arch/powerpc/kernel/perf_callchain.c - maze/linux - Git at Google

 /*
  * Performance counter callchain support - powerpc architecture code
  *
  * Copyright © 2009 Paul Mackerras, IBM Corporation.
  *
  * 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; either version
  * 2 of the License, or (at your option) any later version.
  */
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/perf_event.h>
 #include <linux/percpu.h>
 #include <linux/uaccess.h>
 #include <linux/mm.h>
 #include <asm/ptrace.h>
 #include <asm/pgtable.h>
 #include <asm/sigcontext.h>
 #include <asm/ucontext.h>
 #include <asm/vdso.h>
 #ifdef CONFIG_PPC64
 #include "ppc32.h"
 #endif

 /*
  * Store another value in a callchain_entry.
  */
 static inline void callchain_store(struct perf_callchain_entry *entry, u64 ip)
 {
 	unsigned int nr = entry->nr;

 	if (nr < PERF_MAX_STACK_DEPTH) {
 		entry->ip[nr] = ip;
 		entry->nr = nr + 1;
 	}
 }

 /*
  * Is sp valid as the address of the next kernel stack frame after prev_sp?
  * The next frame may be in a different stack area but should not go
  * back down in the same stack area.
  */
 static int valid_next_sp(unsigned long sp, unsigned long prev_sp)
 {
 	if (sp & 0xf)
 		return 0;		/* must be 16-byte aligned */
 	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
 		return 0;
 	if (sp >= prev_sp + STACK_FRAME_OVERHEAD)
 		return 1;
 	/*
 	 * sp could decrease when we jump off an interrupt stack
 	 * back to the regular process stack.
 	 */
 	if ((sp & ~(THREAD_SIZE - 1)) != (prev_sp & ~(THREAD_SIZE - 1)))
 		return 1;
 	return 0;
 }

 static void perf_callchain_kernel(struct pt_regs *regs,
 				  struct perf_callchain_entry *entry)
 {
 	unsigned long sp, next_sp;
 	unsigned long next_ip;
 	unsigned long lr;
 	long level = 0;
 	unsigned long *fp;

 	lr = regs->link;
 	sp = regs->gpr[1];
 	callchain_store(entry, PERF_CONTEXT_KERNEL);
 	callchain_store(entry, regs->nip);

 	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
 		return;

 	for (;;) {
 		fp = (unsigned long *) sp;
 		next_sp = fp[0];

 		if (next_sp == sp + STACK_INT_FRAME_SIZE &&
 		    fp[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
 			/*
 			 * This looks like an interrupt frame for an
 			 * interrupt that occurred in the kernel
 			 */
 			regs = (struct pt_regs *)(sp + STACK_FRAME_OVERHEAD);
 			next_ip = regs->nip;
 			lr = regs->link;
 			level = 0;
 			callchain_store(entry, PERF_CONTEXT_KERNEL);

 		} else {
 			if (level == 0)
 				next_ip = lr;
 			else
 				next_ip = fp[STACK_FRAME_LR_SAVE];

 			/*
 			 * We can't tell which of the first two addresses
 			 * we get are valid, but we can filter out the
 			 * obviously bogus ones here.  We replace them
 			 * with 0 rather than removing them entirely so
 			 * that userspace can tell which is which.
 			 */
 			if ((level == 1 && next_ip == lr) ||
 			    (level <= 1 && !kernel_text_address(next_ip)))
 				next_ip = 0;

 			++level;
 		}

 		callchain_store(entry, next_ip);
 		if (!valid_next_sp(next_sp, sp))
 			return;
 		sp = next_sp;
 	}
 }

 #ifdef CONFIG_PPC64
 /*
  * On 64-bit we don't want to invoke hash_page on user addresses from
  * interrupt context, so if the access faults, we read the page tables
  * to find which page (if any) is mapped and access it directly.
  */
 static int read_user_stack_slow(void __user *ptr, void *ret, int nb)
 {
 	pgd_t *pgdir;
 	pte_t *ptep, pte;
 	unsigned shift;
 	unsigned long addr = (unsigned long) ptr;
 	unsigned long offset;
 	unsigned long pfn;
 	void *kaddr;

 	pgdir = current->mm->pgd;
 	if (!pgdir)
 		return -EFAULT;

