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Commit fff96d69 authored by Max Filippov's avatar Max Filippov Committed by Chris Zankel
Browse files

xtensa: new fast_alloca handler 



Instead of emulating movsp instruction in the kernel use window
underflow handler to load missing register window and retry failed
movsp.

Signed-off-by: default avatarMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: default avatarChris Zankel <chris@zankel.net>
parent 99d5040e

arch/xtensa/kernel/entry.S

+40 −152
Original line number Diff line number Diff line
@@ -31,7 +31,6 @@ 
/* Unimplemented features. */



#undef KERNEL_STACK_OVERFLOW_CHECK

#undef ALLOCA_EXCEPTION_IN_IRAM



/* Not well tested.

 *
@@ -819,11 +818,27 @@ ENDPROC(unrecoverable_exception) 
 *

 *  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.

 * 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:

 *
@@ -838,155 +853,28 @@ ENDPROC(unrecoverable_exception) 
 *	     <  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)

	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



	/* 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	a3, a2, PT_AREG3

	s32i	a0, a2, PT_AREG2	# a2 to stack



	/* Exit critical section. */



	movi	a0, 0

	rsr	a3, excsave1

	s32i	a0, a3, EXC_TABLE_FIXUP



	rsr	a4, epc1		# get exception address



#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, excsave1

	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, epc1		# 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



	_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)



/*