arch/avr32/kernel/ptrace.c - linux - Git at Google

 /*
  * Copyright (C) 2004-2006 Atmel Corporation
  *
  * 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.
  */
 #undef DEBUG
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <linux/ptrace.h>
 #include <linux/errno.h>
 #include <linux/user.h>
 #include <linux/security.h>
 #include <linux/unistd.h>
 #include <linux/notifier.h>

 #include <asm/traps.h>
 #include <asm/uaccess.h>
 #include <asm/ocd.h>
 #include <asm/mmu_context.h>
 #include <linux/kdebug.h>

 static struct pt_regs *get_user_regs(struct task_struct *tsk)
 {
 	return (struct pt_regs *)((unsigned long)task_stack_page(tsk) +
 				  THREAD_SIZE - sizeof(struct pt_regs));
 }

 static void ptrace_single_step(struct task_struct *tsk)
 {
 	pr_debug("ptrace_single_step: pid=%u, PC=0x%08lx, SR=0x%08lx\n",
 		 tsk->pid, task_pt_regs(tsk)->pc, task_pt_regs(tsk)->sr);

 	/*
 	 * We can't schedule in Debug mode, so when TIF_BREAKPOINT is
 	 * set, the system call or exception handler will do a
 	 * breakpoint to enter monitor mode before returning to
 	 * userspace.
 	 *
 	 * The monitor code will then notice that TIF_SINGLE_STEP is
 	 * set and return to userspace with single stepping enabled.
 	 * The CPU will then enter monitor mode again after exactly
 	 * one instruction has been executed, and the monitor code
 	 * will then send a SIGTRAP to the process.
 	 */
 	set_tsk_thread_flag(tsk, TIF_BREAKPOINT);
 	set_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
 }

 /*
  * Called by kernel/ptrace.c when detaching
  *
  * Make sure any single step bits, etc. are not set
  */
 void ptrace_disable(struct task_struct *child)
 {
 	clear_tsk_thread_flag(child, TIF_SINGLE_STEP);
 	clear_tsk_thread_flag(child, TIF_BREAKPOINT);
 }

 /*
  * Read the word at offset "offset" into the task's "struct user". We
  * actually access the pt_regs struct stored on the kernel stack.
  */
 static int ptrace_read_user(struct task_struct *tsk, unsigned long offset,
 			    unsigned long __user *data)
 {
 	unsigned long *regs;
 	unsigned long value;

 	if (offset & 3 || offset >= sizeof(struct user)) {
 		printk("ptrace_read_user: invalid offset 0x%08lx\n", offset);
 		return -EIO;
 	}

 	regs = (unsigned long *)get_user_regs(tsk);

 	value = 0;
 	if (offset < sizeof(struct pt_regs))
 		value = regs[offset / sizeof(regs[0])];

 	pr_debug("ptrace_read_user(%s[%u], %#lx, %p) -> %#lx\n",
 		 tsk->comm, tsk->pid, offset, data, value);

 	return put_user(value, data);
 }

 /*
  * Write the word "value" to offset "offset" into the task's "struct
  * user". We actually access the pt_regs struct stored on the kernel
  * stack.
  */
 static int ptrace_write_user(struct task_struct *tsk, unsigned long offset,
 			     unsigned long value)
 {
 	unsigned long *regs;

 	pr_debug("ptrace_write_user(%s[%u], %#lx, %#lx)\n",
 			tsk->comm, tsk->pid, offset, value);

 	if (offset & 3 || offset >= sizeof(struct user)) {
 		pr_debug("  invalid offset 0x%08lx\n", offset);
 		return -EIO;
 	}

 	if (offset >= sizeof(struct pt_regs))
 		return 0;

 	regs = (unsigned long *)get_user_regs(tsk);
 	regs[offset / sizeof(regs[0])] = value;

 	return 0;
 }

 static int ptrace_getregs(struct task_struct *tsk, void __user *uregs)
 {
 	struct pt_regs *regs = get_user_regs(tsk);

 	return copy_to_user(uregs, regs, sizeof(*regs)) ? -EFAULT : 0;
 }

 static int ptrace_setregs(struct task_struct *tsk, const void __user *uregs)
 {
 	struct pt_regs newregs;
 	int ret;

