xref: /linux/arch/arm64/kernel/entry-ftrace.S (revision 9a379e77033f02c4a071891afdf0f0a01eff8ccb) 
1/*
2 * arch/arm64/kernel/entry-ftrace.S
3 *
4 * Copyright (C) 2013 Linaro Limited
5 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 */
11
12#include <linux/linkage.h>
13#include <asm/assembler.h>
14#include <asm/ftrace.h>
15#include <asm/insn.h>
16
17/*
18 * Gcc with -pg will put the following code in the beginning of each function:
19 *      mov x0, x30
20 *      bl _mcount
21 *	[function's body ...]
22 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
23 * ftrace is enabled.
24 *
25 * Please note that x0 as an argument will not be used here because we can
26 * get lr(x30) of instrumented function at any time by winding up call stack
27 * as long as the kernel is compiled without -fomit-frame-pointer.
28 * (or CONFIG_FRAME_POINTER, this is forced on arm64)
29 *
30 * stack layout after mcount_enter in _mcount():
31 *
32 * current sp/fp =>  0:+-----+
33 * in _mcount()        | x29 | -> instrumented function's fp
34 *                     +-----+
35 *                     | x30 | -> _mcount()'s lr (= instrumented function's pc)
36 * old sp       => +16:+-----+
37 * when instrumented   |     |
38 * function calls      | ... |
39 * _mcount()           |     |
40 *                     |     |
41 * instrumented => +xx:+-----+
42 * function's fp       | x29 | -> parent's fp
43 *                     +-----+
44 *                     | x30 | -> instrumented function's lr (= parent's pc)
45 *                     +-----+
46 *                     | ... |
47 */
48
49	.macro mcount_enter
50	stp	x29, x30, [sp, #-16]!
51	mov	x29, sp
52	.endm
53
54	.macro mcount_exit
55	ldp	x29, x30, [sp], #16
56	ret
57	.endm
58
59	.macro mcount_adjust_addr rd, rn
60	sub	\rd, \rn, #AARCH64_INSN_SIZE
61	.endm
62
63	/* for instrumented function's parent */
64	.macro mcount_get_parent_fp reg
65	ldr	\reg, [x29]
66	ldr	\reg, [\reg]
67	.endm
68
69	/* for instrumented function */
70	.macro mcount_get_pc0 reg
71	mcount_adjust_addr	\reg, x30
72	.endm
73
74	.macro mcount_get_pc reg
75	ldr	\reg, [x29, #8]
76	mcount_adjust_addr	\reg, \reg
77	.endm
78
79	.macro mcount_get_lr reg
80	ldr	\reg, [x29]
81	ldr	\reg, [\reg, #8]
82	mcount_adjust_addr	\reg, \reg
83	.endm
84
85	.macro mcount_get_lr_addr reg
86	ldr	\reg, [x29]
87	add	\reg, \reg, #8
88	.endm
89
90#ifndef CONFIG_DYNAMIC_FTRACE
91/*
92 * void _mcount(unsigned long return_address)
93 * @return_address: return address to instrumented function
94 *
95 * This function makes calls, if enabled, to:
96 *     - tracer function to probe instrumented function's entry,
97 *     - ftrace_graph_caller to set up an exit hook
98 */
99ENTRY(_mcount)
100	mcount_enter
101
102	ldr_l	x2, ftrace_trace_function
103	adr	x0, ftrace_stub
104	cmp	x0, x2			// if (ftrace_trace_function
105	b.eq	skip_ftrace_call	//     != ftrace_stub) {
106
107	mcount_get_pc	x0		//       function's pc
108	mcount_get_lr	x1		//       function's lr (= parent's pc)
109	blr	x2			//   (*ftrace_trace_function)(pc, lr);
110
111skip_ftrace_call:			// }
112#ifdef CONFIG_FUNCTION_GRAPH_TRACER
113	ldr_l	x2, ftrace_graph_return
114	cmp	x0, x2			//   if ((ftrace_graph_return
115	b.ne	ftrace_graph_caller	//        != ftrace_stub)
116
117	ldr_l	x2, ftrace_graph_entry	//     || (ftrace_graph_entry
118	adr_l	x0, ftrace_graph_entry_stub //     != ftrace_graph_entry_stub))
119	cmp	x0, x2
120	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();
121#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
122	mcount_exit
123ENDPROC(_mcount)
124
125#else /* CONFIG_DYNAMIC_FTRACE */
126/*
127 * _mcount() is used to build the kernel with -pg option, but all the branch
128 * instructions to _mcount() are replaced to NOP initially at kernel start up,
129 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
130 * NOP when disabled per-function base.
