1/* 2 * arch/xtensa/kernel/vectors.S 3 * 4 * This file contains all exception vectors (user, kernel, and double), 5 * as well as the window vectors (overflow and underflow), and the debug 6 * vector. These are the primary vectors executed by the processor if an 7 * exception occurs. 8 * 9 * This file is subject to the terms and conditions of the GNU General 10 * Public License. See the file "COPYING" in the main directory of 11 * this archive for more details. 12 * 13 * Copyright (C) 2005 - 2008 Tensilica, Inc. 14 * 15 * Chris Zankel <chris@zankel.net> 16 * 17 */ 18 19/* 20 * We use a two-level table approach. The user and kernel exception vectors 21 * use a first-level dispatch table to dispatch the exception to a registered 22 * fast handler or the default handler, if no fast handler was registered. 23 * The default handler sets up a C-stack and dispatches the exception to a 24 * registerd C handler in the second-level dispatch table. 25 * 26 * Fast handler entry condition: 27 * 28 * a0: trashed, original value saved on stack (PT_AREG0) 29 * a1: a1 30 * a2: new stack pointer, original value in depc 31 * a3: dispatch table 32 * depc: a2, original value saved on stack (PT_DEPC) 33 * excsave_1: a3 34 * 35 * The value for PT_DEPC saved to stack also functions as a boolean to 36 * indicate that the exception is either a double or a regular exception: 37 * 38 * PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception 39 * < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception 40 * 41 * Note: Neither the kernel nor the user exception handler generate literals. 42 * 43 */ 44 45#include <linux/linkage.h> 46#include <asm/ptrace.h> 47#include <asm/current.h> 48#include <asm/asm-offsets.h> 49#include <asm/pgtable.h> 50#include <asm/processor.h> 51#include <asm/page.h> 52#include <asm/thread_info.h> 53#include <asm/vectors.h> 54 55#define WINDOW_VECTORS_SIZE 0x180 56 57 58/* 59 * User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0) 60 * 61 * We get here when an exception occurred while we were in userland. 62 * We switch to the kernel stack and jump to the first level handler 63 * associated to the exception cause. 64 * 65 * Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already 66 * decremented by PT_USER_SIZE. 67 */ 68 69 .section .UserExceptionVector.text, "ax" 70 71ENTRY(_UserExceptionVector) 72 73 xsr a3, excsave1 # save a3 and get dispatch table 74 wsr a2, depc # save a2 75 l32i a2, a3, EXC_TABLE_KSTK # load kernel stack to a2 76 s32i a0, a2, PT_AREG0 # save a0 to ESF 77 rsr a0, exccause # retrieve exception cause 78 s32i a0, a2, PT_DEPC # mark it as a regular exception 79 addx4 a0, a0, a3 # find entry in table 80 l32i a0, a0, EXC_TABLE_FAST_USER # load handler 81 xsr a3, excsave1 # restore a3 and dispatch table 82 jx a0 83 84ENDPROC(_UserExceptionVector) 85 86/* 87 * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0) 88 * 89 * We get this exception when we were already in kernel space. 90 * We decrement the current stack pointer (kernel) by PT_SIZE and 91 * jump to the first-level handler associated with the exception cause. 92 * 93 * Note: we need to preserve space for the spill region. 