inline syscall support for mips

this drastically reduces the size of some functions which are purely
syscall wrappers.

disabled for clang due to known bugs satisfying register constraints.

arch/mips/syscall_arch.h

@@ -5,6 +5,61 @@
 
 #define __SYSCALL_SSLEN 16
 
+#ifndef __clang__
+
+#define __asm_syscall(...) do { \
+	register long r2 __asm__("$2"); \
+	register long r7 __asm__("$7"); \
+	__asm__ __volatile__ ( \
+	"move $2,%2 ; syscall" \
+	: "=&r"(r2), "=r"(r7) : __VA_ARGS__ \
+	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13", \
+	  "$14", "$15", "$24", "hi", "lo", "memory"); \
+	return r7 ? -r2 : r2; \
+	} while (0)
+
+static inline long __syscall0(long n)
+{
+	register long r25 __asm__("$25") = n;
+	__asm_syscall("r"(r25));
+}
+
+static inline long __syscall1(long n, long a)
+{
+	register long r25 __asm__("$25") = n;
+	register long r4 __asm__("$4") = a;
+	__asm_syscall("r"(r25), "r"(r4));
+}
+
+static inline long __syscall2(long n, long a, long b)
+{
+	register long r25 __asm__("$25") = n;
+	register long r4 __asm__("$4") = a;
+	register long r5 __asm__("$5") = b;
+	__asm_syscall("r"(r25), "r"(r4), "r"(r5));
+}
+
+static inline long __syscall3(long n, long a, long b, long c)
+{
+	register long r25 __asm__("$25") = n;
+	register long r4 __asm__("$4") = a;
+	register long r5 __asm__("$5") = b;
+	register long r6 __asm__("$6") = c;
+	__asm_syscall("r"(r25), "r"(r4), "r"(r5), "r"(r6));
+}
+
+static inline long __syscall4(long n, long a, long b, long c, long d)
+{
+	register long r25 __asm__("$25") = n;
+	register long r4 __asm__("$4") = a;
+	register long r5 __asm__("$5") = b;
+	register long r6 __asm__("$6") = c;
+	register long r7 __asm__("$7") = d;
+	__asm_syscall("r"(r25), "r"(r4), "r"(r5), "r"(r6), "r"(r7));
+}
+
+#else
+
 static inline long __syscall0(long n)
 {
 	return (__syscall)(n);
@@ -30,6 +85,8 @@ static inline long __syscall4(long n, long a, long b, long c, long d)
 	return (__syscall)(n, a, b, c, d);
 }
 
+#endif
+
 static inline long __syscall5(long n, long a, long b, long c, long d, long e)
 {
 	return (__syscall)(n, a, b, c, d, e);