xref: /openbmc/linux/arch/arm64/kernel/entry-ftrace.S (revision d2999e1b) 
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/ftrace.h>
14#include <asm/insn.h>
15
16/*
17 * Gcc with -pg will put the following code in the beginning of each function:
18 *      mov x0, x30
19 *      bl _mcount
20 *	[function's body ...]
21 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
22 * ftrace is enabled.
23 *
24 * Please note that x0 as an argument will not be used here because we can
25 * get lr(x30) of instrumented function at any time by winding up call stack
26 * as long as the kernel is compiled without -fomit-frame-pointer.
27 * (or CONFIG_FRAME_POINTER, this is forced on arm64)
28 *
29 * stack layout after mcount_enter in _mcount():
30 *
31 * current sp/fp =>  0:+-----+
32 * in _mcount()        | x29 | -> instrumented function's fp
33 *                     +-----+
34 *                     | x30 | -> _mcount()'s lr (= instrumented function's pc)
35 * old sp       => +16:+-----+
36 * when instrumented   |     |
37 * function calls      | ... |
38 * _mcount()           |     |
39 *                     |     |
40 * instrumented => +xx:+-----+
41 * function's fp       | x29 | -> parent's fp
42 *                     +-----+
43 *                     | x30 | -> instrumented function's lr (= parent's pc)
44 *                     +-----+
45 *                     | ... |
46 */
47
48	.macro mcount_enter
49	stp	x29, x30, [sp, #-16]!
50	mov	x29, sp
51	.endm
52
53	.macro mcount_exit
54	ldp	x29, x30, [sp], #16
55	ret
56	.endm
57
58	.macro mcount_adjust_addr rd, rn
59	sub	\rd, \rn, #AARCH64_INSN_SIZE
60	.endm
61
62	/* for instrumented function's parent */
63	.macro mcount_get_parent_fp reg
64	ldr	\reg, [x29]
65	ldr	\reg, [\reg]
66	.endm
67
68	/* for instrumented function */
69	.macro mcount_get_pc0 reg
70	mcount_adjust_addr	\reg, x30
71	.endm
72
73	.macro mcount_get_pc reg
74	ldr	\reg, [x29, #8]
75	mcount_adjust_addr	\reg, \reg
76	.endm
77
78	.macro mcount_get_lr reg
79	ldr	\reg, [x29]
80	ldr	\reg, [\reg, #8]
81	mcount_adjust_addr	\reg, \reg
82	.endm
83
84	.macro mcount_get_lr_addr reg
85	ldr	\reg, [x29]
86	add	\reg, \reg, #8
87	.endm
88
89#ifndef CONFIG_DYNAMIC_FTRACE
90/*
91 * void _mcount(unsigned long return_address)
92 * @return_address: return address to instrumented function
93 *
94 * This function makes calls, if enabled, to:
95 *     - tracer function to probe instrumented function's entry,
96 *     - ftrace_graph_caller to set up an exit hook
97 */
98ENTRY(_mcount)
99#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
100	ldr	x0, =ftrace_trace_stop
101	ldr	x0, [x0]		// if ftrace_trace_stop
102	ret				//   return;
103#endif
104	mcount_enter
105
106	ldr	x0, =ftrace_trace_function
107	ldr	x2, [x0]
108	adr	x0, ftrace_stub
109	cmp	x0, x2			// if (ftrace_trace_function
110	b.eq	skip_ftrace_call	//     != ftrace_stub) {
111
112	mcount_get_pc	x0		//       function's pc
113	mcount_get_lr	x1		//       function's lr (= parent's pc)
114	blr	x2			//   (*ftrace_trace_function)(pc, lr);
115
116#ifndef CONFIG_FUNCTION_GRAPH_TRACER
117skip_ftrace_call:			//   return;
118	mcount_exit			// }
119#else
120	mcount_exit			//   return;
121					// }
122skip_ftrace_call:
123	ldr	x1, =ftrace_graph_return
124	ldr	x2, [x1]		//   if ((ftrace_graph_return
125	cmp	x0, x2			//        != ftrace_stub)
126	b.ne	ftrace_graph_caller
127
128	ldr	x1, =ftrace_graph_entry	//     || (ftrace_graph_entry
129	ldr	x2, [x1]		//        != ftrace_graph_entry_stub))
130	ldr	x0, =ftrace_graph_entry_stub
131	cmp	x0, x2
132	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();
133
134	mcount_exit
135#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
136ENDPROC(_mcount)
137
138#else /* CONFIG_DYNAMIC_FTRACE */
139/*
140 * _mcount() is used to build the kernel with -pg option, but all the branch
141 * instructions to _mcount() are replaced to NOP initially at kernel start up,
142 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
143 * NOP when disabled per-function base.
144 */
145ENTRY(_mcount)
146	ret
147ENDPROC(_mcount)
148
149/*
150 * void ftrace_caller(unsigned long return_address)
151 * @return_address: return address to instrumented function
152 *
153 * This function is a counterpart of _mcount() in 'static' ftrace, and
154 * makes calls to:
155 *     - tracer function to probe instrumented function's entry,
156 *     - ftrace_graph_caller to set up an exit hook
157 */
158ENTRY(ftrace_caller)
159	mcount_enter
160
161	mcount_get_pc0	x0		//     function's pc
162	mcount_get_lr	x1		//     function's lr
163
164	.global ftrace_call
165ftrace_call:				// tracer(pc, lr);
166	nop				// This will be replaced with "bl xxx"
167					// where xxx can be any kind of tracer.
168
169#ifdef CONFIG_FUNCTION_GRAPH_TRACER
170	.global ftrace_graph_call
171ftrace_graph_call:			// ftrace_graph_caller();
172	nop				// If enabled, this will be replaced
173					// "b ftrace_graph_caller"
174#endif
175
176	mcount_exit
177ENDPROC(ftrace_caller)
178#endif /* CONFIG_DYNAMIC_FTRACE */
179
180ENTRY(ftrace_stub)
181	ret
182ENDPROC(ftrace_stub)
183
184#ifdef CONFIG_FUNCTION_GRAPH_TRACER
185/*
186 * void ftrace_graph_caller(void)
187 *
188 * Called from _mcount() or ftrace_caller() when function_graph tracer is
189 * selected.
190 * This function w/ prepare_ftrace_return() fakes link register's value on
191 * the call stack in order to intercept instrumented function's return path
192 * and run return_to_handler() later on its exit.
193 */
194ENTRY(ftrace_graph_caller)
195	mcount_get_lr_addr	  x0	//     pointer to function's saved lr
196	mcount_get_pc		  x1	//     function's pc
197	mcount_get_parent_fp	  x2	//     parent's fp
198	bl	prepare_ftrace_return	// prepare_ftrace_return(&lr, pc, fp)
199
200	mcount_exit
201ENDPROC(ftrace_graph_caller)
202
203/*
204 * void return_to_handler(void)
205 *
206 * Run ftrace_return_to_handler() before going back to parent.
207 * @fp is checked against the value passed by ftrace_graph_caller()
208 * only when CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
209 */
210ENTRY(return_to_handler)
211	str	x0, [sp, #-16]!
212	mov	x0, x29			//     parent's fp
213	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
214	mov	x30, x0			// restore the original return address
215	ldr	x0, [sp], #16
216	ret
217END(return_to_handler)
218#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
219