During installation of pintos, I had to run make.
Following is the Makefile.
all: setitimer-helper squish-pty squish-unix
CC = gcc
CFLAGS = -Wall -W
LDFLAGS = -lm
setitimer-helper: setitimer-helper.o
squish-pty: squish-pty.o
squish-unix: squish-unix.o
clean:
rm -f *.o setitimer-helper squish-pty squish-unix
In one computer it executed correctly. (output for the command is given below)
gcc -Wall -W -c -o setitimer-helper.o setitimer-helper.c
gcc -lm setitimer-helper.o -o setitimer-helper
gcc -Wall -W -c -o squish-pty.o squish-pty.c
gcc -lm squish-pty.o -o squish-pty
gcc -Wall -W -c -o squish-unix.o squish-unix.c
gcc -lm squish-unix.o -o squish-unix
but in other computer I got the following error
gcc -lm setitimer-helper.o -o setitimer-helper
setitimer-helper.o: In function `main':
setitimer-helper.c:(.text+0xc9): undefined reference to `floor'
collect2: error: ld returned 1 exit status
<builtin>: recipe for target 'setitimer-helper' failed
make: *** [setitimer-helper] Error 1
If looked at first line of outputs of both make commands
gcc -Wall -W -c -o setitimer-helper.o setitimer-helper.c
and
gcc -lm setitimer-helper.o -o setitimer-helper
They are different.
Why make is executing different commands for the same Makefile? and What should I do to remove error?
答案 0 :(得分：1)
在第一台计算机中，setitimer-helper.o文件不存在或setitimer-helper.c文件较新，因此需要重建它。因此它运行编译器，然后执行链接操作：
gcc -Wall -W -c -o setitimer-helper.o setitimer-helper.c
gcc -lm setitimer-helper.o -o setitimer-helper
在第二台计算机上，setitimer-helper.o文件已存在并且比setitimer-helper.c文件更新，因此不需要编译命令，第二台计算机直接进入链接行：
gcc -lm setitimer-helper.o -o setitimer-helper
真正的问题是你在第二台计算机上遇到链接器错误的原因。
答案是在目标文件之后，-lm标志需要在链接器行上。发生这种情况是因为您将-lm添加到LDFLAGS变量中，而该变量不是正确的：它应该包含告诉链接器在哪里查找文件的选项等（例如，{{1} }选项）。
应将库添加到-L变量，而不是LDLIBS。将您的makefile更改为：
LDFLAGS您的链接行将如下所示：
all: setitimer-helper squish-pty squish-unix
CC = gcc
CFLAGS = -Wall -W
LDLIBS = -lm
setitimer-helper: setitimer-helper.o
squish-pty: squish-pty.o
squish-unix: squish-unix.o
clean:
rm -f *.o setitimer-helper squish-pty squish-unix
并且应该正常工作。