Add supervisor.get_previous_traceback() function.

Useful for #1084.

lib/utils/pyexec.c

@@ -167,7 +167,7 @@ STATIC int parse_compile_execute(const void *source, mp_parse_input_kind_t input
         result->return_code = ret;
         if (ret != 0) {
             mp_obj_t return_value = (mp_obj_t)nlr.ret_val;
-            result->exception_type = mp_obj_get_type(return_value);
+            result->exception = return_value;
             result->exception_line = -1;
 
             if (mp_obj_is_exception_instance(return_value)) {

lib/utils/pyexec.h

@@ -35,7 +35,7 @@ typedef enum {
 
 typedef struct {
     int return_code;
-    const mp_obj_type_t *exception_type;
+    mp_obj_t exception;
     int exception_line;
 } pyexec_result_t;
 

main.c

@@ -56,6 +56,7 @@
 #include "supervisor/shared/safe_mode.h"
 #include "supervisor/shared/stack.h"
 #include "supervisor/shared/status_leds.h"
+#include "supervisor/shared/traceback.h"
 #include "supervisor/shared/translate.h"
 #include "supervisor/shared/workflow.h"
 #include "supervisor/usb.h"
@@ -227,7 +228,41 @@ STATIC bool maybe_run_list(const char * const * filenames, pyexec_result_t* exec
     return true;
 }
 
-STATIC void cleanup_after_vm(supervisor_allocation* heap) {
+STATIC void count_strn(void *data, const char *str, size_t len) {
+    *(size_t*)data += len;
+}
+
+STATIC void cleanup_after_vm(supervisor_allocation* heap, mp_obj_t exception) {
+    // Get the traceback of any exception from this run off the heap.
+    // MP_OBJ_SENTINEL means "this run does not contribute to traceback storage, don't touch it"
+    // MP_OBJ_NULL (=0) means "this run completed successfully, clear any stored traceback"
+    if (exception != MP_OBJ_SENTINEL) {
+        free_memory(prev_traceback_allocation);
+        // ReloadException is exempt from traceback printing in pyexec_file(), so treat it as "no
+        // traceback" here too.
+        if (exception && exception != MP_OBJ_FROM_PTR(&MP_STATE_VM(mp_reload_exception))) {
+            size_t traceback_len = 0;
+            mp_print_t print_count = {&traceback_len, count_strn};
+            mp_obj_print_exception(&print_count, exception);
+            prev_traceback_allocation = allocate_memory(align32_size(traceback_len + 1), false, true);
+            // Empirically, this never fails in practice - even when the heap is totally filled up
+            // with single-block-sized objects referenced by a root pointer, exiting the VM frees
+            // up several hundred bytes, sufficient for the traceback (which tends to be shortened
+            // because there wasn't memory for the full one). There may be convoluted ways of
+            // making it fail, but at this point I believe they are not worth spending code on.
+            if (prev_traceback_allocation != NULL) {
+                vstr_t vstr;
+                vstr_init_fixed_buf(&vstr, traceback_len, (char*)prev_traceback_allocation->ptr);
+                mp_print_t print = {&vstr, (mp_print_strn_t)vstr_add_strn};
+                mp_obj_print_exception(&print, exception);
+                ((char*)prev_traceback_allocation->ptr)[traceback_len] = '\0';
+            }
+        }
+        else {
+            prev_traceback_allocation = NULL;
+        }
+    }
+
     // Reset port-independent devices, like CIRCUITPY_BLEIO_HCI.
     reset_devices();
     // Turn off the display and flush the filesystem before the heap disappears.
@@ -287,7 +322,7 @@ STATIC bool run_code_py(safe_mode_t safe_mode) {
     pyexec_result_t result;
 
     result.return_code = 0;
-    result.exception_type = NULL;
+    result.exception = MP_OBJ_NULL;
     result.exception_line = 0;
 
     bool skip_repl;
@@ -357,7 +392,7 @@ STATIC bool run_code_py(safe_mode_t safe_mode) {
         }
 
         // Finished executing python code. Cleanup includes a board reset.
-        cleanup_after_vm(heap);
+        cleanup_after_vm(heap, result.exception);
 
         // If a new next code file was set, that is a reason to keep it (obviously). Stuff this into
         // the options because it can be treated like any other reason-for-stickiness bit. The
@@ -674,8 +709,9 @@ STATIC void __attribute__ ((noinline)) run_boot_py(safe_mode_t safe_mode) {
     usb_set_defaults();
 #endif
 
+    pyexec_result_t result = {0, MP_OBJ_NULL, 0};
     if (ok_to_run) {
-        bool found_boot = maybe_run_list(boot_py_filenames, NULL);
+        bool found_boot = maybe_run_list(boot_py_filenames, &result);
         (void) found_boot;
 
         #ifdef CIRCUITPY_BOOT_OUTPUT_FILE
@@ -687,21 +723,18 @@ STATIC void __attribute__ ((noinline)) run_boot_py(safe_mode_t safe_mode) {
         #endif
     }
 
