arch/tile/kernel/stack.c - maze/linux - Git at Google

 /*
  * Copyright 2010 Tilera Corporation. All Rights Reserved.
  *
  *   This program is free software; you can redistribute it and/or
  *   modify it under the terms of the GNU General Public License
  *   as published by the Free Software Foundation, version 2.
  *
  *   This program is distributed in the hope that it will be useful, but
  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  *   NON INFRINGEMENT.  See the GNU General Public License for
  *   more details.
  */

 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/kprobes.h>
 #include <linux/module.h>
 #include <linux/pfn.h>
 #include <linux/kallsyms.h>
 #include <linux/stacktrace.h>
 #include <linux/uaccess.h>
 #include <linux/mmzone.h>
 #include <asm/backtrace.h>
 #include <asm/page.h>
 #include <asm/tlbflush.h>
 #include <asm/ucontext.h>
 #include <asm/sigframe.h>
 #include <asm/stack.h>
 #include <arch/abi.h>
 #include <arch/interrupts.h>

 #define KBT_ONGOING	0  /* Backtrace still ongoing */
 #define KBT_DONE	1  /* Backtrace cleanly completed */
 #define KBT_RUNNING	2  /* Can't run backtrace on a running task */
 #define KBT_LOOP	3  /* Backtrace entered a loop */

 /* Is address on the specified kernel stack? */
 static int in_kernel_stack(struct KBacktraceIterator *kbt, unsigned long sp)
 {
 	ulong kstack_base = (ulong) kbt->task->stack;
 	if (kstack_base == 0)  /* corrupt task pointer; just follow stack... */
 		return sp >= PAGE_OFFSET && sp < (unsigned long)high_memory;
 	return sp >= kstack_base && sp < kstack_base + THREAD_SIZE;
 }

 /* Is address valid for reading? */
 static int valid_address(struct KBacktraceIterator *kbt, unsigned long address)
 {
 	HV_PTE *l1_pgtable = kbt->pgtable;
 	HV_PTE *l2_pgtable;
 	unsigned long pfn;
 	HV_PTE pte;
 	struct page *page;

 	if (l1_pgtable == NULL)
 		return 0;	/* can't read user space in other tasks */

 #ifdef CONFIG_64BIT
 	/* Find the real l1_pgtable by looking in the l0_pgtable. */
 	pte = l1_pgtable[HV_L0_INDEX(address)];
 	if (!hv_pte_get_present(pte))
 		return 0;
 	pfn = hv_pte_get_pfn(pte);
 	if (pte_huge(pte)) {
 		if (!pfn_valid(pfn)) {
 			pr_err("L0 huge page has bad pfn %#lx\n", pfn);
 			return 0;
 		}
 		return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
 	}
 	page = pfn_to_page(pfn);
 	BUG_ON(PageHighMem(page));  /* No HIGHMEM on 64-bit. */
 	l1_pgtable = (HV_PTE *)pfn_to_kaddr(pfn);
 #endif
 	pte = l1_pgtable[HV_L1_INDEX(address)];
 	if (!hv_pte_get_present(pte))
 		return 0;
 	pfn = hv_pte_get_pfn(pte);
 	if (pte_huge(pte)) {
 		if (!pfn_valid(pfn)) {
 			pr_err("huge page has bad pfn %#lx\n", pfn);
 			return 0;
 		}
 		return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
 	}

 	page = pfn_to_page(pfn);
 	if (PageHighMem(page)) {
 		pr_err("L2 page table not in LOWMEM (%#llx)\n",
 		       HV_PFN_TO_CPA(pfn));
 		return 0;
 	}
 	l2_pgtable = (HV_PTE *)pfn_to_kaddr(pfn);
 	pte = l2_pgtable[HV_L2_INDEX(address)];
 	return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
 }

 /* Callback for backtracer; basically a glorified memcpy */
 static bool read_memory_func(void *result, unsigned long address,
 			     unsigned int size, void *vkbt)
 {
 	int retval;
 	struct KBacktraceIterator *kbt = (struct KBacktraceIterator *)vkbt;
 	if (__kernel_text_address(address)) {
 		/* OK to read kernel code. */
 	} else if (address >= PAGE_OFFSET) {
 		/* We only tolerate kernel-space reads of this task's stack */
 		if (!in_kernel_stack(kbt, address))
 			return 0;
 	} else if (!valid_address(kbt, address)) {
 		return 0;	/* invalid user-space address */
 	}
 	pagefault_disable();
 	retval = __copy_from_user_inatomic(result,
 					   (void __user __force *)address,
 					   size);
 	pagefault_enable();
 	return (retval == 0);
 }