 	ret = -EFAULT;
 	if (copy_from_user(&newregs, uregs, sizeof(newregs)) == 0) {
 		struct pt_regs *regs = get_user_regs(tsk);

 		ret = -EINVAL;
 		if (valid_user_regs(&newregs)) {
 			*regs = newregs;
 			ret = 0;
 		}
 	}

 	return ret;
 }

 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 {
 	int ret;

 	pr_debug("ptrace: Enabling monitor mode...\n");
 	ocd_write(DC, ocd_read(DC) | (1 << OCD_DC_MM_BIT)
 			| (1 << OCD_DC_DBE_BIT));

 	switch (request) {
 	/* Read the word at location addr in the child process */
 	case PTRACE_PEEKTEXT:
 	case PTRACE_PEEKDATA:
 		ret = generic_ptrace_peekdata(child, addr, data);
 		break;

 	case PTRACE_PEEKUSR:
 		ret = ptrace_read_user(child, addr,
 				       (unsigned long __user *)data);
 		break;

 	/* Write the word in data at location addr */
 	case PTRACE_POKETEXT:
 	case PTRACE_POKEDATA:
 		ret = generic_ptrace_pokedata(child, addr, data);
 		break;

 	case PTRACE_POKEUSR:
 		ret = ptrace_write_user(child, addr, data);
 		break;

 	/* continue and stop at next (return from) syscall */
 	case PTRACE_SYSCALL:
 	/* restart after signal */
 	case PTRACE_CONT:
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
 		if (request == PTRACE_SYSCALL)
 			set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		else
 			clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		child->exit_code = data;
 		/* XXX: Are we sure no breakpoints are active here? */
 		wake_up_process(child);
 		ret = 0;
 		break;

 	/*
 	 * Make the child exit. Best I can do is send it a
 	 * SIGKILL. Perhaps it should be put in the status that it
 	 * wants to exit.
 	 */
 	case PTRACE_KILL:
 		ret = 0;
 		if (child->exit_state == EXIT_ZOMBIE)
 			break;
 		child->exit_code = SIGKILL;
 		wake_up_process(child);
 		break;

 	/*
 	 * execute single instruction.
 	 */
 	case PTRACE_SINGLESTEP:
 		ret = -EIO;
 		if (!valid_signal(data))
 			break;
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
 		ptrace_single_step(child);
 		child->exit_code = data;
 		wake_up_process(child);
 		ret = 0;
 		break;

 	case PTRACE_GETREGS:
 		ret = ptrace_getregs(child, (void __user *)data);
 		break;

 	case PTRACE_SETREGS:
 		ret = ptrace_setregs(child, (const void __user *)data);
 		break;

 	default:
 		ret = ptrace_request(child, request, addr, data);
 		break;
 	}

 	return ret;
 }

 asmlinkage void syscall_trace(void)
 {
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
 		return;
 	if (!(current->ptrace & PT_PTRACED))
 		return;

 	/* The 0x80 provides a way for the tracing parent to
 	 * distinguish between a syscall stop and SIGTRAP delivery */
 	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
 				 ? 0x80 : 0));

 	/*
 	 * this isn't the same as continuing with a signal, but it
 	 * will do for normal use.  strace only continues with a
 	 * signal if the stopping signal is not SIGTRAP.  -brl
 	 */
 	if (current->exit_code) {
 		pr_debug("syscall_trace: sending signal %d to PID %u\n",
 			 current->exit_code, current->pid);
 		send_sig(current->exit_code, current, 1);
 		current->exit_code = 0;
 	}
 }

 /*
  * debug_trampoline() is an assembly stub which will store all user
  * registers on the stack and execute a breakpoint instruction.
  *
  * If we single-step into an exception handler which runs with
  * interrupts disabled the whole time so it doesn't have to check for
  * pending work, its return address will be modified so that it ends
  * up returning to debug_trampoline.
  *
  * If the exception handler decides to store the user context and
  * enable interrupts after all, it will restore the original return
  * address and status register value. Before it returns, it will
  * notice that TIF_BREAKPOINT is set and execute a breakpoint
  * instruction.
  */
 extern void debug_trampoline(void);

 asmlinkage struct pt_regs *do_debug(struct pt_regs *regs)
 {
 	struct thread_info	*ti;
 	unsigned long		trampoline_addr;
 	u32			status;
 	u32			ctrl;
 	int			code;

