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 #include <asm/uaccess.h>
  16
  17 struct frame_head {
  18         struct frame_head * ebp;
  19         unsigned long ret;
  20 } __attribute__((packed));
  21
  22 static struct frame_head *
  23 dump_backtrace(struct frame_head * head)
  24 {
  25         struct frame_head bufhead[2];
  26
  27         /* Also check accessibility of one struct frame_head beyond */
  28         if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
  29                 return NULL;
  30         if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
  31                 return NULL;
  32
  33         oprofile_add_trace(bufhead[0].ret);
  34
  35         /* frame pointers should strictly progress back up the stack
  36          * (towards higher addresses) */
  37         if (head >= bufhead[0].ebp)
  38                 return NULL;
  39
  40         return bufhead[0].ebp;
  41 }
  42
  43 /*
  44  * |             | /\ Higher addresses
  45  * |             |
  46  * --------------- stack base (address of current_thread_info)
  47  * | thread info |
  48  * .             .
  49  * |    stack    |
  50  * --------------- saved regs->ebp value if valid (frame_head address)
  51  * .             .
  52  * --------------- struct pt_regs stored on stack (struct pt_regs *)
  53  * |             |
  54  * .             .
  55  * |             |
  56  * --------------- %esp
  57  * |             |
  58  * |             | \/ Lower addresses
  59  *
  60  * Thus, &pt_regs <-> stack base restricts the valid(ish) ebp values
  61  */
  62 #ifdef CONFIG_FRAME_POINTER
  63 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  64 {
  65         unsigned long headaddr = (unsigned long)head;
  66         unsigned long stack = (unsigned long)regs;
  67         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
  68
  69         return headaddr > stack && headaddr < stack_base;
  70 }
  71 #else
  72 /* without fp, it's just junk */
  73 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  74 {
  75         return 0;
  76 }
  77 #endif
  78
  79
  80 void
  81 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
  82 {
  83         struct frame_head *head;
  84
  85 #ifdef CONFIG_X86_64
  86         head = (struct frame_head *)regs->rbp;
  87 #else
  88         head = (struct frame_head *)regs->ebp;
  89 #endif
  90
  91         if (!user_mode_vm(regs)) {
  92                 while (depth-- && valid_kernel_stack(head, regs))
  93                         head = dump_backtrace(head);
  94                 return;
  95         }
  96
  97         while (depth-- && head)
  98                 head = dump_backtrace(head);
  99 }