arch/mips/kernel/process.c - linux - Git at Google

 /*
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive
  * for more details.
  *
  * Copyright (C) 1994 - 1999, 2000 by Ralf Baechle and others.
  * Copyright (C) 2005, 2006 by Ralf Baechle (ralf@linux-mips.org)
  * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
  * Copyright (C) 2004 Thiemo Seufer
  */
 #include <linux/errno.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/stddef.h>
 #include <linux/unistd.h>
 #include <linux/ptrace.h>
 #include <linux/slab.h>
 #include <linux/mman.h>
 #include <linux/personality.h>
 #include <linux/sys.h>
 #include <linux/user.h>
 #include <linux/a.out.h>
 #include <linux/init.h>
 #include <linux/completion.h>
 #include <linux/kallsyms.h>

 #include <asm/abi.h>
 #include <asm/bootinfo.h>
 #include <asm/cpu.h>
 #include <asm/dsp.h>
 #include <asm/fpu.h>
 #include <asm/pgtable.h>
 #include <asm/system.h>
 #include <asm/mipsregs.h>
 #include <asm/processor.h>
 #include <asm/uaccess.h>
 #include <asm/io.h>
 #include <asm/elf.h>
 #include <asm/isadep.h>
 #include <asm/inst.h>
 #include <asm/stacktrace.h>

 /*
  * The idle thread. There's no useful work to be done, so just try to conserve
  * power and have a low exit latency (ie sit in a loop waiting for somebody to
  * say that they'd like to reschedule)
  */
 ATTRIB_NORET void cpu_idle(void)
 {
 	/* endless idle loop with no priority at all */
 	while (1) {
 		while (!need_resched()) {
 #ifdef CONFIG_MIPS_MT_SMTC
 			extern void smtc_idle_loop_hook(void);

 			smtc_idle_loop_hook();
 #endif /* CONFIG_MIPS_MT_SMTC */
 			if (cpu_wait)
 				(*cpu_wait)();
 		}
 		preempt_enable_no_resched();
 		schedule();
 		preempt_disable();
 	}
 }

 /*
  * Native o32 and N64 ABI without DSP ASE
  */
 struct mips_abi mips_abi = {
 	.do_signal	= do_signal,
 #ifdef CONFIG_TRAD_SIGNALS
 	.setup_frame	= setup_frame,
 #endif
 	.setup_rt_frame	= setup_rt_frame
 };

 #ifdef CONFIG_MIPS32_O32
 /*
  * o32 compatibility on 64-bit kernels, without DSP ASE
  */
 struct mips_abi mips_abi_32 = {
 	.do_signal	= do_signal32,
 	.setup_frame	= setup_frame_32,
 	.setup_rt_frame	= setup_rt_frame_32
 };
 #endif /* CONFIG_MIPS32_O32 */

 #ifdef CONFIG_MIPS32_N32
 /*
  * N32 on 64-bit kernels, without DSP ASE
  */
 struct mips_abi mips_abi_n32 = {
 	.do_signal	= do_signal,
 	.setup_rt_frame	= setup_rt_frame_n32
 };
 #endif /* CONFIG_MIPS32_N32 */

 asmlinkage void ret_from_fork(void);

 void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
 {
 	unsigned long status;

 	/* New thread loses kernel privileges. */
 	status = regs->cp0_status & ~(ST0_CU0|ST0_CU1|KU_MASK);
 #ifdef CONFIG_64BIT
 	status &= ~ST0_FR;
 	status |= (current->thread.mflags & MF_32BIT_REGS) ? 0 : ST0_FR;
 #endif
 	status |= KU_USER;
 	regs->cp0_status = status;
 	clear_used_math();
 	clear_fpu_owner();
 	if (cpu_has_dsp)
 		__init_dsp();
 	regs->cp0_epc = pc;
 	regs->regs[29] = sp;
 	current_thread_info()->addr_limit = USER_DS;
 }

 void exit_thread(void)
 {
 }

 void flush_thread(void)
 {
 }

 int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
 	unsigned long unused, struct task_struct *p, struct pt_regs *regs)
 {
 	struct thread_info *ti = task_thread_info(p);
 	struct pt_regs *childregs;
 	long childksp;
 	p->set_child_tid = p->clear_child_tid = NULL;