94 */ 95 96 .section .KernelExceptionVector.text, "ax" 97 98ENTRY(_KernelExceptionVector) 99 100 xsr a3, excsave1 # save a3, and get dispatch table 101 wsr a2, depc # save a2 102 addi a2, a1, -16-PT_SIZE # adjust stack pointer 103 s32i a0, a2, PT_AREG0 # save a0 to ESF 104 rsr a0, exccause # retrieve exception cause 105 s32i a0, a2, PT_DEPC # mark it as a regular exception 106 addx4 a0, a0, a3 # find entry in table 107 l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address 108 xsr a3, excsave1 # restore a3 and dispatch table 109 jx a0 110 111ENDPROC(_KernelExceptionVector) 112 113/* 114 * Double exception vector (Exceptions with PS.EXCM == 1) 115 * We get this exception when another exception occurs while were are 116 * already in an exception, such as window overflow/underflow exception, 117 * or 'expected' exceptions, for example memory exception when we were trying 118 * to read data from an invalid address in user space. 119 * 120 * Note that this vector is never invoked for level-1 interrupts, because such 121 * interrupts are disabled (masked) when PS.EXCM is set. 122 * 123 * We decode the exception and take the appropriate action. However, the 124 * double exception vector is much more careful, because a lot more error 125 * cases go through the double exception vector than through the user and 126 * kernel exception vectors. 127 * 128 * Occasionally, the kernel expects a double exception to occur. This usually 129 * happens when accessing user-space memory with the user's permissions 130 * (l32e/s32e instructions). The kernel state, though, is not always suitable 131 * for immediate transfer of control to handle_double, where "normal" exception 132 * processing occurs. Also in kernel mode, TLB misses can occur if accessing 133 * vmalloc memory, possibly requiring repair in a double exception handler. 134 * 135 * The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as 136 * a boolean variable and a pointer to a fixup routine. If the variable 137 * EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of 138 * zero indicates to use the default kernel/user exception handler. 139 * There is only one exception, when the value is identical to the exc_table 140 * label, the kernel is in trouble. This mechanism is used to protect critical 141 * sections, mainly when the handler writes to the stack to assert the stack 142 * pointer is valid. Once the fixup/default handler leaves that area, the 143 * EXC_TABLE_FIXUP variable is reset to the fixup handler or zero. 144 * 145 * Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the 146 * nonzero address of a fixup routine before it could cause a double exception 147 * and reset it before it returns. 148 * 149 * Some other things to take care of when a fast exception handler doesn't 150 * specify a particular fixup handler but wants to use the default handlers: 151 * 152 * - The original stack pointer (in a1) must not be modified. The fast 153 * exception handler should only use a2 as the stack pointer. 154 * 155 * - If the fast handler manipulates the stack pointer (in a2), it has to 156 * register a valid fixup handler and cannot use the default handlers. 157 * 158 * - The handler can use any other generic register from a3 to a15, but it 159 * must save the content of these registers to stack (PT_AREG3...PT_AREGx) 160 * 161 * - These registers must be saved before a double exception can occur. 162 * 163 * - If we ever implement handling signals while in double exceptions, the 164 * number of registers a fast handler has saved (excluding a0 and a1) must 165 * be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. ) 166 * 167 * The fixup handlers are special handlers: 168 * 169 * - Fixup entry conditions differ from regular exceptions: 170 * 171 * a0: DEPC 172 * a1: a1 173 * a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE 174 * a3: exctable 175 * depc: a0 176 * excsave_1: a3 177 * 178 * - When the kernel enters the fixup handler, it still assumes it is in a 179 * critical section, so EXC_TABLE_FIXUP variable is set to exc_table. 