C calls assembly methods

Part c is very simple, with a random file name, such as main.c:

#include <stdio.h>
#include <stdlib.h>
void decToBin(long dec,char *b); //Declare external assembly functions
int main()
{
          long dec=254;
          char *bin=(char*)malloc(sizeof(char)*64);
          decToBin(dec,bin);
          printf("%sn",bin);   
          free(bin);   
          return 0;   
}    

  I use a MAC 64-bit system, so the 64bit register is r, such as: rax, RBX, etc.

C calls the following code, save the name of any name, such as decbin.s or decbin.s.

.global _decToBin # Underlining is required 
_decToBin:
    pushq     %rbp
    movq    %rsp,%rbp
    movq     %rdi,-8(%rbp) # First parameter 
    movq     %rsi,-16(%rbp) # Second parameter 
    movq    -8(%rbp),%rax
    movq    -16(%rbp),%rbx
    movq    $63,%rcx
A:
    rclq     $1,%rax
    jnc    B
    movb     $49,(%rbx)
    jmp C
B:
    movb     $48,(%rbx)
C:
    addq    $1,%rbx
    loop A
    popq     %rbp
    ret

There are many AT&T grammars on the web, but I won't cover them.
The clang compiler is actually used on the MAC, which in turn involves the LLVM project, which is the framework for building the compiler (compiler), and Apple is the main funder of the LLVM program.

Cc links to the clang, Makefle file:

main:main.o decBin.o
main.o:main.c

decBin.o:decBin.s
    cc -c $<
clean:
    -rm main.o decBin.o main