arch/arm/oprofile/backtrace.c

   1 /*
   2  * Arm specific backtracing code for oprofile
   3  *
   4  * Copyright 2005 Openedhand Ltd.
   5  *
   6  * Author: Richard Purdie <rpurdie@openedhand.com>
   7  *
   8  * Based on i386 oprofile backtrace code by John Levon, David Smith
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License version 2 as
  12  * published by the Free Software Foundation.
  13  *
  14  */
  15
  16 #include <linux/oprofile.h>
  17 #include <linux/sched.h>
  18 #include <linux/mm.h>
  19 #include <asm/ptrace.h>
  20 #include <asm/uaccess.h>
  21
  22
  23 /*
  24  * The registers we're interested in are at the end of the variable
  25  * length saved register structure. The fp points at the end of this
  26  * structure so the address of this struct is:
  27  * (struct frame_tail *)(xxx->fp)-1
  28  */
  29 struct frame_tail {
  30         struct frame_tail *fp;
  31         unsigned long sp;
  32         unsigned long lr;
  33 } __attribute__((packed));
  34
  35
  36 #ifdef CONFIG_FRAME_POINTER
  37 static struct frame_tail* kernel_backtrace(struct frame_tail *tail)
  38 {
  39         oprofile_add_trace(tail->lr);
  40
  41         /* frame pointers should strictly progress back up the stack
  42          * (towards higher addresses) */
  43         if (tail >= tail->fp)
  44                 return NULL;
  45
  46         return tail->fp-1;
  47 }
  48 #endif
  49
  50 static struct frame_tail* user_backtrace(struct frame_tail *tail)
  51 {
  52         struct frame_tail buftail[2];
  53
  54         /* Also check accessibility of one struct frame_tail beyond */
  55         if (!access_ok(VERIFY_READ, tail, sizeof(buftail)))
  56                 return NULL;
  57         if (__copy_from_user_inatomic(buftail, tail, sizeof(buftail)))
  58                 return NULL;
  59
  60         oprofile_add_trace(buftail[0].lr);
  61
  62         /* frame pointers should strictly progress back up the stack
  63          * (towards higher addresses) */
  64         if (tail >= buftail[0].fp)
  65                 return NULL;
  66
  67         return buftail[0].fp-1;
  68 }
  69
  70 /*
  71  * |             | /\ Higher addresses
  72  * |             |
  73  * --------------- stack base (address of current_thread_info)
  74  * | thread info |
  75  * .             .
  76  * |    stack    |
  77  * --------------- saved regs->ARM_fp value if valid (frame_tail address)
  78  * .             .
  79  * --------------- struct pt_regs stored on stack (struct pt_regs *)
  80  * |             |
  81  * .             .
  82  * |             |
  83  * --------------- %esp
  84  * |             |
  85  * |             | \/ Lower addresses
  86  *
  87  * Thus, &pt_regs <-> stack base restricts the valid(ish) fp values
  88  */
  89 static int valid_kernel_stack(struct frame_tail *tail, struct pt_regs *regs)
  90 {
  91         unsigned long tailaddr = (unsigned long)tail;
  92         unsigned long stack = (unsigned long)regs;
  93         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
  94
  95         return (tailaddr > stack) && (tailaddr < stack_base);
  96 }
  97
  98 void arm_backtrace(struct pt_regs * const regs, unsigned int depth)
  99 {
 100         struct frame_tail *tail;
 101
 102         tail = ((struct frame_tail *) regs->ARM_fp) - 1;
 103
 104         if (!user_mode(regs)) {
 105
 106 #ifdef CONFIG_FRAME_POINTER
 107                 while (depth-- && tail && valid_kernel_stack(tail, regs)) {
 108                         tail = kernel_backtrace(tail);
 109                 }
 110 #endif
 111                 return;
 112         }
 113
 114         while (depth-- && tail && !((unsigned long) tail & 3))
 115                 tail = user_backtrace(tail);
 116 }