 /* Return a pt_regs pointer for a valid fault handler frame */
 static struct pt_regs *valid_fault_handler(struct KBacktraceIterator* kbt)
 {
 	const char *fault = NULL;  /* happy compiler */
 	char fault_buf[64];
 	unsigned long sp = kbt->it.sp;
 	struct pt_regs *p;

 	if (!in_kernel_stack(kbt, sp))
 		return NULL;
 	if (!in_kernel_stack(kbt, sp + C_ABI_SAVE_AREA_SIZE + PTREGS_SIZE-1))
 		return NULL;
 	p = (struct pt_regs *)(sp + C_ABI_SAVE_AREA_SIZE);
 	if (p->faultnum == INT_SWINT_1 || p->faultnum == INT_SWINT_1_SIGRETURN)
 		fault = "syscall";
 	else {
 		if (kbt->verbose) {     /* else we aren't going to use it */
 			snprintf(fault_buf, sizeof(fault_buf),
 				 "interrupt %ld", p->faultnum);
 			fault = fault_buf;
 		}
 	}
 	if (EX1_PL(p->ex1) == KERNEL_PL &&
 	    __kernel_text_address(p->pc) &&
 	    in_kernel_stack(kbt, p->sp) &&
 	    p->sp >= sp) {
 		if (kbt->verbose)
 			pr_err("  <%s while in kernel mode>\n", fault);
 	} else if (EX1_PL(p->ex1) == USER_PL &&
 	    p->pc < PAGE_OFFSET &&
 	    p->sp < PAGE_OFFSET) {
 		if (kbt->verbose)
 			pr_err("  <%s while in user mode>\n", fault);
 	} else if (kbt->verbose) {
 		pr_err("  (odd fault: pc %#lx, sp %#lx, ex1 %#lx?)\n",
 		       p->pc, p->sp, p->ex1);
 		p = NULL;
 	}
 	if (!kbt->profile || (INT_MASK(p->faultnum) & QUEUED_INTERRUPTS) == 0)
 		return p;
 	return NULL;
 }

 /* Is the pc pointing to a sigreturn trampoline? */
 static int is_sigreturn(unsigned long pc)
 {
 	return (pc == VDSO_BASE);
 }

 /* Return a pt_regs pointer for a valid signal handler frame */
 static struct pt_regs *valid_sigframe(struct KBacktraceIterator* kbt)
 {
 	BacktraceIterator *b = &kbt->it;

 	if (b->pc == VDSO_BASE) {
 		struct rt_sigframe *frame;
 		unsigned long sigframe_top =
 			b->sp + sizeof(struct rt_sigframe) - 1;
 		if (!valid_address(kbt, b->sp) ||
 		    !valid_address(kbt, sigframe_top)) {
 			if (kbt->verbose)
 				pr_err("  (odd signal: sp %#lx?)\n",
 				       (unsigned long)(b->sp));
 			return NULL;
 		}
 		frame = (struct rt_sigframe *)b->sp;
 		if (kbt->verbose) {
 			pr_err("  <received signal %d>\n",
 			       frame->info.si_signo);
 		}
 		return (struct pt_regs *)&frame->uc.uc_mcontext;
 	}
 	return NULL;
 }

 static int KBacktraceIterator_is_sigreturn(struct KBacktraceIterator *kbt)
 {
 	return is_sigreturn(kbt->it.pc);
 }

 static int KBacktraceIterator_restart(struct KBacktraceIterator *kbt)
 {
 	struct pt_regs *p;

 	p = valid_fault_handler(kbt);
 	if (p == NULL)
 		p = valid_sigframe(kbt);
 	if (p == NULL)
 		return 0;
 	backtrace_init(&kbt->it, read_memory_func, kbt,
 		       p->pc, p->lr, p->sp, p->regs[52]);
 	kbt->new_context = 1;
 	return 1;
 }

