2 * arch/xtensa/kernel/vectors.S
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
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.
13 * Copyright (C) 2005 - 2008 Tensilica, Inc.
15 * Chris Zankel <chris@zankel.net>
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.
26 * Fast handler entry condition:
28 * a0: trashed, original value saved on stack (PT_AREG0)
30 * a2: new stack pointer, original value in depc
32 * depc: a2, original value saved on stack (PT_DEPC)
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:
38 * PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception
39 * < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
41 * Note: Neither the kernel nor the user exception handler generate literals.
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>
52 #include <asm/thread_info.h>
53 #include <asm/vectors.h>
55 #define WINDOW_VECTORS_SIZE 0x180
59 * User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0)
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.
65 * Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already
66 * decremented by PT_USER_SIZE.
69 .section .UserExceptionVector.text, "ax"
71 ENTRY(_UserExceptionVector)
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
83 ENDPROC(_UserExceptionVector)
86 * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0)
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.
92 * Note: we need to preserve space for the spill region.
95 .section .KernelExceptionVector.text, "ax"
97 ENTRY(_KernelExceptionVector)
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
109 ENDPROC(_KernelExceptionVector)
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.
118 * Note that this vector is never invoked for level-1 interrupts, because such
119 * interrupts are disabled (masked) when PS.EXCM is set.
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.
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.
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.
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.
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:
150 * - The original stack pointer (in a1) must not be modified. The fast
151 * exception handler should only use a2 as the stack pointer.
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.
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)
159 * - These registers must be saved before a double exception can occur.
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. )
165 * The fixup handlers are special handlers:
167 * - Fixup entry conditions differ from regular exceptions:
171 * a2: trashed, original value in EXC_TABLE_DOUBLE_A2
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.
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.
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
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:
195 * a0: last address before we jumped to the unrecoverable_exception.
199 * See the handle_alloca_user and spill_registers routines for example clients.
201 * FIXME: Note: we currently don't allow signal handling coming from a double
202 * exception, so the item markt with (*) is not required.
205 .section .DoubleExceptionVector.text, "ax"
206 .begin literal_prefix .DoubleExceptionVector
208 ENTRY(_DoubleExceptionVector)
210 /* Deliberately destroy excsave (don't assume it's value was valid). */
212 wsr a3, excsave1 # save a3
214 /* Check for kernel double exception (usually fatal). */
217 _bbci.l a3, PS_UM_BIT, .Lksp
219 /* Check if we are currently handling a window exception. */
220 /* Note: We don't need to indicate that we enter a critical section. */
222 xsr a0, depc # get DEPC, save a0
224 movi a3, WINDOW_VECTORS_VADDR
225 _bltu a0, a3, .Lfixup
226 addi a3, a3, WINDOW_VECTORS_SIZE
227 _bgeu a0, a3, .Lfixup
229 /* Window overflow/underflow exception. Get stack pointer. */
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
237 .literal .Lexc_table, exc_table
239 l32i a2, a2, EXC_TABLE_KSTK
241 /* Check for overflow/underflow exception, jump if overflow. */
243 _bbci.l a0, 6, .Lovfl
245 /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */
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!
256 wsr a2, depc # save stack pointer temporarily
258 extui a0, a0, PS_OWB_SHIFT, 4
262 /* We are now in the previous window frame. Save registers again. */
264 xsr a2, depc # save a2 and get stack pointer
265 s32i a0, a2, PT_AREG0
267 wsr a3, excsave1 # save a3
271 s32i a0, a2, PT_DEPC # mark it as a regular exception
273 l32i a0, a0, EXC_TABLE_FAST_USER
276 .Lfixup:/* Check for a fixup handler or if we were in a critical section. */
278 /* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */
281 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE # temporary variable
283 /* Enter critical section. */
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
290 /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */
294 .Ldflt: /* Get stack pointer. */
296 l32i a3, a3, EXC_TABLE_DOUBLE_SAVE
297 addi a2, a3, -PT_USER_SIZE
299 .Lovfl: /* Jump to default handlers. */
301 /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */
305 s32i a3, a2, PT_AREG0
307 /* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */
312 l32i a0, a0, EXC_TABLE_FAST_USER
316 * We only allow the ITLB miss exception if we are in kernel space.
317 * All other exceptions are unexpected and thus unrecoverable!
321 .extern fast_second_level_miss_double_kernel
323 .Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */
326 beqi a3, EXCCAUSE_ITLB_MISS, 1f
327 addi a3, a3, -EXCCAUSE_DTLB_MISS
328 bnez a3, .Lunrecoverable
329 1: movi a3, fast_second_level_miss_double_kernel
332 .equ .Lksp, .Lunrecoverable
335 /* Critical! We can't handle this situation. PANIC! */
337 .extern unrecoverable_exception
339 .Lunrecoverable_fixup:
340 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE
346 movi a0, unrecoverable_exception
351 ENDPROC(_DoubleExceptionVector)
354 * Debug interrupt vector
356 * There is not much space here, so simply jump to another handler.
357 * EXCSAVE[DEBUGLEVEL] has been set to that handler.
360 .section .DebugInterruptVector.text, "ax"
362 ENTRY(_DebugInterruptVector)
364 xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL
367 ENDPROC(_DebugInterruptVector)
372 * Medium priority level interrupt vectors
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.
380 * common_exception code gets current IRQ level in PS.INTLEVEL
381 * and preserves it for the IRQ handling time.
384 .macro irq_entry_level level
386 .if XCHAL_EXCM_LEVEL >= \level
387 .section .Level\level\()InterruptVector.text, "ax"
388 ENTRY(_Level\level\()InterruptVector)
392 movi a0, EXCCAUSE_LEVEL1_INTERRUPT
395 # branch to user or kernel vector
396 j _SimulateUserKernelVectorException
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.
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.
417 #define ENTRY_ALIGN64(name) \
422 .section .WindowVectors.text, "ax"
425 /* 4-Register Window Overflow Vector (Handler) */
427 ENTRY_ALIGN64(_WindowOverflow4)
435 ENDPROC(_WindowOverflow4)
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:
445 _SimulateUserKernelVectorException:
446 addi a0, a0, (1 << PS_EXCM_BIT)
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
451 1: rsr a0, excsave2 # restore a0
452 j _UserExceptionVector # simulate user vector exception
456 /* 4-Register Window Underflow Vector (Handler) */
458 ENTRY_ALIGN64(_WindowUnderflow4)
466 ENDPROC(_WindowUnderflow4)
468 /* 8-Register Window Overflow Vector (Handler) */
470 ENTRY_ALIGN64(_WindowOverflow8)
483 ENDPROC(_WindowOverflow8)
485 /* 8-Register Window Underflow Vector (Handler) */
487 ENTRY_ALIGN64(_WindowUnderflow8)
500 ENDPROC(_WindowUnderflow8)
502 /* 12-Register Window Overflow Vector (Handler) */
504 ENTRY_ALIGN64(_WindowOverflow12)
521 ENDPROC(_WindowOverflow12)
523 /* 12-Register Window Underflow Vector (Handler) */
525 ENTRY_ALIGN64(_WindowUnderflow12)
542 ENDPROC(_WindowUnderflow12)