// SPDX-License-Identifier: GPL-2.0
/*  arch/sparc64/kernel/signal32.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
 *  Copyright (C) 1996 Miguel de Icaza (miguel@nuclecu.unam.mx)
 *  Copyright (C) 1997 Eddie C. Dost   (ecd@skynet.be)
 *  Copyright (C) 1997,1998 Jakub Jelinek   (jj@sunsite.mff.cuni.cz)
 */

#include <linux/sched.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/mm.h>
#include <linux/tty.h>
#include <linux/binfmts.h>
#include <linux/compat.h>
#include <linux/bitops.h>
#include <linux/tracehook.h>

#include <linux/uaccess.h>
#include <asm/ptrace.h>
#include <asm/pgtable.h>
#include <asm/psrcompat.h>
#include <asm/fpumacro.h>
#include <asm/visasm.h>
#include <asm/compat_signal.h>
#include <asm/switch_to.h>

#include "sigutil.h"
#include "kernel.h"

/* This magic should be in g_upper[0] for all upper parts
 * to be valid.
 */
#define SIGINFO_EXTRA_V8PLUS_MAGIC      0x130e269
typedef struct {
        unsigned int g_upper[8];
        unsigned int o_upper[8];
        unsigned int asi;
} siginfo_extra_v8plus_t;

struct signal_frame32 {
        struct sparc_stackf32   ss;
        __siginfo32_t           info;
        /* __siginfo_fpu_t * */ u32 fpu_save;
        unsigned int            insns[2];
        unsigned int            extramask[_COMPAT_NSIG_WORDS - 1];
        unsigned int            extra_size; /* Should be sizeof(siginfo_extra_v8plus_t) */
        /* Only valid if (info.si_regs.psr & (PSR_VERS|PSR_IMPL)) == PSR_V8PLUS */
        siginfo_extra_v8plus_t  v8plus;
        /* __siginfo_rwin_t * */u32 rwin_save;
} __attribute__((aligned(8)));

struct rt_signal_frame32 {
        struct sparc_stackf32   ss;
        compat_siginfo_t        info;
        struct pt_regs32        regs;
        compat_sigset_t         mask;
        /* __siginfo_fpu_t * */ u32 fpu_save;
        unsigned int            insns[2];
        compat_stack_t          stack;
        unsigned int            extra_size; /* Should be sizeof(siginfo_extra_v8plus_t) */
        /* Only valid if (regs.psr & (PSR_VERS|PSR_IMPL)) == PSR_V8PLUS */
        siginfo_extra_v8plus_t  v8plus;
        /* __siginfo_rwin_t * */u32 rwin_save;
} __attribute__((aligned(8)));

/* Checks if the fp is valid.  We always build signal frames which are
 * 16-byte aligned, therefore we can always enforce that the restore
 * frame has that property as well.
 */
static bool invalid_frame_pointer(void __user *fp, int fplen)
{
        if ((((unsigned long) fp) & 15) ||
            ((unsigned long)fp) > 0x100000000ULL - fplen)
                return true;
        return false;
}

void do_sigreturn32(struct pt_regs *regs)
{
        struct signal_frame32 __user *sf;
        compat_uptr_t fpu_save;
        compat_uptr_t rwin_save;
        unsigned int psr, ufp;
        unsigned int pc, npc;
        sigset_t set;
        compat_sigset_t seta;
        int err, i;
        
        /* Always make any pending restarted system calls return -EINTR */
        current->restart_block.fn = do_no_restart_syscall;

        synchronize_user_stack();

        regs->u_regs[UREG_FP] &= 0x00000000ffffffffUL;
        sf = (struct signal_frame32 __user *) regs->u_regs[UREG_FP];

        /* 1. Make sure we are not getting garbage from the user */
        if (invalid_frame_pointer(sf, sizeof(*sf)))
                goto segv;

        if (get_user(ufp, &sf->info.si_regs.u_regs[UREG_FP]))
                goto segv;

        if (ufp & 0x7)
                goto segv;

        if (__get_user(pc, &sf->info.si_regs.pc) ||
            __get_user(npc, &sf->info.si_regs.npc))
                goto segv;

        if ((pc | npc) & 3)
                goto segv;

        if (test_thread_flag(TIF_32BIT)) {
                pc &= 0xffffffff;
                npc &= 0xffffffff;
        }
        regs->tpc = pc;
        regs->tnpc = npc;

