c - 从内存执行代码

Question

假设我想用C进行JIT编译。我反汇编函数并将其代码插入我的程序的内存中：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>

void* alloc_executable_memory(size_t size) {
  void *ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
  if (ptr == MAP_FAILED) {
      fprintf(stderr, "%sn", "mmap failed");
      return NULL;
  }
  return ptr;
}
void push_code_into_memory(unsigned char *memory) {
  unsigned char code[] = {
    0x48, 0x89, 0xf8,       // mov %rdi, %rax
    0,48, 0x83, 0xc0, 0x04, // add $4, %rax
    0xc3                    // ret
  };
  memcpy(memory, code, sizeof(code));
}
int make_memory_executable(void* memory, size_t size) {
  if (mprotect(memory, size, PROT_READ | PROT_EXEC) == -1) {
      fprintf(stderr, "%sn", "mprotect failed");
      return -1;
  }
  return 0;
}
const size_t SIZE = 512;
typedef long (*jitFunc)(long);
int main(int argc, char const *argv[]) {
  void *mem = alloc_executable_memory(SIZE);
  push_code_into_memory((unsigned char *)mem);
  make_memory_executable(mem, SIZE);
  jitFunc foo = (jitFunc)mem;
  int res = foo(2);
  printf("%dn", res);
  return 0;
}

但是，我总是在调用foo后出现段错误11(macOS(。这段代码有什么问题？首先，我认为问题出在访问权限上，但标志似乎设置正确。

Answer 1

我想我找到了：

0,48, 0x83, 0xc0, 0x04

应该是

0x48, 0x83, 0xc0, 0x04