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 jx a0 82 83ENDPROC(_UserExceptionVector) 84 85/* 86 * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0) 87 * 88 * We get this exception when we were already in kernel space. 89 * We decrement the current stack pointer (kernel) by PT_SIZE and 90 * jump to the first-level handler associated with the exception cause. 91 * 92 * Note: we need to preserve space for the spill region. 93 */ 94 95 .section .KernelExceptionVector.text, "ax" 96 97ENTRY(_KernelExceptionVector) 98 99 xsr a3, excsave1 # save a3, and get dispatch table 100 wsr a2, depc # save a2 101 addi a2, a1, -16-PT_SIZE # adjust stack pointer 102 s32i a0, a2, PT_AREG0 # save a0 to ESF 103 rsr a0, exccause # retrieve exception cause 104 s32i a0, a2, PT_DEPC # mark it as a regular exception 105 addx4 a0, a0, a3 # find entry in table 106 l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address 107 jx a0 108 109ENDPROC(_KernelExceptionVector) 110 111/* 112 * Double exception vector (Exceptions with PS.EXCM == 1) 113 * We get this exception when another exception occurs while were are 114 * already in an exception, such as window overflow/underflow exception, 115 * or 'expected' exceptions, for example memory exception when we were trying 116 * to read data from an invalid address in user space. 117 * 118 * Note that this vector is never invoked for level-1 interrupts, because such 119 * interrupts are disabled (masked) when PS.EXCM is set. 120 * 121 * We decode the exception and take the appropriate action. However, the 122 * double exception vector is much more careful, because a lot more error 123 * cases go through the double exception vector than through the user and 124 * kernel exception vectors. 125 * 126 * Occasionally, the kernel expects a double exception to occur. This usually 127 * happens when accessing user-space memory with the user's permissions 128 * (l32e/s32e instructions). The kernel state, though, is not always suitable 129 * for immediate transfer of control to handle_double, where "normal" exception 130 * processing occurs. Also in kernel mode, TLB misses can occur if accessing 131 * vmalloc memory, possibly requiring repair in a double exception handler. 132 * 133 * The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as 134 * a boolean variable and a pointer to a fixup routine. If the variable 135 * EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of 136 * zero indicates to use the default kernel/user exception handler. 137 * There is only one exception, when the value is identical to the exc_table 138 * label, the kernel is in trouble. This mechanism is used to protect critical 139 * sections, mainly when the handler writes to the stack to assert the stack 140 * pointer is valid. Once the fixup/default handler leaves that area, the 141 * EXC_TABLE_FIXUP variable is reset to the fixup handler or zero. 142 * 143 * Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the 144 * nonzero address of a fixup routine before it could cause a double exception 145 * and reset it before it returns. 146 * 147 * Some other things to take care of when a fast exception handler doesn't 148 * specify a particular fixup handler but wants to use the default handlers: 149 * 150 * - The original stack pointer (in a1) must not be modified. The fast 151 * exception handler should only use a2 as the stack pointer. 152 * 153 * - If the fast handler manipulates the stack pointer (in a2), it has to 154 * register a valid fixup handler and cannot use the default handlers. 