entry.s

linux 内核源代码

kernel_exception_exit:

	/* Disable interrupts (a3 holds PT_PS) */

	wsr	a3, PS

#ifdef PREEMPTIBLE_KERNEL

#ifdef CONFIG_PREEMPT

	/*
	 * Note: We've just returned from a call4, so we have
	 * at least 4 addt'l regs.
	 */

	/* Check current_thread_info->preempt_count */

	GET_THREAD_INFO(a2)
	l32i	a3, a2, TI_PREEMPT
	bnez	a3, 1f

	l32i	a2, a2, TI_FLAGS

1:

#endif

#endif

	/* 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:

	_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, EPC_1
	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

/*
 * 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, EPS + XCHAL_DEBUGLEVEL
	bbsi.l	a0, PS_EXCM_BIT, 1f	# exception mode

	/* Set EPC_1 and EXCCAUSE */

	wsr	a2, DEPC		# save a2 temporarily
	rsr	a2, EPC + XCHAL_DEBUGLEVEL
	wsr	a2, EPC_1

	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, 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, EXCSAVE_1
	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!!


/*
 * 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) | 1
	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


/* -------------------------- 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.
 *  In this case, the caller frame's a0..a3 are on the stack just
 *  below sp (a1), and this handler moves them.
 *
 *  For "MOVSP <ar>,<as>" without destination register a1, this routine
 *  simply moves the value from <as> to <ar> without moving the save area.
 *
 * Entry condition:
 *
 *   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
 */

#if XCHAL_HAVE_BE
#define _EXTUI_MOVSP_SRC(ar)	extui ar, ar, 4, 4
#define _EXTUI_MOVSP_DST(ar)	extui ar, ar, 0, 4
#else
#define _EXTUI_MOVSP_SRC(ar)	extui ar, ar, 0, 4
#define _EXTUI_MOVSP_DST(ar)	extui ar, ar, 4, 4
#endif

ENTRY(fast_alloca)

	/* We shouldn't be in a double exception. */

	l32i	a0, a2, PT_DEPC
	_bgeui	a0, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lunhandled_double

	rsr	a0, DEPC		# get a2
	s32i	a4, a2, PT_AREG4	# save a4 and
	s32i	a0, a2, PT_AREG2	# a2 to stack

	/* Exit critical section. */

	movi	a0, 0
	s32i	a0, a3, EXC_TABLE_FIXUP

	/* Restore a3, excsave_1 */

	xsr	a3, EXCSAVE_1		# make sure excsave_1 is valid for dbl.
	rsr	a4, EPC_1		# get exception address
	s32i	a3, a2, PT_AREG3	# save a3 to stack

#ifdef ALLOCA_EXCEPTION_IN_IRAM
#error	iram not supported
#else
	/* Note: l8ui not allowed in IRAM/IROM!! */
	l8ui	a0, a4, 1		# read as(src) from MOVSP instruction
#endif
	movi	a3, .Lmovsp_src
	_EXTUI_MOVSP_SRC(a0)		# extract source register number
	addx8	a3, a0, a3
	jx	a3

.Lunhandled_double:
	wsr	a0, EXCSAVE_1
	movi	a0, unrecoverable_exception
	callx0	a0

	.align 8
.Lmovsp_src:
	l32i	a3, a2, PT_AREG0;	_j 1f;	.align 8
	mov	a3, a1;			_j 1f;	.align 8
	l32i	a3, a2, PT_AREG2;	_j 1f;	.align 8
	l32i	a3, a2, PT_AREG3;	_j 1f;	.align 8
	l32i	a3, a2, PT_AREG4;	_j 1f;	.align 8
	mov	a3, a5;			_j 1f;	.align 8
	mov	a3, a6;			_j 1f;	.align 8
	mov	a3, a7;			_j 1f;	.align 8
	mov	a3, a8;			_j 1f;	.align 8
	mov	a3, a9;			_j 1f;	.align 8
	mov	a3, a10;		_j 1f;	.align 8
	mov	a3, a11;		_j 1f;	.align 8
	mov	a3, a12;		_j 1f;	.align 8
	mov	a3, a13;		_j 1f;	.align 8
	mov	a3, a14;		_j 1f;	.align 8
	mov	a3, a15;		_j 1f;	.align 8

1:

#ifdef ALLOCA_EXCEPTION_IN_IRAM
#error	iram not supported
#else
	l8ui	a0, a4, 0		# read ar(dst) from MOVSP instruction
#endif
	addi	a4, a4, 3		# step over movsp
	_EXTUI_MOVSP_DST(a0)		# extract destination register
	wsr	a4, EPC_1		# save new epc_1

