为何Make会自动执行cc编译命令？Makefile编译报错排查

我正在学习使用Make工具，编写了如下简单的Makefile：

all: main other

main: main.c other.o
    gcc main.c -o main
    echo "Compiled main.exe"

other: other.o

other.c:
    touch $@
    echo "int main(){return 0;}" > $@
    echo "Created other.c"

other.o: other.c
    gcc other.c -o other.o
    echo "Compiled other.o"

clean:
    rm -f main.exe other.o other.c

执行make all时，大部分步骤均正常执行，但最后自动触发了一条cc other.o -o other命令，引发了多重定义的链接错误，具体执行输出如下：

> make all  
touch other.c
echo "int main(){return 0;}" > other.c
echo "Created other.c"
Created other.c
gcc other.c -o other.o
echo "Compiled other.o"
Compiled other.o
gcc main.c -o main
echo "Compiled main.exe"
Compiled main.exe
cc   other.o   -o other     <---
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o: in function `mainCRTStartup':
/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: multiple definition of `mainCRTStartup'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../crt0.o:/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o: in function `mainCRTStartup':
/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: multiple definition of `WinMainCRTStartup'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../crt0.o:/c/S/B/src/msys2-runtime/winsup/cygwin/crt0.c:20: first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crtbeg:(.text+0x50): multiple definition of `__gcc_register_frame'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/crtbegin.o:cygming-crtbeg:(.text+0x0): first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crtbeg:(.text+0x70): multiple definition of `__gcc_deregister_frame'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/crtbegin.o:cygming-crtbeg:(.text+0x20): first defined here
/usr/lib/gcc/x86_64-pc-msys/13.2.0/../../../../x86_64-pc-msys/bin/ld: other.o:cygming-crtbeg:(.data+0x0): multiple definition of `__dso_handle'; /usr/lib/gcc/x86_64-pc-msys/13.2.0/crtbegin.o:cygming-crtbeg:(.data+0x0): first defined here
collect2: error: ld returned 1 exit status
make: *** [<builtin>: other] Error 1

请问这条cc命令为何会被Make自动执行？

原因 #

你定义的other: other.o规则没有指定具体的执行命令，Make会触发内置隐式规则来尝试生成目标other。

Make的内置规则中，存在从.o文件生成可执行文件的默认逻辑，对应的命令就是cc $^ -o $@——这就是那条自动执行的cc other.o -o other的来源。

而你的other.o是从包含main函数的other.c编译而来，链接时会和系统默认的启动代码（包含mainCRTStartup等符号）产生重复定义，因此触发链接错误。

解决办法 #

根据实际需求，有两种常见修复方式：

• 如果other只是用于确保other.o被构建的中间目标（不需要生成可执行文件），可以将其标记为伪目标：

  .PHONY: other
  other: other.o
  

  这样Make就不会尝试为它寻找隐式规则生成文件，只会执行规则依赖检查。

• 如果other确实需要生成可执行文件，需要显式写出链接命令，同时建议修改other.c的内容（比如移除main函数，改为普通函数）避免符号冲突：

  other: other.o
      gcc other.o -o other
      echo "Compiled other.exe"
  

内容的提问来源于stack exchange，提问作者verpas