[apps] Fix Python assert crash on malloc free

Change-Id: I48f86422f7d6af5227e2556e6ef531dfad696da4

apps/main.cpp

@@ -2,6 +2,19 @@
 #include "global_preferences.h"
 #include <poincare/init.h>
 
+#if PLATFORM_DEVICE
+// On device, stack start address is always known. TODO : Factorize address
+static void * s_stackStart = reinterpret_cast<void *>(0x20000000 + 256*1024);
+#else
+// Stack start will be defined in ion_main.
+static void * s_stackStart = nullptr;
+#endif
+
+void * Ion::stackStart() {
+  assert(s_stackStart != nullptr);
+  return s_stackStart;
+}
+
 #define DUMMY_MAIN 0
 #if DUMMY_MAIN
 
@@ -60,6 +73,16 @@ void ion_main(int argc, const char * const argv[]) {
     }
   }
 #endif
+
+#if !PLATFORM_DEVICE
+  /* s_stackStart must be defined as early as possible to ensure that there
+   * cannot be allocated memory pointers before. Otherwise, with MicroPython for
+   * example, stack pointer could go backward after initialization and allocated
+   * memory pointers could be overlooked during mark procedure. */
+  volatile int stackTop;
+  s_stackStart = (void *)(&stackTop);
+#endif
+
   AppsContainer::sharedAppsContainer()->run();
 }
 

ion/include/ion.h

@@ -46,6 +46,8 @@ uint32_t random();
 // Decompress data
 void decompress(const uint8_t * src, uint8_t * dst, int srcSize, int dstSize);
 
+// Returns address to the first object that can be allocated on stack
+void * stackStart();
 // Tells whether the stack pointer is within acceptable bounds
 bool stackSafe();
 

python/port/port.cpp

@@ -122,15 +122,16 @@ void MicroPython::init(void * heapStart, void * heapEnd) {
   static mp_obj_t pystack[1024];
   mp_pystack_init(pystack, &pystack[MP_ARRAY_SIZE(pystack)]);
 #endif
-
-  volatile int stackTop;
-  void * stackTopAddress = (void *)(&stackTop);
   /* We delimit the stack part that will be used by Python. The stackTop is the
    * address of the first object that can be allocated on Python stack. This
    * boundaries are used:
    * - by gc_collect to determine where to collect roots of the objects that
    *   must be kept on the heap
-   * - to check if the maximal recursion depth has been reached. */
+   * - to check if the maximal recursion depth has been reached.
+   * Current stack pointer could go backward after initialization. A stack start
+   * pointer defined in main is therefore used. */
+  void * stackTopAddress = Ion::stackStart();
+
 #if MP_PORT_USE_STACK_SYMBOLS
   mp_stack_set_top(stackTopAddress);
   size_t stackLimitInBytes = (char *)stackTopAddress - (char *)&_stack_end;