        /* 2. Restore the state */
        err = __get_user(regs->y, &sf->info.si_regs.y);
        err |= __get_user(psr, &sf->info.si_regs.psr);

        for (i = UREG_G1; i <= UREG_I7; i++)
                err |= __get_user(regs->u_regs[i], &sf->info.si_regs.u_regs[i]);
        if ((psr & (PSR_VERS|PSR_IMPL)) == PSR_V8PLUS) {
                err |= __get_user(i, &sf->v8plus.g_upper[0]);
                if (i == SIGINFO_EXTRA_V8PLUS_MAGIC) {
                        unsigned long asi;

                        for (i = UREG_G1; i <= UREG_I7; i++)
                                err |= __get_user(((u32 *)regs->u_regs)[2*i], &sf->v8plus.g_upper[i]);
                        err |= __get_user(asi, &sf->v8plus.asi);
                        regs->tstate &= ~TSTATE_ASI;
                        regs->tstate |= ((asi & 0xffUL) << 24UL);
                }
        }

        /* User can only change condition codes in %tstate. */
        regs->tstate &= ~(TSTATE_ICC|TSTATE_XCC);
        regs->tstate |= psr_to_tstate_icc(psr);

        /* Prevent syscall restart.  */
        pt_regs_clear_syscall(regs);

        err |= __get_user(fpu_save, &sf->fpu_save);
        if (!err && fpu_save)
                err |= restore_fpu_state(regs, compat_ptr(fpu_save));
        err |= __get_user(rwin_save, &sf->rwin_save);
        if (!err && rwin_save) {
                if (restore_rwin_state(compat_ptr(rwin_save)))
                        goto segv;
        }
        err |= __get_user(seta.sig[0], &sf->info.si_mask);
        err |= copy_from_user(&seta.sig[1], &sf->extramask,
                              (_COMPAT_NSIG_WORDS - 1) * sizeof(unsigned int));
        if (err)
                goto segv;

        set.sig[0] = seta.sig[0] + (((long)seta.sig[1]) << 32);
        set_current_blocked(&set);
        return;

segv:
        force_sig(SIGSEGV, current);
}

asmlinkage void do_rt_sigreturn32(struct pt_regs *regs)
{
        struct rt_signal_frame32 __user *sf;
        unsigned int psr, pc, npc, ufp;
        compat_uptr_t fpu_save;
        compat_uptr_t rwin_save;
        sigset_t set;
        int err, i;
        
        /* Always make any pending restarted system calls return -EINTR */
        current->restart_block.fn = do_no_restart_syscall;

        synchronize_user_stack();
        regs->u_regs[UREG_FP] &= 0x00000000ffffffffUL;
        sf = (struct rt_signal_frame32 __user *) regs->u_regs[UREG_FP];

        /* 1. Make sure we are not getting garbage from the user */
        if (invalid_frame_pointer(sf, sizeof(*sf)))
                goto segv;

        if (get_user(ufp, &sf->regs.u_regs[UREG_FP]))
                goto segv;

        if (ufp & 0x7)
                goto segv;

        if (__get_user(pc, &sf->regs.pc) || 
            __get_user(npc, &sf->regs.npc))
                goto segv;

        if ((pc | npc) & 3)
                goto segv;

        if (test_thread_flag(TIF_32BIT)) {
                pc &= 0xffffffff;
                npc &= 0xffffffff;
        }
        regs->tpc = pc;
        regs->tnpc = npc;

