2 * arch/arm64/kernel/entry-ftrace.S
4 * Copyright (C) 2013 Linaro Limited
5 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
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.
12 #include <linux/linkage.h>
13 #include <asm/assembler.h>
14 #include <asm/ftrace.h>
18 * Gcc with -pg will put the following code in the beginning of each function:
21 * [function's body ...]
22 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
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)
30 * stack layout after mcount_enter in _mcount():
32 * current sp/fp => 0:+-----+
33 * in _mcount() | x29 | -> instrumented function's fp
35 * | x30 | -> _mcount()'s lr (= instrumented function's pc)
36 * old sp => +16:+-----+
37 * when instrumented | |
38 * function calls | ... |
41 * instrumented => +xx:+-----+
42 * function's fp | x29 | -> parent's fp
44 * | x30 | -> instrumented function's lr (= parent's pc)
50 stp x29, x30, [sp, #-16]!
55 ldp x29, x30, [sp], #16
59 .macro mcount_adjust_addr rd, rn
60 sub \rd, \rn, #AARCH64_INSN_SIZE
63 /* for instrumented function's parent */
64 .macro mcount_get_parent_fp reg
69 /* for instrumented function */
70 .macro mcount_get_pc0 reg
71 mcount_adjust_addr \reg, x30
74 .macro mcount_get_pc reg
76 mcount_adjust_addr \reg, \reg
79 .macro mcount_get_lr reg
84 .macro mcount_get_lr_addr reg
89 #ifndef CONFIG_DYNAMIC_FTRACE
91 * void _mcount(unsigned long return_address)
92 * @return_address: return address to instrumented function
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
101 ldr_l x2, ftrace_trace_function
103 cmp x0, x2 // if (ftrace_trace_function
104 b.eq skip_ftrace_call // != ftrace_stub) {
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);
110 #ifndef CONFIG_FUNCTION_GRAPH_TRACER
111 skip_ftrace_call: // return;
114 mcount_exit // return;
117 ldr_l x2, ftrace_graph_return
118 cmp x0, x2 // if ((ftrace_graph_return
119 b.ne ftrace_graph_caller // != ftrace_stub)
121 ldr_l x2, ftrace_graph_entry // || (ftrace_graph_entry
122 adr_l x0, ftrace_graph_entry_stub // != ftrace_graph_entry_stub))
124 b.ne ftrace_graph_caller // ftrace_graph_caller();
127 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
130 #else /* CONFIG_DYNAMIC_FTRACE */
132 * _mcount() is used to build the kernel with -pg option, but all the branch
133 * instructions to _mcount() are replaced to NOP initially at kernel start up,
134 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
135 * NOP when disabled per-function base.
142 * void ftrace_caller(unsigned long return_address)
143 * @return_address: return address to instrumented function
145 * This function is a counterpart of _mcount() in 'static' ftrace, and
147 * - tracer function to probe instrumented function's entry,
148 * - ftrace_graph_caller to set up an exit hook
153 mcount_get_pc0 x0 // function's pc
154 mcount_get_lr x1 // function's lr
157 ftrace_call: // tracer(pc, lr);
158 nop // This will be replaced with "bl xxx"
159 // where xxx can be any kind of tracer.
161 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
162 .global ftrace_graph_call
163 ftrace_graph_call: // ftrace_graph_caller();
164 nop // If enabled, this will be replaced
165 // "b ftrace_graph_caller"
169 ENDPROC(ftrace_caller)
170 #endif /* CONFIG_DYNAMIC_FTRACE */
176 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
177 /* save return value regs*/
178 .macro save_return_regs
181 stp x2, x3, [sp, #16]
182 stp x4, x5, [sp, #32]
183 stp x6, x7, [sp, #48]
186 /* restore return value regs*/
187 .macro restore_return_regs
189 ldp x2, x3, [sp, #16]
190 ldp x4, x5, [sp, #32]
191 ldp x6, x7, [sp, #48]
196 * void ftrace_graph_caller(void)
198 * Called from _mcount() or ftrace_caller() when function_graph tracer is
200 * This function w/ prepare_ftrace_return() fakes link register's value on
201 * the call stack in order to intercept instrumented function's return path
202 * and run return_to_handler() later on its exit.
204 ENTRY(ftrace_graph_caller)
205 mcount_get_lr_addr x0 // pointer to function's saved lr
206 mcount_get_pc x1 // function's pc
207 mcount_get_parent_fp x2 // parent's fp
208 bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)
211 ENDPROC(ftrace_graph_caller)
214 * void return_to_handler(void)
216 * Run ftrace_return_to_handler() before going back to parent.
217 * @fp is checked against the value passed by ftrace_graph_caller()
218 * only when HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
220 ENTRY(return_to_handler)
222 mov x0, x29 // parent's fp
223 bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
224 mov x30, x0 // restore the original return address
227 END(return_to_handler)
228 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */