1/* 2 * Low-level exception handling code 3 * 4 * Copyright (C) 2012 ARM Ltd. 5 * Authors: Catalin Marinas <catalin.marinas@arm.com> 6 * Will Deacon <will.deacon@arm.com> 7 * 8 * This program is free software; you can redistribute it and/or modify 9 * it under the terms of the GNU General Public License version 2 as 10 * published by the Free Software Foundation. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 * 17 * You should have received a copy of the GNU General Public License 18 * along with this program. If not, see <http://www.gnu.org/licenses/>. 19 */ 20 21#include <linux/init.h> 22#include <linux/linkage.h> 23 24#include <asm/assembler.h> 25#include <asm/asm-offsets.h> 26#include <asm/errno.h> 27#include <asm/esr.h> 28#include <asm/thread_info.h> 29#include <asm/unistd.h> 30 31/* 32 * Context tracking subsystem. Used to instrument transitions 33 * between user and kernel mode. 34 */ 35 .macro ct_user_exit, syscall = 0 36#ifdef CONFIG_CONTEXT_TRACKING 37 bl context_tracking_user_exit 38 .if \syscall == 1 39 /* 40 * Save/restore needed during syscalls. Restore syscall arguments from 41 * the values already saved on stack during kernel_entry. 42 */ 43 ldp x0, x1, [sp] 44 ldp x2, x3, [sp, #S_X2] 45 ldp x4, x5, [sp, #S_X4] 46 ldp x6, x7, [sp, #S_X6] 47 .endif 48#endif 49 .endm 50 51 .macro ct_user_enter 52#ifdef CONFIG_CONTEXT_TRACKING 53 bl context_tracking_user_enter 54#endif 55 .endm 56 57/* 58 * Bad Abort numbers 59 *----------------- 60 */ 61#define BAD_SYNC 0 62#define BAD_IRQ 1 63#define BAD_FIQ 2 64#define BAD_ERROR 3 65 66 .macro kernel_entry, el, regsize = 64 67 sub sp, sp, #S_FRAME_SIZE 68 .if \regsize == 32 69 mov w0, w0 // zero upper 32 bits of x0 70 .endif 71 stp x0, x1, [sp, #16 * 0] 72 stp x2, x3, [sp, #16 * 1] 73 stp x4, x5, [sp, #16 * 2] 74 stp x6, x7, [sp, #16 * 3] 75 stp x8, x9, [sp, #16 * 4] 76 stp x10, x11, [sp, #16 * 5] 77 stp x12, x13, [sp, #16 * 6] 78 stp x14, x15, [sp, #16 * 7] 79 stp x16, x17, [sp, #16 * 8] 80 stp x18, x19, [sp, #16 * 9] 81 stp x20, x21, [sp, #16 * 10] 82 stp x22, x23, [sp, #16 * 11] 83 stp x24, x25, [sp, #16 * 12] 84 stp x26, x27, [sp, #16 * 13] 85 stp x28, x29, [sp, #16 * 14] 86 87 .if \el == 0 88 mrs x21, sp_el0 89 get_thread_info tsk // Ensure MDSCR_EL1.SS is clear, 90 ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug 91 disable_step_tsk x19, x20 // exceptions when scheduling. 92 .else 93 add x21, sp, #S_FRAME_SIZE 94 .endif 95 mrs x22, elr_el1 96 mrs x23, spsr_el1 97 stp lr, x21, [sp, #S_LR] 98 stp x22, x23, [sp, #S_PC] 99 100 /* 101 * Set syscallno to -1 by default (overridden later if real syscall). 