        /* 2. Restore the state */
        err = __get_user(regs->y, &sf->regs.y);
        err |= __get_user(psr, &sf->regs.psr);
        
        for (i = UREG_G1; i <= UREG_I7; i++)
                err |= __get_user(regs->u_regs[i], &sf->regs.u_regs[i]);
        if ((psr & (PSR_VERS|PSR_IMPL)) == PSR_V8PLUS) {
                err |= __get_user(i, &sf->v8plus.g_upper[0]);
                if (i == SIGINFO_EXTRA_V8PLUS_MAGIC) {
                        unsigned long asi;

                        for (i = UREG_G1; i <= UREG_I7; i++)
                                err |= __get_user(((u32 *)regs->u_regs)[2*i], &sf->v8plus.g_upper[i]);
                        err |= __get_user(asi, &sf->v8plus.asi);
                        regs->tstate &= ~TSTATE_ASI;
                        regs->tstate |= ((asi & 0xffUL) << 24UL);
                }
        }

        /* User can only change condition codes in %tstate. */
        regs->tstate &= ~(TSTATE_ICC|TSTATE_XCC);
        regs->tstate |= psr_to_tstate_icc(psr);

        /* Prevent syscall restart.  */
        pt_regs_clear_syscall(regs);

        err |= __get_user(fpu_save, &sf->fpu_save);
        if (!err && fpu_save)
                err |= restore_fpu_state(regs, compat_ptr(fpu_save));
        err |= get_compat_sigset(&set, &sf->mask);
        err |= compat_restore_altstack(&sf->stack);
        if (err)
                goto segv;
                
        err |= __get_user(rwin_save, &sf->rwin_save);
        if (!err && rwin_save) {
                if (restore_rwin_state(compat_ptr(rwin_save)))
                        goto segv;
        }

        set_current_blocked(&set);
        return;
segv:
        force_sig(SIGSEGV, current);
}

static void __user *get_sigframe(struct ksignal *ksig, struct pt_regs *regs, unsigned long framesize)
{
        unsigned long sp;
        
        regs->u_regs[UREG_FP] &= 0x00000000ffffffffUL;
        sp = regs->u_regs[UREG_FP];
        
        /*
         * If we are on the alternate signal stack and would overflow it, don't.
         * Return an always-bogus address instead so we will die with SIGSEGV.
         */
        if (on_sig_stack(sp) && !likely(on_sig_stack(sp - framesize)))
                return (void __user *) -1L;

        /* This is the X/Open sanctioned signal stack switching.  */
        sp = sigsp(sp, ksig) - framesize;

        /* Always align the stack frame.  This handles two cases.  First,
         * sigaltstack need not be mindful of platform specific stack
         * alignment.  Second, if we took this signal because the stack
         * is not aligned properly, we'd like to take the signal cleanly
         * and report that.
         */
        sp &= ~15UL;

        return (void __user *) sp;
}

/* The I-cache flush instruction only works in the primary ASI, which
 * right now is the nucleus, aka. kernel space.
 *
 * Therefore we have to kick the instructions out using the kernel
 * side linear mapping of the physical address backing the user
 * instructions.
 */
static void flush_signal_insns(unsigned long address)
{
        unsigned long pstate, paddr;
        pte_t *ptep, pte;
        pgd_t *pgdp;
        pud_t *pudp;
        pmd_t *pmdp;

        /* Commit all stores of the instructions we are about to flush.  */
        wmb();

        /* Disable cross-call reception.  In this way even a very wide
         * munmap() on another cpu can't tear down the page table
         * hierarchy from underneath us, since that can't complete
         * until the IPI tlb flush returns.
         */

        __asm__ __volatile__("rdpr %%pstate, %0" : "=r" (pstate));
        __asm__ __volatile__("wrpr %0, %1, %%pstate"
                                : : "r" (pstate), "i" (PSTATE_IE));

        pgdp = pgd_offset(current->mm, address);
        if (pgd_none(*pgdp))
                goto out_irqs_on;
        pudp = pud_offset(pgdp, address);
        if (pud_none(*pudp))
                goto out_irqs_on;
        pmdp = pmd_offset(pudp, address);
        if (pmd_none(*pmdp))
                goto out_irqs_on;

        ptep = pte_offset_map(pmdp, address);
        pte = *ptep;
        if (!pte_present(pte))
                goto out_unmap;

        paddr = (unsigned long) page_address(pte_page(pte));

