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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
27void ftrace_disable_code(void);
28void 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 */
55asm(
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 */
99asm(
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
116int 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
125int 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
133int ftrace_update_ftrace_func(ftrace_func_t func)
134{
135 return 0;
136}
137
138int __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 */
151unsigned 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;
167out:
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 */
179int 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
189int 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 */
1/*
2 * Dynamic function tracer architecture backend.
3 *
4 * Copyright IBM Corp. 2009,2014
5 *
6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
7 * Martin Schwidefsky <schwidefsky@de.ibm.com>
8 */
9
10#include <linux/moduleloader.h>
11#include <linux/hardirq.h>
12#include <linux/uaccess.h>
13#include <linux/ftrace.h>
14#include <linux/kernel.h>
15#include <linux/types.h>
16#include <linux/kprobes.h>
17#include <trace/syscall.h>
18#include <asm/asm-offsets.h>
19#include <asm/cacheflush.h>
20#include "entry.h"
21
22/*
23 * The mcount code looks like this:
24 * stg %r14,8(%r15) # offset 0
25 * larl %r1,<&counter> # offset 6
26 * brasl %r14,_mcount # offset 12
27 * lg %r14,8(%r15) # offset 18
28 * Total length is 24 bytes. Only the first instruction will be patched
29 * by ftrace_make_call / ftrace_make_nop.
30 * The enabled ftrace code block looks like this:
31 * > brasl %r0,ftrace_caller # offset 0
32 * larl %r1,<&counter> # offset 6
33 * brasl %r14,_mcount # offset 12
34 * lg %r14,8(%r15) # offset 18
35 * The ftrace function gets called with a non-standard C function call ABI
36 * where r0 contains the return address. It is also expected that the called
37 * function only clobbers r0 and r1, but restores r2-r15.
38 * For module code we can't directly jump to ftrace caller, but need a
39 * trampoline (ftrace_plt), which clobbers also r1.
40 * The return point of the ftrace function has offset 24, so execution
41 * continues behind the mcount block.
42 * The disabled ftrace code block looks like this:
43 * > jg .+24 # offset 0
44 * larl %r1,<&counter> # offset 6
45 * brasl %r14,_mcount # offset 12
46 * lg %r14,8(%r15) # offset 18
47 * The jg instruction branches to offset 24 to skip as many instructions
48 * as possible.
49 * In case we use gcc's hotpatch feature the original and also the disabled
50 * function prologue contains only a single six byte instruction and looks
51 * like this:
52 * > brcl 0,0 # offset 0
53 * To enable ftrace the code gets patched like above and afterwards looks
54 * like this:
55 * > brasl %r0,ftrace_caller # offset 0
56 */
57
58unsigned long ftrace_plt;
59
60static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
61{
62#ifdef CC_USING_HOTPATCH
63 /* brcl 0,0 */
64 insn->opc = 0xc004;
65 insn->disp = 0;
66#else
67 /* stg r14,8(r15) */
68 insn->opc = 0xe3e0;
69 insn->disp = 0xf0080024;
70#endif
71}
72
73static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
74{
75#ifdef CONFIG_KPROBES
76 if (insn->opc == BREAKPOINT_INSTRUCTION)
77 return 1;
78#endif
79 return 0;
80}
81
82static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
83{
84#ifdef CONFIG_KPROBES
85 insn->opc = BREAKPOINT_INSTRUCTION;
86 insn->disp = KPROBE_ON_FTRACE_NOP;
87#endif
88}
89
90static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
91{
92#ifdef CONFIG_KPROBES
93 insn->opc = BREAKPOINT_INSTRUCTION;
94 insn->disp = KPROBE_ON_FTRACE_CALL;
95#endif
96}
97
98int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
99 unsigned long addr)
100{
101 return 0;
102}
103
104int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
105 unsigned long addr)
106{
107 struct ftrace_insn orig, new, old;
108
109 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
110 return -EFAULT;
111 if (addr == MCOUNT_ADDR) {
112 /* Initial code replacement */
113 ftrace_generate_orig_insn(&orig);
114 ftrace_generate_nop_insn(&new);
115 } else if (is_kprobe_on_ftrace(&old)) {
116 /*
117 * If we find a breakpoint instruction, a kprobe has been
118 * placed at the beginning of the function. We write the
119 * constant KPROBE_ON_FTRACE_NOP into the remaining four
120 * bytes of the original instruction so that the kprobes
121 * handler can execute a nop, if it reaches this breakpoint.
