我希望能在我的C程序中调用打印函数。
汇编程序:
#test.s
.text
.global _start
.global print
.type print, @function
_start:
call print
# and exit.
movl $0,%ebx # first argument: exit code.
movl $1,%eax # system call number (sys_exit).
int $0x80 # call kernel.
print:
# write our string to stdout.
movl $len,%edx # third argument: message length.
movl $msg,%ecx # second argument: pointer to message to write.
movl $1,%ebx # first argument: file handle (stdout).
movl $4,%eax # system call number (sys_write).
int $0x80 # call kernel.
mov $0, %eax
ret
.data
msg:
.ascii "Hello, world!\n" # the string to print.
len = . - msg # length of the string.
我可以使用以下方法组装和链接它:
$as test.s -o test.o
$ld test.o -o test
我可以执行它作为一个程序,然后它输出"Hello, world!"。但是当我试图像这样从C代码中调用打印函数时:
#include <stdio.h>
extern int print();
int main(){
int g;
g = print();
printf("Hello from c!, %d\n", g);
}
这个程序是用以下工具编译的:
$gcc -c main.c test
它只打印“Hello from c,13”,这意味着函数被调用并返回字符数,但不会打印任何内容!
我做错了什么?
P.S. 当我尝试编译这样的程序时:
$as test.s -o test.o
$gcc -c main.c -o main.o
$gcc main.c test.o
我有一个错误:
/usr/bin/ld: test.o: in function `_start':
(.text+0x0): multiple definition of `_start'; /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../lib/Scrt1.o:(.text+0x0): first defined here
/usr/bin/ld: test.o: relocation R_X86_64_32 against `.data' can not be used when making a PIE object; recompile with -fPIE
/usr/bin/ld: final link failed: nonrepresentable section on output
collect2: error: ld returned 1 exit status
gcc -no-pie -c test.s -o test.o
和gcc -no-pie -o main main.c test.o
进行编译似乎可以解决问题... - dragoshtgcc -m32 main.c test.s -o main
进行构建。您可以选择使用-fno-pie -no-pie
,因为对于32位来说这是一个很好的提高效率的想法。 - Peter Cordes