155 * 156 * - The handler can use any other generic register from a3 to a15, but it 157 * must save the content of these registers to stack (PT_AREG3...PT_AREGx) 158 * 159 * - These registers must be saved before a double exception can occur. 160 * 161 * - If we ever implement handling signals while in double exceptions, the 162 * number of registers a fast handler has saved (excluding a0 and a1) must 163 * be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. ) 164 * 165 * The fixup handlers are special handlers: 166 * 167 * - Fixup entry conditions differ from regular exceptions: 168 * 169 * a0: DEPC 170 * a1: a1 171 * a2: trashed, original value in EXC_TABLE_DOUBLE_A2 172 * a3: exctable 173 * depc: a0 174 * excsave_1: a3 175 * 176 * - When the kernel enters the fixup handler, it still assumes it is in a 177 * critical section, so EXC_TABLE_FIXUP variable is set to exc_table. 178 * The fixup handler, therefore, has to re-register itself as the fixup 179 * handler before it returns from the double exception. 180 * 181 * - Fixup handler can share the same exception frame with the fast handler. 182 * The kernel stack pointer is not changed when entering the fixup handler. 183 * 184 * - Fixup handlers can jump to the default kernel and user exception 185 * handlers. Before it jumps, though, it has to setup a exception frame 186 * on stack. Because the default handler resets the register fixup handler 187 * the fixup handler must make sure that the default handler returns to 188 * it instead of the exception address, so it can re-register itself as 189 * the fixup handler. 190 * 191 * In case of a critical condition where the kernel cannot recover, we jump 192 * to unrecoverable_exception with the following entry conditions. 193 * All registers a0...a15 are unchanged from the last exception, except: 194 * 195 * a0: last address before we jumped to the unrecoverable_exception. 196 * excsave_1: a0 197 * 198 * 199 * See the handle_alloca_user and spill_registers routines for example clients. 200 * 201 * FIXME: Note: we currently don't allow signal handling coming from a double 202 * exception, so the item markt with (*) is not required. 203 */ 204 205 .section .DoubleExceptionVector.text, "ax" 206 .begin literal_prefix .DoubleExceptionVector 207 208ENTRY(_DoubleExceptionVector) 209 210 /* Deliberately destroy excsave (don't assume it's value was valid). */ 211 212 wsr a3, excsave1 # save a3 213 214 /* Check for kernel double exception (usually fatal). */ 215 216 rsr a3, ps 217 _bbci.l a3, PS_UM_BIT, .Lksp 218 219 /* Check if we are currently handling a window exception. */ 220 /* Note: We don't need to indicate that we enter a critical section. */ 221 222 xsr a0, depc # get DEPC, save a0 223 224 movi a3, WINDOW_VECTORS_VADDR 225 _bltu a0, a3, .Lfixup 226 addi a3, a3, WINDOW_VECTORS_SIZE 227 _bgeu a0, a3, .Lfixup 228 229 /* Window overflow/underflow exception. Get stack pointer. */ 230 231 mov a3, a2 232 /* This explicit literal and the following references to it are made 233 * in order to fit DoubleExceptionVector.literals into the available 234 * 16-byte gap before DoubleExceptionVector.text in the absence of 235 * link time relaxation. See kernel/vmlinux.lds.S 236 */ 237 .literal .Lexc_table, exc_table 238 l32r a2, .Lexc_table 239 l32i a2, a2, EXC_TABLE_KSTK 240 241 /* Check for overflow/underflow exception, jump if overflow. */ 242 243 _bbci.l a0, 6, .Lovfl 244 245 /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ 246 247 /* Restart window underflow exception. 248 * We return to the instruction in user space that caused the window 249 * underflow exception. Therefore, we change window base to the value 250 * before we entered the window underflow exception and prepare the 251 * registers to return as if we were coming from a regular exception 252 * by changing depc (in a0). 