        __asm__ __volatile__("flush     %0 + %1"
                             : /* no outputs */
                             : "r" (paddr),
                               "r" (address & (PAGE_SIZE - 1))
                             : "memory");

out_unmap:
        pte_unmap(ptep);
out_irqs_on:
        __asm__ __volatile__("wrpr %0, 0x0, %%pstate" : : "r" (pstate));

}

static int setup_frame32(struct ksignal *ksig, struct pt_regs *regs,
                         sigset_t *oldset)
{
        struct signal_frame32 __user *sf;
        int i, err, wsaved;
        void __user *tail;
        int sigframe_size;
        u32 psr;
        compat_sigset_t seta;

        /* 1. Make sure everything is clean */
        synchronize_user_stack();
        save_and_clear_fpu();
        
        wsaved = get_thread_wsaved();

        sigframe_size = sizeof(*sf);
        if (current_thread_info()->fpsaved[0] & FPRS_FEF)
                sigframe_size += sizeof(__siginfo_fpu_t);
        if (wsaved)
                sigframe_size += sizeof(__siginfo_rwin_t);

        sf = (struct signal_frame32 __user *)
                get_sigframe(ksig, regs, sigframe_size);
        
        if (invalid_frame_pointer(sf, sigframe_size)) {
                if (show_unhandled_signals)
                        pr_info("%s[%d] bad frame in setup_frame32: %08lx TPC %08lx O7 %08lx\n",
                                current->comm, current->pid, (unsigned long)sf,
                                regs->tpc, regs->u_regs[UREG_I7]);
                force_sigsegv(ksig->sig, current);
                return -EINVAL;
        }

        tail = (sf + 1);

        /* 2. Save the current process state */
        if (test_thread_flag(TIF_32BIT)) {
                regs->tpc &= 0xffffffff;
                regs->tnpc &= 0xffffffff;
        }
        err  = put_user(regs->tpc, &sf->info.si_regs.pc);
        err |= __put_user(regs->tnpc, &sf->info.si_regs.npc);
        err |= __put_user(regs->y, &sf->info.si_regs.y);
        psr = tstate_to_psr(regs->tstate);
        if (current_thread_info()->fpsaved[0] & FPRS_FEF)
                psr |= PSR_EF;
        err |= __put_user(psr, &sf->info.si_regs.psr);
        for (i = 0; i < 16; i++)
                err |= __put_user(regs->u_regs[i], &sf->info.si_regs.u_regs[i]);
        err |= __put_user(sizeof(siginfo_extra_v8plus_t), &sf->extra_size);
        err |= __put_user(SIGINFO_EXTRA_V8PLUS_MAGIC, &sf->v8plus.g_upper[0]);
        for (i = 1; i < 16; i++)
                err |= __put_user(((u32 *)regs->u_regs)[2*i],
                                  &sf->v8plus.g_upper[i]);
        err |= __put_user((regs->tstate & TSTATE_ASI) >> 24UL,
                          &sf->v8plus.asi);

        if (psr & PSR_EF) {
                __siginfo_fpu_t __user *fp = tail;
                tail += sizeof(*fp);
                err |= save_fpu_state(regs, fp);
                err |= __put_user((u64)fp, &sf->fpu_save);
        } else {
                err |= __put_user(0, &sf->fpu_save);
        }
        if (wsaved) {
                __siginfo_rwin_t __user *rwp = tail;
                tail += sizeof(*rwp);
                err |= save_rwin_state(wsaved, rwp);
                err |= __put_user((u64)rwp, &sf->rwin_save);
                set_thread_wsaved(0);
        } else {
                err |= __put_user(0, &sf->rwin_save);
        }