102 */ 103 .if \el == 0 104 mvn x21, xzr 105 str x21, [sp, #S_SYSCALLNO] 106 .endif 107 108 /* 109 * Registers that may be useful after this macro is invoked: 110 * 111 * x21 - aborted SP 112 * x22 - aborted PC 113 * x23 - aborted PSTATE 114 */ 115 .endm 116 117 .macro kernel_exit, el, ret = 0 118 ldp x21, x22, [sp, #S_PC] // load ELR, SPSR 119 .if \el == 0 120 ct_user_enter 121 ldr x23, [sp, #S_SP] // load return stack pointer 122 msr sp_el0, x23 123 .endif 124 msr elr_el1, x21 // set up the return data 125 msr spsr_el1, x22 126 .if \ret 127 ldr x1, [sp, #S_X1] // preserve x0 (syscall return) 128 .else 129 ldp x0, x1, [sp, #16 * 0] 130 .endif 131 ldp x2, x3, [sp, #16 * 1] 132 ldp x4, x5, [sp, #16 * 2] 133 ldp x6, x7, [sp, #16 * 3] 134 ldp x8, x9, [sp, #16 * 4] 135 ldp x10, x11, [sp, #16 * 5] 136 ldp x12, x13, [sp, #16 * 6] 137 ldp x14, x15, [sp, #16 * 7] 138 ldp x16, x17, [sp, #16 * 8] 139 ldp x18, x19, [sp, #16 * 9] 140 ldp x20, x21, [sp, #16 * 10] 141 ldp x22, x23, [sp, #16 * 11] 142 ldp x24, x25, [sp, #16 * 12] 143 ldp x26, x27, [sp, #16 * 13] 144 ldp x28, x29, [sp, #16 * 14] 145 ldr lr, [sp, #S_LR] 146 add sp, sp, #S_FRAME_SIZE // restore sp 147 eret // return to kernel 148 .endm 149 150 .macro get_thread_info, rd 151 mov \rd, sp 152 and \rd, \rd, #~(THREAD_SIZE - 1) // top of stack 153 .endm 154 155/* 156 * These are the registers used in the syscall handler, and allow us to 157 * have in theory up to 7 arguments to a function - x0 to x6. 158 * 159 * x7 is reserved for the system call number in 32-bit mode. 160 */ 161sc_nr .req x25 // number of system calls 162scno .req x26 // syscall number 163stbl .req x27 // syscall table pointer 164tsk .req x28 // current thread_info 165 166/* 167 * Interrupt handling. 168 */ 169 .macro irq_handler 170 adrp x1, handle_arch_irq 171 ldr x1, [x1, #:lo12:handle_arch_irq] 172 mov x0, sp 173 blr x1 174 .endm 175 176 .text 177 178/* 179 * Exception vectors. 180 */ 181 182 .align 11 183ENTRY(vectors) 184 ventry el1_sync_invalid // Synchronous EL1t 185 ventry el1_irq_invalid // IRQ EL1t 186 ventry el1_fiq_invalid // FIQ EL1t 187 ventry el1_error_invalid // Error EL1t 188 189 ventry el1_sync // Synchronous EL1h 190 ventry el1_irq // IRQ EL1h 191 ventry el1_fiq_invalid // FIQ EL1h 192 ventry el1_error_invalid // Error EL1h 193 194 ventry el0_sync // Synchronous 64-bit EL0 195 ventry el0_irq // IRQ 64-bit EL0 196 ventry el0_fiq_invalid // FIQ 64-bit EL0 197 ventry el0_error_invalid // Error 64-bit EL0 198 199#ifdef CONFIG_COMPAT 200 ventry el0_sync_compat // Synchronous 32-bit EL0 201 ventry el0_irq_compat // IRQ 32-bit EL0 202 ventry el0_fiq_invalid_compat // FIQ 32-bit EL0 203 ventry el0_error_invalid_compat // Error 32-bit EL0 204#else 205 ventry el0_sync_invalid // Synchronous 32-bit EL0 206 ventry el0_irq_invalid // IRQ 32-bit EL0 207 ventry el0_fiq_invalid // FIQ 32-bit EL0 208 ventry el0_error_invalid // Error 32-bit EL0 209#endif 210END(vectors) 211 212/* 213 * Invalid mode handlers 214 */ 215 .macro inv_entry, el, reason, regsize = 64 216 kernel_entry el, \regsize 217 mov x0, sp 218 mov x1, #\reason 219 mrs x2, esr_el1 220 b bad_mode 221 .endm 222 223el0_sync_invalid: 224 inv_entry 0, BAD_SYNC 225ENDPROC(el0_sync_invalid) 226 227el0_irq_invalid: 228 inv_entry 0, BAD_IRQ 229ENDPROC(el0_irq_invalid) 230 231el0_fiq_invalid: 232 inv_entry 0, BAD_FIQ 233ENDPROC(el0_fiq_invalid) 234 