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backtrace.c

/*
 * 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 <linux/uaccess.h>
#include <asm/ptrace.h>
#include <asm/stacktrace.h>

static int report_trace(struct stackframe *frame, void *d)
{
      unsigned int *depth = d;

      if (*depth) {
            oprofile_add_trace(frame->pc);
            (*depth)--;
      }

      return *depth == 0;
}

/*
 * 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
 */
00041 struct frame_tail {
      struct frame_tail *fp;
      unsigned long sp;
      unsigned long lr;
} __attribute__((packed));

static struct frame_tail* user_backtrace(struct frame_tail *tail)
{
      struct frame_tail buftail[2];

      /* Also check accessibility of one struct frame_tail beyond */
      if (!access_ok(VERIFY_READ, tail, sizeof(buftail)))
            return NULL;
      if (__copy_from_user_inatomic(buftail, tail, sizeof(buftail)))
            return NULL;

      oprofile_add_trace(buftail[0].lr);

      /* frame pointers should strictly progress back up the stack
       * (towards higher addresses) */
      if (tail >= buftail[0].fp)
            return NULL;

      return buftail[0].fp-1;
}

void arm_backtrace(struct pt_regs * const regs, unsigned int depth)
{
      struct frame_tail *tail = ((struct frame_tail *) regs->ARM_fp) - 1;

      if (!user_mode(regs)) {
            struct stackframe frame;
            frame.fp = regs->ARM_fp;
            frame.sp = regs->ARM_sp;
            frame.lr = regs->ARM_lr;
            frame.pc = regs->ARM_pc;
            walk_stackframe(&frame, report_trace, &depth);
            return;
      }

      while (depth-- && tail && !((unsigned long) tail & 3))
            tail = user_backtrace(tail);
}

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