Merge Christoph's freeze cleanup patch

[linux-2.6] / arch / ppc / kernel / signal.c

/*
 *  arch/ppc/kernel/signal.c
 *
 *  PowerPC version
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Derived from "arch/i386/kernel/signal.c"
 *    Copyright (C) 1991, 1992 Linus Torvalds
 *    1997-11-28  Modified for POSIX.1b signals by Richard Henderson
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/elf.h>
#include <linux/tty.h>
#include <linux/binfmts.h>
#include <linux/suspend.h>
#include <asm/ucontext.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>

#undef DEBUG_SIG

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

extern void sigreturn_exit(struct pt_regs *);

#define GP_REGS_SIZE    min(sizeof(elf_gregset_t), sizeof(struct pt_regs))

int do_signal(sigset_t *oldset, struct pt_regs *regs);

/*
 * Atomically swap in the new signal mask, and wait for a signal.
 */
int
sys_sigsuspend(old_sigset_t mask, int p2, int p3, int p4, int p6, int p7,
               struct pt_regs *regs)
{
        sigset_t saveset;

        mask &= _BLOCKABLE;
        spin_lock_irq(&current->sighand->siglock);
        saveset = current->blocked;
        siginitset(&current->blocked, mask);
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        regs->result = -EINTR;
        regs->gpr[3] = EINTR;
        regs->ccr |= 0x10000000;
        while (1) {
                current->state = TASK_INTERRUPTIBLE;
                schedule();
                if (do_signal(&saveset, regs))
                        sigreturn_exit(regs);
        }
}

int
sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize, int p3, int p4,
                  int p6, int p7, struct pt_regs *regs)
{
        sigset_t saveset, newset;

        /* XXX: Don't preclude handling different sized sigset_t's.  */
        if (sigsetsize != sizeof(sigset_t))
                return -EINVAL;

        if (copy_from_user(&newset, unewset, sizeof(newset)))
                return -EFAULT;
        sigdelsetmask(&newset, ~_BLOCKABLE);

        spin_lock_irq(&current->sighand->siglock);
        saveset = current->blocked;
        current->blocked = newset;
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

        regs->result = -EINTR;
        regs->gpr[3] = EINTR;
        regs->ccr |= 0x10000000;
        while (1) {
                current->state = TASK_INTERRUPTIBLE;
                schedule();
                if (do_signal(&saveset, regs))
                        sigreturn_exit(regs);
        }
}


int
sys_sigaltstack(const stack_t __user *uss, stack_t __user *uoss, int r5,
                int r6, int r7, int r8, struct pt_regs *regs)
{
        return do_sigaltstack(uss, uoss, regs->gpr[1]);
}

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))
                        return -EFAULT;
                __get_user(new_ka.sa.sa_flags, &act->sa_flags);
                __get_user(mask, &act->sa_mask);
                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))
                        return -EFAULT;
                __put_user(old_ka.sa.sa_flags, &oact->sa_flags);
                __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask);
        }

        return ret;
}

/*
 * When we have signals to deliver, we set up on the
 * user stack, going down from the original stack pointer:
 *      a sigregs struct
 *      a sigcontext struct
 *      a gap of __SIGNAL_FRAMESIZE bytes
 *
 * Each of these things must be a multiple of 16 bytes in size.
 *
 */
struct sigregs {
        struct mcontext mctx;           /* all the register values */
        /* Programs using the rs6000/xcoff abi can save up to 19 gp regs
           and 18 fp regs below sp before decrementing it. */
        int             abigap[56];
};

/* We use the mc_pad field for the signal return trampoline. */
#define tramp   mc_pad

/*
 *  When we have rt signals to deliver, we set up on the
 *  user stack, going down from the original stack pointer:
 *      one rt_sigframe struct (siginfo + ucontext + ABI gap)
 *      a gap of __SIGNAL_FRAMESIZE+16 bytes
 *  (the +16 is to get the siginfo and ucontext in the same
 *  positions as in older kernels).
 *
 *  Each of these things must be a multiple of 16 bytes in size.
 *
 */
struct rt_sigframe
{
        struct siginfo info;
        struct ucontext uc;
        /* Programs using the rs6000/xcoff abi can save up to 19 gp regs
           and 18 fp regs below sp before decrementing it. */
        int             abigap[56];
};

