1 /*
2 * Dynamic function tracer architecture backend.
3 *
4 * Copyright IBM Corp. 2009
5 *
6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
7 * Martin Schwidefsky <schwidefsky@de.ibm.com>
8 */
9
10 #include <linux/hardirq.h>
11 #include <linux/uaccess.h>
12 #include <linux/ftrace.h>
13 #include <linux/kernel.h>
14 #include <linux/types.h>
15 #include <linux/kprobes.h>
16 #include <trace/syscall.h>
17 #include <asm/asm-offsets.h>
18
19 #ifdef CONFIG_64BIT
20 #define MCOUNT_OFFSET_RET 12
21 #else
22 #define MCOUNT_OFFSET_RET 22
23 #endif
24
25 #ifdef CONFIG_DYNAMIC_FTRACE
26
27 void ftrace_disable_code(void);
28 void ftrace_enable_insn(void);
29
30 #ifdef CONFIG_64BIT
31 /*
32 * The 64-bit mcount code looks like this:
33 * stg %r14,8(%r15) # offset 0
34 * > larl %r1,<&counter> # offset 6
35 * > brasl %r14,_mcount # offset 12
36 * lg %r14,8(%r15) # offset 18
37 * Total length is 24 bytes. The middle two instructions of the mcount
38 * block get overwritten by ftrace_make_nop / ftrace_make_call.
39 * The 64-bit enabled ftrace code block looks like this:
40 * stg %r14,8(%r15) # offset 0
41 * > lg %r1,__LC_FTRACE_FUNC # offset 6
42 * > lgr %r0,%r0 # offset 12
43 * > basr %r14,%r1 # offset 16
44 * lg %r14,8(%15) # offset 18
45 * The return points of the mcount/ftrace function have the same offset 18.
46 * The 64-bit disable ftrace code block looks like this:
47 * stg %r14,8(%r15) # offset 0
48 * > jg .+18 # offset 6
49 * > lgr %r0,%r0 # offset 12
50 * > basr %r14,%r1 # offset 16
51 * lg %r14,8(%15) # offset 18
52 * The jg instruction branches to offset 24 to skip as many instructions
53 * as possible.
54 */
55 asm(
56 " .align 4\n"
57 "ftrace_disable_code:\n"
58 " jg 0f\n"
59 " lgr %r0,%r0\n"
60 " basr %r14,%r1\n"
61 "0:\n"
62 " .align 4\n"
63 "ftrace_enable_insn:\n"
64 " lg %r1,"__stringify(__LC_FTRACE_FUNC)"\n");
65
66 #define FTRACE_INSN_SIZE 6
67
68 #else /* CONFIG_64BIT */
69 /*
70 * The 31-bit mcount code looks like this:
71 * st %r14,4(%r15) # offset 0
72 * > bras %r1,0f # offset 4
73 * > .long _mcount # offset 8
74 * > .long <&counter> # offset 12
75 * > 0: l %r14,0(%r1) # offset 16
76 * > l %r1,4(%r1) # offset 20
77 * basr %r14,%r14 # offset 24
78 * l %r14,4(%r15) # offset 26
79 * Total length is 30 bytes. The twenty bytes starting from offset 4
80 * to offset 24 get overwritten by ftrace_make_nop / ftrace_make_call.
81 * The 31-bit enabled ftrace code block looks like this:
82 * st %r14,4(%r15) # offset 0
83 * > l %r14,__LC_FTRACE_FUNC # offset 4
84 * > j 0f # offset 8
85 * > .fill 12,1,0x07 # offset 12
86 * 0: basr %r14,%r14 # offset 24
87 * l %r14,4(%r14) # offset 26
88 * The return points of the mcount/ftrace function have the same offset 26.
89 * The 31-bit disabled ftrace code block looks like this:
90 * st %r14,4(%r15) # offset 0
91 * > j .+26 # offset 4
92 * > j 0f # offset 8
93 * > .fill 12,1,0x07 # offset 12
94 * 0: basr %r14,%r14 # offset 24
95 * l %r14,4(%r14) # offset 26
96 * The j instruction branches to offset 30 to skip as many instructions
97 * as possible.
98 */
99 asm(
100 " .align 4\n"
101 "ftrace_disable_code:\n"
102 " j 1f\n"
103 " j 0f\n"
104 " .fill 12,1,0x07\n"
105 "0: basr %r14,%r14\n"
106 "1:\n"
107 " .align 4\n"
108 "ftrace_enable_insn:\n"
109 " l %r14,"__stringify(__LC_FTRACE_FUNC)"\n");
110
111 #define FTRACE_INSN_SIZE 4
112
113 #endif /* CONFIG_64BIT */
114
115
ftrace_make_nop(struct module * mod,struct dyn_ftrace * rec,unsigned long addr)116 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
117 unsigned long addr)
118 {
119 if (probe_kernel_write((void *) rec->ip, ftrace_disable_code,
120 MCOUNT_INSN_SIZE))
121 return -EPERM;
122 return 0;
123 }
124
ftrace_make_call(struct dyn_ftrace * rec,unsigned long addr)125 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
126 {
127 if (probe_kernel_write((void *) rec->ip, ftrace_enable_insn,
128 FTRACE_INSN_SIZE))
129 return -EPERM;
130 return 0;
131 }
132
ftrace_update_ftrace_func(ftrace_func_t func)133 int ftrace_update_ftrace_func(ftrace_func_t func)
134 {
135 return 0;
136 }
137
ftrace_dyn_arch_init(void * data)138 int __init ftrace_dyn_arch_init(void *data)
139 {
140 *(unsigned long *) data = 0;
141 return 0;
142 }
143
144 #endif /* CONFIG_DYNAMIC_FTRACE */
145
146 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
147 /*
148 * Hook the return address and push it in the stack of return addresses
149 * in current thread info.
150 */
prepare_ftrace_return(unsigned long parent,unsigned long ip)151 unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
152 unsigned long ip)
153 {
154 struct ftrace_graph_ent trace;
155
156 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
157 goto out;
158 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
159 goto out;
160 trace.func = (ip & PSW_ADDR_INSN) - MCOUNT_OFFSET_RET;
161 /* Only trace if the calling function expects to. */
162 if (!ftrace_graph_entry(&trace)) {
163 current->curr_ret_stack--;
164 goto out;
165 }
166 parent = (unsigned long) return_to_handler;
167 out:
168 return parent;
169 }
170
171 #ifdef CONFIG_DYNAMIC_FTRACE
172 /*
173 * Patch the kernel code at ftrace_graph_caller location. The instruction
174 * there is branch relative and save to prepare_ftrace_return. To disable
175 * the call to prepare_ftrace_return we patch the bras offset to point
176 * directly after the instructions. To enable the call we calculate
177 * the original offset to prepare_ftrace_return and put it back.
178 */
ftrace_enable_ftrace_graph_caller(void)179 int ftrace_enable_ftrace_graph_caller(void)
180 {
181 unsigned short offset;
182
183 offset = ((void *) prepare_ftrace_return -
184 (void *) ftrace_graph_caller) / 2;
185 return probe_kernel_write(ftrace_graph_caller + 2,
186 &offset, sizeof(offset));
187 }
188
ftrace_disable_ftrace_graph_caller(void)189 int ftrace_disable_ftrace_graph_caller(void)
190 {
191 static unsigned short offset = 0x0002;
192
193 return probe_kernel_write(ftrace_graph_caller + 2,
194 &offset, sizeof(offset));
195 }
196
197 #endif /* CONFIG_DYNAMIC_FTRACE */
198 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
199