Initial import

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diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
new file mode 100644
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+/*
+ * arch/xtensa/kernel/entry.S
+ *
+ * Low-level exception handling
+ *
+ * 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) 2004 - 2008 by Tensilica Inc.
+ *
+ * Chris Zankel <chris@zankel.net>
+ *
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/processor.h>
+#include <asm/coprocessor.h>
+#include <asm/thread_info.h>
+#include <asm/uaccess.h>
+#include <asm/unistd.h>
+#include <asm/ptrace.h>
+#include <asm/current.h>
+#include <asm/pgtable.h>
+#include <asm/page.h>
+#include <asm/signal.h>
+#include <asm/tlbflush.h>
+#include <variant/tie-asm.h>
+
+/* Unimplemented features. */
+
+#undef KERNEL_STACK_OVERFLOW_CHECK
+
+/* Not well tested.
+ *
+ * - fast_coprocessor
+ */
+
+/*
+ * Macro to find first bit set in WINDOWBASE from the left + 1
+ *
+ * 100....0 -> 1
+ * 010....0 -> 2
+ * 000....1 -> WSBITS
+ */
+
+	.macro ffs_ws bit mask
+
+#if XCHAL_HAVE_NSA
+	nsau    \bit, \mask			# 32-WSBITS ... 31 (32 iff 0)
+	addi    \bit, \bit, WSBITS - 32 + 1   	# uppest bit set -> return 1
+#else
+	movi    \bit, WSBITS
+#if WSBITS > 16
+	_bltui  \mask, 0x10000, 99f
+	addi    \bit, \bit, -16
+	extui   \mask, \mask, 16, 16
+#endif
+#if WSBITS > 8
+99:	_bltui  \mask, 0x100, 99f
+	addi    \bit, \bit, -8
+	srli    \mask, \mask, 8
+#endif
+99:	_bltui  \mask, 0x10, 99f
+	addi    \bit, \bit, -4
+	srli    \mask, \mask, 4
+99:	_bltui  \mask, 0x4, 99f
+	addi    \bit, \bit, -2
+	srli    \mask, \mask, 2
+99:	_bltui  \mask, 0x2, 99f
+	addi    \bit, \bit, -1
+99:
+
+#endif
+	.endm
+
+/* ----------------- DEFAULT FIRST LEVEL EXCEPTION HANDLERS ----------------- */
+
+/*
+ * First-level exception handler for user exceptions.
+ * Save some special registers, extra states and all registers in the AR
+ * register file that were in use in the user task, and jump to the common
+ * exception code.
+ * We save SAR (used to calculate WMASK), and WB and WS (we don't have to
+ * save them for kernel exceptions).
+ *
+ * Entry condition for user_exception:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original value in depc
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ *
+ * Entry condition for _user_exception:
+ *
+ *   a0-a3 and depc have been saved to PT_AREG0...PT_AREG3 and PT_DEPC
+ *   excsave has been restored, and
+ *   stack pointer (a1) has been set.
+ *
+ * Note: _user_exception might be at an odd address. Don't use call0..call12
+ */
+
+ENTRY(user_exception)
+
+	/* Save a1, a2, a3, and set SP. */
+
+	rsr	a0, depc
+	s32i	a1, a2, PT_AREG1
+	s32i	a0, a2, PT_AREG2
+	s32i	a3, a2, PT_AREG3
+	mov	a1, a2
+
+	.globl _user_exception
+_user_exception:
+
+	/* Save SAR and turn off single stepping */
+
+	movi	a2, 0
+	rsr	a3, sar
+	xsr	a2, icountlevel
+	s32i	a3, a1, PT_SAR
+	s32i	a2, a1, PT_ICOUNTLEVEL
+
+#if XCHAL_HAVE_THREADPTR
+	rur	a2, threadptr
+	s32i	a2, a1, PT_THREADPTR
+#endif
+
+	/* Rotate ws so that the current windowbase is at bit0. */
+	/* Assume ws = xxwww1yyyy. Rotate ws right, so that a2 = yyyyxxwww1 */
+
+	rsr	a2, windowbase
+	rsr	a3, windowstart
+	ssr	a2
+	s32i	a2, a1, PT_WINDOWBASE
+	s32i	a3, a1, PT_WINDOWSTART
+	slli	a2, a3, 32-WSBITS
+	src	a2, a3, a2
+	srli	a2, a2, 32-WSBITS
+	s32i	a2, a1, PT_WMASK	# needed for restoring registers
+
+	/* Save only live registers. */
+
+	_bbsi.l	a2, 1, 1f
+	s32i	a4, a1, PT_AREG4
+	s32i	a5, a1, PT_AREG5
+	s32i	a6, a1, PT_AREG6
+	s32i	a7, a1, PT_AREG7
+	_bbsi.l	a2, 2, 1f
+	s32i	a8, a1, PT_AREG8
+	s32i	a9, a1, PT_AREG9
+	s32i	a10, a1, PT_AREG10
+	s32i	a11, a1, PT_AREG11
+	_bbsi.l	a2, 3, 1f
+	s32i	a12, a1, PT_AREG12
+	s32i	a13, a1, PT_AREG13
+	s32i	a14, a1, PT_AREG14
+	s32i	a15, a1, PT_AREG15
+	_bnei	a2, 1, 1f		# only one valid frame?
+
+	/* Only one valid frame, skip saving regs. */
+
+	j	2f
+
+	/* Save the remaining registers.
+	 * We have to save all registers up to the first '1' from
+	 * the right, except the current frame (bit 0).
+	 * Assume a2 is:  001001000110001
+	 * All register frames starting from the top field to the marked '1'
+	 * must be saved.
+	 */
+
+1:	addi	a3, a2, -1		# eliminate '1' in bit 0: yyyyxxww0
+	neg	a3, a3			# yyyyxxww0 -> YYYYXXWW1+1
+	and	a3, a3, a2		# max. only one bit is set
+
+	/* Find number of frames to save */
+
+	ffs_ws	a0, a3			# number of frames to the '1' from left
+
+	/* Store information into WMASK:
+	 * bits 0..3: xxx1 masked lower 4 bits of the rotated windowstart,
+	 * bits 4...: number of valid 4-register frames
+	 */
+
+	slli	a3, a0, 4		# number of frames to save in bits 8..4
+	extui	a2, a2, 0, 4		# mask for the first 16 registers
+	or	a2, a3, a2
+	s32i	a2, a1, PT_WMASK	# needed when we restore the reg-file
+
+	/* Save 4 registers at a time */
+
+1:	rotw	-1
+	s32i	a0, a5, PT_AREG_END - 16
+	s32i	a1, a5, PT_AREG_END - 12
+	s32i	a2, a5, PT_AREG_END - 8
+	s32i	a3, a5, PT_AREG_END - 4
+	addi	a0, a4, -1
+	addi	a1, a5, -16
+	_bnez	a0, 1b
+
+	/* WINDOWBASE still in SAR! */
+
+	rsr	a2, sar			# original WINDOWBASE
+	movi	a3, 1
+	ssl	a2
+	sll	a3, a3
+	wsr	a3, windowstart		# set corresponding WINDOWSTART bit
+	wsr	a2, windowbase		# and WINDOWSTART
+	rsync
+
+	/* We are back to the original stack pointer (a1) */
+
+2:	/* Now, jump to the common exception handler. */
+
+	j	common_exception
+
+ENDPROC(user_exception)
+
+/*
+ * First-level exit handler for kernel exceptions
+ * Save special registers and the live window frame.
+ * Note: Even though we changes the stack pointer, we don't have to do a
+ *	 MOVSP here, as we do that when we return from the exception.
+ *	 (See comment in the kernel exception exit code)
+ *
+ * Entry condition for kernel_exception:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ *
+ * Entry condition for _kernel_exception:
+ *
+ *   a0-a3 and depc have been saved to PT_AREG0...PT_AREG3 and PT_DEPC
+ *   excsave has been restored, and
+ *   stack pointer (a1) has been set.