 	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;

 	preempt_disable();

 	if (is_fpu_owner())
 		save_fp(p);

 	if (cpu_has_dsp)
 		save_dsp(p);

 	preempt_enable();

 	/* set up new TSS. */
 	childregs = (struct pt_regs *) childksp - 1;
 	*childregs = *regs;
 	childregs->regs[7] = 0;	/* Clear error flag */

 #if defined(CONFIG_BINFMT_IRIX)
 	if (current->personality != PER_LINUX) {
 		/* Under IRIX things are a little different. */
 		childregs->regs[3] = 1;
 		regs->regs[3] = 0;
 	}
 #endif
 	childregs->regs[2] = 0;	/* Child gets zero as return value */
 	regs->regs[2] = p->pid;

 	if (childregs->cp0_status & ST0_CU0) {
 		childregs->regs[28] = (unsigned long) ti;
 		childregs->regs[29] = childksp;
 		ti->addr_limit = KERNEL_DS;
 	} else {
 		childregs->regs[29] = usp;
 		ti->addr_limit = USER_DS;
 	}
 	p->thread.reg29 = (unsigned long) childregs;
 	p->thread.reg31 = (unsigned long) ret_from_fork;

 	/*
 	 * New tasks lose permission to use the fpu. This accelerates context
 	 * switching for most programs since they don't use the fpu.
 	 */
 	p->thread.cp0_status = read_c0_status() & ~(ST0_CU2|ST0_CU1);
 	childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);
 	clear_tsk_thread_flag(p, TIF_USEDFPU);

 #ifdef CONFIG_MIPS_MT_FPAFF
 	/*
 	 * FPU affinity support is cleaner if we track the
 	 * user-visible CPU affinity from the very beginning.
 	 * The generic cpus_allowed mask will already have
 	 * been copied from the parent before copy_thread
 	 * is invoked.
 	 */
 	p->thread.user_cpus_allowed = p->cpus_allowed;
 #endif /* CONFIG_MIPS_MT_FPAFF */

 	if (clone_flags & CLONE_SETTLS)
 		ti->tp_value = regs->regs[7];

 	return 0;
 }

 /* Fill in the fpu structure for a core dump.. */
 int dump_fpu(struct pt_regs *regs, elf_fpregset_t *r)
 {
 	memcpy(r, &current->thread.fpu, sizeof(current->thread.fpu));

 	return 1;
 }

 void elf_dump_regs(elf_greg_t *gp, struct pt_regs *regs)
 {
 	int i;

 	for (i = 0; i < EF_R0; i++)
 		gp[i] = 0;
 	gp[EF_R0] = 0;
 	for (i = 1; i <= 31; i++)
 		gp[EF_R0 + i] = regs->regs[i];
 	gp[EF_R26] = 0;
 	gp[EF_R27] = 0;
 	gp[EF_LO] = regs->lo;
 	gp[EF_HI] = regs->hi;
 	gp[EF_CP0_EPC] = regs->cp0_epc;
 	gp[EF_CP0_BADVADDR] = regs->cp0_badvaddr;
 	gp[EF_CP0_STATUS] = regs->cp0_status;
 	gp[EF_CP0_CAUSE] = regs->cp0_cause;
 #ifdef EF_UNUSED0
 	gp[EF_UNUSED0] = 0;
 #endif
 }

 int dump_task_regs (struct task_struct *tsk, elf_gregset_t *regs)
 {
 	elf_dump_regs(*regs, task_pt_regs(tsk));
 	return 1;
 }

 int dump_task_fpu (struct task_struct *t, elf_fpregset_t *fpr)
 {
 	memcpy(fpr, &t->thread.fpu, sizeof(current->thread.fpu));

 	return 1;
 }

 /*
  * Create a kernel thread
  */
 ATTRIB_NORET void kernel_thread_helper(void *arg, int (*fn)(void *))
 {
 	do_exit(fn(arg));
 }

 long kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
 {
 	struct pt_regs regs;

 	memset(&regs, 0, sizeof(regs));

 	regs.regs[4] = (unsigned long) arg;
 	regs.regs[5] = (unsigned long) fn;
 	regs.cp0_epc = (unsigned long) kernel_thread_helper;
 	regs.cp0_status = read_c0_status();
 #if defined(CONFIG_CPU_R3000) || defined(CONFIG_CPU_TX39XX)
 	regs.cp0_status &= ~(ST0_KUP | ST0_IEC);
 	regs.cp0_status |= ST0_IEP;
 #else
 	regs.cp0_status |= ST0_EXL;
 #endif