        /* If these change we need to know - assignments to seta relies on these sizes */
        BUILD_BUG_ON(_NSIG_WORDS != 1);
        BUILD_BUG_ON(_COMPAT_NSIG_WORDS != 2);
        seta.sig[1] = (oldset->sig[0] >> 32);
        seta.sig[0] = oldset->sig[0];

        err |= __put_user(seta.sig[0], &sf->info.si_mask);
        err |= __copy_to_user(sf->extramask, &seta.sig[1],
                              (_COMPAT_NSIG_WORDS - 1) * sizeof(unsigned int));

        if (!wsaved) {
                err |= copy_in_user((u32 __user *)sf,
                                    (u32 __user *)(regs->u_regs[UREG_FP]),
                                    sizeof(struct reg_window32));
        } else {
                struct reg_window *rp;

                rp = &current_thread_info()->reg_window[wsaved - 1];
                for (i = 0; i < 8; i++)
                        err |= __put_user(rp->locals[i], &sf->ss.locals[i]);
                for (i = 0; i < 6; i++)
                        err |= __put_user(rp->ins[i], &sf->ss.ins[i]);
                err |= __put_user(rp->ins[6], &sf->ss.fp);
                err |= __put_user(rp->ins[7], &sf->ss.callers_pc);
        }       
        if (err)
                return err;

        /* 3. signal handler back-trampoline and parameters */
        regs->u_regs[UREG_FP] = (unsigned long) sf;
        regs->u_regs[UREG_I0] = ksig->sig;
        regs->u_regs[UREG_I1] = (unsigned long) &sf->info;
        regs->u_regs[UREG_I2] = (unsigned long) &sf->info;

        /* 4. signal handler */
        regs->tpc = (unsigned long) ksig->ka.sa.sa_handler;
        regs->tnpc = (regs->tpc + 4);
        if (test_thread_flag(TIF_32BIT)) {
                regs->tpc &= 0xffffffff;
                regs->tnpc &= 0xffffffff;
        }

        /* 5. return to kernel instructions */
        if (ksig->ka.ka_restorer) {
                regs->u_regs[UREG_I7] = (unsigned long)ksig->ka.ka_restorer;
        } else {
                unsigned long address = ((unsigned long)&(sf->insns[0]));

                regs->u_regs[UREG_I7] = (unsigned long) (&(sf->insns[0]) - 2);
        
                err  = __put_user(0x821020d8, &sf->insns[0]); /*mov __NR_sigreturn, %g1*/
                err |= __put_user(0x91d02010, &sf->insns[1]); /*t 0x10*/
                if (err)
                        return err;
                flush_signal_insns(address);
        }
        return 0;
}

static int setup_rt_frame32(struct ksignal *ksig, struct pt_regs *regs,
                            sigset_t *oldset)
{
        struct rt_signal_frame32 __user *sf;
        int i, err, wsaved;
        void __user *tail;
        int sigframe_size;
        u32 psr;

        /* 1. Make sure everything is clean */
        synchronize_user_stack();
        save_and_clear_fpu();
        
        wsaved = get_thread_wsaved();

        sigframe_size = sizeof(*sf);
        if (current_thread_info()->fpsaved[0] & FPRS_FEF)
                sigframe_size += sizeof(__siginfo_fpu_t);
        if (wsaved)
                sigframe_size += sizeof(__siginfo_rwin_t);

        sf = (struct rt_signal_frame32 __user *)
                get_sigframe(ksig, regs, sigframe_size);
        
        if (invalid_frame_pointer(sf, sigframe_size)) {
                if (show_unhandled_signals)
                        pr_info("%s[%d] bad frame in setup_rt_frame32: %08lx TPC %08lx O7 %08lx\n",
                                current->comm, current->pid, (unsigned long)sf,
                                regs->tpc, regs->u_regs[UREG_I7]);
                force_sigsegv(ksig->sig, current);
                return -EINVAL;
        }

        tail = (sf + 1);

