/*
 *  linux/arch/arm/kernel/signal.c
 *
 *  Copyright (C) 1995-2009 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/freezer.h>
#include <linux/uaccess.h>
#include <linux/tracehook.h>

#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/vfp.h>

#include "signal.h"

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

/*
 * For ARM syscalls, we encode the syscall number into the instruction.
 */
#define SWI_SYS_SIGRETURN       (0xef000000|(__NR_sigreturn)|(__NR_OABI_SYSCALL_BASE))
#define SWI_SYS_RT_SIGRETURN    (0xef000000|(__NR_rt_sigreturn)|(__NR_OABI_SYSCALL_BASE))
#define SWI_SYS_RESTART         (0xef000000|__NR_restart_syscall|__NR_OABI_SYSCALL_BASE)

/*
 * With EABI, the syscall number has to be loaded into r7.
 */
#define MOV_R7_NR_SIGRETURN     (0xe3a07000 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define MOV_R7_NR_RT_SIGRETURN  (0xe3a07000 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))

/*
 * For Thumb syscalls, we pass the syscall number via r7.  We therefore
 * need two 16-bit instructions.
 */
#define SWI_THUMB_SIGRETURN     (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define SWI_THUMB_RT_SIGRETURN  (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))

const unsigned long sigreturn_codes[7] = {
        MOV_R7_NR_SIGRETURN,    SWI_SYS_SIGRETURN,    SWI_THUMB_SIGRETURN,
        MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
};

/*
 * Either we support OABI only, or we have EABI with the OABI
 * compat layer enabled.  In the later case we don't know if
 * user space is EABI or not, and if not we must not clobber r7.
 * Always using the OABI syscall solves that issue and works for
 * all those cases.
 */
const unsigned long syscall_restart_code[2] = {
        SWI_SYS_RESTART,        /* swi  __NR_restart_syscall */
        0xe49df004,             /* ldr  pc, [sp], #4 */
};

/*
 * atomically swap in the new signal mask, and wait for a signal.
 */
asmlinkage int sys_sigsuspend(int restart, unsigned long oldmask, 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))
                        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;
}

#ifdef CONFIG_CRUNCH
static int preserve_crunch_context(struct crunch_sigframe __user *frame)
{
        char kbuf[sizeof(*frame) + 8];
        struct crunch_sigframe *kframe;

        /* the crunch context must be 64 bit aligned */
        kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
        kframe->magic = CRUNCH_MAGIC;
        kframe->size = CRUNCH_STORAGE_SIZE;
        crunch_task_copy(current_thread_info(), &kframe->storage);
        return __copy_to_user(frame, kframe, sizeof(*frame));
}

static int restore_crunch_context(struct crunch_sigframe __user *frame)
{
        char kbuf[sizeof(*frame) + 8];
        struct crunch_sigframe *kframe;

        /* the crunch context must be 64 bit aligned */
        kframe = (struct crunch_sigframe *)((unsigned long)(kbuf + 8) & ~7);
        if (__copy_from_user(kframe, frame, sizeof(*frame)))
                return -1;
        if (kframe->magic != CRUNCH_MAGIC ||
            kframe->size != CRUNCH_STORAGE_SIZE)
                return -1;
        crunch_task_restore(current_thread_info(), &kframe->storage);
        return 0;
}
#endif

#ifdef CONFIG_IWMMXT

static int preserve_iwmmxt_context(struct iwmmxt_sigframe *frame)
{
        char kbuf[sizeof(*frame) + 8];
        struct iwmmxt_sigframe *kframe;

        /* the iWMMXt context must be 64 bit aligned */
        kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
        kframe->magic = IWMMXT_MAGIC;
        kframe->size = IWMMXT_STORAGE_SIZE;
        iwmmxt_task_copy(current_thread_info(), &kframe->storage);
        return __copy_to_user(frame, kframe, sizeof(*frame));
}

static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame)
{
        char kbuf[sizeof(*frame) + 8];
        struct iwmmxt_sigframe *kframe;

        /* the iWMMXt context must be 64 bit aligned */
        kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7);
        if (__copy_from_user(kframe, frame, sizeof(*frame)))
                return -1;
        if (kframe->magic != IWMMXT_MAGIC ||
            kframe->size != IWMMXT_STORAGE_SIZE)
                return -1;
        iwmmxt_task_restore(current_thread_info(), &kframe->storage);
        return 0;
}