/*
 * Save the current user registers on the user stack.
 * We only save the altivec/spe registers if the process has used
 * altivec/spe instructions at some point.
 */
static int
save_user_regs(struct pt_regs *regs, struct mcontext __user *frame, int sigret)
{
        /* save general and floating-point registers */
        CHECK_FULL_REGS(regs);
        preempt_disable();
        if (regs->msr & MSR_FP)
                giveup_fpu(current);
#ifdef CONFIG_ALTIVEC
        if (current->thread.used_vr && (regs->msr & MSR_VEC))
                giveup_altivec(current);
#endif /* CONFIG_ALTIVEC */
#ifdef CONFIG_SPE
        if (current->thread.used_spe && (regs->msr & MSR_SPE))
                giveup_spe(current);
#endif /* CONFIG_ALTIVEC */
        preempt_enable();

        if (__copy_to_user(&frame->mc_gregs, regs, GP_REGS_SIZE)
            || __copy_to_user(&frame->mc_fregs, current->thread.fpr,
                              ELF_NFPREG * sizeof(double)))
                return 1;

        current->thread.fpscr = 0;      /* turn off all fp exceptions */

#ifdef CONFIG_ALTIVEC
        /* save altivec registers */
        if (current->thread.used_vr) {
                if (__copy_to_user(&frame->mc_vregs, current->thread.vr,
                                   ELF_NVRREG * sizeof(vector128)))
                        return 1;
                /* set MSR_VEC in the saved MSR value to indicate that
                   frame->mc_vregs contains valid data */
                if (__put_user(regs->msr | MSR_VEC, &frame->mc_gregs[PT_MSR]))
                        return 1;
        }
        /* else assert((regs->msr & MSR_VEC) == 0) */

        /* We always copy to/from vrsave, it's 0 if we don't have or don't
         * use altivec. Since VSCR only contains 32 bits saved in the least
         * significant bits of a vector, we "cheat" and stuff VRSAVE in the
         * most significant bits of that same vector. --BenH
         */
        if (__put_user(current->thread.vrsave, (u32 __user *)&frame->mc_vregs[32]))
                return 1;
#endif /* CONFIG_ALTIVEC */

#ifdef CONFIG_SPE
        /* save spe registers */
        if (current->thread.used_spe) {
                if (__copy_to_user(&frame->mc_vregs, current->thread.evr,
                                   ELF_NEVRREG * sizeof(u32)))
                        return 1;
                /* set MSR_SPE in the saved MSR value to indicate that
                   frame->mc_vregs contains valid data */
                if (__put_user(regs->msr | MSR_SPE, &frame->mc_gregs[PT_MSR]))
                        return 1;
        }
        /* else assert((regs->msr & MSR_SPE) == 0) */

        /* We always copy to/from spefscr */
        if (__put_user(current->thread.spefscr, (u32 *)&frame->mc_vregs + ELF_NEVRREG))
                return 1;
#endif /* CONFIG_SPE */

        if (sigret) {
                /* Set up the sigreturn trampoline: li r0,sigret; sc */
                if (__put_user(0x38000000UL + sigret, &frame->tramp[0])
                    || __put_user(0x44000002UL, &frame->tramp[1]))
                        return 1;
                flush_icache_range((unsigned long) &frame->tramp[0],
                                   (unsigned long) &frame->tramp[2]);
        }

        return 0;
}

/*
 * Restore the current user register values from the user stack,
 * (except for MSR).
 */
static int
restore_user_regs(struct pt_regs *regs, struct mcontext __user *sr, int sig)
{
        unsigned long save_r2 = 0;
#if defined(CONFIG_ALTIVEC) || defined(CONFIG_SPE)
        unsigned long msr;
#endif

        /* backup/restore the TLS as we don't want it to be modified */
        if (!sig)
                save_r2 = regs->gpr[2];
        /* copy up to but not including MSR */
        if (__copy_from_user(regs, &sr->mc_gregs, PT_MSR * sizeof(elf_greg_t)))
                return 1;
        /* copy from orig_r3 (the word after the MSR) up to the end */
        if (__copy_from_user(&regs->orig_gpr3, &sr->mc_gregs[PT_ORIG_R3],
                             GP_REGS_SIZE - PT_ORIG_R3 * sizeof(elf_greg_t)))
                return 1;
        if (!sig)
                regs->gpr[2] = save_r2;