+ *
+ * Note: _kernel_exception might be at an odd address. Don't use call0..call12
+ */
+
+ENTRY(kernel_exception)
+
+	/* Save a1, a2, a3, and set SP. */
+
+	rsr	a0, depc		# get a2
+	s32i	a1, a2, PT_AREG1
+	s32i	a0, a2, PT_AREG2
+	s32i	a3, a2, PT_AREG3
+	mov	a1, a2
+
+	.globl _kernel_exception
+_kernel_exception:
+
+	/* Save SAR and turn off single stepping */
+
+	movi	a2, 0
+	rsr	a3, sar
+	xsr	a2, icountlevel
+	s32i	a3, a1, PT_SAR
+	s32i	a2, a1, PT_ICOUNTLEVEL
+
+	/* Rotate ws so that the current windowbase is at bit0. */
+	/* Assume ws = xxwww1yyyy. Rotate ws right, so that a2 = yyyyxxwww1 */
+
+	rsr	a2, windowbase		# don't need to save these, we only
+	rsr	a3, windowstart		# need shifted windowstart: windowmask
+	ssr	a2
+	slli	a2, a3, 32-WSBITS
+	src	a2, a3, a2
+	srli	a2, a2, 32-WSBITS
+	s32i	a2, a1, PT_WMASK	# needed for kernel_exception_exit
+
+	/* Save only the live window-frame */
+
+	_bbsi.l	a2, 1, 1f
+	s32i	a4, a1, PT_AREG4
+	s32i	a5, a1, PT_AREG5
+	s32i	a6, a1, PT_AREG6
+	s32i	a7, a1, PT_AREG7
+	_bbsi.l	a2, 2, 1f
+	s32i	a8, a1, PT_AREG8
+	s32i	a9, a1, PT_AREG9
+	s32i	a10, a1, PT_AREG10
+	s32i	a11, a1, PT_AREG11
+	_bbsi.l	a2, 3, 1f
+	s32i	a12, a1, PT_AREG12
+	s32i	a13, a1, PT_AREG13
+	s32i	a14, a1, PT_AREG14
+	s32i	a15, a1, PT_AREG15
+
+1:
+
+#ifdef KERNEL_STACK_OVERFLOW_CHECK
+
+	/*  Stack overflow check, for debugging  */
+	extui	a2, a1, TASK_SIZE_BITS,XX
+	movi	a3, SIZE??
+	_bge	a2, a3, out_of_stack_panic
+
+#endif
+
+/*
+ * This is the common exception handler.
+ * We get here from the user exception handler or simply by falling through
+ * from the kernel exception handler.
+ * Save the remaining special registers, switch to kernel mode, and jump
+ * to the second-level exception handler.
+ *
+ */
+
+common_exception:
+
+	/* Save some registers, disable loops and clear the syscall flag. */
+
+	rsr	a2, debugcause
+	rsr	a3, epc1
+	s32i	a2, a1, PT_DEBUGCAUSE
+	s32i	a3, a1, PT_PC
+
+	movi	a2, -1
+	rsr	a3, excvaddr
+	s32i	a2, a1, PT_SYSCALL
+	movi	a2, 0
+	s32i	a3, a1, PT_EXCVADDR
+	xsr	a2, lcount
+	s32i	a2, a1, PT_LCOUNT
+
+	/* It is now save to restore the EXC_TABLE_FIXUP variable. */
+
+	rsr	a0, exccause
+	movi	a3, 0
+	rsr	a2, excsave1
+	s32i	a0, a1, PT_EXCCAUSE
+	s32i	a3, a2, EXC_TABLE_FIXUP
+
+	/* All unrecoverable states are saved on stack, now, and a1 is valid,
+	 * so we can allow exceptions and interrupts (*) again.
+	 * Set PS(EXCM = 0, UM = 0, RING = 0, OWB = 0, WOE = 1, INTLEVEL = X)
+	 *
+	 * (*) We only allow interrupts if they were previously enabled and
+	 *     we're not handling an IRQ
+	 */
+
+	rsr	a3, ps
+	addi	a0, a0, -EXCCAUSE_LEVEL1_INTERRUPT
+	movi	a2, LOCKLEVEL
+	extui	a3, a3, PS_INTLEVEL_SHIFT, PS_INTLEVEL_WIDTH
+					# a3 = PS.INTLEVEL
+	moveqz	a3, a2, a0		# a3 = LOCKLEVEL iff interrupt
+	movi	a2, 1 << PS_WOE_BIT
+	or	a3, a3, a2
+	rsr	a0, exccause
+	xsr	a3, ps
+
+	s32i	a3, a1, PT_PS		# save ps
+
+	/* Save lbeg, lend */
+
+	rsr	a2, lbeg
+	rsr	a3, lend
+	s32i	a2, a1, PT_LBEG
+	s32i	a3, a1, PT_LEND
+
+	/* Save SCOMPARE1 */
+
+#if XCHAL_HAVE_S32C1I
+	rsr     a2, scompare1
+	s32i    a2, a1, PT_SCOMPARE1
+#endif
+
+	/* Save optional registers. */
+
+	save_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
+	
+#ifdef CONFIG_TRACE_IRQFLAGS
+	l32i	a4, a1, PT_DEPC
+	/* Double exception means we came here with an exception
+	 * while PS.EXCM was set, i.e. interrupts disabled.
+	 */
+	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
+	l32i	a4, a1, PT_EXCCAUSE
+	bnei	a4, EXCCAUSE_LEVEL1_INTERRUPT, 1f
+	/* We came here with an interrupt means interrupts were enabled
+	 * and we've just disabled them.
+	 */
+	movi	a4, trace_hardirqs_off
+	callx4	a4
+1:
+#endif
+
+	/* Go to second-level dispatcher. Set up parameters to pass to the
+	 * exception handler and call the exception handler.
+	 */
+
+	rsr	a4, excsave1
+	mov	a6, a1			# pass stack frame
+	mov	a7, a0			# pass EXCCAUSE
+	addx4	a4, a0, a4
+	l32i	a4, a4, EXC_TABLE_DEFAULT		# load handler
+
+	/* Call the second-level handler */
+
+	callx4	a4
+
+	/* Jump here for exception exit */
+	.global common_exception_return
+common_exception_return:
+
+1:
+	rsil	a2, LOCKLEVEL
+
+	/* Jump if we are returning from kernel exceptions. */
+
+	l32i	a3, a1, PT_PS
+	GET_THREAD_INFO(a2, a1)
+	l32i	a4, a2, TI_FLAGS
+	_bbci.l	a3, PS_UM_BIT, 6f
+
+	/* Specific to a user exception exit:
+	 * We need to check some flags for signal handling and rescheduling,
+	 * and have to restore WB and WS, extra states, and all registers
+	 * in the register file that were in use in the user task.
+	 * Note that we don't disable interrupts here. 
+	 */
+
+	_bbsi.l	a4, TIF_NEED_RESCHED, 3f
+	_bbsi.l	a4, TIF_NOTIFY_RESUME, 2f
+	_bbci.l	a4, TIF_SIGPENDING, 5f
+
+2:	l32i	a4, a1, PT_DEPC
+	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
+
+	/* Call do_signal() */
+
+	rsil	a2, 0
+	movi	a4, do_notify_resume	# int do_notify_resume(struct pt_regs*)
+	mov	a6, a1
+	callx4	a4
+	j	1b
+
+3:	/* Reschedule */
+
+	rsil	a2, 0
+	movi	a4, schedule	# void schedule (void)
+	callx4	a4
+	j	1b
+
+#ifdef CONFIG_PREEMPT
+6:
+	_bbci.l	a4, TIF_NEED_RESCHED, 4f
+
+	/* Check current_thread_info->preempt_count */
+
+	l32i	a4, a2, TI_PRE_COUNT
+	bnez	a4, 4f
+	movi	a4, preempt_schedule_irq
+	callx4	a4
+	j	1b
+#endif
+
+5:
+#ifdef CONFIG_DEBUG_TLB_SANITY
+	l32i	a4, a1, PT_DEPC
+	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
+	movi	a4, check_tlb_sanity
+	callx4	a4
+#endif
+6:
+4:
+#ifdef CONFIG_TRACE_IRQFLAGS
+	l32i	a4, a1, PT_DEPC
+	/* Double exception means we came here with an exception
+	 * while PS.EXCM was set, i.e. interrupts disabled.