 	status = ocd_read(DS);
 	ti = current_thread_info();
 	code = TRAP_BRKPT;

 	pr_debug("do_debug: status=0x%08x PC=0x%08lx SR=0x%08lx tif=0x%08lx\n",
 			status, regs->pc, regs->sr, ti->flags);

 	if (!user_mode(regs)) {
 		unsigned long	die_val = DIE_BREAKPOINT;

 		if (status & (1 << OCD_DS_SSS_BIT))
 			die_val = DIE_SSTEP;

 		if (notify_die(die_val, "ptrace", regs, 0, 0, SIGTRAP)
 				== NOTIFY_STOP)
 			return regs;

 		if ((status & (1 << OCD_DS_SWB_BIT))
 				&& test_and_clear_ti_thread_flag(
 					ti, TIF_BREAKPOINT)) {
 			/*
 			 * Explicit breakpoint from trampoline or
 			 * exception/syscall/interrupt handler.
 			 *
 			 * The real saved regs are on the stack right
 			 * after the ones we saved on entry.
 			 */
 			regs++;
 			pr_debug("  -> TIF_BREAKPOINT done, adjusted regs:"
 					"PC=0x%08lx SR=0x%08lx\n",
 					regs->pc, regs->sr);
 			BUG_ON(!user_mode(regs));

 			if (test_thread_flag(TIF_SINGLE_STEP)) {
 				pr_debug("Going to do single step...\n");
 				return regs;
 			}

 			/*
 			 * No TIF_SINGLE_STEP means we're done
 			 * stepping over a syscall. Do the trap now.
 			 */
 			code = TRAP_TRACE;
 		} else if ((status & (1 << OCD_DS_SSS_BIT))
 				&& test_ti_thread_flag(ti, TIF_SINGLE_STEP)) {

 			pr_debug("Stepped into something, "
 					"setting TIF_BREAKPOINT...\n");
 			set_ti_thread_flag(ti, TIF_BREAKPOINT);

 			/*
 			 * We stepped into an exception, interrupt or
 			 * syscall handler. Some exception handlers
 			 * don't check for pending work, so we need to
 			 * set up a trampoline just in case.
 			 *
 			 * The exception entry code will undo the
 			 * trampoline stuff if it does a full context
 			 * save (which also means that it'll check for
 			 * pending work later.)
 			 */
 			if ((regs->sr & MODE_MASK) == MODE_EXCEPTION) {
 				trampoline_addr
 					= (unsigned long)&debug_trampoline;

 				pr_debug("Setting up trampoline...\n");
 				ti->rar_saved = sysreg_read(RAR_EX);
 				ti->rsr_saved = sysreg_read(RSR_EX);
 				sysreg_write(RAR_EX, trampoline_addr);
 				sysreg_write(RSR_EX, (MODE_EXCEPTION
 							| SR_EM | SR_GM));
 				BUG_ON(ti->rsr_saved & MODE_MASK);
 			}

 			/*
 			 * If we stepped into a system call, we
 			 * shouldn't do a single step after we return
 			 * since the return address is right after the
 			 * "scall" instruction we were told to step
 			 * over.
 			 */
 			if ((regs->sr & MODE_MASK) == MODE_SUPERVISOR) {
 				pr_debug("Supervisor; no single step\n");
 				clear_ti_thread_flag(ti, TIF_SINGLE_STEP);
 			}

 			ctrl = ocd_read(DC);
 			ctrl &= ~(1 << OCD_DC_SS_BIT);
 			ocd_write(DC, ctrl);

 			return regs;
 		} else {
 			printk(KERN_ERR "Unexpected OCD_DS value: 0x%08x\n",
 					status);
 			printk(KERN_ERR "Thread flags: 0x%08lx\n", ti->flags);
 			die("Unhandled debug trap in kernel mode",
 					regs, SIGTRAP);
 		}
 	} else if (status & (1 << OCD_DS_SSS_BIT)) {
 		/* Single step in user mode */
 		code = TRAP_TRACE;

 		ctrl = ocd_read(DC);
 		ctrl &= ~(1 << OCD_DC_SS_BIT);
 		ocd_write(DC, ctrl);
 	}

 	pr_debug("Sending SIGTRAP: code=%d PC=0x%08lx SR=0x%08lx\n",
 			code, regs->pc, regs->sr);

 	clear_thread_flag(TIF_SINGLE_STEP);
 	_exception(SIGTRAP, regs, code, instruction_pointer(regs));

 	return regs;
 }
	/*
	* Copyright (C) 2004-2006 Atmel Corporation
	*
	* 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.
	*/
	#undef DEBUG
	#include <linux/kernel.h>
	#include <linux/sched.h>
	#include <linux/mm.h>
	#include <linux/ptrace.h>
	#include <linux/errno.h>
	#include <linux/user.h>
	#include <linux/security.h>
	#include <linux/unistd.h>
	#include <linux/notifier.h>

