embed: Improve stack top estimation.

Obtaining the stack-top via a few function calls may yield a pointer which
is too deep within the stack.  So require the user to obtain it from a
higher level (or via some other means).

Fixes issue micropython#11781.

Signed-off-by: YAMAMOTO Takashi <yamamoto@midokura.com>

examples/embedding/main.c

@@ -31,7 +31,14 @@ static char heap[8 * 1024];
 
 int main() {
     // Initialise MicroPython.
-    mp_embed_init(&heap[0], sizeof(heap));
+    //
+    // Note: &stack_top below should be good enough for many cases.
+    // However, depending on environment, there might be more appropriate
+    // ways to get the stack top value.
+    // eg. pthread_get_stackaddr_np, pthread_getattr_np,
+    // __builtin_frame_address/__builtin_stack_address, etc.
+    int stack_top;
+    mp_embed_init(&heap[0], sizeof(heap), &stack_top);
 
     // Run the example scripts (they will be compiled first).
     mp_embed_exec_str(example_1);

ports/embed/port/embed_util.c

@@ -34,8 +34,8 @@
 #include "port/micropython_embed.h"
 
 // Initialise the runtime.
-void mp_embed_init(void *gc_heap, size_t gc_heap_size) {
-    mp_stack_ctrl_init();
+void mp_embed_init(void *gc_heap, size_t gc_heap_size, void *stack_top) {
+    mp_stack_set_top(stack_top);
     gc_init(gc_heap, (uint8_t *)gc_heap + gc_heap_size);
     mp_init();
 }

ports/embed/port/micropython_embed.h

@@ -29,7 +29,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
-void mp_embed_init(void *gc_heap, size_t gc_heap_size);
+void mp_embed_init(void *gc_heap, size_t gc_heap_size, void *stack_top);
 void mp_embed_deinit(void);
 
 // Only available if MICROPY_ENABLE_COMPILER is enabled.