+	 */
+	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
+	l32i	a4, a1, PT_EXCCAUSE
+	bnei	a4, EXCCAUSE_LEVEL1_INTERRUPT, 1f
+	/* We came here with an interrupt means interrupts were enabled
+	 * and we'll reenable them on return.
+	 */
+	movi	a4, trace_hardirqs_on
+	callx4	a4
+1:
+#endif
+	/* Restore optional registers. */
+
+	load_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
+
+	/* Restore SCOMPARE1 */
+
+#if XCHAL_HAVE_S32C1I
+	l32i    a2, a1, PT_SCOMPARE1
+	wsr     a2, scompare1
+#endif
+	wsr	a3, ps		/* disable interrupts */
+
+	_bbci.l	a3, PS_UM_BIT, kernel_exception_exit
+
+user_exception_exit:
+
+	/* Restore the state of the task and return from the exception. */
+
+	/* Switch to the user thread WINDOWBASE. Save SP temporarily in DEPC */
+
+	l32i	a2, a1, PT_WINDOWBASE
+	l32i	a3, a1, PT_WINDOWSTART
+	wsr	a1, depc		# use DEPC as temp storage
+	wsr	a3, windowstart		# restore WINDOWSTART
+	ssr	a2			# preserve user's WB in the SAR
+	wsr	a2, windowbase		# switch to user's saved WB
+	rsync
+	rsr	a1, depc		# restore stack pointer
+	l32i	a2, a1, PT_WMASK	# register frames saved (in bits 4...9)
+	rotw	-1			# we restore a4..a7
+	_bltui	a6, 16, 1f		# only have to restore current window?
+
+	/* The working registers are a0 and a3.  We are restoring to
+	 * a4..a7.  Be careful not to destroy what we have just restored.
+	 * Note: wmask has the format YYYYM:
+	 *       Y: number of registers saved in groups of 4
+	 *       M: 4 bit mask of first 16 registers
+	 */
+
+	mov	a2, a6
+	mov	a3, a5
+
+2:	rotw	-1			# a0..a3 become a4..a7
+	addi	a3, a7, -4*4		# next iteration
+	addi	a2, a6, -16		# decrementing Y in WMASK
+	l32i	a4, a3, PT_AREG_END + 0
+	l32i	a5, a3, PT_AREG_END + 4
+	l32i	a6, a3, PT_AREG_END + 8
+	l32i	a7, a3, PT_AREG_END + 12
+	_bgeui	a2, 16, 2b
+
+	/* Clear unrestored registers (don't leak anything to user-land */
+
+1:	rsr	a0, windowbase
+	rsr	a3, sar
+	sub	a3, a0, a3
+	beqz	a3, 2f
+	extui	a3, a3, 0, WBBITS
+
+1:	rotw	-1
+	addi	a3, a7, -1
+	movi	a4, 0
+	movi	a5, 0
+	movi	a6, 0
+	movi	a7, 0
+	bgei	a3, 1, 1b
+
+	/* We are back were we were when we started.
+	 * Note: a2 still contains WMASK (if we've returned to the original
+	 *	 frame where we had loaded a2), or at least the lower 4 bits
+	 *	 (if we have restored WSBITS-1 frames).
+	 */
+
+#if XCHAL_HAVE_THREADPTR
+	l32i	a3, a1, PT_THREADPTR
+	wur	a3, threadptr
+#endif
+
+2:	j	common_exception_exit
+
+	/* This is the kernel exception exit.
+	 * We avoided to do a MOVSP when we entered the exception, but we
+	 * have to do it here.
+	 */
+
+kernel_exception_exit:
+
+	/* Check if we have to do a movsp.
+	 *
+	 * We only have to do a movsp if the previous window-frame has
+	 * been spilled to the *temporary* exception stack instead of the
+	 * task's stack. This is the case if the corresponding bit in
+	 * WINDOWSTART for the previous window-frame was set before
+	 * (not spilled) but is zero now (spilled).
+	 * If this bit is zero, all other bits except the one for the
+	 * current window frame are also zero. So, we can use a simple test:
+	 * 'and' WINDOWSTART and WINDOWSTART-1:
+	 *
+	 *  (XXXXXX1[0]* - 1) AND XXXXXX1[0]* = XXXXXX0[0]*
+	 *
+	 * The result is zero only if one bit was set.
+	 *
+	 * (Note: We might have gone through several task switches before
+	 *        we come back to the current task, so WINDOWBASE might be
+	 *        different from the time the exception occurred.)
+	 */
+
+	/* Test WINDOWSTART before and after the exception.
+	 * We actually have WMASK, so we only have to test if it is 1 or not.
+	 */
+
+	l32i	a2, a1, PT_WMASK
+	_beqi	a2, 1, common_exception_exit	# Spilled before exception,jump
+
+	/* Test WINDOWSTART now. If spilled, do the movsp */
+
+	rsr     a3, windowstart
+	addi	a0, a3, -1
+	and     a3, a3, a0
+	_bnez	a3, common_exception_exit
+
+	/* Do a movsp (we returned from a call4, so we have at least a0..a7) */
+
+	addi    a0, a1, -16
+	l32i    a3, a0, 0
+	l32i    a4, a0, 4
+	s32i    a3, a1, PT_SIZE+0
+	s32i    a4, a1, PT_SIZE+4
+	l32i    a3, a0, 8
+	l32i    a4, a0, 12
+	s32i    a3, a1, PT_SIZE+8
+	s32i    a4, a1, PT_SIZE+12
+
+	/* Common exception exit.
+	 * We restore the special register and the current window frame, and
+	 * return from the exception.
+	 *
+	 * Note: We expect a2 to hold PT_WMASK
+	 */
+
+common_exception_exit:
+
+	/* Restore address registers. */
+
+	_bbsi.l	a2, 1, 1f
+	l32i	a4,  a1, PT_AREG4
+	l32i	a5,  a1, PT_AREG5
+	l32i	a6,  a1, PT_AREG6
+	l32i	a7,  a1, PT_AREG7
+	_bbsi.l	a2, 2, 1f
+	l32i	a8,  a1, PT_AREG8
+	l32i	a9,  a1, PT_AREG9
+	l32i	a10, a1, PT_AREG10
+	l32i	a11, a1, PT_AREG11
+	_bbsi.l	a2, 3, 1f
+	l32i	a12, a1, PT_AREG12
+	l32i	a13, a1, PT_AREG13
+	l32i	a14, a1, PT_AREG14
+	l32i	a15, a1, PT_AREG15
+
+	/* Restore PC, SAR */
+
+1:	l32i	a2, a1, PT_PC
+	l32i	a3, a1, PT_SAR
+	wsr	a2, epc1
+	wsr	a3, sar
+
+	/* Restore LBEG, LEND, LCOUNT */
+
+	l32i	a2, a1, PT_LBEG
+	l32i	a3, a1, PT_LEND
+	wsr	a2, lbeg
+	l32i	a2, a1, PT_LCOUNT
+	wsr	a3, lend
+	wsr	a2, lcount
+
+	/* We control single stepping through the ICOUNTLEVEL register. */
+
+	l32i	a2, a1, PT_ICOUNTLEVEL
+	movi	a3, -2
+	wsr	a2, icountlevel
+	wsr	a3, icount
+
+	/* Check if it was double exception. */
+
+	l32i	a0, a1, PT_DEPC
+	l32i	a3, a1, PT_AREG3
+	l32i	a2, a1, PT_AREG2
+	_bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
+
+	/* Restore a0...a3 and return */
+
+	l32i	a0, a1, PT_AREG0
+	l32i	a1, a1, PT_AREG1
+	rfe
+
+1: 	wsr	a0, depc
+	l32i	a0, a1, PT_AREG0
+	l32i	a1, a1, PT_AREG1
+	rfde
+
+ENDPROC(kernel_exception)
+
+/*
+ * Debug exception handler.
+ *
+ * Currently, we don't support KGDB, so only user application can be debugged.
