/*
 *  linux/arch/m68knommu/kernel/signal.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file COPYING in the main directory of this archive
 * for more details.
 */

/*
 * Linux/m68k support by Hamish Macdonald
 *
 * 68060 fixes by Jesper Skov
 *
 * 1997-12-01  Modified for POSIX.1b signals by Andreas Schwab
 *
 * mathemu support by Roman Zippel
 *  (Note: fpstate in the signal context is completely ignored for the emulator
 *         and the internal floating point format is put on stack)
 */

/*
 * ++roman (07/09/96): implemented signal stacks (specially for tosemu on
 * Atari :-) Current limitation: Only one sigstack can be active at one time.
 * If a second signal with SA_ONSTACK set arrives while working on a sigstack,
 * SA_ONSTACK is ignored. This behaviour avoids lots of trouble with nested
 * signal handlers!
 */

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/syscalls.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/highuid.h>
#include <linux/tty.h>
#include <linux/personality.h>
#include <linux/binfmts.h>

#include <asm/setup.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/traps.h>
#include <asm/ucontext.h>

#define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))

void ret_from_user_signal(void);
void ret_from_user_rt_signal(void);

/*
 * Atomically swap in the new signal mask, and wait for a signal.
 */
asmlinkage int
sys_sigsuspend(int unused0, int unused1, old_sigset_t mask)
{
        mask &= _BLOCKABLE;
        spin_lock_irq(&current->sighand->siglock);
        current->saved_sigmask = current->blocked;
        siginitset(&current->blocked, mask);
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        current->state = TASK_INTERRUPTIBLE;
        schedule();
        set_restore_sigmask();

        return -ERESTARTNOHAND;
}

asmlinkage int
sys_sigaction(int sig, const struct old_sigaction __user *act,
              struct old_sigaction __user *oact)
{
        struct k_sigaction new_ka, old_ka;
        int ret;

        if (act) {
                old_sigset_t mask;
                if (!access_ok(VERIFY_READ, act, sizeof(*act)) ||
                    __get_user(new_ka.sa.sa_handler, &act->sa_handler) ||
                    __get_user(new_ka.sa.sa_restorer, &act->sa_restorer) ||
                    __get_user(new_ka.sa.sa_flags, &act->sa_flags) ||
                    __get_user(mask, &act->sa_mask))
                        return -EFAULT;
                siginitset(&new_ka.sa.sa_mask, mask);
        }

        ret = do_sigaction(sig, act ? &new_ka : NULL, oact ? &old_ka : NULL);

        if (!ret && oact) {
                if (!access_ok(VERIFY_WRITE, oact, sizeof(*oact)) ||
                    __put_user(old_ka.sa.sa_handler, &oact->sa_handler) ||
                    __put_user(old_ka.sa.sa_restorer, &oact->sa_restorer) ||
                    __put_user(old_ka.sa.sa_flags, &oact->sa_flags) ||
                    __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask))
                        return -EFAULT;
        }

        return ret;
}

asmlinkage int
sys_sigaltstack(const stack_t __user *uss, stack_t __user *uoss)
{
        return do_sigaltstack(uss, uoss, rdusp());
}


/*
 * Do a signal return; undo the signal stack.
 *
 * Keep the return code on the stack quadword aligned!
 * That makes the cache flush below easier.
 */

struct sigframe
{
        char __user *pretcode;
        int sig;
        int code;
        struct sigcontext __user *psc;
        char retcode[8];
        unsigned long extramask[_NSIG_WORDS-1];
        struct sigcontext sc;
};

struct rt_sigframe
{
        char __user *pretcode;
        int sig;
        struct siginfo __user *pinfo;
        void __user *puc;
        char retcode[8];
        struct siginfo info;
        struct ucontext uc;
};

#ifdef CONFIG_FPU

static unsigned char fpu_version = 0;   /* version number of fpu, set by setup_frame */

static inline int restore_fpu_state(struct sigcontext *sc)
{
        int err = 1;

        if (FPU_IS_EMU) {
            /* restore registers */
            memcpy(current->thread.fpcntl, sc->sc_fpcntl, 12);
            memcpy(current->thread.fp, sc->sc_fpregs, 24);
            return 0;
        }

        if (sc->sc_fpstate[0]) {
            /* Verify the frame format.  */
            if (sc->sc_fpstate[0] != fpu_version)
                goto out;

