Measure and report maximum stack usage. (#175)

Add max stack usage tracking, visible via debug module ustack.
Add separate cpp flag for enabling modules: MICROPY_DEBUG_MODULES

5 files changed, 43 insertions, 1 deletions

diff --git a/py/mpconfig.h b/py/mpconfig.h
index 39e773183..14c5af3e7 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -446,6 +446,11 @@
 #define MICROPY_STACK_CHECK (0)
 #endif
 
+// Whether to measure maximum stack excursion
+#ifndef MICROPY_MAX_STACK_USAGE
+#define MICROPY_MAX_STACK_USAGE (0)
+#endif
+
 // Whether to have an emergency exception buffer
 #ifndef MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
 #define MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF (0)
diff --git a/py/mpstate.h b/py/mpstate.h
index 30785775b..0b195a096 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -221,6 +221,10 @@ typedef struct _mp_state_thread_t {
     // Stack top at the start of program
     char *stack_top;
 
+    #if MICROPY_MAX_STACK_USAGE
+    char* stack_bottom;
+    #endif
+
     #if MICROPY_STACK_CHECK
     size_t stack_limit;
     #endif
diff --git a/py/objmodule.c b/py/objmodule.c
index 9171b2b22..1b9b9d65e 100644
--- a/py/objmodule.c
+++ b/py/objmodule.c
@@ -226,7 +226,7 @@ STATIC const mp_rom_map_elem_t mp_builtin_module_table[] = {
     // extra builtin modules as defined by a port
     MICROPY_PORT_BUILTIN_MODULES
 
-#if defined(DEBUG) && defined(MICROPY_PORT_BUILTIN_DEBUG_MODULES)
+#if defined(MICROPY_DEBUG_MODULES) && defined(MICROPY_PORT_BUILTIN_DEBUG_MODULES)
     , MICROPY_PORT_BUILTIN_DEBUG_MODULES
 #endif
 };
diff --git a/py/stackctrl.c b/py/stackctrl.c
index d9969b56c..202ae3d48 100644
--- a/py/stackctrl.c
+++ b/py/stackctrl.c
@@ -66,3 +66,28 @@ void mp_stack_check(void) {
 }
 
 #endif // MICROPY_STACK_CHECK
+
+#if MICROPY_MAX_STACK_USAGE
+
+// Fill stack space with this unusual value.
+const char MP_MAX_STACK_USAGE_SENTINEL_BYTE = 0xEE;
+
+// Record absolute bottom (logical limit) of stack.
+void mp_stack_set_bottom(void* stack_bottom) {
+    MP_STATE_THREAD(stack_bottom) = stack_bottom;
+}
+
+// Fill stack space down toward the stack limit with a known unusual value.
+void mp_stack_fill_with_sentinel(void) {
+    // Force routine to not be inlined. Better guarantee than MP_NOINLINE for -flto.
+    __asm volatile ("");
+    volatile char* volatile p;
+    // Start filling stack just below the last variable in the current stack frame, which is p.
+    // Continue until we've hit the bottom of the stack (lowest address, logical "ceiling" of stack).
+    p = (char *) (&p - 1);
+    while(p >= MP_STATE_THREAD(stack_bottom)) {
+	*p-- = MP_MAX_STACK_USAGE_SENTINEL_BYTE;
+    }
+}
+
+#endif // MICROPY_MAX_STACK_USAGE
diff --git a/py/stackctrl.h b/py/stackctrl.h
index e915f5000..2fb3784c5 100644
--- a/py/stackctrl.h
+++ b/py/stackctrl.h
@@ -45,4 +45,12 @@ void mp_stack_check(void);
 
 #endif
 
+#if MICROPY_MAX_STACK_USAGE
+
+const char MP_MAX_STACK_USAGE_SENTINEL_BYTE;
+void mp_stack_set_bottom(void* stack_bottom);
+void mp_stack_fill_with_sentinel(void);
+
+#endif
+
 #endif // __MICROPY_INCLUDED_PY_STACKCTRL_H__