+ *
+ * When we get here,  a0 is trashed and saved to excsave[debuglevel]
+ */
+
+ENTRY(debug_exception)
+
+	rsr	a0, SREG_EPS + XCHAL_DEBUGLEVEL
+	bbsi.l	a0, PS_EXCM_BIT, 1f	# exception mode
+
+	/* Set EPC1 and EXCCAUSE */
+
+	wsr	a2, depc		# save a2 temporarily
+	rsr	a2, SREG_EPC + XCHAL_DEBUGLEVEL
+	wsr	a2, epc1
+
+	movi	a2, EXCCAUSE_MAPPED_DEBUG
+	wsr	a2, exccause
+
+	/* Restore PS to the value before the debug exc but with PS.EXCM set.*/
+
+	movi	a2, 1 << PS_EXCM_BIT
+	or	a2, a0, a2
+	movi	a0, debug_exception	# restore a3, debug jump vector
+	wsr	a2, ps
+	xsr	a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL
+
+	/* Switch to kernel/user stack, restore jump vector, and save a0 */
+
+	bbsi.l	a2, PS_UM_BIT, 2f	# jump if user mode
+
+	addi	a2, a1, -16-PT_SIZE	# assume kernel stack
+	s32i	a0, a2, PT_AREG0
+	movi	a0, 0
+	s32i	a1, a2, PT_AREG1
+	s32i	a0, a2, PT_DEPC		# mark it as a regular exception
+	xsr	a0, depc
+	s32i	a3, a2, PT_AREG3
+	s32i	a0, a2, PT_AREG2
+	mov	a1, a2
+	j	_kernel_exception
+
+2:	rsr	a2, excsave1
+	l32i	a2, a2, EXC_TABLE_KSTK	# load kernel stack pointer
+	s32i	a0, a2, PT_AREG0
+	movi	a0, 0
+	s32i	a1, a2, PT_AREG1
+	s32i	a0, a2, PT_DEPC
+	xsr	a0, depc
+	s32i	a3, a2, PT_AREG3
+	s32i	a0, a2, PT_AREG2
+	mov	a1, a2
+	j	_user_exception
+
+	/* Debug exception while in exception mode. */
+1:	j	1b	// FIXME!!
+
+ENDPROC(debug_exception)
+
+/*
+ * We get here in case of an unrecoverable exception.
+ * The only thing we can do is to be nice and print a panic message.
+ * We only produce a single stack frame for panic, so ???
+ *
+ *
+ * Entry conditions:
+ *
+ *   - a0 contains the caller address; original value saved in excsave1.
+ *   - the original a0 contains a valid return address (backtrace) or 0.
+ *   - a2 contains a valid stackpointer
+ *
+ * Notes:
+ *
+ *   - If the stack pointer could be invalid, the caller has to setup a
+ *     dummy stack pointer (e.g. the stack of the init_task)
+ *
+ *   - If the return address could be invalid, the caller has to set it
+ *     to 0, so the backtrace would stop.
+ *
+ */
+	.align 4
+unrecoverable_text:
+	.ascii "Unrecoverable error in exception handler\0"
+
+ENTRY(unrecoverable_exception)
+
+	movi	a0, 1
+	movi	a1, 0
+
+	wsr	a0, windowstart
+	wsr	a1, windowbase
+	rsync
+
+	movi	a1, (1 << PS_WOE_BIT) | LOCKLEVEL
+	wsr	a1, ps
+	rsync
+
+	movi	a1, init_task
+	movi	a0, 0
+	addi	a1, a1, PT_REGS_OFFSET
+
+	movi	a4, panic
+	movi	a6, unrecoverable_text
+
+	callx4	a4
+
+1:	j	1b
+
+ENDPROC(unrecoverable_exception)
+
+/* -------------------------- FAST EXCEPTION HANDLERS ----------------------- */
+
+/*
+ * Fast-handler for alloca exceptions
+ *
+ *  The ALLOCA handler is entered when user code executes the MOVSP
+ *  instruction and the caller's frame is not in the register file.
+ *
+ * This algorithm was taken from the Ross Morley's RTOS Porting Layer:
+ *
+ *    /home/ross/rtos/porting/XtensaRTOS-PortingLayer-20090507/xtensa_vectors.S
+ *
+ * It leverages the existing window spill/fill routines and their support for
+ * double exceptions. The 'movsp' instruction will only cause an exception if
+ * the next window needs to be loaded. In fact this ALLOCA exception may be
+ * replaced at some point by changing the hardware to do a underflow exception
+ * of the proper size instead.
+ *
+ * This algorithm simply backs out the register changes started by the user
+ * excpetion handler, makes it appear that we have started a window underflow
+ * by rotating the window back and then setting the old window base (OWB) in
+ * the 'ps' register with the rolled back window base. The 'movsp' instruction
+ * will be re-executed and this time since the next window frames is in the
+ * active AR registers it won't cause an exception.
+ *
+ * If the WindowUnderflow code gets a TLB miss the page will get mapped
+ * the the partial windeowUnderflow will be handeled in the double exception
+ * handler.
+ *
+ * Entry condition:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ */
+
+ENTRY(fast_alloca)
+	rsr	a0, windowbase
+	rotw	-1
+	rsr	a2, ps
+	extui	a3, a2, PS_OWB_SHIFT, PS_OWB_WIDTH
+	xor	a3, a3, a4
+	l32i	a4, a6, PT_AREG0
+	l32i	a1, a6, PT_DEPC
+	rsr	a6, depc
+	wsr	a1, depc
+	slli	a3, a3, PS_OWB_SHIFT
+	xor	a2, a2, a3
+	wsr	a2, ps
+	rsync
+
+	_bbci.l	a4, 31, 4f
+	rotw	-1
+	_bbci.l	a8, 30, 8f
+	rotw	-1
+	j	_WindowUnderflow12
+8:	j	_WindowUnderflow8
+4:	j	_WindowUnderflow4
+ENDPROC(fast_alloca)
+
+/*
+ * fast system calls.
+ *
+ * WARNING:  The kernel doesn't save the entire user context before
+ * handling a fast system call.  These functions are small and short,
+ * usually offering some functionality not available to user tasks.
+ *
+ * BE CAREFUL TO PRESERVE THE USER'S CONTEXT.
+ *
+ * Entry condition:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ */
+
+ENTRY(fast_syscall_kernel)
+
+	/* Skip syscall. */
+
+	rsr	a0, epc1
+	addi	a0, a0, 3
+	wsr	a0, epc1
+
+	l32i	a0, a2, PT_DEPC
+	bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, fast_syscall_unrecoverable
+
+	rsr	a0, depc			# get syscall-nr
+	_beqz	a0, fast_syscall_spill_registers
+	_beqi	a0, __NR_xtensa, fast_syscall_xtensa
+
+	j	kernel_exception
+
+ENDPROC(fast_syscall_kernel)
+
+ENTRY(fast_syscall_user)
+
+	/* Skip syscall. */
+
+	rsr	a0, epc1
+	addi	a0, a0, 3
+	wsr	a0, epc1
+
+	l32i	a0, a2, PT_DEPC
+	bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, fast_syscall_unrecoverable
+
+	rsr	a0, depc			# get syscall-nr
+	_beqz	a0, fast_syscall_spill_registers
+	_beqi	a0, __NR_xtensa, fast_syscall_xtensa
+
+	j	user_exception
+
+ENDPROC(fast_syscall_user)
+
+ENTRY(fast_syscall_unrecoverable)
+
+	/* Restore all states. */
+
+	l32i    a0, a2, PT_AREG0        # restore a0
+	xsr     a2, depc                # restore a2, depc
+
+	wsr     a0, excsave1
+	movi    a0, unrecoverable_exception
+	callx0  a0
+
+ENDPROC(fast_syscall_unrecoverable)
+
+/*
+ * sysxtensa syscall handler
+ *
+ * int sysxtensa (SYS_XTENSA_ATOMIC_SET,     ptr, val,    unused);
+ * int sysxtensa (SYS_XTENSA_ATOMIC_ADD,     ptr, val,    unused);
+ * int sysxtensa (SYS_XTENSA_ATOMIC_EXG_ADD, ptr, val,    unused);
+ * int sysxtensa (SYS_XTENSA_ATOMIC_CMP_SWP, ptr, oldval, newval);
+ *        a2            a6                   a3    a4      a5
+ *
+ * Entry condition:
+ *
+ *   a0:	a2 (syscall-nr), original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in a0 and DEPC
+ *   a3:	a3
+ *   a4..a15:	unchanged
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ *
+ * Note: we don't have to save a2; a2 holds the return value
+ *
+ * We use the two macros TRY and CATCH:
+ *
+ * TRY	 adds an entry to the __ex_table fixup table for the immediately
+ *	 following instruction.