235el0_error_invalid: 236 inv_entry 0, BAD_ERROR 237ENDPROC(el0_error_invalid) 238 239#ifdef CONFIG_COMPAT 240el0_fiq_invalid_compat: 241 inv_entry 0, BAD_FIQ, 32 242ENDPROC(el0_fiq_invalid_compat) 243 244el0_error_invalid_compat: 245 inv_entry 0, BAD_ERROR, 32 246ENDPROC(el0_error_invalid_compat) 247#endif 248 249el1_sync_invalid: 250 inv_entry 1, BAD_SYNC 251ENDPROC(el1_sync_invalid) 252 253el1_irq_invalid: 254 inv_entry 1, BAD_IRQ 255ENDPROC(el1_irq_invalid) 256 257el1_fiq_invalid: 258 inv_entry 1, BAD_FIQ 259ENDPROC(el1_fiq_invalid) 260 261el1_error_invalid: 262 inv_entry 1, BAD_ERROR 263ENDPROC(el1_error_invalid) 264 265/* 266 * EL1 mode handlers. 267 */ 268 .align 6 269el1_sync: 270 kernel_entry 1 271 mrs x1, esr_el1 // read the syndrome register 272 lsr x24, x1, #ESR_ELx_EC_SHIFT // exception class 273 cmp x24, #ESR_ELx_EC_DABT_CUR // data abort in EL1 274 b.eq el1_da 275 cmp x24, #ESR_ELx_EC_SYS64 // configurable trap 276 b.eq el1_undef 277 cmp x24, #ESR_ELx_EC_SP_ALIGN // stack alignment exception 278 b.eq el1_sp_pc 279 cmp x24, #ESR_ELx_EC_PC_ALIGN // pc alignment exception 280 b.eq el1_sp_pc 281 cmp x24, #ESR_ELx_EC_UNKNOWN // unknown exception in EL1 282 b.eq el1_undef 283 cmp x24, #ESR_ELx_EC_BREAKPT_CUR // debug exception in EL1 284 b.ge el1_dbg 285 b el1_inv 286el1_da: 287 /* 288 * Data abort handling 289 */ 290 mrs x0, far_el1 291 enable_dbg 292 // re-enable interrupts if they were enabled in the aborted context 293 tbnz x23, #7, 1f // PSR_I_BIT 294 enable_irq 2951: 296 mov x2, sp // struct pt_regs 297 bl do_mem_abort 298 299 // disable interrupts before pulling preserved data off the stack 300 disable_irq 301 kernel_exit 1 302el1_sp_pc: 303 /* 304 * Stack or PC alignment exception handling 305 */ 306 mrs x0, far_el1 307 enable_dbg 308 mov x2, sp 309 b do_sp_pc_abort 310el1_undef: 311 /* 312 * Undefined instruction 313 */ 314 enable_dbg 315 mov x0, sp 316 b do_undefinstr 317el1_dbg: 318 /* 319 * Debug exception handling 320 */ 321 cmp x24, #ESR_ELx_EC_BRK64 // if BRK64 322 cinc x24, x24, eq // set bit '0' 323 tbz x24, #0, el1_inv // EL1 only 324 mrs x0, far_el1 325 mov x2, sp // struct pt_regs 326 bl do_debug_exception 327 kernel_exit 1 328el1_inv: 329 // TODO: add support for undefined instructions in kernel mode 330 enable_dbg 331 mov x0, sp 332 mov x1, #BAD_SYNC 333 mrs x2, esr_el1 334 b bad_mode 335ENDPROC(el1_sync) 336 337 .align 6 338el1_irq: 339 kernel_entry 1 340 enable_dbg 341#ifdef CONFIG_TRACE_IRQFLAGS 342 bl trace_hardirqs_off 343#endif 344 345 irq_handler 346 347#ifdef CONFIG_PREEMPT 348 get_thread_info tsk 349 ldr w24, [tsk, #TI_PREEMPT] // get preempt count 350 cbnz w24, 1f // preempt count != 0 351 ldr x0, [tsk, #TI_FLAGS] // get flags 352 tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling? 353 bl el1_preempt 3541: 355#endif 356#ifdef CONFIG_TRACE_IRQFLAGS 357 bl trace_hardirqs_on 358#endif 359 kernel_exit 1 360ENDPROC(el1_irq) 361 362#ifdef CONFIG_PREEMPT 363el1_preempt: 364 mov x24, lr 3651: bl preempt_schedule_irq // irq en/disable is done inside 366 ldr x0, [tsk, #TI_FLAGS] // get new tasks TI_FLAGS 367 tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling? 368 ret x24 369#endif 370 371/* 372 * EL0 mode handlers. 