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  * --------------- saved regs->rsp value if x86_64
  53  * |             |
  54  * --------------- struct pt_regs * stored on stack if 32-bit
  55  * |             |
  56  * .             .
  57  * |             |
  58  * --------------- %esp
  59  * |             |
  60  * |             | \/ Lower addresses
  61  *
  62  * Thus, regs (or regs->rsp for x86_64) <-> stack base restricts the
  63  * valid(ish) ebp values. Note: (1) for x86_64, NMI and several other
  64  * exceptions use special stacks, maintained by the interrupt stack table
  65  * (IST). These stacks are set up in trap_init() in
  66  * arch/x86_64/kernel/traps.c. Thus, for x86_64, regs now does not point
  67  * to the kernel stack; instead, it points to some location on the NMI
  68  * stack. On the other hand, regs->rsp is the stack pointer saved when the
  69  * NMI occurred. (2) For 32-bit, regs->esp is not valid because the
  70  * processor does not save %esp on the kernel stack when interrupts occur
  71  * in the kernel mode.
  72  */
  73 #ifdef CONFIG_FRAME_POINTER
  74 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  75 {
  76         unsigned long headaddr = (unsigned long)head;
  77 #ifdef CONFIG_X86_64
  78         unsigned long stack = (unsigned long)regs->rsp;
  79 #else
  80         unsigned long stack = (unsigned long)regs;
  81 #endif
  82         unsigned long stack_base = (stack & ~(THREAD_SIZE - 1)) + THREAD_SIZE;
  83
  84         return headaddr > stack && headaddr < stack_base;
  85 }
  86 #else
  87 /* without fp, it's just junk */
  88 static int valid_kernel_stack(struct frame_head * head, struct pt_regs * regs)
  89 {
  90         return 0;
  91 }
  92 #endif
  93
  94
  95 void
  96 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
  97 {
  98         struct frame_head *head;
  99
 100 #ifdef CONFIG_X86_64
 101         head = (struct frame_head *)regs->rbp;
 102 #else
 103         head = (struct frame_head *)regs->ebp;
 104 #endif
 105
 106         if (!user_mode_vm(regs)) {
 107                 while (depth-- && valid_kernel_stack(head, regs))
 108                         head = dump_backtrace(head);
 109                 return;
 110         }
 111
 112         while (depth-- && head)
 113                 head = dump_backtrace(head);
 114 }