(1) Makefile: added a shared library target, (2) no longer compile the main function as part of libabc.a

Makefile

@@ -139,6 +139,8 @@ OBJ := \
 	$(patsubst %.c, %.o,  $(filter %.c, $(SRC)))  \
 	$(patsubst %.y, %.o,  $(filter %.y, $(SRC)))
 
+LIBOBJ := $(filter-out src/base/main/main.o,$(OBJ))
+
 DEP := $(OBJ:.o=.d)
 
 # implicit rules
@@ -186,11 +188,15 @@ $(PROG): $(OBJ)
 	@echo "$(MSG_PREFIX)\`\` Building binary:" $(notdir $@)
 	$(VERBOSE)$(LD) -o $@ $^ $(LIBS)
 
-lib$(PROG).a: $(OBJ)
+lib$(PROG).a: $(LIBOBJ)
 	@echo "$(MSG_PREFIX)\`\` Linking:" $(notdir $@)
 	$(VERBOSE)ar rv $@ $?
 	$(VERBOSE)ranlib $@
 
+lib$(PROG).so: $(LIBOBJ)
+	@echo "$(MSG_PREFIX)\`\` Linking:" $(notdir $@)
+	$(VERBOSE)$(CXX) -shared -o $@ $^ $(LIBS)
+
 docs:
 	@echo "$(MSG_PREFIX)\`\` Building documentation." $(notdir $@)
 	$(VERBOSE)doxygen doxygen.conf

readme.md

@@ -53,6 +53,13 @@ The current version of ABC can be compiled with C compiler or C++ compiler.
  * To compile as C++ code with namespaces: make sure that `CC=g++` and `ABC_NAMESPACE` is set to
    the name of the requested namespace. For example, add `-DABC_NAMESPACE=xxx` to OPTFLAGS.
 
+## Building a shared library
+
+ * Compile the code as position-independent by adding `ABC_USE_PIC=1`.
+ * Build the `libabc.so` target: 
+ 
+     make ABC_USE_PIC=1 libabc.so
+
 ## Bug reporting:
 
 Please try to reproduce all the reported bugs and unexpected features using the latest