being_debugged.cpp

// Ref. chromium/src/base/debug/debugger_posix.cc

#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include <iostream>

#define HANDLE_EINTR(x) ({ \
  typeof(x) __eintr_result__; \
  do { \
    __eintr_result__ = (x); \
  } while (__eintr_result__ == -1 && errno == EINTR); \
  __eintr_result__;\
})

bool BeingDebugged() {
  // NOTE: This code MUST be async-signal safe (it's used by in-process
  // stack dumping signal handler). NO malloc or stdio is allowed here.

  int status_fd = open("/proc/self/status", O_RDONLY);
  if (status_fd == -1)
    return false;

  // We assume our line will be in the first 1024 characters and that we can
  // read this much all at once.  In practice this will generally be true.
  // This simplifies and speeds up things considerably.
  char buf[1024];

  ssize_t num_read = HANDLE_EINTR(read(status_fd, buf, sizeof(buf)));
  if (HANDLE_EINTR(close(status_fd)) < 0)
    return false;

  if (num_read <= 0)
    return false;

  const char *target = "TracerPid:\t";
  char *found = strstr(buf, target);
  if (!found)
    return false;

  // Our pid is 0 without a debugger, assume this for any pid starting with 0.
  int index = found - buf + strlen(target);
  return index < num_read && buf[index] != '0';
}

int main(void) {
  while (true) {
    sleep(1);
    std::cout << getpid() << " is debugged? " << BeingDebugged() << std::endl;
  }
  return 0;
}