1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
|
/*
* Dynamic function tracer architecture backend.
*
* Copyright IBM Corp. 2009,2014
*
* Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
* Martin Schwidefsky <schwidefsky@de.ibm.com>
*/
#include <linux/hardirq.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kprobes.h>
#include <trace/syscall.h>
#include <asm/asm-offsets.h>
#include "entry.h"
void mcount_replace_code(void);
void ftrace_disable_code(void);
void ftrace_enable_insn(void);
/*
* The mcount code looks like this:
* stg %r14,8(%r15) # offset 0
* larl %r1,<&counter> # offset 6
* brasl %r14,_mcount # offset 12
* lg %r14,8(%r15) # offset 18
* Total length is 24 bytes. The complete mcount block initially gets replaced
* by ftrace_make_nop. Subsequent calls to ftrace_make_call / ftrace_make_nop
* only patch the jg/lg instruction within the block.
* Note: we do not patch the first instruction to an unconditional branch,
* since that would break kprobes/jprobes. It is easier to leave the larl
* instruction in and only modify the second instruction.
* The enabled ftrace code block looks like this:
* larl %r0,.+24 # offset 0
* > lg %r1,__LC_FTRACE_FUNC # offset 6
* br %r1 # offset 12
* brcl 0,0 # offset 14
* brc 0,0 # offset 20
* The ftrace function gets called with a non-standard C function call ABI
* where r0 contains the return address. It is also expected that the called
* function only clobbers r0 and r1, but restores r2-r15.
* The return point of the ftrace function has offset 24, so execution
* continues behind the mcount block.
* larl %r0,.+24 # offset 0
* > jg .+18 # offset 6
* br %r1 # offset 12
* brcl 0,0 # offset 14
* brc 0,0 # offset 20
* The jg instruction branches to offset 24 to skip as many instructions
* as possible.
*/
asm(
" .align 4\n"
"mcount_replace_code:\n"
" larl %r0,0f\n"
"ftrace_disable_code:\n"
" jg 0f\n"
" br %r1\n"
" brcl 0,0\n"
" brc 0,0\n"
"0:\n"
" .align 4\n"
"ftrace_enable_insn:\n"
" lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
#define MCOUNT_BLOCK_SIZE 24
#define MCOUNT_INSN_OFFSET 6
#define FTRACE_INSN_SIZE 6
int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
return 0;
}
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
/* Initial replacement of the whole mcount block */
if (addr == MCOUNT_ADDR) {
if (probe_kernel_write((void *) rec->ip - MCOUNT_INSN_OFFSET,
mcount_replace_code,
MCOUNT_BLOCK_SIZE))
return -EPERM;
return 0;
}
if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
MCOUNT_INSN_SIZE))
return -EPERM;
return 0;
}
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
FTRACE_INSN_SIZE))
return -EPERM;
return 0;
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
return 0;
}
int __init ftrace_dyn_arch_init(void)
{
return 0;
}
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
* Hook the return address and push it in the stack of return addresses
* in current thread info.
*/
unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
unsigned long ip)
{
struct ftrace_graph_ent trace;
if (unlikely(atomic_read(¤t->tracing_graph_pause)))
goto out;
ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;
trace.func = ip;
trace.depth = current->curr_ret_stack + 1;
/* Only trace if the calling function expects to. */
if (!ftrace_graph_entry(&trace))
goto out;
if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
goto out;
parent = (unsigned long) return_to_handler;
out:
return parent;
}
/*
* Patch the kernel code at ftrace_graph_caller location. The instruction
* there is branch relative and save to prepare_ftrace_return. To disable
* the call to prepare_ftrace_return we patch the bras offset to point
* directly after the instructions. To enable the call we calculate
* the original offset to prepare_ftrace_return and put it back.
*/
int ftrace_enable_ftrace_graph_caller(void)
{
static unsigned short offset = 0x0002;
return probe_kernel_write((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
int ftrace_disable_ftrace_graph_caller(void)
{
unsigned short offset;
offset = ((void *) &ftrace_graph_caller_end -
(void *) ftrace_graph_caller) / 2;
return probe_kernel_write((void *) ftrace_graph_caller + 2,
&offset, sizeof(offset));
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
|