 /* Find a frame that isn't a sigreturn, if there is one. */
 static int KBacktraceIterator_next_item_inclusive(
 	struct KBacktraceIterator *kbt)
 {
 	for (;;) {
 		do {
 			if (!KBacktraceIterator_is_sigreturn(kbt))
 				return KBT_ONGOING;
 		} while (backtrace_next(&kbt->it));

 		if (!KBacktraceIterator_restart(kbt))
 			return KBT_DONE;
 	}
 }

 /*
  * If the current sp is on a page different than what we recorded
  * as the top-of-kernel-stack last time we context switched, we have
  * probably blown the stack, and nothing is going to work out well.
  * If we can at least get out a warning, that may help the debug,
  * though we probably won't be able to backtrace into the code that
  * actually did the recursive damage.
  */
 static void validate_stack(struct pt_regs *regs)
 {
 	int cpu = smp_processor_id();
 	unsigned long ksp0 = get_current_ksp0();
 	unsigned long ksp0_base = ksp0 - THREAD_SIZE;
 	unsigned long sp = stack_pointer;

 	if (EX1_PL(regs->ex1) == KERNEL_PL && regs->sp >= ksp0) {
 		pr_err("WARNING: cpu %d: kernel stack page %#lx underrun!\n"
 		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
 		       cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
 	}

 	else if (sp < ksp0_base + sizeof(struct thread_info)) {
 		pr_err("WARNING: cpu %d: kernel stack page %#lx overrun!\n"
 		       "  sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
 		       cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
 	}
 }

 void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
 			     struct task_struct *t, struct pt_regs *regs)
 {
 	unsigned long pc, lr, sp, r52;
 	int is_current;

 	/*
 	 * Set up callback information.  We grab the kernel stack base
 	 * so we will allow reads of that address range, and if we're
 	 * asking about the current process we grab the page table
 	 * so we can check user accesses before trying to read them.
 	 * We flush the TLB to avoid any weird skew issues.
 	 */
 	is_current = (t == NULL);
 	kbt->is_current = is_current;
 	if (is_current)
 		t = validate_current();
 	kbt->task = t;
 	kbt->pgtable = NULL;
 	kbt->verbose = 0;   /* override in caller if desired */
 	kbt->profile = 0;   /* override in caller if desired */
 	kbt->end = KBT_ONGOING;
 	kbt->new_context = 0;
 	if (is_current) {
 		HV_PhysAddr pgdir_pa = hv_inquire_context().page_table;
 		if (pgdir_pa == (unsigned long)swapper_pg_dir - PAGE_OFFSET) {
 			/*
 			 * Not just an optimization: this also allows
 			 * this to work at all before va/pa mappings
 			 * are set up.
 			 */
 			kbt->pgtable = swapper_pg_dir;
 		} else {
 			struct page *page = pfn_to_page(PFN_DOWN(pgdir_pa));
 			if (!PageHighMem(page))
 				kbt->pgtable = __va(pgdir_pa);
 			else
 				pr_err("page table not in LOWMEM"
 				       " (%#llx)\n", pgdir_pa);
 		}
 		local_flush_tlb_all();
 		validate_stack(regs);
 	}

 	if (regs == NULL) {
 		if (is_current || t->state == TASK_RUNNING) {
 			/* Can't do this; we need registers */
 			kbt->end = KBT_RUNNING;
 			return;
 		}
 		pc = get_switch_to_pc();
 		lr = t->thread.pc;
 		sp = t->thread.ksp;
 		r52 = 0;
 	} else {
 		pc = regs->pc;
 		lr = regs->lr;
 		sp = regs->sp;
 		r52 = regs->regs[52];
 	}

 	backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
 	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
 }
 EXPORT_SYMBOL(KBacktraceIterator_init);

 int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
 {
 	return kbt->end != KBT_ONGOING;
 }
 EXPORT_SYMBOL(KBacktraceIterator_end);

 void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
 {
 	unsigned long old_pc = kbt->it.pc, old_sp = kbt->it.sp;
 	kbt->new_context = 0;
 	if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
 		kbt->end = KBT_DONE;
 		return;
 	}
 	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
 	if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
 		/* Trapped in a loop; give up. */
 		kbt->end = KBT_LOOP;
 	}
 }
 EXPORT_SYMBOL(KBacktraceIterator_next);

