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 * Modified for Xen by Amitabha Roy
10 *
11 */
12
13 #include <xen/types.h>
14 #include <asm/page.h>
15 #include <xen/xenoprof.h>
16 #include <xen/guest_access.h>
17
18 struct __packed frame_head {
19 struct frame_head * ebp;
20 unsigned long ret;
21 };
22 typedef struct frame_head frame_head_t;
23
24 struct __packed frame_head_32bit {
25 uint32_t ebp;
26 uint32_t ret;
27 };
28 typedef struct frame_head_32bit frame_head32_t;
29
30 static struct frame_head *
dump_hypervisor_backtrace(struct vcpu * vcpu,const struct frame_head * head,int mode)31 dump_hypervisor_backtrace(struct vcpu *vcpu, const struct frame_head *head,
32 int mode)
33 {
34 if (!xenoprof_add_trace(vcpu, head->ret, mode))
35 return 0;
36
37 /* frame pointers should strictly progress back up the stack
38 * (towards higher addresses) */
39 if (head >= head->ebp)
40 return NULL;
41
42 return head->ebp;
43 }
44
is_32bit_vcpu(struct vcpu * vcpu)45 static inline int is_32bit_vcpu(struct vcpu *vcpu)
46 {
47 if (is_hvm_vcpu(vcpu))
48 return !hvm_long_mode_active(vcpu);
49 else
50 return is_pv_32bit_vcpu(vcpu);
51 }
52
53 static struct frame_head *
dump_guest_backtrace(struct vcpu * vcpu,const struct frame_head * head,int mode)54 dump_guest_backtrace(struct vcpu *vcpu, const struct frame_head *head,
55 int mode)
56 {
57 /* Also check accessibility of one struct frame_head beyond. */
58 frame_head_t bufhead[2];
59
60 if ( is_32bit_vcpu(vcpu) )
61 {
62 frame_head32_t bufhead32[2];
63
64 if ( raw_copy_from_guest(bufhead32, head, sizeof(bufhead32)) )
65 return 0;
66 bufhead[0].ebp = (struct frame_head *)(unsigned long)bufhead32[0].ebp;
67 bufhead[0].ret = bufhead32[0].ret;
68 }
69 else if ( raw_copy_from_guest(bufhead, head, sizeof(bufhead)) )
70 return 0;
71
72 if ( !xenoprof_add_trace(vcpu, bufhead[0].ret, mode) )
73 return 0;
74
75 /* frame pointers should strictly progress back up the stack
76 * (towards higher addresses) */
77 if ( head >= bufhead[0].ebp )
78 return NULL;
79
80 return bufhead[0].ebp;
81 }
82
83 /*
84 * | | /\ Higher addresses
85 * | |
86 * --------------- stack base (address of current_thread_info)
87 * | thread info |
88 * . .
89 * | stack |
90 * --------------- saved regs->ebp value if valid (frame_head address)
91 * . .
92 * --------------- saved regs->rsp value if x86_64
93 * | |
94 * --------------- struct pt_regs * stored on stack if 32-bit
95 * | |
96 * . .
97 * | |
98 * --------------- %esp
99 * | |
100 * | | \/ Lower addresses
101 *
102 * Thus, regs (or regs->rsp for x86_64) <-> stack base restricts the
103 * valid(ish) ebp values. Note: (1) for x86_64, NMI and several other
104 * exceptions use special stacks, maintained by the interrupt stack table
105 * (IST). These stacks are set up in trap_init() in
106 * arch/x86_64/kernel/traps.c. Thus, for x86_64, regs now does not point
107 * to the kernel stack; instead, it points to some location on the NMI
108 * stack. On the other hand, regs->rsp is the stack pointer saved when the
109 * NMI occurred. (2) For 32-bit, regs->esp is not valid because the
110 * processor does not save %esp on the kernel stack when interrupts occur
111 * in the kernel mode.
112 */
113 #if defined(CONFIG_FRAME_POINTER)
valid_hypervisor_stack(const struct frame_head * head,const struct cpu_user_regs * regs)114 static int valid_hypervisor_stack(const struct frame_head *head,
115 const struct cpu_user_regs *regs)
116 {
117 unsigned long headaddr = (unsigned long)head;
118 unsigned long stack = (unsigned long)regs->rsp;
119 unsigned long stack_base = (stack & ~(STACK_SIZE - 1)) + STACK_SIZE;
120
121 return headaddr > stack && headaddr < stack_base;
122 }
123 #else
124 /* without fp, it's just junk */
valid_hypervisor_stack(const struct frame_head * head,const struct cpu_user_regs * regs)125 static int valid_hypervisor_stack(const struct frame_head *head,
126 const struct cpu_user_regs *regs)
127 {
128 return 0;
129 }
130 #endif
131
xenoprof_backtrace(struct vcpu * vcpu,const struct cpu_user_regs * regs,unsigned long depth,int mode)132 void xenoprof_backtrace(struct vcpu *vcpu, const struct cpu_user_regs *regs,
133 unsigned long depth, int mode)
134 {
135 const struct frame_head *head = (void *)regs->rbp;
136
137 if (mode > 1) {
138 while (depth-- && valid_hypervisor_stack(head, regs))
139 head = dump_hypervisor_backtrace(vcpu, head, mode);
140 return;
141 }
142
143 while (depth-- && head)
144 head = dump_guest_backtrace(vcpu, head, mode);
145 }
146