text: /*
   * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
   * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   * Copyright (C) 2004 PathScale, Inc
   * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   * Licensed under the GPL
   */
  
  #include <stdlib.h>
  #include <stdarg.h>
  #include <errno.h>
  #include <signal.h>
  #include <strings.h>
  #include <as-layout.h>
  #include <kern_util.h>
  #include <os.h>
  #include <sysdep/mcontext.h>
  
  void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
  	[SIGTRAP]	= relay_signal,
  	[SIGFPE]	= relay_signal,
  	[SIGILL]	= relay_signal,
  	[SIGWINCH]	= winch,
  	[SIGBUS]	= bus_handler,
  	[SIGSEGV]	= segv_handler,
  	[SIGIO]		= sigio_handler,
  	[SIGALRM]	= timer_handler
  };
  
  static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
  {
  	struct uml_pt_regs r;
  	int save_errno = errno;
  
  	r.is_user = 0;
  	if (sig == SIGSEGV) {
  		/* For segfaults, we want the data from the sigcontext. */
  		get_regs_from_mc(&r, mc);
  		GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
  	}
  
  	/* enable signals if sig isn't IRQ signal */
  	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
  		unblock_signals();
  
  	(*sig_info[sig])(sig, si, &r);
  
  	errno = save_errno;
  }
  
  /*
   * These are the asynchronous signals.  SIGPROF is excluded because we want to
   * be able to profile all of UML, not just the non-critical sections.  If
   * profiling is not thread-safe, then that is not my problem.  We can disable
   * profiling when SMP is enabled in that case.
   */
  #define SIGIO_BIT 0
  #define SIGIO_MASK (1 << SIGIO_BIT)
  
  #define SIGALRM_BIT 1
  #define SIGALRM_MASK (1 << SIGALRM_BIT)
  
  static int signals_enabled;
  static unsigned int signals_pending;
  static unsigned int signals_active = 0;
  
  void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
  {
  	int enabled;
  
  	enabled = signals_enabled;
  	if (!enabled && (sig == SIGIO)) {
  		signals_pending |= SIGIO_MASK;
  		return;
  	}
  
  	block_signals();
  
  	sig_handler_common(sig, si, mc);
  
  	set_signals(enabled);
  }
  
  static void timer_real_alarm_handler(mcontext_t *mc)
  {
  	struct uml_pt_regs regs;
  
  	if (mc != NULL)
  		get_regs_from_mc(&regs, mc);
  	timer_handler(SIGALRM, NULL, &regs);
  }
  
  void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
  {
  	int enabled;
  
  	enabled = signals_enabled;
  	if (!signals_enabled) {
  		signals_pending |= SIGALRM_MASK;
  		return;
  	}
  
  	block_signals();
  
  	signals_active |= SIGALRM_MASK;
  
  	timer_real_alarm_handler(mc);
  
  	signals_active &= ~SIGALRM_MASK;
  
  	set_signals(enabled);
  }
  
  void deliver_alarm(void) {
      timer_alarm_handler(SIGALRM, NULL, NULL);
  }
  
  void timer_set_signal_handler(void)
  {
  	set_handler(SIGALRM);
  }
  
  void set_sigstack(void *sig_stack, int size)
  {
  	stack_t stack = {
  		.ss_flags = 0,
  		.ss_sp = sig_stack,
  		.ss_size = size - sizeof(void *)
  	};
  
  	if (sigaltstack(&stack, NULL) != 0)
  		panic("enabling signal stack failed, errno = %d\n", errno);
  }
  
  static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
  	[SIGSEGV] = sig_handler,
  	[SIGBUS] = sig_handler,
  	[SIGILL] = sig_handler,
  	[SIGFPE] = sig_handler,
  	[SIGTRAP] = sig_handler,
  
  	[SIGIO] = sig_handler,
  	[SIGWINCH] = sig_handler,
  	[SIGALRM] = timer_alarm_handler
  };
  
  static void hard_handler(int sig, siginfo_t *si, void *p)
  {
  	struct ucontext *uc = p;
  	mcontext_t *mc = &uc->uc_mcontext;
  	unsigned long pending = 1UL << sig;
  
  	do {
  		int nested, bail;
  