253 * Note: We can trash the current window frame (a0...a3) and depc! 254 */ 255 256 wsr a2, depc # save stack pointer temporarily 257 rsr a0, ps 258 extui a0, a0, PS_OWB_SHIFT, 4 259 wsr a0, windowbase 260 rsync 261 262 /* We are now in the previous window frame. Save registers again. */ 263 264 xsr a2, depc # save a2 and get stack pointer 265 s32i a0, a2, PT_AREG0 266 267 wsr a3, excsave1 # save a3 268 l32r a3, .Lexc_table 269 270 rsr a0, exccause 271 s32i a0, a2, PT_DEPC # mark it as a regular exception 272 addx4 a0, a0, a3 273 l32i a0, a0, EXC_TABLE_FAST_USER 274 jx a0 275 276.Lfixup:/* Check for a fixup handler or if we were in a critical section. */ 277 278 /* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */ 279 280 l32r a3, .Lexc_table 281 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE # temporary variable 282 283 /* Enter critical section. */ 284 285 l32i a2, a3, EXC_TABLE_FIXUP 286 s32i a3, a3, EXC_TABLE_FIXUP 287 beq a2, a3, .Lunrecoverable_fixup # critical! 288 beqz a2, .Ldflt # no handler was registered 289 290 /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */ 291 292 jx a2 293 294.Ldflt: /* Get stack pointer. */ 295 296 l32i a3, a3, EXC_TABLE_DOUBLE_SAVE 297 addi a2, a3, -PT_USER_SIZE 298 299.Lovfl: /* Jump to default handlers. */ 300 301 /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ 302 303 xsr a3, depc 304 s32i a0, a2, PT_DEPC 305 s32i a3, a2, PT_AREG0 306 307 /* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */ 308 309 l32r a3, .Lexc_table 310 rsr a0, exccause 311 addx4 a0, a0, a3 312 l32i a0, a0, EXC_TABLE_FAST_USER 313 jx a0 314 315 /* 316 * We only allow the ITLB miss exception if we are in kernel space. 317 * All other exceptions are unexpected and thus unrecoverable! 318 */ 319 320#ifdef CONFIG_MMU 321 .extern fast_second_level_miss_double_kernel 322 323.Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */ 324 325 rsr a3, exccause 326 beqi a3, EXCCAUSE_ITLB_MISS, 1f 327 addi a3, a3, -EXCCAUSE_DTLB_MISS 328 bnez a3, .Lunrecoverable 3291: movi a3, fast_second_level_miss_double_kernel 330 jx a3 331#else 332.equ .Lksp, .Lunrecoverable 333#endif 334 335 /* Critical! We can't handle this situation. PANIC! */ 336 337 .extern unrecoverable_exception 338 339.Lunrecoverable_fixup: 340 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE 341 xsr a0, depc 342 343.Lunrecoverable: 344 rsr a3, excsave1 345 wsr a0, excsave1 346 movi a0, unrecoverable_exception 347 callx0 a0 348 349 .end literal_prefix 350 351ENDPROC(_DoubleExceptionVector) 352 353/* 354 * Debug interrupt vector 355 * 356 * There is not much space here, so simply jump to another handler. 357 * EXCSAVE[DEBUGLEVEL] has been set to that handler. 358 */ 359 360 .section .DebugInterruptVector.text, "ax" 361 362ENTRY(_DebugInterruptVector) 363 364 xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL 365 jx a0 366 367ENDPROC(_DebugInterruptVector) 368 369 370 371/* 372 * Medium priority level interrupt vectors 373 * 374 * Each takes less than 16 (0x10) bytes, no literals, by placing 375 * the extra 8 bytes that would otherwise be required in the window 376 * vectors area where there is space. With relocatable vectors, 377 * all vectors are within ~ 4 kB range of each other, so we can 378 * simply jump (J) to another vector without having to use JX. 379 * 380 * common_exception code gets current IRQ level in PS.INTLEVEL 381 * and preserves it for the IRQ handling time. 382 */ 383 384 .macro irq_entry_level level 