py: Add new cstack API for stack checking, with limit margin macro.

Currently the stack limit margin is hard-coded in each port's call to
`mp_stack_set_limit()`, but on threaded ports it's fiddlier and can lead to
bugs (such as incorrect thread stack margin on esp32).

This commit provides a new API to initialise the C Stack in one function
call, with a config macro to set the margin.  Where possible the new call
is inlined to reduce code size in thread-free ports.

Intended replacement for `MP_TASK_STACK_LIMIT_MARGIN` on esp32.

The previous `stackctrl.h` API is still present and unmodified apart from a
deprecation comment.  However it's not available when the
`MICROPY_PREVIEW_VERSION_2` macro is set.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

py/cstack.h

@@ -0,0 +1,63 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Paul Sokolovsky
+ * Copyright (c) 2024 Angus Gratton
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#ifndef MICROPY_INCLUDED_PY_CSTACK_H
+#define MICROPY_INCLUDED_PY_CSTACK_H
+
+#include "py/mpstate.h"
+
+// Both init functions below accept the full stack size. Set the
+// MICROPY_STACK_CHECK_MARGIN to the number of bytes subtracted to account
+// for stack usage between checks.
+
+void mp_cstack_init_with_sp_here(size_t stack_size);
+
+inline static void mp_cstack_init_with_top(void *top, size_t stack_size) {
+    MP_STATE_THREAD(stack_top) = (char *)top;
+
+    #if MICROPY_STACK_CHECK
+    assert(stack_size > MICROPY_STACK_CHECK_MARGIN); // Should be enforced by port
+    MP_STATE_THREAD(stack_limit) = stack_size - MICROPY_STACK_CHECK_MARGIN;
+    #else
+    (void)stack_size;
+    #endif
+}
+
+mp_uint_t mp_cstack_usage(void);
+
+#if MICROPY_STACK_CHECK
+
+void mp_cstack_check(void);
+
+#else
+
+inline static void mp_cstack_check(void) {
+    // No-op when stack checking is disabled
+}
+
+#endif
+
+#endif // MICROPY_INCLUDED_PY_CSTACK_H