	_bnei	a0, 1, 1f		# no 'movsp a1, ax': jump

        /* Move the save area. This implies the use of the L32E
	 * and S32E instructions, because this move must be done with
	 * the user's PS.RING privilege levels, not with ring 0
	 * (kernel's) privileges currently active with PS.EXCM
	 * set. Note that we have stil registered a fixup routine with the
	 * double exception vector in case a double exception occurs.
	 */

	/* a0,a4:avail a1:old user stack a2:exc. stack a3:new user stack. */

	l32e	a0, a1, -16
	l32e	a4, a1, -12
	s32e	a0, a3, -16
	s32e	a4, a3, -12
	l32e	a0, a1, -8
	l32e	a4, a1, -4
	s32e	a0, a3, -8
	s32e	a4, a3, -4

	/* Restore stack-pointer and all the other saved registers. */

	mov	a1, a3

	l32i	a4, a2, PT_AREG4
	l32i	a3, a2, PT_AREG3
	l32i	a0, a2, PT_AREG0
	l32i	a2, a2, PT_AREG2
	rfe

	/*  MOVSP <at>,<as>  was invoked with <at> != a1.
	 *  Because the stack pointer is not being modified,
	 *  we should be able to just modify the pointer
	 *  without moving any save area.
	 *  The processor only traps these occurrences if the
	 *  caller window isn't live, so unfortunately we can't
	 *  use this as an alternate trap mechanism.
	 *  So we just do the move.  This requires that we
	 *  resolve the destination register, not just the source,
	 *  so there's some extra work.
	 *  (PERHAPS NOT REALLY NEEDED, BUT CLEANER...)
	 */

	/* a0 dst-reg, a1 user-stack, a2 stack, a3 value of src reg. */

1:	movi	a4, .Lmovsp_dst
	addx8	a4, a0, a4
	jx	a4

	.align 8
.Lmovsp_dst:
	s32i	a3, a2, PT_AREG0;	_j 1f;	.align 8
	mov	a1, a3;			_j 1f;	.align 8
	s32i	a3, a2, PT_AREG2;	_j 1f;	.align 8
	s32i	a3, a2, PT_AREG3;	_j 1f;	.align 8
	s32i	a3, a2, PT_AREG4;	_j 1f;	.align 8
	mov	a5, a3;			_j 1f;	.align 8
	mov	a6, a3;			_j 1f;	.align 8
	mov	a7, a3;			_j 1f;	.align 8
	mov	a8, a3;			_j 1f;	.align 8
	mov	a9, a3;			_j 1f;	.align 8
	mov	a10, a3;		_j 1f;	.align 8
	mov	a11, a3;		_j 1f;	.align 8
	mov	a12, a3;		_j 1f;	.align 8
	mov	a13, a3;		_j 1f;	.align 8
	mov	a14, a3;		_j 1f;	.align 8
	mov	a15, a3;		_j 1f;	.align 8

1:	l32i	a4, a2, PT_AREG4
	l32i	a3, a2, PT_AREG3
	l32i	a0, a2, PT_AREG0
	l32i	a2, a2, PT_AREG2
	rfe


/*
 * 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:	dispatch table
 *   depc:	a2, original value saved on stack (PT_DEPC)
 *   excsave_1:	a3
 */

ENTRY(fast_syscall_kernel)

	/* Skip syscall. */

	rsr	a0, EPC_1
	addi	a0, a0, 3
	wsr	a0, EPC_1

	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

ENTRY(fast_syscall_user)

	/* Skip syscall. */

	rsr	a0, EPC_1
	addi	a0, a0, 3
	wsr	a0, EPC_1

	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

ENTRY(fast_syscall_unrecoverable)

        /* Restore all states. */

        l32i    a0, a2, PT_AREG0        # restore a0
        xsr     a2, DEPC                # restore a2, depc
        rsr     a3, EXCSAVE_1

        wsr     a0, EXCSAVE_1
        movi    a0, unrecoverable_exception
        callx0  a0



/*
 * 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:	dispatch table, original in excsave_1
 *   a4..a15:	unchanged
 *   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
 *
 * 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 preceeding TRY
 *       statements and continues from there
 *
 * Usage TRY	l32i	a0, a1, 0
 *		<other code>
 *	 done:	rfe
 *	 CATCH	<set return code>
 *		j done
 */