arch/arc/proc/arc700/signal.c

/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * 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.
 *
 * vineetg: June 2010:
 *  =Reducing gen code footprint of do_signal which is getting bloated up
 *   due to gcc doing inlining of static fns in this file.
 *      -Synth sigret stub gen function now a seperate fn (never called)
 *       Will get rid of it altogether at some point
 *      -setup_rt_frame, create_sigret_stub, set_frame_exec forced noinline
 *       as they are never called in practise
 *
 * vineetg: Jan 2010 (Restarting of timer related syscalls)
 *
 * vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
 *  -do_signal() supports TIF_RESTORE_SIGMASK
 *  -do_signal() no loner needs oldset, required by OLD sys_sigsuspend
 *  -sys_rt_sigsuspend() now comes from generic code, so discard arch implemen
 *  -sys_sigsuspend() no longer needs to fudge ptregs, hence that arg removed
 *  -sys_sigsuspend() no longer loops for do_signal(), sets TIF_xxx and leaves
 *   the job to do_signal()
 *
 * vineetg: July 2009
 *  -Modified Code to support the uClibc provided userland sigreturn stub
 *   to avoid kernel synthesing it on user stack at runtime, costing TLB
 *   probes and Cache line flushes.
 *  -And just in case uClibc doesnot provide the sigret stub, rewrote the PTE/TLB
 *   permission chg code to not duplicate the code in case of kernel stub
 *   straddling 2 pages
 *
 * vineetg: July 2009
 *  -In setup_sigrame( ) and restore_sigframe( ), save/restore of user regs
 *   in done in block copy rather than one word at a time.
 *   This saves around 2K of code and 500 lines of asm in just 2 functions,
 *   and LMB lat_sig "catch" numbers are lot better
 *
 * rajeshwarr: Feb 2009
 *  - Support for Realtime Signals
 *
 * vineetg: Feb 2009
 *  -small goofup in calculating if Frame straddles 2 pages
 *    now SUPER efficient
 *
 * vineetg: Aug 11th 2008: Bug #94183
 *  -ViXS were still seeing crashes when using insmod to load drivers.
 *   It turned out that the code to change Execute permssions for TLB entries
 *   of user was not guarded for interrupts (mod_tlb_permission)
 *   This was cauing TLB entries to be overwritten on unrelated indexes
 *
 * Vineetg: July 15th 2008: Bug #94183
 *  -Exception happens in Delay slot of a JMP, and before user space resumes,
 *   Signal is delivered (Ctrl + C) = >SIGINT.
 *   setup_frame( ) sets up PC,SP,BLINK to enable user space signal handler
 *   to run, but doesn't clear the Delay slot bit from status32. As a result,
 *   on resuming user mode, signal handler branches off to BTA of orig JMP
 *  -FIX: clear the DE bit from status32 in setup_frame( )
 *
 * Rahul Trivedi, Kanika Nema: Codito Technologies 2004
 */

#include <linux/signal.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/personality.h>
#include <linux/freezer.h>
#include <asm/ucontext.h>
#include <asm/uaccess.h>

/* for changing permissions of stackpage*/
#include <asm/tlb.h>
#include <asm/cacheflush.h>

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

#define EXEC_DISABLE 0
#define EXEC_ENABLE 1

static void noinline
set_frame_exec(unsigned long vaddr, unsigned int exec_enable);


/*
 * 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)
{
    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);

    current->state = TASK_INTERRUPTIBLE;
    schedule();
    set_thread_flag(TIF_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;
    int err;

    if (act) {
        old_sigset_t mask;

        if (!access_ok(VERIFY_READ, act, sizeof(*act)))
            return -EFAULT;

        err = __get_user(new_ka.sa.sa_handler, &act->sa_handler);
        err |= __get_user(new_ka.sa.sa_restorer, &act->sa_restorer);
        err |= __get_user(new_ka.sa.sa_flags, &act->sa_flags);
        err |= __get_user(mask, &act->sa_mask);
        if (err)
            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)))
            return -EFAULT;

