/* * arch/alpha/lib/stxcpy.S * Contributed by Richard Henderson (rth@tamu.edu) * * Copy a null-terminated string from SRC to DST. * * This is an internal routine used by strcpy, stpcpy, and strcat. * As such, it uses special linkage conventions to make implementation * of these public functions more efficient. * * On input: *	t9 = return address *	a0 = DST *	a1 = SRC * * On output: *	t12 = bitmask (with one bit set) indicating the last byte written *	a0  = unaligned address of the last *word* written * * Furthermore, v0, a3-a5, t11, and t12 are untouched. */#include <alpha/regdef.h>	.set noat	.set noreorder	.text/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that   doesn't like putting the entry point for a procedure somewhere in the   middle of the procedure descriptor.  Work around this by putting the   aligned copy in its own procedure descriptor */	.ent stxcpy_aligned	.align 3stxcpy_aligned:	.frame sp, 0, t9	.prologue 0	/* On entry to this basic block:	   t0 == the first destination word for masking back in	   t1 == the first source word.  */	/* Create the 1st output word and detect 0's in the 1st input word.  */	lda	t2, -1		# e1    : build a mask against false zero	mskqh	t2, a1, t2	# e0    :   detection in the src word	mskqh	t1, a1, t3	# e0    :	ornot	t1, t2, t2	# .. e1 :	mskql	t0, a1, t0	# e0    : assemble the first output word	cmpbge	zero, t2, t8	# .. e1 : bits set iff null found	or	t0, t3, t1	# e0    :	bne	t8, $a_eos	# .. e1 :	/* On entry to this basic block:	   t0 == the first destination word for masking back in	   t1 == a source word not containing a null.  */$a_loop:	stq_u	t1, 0(a0)	# e0    :	addq	a0, 8, a0	# .. e1 :	ldq_u	t1, 0(a1)	# e0    :	addq	a1, 8, a1	# .. e1 :	cmpbge	zero, t1, t8	# e0 (stall)	beq	t8, $a_loop	# .. e1 (zdb)	/* Take care of the final (partial) word store.	   On entry to this basic block we have:	   t1 == the source word containing the null	   t8 == the cmpbge mask that found it.  */$a_eos:	negq	t8, t6		# e0    : find low bit set	and	t8, t6, t12	# e1 (stall)	/* For the sake of the cache, don't read a destination word	   if we're not going to need it.  */	and	t12, 0x80, t6	# e0    :	bne	t6, 1f		# .. e1 (zdb)	/* We're doing a partial word store and so need to combine	   our source and original destination words.  */	ldq_u	t0, 0(a0)	# e0    :	subq	t12, 1, t6	# .. e1 :	zapnot	t1, t6, t1	# e0    : clear src bytes >= null	or	t12, t6, t8	# .. e1 :	zap	t0, t8, t0	# e0    : clear dst bytes <= null	or	t0, t1, t1	# e1    :1:	stq_u	t1, 0(a0)	# e0    :	ret	(t9)		# .. e1 :	.end stxcpy_aligned	.align 3	.ent __stxcpy	.globl __stxcpy__stxcpy:	.frame sp, 0, t9	.prologue 0	/* Are source and destination co-aligned?  */	xor	a0, a1, t0	# e0    :	unop			#       :	and	t0, 7, t0	# e0    :	bne	t0, $unaligned	# .. e1 :	/* We are co-aligned; take care of a partial first word.  */	ldq_u	t1, 0(a1)	# e0    : load first src word	and	a0, 7, t0	# .. e1 : take care not to load a word ...	addq	a1, 8, a1		# e0    :	beq	t0, stxcpy_aligned	# .. e1 : ... if we wont need it	ldq_u	t0, 0(a0)	# e0    :	br	stxcpy_aligned	# .. e1 :/* The source and destination are not co-aligned.  Align the destination   and cope.  We have to be very careful about not reading too much and   causing a SEGV.  */	.align 3$u_head:	/* We know just enough now to be able to assemble the first	   full source word.  We can still find a zero at the end of it	   that prevents us from outputting the whole thing.	   On entry to this basic block:	   t0 == the first dest word, for masking back in, if needed else 0	   t1 == the low bits of the first source word	   t6 == bytemask that is -1 in dest word bytes */	ldq_u	t2, 8(a1)	# e0    :	addq	a1, 8, a1	# .. e1 :	extql	t1, a1, t1	# e0    :	extqh	t2, a1, t4	# e0    :	mskql	t0, a0, t0	# e0    :	or	t1, t4, t1	# .. e1 :	mskqh	t1, a0, t1	# e0    :	or	t0, t1, t1	# e1    :	or	t1, t6, t6	# e0    :	cmpbge	zero, t6, t8	# .. e1 :	lda	t6, -1		# e0    : for masking just below	bne	t8, $u_final	# .. e1 :	mskql	t6, a1, t6		# e0    : mask out the bits we have	or	t6, t2, t2		# e1    :   already extracted before	cmpbge	zero, t2, t8		# e0    :   testing eos	bne	t8, $u_late_head_exit	# .. e1 (zdb)	/* Finally, we've got all the stupid leading edge cases taken care	   of and we can set up to enter the main loop.  */	stq_u	t1, 0(a0)	# e0    : store first output word	addq	a0, 8, a0	# .. e1 :	extql	t2, a1, t0	# e0    : position ho-bits of lo word	ldq_u	t2, 8(a1)	# .. e1 : read next high-order source word	addq	a1, 8, a1	# e0    :	cmpbge	zero, t2, t8	# .. e1 :	nop			# e0    :	bne	t8, $u_eos	# .. e1 :	/* Unaligned copy main loop.  In order to avoid reading too much,	   the loop is structured to detect zeros in aligned source words.	   This has, unfortunately, effectively pulled half of a loop	   iteration out into the head and half into the tail, but it does	   prevent nastiness from accumulating in the very thing we want	   to run as fast as possible.	   On entry to this basic block:	   t0 == the shifted high-order bits from the previous source word	   t2 == the unshifted current source word	   We further know that t2 does not contain a null terminator.  */	.align 3$u_loop:	extqh	t2, a1, t1	# e0    : extract high bits for current word	addq	a1, 8, a1	# .. e1 :	extql	t2, a1, t3	# e0    : extract low bits for next time	addq	a0, 8, a0	# .. e1 :	or	t0, t1, t1	# e0    : current dst word now complete	ldq_u	t2, 0(a1)	# .. e1 : load high word for next time	stq_u	t1, -8(a0)	# e0    : save the current word	mov	t3, t0		# .. e1 :	cmpbge	zero, t2, t8	# e0    : test new word for eos	beq	t8, $u_loop	# .. e1 :	/* We've found a zero somewhere in the source word we just read.	   If it resides in the lower half, we have one (probably partial)	   word to write out, and if it resides in the upper half, we	   have one full and one partial word left to write out.	   On entry to this basic block:	   t0 == the shifted high-order bits from the previous source word	   t2 == the unshifted current source word.  */$u_eos:	extqh	t2, a1, t1	# e0    :	or	t0, t1, t1	# e1    : first (partial) source word complete	cmpbge	zero, t1, t8	# e0    : is the null in this first bit?	bne	t8, $u_final	# .. e1 (zdb)$u_late_head_exit:	stq_u	t1, 0(a0)	# e0    : the null was in the high-order bits	addq	a0, 8, a0	# .. e1 :	extql	t2, a1, t1	# e0    :	cmpbge	zero, t1, t8	# .. e1 :	/* Take care of a final (probably partial) result word.	   On entry to this basic block:	   t1 == assembled source word	   t8 == cmpbge mask that found the null.  */$u_final:	negq	t8, t6		# e0    : isolate low bit set	and	t6, t8, t12	# e1    :	and	t12, 0x80, t6	# e0    : avoid dest word load if we can	bne	t6, 1f		# .. e1 (zdb)	ldq_u	t0, 0(a0)	# e0    :	subq	t12, 1, t6	# .. e1 :	or	t6, t12, t8	# e0    :	zapnot	t1, t6, t1	# .. e1 : kill source bytes >= null	zap	t0, t8, t0	# e0    : kill dest bytes <= null	or	t0, t1, t1	# e1    :1:	stq_u	t1, 0(a0)	# e0    :	ret	(t9)		# .. e1 :	/* Unaligned copy entry point.  */	.align 3$unaligned:	ldq_u	t1, 0(a1)	# e0    : load first source word	and	a0, 7, t4	# .. e1 : find dest misalignment	and	a1, 7, t5	# e0    : find src misalignment	/* Conditionally load the first destination word and a bytemask	   with 0xff indicating that the destination byte is sacrosanct.  */	mov	zero, t0	# .. e1 :	mov	zero, t6	# e0    :	beq	t4, 1f		# .. e1 :	ldq_u	t0, 0(a0)	# e0    :	lda	t6, -1		# .. e1 :	mskql	t6, a0, t6	# e0    :1:	subq	a1, t4, a1	# .. e1 : sub dest misalignment from src addr	/* If source misalignment is larger than dest misalignment, we need	   extra startup checks to avoid SEGV.  */	cmplt	t4, t5, t12	# e0    :	beq	t12, $u_head	# .. e1 (zdb)	lda	t2, -1		# e1    : mask out leading garbage in source	mskqh	t2, t5, t2	# e0    :	nop			# e0    :	ornot	t1, t2, t3	# .. e1 :	cmpbge	zero, t3, t8	# e0    : is there a zero?	beq	t8, $u_head	# .. e1 (zdb)	/* At this point we've found a zero in the first partial word of	   the source.  We need to isolate the valid source data and mask	   it into the original destination data.  (Incidentally, we know	   that we'll need at least one byte of that original dest word.) */	ldq_u	t0, 0(a0)	# e0    :	negq	t8, t6		# .. e1 : build bitmask of bytes <= zero	and	t6, t8, t12	# e0    :	and	a1, 7, t5	# .. e1 :	subq	t12, 1, t6	# e0    :	or	t6, t12, t8	# e1    :	srl	t12, t5, t12	# e0    : adjust final null return value	zapnot	t2, t8, t2	# .. e1 : prepare source word; mirror changes	and	t1, t2, t1	# e1    : to source validity mask	extql	t2, a1, t2	# .. e0 :	extql	t1, a1, t1	# e0    :	andnot	t0, t2, t0	# .. e1 : zero place for source to reside	or	t0, t1, t1	# e1    : and put it there	stq_u	t1, 0(a0)	# .. e0 :	ret	(t9)		# e1    :	.end __stxcpy