xref: /linux/arch/arm64/kernel/entry-ftrace.S (revision 96ac6d435100450f0565708d9b885ea2a7400e0a) 
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	.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	mcount_enter
100
101	ldr_l	x2, ftrace_trace_function
102	adr	x0, ftrace_stub
103	cmp	x0, x2			// if (ftrace_trace_function
104	b.eq	skip_ftrace_call	//     != ftrace_stub) {
105
106	mcount_get_pc	x0		//       function's pc
107	mcount_get_lr	x1		//       function's lr (= parent's pc)
108	blr	x2			//   (*ftrace_trace_function)(pc, lr);
109
110skip_ftrace_call:			// }
111#ifdef CONFIG_FUNCTION_GRAPH_TRACER
112	ldr_l	x2, ftrace_graph_return
113	cmp	x0, x2			//   if ((ftrace_graph_return
114	b.ne	ftrace_graph_caller	//        != ftrace_stub)
115
116	ldr_l	x2, ftrace_graph_entry	//     || (ftrace_graph_entry
117	adr_l	x0, ftrace_graph_entry_stub //     != ftrace_graph_entry_stub))
118	cmp	x0, x2
119	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();
120#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
121	mcount_exit
122ENDPROC(_mcount)
123EXPORT_SYMBOL(_mcount)
124NOKPROBE(_mcount)
125
126#else /* CONFIG_DYNAMIC_FTRACE */
127/*
128 * _mcount() is used to build the kernel with -pg option, but all the branch
129 * instructions to _mcount() are replaced to NOP initially at kernel start up,
130 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
131 * NOP when disabled per-function base.
132 */
133ENTRY(_mcount)
134	ret
135ENDPROC(_mcount)
136EXPORT_SYMBOL(_mcount)
137NOKPROBE(_mcount)
138
139/*
140 * void ftrace_caller(unsigned long return_address)
141 * @return_address: return address to instrumented function
142 *
143 * This function is a counterpart of _mcount() in 'static' ftrace, and
144 * makes calls to:
145 *     - tracer function to probe instrumented function's entry,
146 *     - ftrace_graph_caller to set up an exit hook
147 */
148ENTRY(ftrace_caller)
149	mcount_enter
150
151	mcount_get_pc0	x0		//     function's pc
152	mcount_get_lr	x1		//     function's lr
153
154GLOBAL(ftrace_call)			// tracer(pc, lr);
155	nop				// This will be replaced with "bl xxx"
156					// where xxx can be any kind of tracer.
157
158#ifdef CONFIG_FUNCTION_GRAPH_TRACER
159GLOBAL(ftrace_graph_call)		// ftrace_graph_caller();
160	nop				// If enabled, this will be replaced
161					// "b ftrace_graph_caller"
162#endif
163
164	mcount_exit
165ENDPROC(ftrace_caller)
166#endif /* CONFIG_DYNAMIC_FTRACE */
167
168ENTRY(ftrace_stub)
169	ret
170ENDPROC(ftrace_stub)
171
172#ifdef CONFIG_FUNCTION_GRAPH_TRACER
173/*
174 * void ftrace_graph_caller(void)
175 *
176 * Called from _mcount() or ftrace_caller() when function_graph tracer is
177 * selected.
178 * This function w/ prepare_ftrace_return() fakes link register's value on
179 * the call stack in order to intercept instrumented function's return path
180 * and run return_to_handler() later on its exit.
181 */
182ENTRY(ftrace_graph_caller)
183	mcount_get_pc		  x0	//     function's pc
184	mcount_get_lr_addr	  x1	//     pointer to function's saved lr
185	mcount_get_parent_fp	  x2	//     parent's fp
186	bl	prepare_ftrace_return	// prepare_ftrace_return(pc, &lr, fp)
187
188	mcount_exit
189ENDPROC(ftrace_graph_caller)
190
191/*
192 * void return_to_handler(void)
193 *
194 * Run ftrace_return_to_handler() before going back to parent.
195 * @fp is checked against the value passed by ftrace_graph_caller().
196 */
197ENTRY(return_to_handler)
198	/* save return value regs */
199	sub sp, sp, #64
200	stp x0, x1, [sp]
201	stp x2, x3, [sp, #16]
202	stp x4, x5, [sp, #32]
203	stp x6, x7, [sp, #48]
204
205	mov	x0, x29			//     parent's fp
206	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
207	mov	x30, x0			// restore the original return address
208
209	/* restore return value regs */
210	ldp x0, x1, [sp]
211	ldp x2, x3, [sp, #16]
212	ldp x4, x5, [sp, #32]
213	ldp x6, x7, [sp, #48]
214	add sp, sp, #64
215
216	ret
217END(return_to_handler)
218#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
219