        err = __put_user(old_ka.sa.sa_handler, &oact->sa_handler);
        err |= __put_user(old_ka.sa.sa_restorer, &oact->sa_restorer);
        err |= __put_user(old_ka.sa.sa_flags, &oact->sa_flags);
        err |= __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask);
        if (err)
            return -EFAULT;
    }

    return ret;
}

asmlinkage int
sys_sigaltstack(const stack_t * uss, stack_t * uoss)
{
    struct pt_regs *regs = task_pt_regs(current);
    return do_sigaltstack(uss, uoss, regs->sp);
}

/*
 * Do a signal return; undo the signal stack.  These are aligned to 64-bit.
 */
struct sigframe {
    struct ucontext uc;
#define MAGIC_USERLAND_STUB     0x11091976
#define MAGIC_KERNEL_SYNTH_STUB 0x07302004
    unsigned int sigret_magic;
    unsigned long retcode[5];
};

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

static int restore_sigframe(struct pt_regs *regs, struct sigframe __user * sf)
{
    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);
    }

    {
        void *dst_start = &(regs->bta);
        const int sz1 = (void *)&(((struct pt_regs *)0)->r0) -
                        (void *)&(((struct pt_regs *)0)->bta) + 4;

        void *src_start = &(sf->uc.uc_mcontext.bta);
        err |= __copy_from_user(dst_start, src_start, sz1);
    }

    err |= __get_user(regs->sp, &sf->uc.uc_mcontext.sp);

    take_snap(SNAP_SIGRETURN, 0, 0);

    return err;
}

int sys_sigreturn(void)
{
    struct sigframe __user *frame;
    unsigned int sigret_magic;
    int err;
    struct pt_regs *regs = task_pt_regs(current);

    /* 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 word boundary,
     * then 'sp' should be word aligned here.  If it's
     * not, then the user is trying to mess with us.
     */
    if (regs->sp & 3)
        goto badframe;

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

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

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

    err = __get_user(sigret_magic, &frame->sigret_magic);
    if (err)
        goto badframe;

    /* If C-lib provided userland sigret stub, no need to do anything */
    if (MAGIC_USERLAND_STUB != sigret_magic) {

        /* If it's kernel sythesized sigret stub, need to undo
         *  the PTE/TLB changes for making stack executable
         */
        if (MAGIC_KERNEL_SYNTH_STUB == sigret_magic) {
            set_frame_exec((unsigned long)&frame->retcode, EXEC_DISABLE);
        }
        else {  /* user corrupted the signal stack */
            printk("sig stack corrupted");
            goto badframe;
        }
    }

    return regs->r0;

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

int sys_rt_sigreturn(void)
{
    struct rt_sigframe __user *frame;
    unsigned int sigret_magic;
    int err;
    struct pt_regs *regs = task_pt_regs(current);

    /* 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 word boundary,
     * then 'sp' should be word aligned here.  If it's
     * not, then the user is trying to mess with us.
     */
    if (regs->sp & 3)
        goto badframe;

    frame = ((struct rt_sigframe __user *)regs->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->sp) == -EFAULT)
        goto badframe;

    err = __get_user(sigret_magic, &frame->sig.sigret_magic);
    if (err)
        goto badframe;

    /* If C-lib provided userland sigret stub, no need to do anything */
    if (unlikely(MAGIC_USERLAND_STUB != sigret_magic)) {

        /* If it's kernel sythesized sigret stub, need to undo
         *  the PTE/TLB changes for making stack executable
         */
        if (MAGIC_KERNEL_SYNTH_STUB == sigret_magic) {
            set_frame_exec((unsigned long)&frame->sig.retcode, EXEC_DISABLE);
        }
        else {  /* user corrupted the signal stack */
            printk("sig stack corrupted");
            goto badframe;
        }
    }

    return regs->r0;

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

static int noinline
setup_sigframe(struct sigframe __user * sf, struct pt_regs *regs,
           sigset_t * set)
{
    int err;
    void *dst_start = &(sf->uc.uc_mcontext.bta);
    void *src_start = &(regs->bta);

