xref: /openbmc/linux/arch/arm/kernel/entry-ftrace.S (revision 82e6fdd6) 
1/*
2 * This program is free software; you can redistribute it and/or modify
3 * it under the terms of the GNU General Public License version 2 as
4 * published by the Free Software Foundation.
5 */
6
7#include <asm/assembler.h>
8#include <asm/ftrace.h>
9#include <asm/unwind.h>
10
11#include "entry-header.S"
12
13/*
14 * When compiling with -pg, gcc inserts a call to the mcount routine at the
15 * start of every function.  In mcount, apart from the function's address (in
16 * lr), we need to get hold of the function's caller's address.
17 *
18 * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
19 *
20 *	bl	mcount
21 *
22 * These versions have the limitation that in order for the mcount routine to
23 * be able to determine the function's caller's address, an APCS-style frame
24 * pointer (which is set up with something like the code below) is required.
25 *
26 *	mov     ip, sp
27 *	push    {fp, ip, lr, pc}
28 *	sub     fp, ip, #4
29 *
30 * With EABI, these frame pointers are not available unless -mapcs-frame is
31 * specified, and if building as Thumb-2, not even then.
32 *
33 * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
34 * with call sites like:
35 *
36 *	push	{lr}
37 *	bl	__gnu_mcount_nc
38 *
39 * With these compilers, frame pointers are not necessary.
40 *
41 * mcount can be thought of as a function called in the middle of a subroutine
42 * call.  As such, it needs to be transparent for both the caller and the
43 * callee: the original lr needs to be restored when leaving mcount, and no
44 * registers should be clobbered.  (In the __gnu_mcount_nc implementation, we
45 * clobber the ip register.  This is OK because the ARM calling convention
46 * allows it to be clobbered in subroutines and doesn't use it to hold
47 * parameters.)
48 *
49 * When using dynamic ftrace, we patch out the mcount call by a "mov r0, r0"
50 * for the mcount case, and a "pop {lr}" for the __gnu_mcount_nc case (see
51 * arch/arm/kernel/ftrace.c).
52 */
53
54#ifndef CONFIG_OLD_MCOUNT
55#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
56#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
57#endif
58#endif
59
60.macro mcount_adjust_addr rd, rn
61	bic	\rd, \rn, #1		@ clear the Thumb bit if present
62	sub	\rd, \rd, #MCOUNT_INSN_SIZE
63.endm
64
65.macro __mcount suffix
66	mcount_enter
67	ldr	r0, =ftrace_trace_function
68	ldr	r2, [r0]
69	adr	r0, .Lftrace_stub
70	cmp	r0, r2
71	bne	1f
72
73#ifdef CONFIG_FUNCTION_GRAPH_TRACER
74	ldr     r1, =ftrace_graph_return
75	ldr     r2, [r1]
76	cmp     r0, r2
77	bne     ftrace_graph_caller\suffix
78
79	ldr     r1, =ftrace_graph_entry
80	ldr     r2, [r1]
81	ldr     r0, =ftrace_graph_entry_stub
82	cmp     r0, r2
83	bne     ftrace_graph_caller\suffix
84#endif
85
86	mcount_exit
87
881: 	mcount_get_lr	r1			@ lr of instrumented func
89	mcount_adjust_addr	r0, lr		@ instrumented function