 /*
  * This method wraps the backtracer's more generic support.
  * It is only invoked from the architecture-specific code; show_stack()
  * and dump_stack() (in entry.S) are architecture-independent entry points.
  */
 void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
 {
 	int i;

 	if (headers) {
 		/*
 		 * Add a blank line since if we are called from panic(),
 		 * then bust_spinlocks() spit out a space in front of us
 		 * and it will mess up our KERN_ERR.
 		 */
 		pr_err("\n");
 		pr_err("Starting stack dump of tid %d, pid %d (%s)"
 		       " on cpu %d at cycle %lld\n",
 		       kbt->task->pid, kbt->task->tgid, kbt->task->comm,
 		       smp_processor_id(), get_cycles());
 	}
 	kbt->verbose = 1;
 	i = 0;
 	for (; !KBacktraceIterator_end(kbt); KBacktraceIterator_next(kbt)) {
 		char *modname;
 		const char *name;
 		unsigned long address = kbt->it.pc;
 		unsigned long offset, size;
 		char namebuf[KSYM_NAME_LEN+100];

 		if (address >= PAGE_OFFSET)
 			name = kallsyms_lookup(address, &size, &offset,
 					       &modname, namebuf);
 		else
 			name = NULL;

 		if (!name)
 			namebuf[0] = '\0';
 		else {
 			size_t namelen = strlen(namebuf);
 			size_t remaining = (sizeof(namebuf) - 1) - namelen;
 			char *p = namebuf + namelen;
 			int rc = snprintf(p, remaining, "+%#lx/%#lx ",
 					  offset, size);
 			if (modname && rc < remaining)
 				snprintf(p + rc, remaining - rc,
 					 "[%s] ", modname);
 			namebuf[sizeof(namebuf)-1] = '\0';
 		}

 		pr_err("  frame %d: 0x%lx %s(sp 0x%lx)\n",
 		       i++, address, namebuf, (unsigned long)(kbt->it.sp));

 		if (i >= 100) {
 			pr_err("Stack dump truncated"
 			       " (%d frames)\n", i);
 			break;
 		}
 	}
 	if (kbt->end == KBT_LOOP)
 		pr_err("Stack dump stopped; next frame identical to this one\n");
 	if (headers)
 		pr_err("Stack dump complete\n");
 }
 EXPORT_SYMBOL(tile_show_stack);


 /* This is called from show_regs() and _dump_stack() */
 void dump_stack_regs(struct pt_regs *regs)
 {
 	struct KBacktraceIterator kbt;
 	KBacktraceIterator_init(&kbt, NULL, regs);
 	tile_show_stack(&kbt, 1);
 }
 EXPORT_SYMBOL(dump_stack_regs);

 static struct pt_regs *regs_to_pt_regs(struct pt_regs *regs,
 				       ulong pc, ulong lr, ulong sp, ulong r52)
 {
 	memset(regs, 0, sizeof(struct pt_regs));
 	regs->pc = pc;
 	regs->lr = lr;
 	regs->sp = sp;
 	regs->regs[52] = r52;
 	return regs;
 }

 /* This is called from dump_stack() and just converts to pt_regs */
 void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
 {
 	struct pt_regs regs;
 	dump_stack_regs(regs_to_pt_regs(&regs, pc, lr, sp, r52));
 }

 /* This is called from KBacktraceIterator_init_current() */
 void _KBacktraceIterator_init_current(struct KBacktraceIterator *kbt, ulong pc,
 				      ulong lr, ulong sp, ulong r52)
 {
 	struct pt_regs regs;
 	KBacktraceIterator_init(kbt, NULL,
 				regs_to_pt_regs(&regs, pc, lr, sp, r52));
 }

 /* This is called only from kernel/sched.c, with esp == NULL */
 void show_stack(struct task_struct *task, unsigned long *esp)
 {
 	struct KBacktraceIterator kbt;
 	if (task == NULL || task == current)
 		KBacktraceIterator_init_current(&kbt);
 	else
 		KBacktraceIterator_init(&kbt, task, NULL);
 	tile_show_stack(&kbt, 0);
 }

 #ifdef CONFIG_STACKTRACE

 /* Support generic Linux stack API too */

 void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
 {
 	struct KBacktraceIterator kbt;
 	int skip = trace->skip;
 	int i = 0;

 	if (task == NULL || task == current)
 		KBacktraceIterator_init_current(&kbt);
 	else
 		KBacktraceIterator_init(&kbt, task, NULL);
 	for (; !KBacktraceIterator_end(&kbt); KBacktraceIterator_next(&kbt)) {
 		if (skip) {
 			--skip;
 			continue;
 		}
 		if (i >= trace->max_entries || kbt.it.pc < PAGE_OFFSET)
 			break;
 		trace->entries[i++] = kbt.it.pc;
 	}
 	trace->nr_entries = i;
 }
 EXPORT_SYMBOL(save_stack_trace_tsk);

 void save_stack_trace(struct stack_trace *trace)
 {
 	save_stack_trace_tsk(NULL, trace);
 }

