[kernel] Add automatic verification to syscalls

Since we have a DSL for specifying syscalls, we can create a verificaton
method for each syscall that can cover most argument (and eventually
capability) verification instead of doing it piecemeal in each syscall
implementation, which can be more error-prone.

Now a new _syscall_verify_* function exists for every syscall, which
calls the real implementation. The syscall table for the syscall handler
now maps to these verify functions.

Other changes:

- Updated the definition grammar to allow options to have a "key:value"
  style, to eventually support capabilities.
- Added an "optional" option for parameters that says a syscall will
  accept a null value.
- Some bonnibel fixes, as definition file changes weren't always
  properly causing updates in the build dep graph.
- The syscall implementation function signatures are no longer exposed
  in syscall.h. Also, the unused syscall enum has been removed.

src/kernel/syscalls/system.cpp

@@ -19,9 +19,6 @@ namespace syscalls {
 j6_status_t
 log(const char *message)
 {
-    if (message == nullptr)
-        return j6_err_invalid_arg;
-
     thread &th = thread::current();
     log::info(logs::syscall, "Message[%llx]: %s", th.koid(), message);
     return j6_status_ok;
@@ -36,23 +33,24 @@ noop()
 }
 
 j6_status_t
-system_get_log(j6_handle_t sys, void *buffer, size_t *size)
+system_get_log(j6_handle_t sys, void *buffer, size_t *buffer_len)
 {
-    if (!size || (*size && !buffer))
+    // Buffer is marked optional, but we need the length, and if length > 0,
+    // buffer is not optional.
+    if (!buffer_len || (*buffer_len && !buffer))
         return j6_err_invalid_arg;
 
-    size_t orig_size = *size;
-    *size = g_logger.get_entry(buffer, *size);
+    size_t orig_size = *buffer_len;
+    *buffer_len = g_logger.get_entry(buffer, *buffer_len);
     if (!g_logger.has_log())
         system::get().deassert_signal(j6_signal_system_has_log);
 
-    return (*size > orig_size) ? j6_err_insufficient : j6_status_ok;
+    return (*buffer_len > orig_size) ? j6_err_insufficient : j6_status_ok;
 }
 
 j6_status_t
 system_bind_irq(j6_handle_t sys, j6_handle_t endp, unsigned irq)
 {
-    // TODO: check capabilities on sys handle
     endpoint *e = get_handle<endpoint>(endp);
     if (!e) return j6_err_invalid_arg;
 
@@ -65,9 +63,6 @@ system_bind_irq(j6_handle_t sys, j6_handle_t endp, unsigned irq)
 j6_status_t
 system_map_phys(j6_handle_t handle, j6_handle_t * area, uintptr_t phys, size_t size, uint32_t flags)
 {
-    // TODO: check capabilities on sys handle
-    if (!area) return j6_err_invalid_arg;
-
     // TODO: check to see if frames are already used? How would that collide with
     // the bootloader's allocated pages already being marked used?
     if (!(flags & vm_flags::mmio))
@@ -82,7 +77,6 @@ system_map_phys(j6_handle_t handle, j6_handle_t * area, uintptr_t phys, size_t s
 j6_status_t
 system_request_iopl(j6_handle_t handle, unsigned iopl)
 {
-    // TODO: check capabilities on sys handle
     if (iopl != 0 && iopl != 3)
         return j6_err_invalid_arg;