373 */ 374 .align 6 375el0_sync: 376 kernel_entry 0 377 mrs x25, esr_el1 // read the syndrome register 378 lsr x24, x25, #ESR_ELx_EC_SHIFT // exception class 379 cmp x24, #ESR_ELx_EC_SVC64 // SVC in 64-bit state 380 b.eq el0_svc 381 cmp x24, #ESR_ELx_EC_DABT_LOW // data abort in EL0 382 b.eq el0_da 383 cmp x24, #ESR_ELx_EC_IABT_LOW // instruction abort in EL0 384 b.eq el0_ia 385 cmp x24, #ESR_ELx_EC_FP_ASIMD // FP/ASIMD access 386 b.eq el0_fpsimd_acc 387 cmp x24, #ESR_ELx_EC_FP_EXC64 // FP/ASIMD exception 388 b.eq el0_fpsimd_exc 389 cmp x24, #ESR_ELx_EC_SYS64 // configurable trap 390 b.eq el0_undef 391 cmp x24, #ESR_ELx_EC_SP_ALIGN // stack alignment exception 392 b.eq el0_sp_pc 393 cmp x24, #ESR_ELx_EC_PC_ALIGN // pc alignment exception 394 b.eq el0_sp_pc 395 cmp x24, #ESR_ELx_EC_UNKNOWN // unknown exception in EL0 396 b.eq el0_undef 397 cmp x24, #ESR_ELx_EC_BREAKPT_LOW // debug exception in EL0 398 b.ge el0_dbg 399 b el0_inv 400 401#ifdef CONFIG_COMPAT 402 .align 6 403el0_sync_compat: 404 kernel_entry 0, 32 405 mrs x25, esr_el1 // read the syndrome register 406 lsr x24, x25, #ESR_ELx_EC_SHIFT // exception class 407 cmp x24, #ESR_ELx_EC_SVC32 // SVC in 32-bit state 408 b.eq el0_svc_compat 409 cmp x24, #ESR_ELx_EC_DABT_LOW // data abort in EL0 410 b.eq el0_da 411 cmp x24, #ESR_ELx_EC_IABT_LOW // instruction abort in EL0 412 b.eq el0_ia 413 cmp x24, #ESR_ELx_EC_FP_ASIMD // FP/ASIMD access 414 b.eq el0_fpsimd_acc 415 cmp x24, #ESR_ELx_EC_FP_EXC32 // FP/ASIMD exception 416 b.eq el0_fpsimd_exc 417 cmp x24, #ESR_ELx_EC_UNKNOWN // unknown exception in EL0 418 b.eq el0_undef 419 cmp x24, #ESR_ELx_EC_CP15_32 // CP15 MRC/MCR trap 420 b.eq el0_undef 421 cmp x24, #ESR_ELx_EC_CP15_64 // CP15 MRRC/MCRR trap 422 b.eq el0_undef 423 cmp x24, #ESR_ELx_EC_CP14_MR // CP14 MRC/MCR trap 424 b.eq el0_undef 425 cmp x24, #ESR_ELx_EC_CP14_LS // CP14 LDC/STC trap 426 b.eq el0_undef 427 cmp x24, #ESR_ELx_EC_CP14_64 // CP14 MRRC/MCRR trap 428 b.eq el0_undef 429 cmp x24, #ESR_ELx_EC_BREAKPT_LOW // debug exception in EL0 430 b.ge el0_dbg 431 b el0_inv 432el0_svc_compat: 433 /* 434 * AArch32 syscall handling 435 */ 436 adrp stbl, compat_sys_call_table // load compat syscall table pointer 437 uxtw scno, w7 // syscall number in w7 (r7) 438 mov sc_nr, #__NR_compat_syscalls 439 b el0_svc_naked 440 441 .align 6 442el0_irq_compat: 443 kernel_entry 0, 32 444 b el0_irq_naked 445#endif 446 447el0_da: 448 /* 449 * Data abort handling 450 */ 451 mrs x26, far_el1 452 // enable interrupts before calling the main handler 453 enable_dbg_and_irq 454 ct_user_exit 455 bic x0, x26, #(0xff << 56) 456 mov x1, x25 457 mov x2, sp 458 bl do_mem_abort 459 b ret_to_user 460el0_ia: 461 /* 462 * Instruction abort handling 463 */ 464 mrs x26, far_el1 465 // enable interrupts before