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/*
* Arm specific backtracing code for oprofile
*
* Copyright 2005 Openedhand Ltd.
*
* Author: Richard Purdie <rpurdie@openedhand.com>
*
* Based on i386 oprofile backtrace code by John Levon, David Smith
*
* 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.
*
*/
#include <linux/oprofile.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <asm/ptrace.h>
#include <asm/uaccess.h>
/*
* The registers we're interested in are at the end of the variable
* length saved register structure. The fp points at the end of this
* structure so the address of this struct is:
* (struct frame_tail *)(xxx->fp)-1
*/
struct frame_tail {
struct frame_tail *fp;
unsigned long sp;
unsigned long lr;
} __attribute__((packed));
#ifdef CONFIG_FRAME_POINTER
static struct frame_tail* kernel_backtrace(struct frame_tail *tail)
{
oprofile_add_trace(tail->lr);
/* frame pointers should strictly progress back up the stack
* (towards higher addresses) */
if (tail >= tail->fp)
return NULL;
return tail->fp-1;
}
#endif
static struct frame_tail* user_backtrace(struct frame_tail *tail)
{
struct frame_tail buftail;
/* hardware pte might not be valid due to dirty/accessed bit emulation
* so we use copy_from_user and benefit from exception fixups */
if (copy_from_user(&buftail, tail, sizeof(struct frame_tail)))
return NULL;
oprofile_add_trace(buftail.lr);
/* frame pointers should strictly progress back up the stack
* (towards higher addresses) */
if (tail >= buftail.fp)
return NULL;
return buftail.fp-1;
}
/* Compare two addresses and see if they're on the same page */
#define CMP_ADDR_EQUAL(x,y,offset) ((((unsigned long) x) >> PAGE_SHIFT) \
== ((((unsigned long) y) + offset) >> PAGE_SHIFT))
/* check that the page(s) containing the frame tail are present */
static int pages_present(struct frame_tail *tail)
{
struct mm_struct * mm = current->mm;
if (!check_user_page_readable(mm, (unsigned long)tail))
return 0;
if (CMP_ADDR_EQUAL(tail, tail, 8))
return 1;
if (!check_user_page_readable(mm, ((unsigned long)tail) + 8))
return 0;
return 1;
}
/*
* | | /\ Higher addresses
* | |
* --------------- stack base (address of current_thread_info)
* | thread info |
* . .
* | stack |
* --------------- saved regs->ARM_fp value if valid (frame_tail address)
* . .
* --------------- struct pt_regs stored on stack (struct pt_regs *)
* | |
* . .
* | |
* --------------- %esp
* | |
* | | \/ Lower addresses
*
* Thus, &pt_regs <-> stack base restricts the valid(ish) fp values
*/
static int valid_kernel_stack(struct frame_tail *tail, struct pt_regs *regs)
{
unsigned long tailaddr = (unsigned long)tail;
unsigned long stack = (unsigned long)regs;
unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
return (tailaddr > stack) && (tailaddr < stack_base);
}
void arm_backtrace(struct pt_regs * const regs, unsigned int depth)
{
struct frame_tail *tail;
unsigned long last_address = 0;
tail = ((struct frame_tail *) regs->ARM_fp) - 1;
if (!user_mode(regs)) {
#ifdef CONFIG_FRAME_POINTER
while (depth-- && tail && valid_kernel_stack(tail, regs)) {
tail = kernel_backtrace(tail);
}
#endif
return;
}
while (depth-- && tail && !((unsigned long) tail & 3)) {
if ((!CMP_ADDR_EQUAL(last_address, tail, 0)
|| !CMP_ADDR_EQUAL(last_address, tail, 8))
&& !pages_present(tail))
return;
last_address = (unsigned long) tail;
tail = user_backtrace(tail);
}
}
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