            __asm__ volatile (".chip 68k/68881\n\t"
                              "fmovemx %0,%%fp0-%%fp1\n\t"
                              "fmoveml %1,%%fpcr/%%fpsr/%%fpiar\n\t"
                              ".chip 68k"
                              : /* no outputs */
                              : "m" (*sc->sc_fpregs), "m" (*sc->sc_fpcntl));
        }
        __asm__ volatile (".chip 68k/68881\n\t"
                          "frestore %0\n\t"
                          ".chip 68k" : : "m" (*sc->sc_fpstate));
        err = 0;

out:
        return err;
}

#define FPCONTEXT_SIZE  216
#define uc_fpstate      uc_filler[0]
#define uc_formatvec    uc_filler[FPCONTEXT_SIZE/4]
#define uc_extra        uc_filler[FPCONTEXT_SIZE/4+1]

static inline int rt_restore_fpu_state(struct ucontext __user *uc)
{
        unsigned char fpstate[FPCONTEXT_SIZE];
        int context_size = 0;
        fpregset_t fpregs;
        int err = 1;

        if (FPU_IS_EMU) {
                /* restore fpu control register */
                if (__copy_from_user(current->thread.fpcntl,
                                uc->uc_mcontext.fpregs.f_fpcntl, 12))
                        goto out;
                /* restore all other fpu register */
                if (__copy_from_user(current->thread.fp,
                                uc->uc_mcontext.fpregs.f_fpregs, 96))
                        goto out;
                return 0;
        }

        if (__get_user(*(long *)fpstate, (long __user *)&uc->uc_fpstate))
                goto out;
        if (fpstate[0]) {
                context_size = fpstate[1];

                /* Verify the frame format.  */
                if (fpstate[0] != fpu_version)
                        goto out;
                if (__copy_from_user(&fpregs, &uc->uc_mcontext.fpregs,
                     sizeof(fpregs)))
                        goto out;
                __asm__ volatile (".chip 68k/68881\n\t"
                                  "fmovemx %0,%%fp0-%%fp7\n\t"
                                  "fmoveml %1,%%fpcr/%%fpsr/%%fpiar\n\t"
                                  ".chip 68k"
                                  : /* no outputs */
                                  : "m" (*fpregs.f_fpregs),
                                    "m" (*fpregs.f_fpcntl));
        }
        if (context_size &&
            __copy_from_user(fpstate + 4, (long __user *)&uc->uc_fpstate + 1,
                             context_size))
                goto out;
        __asm__ volatile (".chip 68k/68881\n\t"
                          "frestore %0\n\t"
                          ".chip 68k" : : "m" (*fpstate));
        err = 0;

out:
        return err;
}

#endif

static inline int
restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *usc, void __user *fp,
                   int *pd0)
{
        int formatvec;
        struct sigcontext context;
        int err = 0;

        /* Always make any pending restarted system calls return -EINTR */
        current_thread_info()->restart_block.fn = do_no_restart_syscall;

        /* get previous context */
        if (copy_from_user(&context, usc, sizeof(context)))
                goto badframe;
        
        /* restore passed registers */
        regs->d1 = context.sc_d1;
        regs->a0 = context.sc_a0;
        regs->a1 = context.sc_a1;
        ((struct switch_stack *)regs - 1)->a5 = context.sc_a5;
        regs->sr = (regs->sr & 0xff00) | (context.sc_sr & 0xff);
        regs->pc = context.sc_pc;
        regs->orig_d0 = -1;             /* disable syscall checks */
        wrusp(context.sc_usp);
        formatvec = context.sc_formatvec;
        regs->format = formatvec >> 12;
        regs->vector = formatvec & 0xfff;

#ifdef CONFIG_FPU
        err = restore_fpu_state(&context);
#endif

        *pd0 = context.sc_d0;
        return err;

badframe:
        return 1;
}

static inline int
rt_restore_ucontext(struct pt_regs *regs, struct switch_stack *sw,
                    struct ucontext __user *uc, int *pd0)
{
        int temp;
        greg_t __user *gregs = uc->uc_mcontext.gregs;
        unsigned long usp;
        int err;