 #endif

 /* In entry.S */
 EXPORT_SYMBOL(KBacktraceIterator_init_current);
	/*
	* Copyright 2010 Tilera Corporation. All Rights Reserved.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation, version 2.
	*
	* This program is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
	* NON INFRINGEMENT. See the GNU General Public License for
	* more details.
	*/

	#include <linux/sched.h>
	#include <linux/kernel.h>
	#include <linux/kprobes.h>
	#include <linux/module.h>
	#include <linux/pfn.h>
	#include <linux/kallsyms.h>
	#include <linux/stacktrace.h>
	#include <linux/uaccess.h>
	#include <linux/mmzone.h>
	#include <asm/backtrace.h>
	#include <asm/page.h>
	#include <asm/tlbflush.h>
	#include <asm/ucontext.h>
	#include <asm/sigframe.h>
	#include <asm/stack.h>
	#include <arch/abi.h>
	#include <arch/interrupts.h>

	#define KBT_ONGOING 0 /* Backtrace still ongoing */
	#define KBT_DONE 1 /* Backtrace cleanly completed */
	#define KBT_RUNNING 2 /* Can't run backtrace on a running task */
	#define KBT_LOOP 3 /* Backtrace entered a loop */

	/* Is address on the specified kernel stack? */
	static int in_kernel_stack(struct KBacktraceIterator *kbt, unsigned long sp)
	{
	ulong kstack_base = (ulong) kbt->task->stack;
	if (kstack_base == 0) /* corrupt task pointer; just follow stack... */
	return sp >= PAGE_OFFSET && sp < (unsigned long)high_memory;
	return sp >= kstack_base && sp < kstack_base + THREAD_SIZE;
	}

	/* Is address valid for reading? */
	static int valid_address(struct KBacktraceIterator *kbt, unsigned long address)
	{
	HV_PTE *l1_pgtable = kbt->pgtable;
	HV_PTE *l2_pgtable;
	unsigned long pfn;
	HV_PTE pte;
	struct page *page;

	if (l1_pgtable == NULL)
	return 0; /* can't read user space in other tasks */

	#ifdef CONFIG_64BIT
	/* Find the real l1_pgtable by looking in the l0_pgtable. */
	pte = l1_pgtable[HV_L0_INDEX(address)];
	if (!hv_pte_get_present(pte))
	return 0;
	pfn = hv_pte_get_pfn(pte);
	if (pte_huge(pte)) {
	if (!pfn_valid(pfn)) {
	pr_err("L0 huge page has bad pfn %#lx\n", pfn);
	return 0;
	}
	return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
	}
	page = pfn_to_page(pfn);
	BUG_ON(PageHighMem(page)); /* No HIGHMEM on 64-bit. */
	l1_pgtable = (HV_PTE *)pfn_to_kaddr(pfn);
	#endif
	pte = l1_pgtable[HV_L1_INDEX(address)];
	if (!hv_pte_get_present(pte))
	return 0;
	pfn = hv_pte_get_pfn(pte);
	if (pte_huge(pte)) {
	if (!pfn_valid(pfn)) {
	pr_err("huge page has bad pfn %#lx\n", pfn);
	return 0;
	}
	return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
	}

	page = pfn_to_page(pfn);
	if (PageHighMem(page)) {
	pr_err("L2 page table not in LOWMEM (%#llx)\n",
	HV_PFN_TO_CPA(pfn));
	return 0;
	}
	l2_pgtable = (HV_PTE *)pfn_to_kaddr(pfn);
	pte = l2_pgtable[HV_L2_INDEX(address)];
	return hv_pte_get_present(pte) && hv_pte_get_readable(pte);
	}

