Linux Sys Func Hook

hook_write.cc

#include <assert.h>
#include <dlfcn.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

static bool is_hook = false;

int main() {
  int fd = open("/dev/null", O_WRONLY);
  const char *buffer = "hello dlsym";
  size_t len = write(fd, buffer, strlen(buffer));
  assert(len == strlen(buffer));
  assert(is_hook);
  close(fd);
}

typedef ssize_t (*WriteFunc)(int fd, const void *buf, size_t nbyte);
static WriteFunc sys_write = (WriteFunc)dlsym(RTLD_NEXT, "write");  // need C++

ssize_t write(int fd, const void *buf, size_t nbyte) {
  is_hook = true;
  return sys_write(fd, buf, nbyte);
}