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