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 bti c 81 ftrace_regs_entry 1 82 b ftrace_common 83SYM_CODE_END(ftrace_regs_caller) 84 85SYM_CODE_START(ftrace_caller) 86 bti c 87 ftrace_regs_entry 0 88 b ftrace_common 89SYM_CODE_END(ftrace_caller) 90 91SYM_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 95 mov x3, sp // regs 96 97SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) 98 bl ftrace_stub 99 100#ifdef CONFIG_FUNCTION_GRAPH_TRACER 101SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); 102 nop // If enabled, this will be replaced 103 // "b ftrace_graph_caller" 104#endif 105 106/* 107 * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved 108 * x19-x29 per the AAPCS, and we created frame records upon entry, so we need 109 * to restore x0-x8, x29, and x30. 110 */ 111ftrace_common_return: 112 /* Restore function arguments */ 113 ldp x0, x1, [sp] 114 ldp x2, x3, [sp, #S_X2] 115 ldp x4, x5, [sp, #S_X4] 116 ldp x6, x7, [sp, #S_X6] 117 ldr x8, [sp, #S_X8] 118 119 /* Restore the callsite's FP, LR, PC */ 120 ldr x29, [sp, #S_FP] 121 ldr x30, [sp, #S_LR] 122 ldr x9, [sp, #S_PC] 123 124 /* Restore the callsite's SP */ 125 add sp, sp, #PT_REGS_SIZE + 16 126 127 ret x9 128SYM_CODE_END(ftrace_common) 129 130#ifdef CONFIG_FUNCTION_GRAPH_TRACER 131SYM_CODE_START(ftrace_graph_caller) 132 ldr x0, [sp, #S_PC] 133 sub x0, x0, #AARCH64_INSN_SIZE // ip (callsite's BL insn) 134 add x1, sp, #S_LR // parent_ip (callsite's LR) 135 ldr x2, [sp, #PT_REGS_SIZE] // parent fp (callsite's FP) 136 bl prepare_ftrace_return 137 b ftrace_common_return 138SYM_CODE_END(ftrace_graph_caller) 139#endif 140 141#else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */ 142 143/* 144 * Gcc with -pg will put the following code in the beginning of each function: 145 * mov x0, x30 146 * bl _mcount 147 * [function's body ...] 148 * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic 149 * ftrace is enabled. 150 * 151 * Please note that x0 as an argument will not be used here because we can 152 * get lr(x30) of instrumented function at any time by winding up call stack 153 * as long as the kernel is compiled without -fomit-frame-pointer. 154 * (or CONFIG_FRAME_POINTER, this is forced on arm64) 155 * 156 * stack layout after mcount_enter in _mcount(): 157 * 158 * current sp/fp => 0:+-----+ 159 * in _mcount() | x29 | -> instrumented function's fp 160 * +-----+ 161 * | x30 | -> _mcount()'s lr (= instrumented function's pc) 162 * old sp => +16:+-----+ 163 * when instrumented | | 164 * function calls | ... | 165 * _mcount() | | 166 * | | 167 * instrumented => +xx:+-----+ 168 * function's fp | x29 | -> parent's fp 169 * +-----+ 170 * | x30 | -> instrumented function's lr (= parent's pc) 171 * +-----+ 172 * | ... | 173 */ 174 175 .macro mcount_enter 176 stp x29, x30, [sp, #-16]! 177 mov x29, sp 178 .endm 179 180 .macro mcount_exit 181 ldp x29, x30, [sp], #16 182 ret 183 .endm 184 185 .macro mcount_adjust_addr rd, rn 186 sub \rd, \rn, #AARCH64_INSN_SIZE 187 .endm 188 189 /* for instrumented function's parent */ 190 .macro mcount_get_parent_fp reg 191 ldr \reg, [x29] 192 ldr \reg, [\reg] 193 .endm 194 195 /* for instrumented function */ 196 .macro mcount_get_pc0 reg 197 mcount_adjust_addr \reg, x30 198 .endm 199 200 .macro mcount_get_pc reg 201 ldr \reg, [x29, #8] 202 mcount_adjust_addr \reg, \reg 203 .endm 204 205 .macro mcount_get_lr reg 206 ldr \reg, [x29] 207 ldr \reg, [\reg, #8] 208 .endm 209 210 .macro mcount_get_lr_addr reg 211 ldr \reg, [x29] 212 add \reg, \reg, #8 213 .endm 214 215#ifndef CONFIG_DYNAMIC_FTRACE 216/* 217 * void _mcount(unsigned long return_address) 218 * @return_address: return address to instrumented function 219 * 220 * This function makes calls, if enabled, to: 221 * - tracer function to probe instrumented function's entry, 222 * - ftrace_graph_caller to set up an exit hook 223 */ 224SYM_FUNC_START(_mcount) 225 mcount_enter 226 227 ldr_l x2, ftrace_trace_function 