        /* force the process to reload the FP registers from
           current->thread when it next does FP instructions */
        regs->msr &= ~(MSR_FP | MSR_FE0 | MSR_FE1);
        if (__copy_from_user(current->thread.fpr, &sr->mc_fregs,
                             sizeof(sr->mc_fregs)))
                return 1;

#ifdef CONFIG_ALTIVEC
        /* force the process to reload the altivec registers from
           current->thread when it next does altivec instructions */
        regs->msr &= ~MSR_VEC;
        if (!__get_user(msr, &sr->mc_gregs[PT_MSR]) && (msr & MSR_VEC) != 0) {
                /* restore altivec registers from the stack */
                if (__copy_from_user(current->thread.vr, &sr->mc_vregs,
                                     sizeof(sr->mc_vregs)))
                        return 1;
        } else if (current->thread.used_vr)
                memset(&current->thread.vr, 0, ELF_NVRREG * sizeof(vector128));

        /* Always get VRSAVE back */
        if (__get_user(current->thread.vrsave, (u32 __user *)&sr->mc_vregs[32]))
                return 1;
#endif /* CONFIG_ALTIVEC */

#ifdef CONFIG_SPE
        /* force the process to reload the spe registers from
           current->thread when it next does spe instructions */
        regs->msr &= ~MSR_SPE;
        if (!__get_user(msr, &sr->mc_gregs[PT_MSR]) && (msr & MSR_SPE) != 0) {
                /* restore spe registers from the stack */
                if (__copy_from_user(current->thread.evr, &sr->mc_vregs,
                                     ELF_NEVRREG * sizeof(u32)))
                        return 1;
        } else if (current->thread.used_spe)
                memset(&current->thread.evr, 0, ELF_NEVRREG * sizeof(u32));

        /* Always get SPEFSCR back */
        if (__get_user(current->thread.spefscr, (u32 *)&sr->mc_vregs + ELF_NEVRREG))
                return 1;
#endif /* CONFIG_SPE */

#ifndef CONFIG_SMP
        preempt_disable();
        if (last_task_used_math == current)
                last_task_used_math = NULL;
        if (last_task_used_altivec == current)
                last_task_used_altivec = NULL;
        if (last_task_used_spe == current)
                last_task_used_spe = NULL;
        preempt_enable();
#endif
        return 0;
}

/*
 * Restore the user process's signal mask
 */
static void
restore_sigmask(sigset_t *set)
{
        sigdelsetmask(set, ~_BLOCKABLE);
        spin_lock_irq(&current->sighand->siglock);
        current->blocked = *set;
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);
}

/*
 * Set up a signal frame for a "real-time" signal handler
 * (one which gets siginfo).
 */
static void
handle_rt_signal(unsigned long sig, struct k_sigaction *ka,
                 siginfo_t *info, sigset_t *oldset, struct pt_regs * regs,
                 unsigned long newsp)
{
        struct rt_sigframe __user *rt_sf;
        struct mcontext __user *frame;
        unsigned long origsp = newsp;

        /* Set up Signal Frame */
        /* Put a Real Time Context onto stack */
        newsp -= sizeof(*rt_sf);
        rt_sf = (struct rt_sigframe __user *) newsp;

        /* create a stack frame for the caller of the handler */
        newsp -= __SIGNAL_FRAMESIZE + 16;

        if (!access_ok(VERIFY_WRITE, (void __user *) newsp, origsp - newsp))
                goto badframe;

        /* Put the siginfo & fill in most of the ucontext */
        if (copy_siginfo_to_user(&rt_sf->info, info)
            || __put_user(0, &rt_sf->uc.uc_flags)
            || __put_user(0, &rt_sf->uc.uc_link)
            || __put_user(current->sas_ss_sp, &rt_sf->uc.uc_stack.ss_sp)
            || __put_user(sas_ss_flags(regs->gpr[1]),
                          &rt_sf->uc.uc_stack.ss_flags)
            || __put_user(current->sas_ss_size, &rt_sf->uc.uc_stack.ss_size)
            || __put_user(&rt_sf->uc.uc_mcontext, &rt_sf->uc.uc_regs)
            || __copy_to_user(&rt_sf->uc.uc_sigmask, oldset, sizeof(*oldset)))
                goto badframe;