122 */
123 ftrace_generate_kprobe_call_insn(&orig);
124 ftrace_generate_kprobe_nop_insn(&new);
125 } else {
126 /* Replace ftrace call with a nop. */
127 ftrace_generate_call_insn(&orig, rec->ip);
128 ftrace_generate_nop_insn(&new);
129 }
130 /* Verify that the to be replaced code matches what we expect. */
131 if (memcmp(&orig, &old, sizeof(old)))
132 return -EINVAL;
133 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
134 return 0;
135}
136
137int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
138{
139 struct ftrace_insn orig, new, old;
140
141 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
142 return -EFAULT;
143 if (is_kprobe_on_ftrace(&old)) {
144 /*
145 * If we find a breakpoint instruction, a kprobe has been
146 * placed at the beginning of the function. We write the
147 * constant KPROBE_ON_FTRACE_CALL into the remaining four
148 * bytes of the original instruction so that the kprobes
149 * handler can execute a brasl if it reaches this breakpoint.
150 */
151 ftrace_generate_kprobe_nop_insn(&orig);
152 ftrace_generate_kprobe_call_insn(&new);
153 } else {
154 /* Replace nop with an ftrace call. */
155 ftrace_generate_nop_insn(&orig);
156 ftrace_generate_call_insn(&new, rec->ip);
157 }
158 /* Verify that the to be replaced code matches what we expect. */
159 if (memcmp(&orig, &old, sizeof(old)))
160 return -EINVAL;
161 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
162 return 0;
163}
164
165int ftrace_update_ftrace_func(ftrace_func_t func)
166{
167 return 0;
168}
169
170int __init ftrace_dyn_arch_init(void)
171{
172 return 0;
173}
174
175static int __init ftrace_plt_init(void)
176{
177 unsigned int *ip;
178
179 ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
180 if (!ftrace_plt)
181 panic("cannot allocate ftrace plt\n");
182 ip = (unsigned int *) ftrace_plt;
183 ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
184 ip[1] = 0x100a0004;
185 ip[2] = 0x07f10000;
186 ip[3] = FTRACE_ADDR >> 32;
187 ip[4] = FTRACE_ADDR & 0xffffffff;
188 set_memory_ro(ftrace_plt, 1);
189 return 0;
190}
191device_initcall(ftrace_plt_init);
192
193#ifdef CONFIG_FUNCTION_GRAPH_TRACER
194/*
195 * Hook the return address and push it in the stack of return addresses
196 * in current thread info.
197 */
198unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip)
199{
200 struct ftrace_graph_ent trace;
201
202 if (unlikely(ftrace_graph_is_dead()))
203 goto out;
204 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
205 goto out;
206 ip -= MCOUNT_INSN_SIZE;
207 trace.func = ip;
208 trace.depth = current->curr_ret_stack + 1;
209 /* Only trace if the calling function expects to. */
210 if (!ftrace_graph_entry(&trace))
211 goto out;
212 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
213 goto out;
214 parent = (unsigned long) return_to_handler;
215out:
216 return parent;
217}
218NOKPROBE_SYMBOL(prepare_ftrace_return);
219
220/*
221 * Patch the kernel code at ftrace_graph_caller location. The instruction
222 * there is branch relative on condition. To enable the ftrace graph code
223 * block, we simply patch the mask field of the instruction to zero and
224 * turn the instruction into a nop.
225 * To disable the ftrace graph code the mask field will be patched to
226 * all ones, which turns the instruction into an unconditional branch.
227 */
228int ftrace_enable_ftrace_graph_caller(void)
229{
230 u8 op = 0x04; /* set mask field to zero */
231
232 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
233 return 0;
234}
235
236int ftrace_disable_ftrace_graph_caller(void)
237{
238 u8 op = 0xf4; /* set mask field to all ones */
239
240 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
241 return 0;
242}
243
244#endif /* CONFIG_FUNCTION_GRAPH_TRACER */