-
 #if CIRCUITPY_USB
-
     // Some data needs to be carried over from the USB settings in boot.py
     // to the next VM, while the heap is still available.
     // Its size can vary, so save it temporarily on the stack,
     // and then when the heap goes away, copy it in into a
     // storage_allocation.
-
     size_t size = usb_boot_py_data_size();
     uint8_t usb_boot_py_data[size];
     usb_get_boot_py_data(usb_boot_py_data, size);
 #endif
 
-    cleanup_after_vm(heap);
+    cleanup_after_vm(heap, result.exception);
 
 #if CIRCUITPY_USB
     // Now give back the data we saved from the heap going away.
@@ -736,12 +769,13 @@ STATIC int run_repl(void) {
     } else {
         exit_code = pyexec_friendly_repl();
     }
-    cleanup_after_vm(heap);
+    cleanup_after_vm(heap, MP_OBJ_SENTINEL);
     #if CIRCUITPY_STATUS_LED
     status_led_init();
     new_status_color(BLACK);
     status_led_deinit();
     #endif
+
     autoreload_resume();
     return exit_code;
 }

shared-bindings/supervisor/__init__.c

@@ -34,6 +34,7 @@
 #include "supervisor/shared/autoreload.h"
 #include "supervisor/shared/status_leds.h"
 #include "supervisor/shared/stack.h"
+#include "supervisor/shared/traceback.h"
 #include "supervisor/shared/translate.h"
 #include "supervisor/shared/workflow.h"
 
@@ -255,7 +256,33 @@ STATIC mp_obj_t supervisor_ticks_ms(void) {
 }
 MP_DEFINE_CONST_FUN_OBJ_0(supervisor_ticks_ms_obj, supervisor_ticks_ms);
 
-
+//| def get_previous_traceback() -> Optional[str]:
+//|     """If the last vm run ended with an exception (including the KeyboardInterrupt caused by
+//|     CTRL-C), returns the traceback as a string.
+//|     Otherwise, returns ``None``.
+//|
+//|     An exception traceback is only preserved over a soft reload, a hard reset clears it.
+//|
+//|     Only code (main or boot) runs are considered, not REPL runs."""
+//|     ...
+//|
+STATIC mp_obj_t supervisor_get_previous_traceback(void) {
+    //TODO is this a safe and proper way of making a heap-allocated string object that points at long-lived (and likely long and unique) data outside the heap?
+    if (prev_traceback_allocation) {
+        size_t len = strlen((const char*)prev_traceback_allocation->ptr);
+        if (len > 0) {
+            mp_obj_str_t *o = m_new_obj(mp_obj_str_t);
+            o->base.type = &mp_type_str;
+            o->len = len;
+            //TODO is it a good assumption that callers probably aren't going to compare this string, so skip computing the hash?
+            o->hash = 0;
+            o->data = (const byte*)prev_traceback_allocation->ptr;
+            return MP_OBJ_FROM_PTR(o);
+        }
+    }
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_0(supervisor_get_previous_traceback_obj, supervisor_get_previous_traceback);
 
 STATIC const mp_rom_map_elem_t supervisor_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_supervisor) },
@@ -268,6 +295,7 @@ STATIC const mp_rom_map_elem_t supervisor_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_set_next_stack_limit),  MP_ROM_PTR(&supervisor_set_next_stack_limit_obj) },
     { MP_ROM_QSTR(MP_QSTR_set_next_code_file),  MP_ROM_PTR(&supervisor_set_next_code_file_obj) },
     { MP_ROM_QSTR(MP_QSTR_ticks_ms),  MP_ROM_PTR(&supervisor_ticks_ms_obj) },
+    { MP_ROM_QSTR(MP_QSTR_get_previous_traceback),  MP_ROM_PTR(&supervisor_get_previous_traceback_obj) },
 };
 
 STATIC MP_DEFINE_CONST_DICT(supervisor_module_globals, supervisor_module_globals_table);

supervisor/shared/memory.c

@@ -38,6 +38,8 @@ enum {
         2
         // next_code_allocation
         + 1
+        // prev_traceback_allocation
+        + 1
 
         #if INTERNAL_FLASH_FILESYSTEM == 0
         + 1

supervisor/shared/traceback.c

@@ -0,0 +1,29 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Christian Walther
+ *
+ * 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.
+ */
+
+#include "traceback.h"
+
+supervisor_allocation* prev_traceback_allocation;

supervisor/shared/traceback.h

@@ -0,0 +1,34 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2020 Christian Walther
+ *
+ * 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_SUPERVISOR_TRACEBACK_H
+#define MICROPY_INCLUDED_SUPERVISOR_TRACEBACK_H
+
+#include "supervisor/memory.h"
+
+extern supervisor_allocation* prev_traceback_allocation;
+
+#endif  // MICROPY_INCLUDED_SUPERVISOR_TRACEBACK_H

supervisor/supervisor.mk

@@ -14,6 +14,7 @@ SRC_SUPERVISOR = \
 	supervisor/shared/stack.c \
 	supervisor/shared/status_leds.c \
 	supervisor/shared/tick.c \
+	supervisor/shared/traceback.c \
 	supervisor/shared/translate.c
 
 NO_USB ?= $(wildcard supervisor/usb.c)