calling the main handler 466 enable_dbg_and_irq 467 ct_user_exit 468 mov x0, x26 469 orr x1, x25, #1 << 24 // use reserved ISS bit for instruction aborts 470 mov x2, sp 471 bl do_mem_abort 472 b ret_to_user 473el0_fpsimd_acc: 474 /* 475 * Floating Point or Advanced SIMD access 476 */ 477 enable_dbg 478 ct_user_exit 479 mov x0, x25 480 mov x1, sp 481 bl do_fpsimd_acc 482 b ret_to_user 483el0_fpsimd_exc: 484 /* 485 * Floating Point or Advanced SIMD exception 486 */ 487 enable_dbg 488 ct_user_exit 489 mov x0, x25 490 mov x1, sp 491 bl do_fpsimd_exc 492 b ret_to_user 493el0_sp_pc: 494 /* 495 * Stack or PC alignment exception handling 496 */ 497 mrs x26, far_el1 498 // enable interrupts before calling the main handler 499 enable_dbg_and_irq 500 mov x0, x26 501 mov x1, x25 502 mov x2, sp 503 bl do_sp_pc_abort 504 b ret_to_user 505el0_undef: 506 /* 507 * Undefined instruction 508 */ 509 // enable interrupts before calling the main handler 510 enable_dbg_and_irq 511 ct_user_exit 512 mov x0, sp 513 bl do_undefinstr 514 b ret_to_user 515el0_dbg: 516 /* 517 * Debug exception handling 518 */ 519 tbnz x24, #0, el0_inv // EL0 only 520 mrs x0, far_el1 521 mov x1, x25 522 mov x2, sp 523 bl do_debug_exception 524 enable_dbg 525 ct_user_exit 526 b ret_to_user 527el0_inv: 528 enable_dbg 529 ct_user_exit 530 mov x0, sp 531 mov x1, #BAD_SYNC 532 mrs x2, esr_el1 533 bl bad_mode 534 b ret_to_user 535ENDPROC(el0_sync) 536 537 .align 6 538el0_irq: 539 kernel_entry 0 540el0_irq_naked: 541 enable_dbg 542#ifdef CONFIG_TRACE_IRQFLAGS 543 bl trace_hardirqs_off 544#endif 545 546 ct_user_exit 547 irq_handler 548 549#ifdef CONFIG_TRACE_IRQFLAGS 550 bl trace_hardirqs_on 551#endif 552 b ret_to_user 553ENDPROC(el0_irq) 554 555/* 556 * Register switch for AArch64. The callee-saved registers need to be saved 557 * and restored. On entry: 558 * x0 = previous task_struct (must be preserved across the switch) 559 * x1 = next task_struct 560 * Previous and next are guaranteed not to be the same. 561 * 562 */ 563ENTRY(cpu_switch_to) 564 add x8, x0, #THREAD_CPU_CONTEXT 565 mov x9, sp 566 stp x19, x20, [x8], #16 // store callee-saved registers 567 stp x21, x22, [x8], #16 568 stp x23, x24, [x8], #16 569 stp x25, x26, [x8], #16 570 stp x27, x28, [x8], #16 571 stp x29, x9, [x8], #16 572 str lr, [x8] 573 add x8, x1, #THREAD_CPU_CONTEXT 574 ldp x19, x20, [x8], #16 // restore callee-saved registers 575 ldp x21, x22, [x8], #16 576 ldp x23, x24, [x8], #16 577 ldp x25, x26, [x8], #16 578 ldp x27, x28, [x8], #16 579 ldp x29, x9, [x8], #16 580 ldr lr, [x8] 581 mov sp, x9 582 ret 583ENDPROC(cpu_switch_to) 584 585/* 586 * This is the fast syscall return path. We do as little as possible here, 587 * and this includes saving x0 back into the kernel stack. 