 	/* Ok, create the new process.. */
 	return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
 }

 /*
  *
  */
 struct mips_frame_info {
 	void		*func;
 	unsigned long	func_size;
 	int		frame_size;
 	int		pc_offset;
 };

 static inline int is_ra_save_ins(union mips_instruction *ip)
 {
 	/* sw / sd $ra, offset($sp) */
 	return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
 		ip->i_format.rs == 29 &&
 		ip->i_format.rt == 31;
 }

 static inline int is_jal_jalr_jr_ins(union mips_instruction *ip)
 {
 	if (ip->j_format.opcode == jal_op)
 		return 1;
 	if (ip->r_format.opcode != spec_op)
 		return 0;
 	return ip->r_format.func == jalr_op || ip->r_format.func == jr_op;
 }

 static inline int is_sp_move_ins(union mips_instruction *ip)
 {
 	/* addiu/daddiu sp,sp,-imm */
 	if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
 		return 0;
 	if (ip->i_format.opcode == addiu_op || ip->i_format.opcode == daddiu_op)
 		return 1;
 	return 0;
 }

 static int get_frame_info(struct mips_frame_info *info)
 {
 	union mips_instruction *ip = info->func;
 	unsigned max_insns = info->func_size / sizeof(union mips_instruction);
 	unsigned i;

 	info->pc_offset = -1;
 	info->frame_size = 0;

 	if (!ip)
 		goto err;

 	if (max_insns == 0)
 		max_insns = 128U;	/* unknown function size */
 	max_insns = min(128U, max_insns);

 	for (i = 0; i < max_insns; i++, ip++) {

 		if (is_jal_jalr_jr_ins(ip))
 			break;
 		if (!info->frame_size) {
 			if (is_sp_move_ins(ip))
 				info->frame_size = - ip->i_format.simmediate;
 			continue;
 		}
 		if (info->pc_offset == -1 && is_ra_save_ins(ip)) {
 			info->pc_offset =
 				ip->i_format.simmediate / sizeof(long);
 			break;
 		}
 	}
 	if (info->frame_size && info->pc_offset >= 0) /* nested */
 		return 0;
 	if (info->pc_offset < 0) /* leaf */
 		return 1;
 	/* prologue seems boggus... */
 err:
 	return -1;
 }

 static struct mips_frame_info schedule_mfi __read_mostly;

 static int __init frame_info_init(void)
 {
 	unsigned long size = 0;
 #ifdef CONFIG_KALLSYMS
 	unsigned long ofs;

 	kallsyms_lookup_size_offset((unsigned long)schedule, &size, &ofs);
 #endif
 	schedule_mfi.func = schedule;
 	schedule_mfi.func_size = size;

 	get_frame_info(&schedule_mfi);

 	/*
 	 * Without schedule() frame info, result given by
 	 * thread_saved_pc() and get_wchan() are not reliable.
 	 */
 	if (schedule_mfi.pc_offset < 0)
 		printk("Can't analyze schedule() prologue at %p\n", schedule);

 	return 0;
 }

 arch_initcall(frame_info_init);

 /*
  * Return saved PC of a blocked thread.
  */
 unsigned long thread_saved_pc(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;

 	/* New born processes are a special case */
 	if (t->reg31 == (unsigned long) ret_from_fork)
 		return t->reg31;
 	if (schedule_mfi.pc_offset < 0)
 		return 0;
 	return ((unsigned long *)t->reg29)[schedule_mfi.pc_offset];
 }


 #ifdef CONFIG_KALLSYMS
 /* used by show_backtrace() */
 unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
 			   unsigned long pc, unsigned long *ra)
 {
 	unsigned long stack_page;
 	struct mips_frame_info info;
 	unsigned long size, ofs;
 	int leaf;
 	extern void ret_from_irq(void);
 	extern void ret_from_exception(void);

 	stack_page = (unsigned long)task_stack_page(task);
 	if (!stack_page)
 		return 0;