        /* Always make any pending restarted system calls return -EINTR */
        current_thread_info()->restart_block.fn = do_no_restart_syscall;

        err = __get_user(temp, &uc->uc_mcontext.version);
        if (temp != MCONTEXT_VERSION)
                goto badframe;
        /* restore passed registers */
        err |= __get_user(regs->d0, &gregs[0]);
        err |= __get_user(regs->d1, &gregs[1]);
        err |= __get_user(regs->d2, &gregs[2]);
        err |= __get_user(regs->d3, &gregs[3]);
        err |= __get_user(regs->d4, &gregs[4]);
        err |= __get_user(regs->d5, &gregs[5]);
        err |= __get_user(sw->d6, &gregs[6]);
        err |= __get_user(sw->d7, &gregs[7]);
        err |= __get_user(regs->a0, &gregs[8]);
        err |= __get_user(regs->a1, &gregs[9]);
        err |= __get_user(regs->a2, &gregs[10]);
        err |= __get_user(sw->a3, &gregs[11]);
        err |= __get_user(sw->a4, &gregs[12]);
        err |= __get_user(sw->a5, &gregs[13]);
        err |= __get_user(sw->a6, &gregs[14]);
        err |= __get_user(usp, &gregs[15]);
        wrusp(usp);
        err |= __get_user(regs->pc, &gregs[16]);
        err |= __get_user(temp, &gregs[17]);
        regs->sr = (regs->sr & 0xff00) | (temp & 0xff);
        regs->orig_d0 = -1;             /* disable syscall checks */
        regs->format = temp >> 12;
        regs->vector = temp & 0xfff;

        if (do_sigaltstack(&uc->uc_stack, NULL, usp) == -EFAULT)
                goto badframe;

        *pd0 = regs->d0;
        return err;

badframe:
        return 1;
}

asmlinkage int do_sigreturn(unsigned long __unused)
{
        struct switch_stack *sw = (struct switch_stack *) &__unused;
        struct pt_regs *regs = (struct pt_regs *) (sw + 1);
        unsigned long usp = rdusp();
        struct sigframe __user *frame = (struct sigframe __user *)(usp - 4);
        sigset_t set;
        int d0;

        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
                goto badframe;
        if (__get_user(set.sig[0], &frame->sc.sc_mask) ||
            (_NSIG_WORDS > 1 &&
             __copy_from_user(&set.sig[1], &frame->extramask,
                              sizeof(frame->extramask))))
                goto badframe;

        sigdelsetmask(&set, ~_BLOCKABLE);
        spin_lock_irq(&current->sighand->siglock);
        current->blocked = set;
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
        
        if (restore_sigcontext(regs, &frame->sc, frame + 1, &d0))
                goto badframe;
        return d0;

badframe:
        force_sig(SIGSEGV, current);
        return 0;
}

asmlinkage int do_rt_sigreturn(unsigned long __unused)
{
        struct switch_stack *sw = (struct switch_stack *) &__unused;
        struct pt_regs *regs = (struct pt_regs *) (sw + 1);
        unsigned long usp = rdusp();
        struct rt_sigframe __user *frame = (struct rt_sigframe __user *)(usp - 4);
        sigset_t set;
        int d0;

        if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
                goto badframe;
        if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
                goto badframe;

        sigdelsetmask(&set, ~_BLOCKABLE);
        spin_lock_irq(&current->sighand->siglock);
        current->blocked = set;
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
        
        if (rt_restore_ucontext(regs, sw, &frame->uc, &d0))
                goto badframe;
        return d0;

badframe:
        force_sig(SIGSEGV, current);
        return 0;
}

#ifdef CONFIG_FPU
/*
 * Set up a signal frame.
 */

static inline void save_fpu_state(struct sigcontext *sc, struct pt_regs *regs)
{
        if (FPU_IS_EMU) {
                /* save registers */
                memcpy(sc->sc_fpcntl, current->thread.fpcntl, 12);
                memcpy(sc->sc_fpregs, current->thread.fp, 24);
                return;
        }

