Question

As you might know, all threads in the application die in a forked process, other than the thread doing the fork. However, I plan to ressurrect those threads in the forked process by calling pthread_create and using pthread_attr_setstack, so as to assign the newly created threads the same stack as the dead threads. Something like as follows.

// stackAddr and stacksize taken from the dead thread    
pthread_attr_setstack(&attr, stackAddr, stacksize);
rc = pthread_create(&thread, &attr, threadRoutine, NULL); 

However, I would still need to get the CPU register values, such as stack pointer, base pointer, instruction pointer etc, to restart threads from the same point. How can I do that? And what else do I need to do to successfully achieve my goal?

Also note that I’m using a 64-bit architecture. What additional difficulties would it have as compared to 32-bit one?

Answer 1

I see two possible ways to shoot yourself in the foot and lose hair^W^W^W^W^W^W^W^Wtry to do this:

• Try to force each thread into calling getcontext() before the fork(), and then restore the context of each thread via setcontext(). Probably won’t work, but you can try for fun.
• Save ptrace(PTRACE_GETREGS), ptrace(PTRACE_GETFPREGS), and restore with ptrace(PTRACE_SETREGS), ptrace(PTRACE_SETFPREGS).