mov %rsi,8(%rdi) /* push start onto child_stack as return ptr */
mov %rdx,0(%rdi) /* push pthread_struct onto child_stack */
mov %rdx,%r8 /* r8 = tls */
mov %rsi,8(%rdi) /* push start onto child_stack as return ptr */
mov %rdx,0(%rdi) /* push pthread_struct onto child_stack */
mov %rdx,%r8 /* r8 = tls */