+ *
+ * CATCH catches any exception that occurred at one of the preceding TRY
+ *       statements and continues from there
+ *
+ * Usage TRY	l32i	a0, a1, 0
+ *		<other code>
+ *	 done:	rfe
+ *	 CATCH	<set return code>
+ *		j done
+ */
+
+#ifdef CONFIG_FAST_SYSCALL_XTENSA
+
+#define TRY								\
+	.section __ex_table, "a";					\
+	.word	66f, 67f;						\
+	.text;								\
+66:
+
+#define CATCH								\
+67:
+
+ENTRY(fast_syscall_xtensa)
+
+	s32i	a7, a2, PT_AREG7	# we need an additional register
+	movi	a7, 4			# sizeof(unsigned int)
+	access_ok a3, a7, a0, a2, .Leac	# a0: scratch reg, a2: sp
+
+	_bgeui	a6, SYS_XTENSA_COUNT, .Lill
+	_bnei	a6, SYS_XTENSA_ATOMIC_CMP_SWP, .Lnswp
+
+	/* Fall through for ATOMIC_CMP_SWP. */
+
+.Lswp:	/* Atomic compare and swap */
+
+TRY	l32i	a0, a3, 0		# read old value
+	bne	a0, a4, 1f		# same as old value? jump
+TRY	s32i	a5, a3, 0		# different, modify value
+	l32i	a7, a2, PT_AREG7	# restore a7
+	l32i	a0, a2, PT_AREG0	# restore a0
+	movi	a2, 1			# and return 1
+	rfe
+
+1:	l32i	a7, a2, PT_AREG7	# restore a7
+	l32i	a0, a2, PT_AREG0	# restore a0
+	movi	a2, 0			# return 0 (note that we cannot set
+	rfe
+
+.Lnswp:	/* Atomic set, add, and exg_add. */
+
+TRY	l32i	a7, a3, 0		# orig
+	addi	a6, a6, -SYS_XTENSA_ATOMIC_SET
+	add	a0, a4, a7		# + arg
+	moveqz	a0, a4, a6		# set
+	addi	a6, a6, SYS_XTENSA_ATOMIC_SET
+TRY	s32i	a0, a3, 0		# write new value
+
+	mov	a0, a2
+	mov	a2, a7
+	l32i	a7, a0, PT_AREG7	# restore a7
+	l32i	a0, a0, PT_AREG0	# restore a0
+	rfe
+
+CATCH
+.Leac:	l32i	a7, a2, PT_AREG7	# restore a7
+	l32i	a0, a2, PT_AREG0	# restore a0
+	movi	a2, -EFAULT
+	rfe
+
+.Lill:	l32i	a7, a2, PT_AREG7	# restore a7
+	l32i	a0, a2, PT_AREG0	# restore a0
+	movi	a2, -EINVAL
+	rfe
+
+ENDPROC(fast_syscall_xtensa)
+
+#else /* CONFIG_FAST_SYSCALL_XTENSA */
+
+ENTRY(fast_syscall_xtensa)
+
+	l32i    a0, a2, PT_AREG0        # restore a0
+	movi	a2, -ENOSYS
+	rfe
+
+ENDPROC(fast_syscall_xtensa)
+
+#endif /* CONFIG_FAST_SYSCALL_XTENSA */
+
+
+/* fast_syscall_spill_registers.
+ *
+ * Entry condition:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ * Note: We assume the stack pointer is EXC_TABLE_KSTK in the fixup handler.
+ */
+
+#ifdef CONFIG_FAST_SYSCALL_SPILL_REGISTERS
+
+ENTRY(fast_syscall_spill_registers)
+
+	/* Register a FIXUP handler (pass current wb as a parameter) */
+
+	xsr	a3, excsave1
+	movi	a0, fast_syscall_spill_registers_fixup
+	s32i	a0, a3, EXC_TABLE_FIXUP
+	rsr	a0, windowbase
+	s32i	a0, a3, EXC_TABLE_PARAM
+	xsr	a3, excsave1		# restore a3 and excsave_1
+
+	/* Save a3, a4 and SAR on stack. */
+
+	rsr	a0, sar
+	s32i	a3, a2, PT_AREG3
+	s32i	a0, a2, PT_SAR
+
+	/* The spill routine might clobber a4, a7, a8, a11, a12, and a15. */
+
+	s32i	a4, a2, PT_AREG4
+	s32i	a7, a2, PT_AREG7
+	s32i	a8, a2, PT_AREG8
+	s32i	a11, a2, PT_AREG11
+	s32i	a12, a2, PT_AREG12
+	s32i	a15, a2, PT_AREG15
+
+	/*
+	 * Rotate ws so that the current windowbase is at bit 0.
+	 * Assume ws = xxxwww1yy (www1 current window frame).
+	 * Rotate ws right so that a4 = yyxxxwww1.
+	 */
+
+	rsr	a0, windowbase
+	rsr	a3, windowstart		# a3 = xxxwww1yy
+	ssr	a0			# holds WB
+	slli	a0, a3, WSBITS
+	or	a3, a3, a0		# a3 = xxxwww1yyxxxwww1yy
+	srl	a3, a3			# a3 = 00xxxwww1yyxxxwww1
+
+	/* We are done if there are no more than the current register frame. */
+
+	extui	a3, a3, 1, WSBITS-1	# a3 = 0yyxxxwww
+	movi	a0, (1 << (WSBITS-1))
+	_beqz	a3, .Lnospill		# only one active frame? jump
+
+	/* We want 1 at the top, so that we return to the current windowbase */
+
+	or	a3, a3, a0		# 1yyxxxwww
+
+	/* Skip empty frames - get 'oldest' WINDOWSTART-bit. */
+
+	wsr	a3, windowstart		# save shifted windowstart
+	neg	a0, a3
+	and	a3, a0, a3		# first bit set from right: 000010000
+
+	ffs_ws	a0, a3			# a0: shifts to skip empty frames
+	movi	a3, WSBITS
+	sub	a0, a3, a0		# WSBITS-a0:number of 0-bits from right
+	ssr	a0			# save in SAR for later.
+
+	rsr	a3, windowbase
+	add	a3, a3, a0
+	wsr	a3, windowbase
+	rsync
+
+	rsr	a3, windowstart
+	srl	a3, a3			# shift windowstart
+
+	/* WB is now just one frame below the oldest frame in the register
+	   window. WS is shifted so the oldest frame is in bit 0, thus, WB
+	   and WS differ by one 4-register frame. */
+
+	/* Save frames. Depending what call was used (call4, call8, call12),
+	 * we have to save 4,8. or 12 registers.
+	 */
+
+
+.Lloop: _bbsi.l	a3, 1, .Lc4
+	_bbci.l	a3, 2, .Lc12
+
+.Lc8:	s32e	a4, a13, -16
+	l32e	a4, a5, -12
+	s32e	a8, a4, -32
+	s32e	a5, a13, -12
+	s32e	a6, a13, -8
+	s32e	a7, a13, -4
+	s32e	a9, a4, -28
+	s32e	a10, a4, -24
+	s32e	a11, a4, -20
+	srli	a11, a3, 2		# shift windowbase by 2
+	rotw	2
+	_bnei	a3, 1, .Lloop
+	j	.Lexit
+
+.Lc4:	s32e	a4, a9, -16
+	s32e	a5, a9, -12
+	s32e	a6, a9, -8
+	s32e	a7, a9, -4
+
+	srli	a7, a3, 1
+	rotw	1
+	_bnei	a3, 1, .Lloop
+	j	.Lexit
+
+.Lc12:	_bbci.l	a3, 3, .Linvalid_mask	# bit 2 shouldn't be zero!
+
+	/* 12-register frame (call12) */
+
+	l32e	a0, a5, -12
+	s32e	a8, a0, -48
+	mov	a8, a0
+
+	s32e	a9, a8, -44
+	s32e	a10, a8, -40
+	s32e	a11, a8, -36
+	s32e	a12, a8, -32
+	s32e	a13, a8, -28
+	s32e	a14, a8, -24
+	s32e	a15, a8, -20
+	srli	a15, a3, 3
+
+	/* The stack pointer for a4..a7 is out of reach, so we rotate the
+	 * window, grab the stackpointer, and rotate back.