	/* Callback for backtracer; basically a glorified memcpy */
	static bool read_memory_func(void *result, unsigned long address,
	unsigned int size, void *vkbt)
	{
	int retval;
	struct KBacktraceIterator kbt = (struct KBacktraceIterator )vkbt;
	if (__kernel_text_address(address)) {
	/* OK to read kernel code. */
	} else if (address >= PAGE_OFFSET) {
	/* We only tolerate kernel-space reads of this task's stack */
	if (!in_kernel_stack(kbt, address))
	return 0;
	} else if (!valid_address(kbt, address)) {
	return 0; /* invalid user-space address */
	}
	pagefault_disable();
	retval = __copy_from_user_inatomic(result,
	(void __user __force *)address,
	size);
	pagefault_enable();
	return (retval == 0);
	}

	/* Return a pt_regs pointer for a valid fault handler frame */
	static struct pt_regs valid_fault_handler(struct KBacktraceIterator kbt)
	{
	const char fault = NULL; / happy compiler */
	char fault_buf[64];
	unsigned long sp = kbt->it.sp;
	struct pt_regs *p;

	if (!in_kernel_stack(kbt, sp))
	return NULL;
	if (!in_kernel_stack(kbt, sp + C_ABI_SAVE_AREA_SIZE + PTREGS_SIZE-1))
	return NULL;
	p = (struct pt_regs *)(sp + C_ABI_SAVE_AREA_SIZE);
	if (p->faultnum == INT_SWINT_1 \|\| p->faultnum == INT_SWINT_1_SIGRETURN)
	fault = "syscall";
	else {
	if (kbt->verbose) { /* else we aren't going to use it */
	snprintf(fault_buf, sizeof(fault_buf),
	"interrupt %ld", p->faultnum);
	fault = fault_buf;
	}
	}
	if (EX1_PL(p->ex1) == KERNEL_PL &&
	__kernel_text_address(p->pc) &&
	in_kernel_stack(kbt, p->sp) &&
	p->sp >= sp) {
	if (kbt->verbose)
	pr_err(" <%s while in kernel mode>\n", fault);
	} else if (EX1_PL(p->ex1) == USER_PL &&
	p->pc < PAGE_OFFSET &&
	p->sp < PAGE_OFFSET) {
	if (kbt->verbose)
	pr_err(" <%s while in user mode>\n", fault);
	} else if (kbt->verbose) {
	pr_err(" (odd fault: pc %#lx, sp %#lx, ex1 %#lx?)\n",
	p->pc, p->sp, p->ex1);
	p = NULL;
	}
	if (!kbt->profile \|\| (INT_MASK(p->faultnum) & QUEUED_INTERRUPTS) == 0)
	return p;
	return NULL;
	}

	/* Is the pc pointing to a sigreturn trampoline? */
	static int is_sigreturn(unsigned long pc)
	{
	return (pc == VDSO_BASE);
	}

	/* Return a pt_regs pointer for a valid signal handler frame */
	static struct pt_regs valid_sigframe(struct KBacktraceIterator kbt)
	{
	BacktraceIterator *b = &kbt->it;

	if (b->pc == VDSO_BASE) {
	struct rt_sigframe *frame;
	unsigned long sigframe_top =
	b->sp + sizeof(struct rt_sigframe) - 1;
	if (!valid_address(kbt, b->sp) \|\|
	!valid_address(kbt, sigframe_top)) {
	if (kbt->verbose)
	pr_err(" (odd signal: sp %#lx?)\n",
	(unsigned long)(b->sp));
	return NULL;
	}
	frame = (struct rt_sigframe *)b->sp;
	if (kbt->verbose) {
	pr_err(" <received signal %d>\n",
	frame->info.si_signo);
	}
	return (struct pt_regs *)&frame->uc.uc_mcontext;
	}
	return NULL;
	}

	static int KBacktraceIterator_is_sigreturn(struct KBacktraceIterator *kbt)
	{
	return is_sigreturn(kbt->it.pc);
	}

	static int KBacktraceIterator_restart(struct KBacktraceIterator *kbt)
	{
	struct pt_regs *p;

	p = valid_fault_handler(kbt);
	if (p == NULL)
	p = valid_sigframe(kbt);
	if (p == NULL)
	return 0;
	backtrace_init(&kbt->it, read_memory_func, kbt,
	p->pc, p->lr, p->sp, p->regs[52]);
	kbt->new_context = 1;
	return 1;
	}

