emu,ram: add assert() to catch out-of-bound memory accessing

src/test/csrc/ram.cpp

@@ -95,6 +95,10 @@ void init_ram(const char *img) {
 
 extern "C" void ram_helper(
     uint64_t rIdx, uint64_t *rdata, uint64_t wIdx, uint64_t wdata, uint64_t wmask, uint8_t wen) {
+  assert(rIdx < RAMSIZE / sizeof(uint64_t));
   *rdata = ram[rIdx];
-  if (wen) { ram[wIdx] = (ram[wIdx] & ~wmask) | (wdata & wmask); }
+  if (wen) {
+    assert(wIdx < RAMSIZE / sizeof(uint64_t));
+    ram[wIdx] = (ram[wIdx] & ~wmask) | (wdata & wmask);
+  }
 }