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;
  53
  54         /* hardware pte might not be valid due to dirty/accessed bit emulation
  55          * so we use copy_from_user and benefit from exception fixups */
  56         if (copy_from_user(&buftail, tail, sizeof(struct frame_tail)))
  57                 return NULL;
  58
  59         oprofile_add_trace(buftail.lr);
  60
  61         /* frame pointers should strictly progress back up the stack
  62          * (towards higher addresses) */
  63         if (tail >= buftail.fp)
  64                 return NULL;
  65
  66         return buftail.fp-1;
  67 }
  68
  69 /* Compare two addresses and see if they're on the same page */
  70 #define CMP_ADDR_EQUAL(x,y,offset) ((((unsigned long) x) >> PAGE_SHIFT) \
  71         == ((((unsigned long) y) + offset) >> PAGE_SHIFT))
  72
  73 /* check that the page(s) containing the frame tail are present */
  74 static int pages_present(struct frame_tail *tail)
  75 {
  76         struct mm_struct * mm = current->mm;
  77
  78         if (!check_user_page_readable(mm, (unsigned long)tail))
  79                 return 0;
  80
  81         if (CMP_ADDR_EQUAL(tail, tail, 8))
  82                 return 1;
  83
  84         if (!check_user_page_readable(mm, ((unsigned long)tail) + 8))
  85                 return 0;
  86
  87         return 1;
  88 }
  89
  90 /*
  91  * |             | /\ Higher addresses
  92  * |             |
  93  * --------------- stack base (address of current_thread_info)
  94  * | thread info |
  95  * .             .
  96  * |    stack    |
  97  * --------------- saved regs->ARM_fp value if valid (frame_tail address)
  98  * .             .
  99  * --------------- struct pt_regs stored on stack (struct pt_regs *)
 100  * |             |
 101  * .             .
 102  * |             |
 103  * --------------- %esp
 104  * |             |
 105  * |             | \/ Lower addresses
 106  *
 107  * Thus, &pt_regs <-> stack base restricts the valid(ish) fp values
 108  */
 109 static int valid_kernel_stack(struct frame_tail *tail, struct pt_regs *regs)
 110 {
 111         unsigned long tailaddr = (unsigned long)tail;
 112         unsigned long stack = (unsigned long)regs;
 113         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
 114
 115         return (tailaddr > stack) && (tailaddr < stack_base);
 116 }
 117
 118 void arm_backtrace(struct pt_regs const *regs, unsigned int depth)
 119 {
 120         struct frame_tail *tail;
 121         unsigned long last_address = 0;
 122
 123         tail = ((struct frame_tail *) regs->ARM_fp) - 1;
 124
 125         if (!user_mode(regs)) {
 126
 127 #ifdef CONFIG_FRAME_POINTER
 128                 while (depth-- && tail && valid_kernel_stack(tail, regs)) {
 129                         tail = kernel_backtrace(tail);
 130                 }
 131 #endif
 132                 return;
 133         }
 134
 135         while (depth-- && tail && !((unsigned long) tail & 3)) {
 136                 if ((!CMP_ADDR_EQUAL(last_address, tail, 0)
 137                         || !CMP_ADDR_EQUAL(last_address, tail, 8))
 138                                 && !pages_present(tail))
 139                         return;
 140                 last_address = (unsigned long) tail;
 141                 tail = user_backtrace(tail);
 142         }
 143 }
 144