xref: /openbmc/linux/arch/arm64/kernel/entry-ftrace.S (revision 84b102f5) 
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/asm-offsets.h>
11#include <asm/assembler.h>
12#include <asm/ftrace.h>
13#include <asm/insn.h>
14
15#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
16/*
17 * Due to -fpatchable-function-entry=2, the compiler has placed two NOPs before
18 * the regular function prologue. For an enabled callsite, ftrace_init_nop() and
19 * ftrace_make_call() have patched those NOPs to:
20 *
21 * 	MOV	X9, LR
22 * 	BL	<entry>
23 *
24 * ... where <entry> is either ftrace_caller or ftrace_regs_caller.
25 *
26 * Each instrumented function follows the AAPCS, so here x0-x8 and x18-x30 are
27 * live (x18 holds the Shadow Call Stack pointer), and x9-x17 are safe to
28 * clobber.
29 *
30 * We save the callsite's context into a pt_regs before invoking any ftrace
31 * callbacks. So that we can get a sensible backtrace, we create a stack record
32 * for the callsite and the ftrace entry assembly. This is not sufficient for
33 * reliable stacktrace: until we create the callsite stack record, its caller
34 * is missing from the LR and existing chain of frame records.
35 */
36	.macro  ftrace_regs_entry, allregs=0
37	/* Make room for pt_regs, plus a callee frame */
38	sub	sp, sp, #(PT_REGS_SIZE + 16)
39
40	/* Save function arguments (and x9 for simplicity) */
41	stp	x0, x1, [sp, #S_X0]
42	stp	x2, x3, [sp, #S_X2]
43	stp	x4, x5, [sp, #S_X4]
44	stp	x6, x7, [sp, #S_X6]
45	stp	x8, x9, [sp, #S_X8]
46
47	/* Optionally save the callee-saved registers, always save the FP */
48	.if \allregs == 1
49	stp	x10, x11, [sp, #S_X10]
50	stp	x12, x13, [sp, #S_X12]
51	stp	x14, x15, [sp, #S_X14]
52	stp	x16, x17, [sp, #S_X16]
53	stp	x18, x19, [sp, #S_X18]
54	stp	x20, x21, [sp, #S_X20]
55	stp	x22, x23, [sp, #S_X22]
56	stp	x24, x25, [sp, #S_X24]
57	stp	x26, x27, [sp, #S_X26]
58	stp	x28, x29, [sp, #S_X28]
59	.else
60	str	x29, [sp, #S_FP]
61	.endif
62
63	/* Save the callsite's SP and LR */
64	add	x10, sp, #(PT_REGS_SIZE + 16)
65	stp	x9, x10, [sp, #S_LR]
66
67	/* Save the PC after the ftrace callsite */
68	str	x30, [sp, #S_PC]
69
70	/* Create a frame record for the callsite above pt_regs */
71	stp	x29, x9, [sp, #PT_REGS_SIZE]
72	add	x29, sp, #PT_REGS_SIZE
73
74	/* Create our frame record within pt_regs. */
75	stp	x29, x30, [sp, #S_STACKFRAME]
76	add	x29, sp, #S_STACKFRAME
77	.endm
78
79SYM_CODE_START(ftrace_regs_caller)
80	ftrace_regs_entry	1
81	b	ftrace_common
82SYM_CODE_END(ftrace_regs_caller)
83
84SYM_CODE_START(ftrace_caller)
85	ftrace_regs_entry	0
86	b	ftrace_common
87SYM_CODE_END(ftrace_caller)
88
89SYM_CODE_START(ftrace_common)
90	sub	x0, x30, #AARCH64_INSN_SIZE	// ip (callsite's BL insn)
91	mov	x1, x9				// parent_ip (callsite's LR)
92	ldr_l	x2, function_trace_op		// op
93	mov	x3, sp				// regs
94
95SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
96	bl	ftrace_stub
97
98#ifdef CONFIG_FUNCTION_GRAPH_TRACER
99SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
100	nop				// If enabled, this will be replaced
101					// "b ftrace_graph_caller"
102#endif
103
104/*
105 * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
106 * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
107 * to restore x0-x8, x29, and x30.
