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   1 /**
   2  * @file backtrace.c
   3  *
   4  * @remark Copyright 2002 OProfile authors
   5  * @remark Read the file COPYING
   6  *
   7  * @author John Levon
   8  * @author David Smith
   9  */
  10
  11 #include <linux/oprofile.h>
  12 #include <linux/sched.h>
  13 #include <linux/mm.h>
  14 #include <asm/ptrace.h>
  15
  16 struct frame_head {
  17         struct frame_head * ebp;
  18         unsigned long ret;
  19 } __attribute__((packed));
  20
  21 static struct frame_head *
  22 dump_backtrace(struct frame_head * head)
  23 {
  24         oprofile_add_trace(head->ret);
  25
  26         /* frame pointers should strictly progress back up the stack
  27          * (towards higher addresses) */
  28         if (head >= head->ebp)
  29                 return NULL;
  30
  31         return head->ebp;
  32 }
  33
  34 /* check that the page(s) containing the frame head are present */
  35 static int pages_present(struct frame_head * head)
  36 {
  37         struct mm_struct * mm = current->mm;
  38
  39         /* FIXME: only necessary once per page */
  40         if (!check_user_page_readable(mm, (unsigned long)head))
  41                 return 0;
  42
  43         return check_user_page_readable(mm, (unsigned long)(head + 1));
  44 }
  45
  46 /*
  47  * |             | /\ Higher addresses
  48  * |             |
  49  * --------------- stack base (address of current_thread_info)
  50  * | thread info |
  51  * .             .
  52  * |    stack    |
  53  * --------------- saved regs->ebp value if valid (frame_head address)
  54  * .             .
  55  * --------------- struct pt_regs stored on stack (struct pt_regs *)
  56  * |             |
  57  * .             .
  58  * |             |
  59  * --------------- %esp
  60  * |             |
  61  * |             | \/ Lower addresses
  62  *
  63  * Thus, &pt_regs <-> stack base restricts the valid(ish) ebp values
  64  */
  65 #ifdef CONFIG_FRAME_POINTER
  66 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  67 {
  68         unsigned long headaddr = (unsigned long)head;
  69         unsigned long stack = (unsigned long)regs;
  70         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
  71
  72         return headaddr > stack && headaddr < stack_base;
  73 }
  74 #else
  75 /* without fp, it's just junk */
  76 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  77 {
  78         return 0;
  79 }
  80 #endif
  81
  82
  83 void
  84 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
  85 {
  86         struct frame_head *head;
  87
  88 #ifdef CONFIG_X86_64
  89         head = (struct frame_head *)regs->rbp;
  90 #else
  91         head = (struct frame_head *)regs->ebp;
  92 #endif
  93
  94         if (!user_mode(regs)) {
  95                 while (depth-- && valid_kernel_stack(head, regs))
  96                         head = dump_backtrace(head);
  97                 return;
  98         }
  99
 100 #ifdef CONFIG_SMP
 101         if (!spin_trylock(&current->mm->page_table_lock))
 102                 return;
 103 #endif
 104
 105         while (depth-- && head && pages_present(head))
 106                 head = dump_backtrace(head);
 107
 108 #ifdef CONFIG_SMP
 109         spin_unlock(&current->mm->page_table_lock);
 110 #endif
 111 }