arch/xtensa/kernel/vectors.S - maze/linux - Git at Google

 /*
  * 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/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
	/*
	* 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/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