#endif

#ifdef CONFIG_VFP

static int preserve_vfp_context(struct vfp_sigframe __user *frame)
{
        struct thread_info *thread = current_thread_info();
        struct vfp_hard_struct *h = &thread->vfpstate.hard;
        const unsigned long magic = VFP_MAGIC;
        const unsigned long size = VFP_STORAGE_SIZE;
        int err = 0;

        vfp_sync_hwstate(thread);
        __put_user_error(magic, &frame->magic, err);
        __put_user_error(size, &frame->size, err);

        /*
         * Copy the floating point registers. There can be unused
         * registers see asm/hwcap.h for details.
         */
        err |= __copy_to_user(&frame->ufp.fpregs, &h->fpregs,
                              sizeof(h->fpregs));
        /*
         * Copy the status and control register.
         */
        __put_user_error(h->fpscr, &frame->ufp.fpscr, err);

        /*
         * Copy the exception registers.
         */
        __put_user_error(h->fpexc, &frame->ufp_exc.fpexc, err);
        __put_user_error(h->fpinst, &frame->ufp_exc.fpinst, err);
        __put_user_error(h->fpinst2, &frame->ufp_exc.fpinst2, err);

        return err ? -EFAULT : 0;
}

static int restore_vfp_context(struct vfp_sigframe __user *frame)
{
        struct thread_info *thread = current_thread_info();
        struct vfp_hard_struct *h = &thread->vfpstate.hard;
        unsigned long magic;
        unsigned long size;
        unsigned long fpexc;
        int err = 0;

        __get_user_error(magic, &frame->magic, err);
        __get_user_error(size, &frame->size, err);

        if (err)
                return -EFAULT;
        if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
                return -EINVAL;

        /*
         * Copy the floating point registers. There can be unused
         * registers see asm/hwcap.h for details.
         */
        err |= __copy_from_user(&h->fpregs, &frame->ufp.fpregs,
                                sizeof(h->fpregs));
        /*
         * Copy the status and control register.
         */
        __get_user_error(h->fpscr, &frame->ufp.fpscr, err);

        /*
         * Sanitise and restore the exception registers.
         */
        __get_user_error(fpexc, &frame->ufp_exc.fpexc, err);
        /* Ensure the VFP is enabled. */
        fpexc |= FPEXC_EN;
        /* Ensure FPINST2 is invalid and the exception flag is cleared. */
        fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
        h->fpexc = fpexc;

        __get_user_error(h->fpinst, &frame->ufp_exc.fpinst, err);
        __get_user_error(h->fpinst2, &frame->ufp_exc.fpinst2, err);

        if (!err)
                vfp_flush_hwstate(thread);

        return err ? -EFAULT : 0;
}

#endif

/*
 * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
 */
struct sigframe {
        struct ucontext uc;
        unsigned long retcode[2];
};

struct rt_sigframe {
        struct siginfo info;
        struct sigframe sig;
};

static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
{
        struct aux_sigframe __user *aux;
        sigset_t set;
        int err;

        err = __copy_from_user(&set, &sf->uc.uc_sigmask, sizeof(set));
        if (err == 0) {
                sigdelsetmask(&set, ~_BLOCKABLE);
                spin_lock_irq(&current->sighand->siglock);
                current->blocked = set;
                recalc_sigpending();
                spin_unlock_irq(&current->sighand->siglock);
        }

        __get_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
        __get_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
        __get_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
        __get_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
        __get_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
        __get_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
        __get_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
        __get_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
        __get_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
        __get_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
        __get_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
        __get_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
        __get_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
        __get_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
        __get_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
        __get_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
        __get_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);

        err |= !valid_user_regs(regs);

        aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
#ifdef CONFIG_CRUNCH
        if (err == 0)
                err |= restore_crunch_context(&aux->crunch);
#endif
#ifdef CONFIG_IWMMXT
        if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
                err |= restore_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
        if (err == 0)
                err |= restore_vfp_context(&aux->vfp);
#endif

        return err;
}

asmlinkage int sys_sigreturn(struct pt_regs *regs)
{
        struct sigframe __user *frame;

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

        /*
         * Since we stacked the signal on a 64-bit boundary,
         * then 'sp' should be word aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        if (regs->ARM_sp & 7)
                goto badframe;

        frame = (struct sigframe __user *)regs->ARM_sp;

        if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
                goto badframe;

        if (restore_sigframe(regs, frame))
                goto badframe;

        return regs->ARM_r0;

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

asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
{
        struct rt_sigframe __user *frame;

