xref: /openbmc/linux/arch/arm64/kernel/entry-ftrace.S (revision b830f94f) 
1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * arch/arm64/kernel/entry-ftrace.S
4 *
5 * Copyright (C) 2013 Linaro Limited
6 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
7 */
8
9#include <linux/linkage.h>
10#include <asm/assembler.h>
11#include <asm/ftrace.h>
12#include <asm/insn.h>
13
14/*
15 * Gcc with -pg will put the following code in the beginning of each function:
16 *      mov x0, x30
17 *      bl _mcount
18 *	[function's body ...]
19 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
20 * ftrace is enabled.
21 *
22 * Please note that x0 as an argument will not be used here because we can
23 * get lr(x30) of instrumented function at any time by winding up call stack
24 * as long as the kernel is compiled without -fomit-frame-pointer.
25 * (or CONFIG_FRAME_POINTER, this is forced on arm64)
26 *
27 * stack layout after mcount_enter in _mcount():
28 *
29 * current sp/fp =>  0:+-----+
30 * in _mcount()        | x29 | -> instrumented function's fp
31 *                     +-----+
32 *                     | x30 | -> _mcount()'s lr (= instrumented function's pc)
33 * old sp       => +16:+-----+
34 * when instrumented   |     |
35 * function calls      | ... |
36 * _mcount()           |     |
37 *                     |     |
38 * instrumented => +xx:+-----+
39 * function's fp       | x29 | -> parent's fp
40 *                     +-----+
41 *                     | x30 | -> instrumented function's lr (= parent's pc)
42 *                     +-----+
43 *                     | ... |
44 */
45
46	.macro mcount_enter
47	stp	x29, x30, [sp, #-16]!
48	mov	x29, sp
49	.endm
50
51	.macro mcount_exit
52	ldp	x29, x30, [sp], #16
53	ret
54	.endm
55
56	.macro mcount_adjust_addr rd, rn
57	sub	\rd, \rn, #AARCH64_INSN_SIZE
58	.endm
59
60	/* for instrumented function's parent */
61	.macro mcount_get_parent_fp reg
62	ldr	\reg, [x29]
63	ldr	\reg, [\reg]
64	.endm
65
66	/* for instrumented function */
67	.macro mcount_get_pc0 reg
68	mcount_adjust_addr	\reg, x30
69	.endm
70
71	.macro mcount_get_pc reg
72	ldr	\reg, [x29, #8]
73	mcount_adjust_addr	\reg, \reg
74	.endm
75
76	.macro mcount_get_lr reg
77	ldr	\reg, [x29]
78	ldr	\reg, [\reg, #8]
79	.endm
80
81	.macro mcount_get_lr_addr reg
82	ldr	\reg, [x29]
83	add	\reg, \reg, #8
84	.endm
85
86#ifndef CONFIG_DYNAMIC_FTRACE
87/*
88 * void _mcount(unsigned long return_address)
89 * @return_address: return address to instrumented function
90 *
91 * This function makes calls, if enabled, to:
92 *     - tracer function to probe instrumented function's entry,
93 *     - ftrace_graph_caller to set up an exit hook
94 */
95ENTRY(_mcount)
96	mcount_enter
97
98	ldr_l	x2, ftrace_trace_function
99	adr	x0, ftrace_stub
100	cmp	x0, x2			// if (ftrace_trace_function
101	b.eq	skip_ftrace_call	//     != ftrace_stub) {
102
103	mcount_get_pc	x0		//       function's pc
104	mcount_get_lr	x1		//       function's lr (= parent's pc)
105	blr	x2			//   (*ftrace_trace_function)(pc, lr);
106
107skip_ftrace_call:			// }
108#ifdef CONFIG_FUNCTION_GRAPH_TRACER
109	ldr_l	x2, ftrace_graph_return
110	cmp	x0, x2			//   if ((ftrace_graph_return
111	b.ne	ftrace_graph_caller	//        != ftrace_stub)
112
113	ldr_l	x2, ftrace_graph_entry	//     || (ftrace_graph_entry
114	adr_l	x0, ftrace_graph_entry_stub //     != ftrace_graph_entry_stub))
115	cmp	x0, x2
116	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();
117#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
118	mcount_exit
119ENDPROC(_mcount)
120EXPORT_SYMBOL(_mcount)
121NOKPROBE(_mcount)
122
123#else /* CONFIG_DYNAMIC_FTRACE */
124/*
125 * _mcount() is used to build the kernel with -pg option, but all the branch
126 * instructions to _mcount() are replaced to NOP initially at kernel start up,
127 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
128 * NOP when disabled per-function base.
129 */
130ENTRY(_mcount)
131	ret
132ENDPROC(_mcount)
133EXPORT_SYMBOL(_mcount)
134NOKPROBE(_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
151GLOBAL(ftrace_call)			// tracer(pc, lr);
152	nop				// This will be replaced with "bl xxx"
153					// where xxx can be any kind of tracer.
154
155#ifdef CONFIG_FUNCTION_GRAPH_TRACER
156GLOBAL(ftrace_graph_call)		// ftrace_graph_caller();
157	nop				// If enabled, this will be replaced
158					// "b ftrace_graph_caller"
159#endif
160
161	mcount_exit
162ENDPROC(ftrace_caller)
163#endif /* CONFIG_DYNAMIC_FTRACE */
164
165ENTRY(ftrace_stub)
166	ret
167ENDPROC(ftrace_stub)
168
169#ifdef CONFIG_FUNCTION_GRAPH_TRACER
170/*
171 * void ftrace_graph_caller(void)
172 *
173 * Called from _mcount() or ftrace_caller() when function_graph tracer is
174 * selected.
175 * This function w/ prepare_ftrace_return() fakes link register's value on
176 * the call stack in order to intercept instrumented function's return path
177 * and run return_to_handler() later on its exit.
178 */
179ENTRY(ftrace_graph_caller)
180	mcount_get_pc		  x0	//     function's pc
181	mcount_get_lr_addr	  x1	//     pointer to function's saved lr
182	mcount_get_parent_fp	  x2	//     parent's fp
183	bl	prepare_ftrace_return	// prepare_ftrace_return(pc, &lr, fp)
184
185	mcount_exit
186ENDPROC(ftrace_graph_caller)
187
188/*
189 * void return_to_handler(void)
190 *
191 * Run ftrace_return_to_handler() before going back to parent.
192 * @fp is checked against the value passed by ftrace_graph_caller().
193 */
194ENTRY(return_to_handler)
195	/* save return value regs */
196	sub sp, sp, #64
197	stp x0, x1, [sp]
198	stp x2, x3, [sp, #16]
199	stp x4, x5, [sp, #32]
200	stp x6, x7, [sp, #48]
201
202	mov	x0, x29			//     parent's fp
203	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
204	mov	x30, x0			// restore the original return address
205
206	/* restore return value regs */
207	ldp x0, x1, [sp]
208	ldp x2, x3, [sp, #16]
209	ldp x4, x5, [sp, #32]
210	ldp x6, x7, [sp, #48]
211	add sp, sp, #64
212
213	ret
214END(return_to_handler)
215#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
216