init: Add system call handling code

system/init/kernel.zig

@@ -0,0 +1,41 @@
+const SystemCall = enum(u64) {
+    Print,
+    AllocFrame,
+    LockFrame,
+    FreeFrame,
+    Yield,
+};
+
+const SystemError = error{
+    OutOfMemory,
+};
+
+fn syscall(num: SystemCall, arg: u64) i64 {
+    return asm volatile ("int $66"
+        : [result] "=r" (-> i64),
+        : [num] "{rax}" (@intFromEnum(num)),
+          [arg] "{rdi}" (arg),
+    );
+}
+
+pub fn print(arg: u64) void {
+    _ = syscall(.Print, arg);
+}
+
+pub fn allocFrame() !usize {
+    const retval = syscall(.AllocFrame, 0);
+    if (retval < 0) return error.OutOfMemory;
+    return @bitCast(retval);
+}
+
+pub fn lockFrame(address: u64) void {
+    _ = syscall(.LockFrame, address);
+}
+
+pub fn freeFrame(address: u64) void {
+    _ = syscall(.FreeFrame, address);
+}
+
+pub fn yield() void {
+    _ = syscall(.Yield, 0);
+}

system/init/main.zig

@@ -1,13 +1,9 @@
-fn syscall(num: u64, arg: u64) void {
-    asm volatile ("int $66"
-        :
-        : [num] "{rax}" (num),
-          [arg] "{rdi}" (arg),
-    );
-}
+const kernel = @import("kernel.zig");
 
 export fn _start(base: u64) callconv(.C) noreturn {
-    syscall(0, base);
+    kernel.print(base);
 
-    while (true) {}
+    while (true) {
+        kernel.yield();
+    }
 }