108 */
109ftrace_common_return:
110	/* Restore function arguments */
111	ldp	x0, x1, [sp]
112	ldp	x2, x3, [sp, #S_X2]
113	ldp	x4, x5, [sp, #S_X4]
114	ldp	x6, x7, [sp, #S_X6]
115	ldr	x8, [sp, #S_X8]
116
117	/* Restore the callsite's FP, LR, PC */
118	ldr	x29, [sp, #S_FP]
119	ldr	x30, [sp, #S_LR]
120	ldr	x9, [sp, #S_PC]
121
122	/* Restore the callsite's SP */
123	add	sp, sp, #PT_REGS_SIZE + 16
124
125	ret	x9
126SYM_CODE_END(ftrace_common)
127
128#ifdef CONFIG_FUNCTION_GRAPH_TRACER
129SYM_CODE_START(ftrace_graph_caller)
130	ldr	x0, [sp, #S_PC]
131	sub	x0, x0, #AARCH64_INSN_SIZE	// ip (callsite's BL insn)
132	add	x1, sp, #S_LR			// parent_ip (callsite's LR)
133	ldr	x2, [sp, #PT_REGS_SIZE]	   	// parent fp (callsite's FP)
134	bl	prepare_ftrace_return
135	b	ftrace_common_return
136SYM_CODE_END(ftrace_graph_caller)
137#endif
138
139#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
140
141/*
142 * Gcc with -pg will put the following code in the beginning of each function:
143 *      mov x0, x30
144 *      bl _mcount
145 *	[function's body ...]
146 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
147 * ftrace is enabled.
148 *
149 * Please note that x0 as an argument will not be used here because we can
150 * get lr(x30) of instrumented function at any time by winding up call stack
151 * as long as the kernel is compiled without -fomit-frame-pointer.
152 * (or CONFIG_FRAME_POINTER, this is forced on arm64)
153 *
154 * stack layout after mcount_enter in _mcount():
155 *
156 * current sp/fp =>  0:+-----+
157 * in _mcount()        | x29 | -> instrumented function's fp
158 *                     +-----+
159 *                     | x30 | -> _mcount()'s lr (= instrumented function's pc)
160 * old sp       => +16:+-----+
161 * when instrumented   |     |
162 * function calls      | ... |
163 * _mcount()           |     |
164 *                     |     |
165 * instrumented => +xx:+-----+
166 * function's fp       | x29 | -> parent's fp
167 *                     +-----+
168 *                     | x30 | -> instrumented function's lr (= parent's pc)
169 *                     +-----+
170 *                     | ... |
171 */
172
173	.macro mcount_enter
174	stp	x29, x30, [sp, #-16]!
175	mov	x29, sp
176	.endm
177
178	.macro mcount_exit
179	ldp	x29, x30, [sp], #16
180	ret
181	.endm
182
183	.macro mcount_adjust_addr rd, rn
184	sub	\rd, \rn, #AARCH64_INSN_SIZE
185	.endm
186
187	/* for instrumented function's parent */
188	.macro mcount_get_parent_fp reg
189	ldr	\reg, [x29]
190	ldr	\reg, [\reg]
191	.endm
192
193	/* for instrumented function */
194	.macro mcount_get_pc0 reg
195	mcount_adjust_addr	\reg, x30
196	.endm
197
198	.macro mcount_get_pc reg
199	ldr	\reg, [x29, #8]
200	mcount_adjust_addr	\reg, \reg
201	.endm
202
203	.macro mcount_get_lr reg
204	ldr	\reg, [x29]
205	ldr	\reg, [\reg, #8]
206	.endm
207
208	.macro mcount_get_lr_addr reg
209	ldr	\reg, [x29]
210	add	\reg, \reg, #8
211	.endm
212
213#ifndef CONFIG_DYNAMIC_FTRACE
214/*
215 * void _mcount(unsigned long return_address)
216 * @return_address: return address to instrumented function
217 *
218 * This function makes calls, if enabled, to:
219 *     - tracer function to probe instrumented function's entry,
220 *     - ftrace_graph_caller to set up an exit hook
221 */
222SYM_FUNC_START(_mcount)
223	mcount_enter
224
225	ldr_l	x2, ftrace_trace_function
226	adr	x0, ftrace_stub
227	cmp	x0, x2			// if (ftrace_trace_function
228	b.eq	skip_ftrace_call	//     != ftrace_stub) {
229
230	mcount_get_pc	x0		//       function's pc
231	mcount_get_lr	x1		//       function's lr (= parent's pc)
232	blr	x2			//   (*ftrace_trace_function)(pc, lr);
233
234skip_ftrace_call:			// }
235#ifdef CONFIG_FUNCTION_GRAPH_TRACER
236	ldr_l	x2, ftrace_graph_return
237	cmp	x0, x2			//   if ((ftrace_graph_return
238	b.ne	ftrace_graph_caller	//        != ftrace_stub)
239
240	ldr_l	x2, ftrace_graph_entry	//     || (ftrace_graph_entry
241	adr_l	x0, ftrace_graph_entry_stub //     != ftrace_graph_entry_stub))
242	cmp	x0, x2
243	b.ne	ftrace_graph_caller	//     ftrace_graph_caller();
244#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
245	mcount_exit
246SYM_FUNC_END(_mcount)
247EXPORT_SYMBOL(_mcount)
248NOKPROBE(_mcount)
249
250#else /* CONFIG_DYNAMIC_FTRACE */
251/*
252 * _mcount() is used to build the kernel with -pg option, but all the branch
253 * instructions to _mcount() are replaced to NOP initially at kernel start up,
254 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
255 * NOP when disabled per-function base.
