[ion] Add Ion::stackSafe

This allows asserting the stack is within bounds

escher/src/image_view.cpp

@@ -23,8 +23,8 @@ void ImageView::drawRect(KDContext * ctx, KDRect rect) const {
 
   KDColor pixelBuffer[maxPixelBufferSize];
   int pixelBufferSize = m_image->width() * m_image->height();
-  // CAUTION: That's a VERY big buffer we're allocating on the stack
   assert(pixelBufferSize <= maxPixelBufferSize);
+  assert(Ion::stackSafe()); // That's a VERY big buffer we're allocating on the stack
 
   Ion::decompress(
     m_image->compressedPixelData(),

ion/include/ion.h

@@ -43,6 +43,9 @@ uint32_t random();
 // Decompress data
 void decompress(const uint8_t * src, uint8_t * dst, int srcSize, int dstSize);
 
+// Tells wether the stack pointer is within acceptable bounds
+bool stackSafe();
+
 }
 
 #endif

ion/src/blackbox/Makefile

@@ -19,6 +19,7 @@ objs += $(addprefix ion/src/shared/, \
   dummy/led.o \
   dummy/keyboard.o \
   dummy/serial_number.o \
+  dummy/stack.o \
   dummy/usb.o \
 )
 

ion/src/device/Makefile

@@ -25,6 +25,7 @@ objs += $(addprefix ion/src/device/, \
   led.o\
   power.o\
   sd_card.o\
+  stack.o\
   swd.o \
   usb.o \
   wakeup.o \

ion/src/device/stack.cpp

@@ -0,0 +1,10 @@
+#include <ion.h>
+
+extern const void * _stack_start;
+extern const void * _stack_end;
+
+bool Ion::stackSafe() {
+  volatile int stackDummy;
+  volatile void * stackPointer = &stackDummy;
+  return (stackPointer >= &_stack_end && stackPointer <= &_stack_start);
+}

ion/src/emscripten/Makefile

@@ -15,5 +15,6 @@ objs += $(addprefix ion/src/shared/, \
   dummy/fcc_id.o \
   dummy/led.o \
   dummy/serial_number.o \
+  dummy/stack.o \
   dummy/usb.o \
 )

ion/src/shared/dummy/stack.cpp

@@ -0,0 +1,5 @@
+#include <ion.h>
+
+bool Ion::stackSafe() {
+  return true;
+}

ion/src/simulator/Makefile

@@ -18,6 +18,7 @@ objs += $(addprefix ion/src/shared/, \
   dummy/fcc_id.o \
   dummy/led.o \
   dummy/serial_number.o \
+  dummy/stack.o \
   dummy/usb.o \
 )