    /* bta to r0 is laid out same in both pt_regs and sigcontext */
    const int sz1 = (void *)&(((struct pt_regs *)0)->r0) -
                        (void *)&(((struct pt_regs *)0)->bta) + 4;

    /* Bulk Copy the part of reg file which is common in layout in
     * both the structs
     */
    err = __copy_to_user(dst_start, src_start, sz1);

    /* Hand Copy whatever is left */
    err |= __put_user(regs->sp, &sf->uc.uc_mcontext.sp);

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

    return err;
}

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

    /* No matter what happens, 'sp' must be word
     * aligned otherwise nasty things could happen
     */

    /* 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 noinline
create_sigret_stub(struct k_sigaction *ka, struct pt_regs *regs,
                    struct sigframe __user *frame, unsigned long *retcode)
{
        unsigned int code;
        int err;

        /* A7 is middle endian ! */
        if (ka->sa.sa_flags & SA_SIGINFO)
            code = 0x1b42208a;        /* code for mov r8, __NR_RT_SIGRETURN */
        else
            code = 0x1dc1208a;        /* code for mov r8, __NR_SIGRETURN */
        err = __put_user(code, retcode);

        code = 0x003f226f;            /* code for trap0 */
        err |= __put_user(code, retcode + 1);
        code = 0x7000264a;            /* code for nop */
        err |= __put_user(code, retcode + 2);
        code = 0x7000264a;            /* code for nop */
        err |= __put_user(code, retcode + 3);

        err |= __put_user(MAGIC_KERNEL_SYNTH_STUB, &frame->sigret_magic);
        if (err)
            return err;

    /* To be able execute the code on the stack(retcode), we need to enable the
     * execute permissions of the stack: In the pte entry and in the TLB entry.
     */
        set_frame_exec((unsigned long)retcode, EXEC_ENABLE);
        return 0;
}

/* Set up to return from userspace signal handler back into kernel */
static int
setup_ret_from_usr_sighdlr(struct k_sigaction *ka, struct pt_regs *regs,
                    struct sigframe __user *frame)
{
    unsigned long *retcode;
    int err = 0;

    /* Setup for returning from signal handler(USER Mode => KERNEL Mode)*/

    /* If provided, use a stub already in userspace */
    if (likely(ka->sa.sa_flags & SA_RESTORER)) {
        retcode = (unsigned long *)ka->sa.sa_restorer;
        err = __put_user(MAGIC_USERLAND_STUB, &frame->sigret_magic);
    }
    else {  /* Note that with uClibc providing userland sigreturn stub,
               this code is more of a legacy and will not be executed.
               The really bad part was flushing the TLB and caches which
               we no longer have to do
             */
        retcode = frame->retcode;
        err = create_sigret_stub(ka, regs, frame, retcode);
    }

    if (err)
        return err;

    /* Modify critical regs, so that when control goes back to user-mode
     * it starts executing the user space Signal handler and when that handler
     * returns, it invokes sigreturn sys call
     */
    regs->blink = (unsigned long)retcode;
    regs->ret = (unsigned long)ka->sa.sa_handler;

    /* Bug 94183, Clear the DE bit, so that when signal handler
     * starts to run, it doesn't use BTA
     */
    regs->status32 &= ~STATUS_DE_MASK;
    regs->status32 |= STATUS_L_MASK;

    take_snap(SNAP_BEFORE_SIG, 0, 0);

    return 0;
}


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

    frame = get_sigframe(ka, regs, sizeof(struct sigframe));

    if (!frame)
        return 1;

    err = setup_sigframe(frame, regs, set);

    if(!err)
        err |= setup_ret_from_usr_sighdlr(ka, regs, frame);

    /* Arguements to the user Signal handler */
    regs->r0 = sig;