 	ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift);
 	if (!shift)
 		shift = PAGE_SHIFT;

 	/* align address to page boundary */
 	offset = addr & ((1UL << shift) - 1);
 	addr -= offset;

 	if (ptep == NULL)
 		return -EFAULT;
 	pte = *ptep;
 	if (!pte_present(pte) || !(pte_val(pte) & _PAGE_USER))
 		return -EFAULT;
 	pfn = pte_pfn(pte);
 	if (!page_is_ram(pfn))
 		return -EFAULT;

 	/* no highmem to worry about here */
 	kaddr = pfn_to_kaddr(pfn);
 	memcpy(ret, kaddr + offset, nb);
 	return 0;
 }

 static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)
 {
 	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned long) ||
 	    ((unsigned long)ptr & 7))
 		return -EFAULT;

 	if (!__get_user_inatomic(*ret, ptr))
 		return 0;

 	return read_user_stack_slow(ptr, ret, 8);
 }

 static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
 {
 	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
 	    ((unsigned long)ptr & 3))
 		return -EFAULT;

 	if (!__get_user_inatomic(*ret, ptr))
 		return 0;

 	return read_user_stack_slow(ptr, ret, 4);
 }

 static inline int valid_user_sp(unsigned long sp, int is_64)
 {
 	if (!sp || (sp & 7) || sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
 		return 0;
 	return 1;
 }

 /*
  * 64-bit user processes use the same stack frame for RT and non-RT signals.
  */
 struct signal_frame_64 {
 	char		dummy[__SIGNAL_FRAMESIZE];
 	struct ucontext	uc;
 	unsigned long	unused[2];
 	unsigned int	tramp[6];
 	struct siginfo	*pinfo;
 	void		*puc;
 	struct siginfo	info;
 	char		abigap[288];
 };

 static int is_sigreturn_64_address(unsigned long nip, unsigned long fp)
 {
 	if (nip == fp + offsetof(struct signal_frame_64, tramp))
 		return 1;
 	if (vdso64_rt_sigtramp && current->mm->context.vdso_base &&
 	    nip == current->mm->context.vdso_base + vdso64_rt_sigtramp)
 		return 1;
 	return 0;
 }

 /*
  * Do some sanity checking on the signal frame pointed to by sp.
  * We check the pinfo and puc pointers in the frame.
  */
 static int sane_signal_64_frame(unsigned long sp)
 {
 	struct signal_frame_64 __user *sf;
 	unsigned long pinfo, puc;

 	sf = (struct signal_frame_64 __user *) sp;
 	if (read_user_stack_64((unsigned long __user *) &sf->pinfo, &pinfo) ||
 	    read_user_stack_64((unsigned long __user *) &sf->puc, &puc))
 		return 0;
 	return pinfo == (unsigned long) &sf->info &&
 		puc == (unsigned long) &sf->uc;
 }

 static void perf_callchain_user_64(struct pt_regs *regs,
 				   struct perf_callchain_entry *entry)
 {
 	unsigned long sp, next_sp;
 	unsigned long next_ip;
 	unsigned long lr;
 	long level = 0;
 	struct signal_frame_64 __user *sigframe;
 	unsigned long __user *fp, *uregs;

 	next_ip = regs->nip;
 	lr = regs->link;
 	sp = regs->gpr[1];
 	callchain_store(entry, PERF_CONTEXT_USER);
 	callchain_store(entry, next_ip);

 	for (;;) {
 		fp = (unsigned long __user *) sp;
 		if (!valid_user_sp(sp, 1) || read_user_stack_64(fp, &next_sp))
 			return;
 		if (level > 0 && read_user_stack_64(&fp[2], &next_ip))
 			return;

