entry.s

linux 内核源代码

/*
 * 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) 2004-2007 by Tensilica Inc.
 *
 * Chris Zankel <[e-mail]>
 *
 */

#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/processor.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>

/* Unimplemented features. */

#undef SIGNAL_HANDLING_IN_DOUBLE_EXCEPTION
#undef KERNEL_STACK_OVERFLOW_CHECK
#undef PREEMPTIBLE_KERNEL
#undef ALLOCA_EXCEPTION_IN_IRAM

/* 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:	dispatch table
 *   depc:	a2, original value saved on stack (PT_DEPC)
 *   excsave1:	a3
 *
 *   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 adress. Don't use call0..call12
 */

ENTRY(user_exception)

	/* Save a2, a3, and depc, restore excsave_1 and set SP. */

	xsr	a3, EXCSAVE_1
	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

	/* 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:
#if XCHAL_EXTRA_SA_SIZE

	/* For user exceptions, save the extra state into the user's TCB.
	 * Note: We must assume that xchal_extra_store_funcbody destroys a2..a15
	 */

	GET_CURRENT(a2,a1)
	addi	a2, a2, THREAD_CP_SAVE
	xchal_extra_store_funcbody
#endif

	/* Now, jump to the common exception handler. */

	j	common_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:	dispatch table
 *   depc:	a2, original value saved on stack (PT_DEPC)
 *   excsave_1:	a3
 *
 *   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 adress. Don't use call0..call12
 */

ENTRY(kernel_exception)

	/* Save a0, a2, a3, DEPC and set SP. */

	xsr	a3, EXCSAVE_1		# restore a3, excsave_1
	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, EPC_1
	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, EXCSAVE_1
	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 PS.INTLEVEL was not set to 1 before
	 *     (interrupts disabled) and if this exception is not an interrupt.
	 */

	rsr	a3, PS
	addi	a0, a0, -4
	movi	a2, 1
	extui	a3, a3, 0, 1		# a3 = PS.INTLEVEL[0]
	moveqz	a3, a2, a0		# a3 = 1 iff interrupt exception
	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

	/* Go to second-level dispatcher. Set up parameters to pass to the
	 * exception handler and call the exception handler.
	 */

	movi	a4, exc_table
	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 */

common_exception_return:

	/* Jump if we are returning from kernel exceptions. */

1:	l32i	a3, a1, PT_PS
	_bbsi.l	a3, PS_UM_BIT, 2f
	j	kernel_exception_exit

	/* 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.
	 */

2:	wsr	a3, PS		/* disable interrupts */

	/* Check for signals (keep interrupts disabled while we read TI_FLAGS)
	 * Note: PS.INTLEVEL = 0, PS.EXCM = 1
	 */

	GET_THREAD_INFO(a2,a1)
	l32i	a4, a2, TI_FLAGS

	/* Enable interrupts again.
	 * Note: When we get here, we certainly have handled any interrupts.
	 *       (Hint: There is only one user exception frame on stack)
	 */

	movi	a3, 1 << PS_WOE_BIT

	_bbsi.l	a4, TIF_NEED_RESCHED, 3f
	_bbci.l	a4, TIF_SIGPENDING, 4f

#ifndef SIGNAL_HANDLING_IN_DOUBLE_EXCEPTION
	l32i	a4, a1, PT_DEPC
	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
#endif

	/* Reenable interrupts and call do_signal() */

	wsr	a3, PS
	movi	a4, do_signal	# int do_signal(struct pt_regs*, sigset_t*)
	mov	a6, a1
	movi	a7, 0
	callx4	a4
	j	1b

3:	/* Reenable interrupts and reschedule */

	wsr	a3, PS
	movi	a4, schedule	# void schedule (void)
	callx4	a4
	j	1b

	/* Restore the state of the task and return from the exception. */

4:	/* a2 holds GET_CURRENT(a2,a1)  */

#if XCHAL_EXTRA_SA_SIZE

	/* For user exceptions, restore the extra state from the user's TCB. */

	/* Note: a2 still contains GET_CURRENT(a2,a1) */
	addi	a2, a2, THREAD_CP_SAVE
	xchal_extra_load_funcbody

	/* We must assume that xchal_extra_store_funcbody destroys
	 * registers a2..a15.  FIXME, this list can eventually be
	 * reduced once real register requirements of the macro are
	 * finalized. */

#endif /* XCHAL_EXTRA_SA_SIZE */


	/* 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).
	 */

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.
	 */