	#include <asm/traps.h>
	#include <asm/uaccess.h>
	#include <asm/ocd.h>
	#include <asm/mmu_context.h>
	#include <linux/kdebug.h>

	static struct pt_regs get_user_regs(struct task_struct tsk)
	{
	return (struct pt_regs *)((unsigned long)task_stack_page(tsk) +
	THREAD_SIZE - sizeof(struct pt_regs));
	}

	static void ptrace_single_step(struct task_struct *tsk)
	{
	pr_debug("ptrace_single_step: pid=%u, PC=0x%08lx, SR=0x%08lx\n",
	tsk->pid, task_pt_regs(tsk)->pc, task_pt_regs(tsk)->sr);

	/*
	* We can't schedule in Debug mode, so when TIF_BREAKPOINT is
	* set, the system call or exception handler will do a
	* breakpoint to enter monitor mode before returning to
	* userspace.
	*
	* The monitor code will then notice that TIF_SINGLE_STEP is
	* set and return to userspace with single stepping enabled.
	* The CPU will then enter monitor mode again after exactly
	* one instruction has been executed, and the monitor code
	* will then send a SIGTRAP to the process.
	*/
	set_tsk_thread_flag(tsk, TIF_BREAKPOINT);
	set_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
	}

	/*
	* Called by kernel/ptrace.c when detaching
	*
	* Make sure any single step bits, etc. are not set
	*/
	void ptrace_disable(struct task_struct *child)
	{
	clear_tsk_thread_flag(child, TIF_SINGLE_STEP);
	clear_tsk_thread_flag(child, TIF_BREAKPOINT);
	}

	/*
	* Read the word at offset "offset" into the task's "struct user". We
	* actually access the pt_regs struct stored on the kernel stack.
	*/
	static int ptrace_read_user(struct task_struct *tsk, unsigned long offset,
	unsigned long __user *data)
	{
	unsigned long *regs;
	unsigned long value;

	if (offset & 3 \|\| offset >= sizeof(struct user)) {
	printk("ptrace_read_user: invalid offset 0x%08lx\n", offset);
	return -EIO;
	}

	regs = (unsigned long *)get_user_regs(tsk);

	value = 0;
	if (offset < sizeof(struct pt_regs))
	value = regs[offset / sizeof(regs[0])];

	pr_debug("ptrace_read_user(%s[%u], %#lx, %p) -> %#lx\n",
	tsk->comm, tsk->pid, offset, data, value);

	return put_user(value, data);
	}

	/*
	* Write the word "value" to offset "offset" into the task's "struct
	* user". We actually access the pt_regs struct stored on the kernel
	* stack.
	*/
	static int ptrace_write_user(struct task_struct *tsk, unsigned long offset,
	unsigned long value)
	{
	unsigned long *regs;

	pr_debug("ptrace_write_user(%s[%u], %#lx, %#lx)\n",
	tsk->comm, tsk->pid, offset, value);

	if (offset & 3 \|\| offset >= sizeof(struct user)) {
	pr_debug(" invalid offset 0x%08lx\n", offset);
	return -EIO;
	}

	if (offset >= sizeof(struct pt_regs))
	return 0;

	regs = (unsigned long *)get_user_regs(tsk);
	regs[offset / sizeof(regs[0])] = value;

	return 0;
	}

	static int ptrace_getregs(struct task_struct tsk, void __user uregs)
	{
	struct pt_regs *regs = get_user_regs(tsk);

	return copy_to_user(uregs, regs, sizeof(*regs)) ? -EFAULT : 0;
	}

	static int ptrace_setregs(struct task_struct tsk, const void __user uregs)
	{
	struct pt_regs newregs;
	int ret;