 	/*
 	 * If we reached the bottom of interrupt context,
 	 * return saved pc in pt_regs.
 	 */
 	if (pc == (unsigned long)ret_from_irq ||
 	    pc == (unsigned long)ret_from_exception) {
 		struct pt_regs *regs;
 		if (*sp >= stack_page &&
 		    *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) {
 			regs = (struct pt_regs *)*sp;
 			pc = regs->cp0_epc;
 			if (__kernel_text_address(pc)) {
 				*sp = regs->regs[29];
 				*ra = regs->regs[31];
 				return pc;
 			}
 		}
 		return 0;
 	}
 	if (!kallsyms_lookup_size_offset(pc, &size, &ofs))
 		return 0;
 	/*
 	 * Return ra if an exception occured at the first instruction
 	 */
 	if (unlikely(ofs == 0)) {
 		pc = *ra;
 		*ra = 0;
 		return pc;
 	}

 	info.func = (void *)(pc - ofs);
 	info.func_size = ofs;	/* analyze from start to ofs */
 	leaf = get_frame_info(&info);
 	if (leaf < 0)
 		return 0;

 	if (*sp < stack_page ||
 	    *sp + info.frame_size > stack_page + THREAD_SIZE - 32)
 		return 0;

 	if (leaf)
 		/*
 		 * For some extreme cases, get_frame_info() can
 		 * consider wrongly a nested function as a leaf
 		 * one. In that cases avoid to return always the
 		 * same value.
 		 */
 		pc = pc != *ra ? *ra : 0;
 	else
 		pc = ((unsigned long *)(*sp))[info.pc_offset];

 	*sp += info.frame_size;
 	*ra = 0;
 	return __kernel_text_address(pc) ? pc : 0;
 }
 #endif

 /*
  * get_wchan - a maintenance nightmare^W^Wpain in the ass ...
  */
 unsigned long get_wchan(struct task_struct *task)
 {
 	unsigned long pc = 0;
 #ifdef CONFIG_KALLSYMS
 	unsigned long sp;
 	unsigned long ra = 0;
 #endif

 	if (!task || task == current || task->state == TASK_RUNNING)
 		goto out;
 	if (!task_stack_page(task))
 		goto out;

 	pc = thread_saved_pc(task);

 #ifdef CONFIG_KALLSYMS
 	sp = task->thread.reg29 + schedule_mfi.frame_size;

 	while (in_sched_functions(pc))
 		pc = unwind_stack(task, &sp, pc, &ra);
 #endif

 out:
 	return pc;
 }
	/*
	* This file is subject to the terms and conditions of the GNU General Public
	* License. See the file "COPYING" in the main directory of this archive
	* for more details.
	*
	* Copyright (C) 1994 - 1999, 2000 by Ralf Baechle and others.
	* Copyright (C) 2005, 2006 by Ralf Baechle (ralf@linux-mips.org)
	* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
	* Copyright (C) 2004 Thiemo Seufer
	*/
	#include <linux/errno.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/stddef.h>
	#include <linux/unistd.h>
	#include <linux/ptrace.h>
	#include <linux/slab.h>
	#include <linux/mman.h>
	#include <linux/personality.h>
	#include <linux/sys.h>
	#include <linux/user.h>
	#include <linux/a.out.h>
	#include <linux/init.h>
	#include <linux/completion.h>
	#include <linux/kallsyms.h>

	#include <asm/abi.h>
	#include <asm/bootinfo.h>
	#include <asm/cpu.h>
	#include <asm/dsp.h>
	#include <asm/fpu.h>
	#include <asm/pgtable.h>
	#include <asm/system.h>
	#include <asm/mipsregs.h>
	#include <asm/processor.h>
	#include <asm/uaccess.h>
	#include <asm/io.h>
	#include <asm/elf.h>
	#include <asm/isadep.h>
	#include <asm/inst.h>
	#include <asm/stacktrace.h>

	/*
	* The idle thread. There's no useful work to be done, so just try to conserve
	* power and have a low exit latency (ie sit in a loop waiting for somebody to
	* say that they'd like to reschedule)
	*/
	ATTRIB_NORET void cpu_idle(void)
	{
	/* endless idle loop with no priority at all */
	while (1) {
	while (!need_resched()) {
	#ifdef CONFIG_MIPS_MT_SMTC
	extern void smtc_idle_loop_hook(void);

	smtc_idle_loop_hook();
	#endif /* CONFIG_MIPS_MT_SMTC */
	if (cpu_wait)
	(*cpu_wait)();
	}
	preempt_enable_no_resched();
	schedule();
	preempt_disable();
	}
	}

