summaryrefslogtreecommitdiffstats
path: root/arch/arm/kernel/entry-ftrace.S
blob: b629d3f11c3da31af54c09159b581ebe30e390b2 (plain)
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
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <asm/assembler.h>
#include <asm/ftrace.h>
#include <asm/unwind.h>
#include <asm/export.h>

#include "entry-header.S"

/*
 * When compiling with -pg, gcc inserts a call to the mcount routine at the
 * start of every function.  In mcount, apart from the function's address (in
 * lr), we need to get hold of the function's caller's address.
 *
 * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
 *
 *	bl	mcount
 *
 * These versions have the limitation that in order for the mcount routine to
 * be able to determine the function's caller's address, an APCS-style frame
 * pointer (which is set up with something like the code below) is required.
 *
 *	mov     ip, sp
 *	push    {fp, ip, lr, pc}
 *	sub     fp, ip, #4
 *
 * With EABI, these frame pointers are not available unless -mapcs-frame is
 * specified, and if building as Thumb-2, not even then.
 *
 * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
 * with call sites like:
 *
 *	push	{lr}
 *	bl	__gnu_mcount_nc
 *
 * With these compilers, frame pointers are not necessary.
 *
 * mcount can be thought of as a function called in the middle of a subroutine
 * call.  As such, it needs to be transparent for both the caller and the
 * callee: the original lr needs to be restored when leaving mcount, and no
 * registers should be clobbered.  (In the __gnu_mcount_nc implementation, we
 * clobber the ip register.  This is OK because the ARM calling convention
 * allows it to be clobbered in subroutines and doesn't use it to hold
 * parameters.)
 *
 * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
 * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
 * arch/arm/kernel/ftrace.c).
 */

#ifndef CONFIG_OLD_MCOUNT
#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
#endif
#endif

.macro mcount_adjust_addr rd, rn
	bic	\rd, \rn, #1		@ clear the Thumb bit if present
	sub	\rd, \rd, #MCOUNT_INSN_SIZE
.endm

.macro __mcount suffix
	mcount_enter
	ldr	r0, =ftrace_trace_function
	ldr	r2, [r0]
	adr	r0, .Lftrace_stub
	cmp	r0, r2
	bne	1f

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	ldr     r1, =ftrace_graph_return
	ldr     r2, [r1]
	cmp     r0, r2
	bne     ftrace_graph_caller\suffix

	ldr     r1, =ftrace_graph_entry
	ldr     r2, [r1]
	ldr     r0, =ftrace_graph_entry_stub
	cmp     r0, r2
	bne     ftrace_graph_caller\suffix
#endif

	mcount_exit

1: 	mcount_get_lr	r1			@ lr of instrumented func
	mcount_adjust_addr	r0, lr		@ instrumented function
	badr	lr, 2f
	mov	pc, r2
2:	mcount_exit
.endm

.macro __ftrace_caller suffix
	mcount_enter

	mcount_get_lr	r1			@ lr of instrumented func
	mcount_adjust_addr	r0, lr		@ instrumented function

	.globl ftrace_call\suffix
ftrace_call\suffix:
	bl	ftrace_stub

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	.globl ftrace_graph_call\suffix
ftrace_graph_call\suffix:
	mov	r0, r0
#endif

	mcount_exit
.endm

.macro __ftrace_graph_caller
	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)
#ifdef CONFIG_DYNAMIC_FTRACE
	@ called from __ftrace_caller, saved in mcount_enter
	ldr	r1, [sp, #16]		@ instrumented routine (func)
	mcount_adjust_addr	r1, r1
#else
	@ called from __mcount, untouched in lr
	mcount_adjust_addr	r1, lr	@ instrumented routine (func)
#endif
	mov	r2, fp			@ frame pointer
	bl	prepare_ftrace_return
	mcount_exit
.endm

#ifdef CONFIG_OLD_MCOUNT
/*
 * mcount
 */

.macro mcount_enter
	stmdb	sp!, {r0-r3, lr}
.endm

.macro mcount_get_lr reg
	ldr	\reg, [fp, #-4]
.endm

.macro mcount_exit
	ldr	lr, [fp, #-4]
	ldmia	sp!, {r0-r3, pc}
.endm

ENTRY(mcount)
#ifdef CONFIG_DYNAMIC_FTRACE
	stmdb	sp!, {lr}
	ldr	lr, [fp, #-4]
	ldmia	sp!, {pc}
#else
	__mcount _old
#endif
ENDPROC(mcount)
EXPORT_SYMBOL(mcount)

#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(ftrace_caller_old)
	__ftrace_caller _old
ENDPROC(ftrace_caller_old)
#endif

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller_old)
	__ftrace_graph_caller
ENDPROC(ftrace_graph_caller_old)
#endif

.purgem mcount_enter
.purgem mcount_get_lr
.purgem mcount_exit
#endif

/*
 * __gnu_mcount_nc
 */

.macro mcount_enter
/*
 * This pad compensates for the push {lr} at the call site.  Note that we are
 * unable to unwind through a function which does not otherwise save its lr.
 */
 UNWIND(.pad	#4)
	stmdb	sp!, {r0-r3, lr}
 UNWIND(.save	{r0-r3, lr})
.endm

.macro mcount_get_lr reg
	ldr	\reg, [sp, #20]
.endm

.macro mcount_exit
	ldmia	sp!, {r0-r3, ip, lr}
	ret	ip
.endm

ENTRY(__gnu_mcount_nc)
UNWIND(.fnstart)
#ifdef CONFIG_DYNAMIC_FTRACE
	mov	ip, lr
	ldmia	sp!, {lr}
	ret	ip
#else
	__mcount
#endif
UNWIND(.fnend)
ENDPROC(__gnu_mcount_nc)
EXPORT_SYMBOL(__gnu_mcount_nc)

#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(ftrace_caller)
UNWIND(.fnstart)
	__ftrace_caller
UNWIND(.fnend)
ENDPROC(ftrace_caller)
#endif

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
UNWIND(.fnstart)
	__ftrace_graph_caller
UNWIND(.fnend)
ENDPROC(ftrace_graph_caller)
#endif

.purgem mcount_enter
.purgem mcount_get_lr
.purgem mcount_exit

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	.globl return_to_handler
return_to_handler:
	stmdb	sp!, {r0-r3}
	mov	r0, fp			@ frame pointer
	bl	ftrace_return_to_handler
	mov	lr, r0			@ r0 has real ret addr
	ldmia	sp!, {r0-r3}
	ret	lr
#endif

ENTRY(ftrace_stub)
.Lftrace_stub:
	ret	lr
ENDPROC(ftrace_stub)