連接成功與arm-none-eabi-g ++但不是arm-none-eabi-gcc

Question

我正在使用Launchpad Arm編譯器工具。 特別，

arm-none-eabi-g ++和arm-none-eabi-gcc來自：

（適用於ARM嵌入式處理器的GNU工具）5.2.1 20151202（發布）[ARM / embedded-5-branch revision 231848]

我有一個針對STM32F103處理器的簡單程序，除了證明我可以編寫硬件並從數學庫中調用函數之外沒有任何目的。 這就是全部：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "stm32f10x.h"

void hardwareTest(void){
   // Turn on the clock for PortB
   RCC->APB2ENR = RCC_APB2ENR_IOPBEN; // Turn on IO Port B
   // Put PB0 into push pull 50 MHz mode
   GPIOB->CRL = 0x03;
   // Turn PB0 on
   GPIOB->ODR = 1;
}

volatile int x; // force call to sqrt() later

int main(void) {
   x = sqrt(100.0f);
   x = sqrt(x);
   hardwareTest();
   return (x);
}

當我嘗試構建它時，我收到一個鏈接器錯誤，告訴我有一個未定義的sqrt引用。 構建是用arm-none-eabi-gcc完成的。 我偶然發現，如果使用arm-none-eabi-g ++完成構建，使用相同的命令行參數，則成功執行鏈接。

我寫了一個Makefile來演示差異：

PROJECT = minimal
SOURCES = src/startup_stm32f10x_hd.s \
          src/system_stm32f10x.c \
          src/main.c
OUTPUT = ./out
print-%:
    @echo '$*=$($*)'

TOOLCHAIN = arm-none-eabi-

CXX = $(TOOLCHAIN)g++
CC = $(TOOLCHAIN)gcc
AR = $(TOOLCHAIN)ar
AS = $(TOOLCHAIN)gcc -c -x assembler-with-cpp
LD =  $(TOOLCHAIN)gcc
OBJCOPY = $(TOOLCHAIN)objcopy
OBJDUMP = $(TOOLCHAIN)objdump
SIZE = $(TOOLCHAIN)size
RM = rm -f

CFLAGS  = -O
CFLAGS += -nostartfiles

CXXFLAGS  = -O
CXXFLAGS += -nostartfiles

ARCH = -mcpu=cortex-m3 -mthumb -DSTM32F10X_HD 
LDFLAGS = 

all: clean $(PROJECT).elf $(PROJECT).gcc $(PROJECT).bin

$(PROJECT).bin: $(PROJECT).elf 
    @echo ' ======== '
    @echo ' Generating binaries'
    $(OBJCOPY) -O binary $(OUTPUT)/$< $(OUTPUT)/$(PROJECT).bin
    $(OBJCOPY) -O ihex   $(OUTPUT)/$< $(OUTPUT)/$(PROJECT).hex
    @echo ' ======== '

$(PROJECT).elf: $(SOURCES)
    @echo ' ======== '
    @echo ' Successful build uses g++'
    @echo ' CXXFLAGS = $(CXXFLAGS)'
    @echo ' LDFLAGS = $(LDFLAGS)'
    @echo ' ARCH = $(ARCH)'
    $(CXX) -o $(OUTPUT)/$@ $(ARCH)  $(CXXFLAGS) $(LDFLAGS) -Wl,-Tld_script/stm32.ld,-lm  $^
    @echo ' ======== '

$(PROJECT).gcc: $(SOURCES)
    @echo ' ======== '
    @echo ' Broken build uses gcc'
    @echo ' CFLAGS = $(CFLAGS)'
    @echo ' LDFLAGS = $(LDFLAGS)'
    @echo ' ARCH = $(ARCH)'
    $(CC) -o $(OUTPUT)/$@ $(ARCH)   $(CFLAGS) $(LDFLAGS) -Wl,-Tld_script/stm32.ld,-lm  $^
    @echo ' ======== '

$(PROJECT).gxx: $(SOURCES)
    @echo ' ======== '
    @echo ' build with g++'
    $(CXX) -o $(OUTPUT)/$@ $(ARCH)  $(CXXFLAGS) $(LDFLAGS) -Wl,-Tld_script/stm32.ld  $^
    @echo ' ======== '

# Program the binary to the board using the builtin serial bootloader
program:
    stm32loader.py -p /dev/ttyUSB0 -ewv $(OUTPUT)/$(PROJECT).bin

# Remove the temporary files
clean:
    @echo ' '
    @echo ' Cleaning up: '
    $(RM) $(OUTPUT)/* *.o *.elf *.bin *.hex *.gcc *.gxx *.g++
    @echo ' ======== '

它給出了以下結果：

Cleaning up: 
rm -f ./out/* *.o *.elf *.bin *.hex *.gcc *.gxx *.g++
======== 
======== 
 Successful build uses g++
 CXXFLAGS = -O -nostartfiles
 LDFLAGS = 
 ARCH = -mcpu=cortex-m3 -mthumb -DSTM32F10X_HD 
arm-none-eabi-g++ -o ./out/minimal.elf -mcpu=cortex-m3 -mthumb -DSTM32F10X_HD   -O -nostartfiles  -Wl,-Tld_script/stm32.ld,-lm  src/startup_stm32f10x_hd.s src/system_stm32f10x.c src/main.c
 ======== 
 ======== 
 Broken build uses gcc
 CFLAGS = -O -nostartfiles
 LDFLAGS = 
 ARCH = -mcpu=cortex-m3 -mthumb -DSTM32F10X_HD 
arm-none-eabi-gcc -o ./out/minimal.gcc -mcpu=cortex-m3 -mthumb -DSTM32F10X_HD    -O -nostartfiles  -Wl,-Tld_script/stm32.ld,-lm  src/startup_stm32f10x_hd.s src/system_stm32f10x.c src/main.c
/var/folders/t4/dv7b46055cjgknp4nndn1_zr0000gn/T//ccbl4swG.o: In function `main':
main.c:(.text+0x28): undefined reference to `sqrt'
collect2: error: ld returned 1 exit status
make: *** [minimal.gcc] Error 1
 ======== 
 Generating binaries
arm-none-eabi-objcopy -O binary ./out/minimal.elf ./out/minimal.bin
arm-none-eabi-objcopy -O ihex   ./out/minimal.elf ./out/minimal.hex
make: Target `all' not remade because of errors.

那么有誰能告訴我為什么兩個編譯器的行為不同？ 我忽略了什么簡單的事情？ 如果我想使用arm-none-eabi-gcc，我應該如何確保與libm和其他人的正確鏈接？

我看過Freddie Chopin的文件，但是它們太復雜了我無法解開。

Answer 1

C ++要求數學函數是基本運行時的一部分，而C允許它們在庫中。 GCC實現通過在C ++構建中自動鏈接libm來實現這一點。

鏈接階段還有許多其他差異; 如果使用C鏈接器，C ++鏈接將始終失敗。

對於C鏈接，請使用C鏈接器並指定-lm以使libm可用。