Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ] 
  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 }
125
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