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

        /*
         * Since we stacked the signal on a 64-bit boundary,
         * then 'sp' should be word aligned here.  If it's
         * not, then the user is trying to mess with us.
         */
        if (regs->ARM_sp & 7)
                goto badframe;

        frame = (struct rt_sigframe __user *)regs->ARM_sp;

        if (!access_ok(VERIFY_READ, frame, sizeof (*frame)))
                goto badframe;

        if (restore_sigframe(regs, &frame->sig))
                goto badframe;

        if (do_sigaltstack(&frame->sig.uc.uc_stack, NULL, regs->ARM_sp) == -EFAULT)
                goto badframe;

        return regs->ARM_r0;

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

static int
setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
{
        struct aux_sigframe __user *aux;
        int err = 0;

        __put_user_error(regs->ARM_r0, &sf->uc.uc_mcontext.arm_r0, err);
        __put_user_error(regs->ARM_r1, &sf->uc.uc_mcontext.arm_r1, err);
        __put_user_error(regs->ARM_r2, &sf->uc.uc_mcontext.arm_r2, err);
        __put_user_error(regs->ARM_r3, &sf->uc.uc_mcontext.arm_r3, err);
        __put_user_error(regs->ARM_r4, &sf->uc.uc_mcontext.arm_r4, err);
        __put_user_error(regs->ARM_r5, &sf->uc.uc_mcontext.arm_r5, err);
        __put_user_error(regs->ARM_r6, &sf->uc.uc_mcontext.arm_r6, err);
        __put_user_error(regs->ARM_r7, &sf->uc.uc_mcontext.arm_r7, err);
        __put_user_error(regs->ARM_r8, &sf->uc.uc_mcontext.arm_r8, err);
        __put_user_error(regs->ARM_r9, &sf->uc.uc_mcontext.arm_r9, err);
        __put_user_error(regs->ARM_r10, &sf->uc.uc_mcontext.arm_r10, err);
        __put_user_error(regs->ARM_fp, &sf->uc.uc_mcontext.arm_fp, err);
        __put_user_error(regs->ARM_ip, &sf->uc.uc_mcontext.arm_ip, err);
        __put_user_error(regs->ARM_sp, &sf->uc.uc_mcontext.arm_sp, err);
        __put_user_error(regs->ARM_lr, &sf->uc.uc_mcontext.arm_lr, err);
        __put_user_error(regs->ARM_pc, &sf->uc.uc_mcontext.arm_pc, err);
        __put_user_error(regs->ARM_cpsr, &sf->uc.uc_mcontext.arm_cpsr, err);

        __put_user_error(current->thread.trap_no, &sf->uc.uc_mcontext.trap_no, err);
        __put_user_error(current->thread.error_code, &sf->uc.uc_mcontext.error_code, err);
        __put_user_error(current->thread.address, &sf->uc.uc_mcontext.fault_address, err);
        __put_user_error(set->sig[0], &sf->uc.uc_mcontext.oldmask, err);

        err |= __copy_to_user(&sf->uc.uc_sigmask, set, sizeof(*set));

        aux = (struct aux_sigframe __user *) sf->uc.uc_regspace;
#ifdef CONFIG_CRUNCH
        if (err == 0)
                err |= preserve_crunch_context(&aux->crunch);
#endif
#ifdef CONFIG_IWMMXT
        if (err == 0 && test_thread_flag(TIF_USING_IWMMXT))
                err |= preserve_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
        if (err == 0)
                err |= preserve_vfp_context(&aux->vfp);
#endif
        __put_user_error(0, &aux->end_magic, err);

        return err;
}

static inline void __user *
get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, int framesize)
{
        unsigned long sp = regs->ARM_sp;
        void __user *frame;

        /*
         * This is the X/Open sanctioned signal stack switching.
         */
        if ((ka->sa.sa_flags & SA_ONSTACK) && !sas_ss_flags(sp))
                sp = current->sas_ss_sp + current->sas_ss_size;

        /*
         * ATPCS B01 mandates 8-byte alignment
         */
        frame = (void __user *)((sp - framesize) & ~7);

        /*
         * Check that we can actually write to the signal frame.
         */
        if (!access_ok(VERIFY_WRITE, frame, framesize))
                frame = NULL;

        return frame;
}

static int
setup_return(struct pt_regs *regs, struct k_sigaction *ka,
             unsigned long __user *rc, void __user *frame, int usig)
{
        unsigned long handler = (unsigned long)ka->sa.sa_handler;
        unsigned long retcode;
        int thumb = 0;
        unsigned long cpsr = regs->ARM_cpsr & ~(PSR_f | PSR_E_BIT);

        cpsr |= PSR_ENDSTATE;

