linux 下hook函数

hook在windows下可以说是知名度相当高的一种"高级“技术
想在linux下面实现像windows下的那种hook的功能，不过网上的资料很少（LD_PRELOAD 也可以做类似的事）
自己研究了下，写了个类似功能的函数
思想很简单，就在运行时把一个函数的入口改成jmp到另一个地址

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <sys/mman.h>
#include <errno.h>
#include <unistd.h>

void set_hook(void *to_mock_func, void *mock_func)
{
    uint8_t machine_code[] = {
            //movq $0x0, %rax 后面8个字节的0为64位立即数
            0x48, 0xb8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
            //jmpq *%rax
            0xff, 0xe0
        };

    int pagesize = sysconf(_SC_PAGE_SIZE);
    if (pagesize == -1)
    {
        exit(errno);
    }

    uint8_t *mem = (uint8_t *) to_mock_func;
    void *p = (uint8_t*) (mem - ((uint64_t) mem % pagesize));
    if (mprotect(p, pagesize, PROT_READ | PROT_WRITE | PROT_EXEC))
    {
        perror("mprotect error");
        exit(errno);
    }

    //改写立即数为mock的地址,写入函数入口处
    memcpy(machine_code + 2, &mock_func, sizeof(mock_func));
    memcpy(mem, machine_code, sizeof(machine_code));

    if (mprotect(p, pagesize, PROT_EXEC))
    {
        perror("mprotect error");
        exit(errno);
    }
}

using namespace std;
class Cal
{
public:
    int Sum(int a, int b, long c, long d, long e)
    {
        std::cout << "Cal::Sum called... " << std::endl;
        return 0;
    }
    int m;
};

int MockCalSum(Cal *p, int a, int b, long c, long d, long e)
{
    int x = 0;
    x += a + b + c + d;
    std::cout << "MockCalSum called... " << std::endl;
    p->m = x;
    return x;
}

int main()
{
    int a = 0;
    int b = 1;
    long c = 2;
    long d = 3;
    long e = 4;
    Cal cal;
    cal.Sum(a, b, c, d, e);
    MockCalSum(&cal, a, b, c, d, e);
    set_hook((void*)&Cal::Sum, (void*)MockCalSum);
    cal.Sum(a, b, c, d, e);
    return 0;
}