signal.c

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/*
 * 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 "internal.h"

void (*sig_info[NSIG])(int, siginfo_t *, struct uml_pt_regs *) = {
    [SIGTRAP]   = relay_signal,
    [SIGFPE]    = relay_signal,
    [SIGILL]    = relay_signal,
    [SIGWINCH]  = winch,
    [SIGBUS]    = bus_handler,
    [SIGSEGV]   = segv_handler,
    [SIGIO]     = sigio_handler,
    [SIGVTALRM] = timer_handler };

static void sig_handler_common(int sig, siginfo_t *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 != SIGVTALRM))
        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 SIGVTALRM_BIT 1
#define SIGVTALRM_MASK (1 << SIGVTALRM_BIT)

static int signals_enabled;
static unsigned int signals_pending;

void sig_handler(int sig, siginfo_t *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 real_alarm_handler(mcontext_t *mc)
{
    struct uml_pt_regs regs;

    if (mc != NULL)
        get_regs_from_mc(&regs, mc);
    regs.is_user = 0;
    unblock_signals();
    timer_handler(SIGVTALRM, NULL, &regs);
}

void alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
    int enabled;

    enabled = signals_enabled;
    if (!signals_enabled) {
        signals_pending |= SIGVTALRM_MASK;
        return;
    }

    block_signals();

    real_alarm_handler(mc);
    set_signals(enabled);
}

void timer_init(void)
{
    set_handler(SIGVTALRM);
}

void set_sigstack(void *sig_stack, int size)
{
    stack_t stack = ((stack_t) { .ss_flags  = 0,
                     .ss_sp = (__ptr_t) 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, siginfo_t *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,
    [SIGVTALRM] = 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, 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, SIGVTALRM);
    sigaddset(&action.sa_mask, SIGIO);
    sigaddset(&action.sa_mask, SIGWINCH);

    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);

        if (save_pending & SIGVTALRM_MASK)
            real_alarm_handler(NULL);
    }
}

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;
}