1, n2, n3, s1, s2, s3)\
	____constant_copy_from_user_asm(res, to, from, tmp, n1, n2, n3, s1, s2, s3)
#define __constant_copy_from_user_asm(res, to, from, tmp, n1, n2, n3)	\
	___constant_copy_from_user_asm(res, to, from, tmp, n1, n2, n3,  \
					__suffix##n1, __suffix##n2, __suffix##n3)

static __always_inline unsigned long
__constant_copy_from_user(void *to, const void __user *from, unsigned long n)
{
	unsigned long res = 0, tmp;

	switch (n) {
	case 1:
		__constant_copy_from_user_asm(res, to, from, tmp, 1, 0, 0);
		break;
	case 2:
		__constant_copy_from_user_asm(res, to, from, tmp, 2, 0, 0);
		break;
	case 3:
		__constant_copy_from_user_asm(res, to, from, tmp, 2, 1, 0);
		break;
	case 4:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 0, 0);
		break;
	case 5:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 1, 0);
		break;
	case 6:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 2, 0);
		break;
	case 7:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 2, 1);
		break;
	case 8:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 4, 0);
		break;
	case 9:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 4, 1);
		break;
	case 10:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 4, 2);
		break;
	case 12:
		__constant_copy_from_user_asm(res, to, from, tmp, 4, 4, 4);
		break;
	default:
		/* we limit the inlined version to 3 moves */
		return __generic_copy_from_user(to, from, n);
	}

	return res;
}