90	badr	lr, 2f
91	mov	pc, r2
922:	mcount_exit
93.endm
94
95#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
96
97.macro __ftrace_regs_caller
98
99	sub	sp, sp, #8	@ space for PC and CPSR OLD_R0,
100				@ OLD_R0 will overwrite previous LR
101
102	add 	ip, sp, #12	@ move in IP the value of SP as it was
103				@ before the push {lr} of the mcount mechanism
104
105	str     lr, [sp, #0]    @ store LR instead of PC
106
107	ldr     lr, [sp, #8]    @ get previous LR
108
109	str	r0, [sp, #8]	@ write r0 as OLD_R0 over previous LR
110
111	stmdb   sp!, {ip, lr}
112	stmdb   sp!, {r0-r11, lr}
113
114	@ stack content at this point:
115	@ 0  4          48   52       56            60   64    68       72
116	@ R0 | R1 | ... | LR | SP + 4 | previous LR | LR | PSR | OLD_R0 |
117
118	mov r3, sp				@ struct pt_regs*
119
120	ldr r2, =function_trace_op
121	ldr r2, [r2]				@ pointer to the current
122						@ function tracing op
123
124	ldr	r1, [sp, #S_LR]			@ lr of instrumented func
125
126	ldr	lr, [sp, #S_PC]			@ get LR
127
128	mcount_adjust_addr	r0, lr		@ instrumented function
129
130	.globl ftrace_regs_call
131ftrace_regs_call:
132	bl	ftrace_stub
133
134#ifdef CONFIG_FUNCTION_GRAPH_TRACER
135	.globl ftrace_graph_regs_call
136ftrace_graph_regs_call:
137	mov	r0, r0
138#endif
139
140	@ pop saved regs
141	ldmia   sp!, {r0-r12}			@ restore r0 through r12
142	ldr	ip, [sp, #8]			@ restore PC
143	ldr	lr, [sp, #4]			@ restore LR
144	ldr	sp, [sp, #0]			@ restore SP
145	mov	pc, ip				@ return
146.endm
147
148#ifdef CONFIG_FUNCTION_GRAPH_TRACER
149.macro __ftrace_graph_regs_caller
150
151	sub     r0, fp, #4              @ lr of instrumented routine (parent)
152
153	@ called from __ftrace_regs_caller
154	ldr     r1, [sp, #S_PC]		@ instrumented routine (func)
155	mcount_adjust_addr	r1, r1
156
157	mov	r2, fp			@ frame pointer
158	bl	prepare_ftrace_return
159
160	@ pop registers saved in ftrace_regs_caller
161	ldmia   sp!, {r0-r12}			@ restore r0 through r12
162	ldr	ip, [sp, #8]			@ restore PC
163	ldr	lr, [sp, #4]			@ restore LR
164	ldr	sp, [sp, #0]			@ restore SP
165	mov	pc, ip				@ return
166
167.endm
168#endif
169#endif
170
171.macro __ftrace_caller suffix
172	mcount_enter
173
174	mcount_get_lr	r1			@ lr of instrumented func
175	mcount_adjust_addr	r0, lr		@ instrumented function
176
177#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
178	ldr r2, =function_trace_op
179	ldr r2, [r2]				@ pointer to the current
180						@ function tracing op
181	mov r3, #0				@ regs is NULL
182#endif
183
184	.globl ftrace_call\suffix
185ftrace_call\suffix:
186	bl	ftrace_stub
187
188#ifdef CONFIG_FUNCTION_GRAPH_TRACER
189	.globl ftrace_graph_call\suffix
190ftrace_graph_call\suffix:
191	mov	r0, r0
192#endif
193
194	mcount_exit
195.endm
196
197.macro __ftrace_graph_caller
198	sub	r0, fp, #4		@ &lr of instrumented routine (&parent)
199#ifdef CONFIG_DYNAMIC_FTRACE
200	@ called from __ftrace_caller, saved in mcount_enter