180 * The fixup handler, therefore, has to re-register itself as the fixup 181 * handler before it returns from the double exception. 182 * 183 * - Fixup handler can share the same exception frame with the fast handler. 184 * The kernel stack pointer is not changed when entering the fixup handler. 185 * 186 * - Fixup handlers can jump to the default kernel and user exception 187 * handlers. Before it jumps, though, it has to setup a exception frame 188 * on stack. Because the default handler resets the register fixup handler 189 * the fixup handler must make sure that the default handler returns to 190 * it instead of the exception address, so it can re-register itself as 191 * the fixup handler. 192 * 193 * In case of a critical condition where the kernel cannot recover, we jump 194 * to unrecoverable_exception with the following entry conditions. 195 * All registers a0...a15 are unchanged from the last exception, except: 196 * 197 * a0: last address before we jumped to the unrecoverable_exception. 198 * excsave_1: a0 199 * 200 * 201 * See the handle_alloca_user and spill_registers routines for example clients. 202 * 203 * FIXME: Note: we currently don't allow signal handling coming from a double 204 * exception, so the item markt with (*) is not required. 205 */ 206 207 .section .DoubleExceptionVector.text, "ax" 208 .begin literal_prefix .DoubleExceptionVector 209 .globl _DoubleExceptionVector_WindowUnderflow 210 .globl _DoubleExceptionVector_WindowOverflow 211 212ENTRY(_DoubleExceptionVector) 213 214 xsr a3, excsave1 215 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE 216 217 /* Check for kernel double exception (usually fatal). */ 218 219 rsr a2, ps 220 _bbci.l a2, PS_UM_BIT, .Lksp 221 222 /* Check if we are currently handling a window exception. */ 223 /* Note: We don't need to indicate that we enter a critical section. */ 224 225 xsr a0, depc # get DEPC, save a0 226 227 movi a2, WINDOW_VECTORS_VADDR 228 _bltu a0, a2, .Lfixup 229 addi a2, a2, WINDOW_VECTORS_SIZE 230 _bgeu a0, a2, .Lfixup 231 232 /* Window overflow/underflow exception. Get stack pointer. */ 233 234 l32i a2, a3, EXC_TABLE_KSTK 235 236 /* Check for overflow/underflow exception, jump if overflow. */ 237 238 _bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow 239 240 /* 241 * Restart window underflow exception. 242 * Currently: 243 * depc = orig a0, 244 * a0 = orig DEPC, 245 * a2 = new sp based on KSTK from exc_table 246 * a3 = excsave_1 247 * excsave_1 = orig a3 248 * 249 * We return to the instruction in user space that caused the window 250 * underflow exception. Therefore, we change window base to the value 251 * before we entered the window underflow exception and prepare the 252 * registers to return as if we were coming from a regular exception 253 * by changing depc (in a0). 254 * Note: We can trash the current window frame (a0...a3) and depc! 255 */ 256_DoubleExceptionVector_WindowUnderflow: 257 xsr a3, excsave1 258 wsr a2, depc # save stack pointer temporarily 259 rsr a0, ps 260 extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH 261 wsr a0, windowbase 262 rsync 263 264 /* We are now in the previous window frame. Save registers again. */ 265 266 xsr a2, depc # save a2 and get stack pointer 267 s32i a0, a2, PT_AREG0 268 xsr a3, excsave1 269 rsr a0, exccause 270 s32i a0, a2, PT_DEPC # mark it as a regular exception 271 addx4 a0, a0, a3 272 xsr a3, excsave1 273 l32i a0, a0, EXC_TABLE_FAST_USER 274 jx a0 275 276 /* 277 * We only allow the ITLB miss exception if we are in kernel space. 