arm/arm64: smccc-1.1: Handle function result as parameters

If someone has the silly idea to write something along those lines:

	extern u64 foo(void);

	void bar(struct arm_smccc_res *res)
	{
		arm_smccc_1_1_smc(0xbad, foo(), res);
	}

they are in for a surprise, as this gets compiled as:

	0000000000000588 <bar>:
	 588:   a9be7bfd        stp     x29, x30, [sp, #-32]!
	 58c:   910003fd        mov     x29, sp
	 590:   f9000bf3        str     x19, [sp, #16]
	 594:   aa0003f3        mov     x19, x0
	 598:   aa1e03e0        mov     x0, x30
	 59c:   94000000        bl      0 <_mcount>
	 5a0:   94000000        bl      0 <foo>
	 5a4:   aa0003e1        mov     x1, x0
	 5a8:   d4000003        smc     #0x0
	 5ac:   b4000073        cbz     x19, 5b8 <bar+0x30>
	 5b0:   a9000660        stp     x0, x1, [x19]
	 5b4:   a9010e62        stp     x2, x3, [x19, #16]
	 5b8:   f9400bf3        ldr     x19, [sp, #16]
	 5bc:   a8c27bfd        ldp     x29, x30, [sp], #32
	 5c0:   d65f03c0        ret
	 5c4:   d503201f        nop

The call to foo "overwrites" the x0 register for the return value,
and we end up calling the wrong secure service.

A solution is to evaluate all the parameters before assigning
anything to specific registers, leading to the expected result:

	0000000000000588 <bar>:
	 588:   a9be7bfd        stp     x29, x30, [sp, #-32]!
	 58c:   910003fd        mov     x29, sp
	 590:   f9000bf3        str     x19, [sp, #16]
	 594:   aa0003f3        mov     x19, x0
	 598:   aa1e03e0        mov     x0, x30
	 59c:   94000000        bl      0 <_mcount>
	 5a0:   94000000        bl      0 <foo>
	 5a4:   aa0003e1        mov     x1, x0
	 5a8:   d28175a0        mov     x0, #0xbad
	 5ac:   d4000003        smc     #0x0
	 5b0:   b4000073        cbz     x19, 5bc <bar+0x34>
	 5b4:   a9000660        stp     x0, x1, [x19]
	 5b8:   a9010e62        stp     x2, x3, [x19, #16]
	 5bc:   f9400bf3        ldr     x19, [sp, #16]
	 5c0:   a8c27bfd        ldp     x29, x30, [sp], #32
	 5c4:   d65f03c0        ret

Reported-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

include/linux/arm-smccc.h

@@ -205,41 +205,51 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_1(a0, a1, res)					\
+	typeof(a1) __a1 = a1;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
+	register unsigned long r1 asm("r1") = __a1;			\
 	register unsigned long r2 asm("r2");				\
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_2(a0, a1, a2, res)				\
+	typeof(a1) __a1 = a1;						\
+	typeof(a2) __a2 = a2;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
-	register unsigned long r2 asm("r2") = a2;			\
+	register unsigned long r1 asm("r1") = __a1;			\
+	register unsigned long r2 asm("r2") = __a2;			\
 	register unsigned long r3 asm("r3")
 
 #define __declare_arg_3(a0, a1, a2, a3, res)				\
+	typeof(a1) __a1 = a1;						\
+	typeof(a2) __a2 = a2;						\
+	typeof(a3) __a3 = a3;						\
 	struct arm_smccc_res   *___res = res;				\
 	register unsigned long r0 asm("r0") = (u32)a0;			\
-	register unsigned long r1 asm("r1") = a1;			\
-	register unsigned long r2 asm("r2") = a2;			\
-	register unsigned long r3 asm("r3") = a3
+	register unsigned long r1 asm("r1") = __a1;			\
+	register unsigned long r2 asm("r2") = __a2;			\
+	register unsigned long r3 asm("r3") = __a3
 
 #define __declare_arg_4(a0, a1, a2, a3, a4, res)			\
+	typeof(a4) __a4 = a4;						\
 	__declare_arg_3(a0, a1, a2, a3, res);				\
-	register typeof(a4) r4 asm("r4") = a4
+	register unsigned long r4 asm("r4") = __a4
 
 #define __declare_arg_5(a0, a1, a2, a3, a4, a5, res)			\
+	typeof(a5) __a5 = a5;						\
 	__declare_arg_4(a0, a1, a2, a3, a4, res);			\
-	register typeof(a5) r5 asm("r5") = a5
+	register unsigned long r5 asm("r5") = __a5
 
 #define __declare_arg_6(a0, a1, a2, a3, a4, a5, a6, res)		\
+	typeof(a6) __a6 = a6;						\
 	__declare_arg_5(a0, a1, a2, a3, a4, a5, res);			\
-	register typeof(a6) r6 asm("r6") = a6
+	register unsigned long r6 asm("r6") = __a6
 
 #define __declare_arg_7(a0, a1, a2, a3, a4, a5, a6, a7, res)		\
+	typeof(a7) __a7 = a7;						\
 	__declare_arg_6(a0, a1, a2, a3, a4, a5, a6, res);		\
-	register typeof(a7) r7 asm("r7") = a7
+	register unsigned long r7 asm("r7") = __a7
 
 #define ___declare_args(count, ...) __declare_arg_ ## count(__VA_ARGS__)
 #define __declare_args(count, ...)  ___declare_args(count, __VA_ARGS__)