        __asm__ volatile (".chip 68k/68881\n\t"
                          "fsave %0\n\t"
                          ".chip 68k"
                          : : "m" (*sc->sc_fpstate) : "memory");

        if (sc->sc_fpstate[0]) {
                fpu_version = sc->sc_fpstate[0];
                __asm__ volatile (".chip 68k/68881\n\t"
                                  "fmovemx %%fp0-%%fp1,%0\n\t"
                                  "fmoveml %%fpcr/%%fpsr/%%fpiar,%1\n\t"
                                  ".chip 68k"
                                  : "=m" (*sc->sc_fpregs),
                                    "=m" (*sc->sc_fpcntl)
                                  : /* no inputs */
                                  : "memory");
        }
}

static inline int rt_save_fpu_state(struct ucontext __user *uc, struct pt_regs *regs)
{
        unsigned char fpstate[FPCONTEXT_SIZE];
        int context_size = 0;
        int err = 0;

        if (FPU_IS_EMU) {
                /* save fpu control register */
                err |= copy_to_user(uc->uc_mcontext.fpregs.f_pcntl,
                                current->thread.fpcntl, 12);
                /* save all other fpu register */
                err |= copy_to_user(uc->uc_mcontext.fpregs.f_fpregs,
                                current->thread.fp, 96);
                return err;
        }

        __asm__ volatile (".chip 68k/68881\n\t"
                          "fsave %0\n\t"
                          ".chip 68k"
                          : : "m" (*fpstate) : "memory");

        err |= __put_user(*(long *)fpstate, (long __user *)&uc->uc_fpstate);
        if (fpstate[0]) {
                fpregset_t fpregs;
                context_size = fpstate[1];
                fpu_version = fpstate[0];
                __asm__ volatile (".chip 68k/68881\n\t"
                                  "fmovemx %%fp0-%%fp7,%0\n\t"
                                  "fmoveml %%fpcr/%%fpsr/%%fpiar,%1\n\t"
                                  ".chip 68k"
                                  : "=m" (*fpregs.f_fpregs),
                                    "=m" (*fpregs.f_fpcntl)
                                  : /* no inputs */
                                  : "memory");
                err |= copy_to_user(&uc->uc_mcontext.fpregs, &fpregs,
                                    sizeof(fpregs));
        }
        if (context_size)
                err |= copy_to_user((long __user *)&uc->uc_fpstate + 1, fpstate + 4,
                                    context_size);
        return err;
}

#endif

static void setup_sigcontext(struct sigcontext *sc, struct pt_regs *regs,
                             unsigned long mask)
{
        sc->sc_mask = mask;
        sc->sc_usp = rdusp();
        sc->sc_d0 = regs->d0;
        sc->sc_d1 = regs->d1;
        sc->sc_a0 = regs->a0;
        sc->sc_a1 = regs->a1;
        sc->sc_a5 = ((struct switch_stack *)regs - 1)->a5;
        sc->sc_sr = regs->sr;
        sc->sc_pc = regs->pc;
        sc->sc_formatvec = regs->format << 12 | regs->vector;
#ifdef CONFIG_FPU
        save_fpu_state(sc, regs);
#endif
}

static inline int rt_setup_ucontext(struct ucontext __user *uc, struct pt_regs *regs)
{
        struct switch_stack *sw = (struct switch_stack *)regs - 1;
        greg_t __user *gregs = uc->uc_mcontext.gregs;
        int err = 0;

        err |= __put_user(MCONTEXT_VERSION, &uc->uc_mcontext.version);
        err |= __put_user(regs->d0, &gregs[0]);
        err |= __put_user(regs->d1, &gregs[1]);
        err |= __put_user(regs->d2, &gregs[2]);
        err |= __put_user(regs->d3, &gregs[3]);
        err |= __put_user(regs->d4, &gregs[4]);
        err |= __put_user(regs->d5, &gregs[5]);
        err |= __put_user(sw->d6, &gregs[6]);
        err |= __put_user(sw->d7, &gregs[7]);
        err |= __put_user(regs->a0, &gregs[8]);
        err |= __put_user(regs->a1, &gregs[9]);
        err |= __put_user(regs->a2, &gregs[10]);
        err |= __put_user(sw->a3, &gregs[11]);
        err |= __put_user(sw->a4, &gregs[12]);
        err |= __put_user(sw->a5, &gregs[13]);
        err |= __put_user(sw->a6, &gregs[14]);
        err |= __put_user(rdusp(), &gregs[15]);
        err |= __put_user(regs->pc, &gregs[16]);
        err |= __put_user(regs->sr, &gregs[17]);
#ifdef CONFIG_FPU
        err |= rt_save_fpu_state(uc, regs);
#endif
        return err;
}

static inline void __user *
get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size)
{
        unsigned long usp;

