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Diffstat (limited to 'arch/xtensa/kernel/vectors.S')
| -rw-r--r-- | arch/xtensa/kernel/vectors.S | 464 |
1 files changed, 464 insertions, 0 deletions
diff --git a/arch/xtensa/kernel/vectors.S b/arch/xtensa/kernel/vectors.S new file mode 100644 index 0000000..81808f0 --- /dev/null +++ b/arch/xtensa/kernel/vectors.S @@ -0,0 +1,464 @@ +/* + * arch/xtensa/kernel/vectors.S + * + * This file contains all exception vectors (user, kernel, and double), + * as well as the window vectors (overflow and underflow), and the debug + * vector. These are the primary vectors executed by the processor if an + * exception occurs. + * + * This file is subject to the terms and conditions of the GNU General + * Public License. See the file "COPYING" in the main directory of + * this archive for more details. + * + * Copyright (C) 2005 Tensilica, Inc. + * + * Chris Zankel <chris@zankel.net> + * + */ + +/* + * We use a two-level table approach. The user and kernel exception vectors + * use a first-level dispatch table to dispatch the exception to a registered + * fast handler or the default handler, if no fast handler was registered. + * The default handler sets up a C-stack and dispatches the exception to a + * registerd C handler in the second-level dispatch table. + * + * Fast handler entry condition: + * + * a0: trashed, original value saved on stack (PT_AREG0) + * a1: a1 + * a2: new stack pointer, original value in depc + * a3: dispatch table + * depc: a2, original value saved on stack (PT_DEPC) + * excsave_1: a3 + * + * The value for PT_DEPC saved to stack also functions as a boolean to + * indicate that the exception is either a double or a regular exception: + * + * PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception + * < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception + * + * Note: Neither the kernel nor the user exception handler generate literals. + * + */ + +#include <linux/linkage.h> +#include <asm/ptrace.h> +#include <asm/ptrace.h> +#include <asm/current.h> +#include <asm/offsets.h> +#include <asm/pgtable.h> +#include <asm/processor.h> +#include <asm/page.h> +#include <asm/thread_info.h> +#include <asm/processor.h> + + +/* + * User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0) + * + * We get here when an exception occurred while we were in userland. + * We switch to the kernel stack and jump to the first level handler + * associated to the exception cause. + * + * Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already + * decremented by PT_USER_SIZE. + */ + + .section .UserExceptionVector.text, "ax" + +ENTRY(_UserExceptionVector) + + xsr a3, EXCSAVE_1 # save a3 and get dispatch table + wsr a2, DEPC # save a2 + l32i a2, a3, EXC_TABLE_KSTK # load kernel stack to a2 + s32i a0, a2, PT_AREG0 # save a0 to ESF + rsr a0, EXCCAUSE # retrieve exception cause + s32i a0, a2, PT_DEPC # mark it as a regular exception + addx4 a0, a0, a3 # find entry in table + l32i a0, a0, EXC_TABLE_FAST_USER # load handler + jx a0 + +/* + * Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0) + * + * We get this exception when we were already in kernel space. + * We decrement the current stack pointer (kernel) by PT_SIZE and + * jump to the first-level handler associated with the exception cause. + * + * Note: we need to preserve space for the spill region. + */ + + .section .KernelExceptionVector.text, "ax" + +ENTRY(_KernelExceptionVector) + + xsr a3, EXCSAVE_1 # save a3, and get dispatch table + wsr a2, DEPC # save a2 + addi a2, a1, -16-PT_SIZE # adjust stack pointer + s32i a0, a2, PT_AREG0 # save a0 to ESF + rsr a0, EXCCAUSE # retrieve exception cause + s32i a0, a2, PT_DEPC # mark it as a regular exception + addx4 a0, a0, a3 # find entry in table + l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address + jx a0 + + +/* + * Double exception vector (Exceptions with PS.EXCM == 1) + * We get this exception when another exception occurs while were are + * already in an exception, such as window overflow/underflow exception, + * or 'expected' exceptions, for example memory exception when we were trying + * to read data from an invalid address in user space. + * + * Note that this vector is never invoked for level-1 interrupts, because such + * interrupts are disabled (masked) when PS.EXCM is set. + * + * We decode the exception and take the appropriate action. However, the + * double exception vector is much more careful, because a lot more error + * cases go through the double exception vector than through the user and + * kernel exception vectors. + * + * Occasionally, the kernel expects a double exception to occur. This usually + * happens when accessing user-space memory with the user's permissions + * (l32e/s32e instructions). The kernel state, though, is not