	/* Find a frame that isn't a sigreturn, if there is one. */
	static int KBacktraceIterator_next_item_inclusive(
	struct KBacktraceIterator *kbt)
	{
	for (;;) {
	do {
	if (!KBacktraceIterator_is_sigreturn(kbt))
	return KBT_ONGOING;
	} while (backtrace_next(&kbt->it));

	if (!KBacktraceIterator_restart(kbt))
	return KBT_DONE;
	}
	}

	/*
	* If the current sp is on a page different than what we recorded
	* as the top-of-kernel-stack last time we context switched, we have
	* probably blown the stack, and nothing is going to work out well.
	* If we can at least get out a warning, that may help the debug,
	* though we probably won't be able to backtrace into the code that
	* actually did the recursive damage.
	*/
	static void validate_stack(struct pt_regs *regs)
	{
	int cpu = smp_processor_id();
	unsigned long ksp0 = get_current_ksp0();
	unsigned long ksp0_base = ksp0 - THREAD_SIZE;
	unsigned long sp = stack_pointer;

	if (EX1_PL(regs->ex1) == KERNEL_PL && regs->sp >= ksp0) {
	pr_err("WARNING: cpu %d: kernel stack page %#lx underrun!\n"
	" sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
	cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
	}

	else if (sp < ksp0_base + sizeof(struct thread_info)) {
	pr_err("WARNING: cpu %d: kernel stack page %#lx overrun!\n"
	" sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
	cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
	}
	}

	void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
	struct task_struct t, struct pt_regs regs)
	{
	unsigned long pc, lr, sp, r52;
	int is_current;

	/*
	* Set up callback information. We grab the kernel stack base
	* so we will allow reads of that address range, and if we're
	* asking about the current process we grab the page table
	* so we can check user accesses before trying to read them.
	* We flush the TLB to avoid any weird skew issues.
	*/
	is_current = (t == NULL);
	kbt->is_current = is_current;
	if (is_current)
	t = validate_current();
	kbt->task = t;
	kbt->pgtable = NULL;
	kbt->verbose = 0; /* override in caller if desired */
	kbt->profile = 0; /* override in caller if desired */
	kbt->end = KBT_ONGOING;
	kbt->new_context = 0;
	if (is_current) {
	HV_PhysAddr pgdir_pa = hv_inquire_context().page_table;
	if (pgdir_pa == (unsigned long)swapper_pg_dir - PAGE_OFFSET) {
	/*
	* Not just an optimization: this also allows
	* this to work at all before va/pa mappings
	* are set up.
	*/
	kbt->pgtable = swapper_pg_dir;
	} else {
	struct page *page = pfn_to_page(PFN_DOWN(pgdir_pa));
	if (!PageHighMem(page))
	kbt->pgtable = __va(pgdir_pa);
	else
	pr_err("page table not in LOWMEM"
	" (%#llx)\n", pgdir_pa);
	}
	local_flush_tlb_all();
	validate_stack(regs);
	}

	if (regs == NULL) {
	if (is_current \|\| t->state == TASK_RUNNING) {
	/* Can't do this; we need registers */
	kbt->end = KBT_RUNNING;
	return;
	}
	pc = get_switch_to_pc();
	lr = t->thread.pc;
	sp = t->thread.ksp;
	r52 = 0;
	} else {
	pc = regs->pc;
	lr = regs->lr;
	sp = regs->sp;
	r52 = regs->regs[52];
	}

	backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
	}
	EXPORT_SYMBOL(KBacktraceIterator_init);

	int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
	{
	return kbt->end != KBT_ONGOING;
	}
	EXPORT_SYMBOL(KBacktraceIterator_end);

	void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
	{
	unsigned long old_pc = kbt->it.pc, old_sp = kbt->it.sp;
	kbt->new_context = 0;
	if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
	kbt->end = KBT_DONE;
	return;
	}
	kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
	if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
	/* Trapped in a loop; give up. */
	kbt->end = KBT_LOOP;
	}
	}
	EXPORT_SYMBOL(KBacktraceIterator_next);