 		/*
 		 * Note: the next_sp - sp >= signal frame size check
 		 * is true when next_sp < sp, which can happen when
 		 * transitioning from an alternate signal stack to the
 		 * normal stack.
 		 */
 		if (next_sp - sp >= sizeof(struct signal_frame_64) &&
 		    (is_sigreturn_64_address(next_ip, sp) ||
 		     (level <= 1 && is_sigreturn_64_address(lr, sp))) &&
 		    sane_signal_64_frame(sp)) {
 			/*
 			 * This looks like an signal frame
 			 */
 			sigframe = (struct signal_frame_64 __user *) sp;
 			uregs = sigframe->uc.uc_mcontext.gp_regs;
 			if (read_user_stack_64(&uregs[PT_NIP], &next_ip) ||
 			    read_user_stack_64(&uregs[PT_LNK], &lr) ||
 			    read_user_stack_64(&uregs[PT_R1], &sp))
 				return;
 			level = 0;
 			callchain_store(entry, PERF_CONTEXT_USER);
 			callchain_store(entry, next_ip);
 			continue;
 		}

 		if (level == 0)
 			next_ip = lr;
 		callchain_store(entry, next_ip);
 		++level;
 		sp = next_sp;
 	}
 }

 static inline int current_is_64bit(void)
 {
 	/*
 	 * We can't use test_thread_flag() here because we may be on an
 	 * interrupt stack, and the thread flags don't get copied over
 	 * from the thread_info on the main stack to the interrupt stack.
 	 */
 	return !test_ti_thread_flag(task_thread_info(current), TIF_32BIT);
 }

 #else  /* CONFIG_PPC64 */
 /*
  * On 32-bit we just access the address and let hash_page create a
  * HPTE if necessary, so there is no need to fall back to reading
  * the page tables.  Since this is called at interrupt level,
  * do_page_fault() won't treat a DSI as a page fault.
  */
 static int read_user_stack_32(unsigned int __user *ptr, unsigned int *ret)
 {
 	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) ||
 	    ((unsigned long)ptr & 3))
 		return -EFAULT;

 	return __get_user_inatomic(*ret, ptr);
 }

 static inline void perf_callchain_user_64(struct pt_regs *regs,
 					  struct perf_callchain_entry *entry)
 {
 }

 static inline int current_is_64bit(void)
 {
 	return 0;
 }

 static inline int valid_user_sp(unsigned long sp, int is_64)
 {
 	if (!sp || (sp & 7) || sp > TASK_SIZE - 32)
 		return 0;
 	return 1;
 }

 #define __SIGNAL_FRAMESIZE32	__SIGNAL_FRAMESIZE
 #define sigcontext32		sigcontext
 #define mcontext32		mcontext
 #define ucontext32		ucontext
 #define compat_siginfo_t	struct siginfo

 #endif /* CONFIG_PPC64 */

 /*
  * Layout for non-RT signal frames
  */
 struct signal_frame_32 {
 	char			dummy[__SIGNAL_FRAMESIZE32];
 	struct sigcontext32	sctx;
 	struct mcontext32	mctx;
 	int			abigap[56];
 };

 /*
  * Layout for RT signal frames
  */
 struct rt_signal_frame_32 {
 	char			dummy[__SIGNAL_FRAMESIZE32 + 16];
 	compat_siginfo_t	info;
 	struct ucontext32	uc;
 	int			abigap[56];
 };

 static int is_sigreturn_32_address(unsigned int nip, unsigned int fp)
 {
 	if (nip == fp + offsetof(struct signal_frame_32, mctx.mc_pad))
 		return 1;
 	if (vdso32_sigtramp && current->mm->context.vdso_base &&
 	    nip == current->mm->context.vdso_base + vdso32_sigtramp)
 		return 1;
 	return 0;
 }

 static int is_rt_sigreturn_32_address(unsigned int nip, unsigned int fp)
 {
 	if (nip == fp + offsetof(struct rt_signal_frame_32,
 				 uc.uc_mcontext.mc_pad))
 		return 1;
 	if (vdso32_rt_sigtramp && current->mm->context.vdso_base &&
 	    nip == current->mm->context.vdso_base + vdso32_rt_sigtramp)
 		return 1;
 	return 0;
 }

 static int sane_signal_32_frame(unsigned int sp)
 {
 	struct signal_frame_32 __user *sf;
 	unsigned int regs;

 	sf = (struct signal_frame_32 __user *) (unsigned long) sp;
 	if (read_user_stack_32((unsigned int __user *) &sf->sctx.regs, &regs))
 		return 0;
 	return regs == (unsigned long) &sf->mctx;
 }