278 * All other exceptions are unexpected and thus unrecoverable! 279 */ 280 281#ifdef CONFIG_MMU 282 .extern fast_second_level_miss_double_kernel 283 284.Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */ 285 286 rsr a3, exccause 287 beqi a3, EXCCAUSE_ITLB_MISS, 1f 288 addi a3, a3, -EXCCAUSE_DTLB_MISS 289 bnez a3, .Lunrecoverable 2901: movi a3, fast_second_level_miss_double_kernel 291 jx a3 292#else 293.equ .Lksp, .Lunrecoverable 294#endif 295 296 /* Critical! We can't handle this situation. PANIC! */ 297 298 .extern unrecoverable_exception 299 300.Lunrecoverable_fixup: 301 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE 302 xsr a0, depc 303 304.Lunrecoverable: 305 rsr a3, excsave1 306 wsr a0, excsave1 307 movi a0, unrecoverable_exception 308 callx0 a0 309 310.Lfixup:/* Check for a fixup handler or if we were in a critical section. */ 311 312 /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave1: a3 */ 313 314 /* Enter critical section. */ 315 316 l32i a2, a3, EXC_TABLE_FIXUP 317 s32i a3, a3, EXC_TABLE_FIXUP 318 beq a2, a3, .Lunrecoverable_fixup # critical section 319 beqz a2, .Ldflt # no handler was registered 320 321 /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */ 322 323 jx a2 324 325.Ldflt: /* Get stack pointer. */ 326 327 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE 328 addi a2, a2, -PT_USER_SIZE 329 330 /* a0: depc, a1: a1, a2: kstk, a3: exctable, depc: a0, excsave: a3 */ 331 332 s32i a0, a2, PT_DEPC 333 l32i a0, a3, EXC_TABLE_DOUBLE_SAVE 334 xsr a0, depc 335 s32i a0, a2, PT_AREG0 336 337 /* a0: avail, a1: a1, a2: kstk, a3: exctable, depc: a2, excsave: a3 */ 338 339 rsr a0, exccause 340 addx4 a0, a0, a3 341 xsr a3, excsave1 342 l32i a0, a0, EXC_TABLE_FAST_USER 343 jx a0 344 345 /* 346 * Restart window OVERFLOW exception. 347 * Currently: 348 * depc = orig a0, 349 * a0 = orig DEPC, 350 * a2 = new sp based on KSTK from exc_table 351 * a3 = EXCSAVE_1 352 * excsave_1 = orig a3 353 * 354 * We return to the instruction in user space that caused the window 355 * overflow exception. Therefore, we change window base to the value 356 * before we entered the window overflow exception and prepare the 357 * registers to return as if we were coming from a regular exception 358 * by changing DEPC (in a0). 359 * 360 * NOTE: We CANNOT trash the current window frame (a0...a3), but we 361 * can clobber depc. 362 * 363 * The tricky part here is that overflow8 and overflow12 handlers 364 * save a0, then clobber a0. To restart the handler, we have to restore 365 * a0 if the double exception was past the point where a0 was clobbered. 366 * 367 * To keep things simple, we take advantage of the fact all overflow 368 * handlers save a0 in their very first instruction. If DEPC was past 369 * that instruction, we can safely restore a0 from where it was saved 370 * on the stack. 371 * 372 * a0: depc, a1: a1, a2: kstk, a3: exc_table, depc: a0, excsave1: a3 373 */ 374_DoubleExceptionVector_WindowOverflow: 375 extui a2, a0, 0, 6 # get offset into 64-byte vector handler 376 beqz a2, 1f # if at start of vector, don't restore 377 378 addi a0, a0, -128 379 bbsi a0, 8, 1f # don't restore except for overflow 8 and 12 380 bbsi a0, 7, 2f 381 382 /* 383 * Restore a0 as saved by _WindowOverflow8(). 