py: Add LIBS_USERMOD to LIBS.

This enables C++ modules to correctly postion -l
linker flags at the end of the flags instead of at
the start. Updated the example C++ micropython.mk
accordingly.

Also changed example.cpp to use a std::vector to prove
that libstdc++.a is being correctly linked.

Signed-off-by: Dryw Wade <[email protected]>

Author: sfe-SparkFro

examples/usercmodule/cppexample/example.cpp

@@ -1,3 +1,6 @@
+#include <vector>
+#include <numeric>
+
 extern "C" {
 #include <examplemodule.h>
 #include <py/objstr.h>
@@ -14,8 +17,13 @@ mp_obj_t cppfunc(mp_obj_t a_obj, mp_obj_t b_obj) {
     // Prove we have (at least) C++11 features.
     const auto a = mp_obj_get_int(a_obj);
     const auto b = mp_obj_get_int(b_obj);
+    // Prove that we can use the C++ standard library.
+    std::vector<int> vec;
+    vec.push_back(a);
+    vec.push_back(b);
+    int std_accumulate = std::accumulate(vec.begin(), vec.end(), 0);
     const auto sum = [&]() {
-        return mp_obj_new_int(a + b);
+        return mp_obj_new_int(std_accumulate);
     } ();
     // Prove we're being scanned for QSTRs.
     mp_obj_t tup[] = {sum, MP_ROM_QSTR(MP_QSTR_hellocpp)};

examples/usercmodule/cppexample/micropython.mk

@@ -8,5 +8,8 @@ SRC_USERMOD_CXX += $(CPPEXAMPLE_MOD_DIR)/example.cpp
 CFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR)
 CXXFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR) -std=c++11
 
+# Add any necessary library paths to LDFLAGS_USERMOD
+# LDFLAGS_USERMOD += -Lpath/to/libs
+
 # We use C++ features so have to link against the standard library.
-LDFLAGS_USERMOD += -lstdc++
+LIBS_USERMOD += -lstdc++

py/py.mk

@@ -47,6 +47,7 @@ SRC_USERMOD_LIB_ASM :=
 CFLAGS_USERMOD :=
 CXXFLAGS_USERMOD :=
 LDFLAGS_USERMOD :=
+LIBS_USERMOD :=
 
 # Backwards compatibility with older user c modules that set SRC_USERMOD
 # added to SRC_USERMOD_C below
@@ -69,6 +70,7 @@ SRC_USERMOD_PATHFIX_LIB_ASM += $(patsubst $(USER_C_MODULES)/%.S,%.S,$(SRC_USERMO
 CFLAGS += $(CFLAGS_USERMOD)
 CXXFLAGS += $(CXXFLAGS_USERMOD)
 LDFLAGS += $(LDFLAGS_USERMOD)
+LIBS += $(LIBS_USERMOD)
 
 SRC_QSTR += $(SRC_USERMOD_PATHFIX_C) $(SRC_USERMOD_PATHFIX_CXX)
 PY_O += $(addprefix $(BUILD)/, $(SRC_USERMOD_PATHFIX_C:.c=.o))