        /* Default to using normal stack.  */
        usp = rdusp();

        /* This is the X/Open sanctioned signal stack switching.  */
        if (ka->sa.sa_flags & SA_ONSTACK) {
                if (!sas_ss_flags(usp))
                        usp = current->sas_ss_sp + current->sas_ss_size;
        }
        return (void __user *)((usp - frame_size) & -8UL);
}

static int setup_frame (int sig, struct k_sigaction *ka,
                         sigset_t *set, struct pt_regs *regs)
{
        struct sigframe __user *frame;
        struct sigcontext context;
        int err = 0;

        frame = get_sigframe(ka, regs, sizeof(*frame));

        err |= __put_user((current_thread_info()->exec_domain
                           && current_thread_info()->exec_domain->signal_invmap
                           && sig < 32
                           ? current_thread_info()->exec_domain->signal_invmap[sig]
                           : sig),
                          &frame->sig);

        err |= __put_user(regs->vector, &frame->code);
        err |= __put_user(&frame->sc, &frame->psc);

        if (_NSIG_WORDS > 1)
                err |= copy_to_user(frame->extramask, &set->sig[1],
                                    sizeof(frame->extramask));

        setup_sigcontext(&context, regs, set->sig[0]);
        err |= copy_to_user (&frame->sc, &context, sizeof(context));

        /* Set up to return from userspace.  */
        err |= __put_user((void *) ret_from_user_signal, &frame->pretcode);

        if (err)
                goto give_sigsegv;

        /* Set up registers for signal handler */
        wrusp ((unsigned long) frame);
        regs->pc = (unsigned long) ka->sa.sa_handler;
        ((struct switch_stack *)regs - 1)->a5 = current->mm->start_data;
        regs->format = 0x4; /*set format byte to make stack appear modulo 4 
                                                which it will be when doing the rte */

adjust_stack:
        /* Prepare to skip over the extra stuff in the exception frame.  */
        if (regs->stkadj) {
                struct pt_regs *tregs =
                        (struct pt_regs *)((ulong)regs + regs->stkadj);
#if defined(DEBUG)
                printk(KERN_DEBUG "Performing stackadjust=%04x\n", regs->stkadj);
#endif
                /* This must be copied with decreasing addresses to
                   handle overlaps.  */
                tregs->vector = 0;
                tregs->format = 0;
                tregs->pc = regs->pc;
                tregs->sr = regs->sr;
        }
        return err;

give_sigsegv:
        force_sigsegv(sig, current);
        goto adjust_stack;
}

static int setup_rt_frame (int sig, struct k_sigaction *ka, siginfo_t *info,
                            sigset_t *set, struct pt_regs *regs)
{
        struct rt_sigframe __user *frame;
        int err = 0;

        frame = get_sigframe(ka, regs, sizeof(*frame));

        err |= __put_user((current_thread_info()->exec_domain
                           && current_thread_info()->exec_domain->signal_invmap
                           && sig < 32
                           ? current_thread_info()->exec_domain->signal_invmap[sig]
                           : sig),
                          &frame->sig);
        err |= __put_user(&frame->info, &frame->pinfo);
        err |= __put_user(&frame->uc, &frame->puc);
        err |= copy_siginfo_to_user(&frame->info, info);

        /* Create the ucontext.  */
        err |= __put_user(0, &frame->uc.uc_flags);
        err |= __put_user(NULL, &frame->uc.uc_link);
        err |= __put_user((void __user *)current->sas_ss_sp,
                          &frame->uc.uc_stack.ss_sp);
        err |= __put_user(sas_ss_flags(rdusp()),
                          &frame->uc.uc_stack.ss_flags);
        err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
        err |= rt_setup_ucontext(&frame->uc, regs);
        err |= copy_to_user (&frame->uc.uc_sigmask, set, sizeof(*set));

