py/scheduler: Implement VM abort flag and mp_sched_vm_abort().

This is intended to be used by the very outer caller of the VM/runtime.  It
allows setting a top-level NLR handler that can be jumped to directly, in
order to forcefully abort the VM/runtime.

Enable using:

    #define MICROPY_ENABLE_VM_ABORT (1)

Set up the handler at the top level using:

    nlr_buf_t nlr;
    nlr.ret_val = NULL;
    if (nlr_push(&nlr) == 0) {
        nlr_set_abort(&nlr);
        // call into the VM/runtime
        ...
        nlr_pop();
    } else {
        if (nlr.ret_val == NULL) {
            // handle abort
            ...
        } else {
            // handle other exception that propagated to the top level
            ...
        }
    }
    nlr_set_abort(NULL);

Schedule an abort, eg from an interrupt handler, using:

    mp_sched_vm_abort();

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/py/nlr.c b/py/nlr.c
index a35e7d229c..92db8ffb19 100644
--- a/py/nlr.c
+++ b/py/nlr.c
@@ -49,3 +49,10 @@ void nlr_pop(void) {
     nlr_buf_t **top = &MP_STATE_THREAD(nlr_top);
     *top = (*top)->prev;
 }
+
+#if MICROPY_ENABLE_VM_ABORT
+NORETURN void nlr_jump_abort(void) {
+    MP_STATE_THREAD(nlr_top) = MP_STATE_VM(nlr_abort);
+    nlr_jump(NULL);
+}
+#endif