set up linker for stm32f4 discovery and g++

Question

I am trying compile some code that uses USART and std functions from such as printf() for the stm32f4 discovery. First I compile all code files into a object file using g++ but when I use the linker to create the executable the linker throws errors describing that it can't find any functions implemented in the startup_stm32f4xx.s assembly file.

Could I have a Makefile template form that compiles all source into object files then links it into a *.elf executable?

Also how would I set up the linker to see newlib_stubs.c so I can use printf() in my source code?

Answer 1

This is a generic Makefile for your proyect (compilation tested, but not tested if it will run on MCU)

This script can handle C/C++ and S (gas asm) files. So no need to use C-startup file from coocox

# ELF target name
TARGET=testmode09.elf

# C source files
SRC=src/system_stm32f4xx.c

# C++ source files
CXXSRC=src/main.cpp

# ASM source files
ASRC=lib/startup_stm32f4xx.s

# include directories
INCDIRS=inc lib/inc lib/inc/core lib/inc/peripherals

# search path for .so and .a
LIBDIRS=lib

# libraries to link
LIBS=libstm32f4.a

# Linker script
LDSCRIPT=stm32_flash.ld

# Tool configuration
CROSS=arm-none-eabi-
CC=$(CROSS)gcc
CXX=$(CROSS)g++
AS=$(CROSS)gcc
LD=$(CROSS)gcc
OBJCOPY=$(CROSS)objcopy

# Architecture configuration
ARCH_FLAGS=-mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 

# Flags for gcc
CFLAGS+=-O0 -ggdb3
CFLAGS+=$(ARCH_FLAGS)
CFLAGS+=-flto
CFLAGS+=-ffunction-sections
CFLAGS+=-fdata-sections
CFLAGS+=$(foreach i, $(INCDIRS), -I$(i))

# Flags for g++
CXXFLAGS=$(CFLAGS)
CXXFLAGS+=-fno-rtti -fno-exceptions
CXXFLAGS+=-std=c++11

# Flags for gcc as linker
LDFLAGS=$(ARCH_FLAGS)
LDFLAGS+=-Wl,--gc-sections
LDFLAGS+=$(foreach i, $(LIBDIRS), -L$(i))
LDFLAGS+=-T $(LDSCRIPT)

# No man land! Enter at your risk

OBJS=$(SRC:.c=.o) $(ASRC:.s=.o) $(CXXSRC:.cpp=.o)
DEPS=$(OBJS:.o=.d)

# Default make target (first target)
all: $(TARGET) bins

# include dependency files (*.d)
-include $(DEPS)

# Rules to build c/cpp/s files
%.o: %.c
    @echo " CC $<"
    @$(CC) -MMD $(CFLAGS) -o $@ -c $<

%.o: %.cpp
    @echo " CXX $<"
    @$(CXX) -MMD $(CXXFLAGS) -o $@ -c $<

%.o: %.s
    @echo " AS $<"
    @$(AS) $(CFLAGS) -o $@ -c $<

# Linker rule
$(TARGET): libs $(OBJS)
    @echo " LINK $@"
    @$(LD) -o $@ $(LDFLAGS) $(OBJS)

# Phony rules (not file-asociated)
.PHONY: clean all libs clean_lib bins

libs:
    @$(MAKE) -C lib

clean_lib:
    @$(MAKE) -C lib clean

clean:
    @echo " CLEAN"
    @rm -fR $(OBJS) $(DEPS) $(TARGET) $(TARGET:.elf=hex) $(TARGET:.elf=.bin)

bins: $(TARGET)
    @echo " BUILD HEX & BIN"
    @$(OBJCOPY) -O ihex $(TARGET) $(TARGET:.elf=.hex)
    @$(OBJCOPY) -O binary $(TARGET) $(TARGET:.elf=.bin)

The core reference for make is in the official manual: http://www.gnu.org/software/make/manual/make.html but you need some hacking time to understand it ;-)

Suggestion, put syscalls code into separate C/C++ file called syscall.c/cpp or something like that.