 static int sane_rt_signal_32_frame(unsigned int sp)
 {
 	struct rt_signal_frame_32 __user *sf;
 	unsigned int regs;

 	sf = (struct rt_signal_frame_32 __user *) (unsigned long) sp;
 	if (read_user_stack_32((unsigned int __user *) &sf->uc.uc_regs, &regs))
 		return 0;
 	return regs == (unsigned long) &sf->uc.uc_mcontext;
 }

 static unsigned int __user *signal_frame_32_regs(unsigned int sp,
 				unsigned int next_sp, unsigned int next_ip)
 {
 	struct mcontext32 __user *mctx = NULL;
 	struct signal_frame_32 __user *sf;
 	struct rt_signal_frame_32 __user *rt_sf;

 	/*
 	 * Note: the next_sp - sp >= signal frame size check
 	 * is true when next_sp < sp, for example, when
 	 * transitioning from an alternate signal stack to the
 	 * normal stack.
 	 */
 	if (next_sp - sp >= sizeof(struct signal_frame_32) &&
 	    is_sigreturn_32_address(next_ip, sp) &&
 	    sane_signal_32_frame(sp)) {
 		sf = (struct signal_frame_32 __user *) (unsigned long) sp;
 		mctx = &sf->mctx;
 	}

 	if (!mctx && next_sp - sp >= sizeof(struct rt_signal_frame_32) &&
 	    is_rt_sigreturn_32_address(next_ip, sp) &&
 	    sane_rt_signal_32_frame(sp)) {
 		rt_sf = (struct rt_signal_frame_32 __user *) (unsigned long) sp;
 		mctx = &rt_sf->uc.uc_mcontext;
 	}

 	if (!mctx)
 		return NULL;
 	return mctx->mc_gregs;
 }

 static void perf_callchain_user_32(struct pt_regs *regs,
 				   struct perf_callchain_entry *entry)
 {
 	unsigned int sp, next_sp;
 	unsigned int next_ip;
 	unsigned int lr;
 	long level = 0;
 	unsigned int __user *fp, *uregs;

 	next_ip = regs->nip;
 	lr = regs->link;
 	sp = regs->gpr[1];
 	callchain_store(entry, PERF_CONTEXT_USER);
 	callchain_store(entry, next_ip);

 	while (entry->nr < PERF_MAX_STACK_DEPTH) {
 		fp = (unsigned int __user *) (unsigned long) sp;
 		if (!valid_user_sp(sp, 0) || read_user_stack_32(fp, &next_sp))
 			return;
 		if (level > 0 && read_user_stack_32(&fp[1], &next_ip))
 			return;

 		uregs = signal_frame_32_regs(sp, next_sp, next_ip);
 		if (!uregs && level <= 1)
 			uregs = signal_frame_32_regs(sp, next_sp, lr);
 		if (uregs) {
 			/*
 			 * This looks like an signal frame, so restart
 			 * the stack trace with the values in it.
 			 */
 			if (read_user_stack_32(&uregs[PT_NIP], &next_ip) ||
 			    read_user_stack_32(&uregs[PT_LNK], &lr) ||
 			    read_user_stack_32(&uregs[PT_R1], &sp))
 				return;
 			level = 0;
 			callchain_store(entry, PERF_CONTEXT_USER);
 			callchain_store(entry, next_ip);
 			continue;
 		}

 		if (level == 0)
 			next_ip = lr;
 		callchain_store(entry, next_ip);
 		++level;
 		sp = next_sp;
 	}
 }

 /*
  * Since we can't get PMU interrupts inside a PMU interrupt handler,
  * we don't need separate irq and nmi entries here.
  */
 static DEFINE_PER_CPU(struct perf_callchain_entry, cpu_perf_callchain);

 struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
 {
 	struct perf_callchain_entry *entry = &__get_cpu_var(cpu_perf_callchain);

 	entry->nr = 0;

 	if (current->pid == 0)		/* idle task? */
 		return entry;

 	if (!user_mode(regs)) {
 		perf_callchain_kernel(regs, entry);
 		if (current->mm)
 			regs = task_pt_regs(current);
 		else
 			regs = NULL;
 	}