256 */
257SYM_FUNC_START(_mcount)
258	ret
259SYM_FUNC_END(_mcount)
260EXPORT_SYMBOL(_mcount)
261NOKPROBE(_mcount)
262
263/*
264 * void ftrace_caller(unsigned long return_address)
265 * @return_address: return address to instrumented function
266 *
267 * This function is a counterpart of _mcount() in 'static' ftrace, and
268 * makes calls to:
269 *     - tracer function to probe instrumented function's entry,
270 *     - ftrace_graph_caller to set up an exit hook
271 */
272SYM_FUNC_START(ftrace_caller)
273	mcount_enter
274
275	mcount_get_pc0	x0		//     function's pc
276	mcount_get_lr	x1		//     function's lr
277
278SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)	// tracer(pc, lr);
279	nop				// This will be replaced with "bl xxx"
280					// where xxx can be any kind of tracer.
281
282#ifdef CONFIG_FUNCTION_GRAPH_TRACER
283SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
284	nop				// If enabled, this will be replaced
285					// "b ftrace_graph_caller"
286#endif
287
288	mcount_exit
289SYM_FUNC_END(ftrace_caller)
290#endif /* CONFIG_DYNAMIC_FTRACE */
291
292#ifdef CONFIG_FUNCTION_GRAPH_TRACER
293/*
294 * void ftrace_graph_caller(void)
295 *
296 * Called from _mcount() or ftrace_caller() when function_graph tracer is
297 * selected.
298 * This function w/ prepare_ftrace_return() fakes link register's value on
299 * the call stack in order to intercept instrumented function's return path
300 * and run return_to_handler() later on its exit.
301 */
302SYM_FUNC_START(ftrace_graph_caller)
303	mcount_get_pc		  x0	//     function's pc
304	mcount_get_lr_addr	  x1	//     pointer to function's saved lr
305	mcount_get_parent_fp	  x2	//     parent's fp
306	bl	prepare_ftrace_return	// prepare_ftrace_return(pc, &lr, fp)
307
308	mcount_exit
309SYM_FUNC_END(ftrace_graph_caller)
310#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
311#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
312
313SYM_FUNC_START(ftrace_stub)
314	ret
315SYM_FUNC_END(ftrace_stub)
316
317#ifdef CONFIG_FUNCTION_GRAPH_TRACER
318/*
319 * void return_to_handler(void)
320 *
321 * Run ftrace_return_to_handler() before going back to parent.
322 * @fp is checked against the value passed by ftrace_graph_caller().
323 */
324SYM_CODE_START(return_to_handler)
325	/* save return value regs */
326	sub sp, sp, #64
327	stp x0, x1, [sp]
328	stp x2, x3, [sp, #16]
329	stp x4, x5, [sp, #32]
330	stp x6, x7, [sp, #48]
331
332	mov	x0, x29			//     parent's fp
333	bl	ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
334	mov	x30, x0			// restore the original return address
335
336	/* restore return value regs */
337	ldp x0, x1, [sp]
338	ldp x2, x3, [sp, #16]
339	ldp x4, x5, [sp, #32]
340	ldp x6, x7, [sp, #48]
341	add sp, sp, #64
342
343	ret
344SYM_CODE_END(return_to_handler)
345#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
346