in kernel/signal.c [105:130]
asmlinkage int sys_rt_sigreturn(void)
{
unsigned long usp = rdusp();
struct rt_sigframe *frame = (struct rt_sigframe *)(usp - 4);
sigset_t set;
int er0;
if (!access_ok(frame, sizeof(*frame)))
goto badframe;
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;
set_current_blocked(&set);
if (restore_sigcontext(&frame->uc.uc_mcontext, &er0))
goto badframe;
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
return er0;
badframe:
force_sig(SIGSEGV);
return 0;
}