always suitable + * for immediate transfer of control to handle_double, where "normal" exception + * processing occurs. Also in kernel mode, TLB misses can occur if accessing + * vmalloc memory, possibly requiring repair in a double exception handler. + * + * The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as + * a boolean variable and a pointer to a fixup routine. If the variable + * EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of + * zero indicates to use the default kernel/user exception handler. + * There is only one exception, when the value is identical to the exc_table + * label, the kernel is in trouble. This mechanism is used to protect critical + * sections, mainly when the handler writes to the stack to assert the stack + * pointer is valid. Once the fixup/default handler leaves that area, the + * EXC_TABLE_FIXUP variable is reset to the fixup handler or zero. + * + * Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the + * nonzero address of a fixup routine before it could cause a double exception + * and reset it before it returns. + * + * Some other things to take care of when a fast exception handler doesn't + * specify a particular fixup handler but wants to use the default handlers: + * + * - The original stack pointer (in a1) must not be modified. The fast + * exception handler should only use a2 as the stack pointer. + * + * - If the fast handler manipulates the stack pointer (in a2), it has to + * register a valid fixup handler and cannot use the default handlers. + * + * - The handler can use any other generic register from a3 to a15, but it + * must save the content of these registers to stack (PT_AREG3...PT_AREGx) + * + * - These registers must be saved before a double exception can occur. + * + * - If we ever implement handling signals while in double exceptions, the + * number of registers a fast handler has saved (excluding a0 and a1) must + * be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. ) + * + * The fixup handlers are special handlers: + * + * - Fixup entry conditions differ from regular exceptions: + * + * a0: DEPC + * a1: a1 + * a2: trashed, original value in EXC_TABLE_DOUBLE_A2 + * a3: exctable + * depc: a0 + * excsave_1: a3 + * + * - When the kernel enters the fixup handler, it still assumes it is in a + * critical section, so EXC_TABLE_FIXUP variable is set to exc_table. + * The fixup handler, therefore, has to re-register itself as the fixup + * handler before it returns from the double exception. + * + * - Fixup handler can share the same exception frame with the fast handler. + * The kernel stack pointer is not changed when entering the fixup handler. + * + * - Fixup handlers can jump to the default kernel and user exception + * handlers. Before it jumps, though, it has to setup a exception frame + * on stack. Because the default handler resets the register fixup handler + * the fixup handler must make sure that the default handler returns to + * it instead of the exception address, so it can re-register itself as + * the fixup handler. + * + * In case of a critical condition where the kernel cannot recover, we jump + * to unrecoverable_exception with the following entry conditions. + * All registers a0...a15 are unchanged from the last exception, except: + * + * a0: last address before we jumped to the unrecoverable_exception. + * excsave_1: a0 + * + * + * See the handle_alloca_user and spill_registers routines for example clients. + * + * FIXME: Note: we currently don't allow signal handling coming from a double + * exception, so the item markt with (*) is not required. + */ + + .section .DoubleExceptionVector.text, "ax" + .begin literal_prefix .DoubleExceptionVector + +ENTRY(_DoubleExceptionVector) + + /* Deliberately destroy excsave (don't assume it's value was valid). */ + + wsr a3, EXCSAVE_1 # save a3 + + /* Check for kernel double exception (usually fatal). */ + + rsr a3, PS + _bbci.l a3, PS_UM_SHIFT, .Lksp + + /* Check if we are currently handling a window exception. */ + /* Note: We don't need to indicate that we enter a critical section. */ + + xsr a0, DEPC # get DEPC, save a0 + + movi a3, XCHAL_WINDOW_VECTORS_VADDR + _bltu a0, a3, .Lfixup + addi a3, a3, XSHAL_WINDOW_VECTORS_SIZE + _bgeu a0, a3, .Lfixup + + /* Window overflow/underflow exception. Get stack pointer. */ + + mov a3, a2 + movi a2, exc_table + l32i a2, a2, EXC_TABLE_KSTK + + /* Check for overflow/underflow exception, jump if overflow. */ + + _bbci.l a0, 6, .Lovfl + + /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ + + /* Restart window underflow exception. + * We return to the instruction in user space that caused the window + * underflow exception. Therefore, we change window base to the value + * before we entered the window underflow exception and prepare the + * registers