1 /* SPDX-License-Identifier: GPL-2.0-only */
3 * arch/arm64/kernel/entry-ftrace.S
5 * Copyright (C) 2013 Linaro Limited
6 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
9 #include <linux/linkage.h>
10 #include <asm/asm-offsets.h>
11 #include <asm/assembler.h>
12 #include <asm/ftrace.h>
15 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
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:
24 * ... where <entry> is either ftrace_caller or ftrace_regs_caller.
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
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.
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)
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]
47 /* Optionally save the callee-saved registers, always save the FP */
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]
63 /* Save the callsite's SP and LR */
64 add x10, sp, #(PT_REGS_SIZE + 16)
65 stp x9, x10, [sp, #S_LR]
67 /* Save the PC after the ftrace callsite */
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
74 /* Create our frame record within pt_regs. */
75 stp x29, x30, [sp, #S_STACKFRAME]
76 add x29, sp, #S_STACKFRAME
79 SYM_CODE_START(ftrace_regs_caller)
83 SYM_CODE_END(ftrace_regs_caller)
85 SYM_CODE_START(ftrace_caller)
89 SYM_CODE_END(ftrace_caller)
91 SYM_CODE_START(ftrace_common)
92 sub x0, x30, #AARCH64_INSN_SIZE // ip (callsite's BL insn)
93 mov x1, x9 // parent_ip (callsite's LR)
94 ldr_l x2, function_trace_op // op
97 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
101 * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
102 * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
103 * to restore x0-x8, x29, and x30.
105 ftrace_common_return:
106 /* Restore function arguments */
108 ldp x2, x3, [sp, #S_X2]
109 ldp x4, x5, [sp, #S_X4]
110 ldp x6, x7, [sp, #S_X6]
113 /* Restore the callsite's FP, LR, PC */
118 /* Restore the callsite's SP */
119 add sp, sp, #PT_REGS_SIZE + 16
122 SYM_CODE_END(ftrace_common)
124 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
127 * Gcc with -pg will put the following code in the beginning of each function:
130 * [function's body ...]
131 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
134 * Please note that x0 as an argument will not be used here because we can
135 * get lr(x30) of instrumented function at any time by winding up call stack
136 * as long as the kernel is compiled without -fomit-frame-pointer.
137 * (or CONFIG_FRAME_POINTER, this is forced on arm64)
139 * stack layout after mcount_enter in _mcount():
141 * current sp/fp => 0:+-----+
142 * in _mcount() | x29 | -> instrumented function's fp
144 * | x30 | -> _mcount()'s lr (= instrumented function's pc)
145 * old sp => +16:+-----+
146 * when instrumented | |
147 * function calls | ... |
150 * instrumented => +xx:+-----+
151 * function's fp | x29 | -> parent's fp
153 * | x30 | -> instrumented function's lr (= parent's pc)
159 stp x29, x30, [sp, #-16]!
164 ldp x29, x30, [sp], #16
168 .macro mcount_adjust_addr rd, rn
169 sub \rd, \rn, #AARCH64_INSN_SIZE
172 /* for instrumented function's parent */
173 .macro mcount_get_parent_fp reg
178 /* for instrumented function */
179 .macro mcount_get_pc0 reg
180 mcount_adjust_addr \reg, x30
183 .macro mcount_get_pc reg
185 mcount_adjust_addr \reg, \reg
188 .macro mcount_get_lr reg
193 .macro mcount_get_lr_addr reg
198 #ifndef CONFIG_DYNAMIC_FTRACE
200 * void _mcount(unsigned long return_address)
201 * @return_address: return address to instrumented function
203 * This function makes calls, if enabled, to:
204 * - tracer function to probe instrumented function's entry,
205 * - ftrace_graph_caller to set up an exit hook
207 SYM_FUNC_START(_mcount)
210 ldr_l x2, ftrace_trace_function
212 cmp x0, x2 // if (ftrace_trace_function
213 b.eq skip_ftrace_call // != ftrace_stub) {
215 mcount_get_pc x0 // function's pc
216 mcount_get_lr x1 // function's lr (= parent's pc)
217 blr x2 // (*ftrace_trace_function)(pc, lr);
219 skip_ftrace_call: // }
220 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
221 ldr_l x2, ftrace_graph_return
222 cmp x0, x2 // if ((ftrace_graph_return
223 b.ne ftrace_graph_caller // != ftrace_stub)
225 ldr_l x2, ftrace_graph_entry // || (ftrace_graph_entry
226 adr_l x0, ftrace_graph_entry_stub // != ftrace_graph_entry_stub))
228 b.ne ftrace_graph_caller // ftrace_graph_caller();
229 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
231 SYM_FUNC_END(_mcount)
232 EXPORT_SYMBOL(_mcount)
235 #else /* CONFIG_DYNAMIC_FTRACE */
237 * _mcount() is used to build the kernel with -pg option, but all the branch
238 * instructions to _mcount() are replaced to NOP initially at kernel start up,
239 * and later on, NOP to branch to ftrace_caller() when enabled or branch to
240 * NOP when disabled per-function base.
242 SYM_FUNC_START(_mcount)
244 SYM_FUNC_END(_mcount)
245 EXPORT_SYMBOL(_mcount)
249 * void ftrace_caller(unsigned long return_address)
250 * @return_address: return address to instrumented function
252 * This function is a counterpart of _mcount() in 'static' ftrace, and
254 * - tracer function to probe instrumented function's entry,
255 * - ftrace_graph_caller to set up an exit hook
257 SYM_FUNC_START(ftrace_caller)
260 mcount_get_pc0 x0 // function's pc
261 mcount_get_lr x1 // function's lr
263 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) // tracer(pc, lr);
264 nop // This will be replaced with "bl xxx"
265 // where xxx can be any kind of tracer.
267 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
268 SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
269 nop // If enabled, this will be replaced
270 // "b ftrace_graph_caller"
274 SYM_FUNC_END(ftrace_caller)
275 #endif /* CONFIG_DYNAMIC_FTRACE */
277 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
279 * void ftrace_graph_caller(void)
281 * Called from _mcount() or ftrace_caller() when function_graph tracer is
283 * This function w/ prepare_ftrace_return() fakes link register's value on
284 * the call stack in order to intercept instrumented function's return path
285 * and run return_to_handler() later on its exit.
287 SYM_FUNC_START(ftrace_graph_caller)
288 mcount_get_pc x0 // function's pc
289 mcount_get_lr_addr x1 // pointer to function's saved lr
290 mcount_get_parent_fp x2 // parent's fp
291 bl prepare_ftrace_return // prepare_ftrace_return(pc, &lr, fp)
294 SYM_FUNC_END(ftrace_graph_caller)
295 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
296 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
298 SYM_FUNC_START(ftrace_stub)
300 SYM_FUNC_END(ftrace_stub)
302 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
304 * void return_to_handler(void)
306 * Run ftrace_return_to_handler() before going back to parent.
307 * @fp is checked against the value passed by ftrace_graph_caller().
309 SYM_CODE_START(return_to_handler)
310 /* save return value regs */
313 stp x2, x3, [sp, #16]
314 stp x4, x5, [sp, #32]
315 stp x6, x7, [sp, #48]
317 mov x0, x29 // parent's fp
318 bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
319 mov x30, x0 // restore the original return address
321 /* restore return value regs */
323 ldp x2, x3, [sp, #16]
324 ldp x4, x5, [sp, #32]
325 ldp x6, x7, [sp, #48]
329 SYM_CODE_END(return_to_handler)
330 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */