core+system: Add a "getAddressSpace()" system call

core/src/sys/mem.zig

@@ -46,3 +46,14 @@ pub fn setAddressSpace(_: *platform.Registers, args: *sys.Arguments, _: *isize)
 
     target.address_space = vmm.AddressSpace.create(.{ .address = args.arg1 }, vmm.PHYSICAL_MAPPING_BASE);
 }
+
+pub fn getAddressSpace(_: *platform.Registers, args: *sys.Arguments, result: *isize) anyerror!void {
+    const core = cpu.thisCore();
+    if (!sys.checkToken(core, system.kernel.Token.CreateProcess)) return error.NotAuthorized;
+
+    const target = thread.lookupThreadById(args.arg0) orelse return error.NoSuchThread;
+
+    const space = target.address_space orelse return error.NoAddressSpace;
+
+    result.* = @bitCast(space.phys.address);
+}

core/src/sys/syscall.zig

@@ -36,6 +36,7 @@ const syscalls = [_]SystemCall{
     sched.setThreadStack,
     sched.startThread,
     sched.getThreadId,
+    mem.getAddressSpace,
 };
 
 pub fn invokeSyscall(number: usize, frame: *platform.Registers, args: *Arguments, retval: *isize) void {

system/lib/kernel.zig

@@ -16,6 +16,7 @@ pub const SystemCall = enum(u64) {
     SetThreadStack, // requires Token.CreateProcess
     StartThread, // requires Token.CreateProcess
     GetThreadId,
+    GetAddressSpace, // requires Token.CreateProcess
 };
 
 pub const Token = enum(u64) {

system/lib/syscalls.zig

@@ -95,3 +95,9 @@ pub fn startThread(pid: u64) !void {
 pub fn getThreadId() u64 {
     return @bitCast(syscall(.GetThreadId, 0, 0, 0));
 }
+
+pub fn getAddressSpace(pid: u64) !u64 {
+    const retval = syscall(.GetAddressSpace, pid, 0, 0);
+    if (retval < 0) return error.NoSuchThread;
+    return @bitCast(retval);
+}