 	if (regs) {
 		if (current_is_64bit())
 			perf_callchain_user_64(regs, entry);
 		else
 			perf_callchain_user_32(regs, entry);
 	}

 	return entry;
 }
	/*
	* Performance counter callchain support - powerpc architecture code
	*
	* Copyright © 2009 Paul Mackerras, IBM Corporation.
	*
	* 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; either version
	* 2 of the License, or (at your option) any later version.
	*/
	#include <linux/kernel.h>
	#include <linux/sched.h>
	#include <linux/perf_event.h>
	#include <linux/percpu.h>
	#include <linux/uaccess.h>
	#include <linux/mm.h>
	#include <asm/ptrace.h>
	#include <asm/pgtable.h>
	#include <asm/sigcontext.h>
	#include <asm/ucontext.h>
	#include <asm/vdso.h>
	#ifdef CONFIG_PPC64
	#include "ppc32.h"
	#endif

	/*
	* Store another value in a callchain_entry.
	*/
	static inline void callchain_store(struct perf_callchain_entry *entry, u64 ip)
	{
	unsigned int nr = entry->nr;

	if (nr < PERF_MAX_STACK_DEPTH) {
	entry->ip[nr] = ip;
	entry->nr = nr + 1;
	}
	}

	/*
	* Is sp valid as the address of the next kernel stack frame after prev_sp?
	* The next frame may be in a different stack area but should not go
	* back down in the same stack area.
	*/
	static int valid_next_sp(unsigned long sp, unsigned long prev_sp)
	{
	if (sp & 0xf)
	return 0; /* must be 16-byte aligned */
	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
	return 0;
	if (sp >= prev_sp + STACK_FRAME_OVERHEAD)
	return 1;
	/*
	* sp could decrease when we jump off an interrupt stack
	* back to the regular process stack.
	*/
	if ((sp & ~(THREAD_SIZE - 1)) != (prev_sp & ~(THREAD_SIZE - 1)))
	return 1;
	return 0;
	}

	static void perf_callchain_kernel(struct pt_regs *regs,
	struct perf_callchain_entry *entry)
	{
	unsigned long sp, next_sp;
	unsigned long next_ip;
	unsigned long lr;
	long level = 0;
	unsigned long *fp;

	lr = regs->link;
	sp = regs->gpr[1];
	callchain_store(entry, PERF_CONTEXT_KERNEL);
	callchain_store(entry, regs->nip);

	if (!validate_sp(sp, current, STACK_FRAME_OVERHEAD))
	return;

	for (;;) {
	fp = (unsigned long *) sp;
	next_sp = fp[0];

	if (next_sp == sp + STACK_INT_FRAME_SIZE &&
	fp[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
	/*
	* This looks like an interrupt frame for an
	* interrupt that occurred in the kernel
	*/
	regs = (struct pt_regs *)(sp + STACK_FRAME_OVERHEAD);
	next_ip = regs->nip;
	lr = regs->link;
	level = 0;
	callchain_store(entry, PERF_CONTEXT_KERNEL);

	} else {
	if (level == 0)
	next_ip = lr;
	else
	next_ip = fp[STACK_FRAME_LR_SAVE];

	/*
	* We can't tell which of the first two addresses
	* we get are valid, but we can filter out the
	* obviously bogus ones here. We replace them
	* with 0 rather than removing them entirely so
	* that userspace can tell which is which.
	*/
	if ((level == 1 && next_ip == lr) \|\|
	(level <= 1 && !kernel_text_address(next_ip)))
	next_ip = 0;

	++level;
	}

	callchain_store(entry, next_ip);
	if (!valid_next_sp(next_sp, sp))
	return;
	sp = next_sp;
	}
	}

	#ifdef CONFIG_PPC64
	/*
	* On 64-bit we don't want to invoke hash_page on user addresses from
	* interrupt context, so if the access faults, we read the page tables
	* to find which page (if any) is mapped and access it directly.
	*/
	static int read_user_stack_slow(void __user ptr, void ret, int nb)
	{
	pgd_t *pgdir;
	pte_t *ptep, pte;
	unsigned shift;
	unsigned long addr = (unsigned long) ptr;
	unsigned long offset;
	unsigned long pfn;
	void *kaddr;

	pgdir = current->mm->pgd;
	if (!pgdir)
	return -EFAULT;

	ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift);
	if (!shift)
	shift = PAGE_SHIFT;

	/* align address to page boundary */
	offset = addr & ((1UL << shift) - 1);
	addr -= offset;

	if (ptep == NULL)
	return -EFAULT;
	pte = *ptep;
	if (!pte_present(pte) \|\| !(pte_val(pte) & _PAGE_USER))
	return -EFAULT;
	pfn = pte_pfn(pte);
	if (!page_is_ram(pfn))
	return -EFAULT;

	/* no highmem to worry about here */
	kaddr = pfn_to_kaddr(pfn);
	memcpy(ret, kaddr + offset, nb);
	return 0;
	}

	static int read_user_stack_64(unsigned long __user ptr, unsigned long ret)
	{
	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned long) \|\|
	((unsigned long)ptr & 7))
	return -EFAULT;

	if (!__get_user_inatomic(*ret, ptr))
	return 0;

	return read_user_stack_slow(ptr, ret, 8);
	}

	static int read_user_stack_32(unsigned int __user ptr, unsigned int ret)
	{
	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) \|\|
	((unsigned long)ptr & 3))
	return -EFAULT;

	if (!__get_user_inatomic(*ret, ptr))
	return 0;

	return read_user_stack_slow(ptr, ret, 4);
	}

	static inline int valid_user_sp(unsigned long sp, int is_64)
	{
	if (!sp \|\| (sp & 7) \|\| sp > (is_64 ? TASK_SIZE : 0x100000000UL) - 32)
	return 0;
	return 1;
	}

	/*
	* 64-bit user processes use the same stack frame for RT and non-RT signals.
	*/
	struct signal_frame_64 {
	char dummy[__SIGNAL_FRAMESIZE];
	struct ucontext uc;
	unsigned long unused[2];
	unsigned int tramp[6];
	struct siginfo *pinfo;
	void *puc;
	struct siginfo info;
	char abigap[288];
	};

	static int is_sigreturn_64_address(unsigned long nip, unsigned long fp)
	{
	if (nip == fp + offsetof(struct signal_frame_64, tramp))
	return 1;
	if (vdso64_rt_sigtramp && current->mm->context.vdso_base &&
	nip == current->mm->context.vdso_base + vdso64_rt_sigtramp)
	return 1;
	return 0;
	}

	/*
	* Do some sanity checking on the signal frame pointed to by sp.
	* We check the pinfo and puc pointers in the frame.
	*/
	static int sane_signal_64_frame(unsigned long sp)
	{
	struct signal_frame_64 __user *sf;
	unsigned long pinfo, puc;

	sf = (struct signal_frame_64 __user *) sp;
	if (read_user_stack_64((unsigned long __user *) &sf->pinfo, &pinfo) \|\|
	read_user_stack_64((unsigned long __user *) &sf->puc, &puc))
	return 0;
	return pinfo == (unsigned long) &sf->info &&
	puc == (unsigned long) &sf->uc;
	}

	static void perf_callchain_user_64(struct pt_regs *regs,
	struct perf_callchain_entry *entry)
	{
	unsigned long sp, next_sp;
	unsigned long next_ip;
	unsigned long lr;
	long level = 0;
	struct signal_frame_64 __user *sigframe;
	unsigned long __user fp, uregs;

	next_ip = regs->nip;
	lr = regs->link;
	sp = regs->gpr[1];
	callchain_store(entry, PERF_CONTEXT_USER);
	callchain_store(entry, next_ip);

	for (;;) {
	fp = (unsigned long __user *) sp;
	if (!valid_user_sp(sp, 1) \|\| read_user_stack_64(fp, &next_sp))
	return;
	if (level > 0 && read_user_stack_64(&fp[2], &next_ip))
	return;