588 */ 589ret_fast_syscall: 590 disable_irq // disable interrupts 591 ldr x1, [tsk, #TI_FLAGS] 592 and x2, x1, #_TIF_WORK_MASK 593 cbnz x2, fast_work_pending 594 enable_step_tsk x1, x2 595 kernel_exit 0, ret = 1 596 597/* 598 * Ok, we need to do extra processing, enter the slow path. 599 */ 600fast_work_pending: 601 str x0, [sp, #S_X0] // returned x0 602work_pending: 603 tbnz x1, #TIF_NEED_RESCHED, work_resched 604 /* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */ 605 ldr x2, [sp, #S_PSTATE] 606 mov x0, sp // 'regs' 607 tst x2, #PSR_MODE_MASK // user mode regs? 608 b.ne no_work_pending // returning to kernel 609 enable_irq // enable interrupts for do_notify_resume() 610 bl do_notify_resume 611 b ret_to_user 612work_resched: 613 bl schedule 614 615/* 616 * "slow" syscall return path. 617 */ 618ret_to_user: 619 disable_irq // disable interrupts 620 ldr x1, [tsk, #TI_FLAGS] 621 and x2, x1, #_TIF_WORK_MASK 622 cbnz x2, work_pending 623 enable_step_tsk x1, x2 624no_work_pending: 625 kernel_exit 0, ret = 0 626ENDPROC(ret_to_user) 627 628/* 629 * This is how we return from a fork. 630 */ 631ENTRY(ret_from_fork) 632 bl schedule_tail 633 cbz x19, 1f // not a kernel thread 634 mov x0, x20 635 blr x19 6361: get_thread_info tsk 637 b ret_to_user 638ENDPROC(ret_from_fork) 639 640/* 641 * SVC handler. 642 */ 643 .align 6 644el0_svc: 645 adrp stbl, sys_call_table // load syscall table pointer 646 uxtw scno, w8 // syscall number in w8 647 mov sc_nr, #__NR_syscalls 648el0_svc_naked: // compat entry point 649 stp x0, scno, [sp, #S_ORIG_X0] // save the original x0 and syscall number 650 enable_dbg_and_irq 651 ct_user_exit 1 652 653 ldr x16, [tsk, #TI_FLAGS] // check for syscall hooks 654 tst x16, #_TIF_SYSCALL_WORK 655 b.ne __sys_trace 656 cmp scno, sc_nr // check upper syscall limit 657 b.hs ni_sys 658 ldr x16, [stbl, scno, lsl #3] // address in the syscall table 659 blr x16 // call sys_* routine 660 b ret_fast_syscall 661ni_sys: 662 mov x0, sp 663 bl do_ni_syscall 664 b ret_fast_syscall 665ENDPROC(el0_svc) 666 667 /* 668 * This is the really slow path. We're going to be doing context 669 * switches, and waiting for our parent to respond. 670 */ 671__sys_trace: 672 mov w0, #-1 // set default errno for 673 cmp scno, x0 // user-issued syscall(-1) 674 b.ne 1f 675 mov x0, #-ENOSYS 676 str x0, [sp, #S_X0] 6771: mov x0, sp 678 bl syscall_trace_enter 679 cmp w0, #-1 // skip the syscall? 680 b.eq __sys_trace_return_skipped 681 uxtw scno, w0 // syscall number (possibly new) 682 mov x1, sp // pointer to regs 683 cmp scno, sc_nr // check upper syscall limit 684 b.hs __ni_sys_trace 685 ldp x0, x1, [sp] // restore the syscall args 686 ldp x2, x3, [sp, #S_X2] 687 ldp x4, x5, [sp, #S_X4] 688 ldp x6, x7, [sp, #S_X6] 689 ldr x16, [stbl, scno, lsl #3] // address in the syscall table 690 blr x16 // call sys_* routine 691 692__sys_trace_return: 693 str x0, [sp, #S_X0] // save returned x0 694__sys_trace_return_skipped: 695 mov x0, sp 696 bl syscall_trace_exit 697 b ret_to_user 698 699__ni_sys_trace: 700 mov x0, sp 701 bl do_ni_syscall 702 b __sys_trace_return 703 704/* 705 * Special system call wrappers. 706 */ 707ENTRY(sys_rt_sigreturn_wrapper) 708 mov x0, sp 709 b sys_rt_sigreturn 710ENDPROC(sys_rt_sigreturn_wrapper) 711