	/*
	* Native o32 and N64 ABI without DSP ASE
	*/
	struct mips_abi mips_abi = {
	.do_signal = do_signal,
	#ifdef CONFIG_TRAD_SIGNALS
	.setup_frame = setup_frame,
	#endif
	.setup_rt_frame = setup_rt_frame
	};

	#ifdef CONFIG_MIPS32_O32
	/*
	* o32 compatibility on 64-bit kernels, without DSP ASE
	*/
	struct mips_abi mips_abi_32 = {
	.do_signal = do_signal32,
	.setup_frame = setup_frame_32,
	.setup_rt_frame = setup_rt_frame_32
	};
	#endif /* CONFIG_MIPS32_O32 */

	#ifdef CONFIG_MIPS32_N32
	/*
	* N32 on 64-bit kernels, without DSP ASE
	*/
	struct mips_abi mips_abi_n32 = {
	.do_signal = do_signal,
	.setup_rt_frame = setup_rt_frame_n32
	};
	#endif /* CONFIG_MIPS32_N32 */

	asmlinkage void ret_from_fork(void);

	void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
	{
	unsigned long status;

	/* New thread loses kernel privileges. */
	status = regs->cp0_status & ~(ST0_CU0\|ST0_CU1\|KU_MASK);
	#ifdef CONFIG_64BIT
	status &= ~ST0_FR;
	status \|= (current->thread.mflags & MF_32BIT_REGS) ? 0 : ST0_FR;
	#endif
	status \|= KU_USER;
	regs->cp0_status = status;
	clear_used_math();
	clear_fpu_owner();
	if (cpu_has_dsp)
	__init_dsp();
	regs->cp0_epc = pc;
	regs->regs[29] = sp;
	current_thread_info()->addr_limit = USER_DS;
	}

	void exit_thread(void)
	{
	}

	void flush_thread(void)
	{
	}

	int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
	unsigned long unused, struct task_struct p, struct pt_regs regs)
	{
	struct thread_info *ti = task_thread_info(p);
	struct pt_regs *childregs;
	long childksp;
	p->set_child_tid = p->clear_child_tid = NULL;

	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;

	preempt_disable();

	if (is_fpu_owner())
	save_fp(p);

	if (cpu_has_dsp)
	save_dsp(p);

	preempt_enable();

	/* set up new TSS. */
	childregs = (struct pt_regs *) childksp - 1;
	childregs = regs;
	childregs->regs[7] = 0; /* Clear error flag */

	#if defined(CONFIG_BINFMT_IRIX)
	if (current->personality != PER_LINUX) {
	/* Under IRIX things are a little different. */
	childregs->regs[3] = 1;
	regs->regs[3] = 0;
	}
	#endif
	childregs->regs[2] = 0; /* Child gets zero as return value */
	regs->regs[2] = p->pid;

	if (childregs->cp0_status & ST0_CU0) {
	childregs->regs[28] = (unsigned long) ti;
	childregs->regs[29] = childksp;
	ti->addr_limit = KERNEL_DS;
	} else {
	childregs->regs[29] = usp;
	ti->addr_limit = USER_DS;
	}
	p->thread.reg29 = (unsigned long) childregs;
	p->thread.reg31 = (unsigned long) ret_from_fork;

	/*
	* New tasks lose permission to use the fpu. This accelerates context
	* switching for most programs since they don't use the fpu.
	*/
	p->thread.cp0_status = read_c0_status() & ~(ST0_CU2\|ST0_CU1);
	childregs->cp0_status &= ~(ST0_CU2\|ST0_CU1);
	clear_tsk_thread_flag(p, TIF_USEDFPU);

	#ifdef CONFIG_MIPS_MT_FPAFF
	/*
	* FPU affinity support is cleaner if we track the
	* user-visible CPU affinity from the very beginning.
	* The generic cpus_allowed mask will already have
	* been copied from the parent before copy_thread
	* is invoked.
	*/
	p->thread.user_cpus_allowed = p->cpus_allowed;
	#endif /* CONFIG_MIPS_MT_FPAFF */

	if (clone_flags & CLONE_SETTLS)
	ti->tp_value = regs->regs[7];

	return 0;
	}

	/* Fill in the fpu structure for a core dump.. */
	int dump_fpu(struct pt_regs regs, elf_fpregset_t r)
	{
	memcpy(r, &current->thread.fpu, sizeof(current->thread.fpu));

