feat: add support for aarch64 timer/interrupts, port MontaukOS userspace

programs/lib/libc/libc.c

@@ -32,6 +32,8 @@
    Raw syscall wrappers (C versions matching kernel ABI)
    ======================================================================== */
 
+#if defined(__x86_64__)
+
 static inline long _mtk_syscall0(long nr) {
     long ret;
     __asm__ volatile("syscall" : "=a"(ret) : "a"(nr)
@@ -89,6 +91,55 @@ static inline long _mtk_syscall4(long nr, long a1, long a2, long a3, long a4) {
     return ret;
 }
 
+#elif defined(__aarch64__)
+
+// AArch64: number in x8, arguments in x0-x5, `svc #0`; the kernel
+// preserves every register except x0, which carries the result.
+static inline long _mtk_syscall0(long nr) {
+    register long x8 __asm__("x8") = nr;
+    register long x0 __asm__("x0");
+    __asm__ volatile("svc #0" : "=r"(x0) : "r"(x8) : "memory");
+    return x0;
+}
+
+static inline long _mtk_syscall1(long nr, long a1) {
+    register long x8 __asm__("x8") = nr;
+    register long x0 __asm__("x0") = a1;
+    __asm__ volatile("svc #0" : "+r"(x0) : "r"(x8) : "memory");
+    return x0;
+}
+
+static inline long _mtk_syscall2(long nr, long a1, long a2) {
+    register long x8 __asm__("x8") = nr;
+    register long x0 __asm__("x0") = a1;
+    register long x1 __asm__("x1") = a2;
+    __asm__ volatile("svc #0" : "+r"(x0) : "r"(x8), "r"(x1) : "memory");
+    return x0;
+}
+
+static inline long _mtk_syscall3(long nr, long a1, long a2, long a3) {
+    register long x8 __asm__("x8") = nr;
+    register long x0 __asm__("x0") = a1;
+    register long x1 __asm__("x1") = a2;
+    register long x2 __asm__("x2") = a3;
+    __asm__ volatile("svc #0" : "+r"(x0) : "r"(x8), "r"(x1), "r"(x2) : "memory");
+    return x0;
+}
+
+static inline long _mtk_syscall4(long nr, long a1, long a2, long a3, long a4) {
+    register long x8 __asm__("x8") = nr;
+    register long x0 __asm__("x0") = a1;
+    register long x1 __asm__("x1") = a2;
+    register long x2 __asm__("x2") = a3;
+    register long x3 __asm__("x3") = a4;
+    __asm__ volatile("svc #0" : "+r"(x0) : "r"(x8), "r"(x1), "r"(x2), "r"(x3) : "memory");
+    return x0;
+}
+
+#else
+#error "unsupported architecture"
+#endif
+
 /* Syscall numbers */
 #define SYS_EXIT    0
 #define SYS_YIELD   1