问题
Despite I searched everywhere I couldn't find any solution to my problem.The problem is that I I defined a function "hello_world() " in a C file "hello.c" and I want to call this function in an assembly file . "hello_assembly.asm" .Can anyone help me ? Thank you.
回答1:
You could check the below example which might give some idea.
\#include <stdio.h>
int main(void)
{
signed int a, b;
a=5,b=25;
mymul(&a,&b);
printf("\nresult=%d",b);
return 0;
}
mymul is a function which is being written in assembly language in file called mymul.S
Below is the code for mymul.S
.globl mymul
mymul:
pushl %ebp # save the old base pointer register
movl %esp, %ebp #copy the stack pointer to base pointer register
movl 8(%ebp), %eax # get the address of a
movl 12(%ebp), %ebx # get the address of b
xchg (%eax), %ecx # we get the value of a and store it in ecx
xchg (%ebx), %edx # we get the value of b and stored it in edx
imul %ecx,%edx # do the multiplication
xchg %ecx, (%eax) #save the value back in a
xchg %edx, (%ebx) # save the value back in b
movl %ebp, %esp # get the stack pointer back to ebp
popl %ebp #restore old ebp
ret #back to the main function
We use the command "cc" to compile our above programs
$ cc mymul.S mul.c -o mulprogram
In the mul.c when we call mymul, we are passing address of a and b , and these address are getting pushed to the stack. When the execution of program enters the mymul function, the stack looks like this: addressofb,addressofa, returnaddress, oldebp
we get the value stored in the address of a and address of b using xchg(we could use movl here) , do the multiplication and save the result in b.
I hope the above program helps you.
来源：https://stackoverflow.com/questions/21031072/calling-a-c-function-in-assembly