	/*
	* This method wraps the backtracer's more generic support.
	* It is only invoked from the architecture-specific code; show_stack()
	* and dump_stack() (in entry.S) are architecture-independent entry points.
	*/
	void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
	{
	int i;

	if (headers) {
	/*
	* Add a blank line since if we are called from panic(),
	* then bust_spinlocks() spit out a space in front of us
	* and it will mess up our KERN_ERR.
	*/
	pr_err("\n");
	pr_err("Starting stack dump of tid %d, pid %d (%s)"
	" on cpu %d at cycle %lld\n",
	kbt->task->pid, kbt->task->tgid, kbt->task->comm,
	smp_processor_id(), get_cycles());
	}
	kbt->verbose = 1;
	i = 0;
	for (; !KBacktraceIterator_end(kbt); KBacktraceIterator_next(kbt)) {
	char *modname;
	const char *name;
	unsigned long address = kbt->it.pc;
	unsigned long offset, size;
	char namebuf[KSYM_NAME_LEN+100];

	if (address >= PAGE_OFFSET)
	name = kallsyms_lookup(address, &size, &offset,
	&modname, namebuf);
	else
	name = NULL;

	if (!name)
	namebuf[0] = '\0';
	else {
	size_t namelen = strlen(namebuf);
	size_t remaining = (sizeof(namebuf) - 1) - namelen;
	char *p = namebuf + namelen;
	int rc = snprintf(p, remaining, "+%#lx/%#lx ",
	offset, size);
	if (modname && rc < remaining)
	snprintf(p + rc, remaining - rc,
	"[%s] ", modname);
	namebuf[sizeof(namebuf)-1] = '\0';
	}

	pr_err(" frame %d: 0x%lx %s(sp 0x%lx)\n",
	i++, address, namebuf, (unsigned long)(kbt->it.sp));

	if (i >= 100) {
	pr_err("Stack dump truncated"
	" (%d frames)\n", i);
	break;
	}
	}
	if (kbt->end == KBT_LOOP)
	pr_err("Stack dump stopped; next frame identical to this one\n");
	if (headers)
	pr_err("Stack dump complete\n");
	}
	EXPORT_SYMBOL(tile_show_stack);


	/* This is called from show_regs() and _dump_stack() */
	void dump_stack_regs(struct pt_regs *regs)
	{
	struct KBacktraceIterator kbt;
	KBacktraceIterator_init(&kbt, NULL, regs);
	tile_show_stack(&kbt, 1);
	}
	EXPORT_SYMBOL(dump_stack_regs);

	static struct pt_regs regs_to_pt_regs(struct pt_regs regs,
	ulong pc, ulong lr, ulong sp, ulong r52)
	{
	memset(regs, 0, sizeof(struct pt_regs));
	regs->pc = pc;
	regs->lr = lr;
	regs->sp = sp;
	regs->regs[52] = r52;
	return regs;
	}

	/* This is called from dump_stack() and just converts to pt_regs */
	void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
	{
	struct pt_regs regs;
	dump_stack_regs(regs_to_pt_regs(&regs, pc, lr, sp, r52));
	}

	/* This is called from KBacktraceIterator_init_current() */
	void _KBacktraceIterator_init_current(struct KBacktraceIterator *kbt, ulong pc,
	ulong lr, ulong sp, ulong r52)
	{
	struct pt_regs regs;
	KBacktraceIterator_init(kbt, NULL,
	regs_to_pt_regs(&regs, pc, lr, sp, r52));
	}

	/* This is called only from kernel/sched.c, with esp == NULL */
	void show_stack(struct task_struct task, unsigned long esp)
	{
	struct KBacktraceIterator kbt;
	if (task == NULL \|\| task == current)
	KBacktraceIterator_init_current(&kbt);
	else
	KBacktraceIterator_init(&kbt, task, NULL);
	tile_show_stack(&kbt, 0);
	}

	#ifdef CONFIG_STACKTRACE

	/* Support generic Linux stack API too */

	void save_stack_trace_tsk(struct task_struct task, struct stack_trace trace)
	{
	struct KBacktraceIterator kbt;
	int skip = trace->skip;
	int i = 0;

	if (task == NULL \|\| task == current)
	KBacktraceIterator_init_current(&kbt);
	else
	KBacktraceIterator_init(&kbt, task, NULL);
	for (; !KBacktraceIterator_end(&kbt); KBacktraceIterator_next(&kbt)) {
	if (skip) {
	--skip;
	continue;
	}
	if (i >= trace->max_entries \|\| kbt.it.pc < PAGE_OFFSET)
	break;
	trace->entries[i++] = kbt.it.pc;
	}
	trace->nr_entries = i;
	}
	EXPORT_SYMBOL(save_stack_trace_tsk);

	void save_stack_trace(struct stack_trace *trace)
	{
	save_stack_trace_tsk(NULL, trace);
	}

	#endif

	/* In entry.S */
	EXPORT_SYMBOL(KBacktraceIterator_init_current);