	ret = -EFAULT;
	if (copy_from_user(&newregs, uregs, sizeof(newregs)) == 0) {
	struct pt_regs *regs = get_user_regs(tsk);

	ret = -EINVAL;
	if (valid_user_regs(&newregs)) {
	*regs = newregs;
	ret = 0;
	}
	}

	return ret;
	}

	long arch_ptrace(struct task_struct *child, long request, long addr, long data)
	{
	int ret;

	pr_debug("ptrace: Enabling monitor mode...\n");
	ocd_write(DC, ocd_read(DC) \| (1 << OCD_DC_MM_BIT)
	\| (1 << OCD_DC_DBE_BIT));

	switch (request) {
	/* Read the word at location addr in the child process */
	case PTRACE_PEEKTEXT:
	case PTRACE_PEEKDATA:
	ret = generic_ptrace_peekdata(child, addr, data);
	break;

	case PTRACE_PEEKUSR:
	ret = ptrace_read_user(child, addr,
	(unsigned long __user *)data);
	break;

	/* Write the word in data at location addr */
	case PTRACE_POKETEXT:
	case PTRACE_POKEDATA:
	ret = generic_ptrace_pokedata(child, addr, data);
	break;

	case PTRACE_POKEUSR:
	ret = ptrace_write_user(child, addr, data);
	break;

	/* continue and stop at next (return from) syscall */
	case PTRACE_SYSCALL:
	/* restart after signal */
	case PTRACE_CONT:
	ret = -EIO;
	if (!valid_signal(data))
	break;
	if (request == PTRACE_SYSCALL)
	set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
	else
	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
	child->exit_code = data;
	/* XXX: Are we sure no breakpoints are active here? */
	wake_up_process(child);
	ret = 0;
	break;

	/*
	* Make the child exit. Best I can do is send it a
	* SIGKILL. Perhaps it should be put in the status that it
	* wants to exit.
	*/
	case PTRACE_KILL:
	ret = 0;
	if (child->exit_state == EXIT_ZOMBIE)
	break;
	child->exit_code = SIGKILL;
	wake_up_process(child);
	break;

	/*
	* execute single instruction.
	*/
	case PTRACE_SINGLESTEP:
	ret = -EIO;
	if (!valid_signal(data))
	break;
	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
	ptrace_single_step(child);
	child->exit_code = data;
	wake_up_process(child);
	ret = 0;
	break;

	case PTRACE_GETREGS:
	ret = ptrace_getregs(child, (void __user *)data);
	break;

	case PTRACE_SETREGS:
	ret = ptrace_setregs(child, (const void __user *)data);
	break;

	default:
	ret = ptrace_request(child, request, addr, data);
	break;
	}

	return ret;
	}

	asmlinkage void syscall_trace(void)
	{
	if (!test_thread_flag(TIF_SYSCALL_TRACE))
	return;
	if (!(current->ptrace & PT_PTRACED))
	return;

	/* The 0x80 provides a way for the tracing parent to
	* distinguish between a syscall stop and SIGTRAP delivery */
	ptrace_notify(SIGTRAP \| ((current->ptrace & PT_TRACESYSGOOD)
	? 0x80 : 0));

	/*
	* this isn't the same as continuing with a signal, but it
	* will do for normal use. strace only continues with a
	* signal if the stopping signal is not SIGTRAP. -brl
	*/
	if (current->exit_code) {
	pr_debug("syscall_trace: sending signal %d to PID %u\n",
	current->exit_code, current->pid);
	send_sig(current->exit_code, current, 1);
	current->exit_code = 0;
	}
	}

	/*
	* debug_trampoline() is an assembly stub which will store all user
	* registers on the stack and execute a breakpoint instruction.
	*
	* If we single-step into an exception handler which runs with
	* interrupts disabled the whole time so it doesn't have to check for
	* pending work, its return address will be modified so that it ends
	* up returning to debug_trampoline.
	*
	* If the exception handler decides to store the user context and
	* enable interrupts after all, it will restore the original return
	* address and status register value. Before it returns, it will
	* notice that TIF_BREAKPOINT is set and execute a breakpoint
	* instruction.
	*/
	extern void debug_trampoline(void);