        /* Save user registers on the stack */
        frame = &rt_sf->uc.uc_mcontext;
        if (save_user_regs(regs, frame, __NR_rt_sigreturn))
                goto badframe;

        if (put_user(regs->gpr[1], (unsigned long __user *)newsp))
                goto badframe;
        regs->gpr[1] = newsp;
        regs->gpr[3] = sig;
        regs->gpr[4] = (unsigned long) &rt_sf->info;
        regs->gpr[5] = (unsigned long) &rt_sf->uc;
        regs->gpr[6] = (unsigned long) rt_sf;
        regs->nip = (unsigned long) ka->sa.sa_handler;
        regs->link = (unsigned long) frame->tramp;
        regs->trap = 0;

        return;

badframe:
#ifdef DEBUG_SIG
        printk("badframe in handle_rt_signal, regs=%p frame=%p newsp=%lx\n",
               regs, frame, newsp);
#endif
        force_sigsegv(sig, current);
}

static int do_setcontext(struct ucontext __user *ucp, struct pt_regs *regs, int sig)
{
        sigset_t set;
        struct mcontext __user *mcp;

        if (__copy_from_user(&set, &ucp->uc_sigmask, sizeof(set))
            || __get_user(mcp, &ucp->uc_regs))
                return -EFAULT;
        restore_sigmask(&set);
        if (restore_user_regs(regs, mcp, sig))
                return -EFAULT;

        return 0;
}

int sys_swapcontext(struct ucontext __user *old_ctx,
                    struct ucontext __user *new_ctx,
                    int ctx_size, int r6, int r7, int r8, struct pt_regs *regs)
{
        unsigned char tmp;

        /* Context size is for future use. Right now, we only make sure
         * we are passed something we understand
         */
        if (ctx_size < sizeof(struct ucontext))
                return -EINVAL;

        if (old_ctx != NULL) {
                if (!access_ok(VERIFY_WRITE, old_ctx, sizeof(*old_ctx))
                    || save_user_regs(regs, &old_ctx->uc_mcontext, 0)
                    || __copy_to_user(&old_ctx->uc_sigmask,
                                      &current->blocked, sizeof(sigset_t))
                    || __put_user(&old_ctx->uc_mcontext, &old_ctx->uc_regs))
                        return -EFAULT;
        }
        if (new_ctx == NULL)
                return 0;
        if (!access_ok(VERIFY_READ, new_ctx, sizeof(*new_ctx))
            || __get_user(tmp, (u8 __user *) new_ctx)
            || __get_user(tmp, (u8 __user *) (new_ctx + 1) - 1))
                return -EFAULT;

        /*
         * If we get a fault copying the context into the kernel's
         * image of the user's registers, we can't just return -EFAULT
         * because the user's registers will be corrupted.  For instance
         * the NIP value may have been updated but not some of the
         * other registers.  Given that we have done the access_ok
         * and successfully read the first and last bytes of the region
         * above, this should only happen in an out-of-memory situation
         * or if another thread unmaps the region containing the context.
         * We kill the task with a SIGSEGV in this situation.
         */
        if (do_setcontext(new_ctx, regs, 0))
                do_exit(SIGSEGV);
        sigreturn_exit(regs);
        /* doesn't actually return back to here */
        return 0;
}

int sys_rt_sigreturn(int r3, int r4, int r5, int r6, int r7, int r8,
                     struct pt_regs *regs)
{
        struct rt_sigframe __user *rt_sf;

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

        rt_sf = (struct rt_sigframe __user *)
                (regs->gpr[1] + __SIGNAL_FRAMESIZE + 16);
        if (!access_ok(VERIFY_READ, rt_sf, sizeof(struct rt_sigframe)))
                goto bad;
        if (do_setcontext(&rt_sf->uc, regs, 1))
                goto bad;