385 386 .if XCHAL_EXCM_LEVEL >= \level 387 .section .Level\level\()InterruptVector.text, "ax" 388ENTRY(_Level\level\()InterruptVector) 389 wsr a0, excsave2 390 rsr a0, epc\level 391 wsr a0, epc1 392 movi a0, EXCCAUSE_LEVEL1_INTERRUPT 393 wsr a0, exccause 394 rsr a0, eps\level 395 # branch to user or kernel vector 396 j _SimulateUserKernelVectorException 397 .endif 398 399 .endm 400 401 irq_entry_level 2 402 irq_entry_level 3 403 irq_entry_level 4 404 irq_entry_level 5 405 irq_entry_level 6 406 407 408/* Window overflow and underflow handlers. 409 * The handlers must be 64 bytes apart, first starting with the underflow 410 * handlers underflow-4 to underflow-12, then the overflow handlers 411 * overflow-4 to overflow-12. 412 * 413 * Note: We rerun the underflow handlers if we hit an exception, so 414 * we try to access any page that would cause a page fault early. 415 */ 416 417#define ENTRY_ALIGN64(name) \ 418 .globl name; \ 419 .align 64; \ 420 name: 421 422 .section .WindowVectors.text, "ax" 423 424 425/* 4-Register Window Overflow Vector (Handler) */ 426 427ENTRY_ALIGN64(_WindowOverflow4) 428 429 s32e a0, a5, -16 430 s32e a1, a5, -12 431 s32e a2, a5, -8 432 s32e a3, a5, -4 433 rfwo 434 435ENDPROC(_WindowOverflow4) 436 437 438#if XCHAL_EXCM_LEVEL >= 2 439 /* Not a window vector - but a convenient location 440 * (where we know there's space) for continuation of 441 * medium priority interrupt dispatch code. 442 * On entry here, a0 contains PS, and EPC2 contains saved a0: 443 */ 444 .align 4 445_SimulateUserKernelVectorException: 446 addi a0, a0, (1 << PS_EXCM_BIT) 447 wsr a0, ps 448 bbsi.l a0, PS_UM_BIT, 1f # branch if user mode 449 rsr a0, excsave2 # restore a0 450 j _KernelExceptionVector # simulate kernel vector exception 4511: rsr a0, excsave2 # restore a0 452 j _UserExceptionVector # simulate user vector exception 453#endif 454 455 456/* 4-Register Window Underflow Vector (Handler) */ 457 458ENTRY_ALIGN64(_WindowUnderflow4) 459 460 l32e a0, a5, -16 461 l32e a1, a5, -12 462 l32e a2, a5, -8 463 l32e a3, a5, -4 464 rfwu 465 466ENDPROC(_WindowUnderflow4) 467 468/* 8-Register Window Overflow Vector (Handler) */ 469 470ENTRY_ALIGN64(_WindowOverflow8) 471 472 s32e a0, a9, -16 473 l32e a0, a1, -12 474 s32e a2, a9, -8 475 s32e a1, a9, -12 476 s32e a3, a9, -4 477 s32e a4, a0, -32 478 s32e a5, a0, -28 479 s32e a6, a0, -24 480 s32e a7, a0, -20 481 rfwo 482 483ENDPROC(_WindowOverflow8) 484 485/* 8-Register Window Underflow Vector (Handler) */ 486 487ENTRY_ALIGN64(_WindowUnderflow8) 488 489 l32e a1, a9, -12 490 l32e a0, a9, -16 491 l32e a7, a1, -12 492 l32e a2, a9, -8 493 l32e a4, a7, -32 494 l32e a3, a9, -4 495 l32e a5, a7, -28 496 l32e a6, a7, -24 497 l32e a7, a7, -20 498 rfwu 499 500ENDPROC(_WindowUnderflow8) 501 502/* 12-Register Window Overflow Vector (Handler) */ 503 504ENTRY_ALIGN64(_WindowOverflow12) 505 506 s32e a0, a13, -16 507 l32e a0, a1, -12 508 s32e a1, a13, -12 509 s32e a2, a13, -8 510 s32e a3, a13, -4 511 s32e a4, a0, -48 512 s32e a5, a0, -44 513 s32e a6, a0, -40 514 s32e a7, a0, -36 515 s32e a8, a0, -32 516 s32e a9, a0, -28 517 s32e a10, a0, -24 518 s32e a11, a0, -20 519 rfwo 520 521ENDPROC(_WindowOverflow12) 522 523/* 12-Register Window Underflow Vector (Handler) */ 524 525ENTRY_ALIGN64(_WindowUnderflow12) 526 527 l32e a1, a13, -12 528 l32e a0, a13, -16 529 l32e a11, a1, -12 530 l32e a2, a13, -8 531 l32e a4, a11, -48 532 l32e a8, a11, -32 533 l32e a3, a13, -4 534 l32e a5, a11, -44 535 l32e a6, a11, -40 536 l32e a7, a11, -36 537 l32e a9, a11, -28 538 l32e a10, a11, -24 539 l32e a11, a11, -20 540 rfwu 541 542ENDPROC(_WindowUnderflow12) 543 544 .text 545