arch/i386/oprofile/backtrace.c

   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
  22 static struct frame_head *
  23 dump_backtrace(struct frame_head * head)
  24 {
  25         oprofile_add_trace(head->ret);
  26
  27         /* frame pointers should strictly progress back up the stack
  28          * (towards higher addresses) */
  29         if (head >= head->ebp)
  30                 return 0;
  31
  32         return head->ebp;
  33 }
  34
  35
  36 #ifdef CONFIG_X86_4G
  37 /* With a 4G kernel/user split, user pages are not directly
  38  * accessible from the kernel, so don't try
  39  */
  40 static int pages_present(struct frame_head * head)
  41 {
  42         return 0;
  43 }
  44 #else
  45 /* check that the page(s) containing the frame head are present */
  46 static int pages_present(struct frame_head * head)
  47 {
  48         struct mm_struct * mm = current->mm;
  49
  50         /* FIXME: only necessary once per page */
  51         if (!check_user_page_readable(mm, (unsigned long)head))
  52                 return 0;
  53
  54         return check_user_page_readable(mm, (unsigned long)(head + 1));
  55 }
  56 #endif /* CONFIG_X86_4G */
  57
  58
  59 /*
  60  * |             | /\ Higher addresses
  61  * |             |
  62  * --------------- stack base (address of current_thread_info)
  63  * | thread info |
  64  * .             .
  65  * |    stack    |
  66  * --------------- saved regs->ebp value if valid (frame_head address)
  67  * .             .
  68  * --------------- struct pt_regs stored on stack (struct pt_regs *)
  69  * |             |
  70  * .             .
  71  * |             |
  72  * --------------- %esp
  73  * |             |
  74  * |             | \/ Lower addresses
  75  *
  76  * Thus, &pt_regs <-> stack base restricts the valid(ish) ebp values
  77  */
  78 #ifdef CONFIG_FRAME_POINTER
  79 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  80 {
  81         unsigned long headaddr = (unsigned long)head;
  82         unsigned long stack = (unsigned long)regs;
  83         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
  84
  85         return headaddr > stack && headaddr < stack_base;
  86 }
  87 #else
  88 /* without fp, it's just junk */
  89 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  90 {
  91         return 0;
  92 }
  93 #endif
  94
  95
  96 void
  97 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
  98 {
  99         struct frame_head *head;
 100
 101 #ifdef CONFIG_X86_64
 102         head = (struct frame_head *)regs->rbp;
 103 #else
 104         head = (struct frame_head *)regs->ebp;
 105 #endif
 106
 107         if (!user_mode(regs)) {
 108                 while (depth-- && valid_kernel_stack(head, regs))
 109                         head = dump_backtrace(head);
 110                 return;
 111         }
 112
 113 #ifdef CONFIG_SMP
 114         if (!spin_trylock(&current->mm->page_table_lock))
 115                 return;
 116 #endif
 117
 118         while (depth-- && head && pages_present(head))
 119                 head = dump_backtrace(head);
 120
 121 #ifdef CONFIG_SMP
 122         spin_unlock(&current->mm->page_table_lock);
 123 #endif
 124 }