    /* User Stack for signal handler will be above the frame just carved */
    regs->sp = (unsigned long)frame;

    return err;
}

static int noinline
setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t * info,
    sigset_t * set, struct pt_regs *regs)
{
    struct rt_sigframe __user *rt_frame;
    stack_t stack;
    int err;

    rt_frame = get_sigframe(ka, regs, sizeof(struct rt_sigframe));

    if (!rt_frame)
        return 1;

    err = copy_siginfo_to_user(&rt_frame->info, info);
    err |= __put_user(0, &rt_frame->sig.uc.uc_flags);
    err |= __put_user(NULL, &rt_frame->sig.uc.uc_link);

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

    err |= setup_sigframe(&rt_frame->sig, regs, set);

    if (!err)
        err |= setup_ret_from_usr_sighdlr(ka, regs, &(rt_frame->sig));

    /* Arguements to the user Signal handler */
    regs->r0 = sig;
    regs->r1 = (unsigned long)&rt_frame->info;
    regs->r2 = (unsigned long)&rt_frame->sig.uc;

    /* User Stack for signal handler will be above the frame just carved */
    regs->sp = (unsigned long)rt_frame;

    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, int in_syscall)
{
    struct thread_info *thread = current_thread_info();
    unsigned long usig = sig;
    int ret;

    /* Syscall restarting based on the ret code and other criteria */
    if (in_syscall) {
        switch (regs->r0) {
        case -ERESTART_RESTARTBLOCK:
        case -ERESTARTNOHAND:
            /* ERESTARTNOHAND means that the syscall should
             * only be restarted if there was no handler for
             * the signal, and since we only get here if there
             * is a handler, we don't restart */
            regs->r0 = -EINTR;  // ERESTART_xxx is kernel internal so chg it
            break;

        case -ERESTARTSYS:
            /* ERESTARTSYS means to restart the syscall if
             * there is no handler or the handler was
             * registered with SA_RESTART */
            if (!(ka->sa.sa_flags & SA_RESTART)) {
                regs->r0 = -EINTR;
                break;
            }
            /* fallthrough */

        case -ERESTARTNOINTR:
            /* ERESTARTNOINTR means that the syscall should
             * be called again after the signal handler returns. */
            /* Setup reg state just as it was before doing the trap
             * r0 has been clobbered with sys call ret code thus it needs to
             * be reloaded with orig value. Rest of relevant reg-file
             * r8 (syscall num) and
             * (r1 - r7) will be reset to their orig user space value when
             * we ret from kernel
             */
            regs->r0 = regs->orig_r0;   // No need to worry abt ERESTART_xxx conv
                                        // as nobody is looking at it
                                        // Since swi is re-executed, setup r0
                                        // with the first sys call arg in orig_r0
            regs->ret -= 4;
            break;
        }
    }

    if (thread->exec_domain && thread->exec_domain->signal_invmap && usig < 32)
        usig = thread->exec_domain->signal_invmap[usig];

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

    if (ret) {
        force_sigsegv(sig, current);
        return ret;
    }

    /* Block the signal if we are successful */
    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);

    return ret;
}

/* 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.
 */
void do_signal(struct pt_regs *regs)
{
    struct k_sigaction ka;
    siginfo_t info;
    int signr;
    sigset_t * oldset;
    int insyscall;

    if (try_to_freeze())
        goto no_signal;

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

    signr = get_signal_to_deliver(&info, &ka, regs, NULL);

    /* Are we from a system call? */
    insyscall = in_syscall(regs);

    if (signr > 0) {
        if (handle_signal(signr, &ka, &info, oldset, regs, insyscall) == 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 (insyscall) {
        /* No handler for syscall: restart it */
        if (regs->r0 == -ERESTARTNOHAND ||
            regs->r0 == -ERESTARTSYS ||
            regs->r0 == -ERESTARTNOINTR) {
            regs->r0 = regs->orig_r0;
            regs->ret -= 4;
        }
        else if (regs->r0 == -ERESTART_RESTARTBLOCK) {
            regs->r8 = __NR_restart_syscall;
            regs->ret -= 4;
        }
    }

