esp32,unix: Support building C++ code.

Support building .cpp files and linking them into the micropython
executable in a way similar to how it is done for .c files.  The main
incentive here is to enable user C modules to use C++ files (which are put
in SRC_MOD_CXX by py.mk) since the core itself does not utilize C++.

However, to verify build functionality a unix overage test is added.  The
esp32 port already has CXXFLAGS so just add the user modules' flags to it.
For the unix port use a copy of the CFLAGS but strip the ones which are not
usable for C++.

.travis.yml

@@ -165,7 +165,7 @@ jobs:
     - stage: test
       name: "unix coverage 32-bit build and tests"
       install:
-        - sudo apt-get install gcc-multilib libffi-dev:i386
+        - sudo apt-get install gcc-multilib g++-multilib libffi-dev:i386
         - sudo apt-get install python3-pip
         - sudo pip3 install setuptools
         - sudo pip3 install pyelftools

ports/esp32/Makefile

@@ -268,7 +268,7 @@ CFLAGS += -DMICROPY_ESP_IDF_4=1
 endif
 
 # this is what ESPIDF uses for c++ compilation
-CXXFLAGS = -std=gnu++11 $(CFLAGS_COMMON) $(INC) $(INC_ESPCOMP)
+CXXFLAGS = -std=gnu++11 $(CFLAGS_COMMON) $(INC) $(INC_ESPCOMP) $(CXXFLAGS_MOD)
 
 LDFLAGS = -nostdlib -Map=$(@:.elf=.map) --cref
 LDFLAGS += --gc-sections -static -EL
@@ -354,6 +354,9 @@ SRC_C = \
 	$(wildcard $(BOARD_DIR)/*.c) \
 	$(SRC_MOD)
 
+SRC_CXX += \
+	$(SRC_MOD_CXX)
+
 EXTMOD_SRC_C += $(addprefix extmod/,\
 	modonewire.c \
 	)
@@ -376,6 +379,7 @@ DRIVERS_SRC_C = $(addprefix drivers/,\
 OBJ_MP =
 OBJ_MP += $(PY_O)
 OBJ_MP += $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
+OBJ_MP += $(addprefix $(BUILD)/, $(SRC_CXX:.cpp=.o))
 OBJ_MP += $(addprefix $(BUILD)/, $(EXTMOD_SRC_C:.c=.o))
 OBJ_MP += $(addprefix $(BUILD)/, $(LIB_SRC_C:.c=.o))
 OBJ_MP += $(addprefix $(BUILD)/, $(DRIVERS_SRC_C:.c=.o))
@@ -384,7 +388,7 @@ OBJ_MP += $(addprefix $(BUILD)/, $(DRIVERS_SRC_C:.c=.o))
 $(OBJ_MP): CFLAGS += -Wdouble-promotion -Wfloat-conversion
 
 # List of sources for qstr extraction
-SRC_QSTR += $(SRC_C) $(EXTMOD_SRC_C) $(LIB_SRC_C) $(DRIVERS_SRC_C)
+SRC_QSTR += $(SRC_C) $(SRC_CXX) $(EXTMOD_SRC_C) $(LIB_SRC_C) $(DRIVERS_SRC_C)
 # Append any auto-generated sources that are needed by sources listed in SRC_QSTR
 SRC_QSTR_AUTO_DEPS +=
 

ports/unix/Makefile

@@ -248,13 +248,18 @@ LIB_SRC_C += $(addprefix lib/,\
 	utils/gchelper_generic.c \
 	)
 
+SRC_CXX += \
+	coveragecpp.cpp \
+	$(SRC_MOD_CXX)
+
 OBJ = $(PY_O)
 OBJ += $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
+OBJ += $(addprefix $(BUILD)/, $(SRC_CXX:.cpp=.o))
 OBJ += $(addprefix $(BUILD)/, $(LIB_SRC_C:.c=.o))
 OBJ += $(addprefix $(BUILD)/, $(EXTMOD_SRC_C:.c=.o))
 
 # List of sources for qstr extraction
-SRC_QSTR += $(SRC_C) $(LIB_SRC_C) $(EXTMOD_SRC_C)
+SRC_QSTR += $(SRC_C) $(SRC_CXX) $(LIB_SRC_C) $(EXTMOD_SRC_C)
 # Append any auto-generated sources that are needed by sources listed in
 # SRC_QSTR
 SRC_QSTR_AUTO_DEPS +=
@@ -272,6 +277,14 @@ ifneq ($(FROZEN_MANIFEST)$(FROZEN_DIR),)
 CFLAGS += -DMICROPY_MODULE_FROZEN_STR
 endif
 
+HASCPP17 = $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 7)
+ifeq ($(HASCPP17), 1)
+	CXXFLAGS += -std=c++17
+else
+	CXXFLAGS += -std=c++11
+endif
+CXXFLAGS += $(filter-out -Wmissing-prototypes -Wold-style-definition -std=gnu99,$(CFLAGS) $(CXXFLAGS_MOD))
+
 ifeq ($(MICROPY_FORCE_32BIT),1)
 RUN_TESTS_MPY_CROSS_FLAGS = --mpy-cross-flags='-mcache-lookup-bc -march=x86'
 else

ports/unix/coveragecpp.cpp

@@ -0,0 +1,23 @@
+extern "C" {
+#include "py/obj.h"
+}
+
+#if defined(MICROPY_UNIX_COVERAGE)
+
+// Just to test building of C++ code.
+STATIC mp_obj_t extra_cpp_coverage_impl() {
+    return mp_const_none;
+}
+
+extern "C" {
+mp_obj_t extra_cpp_coverage(void);
+mp_obj_t extra_cpp_coverage(void) {
+    return extra_cpp_coverage_impl();
+}
+
+// This is extern to avoid name mangling.
+extern const mp_obj_fun_builtin_fixed_t extra_cpp_coverage_obj = {{&mp_type_fun_builtin_0}, {extra_cpp_coverage}};
+
+}
+
+#endif

ports/unix/main.c

@@ -531,7 +531,9 @@ MP_NOINLINE int main_(int argc, char **argv) {
     #if defined(MICROPY_UNIX_COVERAGE)
     {
         MP_DECLARE_CONST_FUN_OBJ_0(extra_coverage_obj);
+        MP_DECLARE_CONST_FUN_OBJ_0(extra_cpp_coverage_obj);
         mp_store_global(QSTR_FROM_STR_STATIC("extra_coverage"), MP_OBJ_FROM_PTR(&extra_coverage_obj));
+        mp_store_global(QSTR_FROM_STR_STATIC("extra_cpp_coverage"), MP_OBJ_FROM_PTR(&extra_cpp_coverage_obj));
     }
     #endif
 

tests/unix/extra_coverage.py

@@ -46,6 +46,9 @@ stream.set_error(uerrno.EAGAIN)
 buf = uio.BufferedWriter(stream, 8)
 print(buf.write(bytearray(16)))
 
+# function defined in C++ code
+print("cpp", extra_cpp_coverage())
+
 # test basic import of frozen scripts
 import frzstr1
 

tests/unix/extra_coverage.py.exp

@@ -144,6 +144,7 @@ OSError
 0
 None
 None
+cpp None
 frzstr1
 frzstr1.py
 frzmpy1