/*
 * 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>
#include <um_malloc.h>
#include <sys/ucontext.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)
{
        ucontext_t *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;
}