        /* 2. Save the current process state */
        if (test_thread_flag(TIF_32BIT)) {
                regs->tpc &= 0xffffffff;
                regs->tnpc &= 0xffffffff;
        }
        err  = put_user(regs->tpc, &sf->regs.pc);
        err |= __put_user(regs->tnpc, &sf->regs.npc);
        err |= __put_user(regs->y, &sf->regs.y);
        psr = tstate_to_psr(regs->tstate);
        if (current_thread_info()->fpsaved[0] & FPRS_FEF)
                psr |= PSR_EF;
        err |= __put_user(psr, &sf->regs.psr);
        for (i = 0; i < 16; i++)
                err |= __put_user(regs->u_regs[i], &sf->regs.u_regs[i]);
        err |= __put_user(sizeof(siginfo_extra_v8plus_t), &sf->extra_size);
        err |= __put_user(SIGINFO_EXTRA_V8PLUS_MAGIC, &sf->v8plus.g_upper[0]);
        for (i = 1; i < 16; i++)
                err |= __put_user(((u32 *)regs->u_regs)[2*i],
                                  &sf->v8plus.g_upper[i]);
        err |= __put_user((regs->tstate & TSTATE_ASI) >> 24UL,
                          &sf->v8plus.asi);

        if (psr & PSR_EF) {
                __siginfo_fpu_t __user *fp = tail;
                tail += sizeof(*fp);
                err |= save_fpu_state(regs, fp);
                err |= __put_user((u64)fp, &sf->fpu_save);
        } else {
                err |= __put_user(0, &sf->fpu_save);
        }
        if (wsaved) {
                __siginfo_rwin_t __user *rwp = tail;
                tail += sizeof(*rwp);
                err |= save_rwin_state(wsaved, rwp);
                err |= __put_user((u64)rwp, &sf->rwin_save);
                set_thread_wsaved(0);
        } else {
                err |= __put_user(0, &sf->rwin_save);
        }

        /* Update the siginfo structure.  */
        err |= copy_siginfo_to_user32(&sf->info, &ksig->info);
        
        /* Setup sigaltstack */
        err |= __compat_save_altstack(&sf->stack, regs->u_regs[UREG_FP]);

        err |= put_compat_sigset(&sf->mask, oldset, sizeof(compat_sigset_t));

        if (!wsaved) {
                err |= copy_in_user((u32 __user *)sf,
                                    (u32 __user *)(regs->u_regs[UREG_FP]),
                                    sizeof(struct reg_window32));
        } else {
                struct reg_window *rp;

                rp = &current_thread_info()->reg_window[wsaved - 1];
                for (i = 0; i < 8; i++)
                        err |= __put_user(rp->locals[i], &sf->ss.locals[i]);
                for (i = 0; i < 6; i++)
                        err |= __put_user(rp->ins[i], &sf->ss.ins[i]);
                err |= __put_user(rp->ins[6], &sf->ss.fp);
                err |= __put_user(rp->ins[7], &sf->ss.callers_pc);
        }
        if (err)
                return err;
        
        /* 3. signal handler back-trampoline and parameters */
        regs->u_regs[UREG_FP] = (unsigned long) sf;
        regs->u_regs[UREG_I0] = ksig->sig;
        regs->u_regs[UREG_I1] = (unsigned long) &sf->info;
        regs->u_regs[UREG_I2] = (unsigned long) &sf->regs;

        /* 4. signal handler */
        regs->tpc = (unsigned long) ksig->ka.sa.sa_handler;
        regs->tnpc = (regs->tpc + 4);
        if (test_thread_flag(TIF_32BIT)) {
                regs->tpc &= 0xffffffff;
                regs->tnpc &= 0xffffffff;
        }

        /* 5. return to kernel instructions */
        if (ksig->ka.ka_restorer)
                regs->u_regs[UREG_I7] = (unsigned long)ksig->ka.ka_restorer;
        else {
                unsigned long address = ((unsigned long)&(sf->insns[0]));

                regs->u_regs[UREG_I7] = (unsigned long) (&(sf->insns[0]) - 2);
        
                /* mov __NR_rt_sigreturn, %g1 */
                err |= __put_user(0x82102065, &sf->insns[0]);