+	 * Alternatively, we could also use the following approach, but that
+	 * makes the fixup routine much more complicated:
+	 * rotw	1
+	 * s32e	a0, a13, -16
+	 * ...
+	 * rotw 2
+	 */
+
+	rotw	1
+	mov	a4, a13
+	rotw	-1
+
+	s32e	a4, a8, -16
+	s32e	a5, a8, -12
+	s32e	a6, a8, -8
+	s32e	a7, a8, -4
+
+	rotw	3
+
+	_beqi	a3, 1, .Lexit
+	j	.Lloop
+
+.Lexit:
+
+	/* Done. Do the final rotation and set WS */
+
+	rotw	1
+	rsr	a3, windowbase
+	ssl	a3
+	movi	a3, 1
+	sll	a3, a3
+	wsr	a3, windowstart
+.Lnospill:
+
+	/* Advance PC, restore registers and SAR, and return from exception. */
+
+	l32i	a3, a2, PT_SAR
+	l32i	a0, a2, PT_AREG0
+	wsr	a3, sar
+	l32i	a3, a2, PT_AREG3
+
+	/* Restore clobbered registers. */
+
+	l32i	a4, a2, PT_AREG4
+	l32i	a7, a2, PT_AREG7
+	l32i	a8, a2, PT_AREG8
+	l32i	a11, a2, PT_AREG11
+	l32i	a12, a2, PT_AREG12
+	l32i	a15, a2, PT_AREG15
+
+	movi	a2, 0
+	rfe
+
+.Linvalid_mask:
+
+	/* We get here because of an unrecoverable error in the window
+	 * registers, so set up a dummy frame and kill the user application.
+	 * Note: We assume EXC_TABLE_KSTK contains a valid stack pointer.
+	 */
+
+	movi	a0, 1
+	movi	a1, 0
+
+	wsr	a0, windowstart
+	wsr	a1, windowbase
+	rsync
+
+	movi	a0, 0
+
+	rsr	a3, excsave1
+	l32i	a1, a3, EXC_TABLE_KSTK
+
+	movi	a4, (1 << PS_WOE_BIT) | LOCKLEVEL
+	wsr	a4, ps
+	rsync
+
+	movi	a6, SIGSEGV
+	movi	a4, do_exit
+	callx4	a4
+
+	/* shouldn't return, so panic */
+
+	wsr	a0, excsave1
+	movi	a0, unrecoverable_exception
+	callx0	a0		# should not return
+1:	j	1b
+
+
+ENDPROC(fast_syscall_spill_registers)
+
+/* Fixup handler.
+ *
+ * We get here if the spill routine causes an exception, e.g. tlb miss.
+ * We basically restore WINDOWBASE and WINDOWSTART to the condition when
+ * we entered the spill routine and jump to the user exception handler.
+ *
+ * Note that we only need to restore the bits in windowstart that have not
+ * been spilled yet by the _spill_register routine. Luckily, a3 contains a
+ * rotated windowstart with only those bits set for frames that haven't been
+ * spilled yet. Because a3 is rotated such that bit 0 represents the register
+ * frame for the current windowbase - 1, we need to rotate a3 left by the
+ * value of the current windowbase + 1 and move it to windowstart.
+ *
+ * a0: value of depc, original value in depc
+ * a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE
+ * a3: exctable, original value in excsave1
+ */
+
+ENTRY(fast_syscall_spill_registers_fixup)
+
+	rsr	a2, windowbase	# get current windowbase (a2 is saved)
+	xsr	a0, depc	# restore depc and a0
+	ssl	a2		# set shift (32 - WB)
+
+	/* We need to make sure the current registers (a0-a3) are preserved.
+	 * To do this, we simply set the bit for the current window frame
+	 * in WS, so that the exception handlers save them to the task stack.
+	 *
+	 * Note: we use a3 to set the windowbase, so we take a special care
+	 * of it, saving it in the original _spill_registers frame across
+	 * the exception handler call.
+	 */
+
+	xsr	a3, excsave1	# get spill-mask
+	slli	a3, a3, 1	# shift left by one
+	addi	a3, a3, 1	# set the bit for the current window frame
+
+	slli	a2, a3, 32-WSBITS
+	src	a2, a3, a2	# a2 = xxwww1yyxxxwww1yy......
+	wsr	a2, windowstart	# set corrected windowstart
+
+	srli	a3, a3, 1
+	rsr	a2, excsave1
+	l32i	a2, a2, EXC_TABLE_DOUBLE_SAVE	# restore a2
+	xsr	a2, excsave1
+	s32i	a3, a2, EXC_TABLE_DOUBLE_SAVE	# save a3
+	l32i	a3, a2, EXC_TABLE_PARAM	# original WB (in user task)
+	xsr	a2, excsave1
+
+	/* Return to the original (user task) WINDOWBASE.
+	 * We leave the following frame behind:
+	 * a0, a1, a2	same
+	 * a3:		trashed (saved in EXC_TABLE_DOUBLE_SAVE)
+	 * depc:	depc (we have to return to that address)
+	 * excsave_1:	exctable
+	 */
+
+	wsr	a3, windowbase
+	rsync
+
+	/* We are now in the original frame when we entered _spill_registers:
+	 *  a0: return address
+	 *  a1: used, stack pointer
+	 *  a2: kernel stack pointer
+	 *  a3: available
+	 *  depc: exception address
+	 *  excsave: exctable
+	 * Note: This frame might be the same as above.
+	 */
+
+	/* Setup stack pointer. */
+
+	addi	a2, a2, -PT_USER_SIZE
+	s32i	a0, a2, PT_AREG0
+
+	/* Make sure we return to this fixup handler. */
+
+	movi	a3, fast_syscall_spill_registers_fixup_return
+	s32i	a3, a2, PT_DEPC		# setup depc
+
+	/* Jump to the exception handler. */
+
+	rsr	a3, excsave1
+	rsr	a0, exccause
+	addx4	a0, a0, a3              	# find entry in table
+	l32i	a0, a0, EXC_TABLE_FAST_USER     # load handler
+	l32i	a3, a3, EXC_TABLE_DOUBLE_SAVE
+	jx	a0
+
+ENDPROC(fast_syscall_spill_registers_fixup)
+
+ENTRY(fast_syscall_spill_registers_fixup_return)
+
+	/* When we return here, all registers have been restored (a2: DEPC) */
+
+	wsr	a2, depc		# exception address
+
+	/* Restore fixup handler. */
+
+	rsr	a2, excsave1
+	s32i	a3, a2, EXC_TABLE_DOUBLE_SAVE
+	movi	a3, fast_syscall_spill_registers_fixup
+	s32i	a3, a2, EXC_TABLE_FIXUP
+	rsr	a3, windowbase
+	s32i	a3, a2, EXC_TABLE_PARAM
+	l32i	a2, a2, EXC_TABLE_KSTK
+
+	/* Load WB at the time the exception occurred. */
+
+	rsr	a3, sar			# WB is still in SAR
+	neg	a3, a3
+	wsr	a3, windowbase
+	rsync
+
+	rsr	a3, excsave1
+	l32i	a3, a3, EXC_TABLE_DOUBLE_SAVE
+
+	rfde
+
+ENDPROC(fast_syscall_spill_registers_fixup_return)
+
+#else /* CONFIG_FAST_SYSCALL_SPILL_REGISTERS */
+
+ENTRY(fast_syscall_spill_registers)
+
+	l32i    a0, a2, PT_AREG0        # restore a0
+	movi	a2, -ENOSYS
+	rfe
+
+ENDPROC(fast_syscall_spill_registers)
+
+#endif /* CONFIG_FAST_SYSCALL_SPILL_REGISTERS */
+
+#ifdef CONFIG_MMU
+/*
+ * We should never get here. Bail out!
+ */
+
+ENTRY(fast_second_level_miss_double_kernel)
+
+1:	movi	a0, unrecoverable_exception
+	callx0	a0		# should not return
+1:	j	1b
+
+ENDPROC(fast_second_level_miss_double_kernel)
+
+/* First-level entry handler for user, kernel, and double 2nd-level
+ * TLB miss exceptions.  Note that for now, user and kernel miss
+ * exceptions share the same entry point and are handled identically.