201	ldr	r1, [sp, #16]		@ instrumented routine (func)
202	mcount_adjust_addr	r1, r1
203#else
204	@ called from __mcount, untouched in lr
205	mcount_adjust_addr	r1, lr	@ instrumented routine (func)
206#endif
207	mov	r2, fp			@ frame pointer
208	bl	prepare_ftrace_return
209	mcount_exit
210.endm
211
212#ifdef CONFIG_OLD_MCOUNT
213/*
214 * mcount
215 */
216
217.macro mcount_enter
218	stmdb	sp!, {r0-r3, lr}
219.endm
220
221.macro mcount_get_lr reg
222	ldr	\reg, [fp, #-4]
223.endm
224
225.macro mcount_exit
226	ldr	lr, [fp, #-4]
227	ldmia	sp!, {r0-r3, pc}
228.endm
229
230ENTRY(mcount)
231#ifdef CONFIG_DYNAMIC_FTRACE
232	stmdb	sp!, {lr}
233	ldr	lr, [fp, #-4]
234	ldmia	sp!, {pc}
235#else
236	__mcount _old
237#endif
238ENDPROC(mcount)
239
240#ifdef CONFIG_DYNAMIC_FTRACE
241ENTRY(ftrace_caller_old)
242	__ftrace_caller _old
243ENDPROC(ftrace_caller_old)
244#endif
245
246#ifdef CONFIG_FUNCTION_GRAPH_TRACER
247ENTRY(ftrace_graph_caller_old)
248	__ftrace_graph_caller
249ENDPROC(ftrace_graph_caller_old)
250#endif
251
252.purgem mcount_enter
253.purgem mcount_get_lr
254.purgem mcount_exit
255#endif
256
257/*
258 * __gnu_mcount_nc
259 */
260
261.macro mcount_enter
262/*
263 * This pad compensates for the push {lr} at the call site.  Note that we are
264 * unable to unwind through a function which does not otherwise save its lr.
265 */
266 UNWIND(.pad	#4)
267	stmdb	sp!, {r0-r3, lr}
268 UNWIND(.save	{r0-r3, lr})
269.endm
270
271.macro mcount_get_lr reg
272	ldr	\reg, [sp, #20]
273.endm
274
275.macro mcount_exit
276	ldmia	sp!, {r0-r3, ip, lr}
277	ret	ip
278.endm
279
280ENTRY(__gnu_mcount_nc)
281UNWIND(.fnstart)
282#ifdef CONFIG_DYNAMIC_FTRACE
283	mov	ip, lr
284	ldmia	sp!, {lr}
285	ret	ip
286#else
287	__mcount
288#endif
289UNWIND(.fnend)
290ENDPROC(__gnu_mcount_nc)
291
292#ifdef CONFIG_DYNAMIC_FTRACE
293ENTRY(ftrace_caller)
294UNWIND(.fnstart)
295	__ftrace_caller
296UNWIND(.fnend)
297ENDPROC(ftrace_caller)
298
299#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
300ENTRY(ftrace_regs_caller)
301UNWIND(.fnstart)
302	__ftrace_regs_caller
303UNWIND(.fnend)
304ENDPROC(ftrace_regs_caller)
305#endif
306
307#endif
308
309#ifdef CONFIG_FUNCTION_GRAPH_TRACER
310ENTRY(ftrace_graph_caller)
311UNWIND(.fnstart)
312	__ftrace_graph_caller
313UNWIND(.fnend)
314ENDPROC(ftrace_graph_caller)
315
316#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
317ENTRY(ftrace_graph_regs_caller)
318UNWIND(.fnstart)
319	__ftrace_graph_regs_caller
320UNWIND(.fnend)
321ENDPROC(ftrace_graph_regs_caller)
322#endif
323#endif
324
325.purgem mcount_enter
326.purgem mcount_get_lr
327.purgem mcount_exit
328
329#ifdef CONFIG_FUNCTION_GRAPH_TRACER
330	.globl return_to_handler
331return_to_handler:
332	stmdb	sp!, {r0-r3}
333	mov	r0, fp			@ frame pointer
334	bl	ftrace_return_to_handler
335	mov	lr, r0			@ r0 has real ret addr
336	ldmia	sp!, {r0-r3}
337	ret	lr
338#endif
339
340ENTRY(ftrace_stub)
341.Lftrace_stub:
342	ret	lr
343ENDPROC(ftrace_stub)
344