                /* t 0x10 */
                err |= __put_user(0x91d02010, &sf->insns[1]);
                if (err)
                        return err;

                flush_signal_insns(address);
        }
        return 0;
}

static inline void handle_signal32(struct ksignal *ksig, 
                                  struct pt_regs *regs)
{
        sigset_t *oldset = sigmask_to_save();
        int err;

        if (ksig->ka.sa.sa_flags & SA_SIGINFO)
                err = setup_rt_frame32(ksig, regs, oldset);
        else
                err = setup_frame32(ksig, regs, oldset);

        signal_setup_done(err, ksig, 0);
}

static inline void syscall_restart32(unsigned long orig_i0, struct pt_regs *regs,
                                     struct sigaction *sa)
{
        switch (regs->u_regs[UREG_I0]) {
        case ERESTART_RESTARTBLOCK:
        case ERESTARTNOHAND:
        no_system_call_restart:
                regs->u_regs[UREG_I0] = EINTR;
                regs->tstate |= TSTATE_ICARRY;
                break;
        case ERESTARTSYS:
                if (!(sa->sa_flags & SA_RESTART))
                        goto no_system_call_restart;
                /* fallthrough */
        case ERESTARTNOINTR:
                regs->u_regs[UREG_I0] = orig_i0;
                regs->tpc -= 4;
                regs->tnpc -= 4;
        }
}

/* 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.
 */
void do_signal32(struct pt_regs * regs)
{
        struct ksignal ksig;
        unsigned long orig_i0 = 0;
        int restart_syscall = 0;
        bool has_handler = get_signal(&ksig);

        if (pt_regs_is_syscall(regs) &&
            (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {
                restart_syscall = 1;
                orig_i0 = regs->u_regs[UREG_G6];
        }

        if (has_handler) {
                if (restart_syscall)
                        syscall_restart32(orig_i0, regs, &ksig.ka.sa);
                handle_signal32(&ksig, regs);
        } else {
                if (restart_syscall) {
                        switch (regs->u_regs[UREG_I0]) {
                        case ERESTARTNOHAND:
                        case ERESTARTSYS:
                        case ERESTARTNOINTR:
                                /* replay the system call when we are done */
                                regs->u_regs[UREG_I0] = orig_i0;
                                regs->tpc -= 4;
                                regs->tnpc -= 4;
                                pt_regs_clear_syscall(regs);
                                /* fall through */
                        case ERESTART_RESTARTBLOCK:
                                regs->u_regs[UREG_G1] = __NR_restart_syscall;
                                regs->tpc -= 4;
                                regs->tnpc -= 4;
                                pt_regs_clear_syscall(regs);
                        }
                }
                restore_saved_sigmask();
        }
}

struct sigstack32 {
        u32 the_stack;
        int cur_status;
};

asmlinkage int do_sys32_sigstack(u32 u_ssptr, u32 u_ossptr, unsigned long sp)
{
        struct sigstack32 __user *ssptr =
                (struct sigstack32 __user *)((unsigned long)(u_ssptr));
        struct sigstack32 __user *ossptr =
                (struct sigstack32 __user *)((unsigned long)(u_ossptr));
        int ret = -EFAULT;

        /* First see if old state is wanted. */
        if (ossptr) {
                if (put_user(current->sas_ss_sp + current->sas_ss_size,
                             &ossptr->the_stack) ||
                    __put_user(on_sig_stack(sp), &ossptr->cur_status))
                        goto out;
        }
        
        /* Now see if we want to update the new state. */
        if (ssptr) {
                u32 ss_sp;

                if (get_user(ss_sp, &ssptr->the_stack))
                        goto out;

                /* If the current stack was set with sigaltstack, don't
                 * swap stacks while we are on it.
                 */
                ret = -EPERM;
                if (current->sas_ss_sp && on_sig_stack(sp))
                        goto out;
                        
                /* Since we don't know the extent of the stack, and we don't
                 * track onstack-ness, but rather calculate it, we must
                 * presume a size.  Ho hum this interface is lossy.
                 */
                current->sas_ss_sp = (unsigned long)ss_sp - SIGSTKSZ;
                current->sas_ss_size = SIGSTKSZ;
        }
        
        ret = 0;
out:
        return ret;
}