SlicingBlockDevice should assert, if size does not look valid

features/storage/blockdevice/FlashSimBlockDevice.cpp

@@ -20,6 +20,7 @@
 #include <algorithm>
 #include <stdlib.h>
 #include <string.h>
+#include "mbed_assert.h"
 
 namespace mbed {
 
@@ -34,6 +35,7 @@ FlashSimBlockDevice::FlashSimBlockDevice(BlockDevice *bd, uint8_t erase_value) :
     _erase_value(erase_value), _blank_buf_size(0),
     _blank_buf(0), _bd(bd), _init_ref_count(0), _is_initialized(false)
 {
+    MBED_ASSERT(bd);
 }
 
 FlashSimBlockDevice::~FlashSimBlockDevice()

features/storage/blockdevice/SlicingBlockDevice.cpp

@@ -27,6 +27,11 @@ SlicingBlockDevice::SlicingBlockDevice(BlockDevice *bd, bd_addr_t start, bd_addr
     , _start_from_end(false), _start(start)
     , _stop_from_end(false), _stop(stop)
 {
+    MBED_ASSERT(bd);
+    // SlicingBlockDevice(bd, 0,0) would use the full block, which does not make sense, it must be a programming eror.
+    // SlicingBlockDevice(bd, 100,100) would have no size, which is also a programming error.
+    MBED_ASSERT(start != stop);
+
     if ((int64_t)_start < 0) {
         _start_from_end = true;
         _start = -_start;