  		/*
  		 * pending comes back with one bit set for each
  		 * interrupt that arrived while setting up the stack,
  		 * plus a bit for this interrupt, plus the zero bit is
  		 * set if this is a nested interrupt.
  		 * If bail is true, then we interrupted another
  		 * handler setting up the stack.  In this case, we
  		 * have to return, and the upper handler will deal
  		 * with this interrupt.
  		 */
  		bail = to_irq_stack(&pending);
  		if (bail)
  			return;
  
  		nested = pending & 1;
  		pending &= ~1;
  
  		while ((sig = ffs(pending)) != 0){
  			sig--;
  			pending &= ~(1 << sig);
  			(*handlers[sig])(sig, (struct siginfo *)si, mc);
  		}
  
  		/*
  		 * Again, pending comes back with a mask of signals
  		 * that arrived while tearing down the stack.  If this
  		 * is non-zero, we just go back, set up the stack
  		 * again, and handle the new interrupts.
  		 */
  		if (!nested)
  			pending = from_irq_stack(nested);
  	} while (pending);
  }
  
  void set_handler(int sig)
  {
  	struct sigaction action;
  	int flags = SA_SIGINFO | SA_ONSTACK;
  	sigset_t sig_mask;
  
  	action.sa_sigaction = hard_handler;
  
  	/* block irq ones */
  	sigemptyset(&action.sa_mask);
  	sigaddset(&action.sa_mask, SIGIO);
  	sigaddset(&action.sa_mask, SIGWINCH);
  	sigaddset(&action.sa_mask, SIGALRM);
  
  	if (sig == SIGSEGV)
  		flags |= SA_NODEFER;
  
  	if (sigismember(&action.sa_mask, sig))
  		flags |= SA_RESTART; /* if it's an irq signal */
  
  	action.sa_flags = flags;
  	action.sa_restorer = NULL;
  	if (sigaction(sig, &action, NULL) < 0)
  		panic("sigaction failed - errno = %d\n", errno);
  
  	sigemptyset(&sig_mask);
  	sigaddset(&sig_mask, sig);
  	if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
  		panic("sigprocmask failed - errno = %d\n", errno);
  }
  
  int change_sig(int signal, int on)
  {
  	sigset_t sigset;
  
  	sigemptyset(&sigset);
  	sigaddset(&sigset, signal);
  	if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
  		return -errno;
  
  	return 0;
  }
  
  void block_signals(void)
  {
  	signals_enabled = 0;
  	/*
  	 * This must return with signals disabled, so this barrier
  	 * ensures that writes are flushed out before the return.
  	 * This might matter if gcc figures out how to inline this and
  	 * decides to shuffle this code into the caller.
  	 */
  	barrier();
  }
  
  void unblock_signals(void)
  {
  	int save_pending;
  
  	if (signals_enabled == 1)
  		return;
  
  	/*
  	 * We loop because the IRQ handler returns with interrupts off.  So,
  	 * interrupts may have arrived and we need to re-enable them and
  	 * recheck signals_pending.
  	 */
  	while (1) {
  		/*
  		 * Save and reset save_pending after enabling signals.  This
  		 * way, signals_pending won't be changed while we're reading it.
  		 */
  		signals_enabled = 1;
  
  		/*
  		 * Setting signals_enabled and reading signals_pending must
  		 * happen in this order.
  		 */
  		barrier();
  
  		save_pending = signals_pending;
  		if (save_pending == 0)
  			return;
  
  		signals_pending = 0;
  
  		/*
  		 * We have pending interrupts, so disable signals, as the
  		 * handlers expect them off when they are called.  They will
  		 * be enabled again above.
  		 */
  
  		signals_enabled = 0;
  
  		/*
  		 * Deal with SIGIO first because the alarm handler might
  		 * schedule, leaving the pending SIGIO stranded until we come
  		 * back here.
  		 *
  		 * SIGIO's handler doesn't use siginfo or mcontext,
  		 * so they can be NULL.
  		 */
  		if (save_pending & SIGIO_MASK)
  			sig_handler_common(SIGIO, NULL, NULL);
  
  		/* Do not reenter the handler */
  
  		if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
  			timer_real_alarm_handler(NULL);
  
  		/* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
  
  		if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
  			return;
  
  	}
  }
  
  int get_signals(void)
  {
  	return signals_enabled;
  }
  
  int set_signals(int enable)
  {
  	int ret;
  	if (signals_enabled == enable)
  		return enable;
  
  	ret = signals_enabled;
  	if (enable)
  		unblock_signals();
  	else block_signals();
  
  	return ret;
  }
  
  int os_is_signal_stack(void)
  {
  	stack_t ss;
  	sigaltstack(NULL, &ss);
  
  	return ss.ss_flags & SS_ONSTACK;
  }
  