backtrace.c

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/*
 * AVR32 specific backtracing code for oprofile
 *
 * Copyright 2008 Weinmann GmbH
 *
 * Author: Nikolaus Voss <[email protected]>
 *
 * Based on i386 oprofile backtrace code by John Levon and 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/uaccess.h>

/* The first two words of each frame on the stack look like this if we have
 * frame pointers */
struct frame_head {
    unsigned long lr;
    struct frame_head *fp;
};

/* copied from arch/avr32/kernel/process.c */
static inline int valid_stack_ptr(struct thread_info *tinfo, unsigned long p)
{
    return (p > (unsigned long)tinfo)
        && (p < (unsigned long)tinfo + THREAD_SIZE - 3);
}

/* copied from arch/x86/oprofile/backtrace.c */
static struct frame_head *dump_user_backtrace(struct frame_head *head)
{
    struct frame_head bufhead[2];

    /* Also check accessibility of one struct frame_head beyond */
    if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
        return NULL;
    if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
        return NULL;

    oprofile_add_trace(bufhead[0].lr);

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

    return bufhead[0].fp;
}

void avr32_backtrace(struct pt_regs * const regs, unsigned int depth)
{
    /* Get first frame pointer */
    struct frame_head *head = (struct frame_head *)(regs->r7);

    if (!user_mode(regs)) {
#ifdef CONFIG_FRAME_POINTER
        /*
         * Traverse the kernel stack from frame to frame up to
         * "depth" steps.
         */
        while (depth-- && valid_stack_ptr(task_thread_info(current),
                          (unsigned long)head)) {
            oprofile_add_trace(head->lr);
            if (head->fp <= head)
                break;
            head = head->fp;
        }
#endif
    } else {
        /* Assume we have frame pointers in user mode process */
        while (depth-- && head)
            head = dump_user_backtrace(head);
    }
}