	/*
	* Note: the next_sp - sp >= signal frame size check
	* is true when next_sp < sp, which can happen when
	* transitioning from an alternate signal stack to the
	* normal stack.
	*/
	if (next_sp - sp >= sizeof(struct signal_frame_64) &&
	(is_sigreturn_64_address(next_ip, sp) \|\|
	(level <= 1 && is_sigreturn_64_address(lr, sp))) &&
	sane_signal_64_frame(sp)) {
	/*
	* This looks like an signal frame
	*/
	sigframe = (struct signal_frame_64 __user *) sp;
	uregs = sigframe->uc.uc_mcontext.gp_regs;
	if (read_user_stack_64(&uregs[PT_NIP], &next_ip) \|\|
	read_user_stack_64(&uregs[PT_LNK], &lr) \|\|
	read_user_stack_64(&uregs[PT_R1], &sp))
	return;
	level = 0;
	callchain_store(entry, PERF_CONTEXT_USER);
	callchain_store(entry, next_ip);
	continue;
	}

	if (level == 0)
	next_ip = lr;
	callchain_store(entry, next_ip);
	++level;
	sp = next_sp;
	}
	}

	static inline int current_is_64bit(void)
	{
	/*
	* We can't use test_thread_flag() here because we may be on an
	* interrupt stack, and the thread flags don't get copied over
	* from the thread_info on the main stack to the interrupt stack.
	*/
	return !test_ti_thread_flag(task_thread_info(current), TIF_32BIT);
	}

	#else /* CONFIG_PPC64 */
	/*
	* On 32-bit we just access the address and let hash_page create a
	* HPTE if necessary, so there is no need to fall back to reading
	* the page tables. Since this is called at interrupt level,
	* do_page_fault() won't treat a DSI as a page fault.
	*/
	static int read_user_stack_32(unsigned int __user ptr, unsigned int ret)
	{
	if ((unsigned long)ptr > TASK_SIZE - sizeof(unsigned int) \|\|
	((unsigned long)ptr & 3))
	return -EFAULT;

	return __get_user_inatomic(*ret, ptr);
	}

	static inline void perf_callchain_user_64(struct pt_regs *regs,
	struct perf_callchain_entry *entry)
	{
	}

	static inline int current_is_64bit(void)
	{
	return 0;
	}

	static inline int valid_user_sp(unsigned long sp, int is_64)
	{
	if (!sp \|\| (sp & 7) \|\| sp > TASK_SIZE - 32)
	return 0;
	return 1;
	}

	#define __SIGNAL_FRAMESIZE32 __SIGNAL_FRAMESIZE
	#define sigcontext32 sigcontext
	#define mcontext32 mcontext
	#define ucontext32 ucontext
	#define compat_siginfo_t struct siginfo

	#endif /* CONFIG_PPC64 */

	/*
	* Layout for non-RT signal frames
	*/
	struct signal_frame_32 {
	char dummy[__SIGNAL_FRAMESIZE32];
	struct sigcontext32 sctx;
	struct mcontext32 mctx;
	int abigap[56];
	};

	/*
	* Layout for RT signal frames
	*/
	struct rt_signal_frame_32 {
	char dummy[__SIGNAL_FRAMESIZE32 + 16];
	compat_siginfo_t info;
	struct ucontext32 uc;
	int abigap[56];
	};

	static int is_sigreturn_32_address(unsigned int nip, unsigned int fp)
	{
	if (nip == fp + offsetof(struct signal_frame_32, mctx.mc_pad))
	return 1;
	if (vdso32_sigtramp && current->mm->context.vdso_base &&
	nip == current->mm->context.vdso_base + vdso32_sigtramp)
	return 1;
	return 0;
	}

	static int is_rt_sigreturn_32_address(unsigned int nip, unsigned int fp)
	{
	if (nip == fp + offsetof(struct rt_signal_frame_32,
	uc.uc_mcontext.mc_pad))
	return 1;
	if (vdso32_rt_sigtramp && current->mm->context.vdso_base &&
	nip == current->mm->context.vdso_base + vdso32_rt_sigtramp)
	return 1;
	return 0;
	}

	static int sane_signal_32_frame(unsigned int sp)
	{
	struct signal_frame_32 __user *sf;
	unsigned int regs;

	sf = (struct signal_frame_32 __user *) (unsigned long) sp;
	if (read_user_stack_32((unsigned int __user *) &sf->sctx.regs, &regs))
	return 0;
	return regs == (unsigned long) &sf->mctx;
	}

