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   rbp112e:	48 89 e5             	mov    rbp,rsp1131:	b8 2a 00 00 00       	mov    eax,0x2a1136:	5d                   	pop    rbp1137:	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 || exitgcc -static -o tmp tmp.s./tmpactual="$?"if [ "$actual" = "$expected" ]; thenecho "$input => $actual"elseecho "$input => $expected expected, but got $actual"exit 1fi
}assert 0 0
assert 42 42
assert 21 '5+20-4'echo OK

参考

Compiler Explorer 

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