[vox-tech] Suspending a process by PID

[Peter Jay Salzman]

hey nicole,

yeah, sure it's possible.  i'm surprised that sending SIGSTOP/SIGCONT
doesn't work.  but then again, i've never tried that.

anyway, using ptrace() to attach to a process will make the process a
child and suspend it immediately.  you can then step through
instructions, look at memory maps and all kinds of neat stuff.  for
instnace, you can use this kind of thing to cheat at games.  neat stuff.

more than you wanted, but it has the effect you desire (i think).

here's some code i wrote that attaches to a process:

bool Process::attach(void)
{
   int status;

   if(attached) {
      attached++;
      return true;
   }

   // Request to attach.
   if(ptrace(PTRACE_ATTACH, pid, 0, 0) == -1) {
      return(false);
   }

   // Wait for the child to tell us it worked
   if(waitpid(pid, &status, WUNTRACED) != pid) {
      return false;
   }
   if(!WIFSTOPPED(status)) {
      return false;
   }

   attached++;
   return true;
}

and detach from the process:



bool Process::detach(void)
{

   // Fail if we we're unattached.
   if(! attached)
      return false;

   if(attached - 1 == 0) {

      // I don't know why it's supposed to be 1 either. ;)
      if(ptrace(PTRACE_DETACH, pid, 1, 0) == -1) {
         return(false);
      }

      memoryMaps.clear();
   }

   attached--;
   return true;
}


pete




On Mon 22 Dec 03,  9:57 AM, Nicole TWN <ana.ng@tmbg.org> said:
> Hi gang
> 
> Anyone know how to suspend a process given its PID?
> 
> It seems like it should be possible, via signals or something, but I can't 
> find how.
> 
> Thanks
> 
> --nicole twn
> 
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