Introduce valgrind to the CI pipeline

The static analyzer alone can't catch all the runtime issues. In this 
commit, the dynamic analysis tool Valgrind is added to the CI pipeline.

Reference:
- https://valgrind.org/docs/manual/quick-start.html
- https://linux.die.net/man/1/gcc

.github/workflows/main.yml

@@ -73,6 +73,18 @@ jobs:
       run: |
             make ENABLE_UBSAN=1 clean check
             make ENABLE_JIT=1 ENABLE_UBSAN=1 clean check
+    - name: valgrind check (without JIT)
+      run: | 
+            make clean
+            make ENABLE_JIT=0 ENABLE_VALGRIND=1
+            valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 ./build/rv32emu ./build/hello.elf 
+            valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 ./build/rv32emu ./build/aes.elf 
+    - name: valgrind check (with JIT)
+      run: |
+            make clean
+            make ENABLE_JIT=1 ENABLE_VALGRIND=1
+            valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 ./build/rv32emu ./build/hello.elf 
+            valgrind --leak-check=full --show-leak-kinds=all --error-exitcode=1 ./build/rv32emu ./build/aes.elf 
 
   host-arm64:
     needs: [detect-code-related-file-changes]

Makefile

@@ -11,6 +11,14 @@ CFLAGS = -std=gnu99 -O2 -Wall -Wextra
 CFLAGS += -Wno-unused-label
 CFLAGS += -include src/common.h
 
+ENABLE_VALGRIND ?= 0
+ifeq ("$(ENABLE_UBSAN)", "1")
+# according to gcc's man page: "If you use multiple -O options, with or without level numbers, the last such option is the one that is effective."
+# In order to use Valgrind, we need to compile with -g
+CFLAGS += -g
+LDFLAGS += -g
+endif
+
 # Enable link-time optimization (LTO)
 ENABLE_LTO ?= 1
 ifeq ($(call has, LTO), 1)