I have used ptrace to force a thread within another process to call
sys_clone and create a new thread with pid pid, with the clone flags CLONE_FILES,
CLONE_FS, CLONE_IO, CLONE_PTRACE, CLONE_SIGHAND, CLONE_THREAD and
CLONE_VM.
As I understand from the ptrace man-page, waitpid() is valid on children
processes and ptrace'd processes. However, the following code in my program
succeeds:
assert(ptrace(PTRACE_CONT, pid, NULL, NULL) != -1);
assert(waitpid(pid, NULL, WSTOPPED) == -1);
printf("error: %s\n", strerror(errno));
Output:
error: No child processes
Why could this be? I have checked that when the ptrace is removed, the child thread terminates on a breakpoint instruction (0xcc).