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

static void noinline
mod_tlb_permission(unsigned long frame_vaddr, struct mm_struct *mm,
               int exec_or_not)
{
    unsigned long frame_tlbpd1;
    unsigned int flags, asid;

    if (!mm) return;
    local_irq_save(flags);

    asid = mm->context.asid;

    frame_vaddr = frame_vaddr & PAGE_MASK;
    /* get the ASID */
    frame_vaddr = frame_vaddr | (asid & 0xff);
    write_new_aux_reg(ARC_REG_TLBPD0, frame_vaddr);
    write_new_aux_reg(ARC_REG_TLBCOMMAND, TLBProbe);

    if (read_new_aux_reg(ARC_REG_TLBINDEX) != TLB_LKUP_ERR) {
        write_new_aux_reg(ARC_REG_TLBCOMMAND, TLBRead);
        frame_tlbpd1 = read_new_aux_reg(ARC_REG_TLBPD1);

        if (EXEC_DISABLE == exec_or_not) {
            /* disable execute permissions for the user stack */
            frame_tlbpd1 = frame_tlbpd1 & ~_PAGE_EXECUTE;
        }
        else {
            /* enable execute */
            frame_tlbpd1 = frame_tlbpd1 | _PAGE_EXECUTE;
        }

        write_new_aux_reg(ARC_REG_TLBPD1, frame_tlbpd1);
        write_new_aux_reg(ARC_REG_TLBCOMMAND, TLBWrite);
    }

    local_irq_restore(flags);
}


static void noinline
set_frame_exec(unsigned long vaddr, unsigned int exec_enable)
{
    unsigned long paddr, vaddr_pg, off_from_pg_start;
    pgd_t *pgdp;
    pud_t *pudp;
    pmd_t *pmdp;
    pte_t *ptep, pte;
    unsigned long size_on_pg, size_on_pg2;
    unsigned long fr_sz=sizeof(((struct sigframe *)(0))->retcode);

    off_from_pg_start = vaddr - (vaddr & PAGE_MASK);
    size_on_pg = min(fr_sz, PAGE_SIZE - off_from_pg_start);
    size_on_pg2 = fr_sz - size_on_pg;

do_per_page:

    vaddr_pg = vaddr & PAGE_MASK;       /* Get the virtual page address */

    /* Get the physical page address for the virtual page address*/
    pgdp = pgd_offset_fast(current->mm, vaddr_pg),
    pudp = pud_offset(pgdp, vaddr_pg);
    pmdp = pmd_offset(pudp, vaddr_pg);
    ptep = pte_offset(pmdp, vaddr_pg);

    /* Set the Execution Permission in the pte entry*/
    pte = *ptep;
    if (exec_enable)
        pte = pte_mkexec(pte);
    else
        pte = pte_exprotect(pte);
    set_pte(ptep, pte);

    /* Get the physical page address */
    paddr = (vaddr & ~PAGE_MASK) | (pte_val(pte) & PAGE_MASK);

    /* Flush dcache line, and inv Icache line for frame->retcode */
    flush_icache_range_vaddr(paddr, vaddr, size_on_pg);

    mod_tlb_permission(vaddr_pg, current->mm, exec_enable);

    if (size_on_pg2) {
        vaddr = vaddr_pg + PAGE_SIZE;
        size_on_pg = size_on_pg2;
        size_on_pg2 = 0;
        goto do_per_page;
    }
}

void __init arc_verify_sig_sz(void)
{
    struct sigframe __user sf;
    struct pt_regs regs;

    void *src_end = &(regs.r0);
    void *src_start = &(regs.bta);
    void *dst_end = &(sf.uc.uc_mcontext.r0);
    void *dst_start = &(sf.uc.uc_mcontext.bta);

    unsigned int sz1 = src_end - src_start + 4;
    unsigned int sz2 = dst_end - dst_start + 4;

    if(sz1 != sz2) {
        printk_init("Signals block copy code buggy\n");
        panic("\n");
    }
}