	asmlinkage struct pt_regs do_debug(struct pt_regs regs)
	{
	struct thread_info *ti;
	unsigned long trampoline_addr;
	u32 status;
	u32 ctrl;
	int code;

	status = ocd_read(DS);
	ti = current_thread_info();
	code = TRAP_BRKPT;

	pr_debug("do_debug: status=0x%08x PC=0x%08lx SR=0x%08lx tif=0x%08lx\n",
	status, regs->pc, regs->sr, ti->flags);

	if (!user_mode(regs)) {
	unsigned long die_val = DIE_BREAKPOINT;

	if (status & (1 << OCD_DS_SSS_BIT))
	die_val = DIE_SSTEP;

	if (notify_die(die_val, "ptrace", regs, 0, 0, SIGTRAP)
	== NOTIFY_STOP)
	return regs;

	if ((status & (1 << OCD_DS_SWB_BIT))
	&& test_and_clear_ti_thread_flag(
	ti, TIF_BREAKPOINT)) {
	/*
	* Explicit breakpoint from trampoline or
	* exception/syscall/interrupt handler.
	*
	* The real saved regs are on the stack right
	* after the ones we saved on entry.
	*/
	regs++;
	pr_debug(" -> TIF_BREAKPOINT done, adjusted regs:"
	"PC=0x%08lx SR=0x%08lx\n",
	regs->pc, regs->sr);
	BUG_ON(!user_mode(regs));

	if (test_thread_flag(TIF_SINGLE_STEP)) {
	pr_debug("Going to do single step...\n");
	return regs;
	}

	/*
	* No TIF_SINGLE_STEP means we're done
	* stepping over a syscall. Do the trap now.
	*/
	code = TRAP_TRACE;
	} else if ((status & (1 << OCD_DS_SSS_BIT))
	&& test_ti_thread_flag(ti, TIF_SINGLE_STEP)) {

	pr_debug("Stepped into something, "
	"setting TIF_BREAKPOINT...\n");
	set_ti_thread_flag(ti, TIF_BREAKPOINT);

	/*
	* We stepped into an exception, interrupt or
	* syscall handler. Some exception handlers
	* don't check for pending work, so we need to
	* set up a trampoline just in case.
	*
	* The exception entry code will undo the
	* trampoline stuff if it does a full context
	* save (which also means that it'll check for
	* pending work later.)
	*/
	if ((regs->sr & MODE_MASK) == MODE_EXCEPTION) {
	trampoline_addr
	= (unsigned long)&debug_trampoline;

	pr_debug("Setting up trampoline...\n");
	ti->rar_saved = sysreg_read(RAR_EX);
	ti->rsr_saved = sysreg_read(RSR_EX);
	sysreg_write(RAR_EX, trampoline_addr);
	sysreg_write(RSR_EX, (MODE_EXCEPTION
	\| SR_EM \| SR_GM));
	BUG_ON(ti->rsr_saved & MODE_MASK);
	}

	/*
	* If we stepped into a system call, we
	* shouldn't do a single step after we return
	* since the return address is right after the
	* "scall" instruction we were told to step
	* over.
	*/
	if ((regs->sr & MODE_MASK) == MODE_SUPERVISOR) {
	pr_debug("Supervisor; no single step\n");
	clear_ti_thread_flag(ti, TIF_SINGLE_STEP);
	}

	ctrl = ocd_read(DC);
	ctrl &= ~(1 << OCD_DC_SS_BIT);
	ocd_write(DC, ctrl);

	return regs;
	} else {
	printk(KERN_ERR "Unexpected OCD_DS value: 0x%08x\n",
	status);
	printk(KERN_ERR "Thread flags: 0x%08lx\n", ti->flags);
	die("Unhandled debug trap in kernel mode",
	regs, SIGTRAP);
	}
	} else if (status & (1 << OCD_DS_SSS_BIT)) {
	/* Single step in user mode */
	code = TRAP_TRACE;

	ctrl = ocd_read(DC);
	ctrl &= ~(1 << OCD_DC_SS_BIT);
	ocd_write(DC, ctrl);
	}

	pr_debug("Sending SIGTRAP: code=%d PC=0x%08lx SR=0x%08lx\n",
	code, regs->pc, regs->sr);

	clear_thread_flag(TIF_SINGLE_STEP);
	_exception(SIGTRAP, regs, code, instruction_pointer(regs));

	return regs;
	}