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