384 * 385 * FIXME: we really need a fixup handler for this L32E, 386 * for the extremely unlikely case where the overflow handler's 387 * reference thru a0 gets a hardware TLB refill that bumps out 388 * the (distinct, aliasing) TLB entry that mapped its prior 389 * references thru a9, and where our reference now thru a9 390 * gets a 2nd-level miss exception (not hardware TLB refill). 391 */ 392 393 l32e a2, a9, -16 394 wsr a2, depc # replace the saved a0 395 j 1f 396 3972: 398 /* 399 * Restore a0 as saved by _WindowOverflow12(). 400 * 401 * FIXME: we really need a fixup handler for this L32E, 402 * for the extremely unlikely case where the overflow handler's 403 * reference thru a0 gets a hardware TLB refill that bumps out 404 * the (distinct, aliasing) TLB entry that mapped its prior 405 * references thru a13, and where our reference now thru a13 406 * gets a 2nd-level miss exception (not hardware TLB refill). 407 */ 408 409 l32e a2, a13, -16 410 wsr a2, depc # replace the saved a0 4111: 412 /* 413 * Restore WindowBase while leaving all address registers restored. 414 * We have to use ROTW for this, because WSR.WINDOWBASE requires 415 * an address register (which would prevent restore). 416 * 417 * Window Base goes from 0 ... 7 (Module 8) 418 * Window Start is 8 bits; Ex: (0b1010 1010):0x55 from series of call4s 419 */ 420 421 rsr a0, ps 422 extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH 423 rsr a2, windowbase 424 sub a0, a2, a0 425 extui a0, a0, 0, 3 426 427 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE 428 xsr a3, excsave1 429 beqi a0, 1, .L1pane 430 beqi a0, 3, .L3pane 431 432 rsr a0, depc 433 rotw -2 434 435 /* 436 * We are now in the user code's original window frame. 437 * Process the exception as a user exception as if it was 438 * taken by the user code. 439 * 440 * This is similar to the user exception vector, 441 * except that PT_DEPC isn't set to EXCCAUSE. 442 */ 4431: 444 xsr a3, excsave1 445 wsr a2, depc 446 l32i a2, a3, EXC_TABLE_KSTK 447 s32i a0, a2, PT_AREG0 448 rsr a0, exccause 449 450 s32i a0, a2, PT_DEPC 451 452 addx4 a0, a0, a3 453 l32i a0, a0, EXC_TABLE_FAST_USER 454 xsr a3, excsave1 455 jx a0 456 457.L1pane: 458 rsr a0, depc 459 rotw -1 460 j 1b 461 462.L3pane: 463 rsr a0, depc 464 rotw -3 465 j 1b 466 467 .end literal_prefix 468 469ENDPROC(_DoubleExceptionVector) 470 471/* 472 * Debug interrupt vector 473 * 474 * There is not much space here, so simply jump to another handler. 475 * EXCSAVE[DEBUGLEVEL] has been set to that handler. 476 */ 477 478 .section .DebugInterruptVector.text, "ax" 479 480ENTRY(_DebugInterruptVector) 481 482 xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL 483 jx a0 484 485ENDPROC(_DebugInterruptVector) 486 487 488 489/* 490 * Medium priority level interrupt vectors 491 * 492 * Each takes less than 16 (0x10) bytes, no literals, by placing 493 * the extra 8 bytes that would otherwise be required in the window 494 * vectors area where there is space. With relocatable vectors, 495 * all vectors are within ~ 4 kB range of each other, so we can 496 * simply jump (J) to another vector without having to use JX. 497 * 498 * common_exception code gets current IRQ level in PS.INTLEVEL 499 * and preserves it for the IRQ handling time. 500 */ 501 502 .macro irq_entry_level level 503 504 .if XCHAL_EXCM_LEVEL >= \level 505 .section .Level\level\()InterruptVector.text, "ax" 506ENTRY(_Level\level\()InterruptVector) 507 wsr a0, excsave2 508 rsr a0, epc\level 509 wsr a0, epc1 510 movi a0, EXCCAUSE_LEVEL1_INTERRUPT 511 wsr a0, exccause 512 rsr a0, eps\level 513 # branch to user or kernel vector 514 j _SimulateUserKernelVectorException 515 .endif 516 517 .endm 518 519 irq_entry_level 2 520 irq_entry_level 3 521 irq_entry_level 4 522 irq_entry_level 5 523 irq_entry_level 6 524 525 526/* Window overflow and underflow handlers. 