+ *
+ * An old, less-efficient C version of this function used to exist.
+ * We include it below, interleaved as comments, for reference.
+ *
+ * Entry condition:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ */
+
+ENTRY(fast_second_level_miss)
+
+	/* Save a1 and a3. Note: we don't expect a double exception. */
+
+	s32i	a1, a2, PT_AREG1
+	s32i	a3, a2, PT_AREG3
+
+	/* We need to map the page of PTEs for the user task.  Find
+	 * the pointer to that page.  Also, it's possible for tsk->mm
+	 * to be NULL while tsk->active_mm is nonzero if we faulted on
+	 * a vmalloc address.  In that rare case, we must use
+	 * active_mm instead to avoid a fault in this handler.  See
+	 *
+	 * http://mail.nl.linux.org/linux-mm/2002-08/msg00258.html
+	 *   (or search Internet on "mm vs. active_mm")
+	 *
+	 *	if (!mm)
+	 *		mm = tsk->active_mm;
+	 *	pgd = pgd_offset (mm, regs->excvaddr);
+	 *	pmd = pmd_offset (pgd, regs->excvaddr);
+	 *	pmdval = *pmd;
+	 */
+
+	GET_CURRENT(a1,a2)
+	l32i	a0, a1, TASK_MM		# tsk->mm
+	beqz	a0, 9f
+
+8:	rsr	a3, excvaddr		# fault address
+	_PGD_OFFSET(a0, a3, a1)
+	l32i	a0, a0, 0		# read pmdval
+	beqz	a0, 2f
+
+	/* Read ptevaddr and convert to top of page-table page.
+	 *
+	 * 	vpnval = read_ptevaddr_register() & PAGE_MASK;
+	 * 	vpnval += DTLB_WAY_PGTABLE;
+	 *	pteval = mk_pte (virt_to_page(pmd_val(pmdval)), PAGE_KERNEL);
+	 *	write_dtlb_entry (pteval, vpnval);
+	 *
+	 * The messy computation for 'pteval' above really simplifies
+	 * into the following:
+	 *
+	 * pteval = ((pmdval - PAGE_OFFSET) & PAGE_MASK) | PAGE_DIRECTORY
+	 */
+
+	movi	a1, (-PAGE_OFFSET) & 0xffffffff
+	add	a0, a0, a1		# pmdval - PAGE_OFFSET
+	extui	a1, a0, 0, PAGE_SHIFT	# ... & PAGE_MASK
+	xor	a0, a0, a1
+
+	movi	a1, _PAGE_DIRECTORY
+	or	a0, a0, a1		# ... | PAGE_DIRECTORY
+
+	/*
+	 * We utilize all three wired-ways (7-9) to hold pmd translations.
+	 * Memory regions are mapped to the DTLBs according to bits 28 and 29.
+	 * This allows to map the three most common regions to three different
+	 * DTLBs:
+	 *  0,1 -> way 7	program (0040.0000) and virtual (c000.0000)
+	 *  2   -> way 8	shared libaries (2000.0000)
+	 *  3   -> way 0	stack (3000.0000)
+	 */
+
+	extui	a3, a3, 28, 2		# addr. bit 28 and 29	0,1,2,3
+	rsr	a1, ptevaddr
+	addx2	a3, a3, a3		# ->			0,3,6,9
+	srli	a1, a1, PAGE_SHIFT
+	extui	a3, a3, 2, 2		# ->			0,0,1,2
+	slli	a1, a1, PAGE_SHIFT	# ptevaddr & PAGE_MASK
+	addi	a3, a3, DTLB_WAY_PGD
+	add	a1, a1, a3		# ... + way_number
+
+3:	wdtlb	a0, a1
+	dsync
+
+	/* Exit critical section. */
+
+4:	rsr	a3, excsave1
+	movi	a0, 0
+	s32i	a0, a3, EXC_TABLE_FIXUP
+
+	/* Restore the working registers, and return. */
+
+	l32i	a0, a2, PT_AREG0
+	l32i	a1, a2, PT_AREG1
+	l32i	a3, a2, PT_AREG3
+	l32i	a2, a2, PT_DEPC
+
+	bgeui	a2, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
+
+	/* Restore excsave1 and return. */
+
+	rsr	a2, depc
+	rfe
+
+	/* Return from double exception. */
+
+1:	xsr	a2, depc
+	esync
+	rfde
+
+9:	l32i	a0, a1, TASK_ACTIVE_MM	# unlikely case mm == 0
+	j	8b
+
+#if (DCACHE_WAY_SIZE > PAGE_SIZE)
+
+2:	/* Special case for cache aliasing.
+	 * We (should) only get here if a clear_user_page, copy_user_page
+	 * or the aliased cache flush functions got preemptively interrupted 
+	 * by another task. Re-establish temporary mapping to the 
+	 * TLBTEMP_BASE areas.
+	 */
+
+	/* We shouldn't be in a double exception */
+
+	l32i	a0, a2, PT_DEPC
+	bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, 2f
+
+	/* Make sure the exception originated in the special functions */
+
+	movi	a0, __tlbtemp_mapping_start
+	rsr	a3, epc1
+	bltu	a3, a0, 2f
+	movi	a0, __tlbtemp_mapping_end
+	bgeu	a3, a0, 2f
+
+	/* Check if excvaddr was in one of the TLBTEMP_BASE areas. */
+
+	movi	a3, TLBTEMP_BASE_1
+	rsr	a0, excvaddr
+	bltu	a0, a3, 2f
+
+	addi	a1, a0, -TLBTEMP_SIZE
+	bgeu	a1, a3, 2f
+
+	/* Check if we have to restore an ITLB mapping. */
+
+	movi	a1, __tlbtemp_mapping_itlb
+	rsr	a3, epc1
+	sub	a3, a3, a1
+
+	/* Calculate VPN */
+
+	movi	a1, PAGE_MASK
+	and	a1, a1, a0
+
+	/* Jump for ITLB entry */
+
+	bgez	a3, 1f
+
+	/* We can use up to two TLBTEMP areas, one for src and one for dst. */
+
+	extui	a3, a0, PAGE_SHIFT + DCACHE_ALIAS_ORDER, 1
+	add	a1, a3, a1
+
+	/* PPN is in a6 for the first TLBTEMP area and in a7 for the second. */
+
+	mov	a0, a6
+	movnez	a0, a7, a3
+	j	3b
+
+	/* ITLB entry. We only use dst in a6. */
+
+1:	witlb	a6, a1
+	isync
+	j	4b
+
+
+#endif	// DCACHE_WAY_SIZE > PAGE_SIZE
+
+
+2:	/* Invalid PGD, default exception handling */
+
+	rsr	a1, depc
+	s32i	a1, a2, PT_AREG2
+	mov	a1, a2
+
+	rsr	a2, ps
+	bbsi.l	a2, PS_UM_BIT, 1f
+	j	_kernel_exception
+1:	j	_user_exception
+
+ENDPROC(fast_second_level_miss)
+
+/*
+ * StoreProhibitedException
+ *
+ * Update the pte and invalidate the itlb mapping for this pte.
+ *
+ * Entry condition:
+ *
+ *   a0:	trashed, original value saved on stack (PT_AREG0)
+ *   a1:	a1
+ *   a2:	new stack pointer, original in DEPC
+ *   a3:	a3
+ *   depc:	a2, original value saved on stack (PT_DEPC)
+ *   excsave_1:	dispatch table
+ *
+ *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
+ *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
+ */
+
+ENTRY(fast_store_prohibited)
+
+	/* Save a1 and a3. */
+
+	s32i	a1, a2, PT_AREG1
+	s32i	a3, a2, PT_AREG3
+
+	GET_CURRENT(a1,a2)
+	l32i	a0, a1, TASK_MM		# tsk->mm
+	beqz	a0, 9f
+
+8:	rsr	a1, excvaddr		# fault address
+	_PGD_OFFSET(a0, a1, a3)
+	l32i	a0, a0, 0
+	beqz	a0, 2f
+
+	/*
+	 * Note that we test _PAGE_WRITABLE_BIT only if PTE is present
+	 * and is not PAGE_NONE. See pgtable.h for possible PTE layouts.