        /*
         * It's not clear whether or why it is desirable to save the
         * sigaltstack setting on signal delivery and restore it on
         * signal return.  But other architectures do this and we have
         * always done it up until now so it is probably better not to
         * change it.  -- paulus
         */
        do_sigaltstack(&rt_sf->uc.uc_stack, NULL, regs->gpr[1]);

        sigreturn_exit(regs);           /* doesn't return here */
        return 0;

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

int sys_debug_setcontext(struct ucontext __user *ctx,
                         int ndbg, struct sig_dbg_op __user *dbg,
                         int r6, int r7, int r8,
                         struct pt_regs *regs)
{
        struct sig_dbg_op op;
        int i;
        unsigned long new_msr = regs->msr;
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
        unsigned long new_dbcr0 = current->thread.dbcr0;
#endif

        for (i=0; i<ndbg; i++) {
                if (__copy_from_user(&op, dbg, sizeof(op)))
                        return -EFAULT;
                switch (op.dbg_type) {
                case SIG_DBG_SINGLE_STEPPING:
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
                        if (op.dbg_value) {
                                new_msr |= MSR_DE;
                                new_dbcr0 |= (DBCR0_IDM | DBCR0_IC);
                        } else {
                                new_msr &= ~MSR_DE;
                                new_dbcr0 &= ~(DBCR0_IDM | DBCR0_IC);
                        }
#else
                        if (op.dbg_value)
                                new_msr |= MSR_SE;
                        else
                                new_msr &= ~MSR_SE;
#endif
                        break;
                case SIG_DBG_BRANCH_TRACING:
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
                        return -EINVAL;
#else
                        if (op.dbg_value)
                                new_msr |= MSR_BE;
                        else
                                new_msr &= ~MSR_BE;
#endif
                        break;

                default:
                        return -EINVAL;
                }
        }

        /* We wait until here to actually install the values in the
           registers so if we fail in the above loop, it will not
           affect the contents of these registers.  After this point,
           failure is a problem, anyway, and it's very unlikely unless
           the user is really doing something wrong. */
        regs->msr = new_msr;
#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
        current->thread.dbcr0 = new_dbcr0;
#endif

        /*
         * If we get a fault copying the context into the kernel's
         * image of the user's registers, we can't just return -EFAULT
         * because the user's registers will be corrupted.  For instance
         * the NIP value may have been updated but not some of the
         * other registers.  Given that we have done the access_ok
         * and successfully read the first and last bytes of the region
         * above, this should only happen in an out-of-memory situation
         * or if another thread unmaps the region containing the context.
         * We kill the task with a SIGSEGV in this situation.
         */
        if (do_setcontext(ctx, regs, 1)) {
                force_sig(SIGSEGV, current);
                goto out;
        }

        /*
         * It's not clear whether or why it is desirable to save the
         * sigaltstack setting on signal delivery and restore it on
         * signal return.  But other architectures do this and we have
         * always done it up until now so it is probably better not to
         * change it.  -- paulus
         */
        do_sigaltstack(&ctx->uc_stack, NULL, regs->gpr[1]);

        sigreturn_exit(regs);
        /* doesn't actually return back to here */

 out:
        return 0;
}

/*
 * OK, we're invoking a handler
 */
static void
handle_signal(unsigned long sig, struct k_sigaction *ka,
              siginfo_t *info, sigset_t *oldset, struct pt_regs * regs,
              unsigned long newsp)
{
        struct sigcontext __user *sc;
        struct sigregs __user *frame;
        unsigned long origsp = newsp;

        /* Set up Signal Frame */
        newsp -= sizeof(struct sigregs);
        frame = (struct sigregs __user *) newsp;

        /* Put a sigcontext on the stack */
        newsp -= sizeof(*sc);
        sc = (struct sigcontext __user *) newsp;

        /* create a stack frame for the caller of the handler */
        newsp -= __SIGNAL_FRAMESIZE;

        if (!access_ok(VERIFY_WRITE, (void __user *) newsp, origsp - newsp))
                goto badframe;