        /* Set up to return from userspace.  */
        err |= __put_user((void *) ret_from_user_rt_signal, &frame->pretcode);

        if (err)
                goto give_sigsegv;

        /* Set up registers for signal handler */
        wrusp ((unsigned long) frame);
        regs->pc = (unsigned long) ka->sa.sa_handler;
        ((struct switch_stack *)regs - 1)->a5 = current->mm->start_data;
        regs->format = 0x4; /*set format byte to make stack appear modulo 4 
                                                which it will be when doing the rte */

adjust_stack:
        /* Prepare to skip over the extra stuff in the exception frame.  */
        if (regs->stkadj) {
                struct pt_regs *tregs =
                        (struct pt_regs *)((ulong)regs + regs->stkadj);
#if defined(DEBUG)
                printk(KERN_DEBUG "Performing stackadjust=%04x\n", regs->stkadj);
#endif
                /* This must be copied with decreasing addresses to
                   handle overlaps.  */
                tregs->vector = 0;
                tregs->format = 0;
                tregs->pc = regs->pc;
                tregs->sr = regs->sr;
        }
        return err;

give_sigsegv:
        force_sigsegv(sig, current);
        goto adjust_stack;
}

static inline void
handle_restart(struct pt_regs *regs, struct k_sigaction *ka, int has_handler)
{
        switch (regs->d0) {
        case -ERESTARTNOHAND:
                if (!has_handler)
                        goto do_restart;
                regs->d0 = -EINTR;
                break;

        case -ERESTART_RESTARTBLOCK:
                if (!has_handler) {
                        regs->d0 = __NR_restart_syscall;
                        regs->pc -= 2;
                        break;
                }
                regs->d0 = -EINTR;
                break;

        case -ERESTARTSYS:
                if (has_handler && !(ka->sa.sa_flags & SA_RESTART)) {
                        regs->d0 = -EINTR;
                        break;
                }
        /* fallthrough */
        case -ERESTARTNOINTR:
        do_restart:
                regs->d0 = regs->orig_d0;
                regs->pc -= 2;
                break;
        }
}

/*
 * OK, we're invoking a handler
 */
static void
handle_signal(int sig, struct k_sigaction *ka, siginfo_t *info,
              sigset_t *oldset, struct pt_regs *regs)
{
        int err;
        /* are we from a system call? */
        if (regs->orig_d0 >= 0)
                /* If so, check system call restarting.. */
                handle_restart(regs, ka, 1);

        /* set up the stack frame */
        if (ka->sa.sa_flags & SA_SIGINFO)
                err = setup_rt_frame(sig, ka, info, oldset, regs);
        else
                err = setup_frame(sig, ka, oldset, regs);

        if (err)
                return;

        spin_lock_irq(&current->sighand->siglock);
        sigorsets(&current->blocked,&current->blocked,&ka->sa.sa_mask);
        if (!(ka->sa.sa_flags & SA_NODEFER))
                sigaddset(&current->blocked,sig);
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        clear_thread_flag(TIF_RESTORE_SIGMASK);
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 */
asmlinkage void do_signal(struct pt_regs *regs)
{
        struct k_sigaction ka;
        siginfo_t info;
        int signr;
        sigset_t *oldset;

        /*
         * We want the common case to go fast, which
         * is why we may in certain cases get here from
         * kernel mode. Just return without doing anything
         * if so.
         */
        if (!user_mode(regs))
                return;

        if (test_thread_flag(TIF_RESTORE_SIGMASK))
                oldset = &current->saved_sigmask;
        else
                oldset = &current->blocked;

        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
        if (signr > 0) {
                /* Whee!  Actually deliver the signal.  */
                handle_signal(signr, &ka, &info, oldset, regs);
                return;
        }

        /* Did we come from a system call? */
        if (regs->orig_d0 >= 0) {
                /* Restart the system call - no handlers present */
                handle_restart(regs, NULL, 0);
        }

        /* If there's no signal to deliver, we just restore the saved mask.  */
        if (test_thread_flag(TIF_RESTORE_SIGMASK)) {
                clear_thread_flag(TIF_RESTORE_SIGMASK);
                sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
        }
}