+	 */
+
+	_PTE_OFFSET(a0, a1, a3)
+	l32i	a3, a0, 0		# read pteval
+	movi	a1, _PAGE_CA_INVALID
+	ball	a3, a1, 2f
+	bbci.l	a3, _PAGE_WRITABLE_BIT, 2f
+
+	movi	a1, _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_HW_WRITE
+	or	a3, a3, a1
+	rsr	a1, excvaddr
+	s32i	a3, a0, 0
+
+	/* We need to flush the cache if we have page coloring. */
+#if (DCACHE_WAY_SIZE > PAGE_SIZE) && XCHAL_DCACHE_IS_WRITEBACK
+	dhwb	a0, 0
+#endif
+	pdtlb	a0, a1
+	wdtlb	a3, a0
+
+	/* Exit critical section. */
+
+	movi	a0, 0
+	rsr	a3, excsave1
+	s32i	a0, a3, EXC_TABLE_FIXUP
+
+	/* Restore the working registers, and return. */
+
+	l32i	a3, a2, PT_AREG3
+	l32i	a1, a2, PT_AREG1
+	l32i	a0, a2, PT_AREG0
+	l32i	a2, a2, PT_DEPC
+
+	bgeui	a2, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
+
+	rsr	a2, depc
+	rfe
+
+	/* Double exception. Restore FIXUP handler and return. */
+
+1:	xsr	a2, depc
+	esync
+	rfde
+
+9:	l32i	a0, a1, TASK_ACTIVE_MM	# unlikely case mm == 0
+	j	8b
+
+2:	/* If there was a problem, handle fault in C */
+
+	rsr	a3, depc	# still holds a2
+	s32i	a3, a2, PT_AREG2
+	mov	a1, a2
+
+	rsr	a2, ps
+	bbsi.l	a2, PS_UM_BIT, 1f
+	j	_kernel_exception
+1:	j	_user_exception
+
+ENDPROC(fast_store_prohibited)
+
+#endif /* CONFIG_MMU */
+
+/*
+ * System Calls.
+ *
+ * void system_call (struct pt_regs* regs, int exccause)
+ *                            a2                 a3
+ */
+
+ENTRY(system_call)
+
+	entry	a1, 32
+
+	/* regs->syscall = regs->areg[2] */
+
+	l32i	a3, a2, PT_AREG2
+	mov	a6, a2
+	movi	a4, do_syscall_trace_enter
+	s32i	a3, a2, PT_SYSCALL
+	callx4	a4
+
+	/* syscall = sys_call_table[syscall_nr] */
+
+	movi	a4, sys_call_table;
+	movi	a5, __NR_syscall_count
+	movi	a6, -ENOSYS
+	bgeu	a3, a5, 1f
+
+	addx4	a4, a3, a4
+	l32i	a4, a4, 0
+	movi	a5, sys_ni_syscall;
+	beq	a4, a5, 1f
+
+	/* Load args: arg0 - arg5 are passed via regs. */
+
+	l32i	a6, a2, PT_AREG6
+	l32i	a7, a2, PT_AREG3
+	l32i	a8, a2, PT_AREG4
+	l32i	a9, a2, PT_AREG5
+	l32i	a10, a2, PT_AREG8
+	l32i	a11, a2, PT_AREG9
+
+	/* Pass one additional argument to the syscall: pt_regs (on stack) */
+	s32i	a2, a1, 0
+
+	callx4	a4
+
+1:	/* regs->areg[2] = return_value */
+
+	s32i	a6, a2, PT_AREG2
+	movi	a4, do_syscall_trace_leave
+	mov	a6, a2
+	callx4	a4
+	retw
+
+ENDPROC(system_call)
+
+/*
+ * Spill live registers on the kernel stack macro.
+ *
+ * Entry condition: ps.woe is set, ps.excm is cleared
+ * Exit condition: windowstart has single bit set
+ * May clobber: a12, a13
+ */
+	.macro	spill_registers_kernel
+
+#if XCHAL_NUM_AREGS > 16
+	call12	1f
+	_j	2f
+	retw
+	.align	4
+1:
+	_entry	a1, 48
+	addi	a12, a0, 3
+#if XCHAL_NUM_AREGS > 32
+	.rept	(XCHAL_NUM_AREGS - 32) / 12
+	_entry	a1, 48
+	mov	a12, a0
+	.endr
+#endif
+	_entry	a1, 48
+#if XCHAL_NUM_AREGS % 12 == 0
+	mov	a8, a8
+#elif XCHAL_NUM_AREGS % 12 == 4
+	mov	a12, a12
+#elif XCHAL_NUM_AREGS % 12 == 8
+	mov	a4, a4
+#endif
+	retw
+2:
+#else
+	mov	a12, a12
+#endif
+	.endm
+
+/*
+ * Task switch.
+ *
+ * struct task*  _switch_to (struct task* prev, struct task* next)
+ *         a2                              a2                 a3
+ */
+
+ENTRY(_switch_to)
+
+	entry	a1, 16
+
+	mov	a11, a3			# and 'next' (a3)
+
+	l32i	a4, a2, TASK_THREAD_INFO
+	l32i	a5, a3, TASK_THREAD_INFO
+
+	save_xtregs_user a4 a6 a8 a9 a12 a13 THREAD_XTREGS_USER
+
+#if THREAD_RA > 1020 || THREAD_SP > 1020
+	addi	a10, a2, TASK_THREAD
+	s32i	a0, a10, THREAD_RA - TASK_THREAD	# save return address
+	s32i	a1, a10, THREAD_SP - TASK_THREAD	# save stack pointer
+#else
+	s32i	a0, a2, THREAD_RA	# save return address
+	s32i	a1, a2, THREAD_SP	# save stack pointer
+#endif
+
+	/* Disable ints while we manipulate the stack pointer. */
+
+	rsil	a14, LOCKLEVEL
+	rsr	a3, excsave1
+	rsync
+	s32i	a3, a3, EXC_TABLE_FIXUP	/* enter critical section */
+
+	/* Switch CPENABLE */
+
+#if (XTENSA_HAVE_COPROCESSORS || XTENSA_HAVE_IO_PORTS)
+	l32i	a3, a5, THREAD_CPENABLE
+	xsr	a3, cpenable
+	s32i	a3, a4, THREAD_CPENABLE
+#endif
+
+	/* Flush register file. */
+
+	spill_registers_kernel
+
+	/* Set kernel stack (and leave critical section)
+	 * Note: It's save to set it here. The stack will not be overwritten
+	 *       because the kernel stack will only be loaded again after
+	 *       we return from kernel space.
+	 */
+
+	rsr	a3, excsave1		# exc_table
+	movi	a6, 0
+	addi	a7, a5, PT_REGS_OFFSET
+	s32i	a6, a3, EXC_TABLE_FIXUP
+	s32i	a7, a3, EXC_TABLE_KSTK
+
+	/* restore context of the task 'next' */
+
+	l32i	a0, a11, THREAD_RA	# restore return address
+	l32i	a1, a11, THREAD_SP	# restore stack pointer
+
+	load_xtregs_user a5 a6 a8 a9 a12 a13 THREAD_XTREGS_USER
+
+	wsr	a14, ps
+	rsync
+
+	retw
+
+ENDPROC(_switch_to)
+
+ENTRY(ret_from_fork)
+
+	/* void schedule_tail (struct task_struct *prev)
+	 * Note: prev is still in a6 (return value from fake call4 frame)
+	 */
+	movi	a4, schedule_tail
+	callx4	a4
+
+	movi	a4, do_syscall_trace_leave
+	mov	a6, a1
+	callx4	a4
+
+	j	common_exception_return
+
+ENDPROC(ret_from_fork)
+
+/*
+ * Kernel thread creation helper
+ * On entry, set up by copy_thread: a2 = thread_fn, a3 = thread_fn arg
+ *           left from _switch_to: a6 = prev
+ */
+ENTRY(ret_from_kernel_thread)
+
+	call4	schedule_tail
+	mov	a6, a3
+	callx4	a2
+	j	common_exception_return
+
+ENDPROC(ret_from_kernel_thread)