#if _NSIG != 64
#error "Please adjust handle_signal()"
#endif
        if (__put_user((unsigned long) ka->sa.sa_handler, &sc->handler)
            || __put_user(oldset->sig[0], &sc->oldmask)
            || __put_user(oldset->sig[1], &sc->_unused[3])
            || __put_user((struct pt_regs __user *)frame, &sc->regs)
            || __put_user(sig, &sc->signal))
                goto badframe;

        if (save_user_regs(regs, &frame->mctx, __NR_sigreturn))
                goto badframe;

        if (put_user(regs->gpr[1], (unsigned long __user *)newsp))
                goto badframe;
        regs->gpr[1] = newsp;
        regs->gpr[3] = sig;
        regs->gpr[4] = (unsigned long) sc;
        regs->nip = (unsigned long) ka->sa.sa_handler;
        regs->link = (unsigned long) frame->mctx.tramp;
        regs->trap = 0;

        return;

badframe:
#ifdef DEBUG_SIG
        printk("badframe in handle_signal, regs=%p frame=%p newsp=%lx\n",
               regs, frame, newsp);
#endif
        force_sigsegv(sig, current);
}

/*
 * Do a signal return; undo the signal stack.
 */
int sys_sigreturn(int r3, int r4, int r5, int r6, int r7, int r8,
                  struct pt_regs *regs)
{
        struct sigcontext __user *sc;
        struct sigcontext sigctx;
        struct mcontext __user *sr;
        sigset_t set;

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

        sc = (struct sigcontext __user *)(regs->gpr[1] + __SIGNAL_FRAMESIZE);
        if (copy_from_user(&sigctx, sc, sizeof(sigctx)))
                goto badframe;

        set.sig[0] = sigctx.oldmask;
        set.sig[1] = sigctx._unused[3];
        restore_sigmask(&set);

        sr = (struct mcontext __user *) sigctx.regs;
        if (!access_ok(VERIFY_READ, sr, sizeof(*sr))
            || restore_user_regs(regs, sr, 1))
                goto badframe;

        sigreturn_exit(regs);           /* doesn't return */
        return 0;

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

/*
 * 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.
 */
int do_signal(sigset_t *oldset, struct pt_regs *regs)
{
        siginfo_t info;
        struct k_sigaction ka;
        unsigned long frame, newsp;
        int signr, ret;

        if (try_to_freeze()) {
                signr = 0;
                if (!signal_pending(current))
                        goto no_signal;
        }

        if (!oldset)
                oldset = &current->blocked;

        newsp = frame = 0;

        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 no_signal:
        if (TRAP(regs) == 0x0C00                /* System Call! */
            && regs->ccr & 0x10000000           /* error signalled */
            && ((ret = regs->gpr[3]) == ERESTARTSYS
                || ret == ERESTARTNOHAND || ret == ERESTARTNOINTR
                || ret == ERESTART_RESTARTBLOCK)) {

                if (signr > 0
                    && (ret == ERESTARTNOHAND || ret == ERESTART_RESTARTBLOCK
                        || (ret == ERESTARTSYS
                            && !(ka.sa.sa_flags & SA_RESTART)))) {
                        /* make the system call return an EINTR error */
                        regs->result = -EINTR;
                        regs->gpr[3] = EINTR;
                        /* note that the cr0.SO bit is already set */
                } else {
                        regs->nip -= 4; /* Back up & retry system call */
                        regs->result = 0;
                        regs->trap = 0;
                        if (ret == ERESTART_RESTARTBLOCK)
                                regs->gpr[0] = __NR_restart_syscall;
                        else
                                regs->gpr[3] = regs->orig_gpr3;
                }
        }

        if (signr == 0)
                return 0;               /* no signals delivered */

        if ((ka.sa.sa_flags & SA_ONSTACK) && current->sas_ss_size
            && !on_sig_stack(regs->gpr[1]))
                newsp = current->sas_ss_sp + current->sas_ss_size;
        else
                newsp = regs->gpr[1];
        newsp &= ~0xfUL;

        /* Whee!  Actually deliver the signal.  */
        if (ka.sa.sa_flags & SA_SIGINFO)
                handle_rt_signal(signr, &ka, &info, oldset, regs, newsp);
        else
                handle_signal(signr, &ka, &info, oldset, regs, newsp);

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

        return 1;
}