131 */
132ENTRY(_mcount)
133	ret
134ENDPROC(_mcount)
135
136/*
137 * void ftrace_caller(unsigned long return_address)
138 * @return_address: return address to instrumented function
139 *
140 * This function is a counterpart of _mcount() in 'static' ftrace, and
141 * makes calls to:
142 *     - tracer function to probe instrumented function's entry,
143 *     - ftrace_graph_caller to set up an exit hook
144 */
145ENTRY(ftrace_caller)
146	mcount_enter
147
148	mcount_get_pc0	x0		//     function's pc
149	mcount_get_lr	x1		//     function's lr
150
151	.global ftrace_call
152ftrace_call:				// tracer(pc, lr);
153	nop				// This will be replaced with "bl xxx"
154					// where xxx can be any kind of tracer.
155
156#ifdef CONFIG_FUNCTION_GRAPH_TRACER
157	.global ftrace_graph_call
158ftrace_graph_call:			// ftrace_graph_caller();
159	nop				// If enabled, this will be replaced
160					// "b ftrace_graph_caller"
161#endif
162
163	mcount_exit
164ENDPROC(ftrace_caller)
165#endif /* CONFIG_DYNAMIC_FTRACE */
166
167ENTRY(ftrace_stub)
168	ret
169ENDPROC(ftrace_stub)
170
171#ifdef CONFIG_FUNCTION_GRAPH_TRACER
172	/* save return value regs*/
173	.macro save_return_regs
174	sub sp, sp, #64
175	stp x0, x1, [sp]
176	stp x2, x3, [sp, #16]
177	stp x4, x5, [sp, #32]
178	stp x6, x7, [sp, #48]
179	.endm
180
181	/* restore return value regs*/
182	.macro restore_return_regs
183	ldp x0, x1, [sp]
184	ldp x2, x3, [sp, #16]
185	ldp x4, x5, [sp, #32]
186	ldp x6, x7, [sp, #48]
187	add sp, sp, #64
188	.endm
189
190/*
191 * void ftrace_graph_caller(void)
192 *
193 * Called from _mcount() or ftrace_caller() when function_graph tracer is
194 * selected.
195 * This function w/ prepare_ftrace_return() fakes link register's value on
196 * the call stack in order to intercept instrumented function's return path
197 * and run return_to_handler() later on its exit.
198 */
199ENTRY(ftrace_graph_caller)
200	mcount_get_lr_addr	  x0	//     pointer to function's saved lr
201	mcount_get_pc		  x1	//     function's pc
202	mcount_get_parent_fp	  x2	//     parent's fp
203	bl	prepare_ftrace_return	// prepare_ftrace_return(&lr, pc, fp)
204
205	mcount_exit
206ENDPROC(ftrace_graph_caller)
207
208/*
209 * void return_to_handler(void)
210 *
211 * Run ftrace_return_to_handler() before going back to parent.
212 * @fp is checked against the value passed by ftrace_graph_caller()
213 * only when HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
214 */
215ENTRY(return_to_handler)
216	save_return_regs
217	mov	x0, x29			//     parent's fp
218	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
219	mov	x30, x0			// restore the original return address
220	restore_return_regs
221	ret
222END(return_to_handler)
223#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
224