	static int sane_rt_signal_32_frame(unsigned int sp)
	{
	struct rt_signal_frame_32 __user *sf;
	unsigned int regs;

	sf = (struct rt_signal_frame_32 __user *) (unsigned long) sp;
	if (read_user_stack_32((unsigned int __user *) &sf->uc.uc_regs, &regs))
	return 0;
	return regs == (unsigned long) &sf->uc.uc_mcontext;
	}

	static unsigned int __user *signal_frame_32_regs(unsigned int sp,
	unsigned int next_sp, unsigned int next_ip)
	{
	struct mcontext32 __user *mctx = NULL;
	struct signal_frame_32 __user *sf;
	struct rt_signal_frame_32 __user *rt_sf;

	/*
	* Note: the next_sp - sp >= signal frame size check
	* is true when next_sp < sp, for example, when
	* transitioning from an alternate signal stack to the
	* normal stack.
	*/
	if (next_sp - sp >= sizeof(struct signal_frame_32) &&
	is_sigreturn_32_address(next_ip, sp) &&
	sane_signal_32_frame(sp)) {
	sf = (struct signal_frame_32 __user *) (unsigned long) sp;
	mctx = &sf->mctx;
	}

	if (!mctx && next_sp - sp >= sizeof(struct rt_signal_frame_32) &&
	is_rt_sigreturn_32_address(next_ip, sp) &&
	sane_rt_signal_32_frame(sp)) {
	rt_sf = (struct rt_signal_frame_32 __user *) (unsigned long) sp;
	mctx = &rt_sf->uc.uc_mcontext;
	}

	if (!mctx)
	return NULL;
	return mctx->mc_gregs;
	}

	static void perf_callchain_user_32(struct pt_regs *regs,
	struct perf_callchain_entry *entry)
	{
	unsigned int sp, next_sp;
	unsigned int next_ip;
	unsigned int lr;
	long level = 0;
	unsigned int __user fp, uregs;

	next_ip = regs->nip;
	lr = regs->link;
	sp = regs->gpr[1];
	callchain_store(entry, PERF_CONTEXT_USER);
	callchain_store(entry, next_ip);

	while (entry->nr < PERF_MAX_STACK_DEPTH) {
	fp = (unsigned int __user *) (unsigned long) sp;
	if (!valid_user_sp(sp, 0) \|\| read_user_stack_32(fp, &next_sp))
	return;
	if (level > 0 && read_user_stack_32(&fp[1], &next_ip))
	return;

	uregs = signal_frame_32_regs(sp, next_sp, next_ip);
	if (!uregs && level <= 1)
	uregs = signal_frame_32_regs(sp, next_sp, lr);
	if (uregs) {
	/*
	* This looks like an signal frame, so restart
	* the stack trace with the values in it.
	*/
	if (read_user_stack_32(&uregs[PT_NIP], &next_ip) \|\|
	read_user_stack_32(&uregs[PT_LNK], &lr) \|\|
	read_user_stack_32(&uregs[PT_R1], &sp))
	return;
	level = 0;
	callchain_store(entry, PERF_CONTEXT_USER);
	callchain_store(entry, next_ip);
	continue;
	}

	if (level == 0)
	next_ip = lr;
	callchain_store(entry, next_ip);
	++level;
	sp = next_sp;
	}
	}

	/*
	* Since we can't get PMU interrupts inside a PMU interrupt handler,
	* we don't need separate irq and nmi entries here.
	*/
	static DEFINE_PER_CPU(struct perf_callchain_entry, cpu_perf_callchain);

	struct perf_callchain_entry perf_callchain(struct pt_regs regs)
	{
	struct perf_callchain_entry *entry = &__get_cpu_var(cpu_perf_callchain);

	entry->nr = 0;

	if (current->pid == 0) /* idle task? */
	return entry;

	if (!user_mode(regs)) {
	perf_callchain_kernel(regs, entry);
	if (current->mm)
	regs = task_pt_regs(current);
	else
	regs = NULL;
	}

	if (regs) {
	if (current_is_64bit())
	perf_callchain_user_64(regs, entry);
	else
	perf_callchain_user_32(regs, entry);
	}

	return entry;
	}