	return 1;
	}

	void elf_dump_regs(elf_greg_t gp, struct pt_regs regs)
	{
	int i;

	for (i = 0; i < EF_R0; i++)
	gp[i] = 0;
	gp[EF_R0] = 0;
	for (i = 1; i <= 31; i++)
	gp[EF_R0 + i] = regs->regs[i];
	gp[EF_R26] = 0;
	gp[EF_R27] = 0;
	gp[EF_LO] = regs->lo;
	gp[EF_HI] = regs->hi;
	gp[EF_CP0_EPC] = regs->cp0_epc;
	gp[EF_CP0_BADVADDR] = regs->cp0_badvaddr;
	gp[EF_CP0_STATUS] = regs->cp0_status;
	gp[EF_CP0_CAUSE] = regs->cp0_cause;
	#ifdef EF_UNUSED0
	gp[EF_UNUSED0] = 0;
	#endif
	}

	int dump_task_regs (struct task_struct tsk, elf_gregset_t regs)
	{
	elf_dump_regs(*regs, task_pt_regs(tsk));
	return 1;
	}

	int dump_task_fpu (struct task_struct t, elf_fpregset_t fpr)
	{
	memcpy(fpr, &t->thread.fpu, sizeof(current->thread.fpu));

	return 1;
	}

	/*
	* Create a kernel thread
	*/
	ATTRIB_NORET void kernel_thread_helper(void arg, int (fn)(void *))
	{
	do_exit(fn(arg));
	}

	long kernel_thread(int (fn)(void ), void *arg, unsigned long flags)
	{
	struct pt_regs regs;

	memset(&regs, 0, sizeof(regs));

	regs.regs[4] = (unsigned long) arg;
	regs.regs[5] = (unsigned long) fn;
	regs.cp0_epc = (unsigned long) kernel_thread_helper;
	regs.cp0_status = read_c0_status();
	#if defined(CONFIG_CPU_R3000) \|\| defined(CONFIG_CPU_TX39XX)
	regs.cp0_status &= ~(ST0_KUP \| ST0_IEC);
	regs.cp0_status \|= ST0_IEP;
	#else
	regs.cp0_status \|= ST0_EXL;
	#endif

	/* Ok, create the new process.. */
	return do_fork(flags \| CLONE_VM \| CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
	}

	/*
	*
	*/
	struct mips_frame_info {
	void *func;
	unsigned long func_size;
	int frame_size;
	int pc_offset;
	};

	static inline int is_ra_save_ins(union mips_instruction *ip)
	{
	/* sw / sd $ra, offset($sp) */
	return (ip->i_format.opcode == sw_op \|\| ip->i_format.opcode == sd_op) &&
	ip->i_format.rs == 29 &&
	ip->i_format.rt == 31;
	}

	static inline int is_jal_jalr_jr_ins(union mips_instruction *ip)
	{
	if (ip->j_format.opcode == jal_op)
	return 1;
	if (ip->r_format.opcode != spec_op)
	return 0;
	return ip->r_format.func == jalr_op \|\| ip->r_format.func == jr_op;
	}

	static inline int is_sp_move_ins(union mips_instruction *ip)
	{
	/* addiu/daddiu sp,sp,-imm */
	if (ip->i_format.rs != 29 \|\| ip->i_format.rt != 29)
	return 0;
	if (ip->i_format.opcode == addiu_op \|\| ip->i_format.opcode == daddiu_op)
	return 1;
	return 0;
	}

	static int get_frame_info(struct mips_frame_info *info)
	{
	union mips_instruction *ip = info->func;
	unsigned max_insns = info->func_size / sizeof(union mips_instruction);
	unsigned i;

	info->pc_offset = -1;
	info->frame_size = 0;

	if (!ip)
	goto err;

	if (max_insns == 0)
	max_insns = 128U; /* unknown function size */
	max_insns = min(128U, max_insns);

	for (i = 0; i < max_insns; i++, ip++) {

	if (is_jal_jalr_jr_ins(ip))
	break;
	if (!info->frame_size) {
	if (is_sp_move_ins(ip))
	info->frame_size = - ip->i_format.simmediate;
	continue;
	}
	if (info->pc_offset == -1 && is_ra_save_ins(ip)) {
	info->pc_offset =
	ip->i_format.simmediate / sizeof(long);
	break;
	}
	}
	if (info->frame_size && info->pc_offset >= 0) /* nested */
	return 0;
	if (info->pc_offset < 0) /* leaf */
	return 1;
	/* prologue seems boggus... */
	err:
	return -1;
	}

	static struct mips_frame_info schedule_mfi __read_mostly;

	static int __init frame_info_init(void)
	{
	unsigned long size = 0;
	#ifdef CONFIG_KALLSYMS
	unsigned long ofs;

	kallsyms_lookup_size_offset((unsigned long)schedule, &size, &ofs);
	#endif
	schedule_mfi.func = schedule;
	schedule_mfi.func_size = size;

	get_frame_info(&schedule_mfi);

