Linux C编译器从零开发一

基础程序汇编

test.c

int main() {
  return 42;
}

查看反汇编

cc -o test test.c
objdump -d -M intel test
0000000000001129 <main>:
    1129:	f3 0f 1e fa          	endbr64 
    112d:	55                   	push   rbp
    112e:	48 89 e5             	mov    rbp,rsp
    1131:	b8 2a 00 00 00       	mov    eax,0x2a
    1136:	5d                   	pop    rbp
    1137:	c3                   	ret

函数参数汇编

test.c

int plus(int x, int y) {

return x + y;

}

int main() {

return plus(3, 4);

}

.intel_syntax noprefix

.globl plus, main

plus:

add rsi, rdi

mov rax, rsi

ret

main:

mov rdi, 3

mov rsi, 4

call plus

ret

.globl开头表示函数整个程序可见

call原理

• call将下一条指令（在本例中）ret的地址推入堆栈
• call跳转到作为参数给出的地址

自定义编译器编译基础程序

test.c

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "Please input a Number:\n");
    return 1;
  }
  printf(".intel_syntax noprefix\n");
  printf(".globl main\n");
  printf("main:\n");
  printf("  mov rax, %d\n", atoi(argv[1]));
  printf("  ret\n");
  return 0;
}

编译运行

cc -o test test.c
./test 42 > test.s
cc -o tmp test.s
./tmp
echo $?

自定义编译器编译加减法程序

test.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "Please input a Number\n");
    return 1;
  }

  char *p = argv[1];

  printf(".intel_syntax noprefix\n");
  printf(".globl main\n");
  printf("main:\n");
  printf("  mov rax, %ld\n", strtol(p, &p, 10));
  // strtol读取数字，读完自动跳到下个符号
  while (*p) {
    if (*p == '+') {
      p++;
      printf("  add rax, %ld\n", strtol(p, &p, 10));
      continue;
    }

    if (*p == '-') {
      p++;
      printf("  sub rax, %ld\n", strtol(p, &p, 10));
      continue;
    }

    fprintf(stderr, "illegal sign '%c'\n", *p);
    return 1;
  }

  printf("  ret\n");
  return 0;
}

编译

cc -o test test.c
./test 12+3+4 > tmp.s
cc -o tmp tmp.s
./tmp
echo $?
./test 1*3 > tmp.s //会提示非法符号

测试

test.sh

#!/bin/bash
assert() {
  expected="$1"
  input="$2"

  ./chibicc "$input" > tmp.s || exit
  gcc -static -o tmp tmp.s
  ./tmp
  actual="$?"

  if [ "$actual" = "$expected" ]; then
    echo "$input => $actual"
  else
    echo "$input => $expected expected, but got $actual"
    exit 1
  fi
}

assert 0 0
assert 42 42
assert 21 '5+20-4'

echo OK

参考

Compiler Explorer

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