228 adr x0, ftrace_stub 229 cmp x0, x2 // if (ftrace_trace_function 230 b.eq skip_ftrace_call // != ftrace_stub) { 231 232 mcount_get_pc x0 // function's pc 233 mcount_get_lr x1 // function's lr (= parent's pc) 234 blr x2 // (*ftrace_trace_function)(pc, lr); 235 236skip_ftrace_call: // } 237#ifdef CONFIG_FUNCTION_GRAPH_TRACER 238 ldr_l x2, ftrace_graph_return 239 cmp x0, x2 // if ((ftrace_graph_return 240 b.ne ftrace_graph_caller // != ftrace_stub) 241 242 ldr_l x2, ftrace_graph_entry // || (ftrace_graph_entry 243 adr_l x0, ftrace_graph_entry_stub // != ftrace_graph_entry_stub)) 244 cmp x0, x2 245 b.ne ftrace_graph_caller // ftrace_graph_caller(); 246#endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 247 mcount_exit 248SYM_FUNC_END(_mcount) 249EXPORT_SYMBOL(_mcount) 250NOKPROBE(_mcount) 251 252#else /* CONFIG_DYNAMIC_FTRACE */ 253/* 254 * _mcount() is used to build the kernel with -pg option, but all the branch 255 * instructions to _mcount() are replaced to NOP initially at kernel start up, 256 * and later on, NOP to branch to ftrace_caller() when enabled or branch to 257 * NOP when disabled per-function base. 258 */ 259SYM_FUNC_START(_mcount) 260 ret 261SYM_FUNC_END(_mcount) 262EXPORT_SYMBOL(_mcount) 263NOKPROBE(_mcount) 264 265/* 266 * void ftrace_caller(unsigned long return_address) 267 * @return_address: return address to instrumented function 268 * 269 * This function is a counterpart of _mcount() in 'static' ftrace, and 270 * makes calls to: 271 * - tracer function to probe instrumented function's entry, 272 * - ftrace_graph_caller to set up an exit hook 273 */ 274SYM_FUNC_START(ftrace_caller) 275 mcount_enter 276 277 mcount_get_pc0 x0 // function's pc 278 mcount_get_lr x1 // function's lr 279 280SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) // tracer(pc, lr); 281 nop // This will be replaced with "bl xxx" 282 // where xxx can be any kind of tracer. 283 284#ifdef CONFIG_FUNCTION_GRAPH_TRACER 285SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); 286 nop // If enabled, this will be replaced 287 // "b ftrace_graph_caller" 288#endif 289 290 mcount_exit 291SYM_FUNC_END(ftrace_caller) 292#endif /* CONFIG_DYNAMIC_FTRACE */ 293 294#ifdef CONFIG_FUNCTION_GRAPH_TRACER 295/* 296 * void ftrace_graph_caller(void) 297 * 298 * Called from _mcount() or ftrace_caller() when function_graph tracer is 299 * selected. 300 * This function w/ prepare_ftrace_return() fakes link register's value on 301 * the call stack in order to intercept instrumented function's return path 302 * and run return_to_handler() later on its exit. 303 */ 304SYM_FUNC_START(ftrace_graph_caller) 305 mcount_get_pc x0 // function's pc 306 mcount_get_lr_addr x1 // pointer to function's saved lr 307 mcount_get_parent_fp x2 // parent's fp 308 bl prepare_ftrace_return // prepare_ftrace_return(pc, &lr, fp) 309 310 mcount_exit 311SYM_FUNC_END(ftrace_graph_caller) 312#endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 313#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */ 314 315SYM_FUNC_START(ftrace_stub) 316 ret 317SYM_FUNC_END(ftrace_stub) 318 319#ifdef CONFIG_FUNCTION_GRAPH_TRACER 320/* 321 * void return_to_handler(void) 322 * 323 * Run ftrace_return_to_handler() before going back to parent. 324 * @fp is checked against the value passed by ftrace_graph_caller(). 325 */ 326SYM_CODE_START(return_to_handler) 327 /* save return value regs */ 328 sub sp, sp, #64 329 stp x0, x1, [sp] 330 stp x2, x3, [sp, #16] 331 stp x4, x5, [sp, #32] 332 stp x6, x7, [sp, #48] 333 334 mov x0, x29 // parent's fp 335 bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp); 336 mov x30, x0 // restore the original return address 337 338 /* restore return value regs */ 339 ldp x0, x1, [sp] 340 ldp x2, x3, [sp, #16] 341 ldp x4, x5, [sp, #32] 342 ldp x6, x7, [sp, #48] 343 add sp, sp, #64 344 345 ret 346SYM_CODE_END(return_to_handler) 347#endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 348