        /*
         * Maybe we need to deliver a 32-bit signal to a 26-bit task.
         */
        if (ka->sa.sa_flags & SA_THIRTYTWO)
                cpsr = (cpsr & ~MODE_MASK) | USR_MODE;

#ifdef CONFIG_ARM_THUMB
        if (elf_hwcap & HWCAP_THUMB) {
                /*
                 * The LSB of the handler determines if we're going to
                 * be using THUMB or ARM mode for this signal handler.
                 */
                thumb = handler & 1;

                if (thumb) {
                        cpsr |= PSR_T_BIT;
#if __LINUX_ARM_ARCH__ >= 7
                        /* clear the If-Then Thumb-2 execution state */
                        cpsr &= ~PSR_IT_MASK;
#endif
                } else
                        cpsr &= ~PSR_T_BIT;
        }
#endif

        if (ka->sa.sa_flags & SA_RESTORER) {
                retcode = (unsigned long)ka->sa.sa_restorer;
        } else {
                unsigned int idx = thumb << 1;

                if (ka->sa.sa_flags & SA_SIGINFO)
                        idx += 3;

                if (__put_user(sigreturn_codes[idx],   rc) ||
                    __put_user(sigreturn_codes[idx+1], rc+1))
                        return 1;

                if (cpsr & MODE32_BIT) {
                        /*
                         * 32-bit code can use the new high-page
                         * signal return code support.
                         */
                        retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
                } else {
                        /*
                         * Ensure that the instruction cache sees
                         * the return code written onto the stack.
                         */
                        flush_icache_range((unsigned long)rc,
                                           (unsigned long)(rc + 2));

                        retcode = ((unsigned long)rc) + thumb;
                }
        }

        regs->ARM_r0 = usig;
        regs->ARM_sp = (unsigned long)frame;
        regs->ARM_lr = retcode;
        regs->ARM_pc = handler;
        regs->ARM_cpsr = cpsr;

        return 0;
}

static int
setup_frame(int usig, struct k_sigaction *ka, sigset_t *set, struct pt_regs *regs)
{
        struct sigframe __user *frame = get_sigframe(ka, regs, sizeof(*frame));
        int err = 0;

        if (!frame)
                return 1;

        /*
         * Set uc.uc_flags to a value which sc.trap_no would never have.
         */
        __put_user_error(0x5ac3c35a, &frame->uc.uc_flags, err);

        err |= setup_sigframe(frame, regs, set);
        if (err == 0)
                err = setup_return(regs, ka, frame->retcode, frame, usig);

        return err;
}

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

        if (!frame)
                return 1;

        err |= copy_siginfo_to_user(&frame->info, info);

        __put_user_error(0, &frame->sig.uc.uc_flags, err);
        __put_user_error(NULL, &frame->sig.uc.uc_link, err);

        memset(&stack, 0, sizeof(stack));
        stack.ss_sp = (void __user *)current->sas_ss_sp;
        stack.ss_flags = sas_ss_flags(regs->ARM_sp);
        stack.ss_size = current->sas_ss_size;
        err |= __copy_to_user(&frame->sig.uc.uc_stack, &stack, sizeof(stack));

        err |= setup_sigframe(&frame->sig, regs, set);
        if (err == 0)
                err = setup_return(regs, ka, frame->sig.retcode, frame, usig);

        if (err == 0) {
                /*
                 * For realtime signals we must also set the second and third
                 * arguments for the signal handler.
                 *   -- Peter Maydell <pmaydell@chiark.greenend.org.uk> 2000-12-06
                 */
                regs->ARM_r1 = (unsigned long)&frame->info;
                regs->ARM_r2 = (unsigned long)&frame->sig.uc;
        }

        return err;
}

/*
 * OK, we're invoking a handler
 */     
static int
handle_signal(unsigned long sig, struct k_sigaction *ka,
              siginfo_t *info, sigset_t *oldset,
              struct pt_regs * regs)
{
        struct thread_info *thread = current_thread_info();
        struct task_struct *tsk = current;
        int usig = sig;
        int ret;

        /*
         * translate the signal
         */
        if (usig < 32 && thread->exec_domain && thread->exec_domain->signal_invmap)
                usig = thread->exec_domain->signal_invmap[usig];

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

        /*
         * Check that the resulting registers are actually sane.
         */
        ret |= !valid_user_regs(regs);

        if (ret != 0) {
                force_sigsegv(sig, tsk);
                return ret;
        }

        /*
         * Block the signal if we were successful.
         */
        spin_lock_irq(&tsk->sighand->siglock);
        sigorsets(&tsk->blocked, &tsk->blocked,
                  &ka->sa.sa_mask);
        if (!(ka->sa.sa_flags & SA_NODEFER))
                sigaddset(&tsk->blocked, sig);
        recalc_sigpending();
        spin_unlock_irq(&tsk->sighand->siglock);

        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.
 *
 * Note that we go through the signals twice: once to check the signals that
 * the kernel can handle, and then we build all the user-level signal handling
 * stack-frames in one go after that.
 */
static void do_signal(struct pt_regs *regs, int syscall)
{
        unsigned int retval = 0, continue_addr = 0, restart_addr = 0;
        struct k_sigaction ka;
        siginfo_t info;
        int signr;

        /*
         * 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 we were from a system call, check for system call restarting...
         */
        if (syscall) {
                continue_addr = regs->ARM_pc;
                restart_addr = continue_addr - (thumb_mode(regs) ? 2 : 4);
                retval = regs->ARM_r0;

                /*
                 * Prepare for system call restart.  We do this here so that a
                 * debugger will see the already changed PSW.
                 */
                switch (retval) {
                case -ERESTARTNOHAND:
                case -ERESTARTSYS:
                case -ERESTARTNOINTR:
                        regs->ARM_r0 = regs->ARM_ORIG_r0;
                        regs->ARM_pc = restart_addr;
                        break;
                case -ERESTART_RESTARTBLOCK:
                        regs->ARM_r0 = -EINTR;
                        break;
                }
        }

        if (try_to_freeze())
                goto no_signal;

        /*
         * Get the signal to deliver.  When running under ptrace, at this
         * point the debugger may change all our registers ...
         */
        signr = get_signal_to_deliver(&info, &ka, regs, NULL);
        if (signr > 0) {
                sigset_t *oldset;

                /*
                 * Depending on the signal settings we may need to revert the
                 * decision to restart the system call.  But skip this if a
                 * debugger has chosen to restart at a different PC.
                 */
                if (regs->ARM_pc == restart_addr) {
                        if (retval == -ERESTARTNOHAND
                            || (retval == -ERESTARTSYS
                                && !(ka.sa.sa_flags & SA_RESTART))) {
                                regs->ARM_r0 = -EINTR;
                                regs->ARM_pc = continue_addr;
                        }
                }

                if (test_thread_flag(TIF_RESTORE_SIGMASK))
                        oldset = &current->saved_sigmask;
                else
                        oldset = &current->blocked;
                if (handle_signal(signr, &ka, &info, oldset, regs) == 0) {
                        /*
                         * A signal was successfully delivered; the saved
                         * sigmask will have been stored in the signal frame,
                         * and will be restored by sigreturn, so we can simply
                         * clear the TIF_RESTORE_SIGMASK flag.
                         */
                        if (test_thread_flag(TIF_RESTORE_SIGMASK))
                                clear_thread_flag(TIF_RESTORE_SIGMASK);
                }
                return;
        }

 no_signal:
        if (syscall) {
                /*
                 * Handle restarting a different system call.  As above,
                 * if a debugger has chosen to restart at a different PC,
                 * ignore the restart.
                 */
                if (retval == -ERESTART_RESTARTBLOCK
                    && regs->ARM_pc == continue_addr) {
                        if (thumb_mode(regs)) {
                                regs->ARM_r7 = __NR_restart_syscall - __NR_SYSCALL_BASE;
                                regs->ARM_pc -= 2;
                        } else {
#if defined(CONFIG_AEABI) && !defined(CONFIG_OABI_COMPAT)
                                regs->ARM_r7 = __NR_restart_syscall;
                                regs->ARM_pc -= 4;
#else
                                u32 __user *usp;

                                regs->ARM_sp -= 4;
                                usp = (u32 __user *)regs->ARM_sp;

                                if (put_user(regs->ARM_pc, usp) == 0) {
                                        regs->ARM_pc = KERN_RESTART_CODE;
                                } else {
                                        regs->ARM_sp += 4;
                                        force_sigsegv(0, current);
                                }
#endif
                        }
                }

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

asmlinkage void
do_notify_resume(struct pt_regs *regs, unsigned int thread_flags, int syscall)
{
        if (thread_flags & _TIF_SIGPENDING)
                do_signal(regs, syscall);

        if (thread_flags & _TIF_NOTIFY_RESUME) {
                clear_thread_flag(TIF_NOTIFY_RESUME);
                tracehook_notify_resume(regs);
                if (current->replacement_session_keyring)
                        key_replace_session_keyring();
        }
}