527 * The handlers must be 64 bytes apart, first starting with the underflow 528 * handlers underflow-4 to underflow-12, then the overflow handlers 529 * overflow-4 to overflow-12. 530 * 531 * Note: We rerun the underflow handlers if we hit an exception, so 532 * we try to access any page that would cause a page fault early. 533 */ 534 535#define ENTRY_ALIGN64(name) \ 536 .globl name; \ 537 .align 64; \ 538 name: 539 540 .section .WindowVectors.text, "ax" 541 542 543/* 4-Register Window Overflow Vector (Handler) */ 544 545ENTRY_ALIGN64(_WindowOverflow4) 546 547 s32e a0, a5, -16 548 s32e a1, a5, -12 549 s32e a2, a5, -8 550 s32e a3, a5, -4 551 rfwo 552 553ENDPROC(_WindowOverflow4) 554 555 556#if XCHAL_EXCM_LEVEL >= 2 557 /* Not a window vector - but a convenient location 558 * (where we know there's space) for continuation of 559 * medium priority interrupt dispatch code. 560 * On entry here, a0 contains PS, and EPC2 contains saved a0: 561 */ 562 .align 4 563_SimulateUserKernelVectorException: 564 addi a0, a0, (1 << PS_EXCM_BIT) 565 wsr a0, ps 566 bbsi.l a0, PS_UM_BIT, 1f # branch if user mode 567 rsr a0, excsave2 # restore a0 568 j _KernelExceptionVector # simulate kernel vector exception 5691: rsr a0, excsave2 # restore a0 570 j _UserExceptionVector # simulate user vector exception 571#endif 572 573 574/* 4-Register Window Underflow Vector (Handler) */ 575 576ENTRY_ALIGN64(_WindowUnderflow4) 577 578 l32e a0, a5, -16 579 l32e a1, a5, -12 580 l32e a2, a5, -8 581 l32e a3, a5, -4 582 rfwu 583 584ENDPROC(_WindowUnderflow4) 585 586/* 8-Register Window Overflow Vector (Handler) */ 587 588ENTRY_ALIGN64(_WindowOverflow8) 589 590 s32e a0, a9, -16 591 l32e a0, a1, -12 592 s32e a2, a9, -8 593 s32e a1, a9, -12 594 s32e a3, a9, -4 595 s32e a4, a0, -32 596 s32e a5, a0, -28 597 s32e a6, a0, -24 598 s32e a7, a0, -20 599 rfwo 600 601ENDPROC(_WindowOverflow8) 602 603/* 8-Register Window Underflow Vector (Handler) */ 604 605ENTRY_ALIGN64(_WindowUnderflow8) 606 607 l32e a1, a9, -12 608 l32e a0, a9, -16 609 l32e a7, a1, -12 610 l32e a2, a9, -8 611 l32e a4, a7, -32 612 l32e a3, a9, -4 613 l32e a5, a7, -28 614 l32e a6, a7, -24 615 l32e a7, a7, -20 616 rfwu 617 618ENDPROC(_WindowUnderflow8) 619 620/* 12-Register Window Overflow Vector (Handler) */ 621 622ENTRY_ALIGN64(_WindowOverflow12) 623 624 s32e a0, a13, -16 625 l32e a0, a1, -12 626 s32e a1, a13, -12 627 s32e a2, a13, -8 628 s32e a3, a13, -4 629 s32e a4, a0, -48 630 s32e a5, a0, -44 631 s32e a6, a0, -40 632 s32e a7, a0, -36 633 s32e a8, a0, -32 634 s32e a9, a0, -28 635 s32e a10, a0, -24 636 s32e a11, a0, -20 637 rfwo 638 639ENDPROC(_WindowOverflow12) 640 641/* 12-Register Window Underflow Vector (Handler) */ 642 643ENTRY_ALIGN64(_WindowUnderflow12) 644 645 l32e a1, a13, -12 646 l32e a0, a13, -16 647 l32e a11, a1, -12 648 l32e a2, a13, -8 649 l32e a4, a11, -48 650 l32e a8, a11, -32 651 l32e a3, a13, -4 652 l32e a5, a11, -44 653 l32e a6, a11, -40 654 l32e a7, a11, -36 655 l32e a9, a11, -28 656 l32e a10, a11, -24 657 l32e a11, a11, -20 658 rfwu 659 660ENDPROC(_WindowUnderflow12) 661 662 .text 663