to return as if we were coming from a regular exception + * by changing depc (in a0). + * Note: We can trash the current window frame (a0...a3) and depc! + */ + + wsr a2, DEPC # save stack pointer temporarily + rsr a0, PS + extui a0, a0, XCHAL_PS_OWB_SHIFT, XCHAL_PS_OWB_BITS + wsr a0, WINDOWBASE + rsync + + /* We are now in the previous window frame. Save registers again. */ + + xsr a2, DEPC # save a2 and get stack pointer + s32i a0, a2, PT_AREG0 + + wsr a3, EXCSAVE_1 # save a3 + movi a3, exc_table + + rsr a0, EXCCAUSE + s32i a0, a2, PT_DEPC # mark it as a regular exception + addx4 a0, a0, a3 + l32i a0, a0, EXC_TABLE_FAST_USER + jx a0 + +.Lfixup:/* Check for a fixup handler or if we were in a critical section. */ + + /* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */ + + movi a3, exc_table + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE # temporary variable + + /* Enter critical section. */ + + l32i a2, a3, EXC_TABLE_FIXUP + s32i a3, a3, EXC_TABLE_FIXUP + beq a2, a3, .Lunrecoverable_fixup # critical! + beqz a2, .Ldflt # no handler was registered + + /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */ + + jx a2 + +.Ldflt: /* Get stack pointer. */ + + l32i a3, a3, EXC_TABLE_DOUBLE_SAVE + addi a2, a3, -PT_USER_SIZE + +.Lovfl: /* Jump to default handlers. */ + + /* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */ + + xsr a3, DEPC + s32i a0, a2, PT_DEPC + s32i a3, a2, PT_AREG0 + + /* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */ + + movi a3, exc_table + rsr a0, EXCCAUSE + addx4 a0, a0, a3 + l32i a0, a0, EXC_TABLE_FAST_USER + jx a0 + + /* + * We only allow the ITLB miss exception if we are in kernel space. + * All other exceptions are unexpected and thus unrecoverable! + */ + + .extern fast_second_level_miss_double_kernel + +.Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */ + + rsr a3, EXCCAUSE + beqi a3, XCHAL_EXCCAUSE_ITLB_MISS, 1f + addi a3, a3, -XCHAL_EXCCAUSE_DTLB_MISS + bnez a3, .Lunrecoverable +1: movi a3, fast_second_level_miss_double_kernel + jx a3 + + /* Critical! We can't handle this situation. PANIC! */ + + .extern unrecoverable_exception + +.Lunrecoverable_fixup: + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE + xsr a0, DEPC + +.Lunrecoverable: + rsr a3, EXCSAVE_1 + wsr a0, EXCSAVE_1 + movi a0, unrecoverable_exception + callx0 a0 + + .end literal_prefix + + +/* + * Debug interrupt vector + * + * There is not much space here, so simply jump to another handler. + * EXCSAVE[DEBUGLEVEL] has been set to that handler. + */ + + .section .DebugInterruptVector.text, "ax" + +ENTRY(_DebugInterruptVector) + xsr a0, EXCSAVE + XCHAL_DEBUGLEVEL + jx a0 + + + +/* Window overflow and underflow handlers. + * The handlers must be 64 bytes apart, first starting with the underflow + * handlers underflow-4 to underflow-12, then the overflow handlers + * overflow-4 to overflow-12. + * + * Note: We rerun the underflow handlers if we hit an exception, so + * we try to access any page that would cause a page fault early. + */ + + .section .WindowVectors.text, "ax" + + +/* 4-Register Window Overflow Vector (Handler) */ + + .align 64 +.global _WindowOverflow4 +_WindowOverflow4: + s32e a0, a5, -16 + s32e a1, a5, -12 + s32e a2, a5, -8 + s32e a3, a5, -4 + rfwo + + +/* 4-Register Window Underflow Vector (Handler) */ + + .align 64 +.global _WindowUnderflow4 +_WindowUnderflow4: + l32e a0, a5, -16 + l32e a1, a5, -12 + l32e a2, a5, -8 + l32e a3, a5, -4 + rfwu + + +/* 8-Register Window Overflow Vector (Handler) */ + + .align 64 +.global _WindowOverflow8 +_WindowOverflow8: + s32e a0, a9, -16 + l32e a0, a1, -12 + s32e a2, a9, -8 + s32e a1, a9, -12 + s32e a3, a9, -4 + s32e a4, a0, -32 + s32e a5, a0, -28 + s32e a6, a0, -24 + s32e a7, a0, -20 + rfwo + +/* 8-Register Window Underflow Vector (Handler) */ + + .align 64 +.global _WindowUnderflow8 +_WindowUnderflow8: + l32e a1, a9, -12 + l32e a0, a9, -16 + l32e a7, a1, -12 + l32e a2, a9, -8 + l32e a4, a7, -32 + l32e a3, a9, -4 + l32e a5, a7, -28 + l32e a6, a7, -24 + l32e a7, a7, -20 + rfwu + + +/* 12-Register Window Overflow Vector (Handler) */ + + .align 64 +.global _WindowOverflow12 +_WindowOverflow12: + s32e a0, a13, -16 + l32e a0, a1, -12 + s32e a1, a13, -12 + s32e a2, a13, -8 + s32e a3, a13, -4 + s32e a4, a0, -48 + s32e a5, a0, -44 + s32e a6, a0, -40 + s32e a7, a0, -36 + s32e a8, a0, -32 + s32e a9, a0, -28 + s32e a10, a0, -24 + s32e a11, a0, -20 + rfwo + +/* 12-Register Window Underflow Vector (Handler) */ + + .align 64 +.global _WindowUnderflow12 +_WindowUnderflow12: + l32e a1, a13, -12 + l32e a0, a13, -16 + l32e a11, a1, -12 + l32e a2, a13, -8 + l32e a4, a11, -48 + l32e a8, a11, -32 + l32e a3, a13, -4 + l32e a5, a11, -44 + l32e a6, a11, -40 + l32e a7, a11, -36 + l32e a9, a11, -28 + l32e a10, a11, -24 + l32e a11, a11, -20 + rfwu + + .text + + |