	/*
	* Without schedule() frame info, result given by
	* thread_saved_pc() and get_wchan() are not reliable.
	*/
	if (schedule_mfi.pc_offset < 0)
	printk("Can't analyze schedule() prologue at %p\n", schedule);

	return 0;
	}

	arch_initcall(frame_info_init);

	/*
	* Return saved PC of a blocked thread.
	*/
	unsigned long thread_saved_pc(struct task_struct *tsk)
	{
	struct thread_struct *t = &tsk->thread;

	/* New born processes are a special case */
	if (t->reg31 == (unsigned long) ret_from_fork)
	return t->reg31;
	if (schedule_mfi.pc_offset < 0)
	return 0;
	return ((unsigned long *)t->reg29)[schedule_mfi.pc_offset];
	}


	#ifdef CONFIG_KALLSYMS
	/* used by show_backtrace() */
	unsigned long unwind_stack(struct task_struct task, unsigned long sp,
	unsigned long pc, unsigned long *ra)
	{
	unsigned long stack_page;
	struct mips_frame_info info;
	unsigned long size, ofs;
	int leaf;
	extern void ret_from_irq(void);
	extern void ret_from_exception(void);

	stack_page = (unsigned long)task_stack_page(task);
	if (!stack_page)
	return 0;

	/*
	* If we reached the bottom of interrupt context,
	* return saved pc in pt_regs.
	*/
	if (pc == (unsigned long)ret_from_irq \|\|
	pc == (unsigned long)ret_from_exception) {
	struct pt_regs *regs;
	if (*sp >= stack_page &&
	sp + sizeof(regs) <= stack_page + THREAD_SIZE - 32) {
	regs = (struct pt_regs )sp;
	pc = regs->cp0_epc;
	if (__kernel_text_address(pc)) {
	*sp = regs->regs[29];
	*ra = regs->regs[31];
	return pc;
	}
	}
	return 0;
	}
	if (!kallsyms_lookup_size_offset(pc, &size, &ofs))
	return 0;
	/*
	* Return ra if an exception occured at the first instruction
	*/
	if (unlikely(ofs == 0)) {
	pc = *ra;
	*ra = 0;
	return pc;
	}

	info.func = (void *)(pc - ofs);
	info.func_size = ofs; /* analyze from start to ofs */
	leaf = get_frame_info(&info);
	if (leaf < 0)
	return 0;

	if (*sp < stack_page \|\|
	*sp + info.frame_size > stack_page + THREAD_SIZE - 32)
	return 0;

	if (leaf)
	/*
	* For some extreme cases, get_frame_info() can
	* consider wrongly a nested function as a leaf
	* one. In that cases avoid to return always the
	* same value.
	*/
	pc = pc != ra ? ra : 0;
	else
	pc = ((unsigned long )(sp))[info.pc_offset];

	*sp += info.frame_size;
	*ra = 0;
	return __kernel_text_address(pc) ? pc : 0;
	}
	#endif

	/*
	* get_wchan - a maintenance nightmare^W^Wpain in the ass ...
	*/
	unsigned long get_wchan(struct task_struct *task)
	{
	unsigned long pc = 0;
	#ifdef CONFIG_KALLSYMS
	unsigned long sp;
	unsigned long ra = 0;
	#endif

	if (!task \|\| task == current \|\| task->state == TASK_RUNNING)
	goto out;
	if (!task_stack_page(task))
	goto out;

	pc = thread_saved_pc(task);

	#ifdef CONFIG_KALLSYMS
	sp = task->thread.reg29 + schedule_mfi.frame_size;

	while (in_sched_functions(pc))
	pc = unwind_stack(task, &sp, pc, &ra);
	#endif

	out:
	return pc;
	}