patch-2.4.0-test12 linux/arch/alpha/lib/ev6-strncpy_from_user.S

• Lines: 426
• Date: Sun Dec 3 17:45:20 2000
• Orig file: v2.4.0-test11/linux/arch/alpha/lib/ev6-strncpy_from_user.S
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.0-test11/linux/arch/alpha/lib/ev6-strncpy_from_user.S linux/arch/alpha/lib/ev6-strncpy_from_user.S
@@ -0,0 +1,425 @@
+/*
+ * arch/alpha/lib/ev6-strncpy_from_user.S
+ * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
+ *
+ * Just like strncpy except in the return value:
+ *
+ * -EFAULT       if an exception occurs before the terminator is copied.
+ * N             if the buffer filled.
+ *
+ * Otherwise the length of the string is returned.
+ *
+ * Much of the information about 21264 scheduling/coding comes from:
+ *	Compiler Writer's Guide for the Alpha 21264
+ *	abbreviated as 'CWG' in other comments here
+ *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
+ * Scheduling notation:
+ *	E	- either cluster
+ *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
+ *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
+ * A bunch of instructions got moved and temp registers were changed
+ * to aid in scheduling.  Control flow was also re-arranged to eliminate
+ * branches, and to provide longer code sequences to enable better scheduling.
+ * A total rewrite (using byte load/stores for start & tail sequences)
+ * is desirable, but very difficult to do without a from-scratch rewrite.
+ * Save that for the future.
+ */
+
+
+#include <asm/errno.h>
+#include <alpha/regdef.h>
+
+
+/* Allow an exception for an insn; exit if we get one.  */
+#define EX(x,y...)			\
+	99: x,##y;			\
+	.section __ex_table,"a";	\
+	.gprel32 99b;			\
+	lda $31, $exception-99b($0); 	\
+	.previous
+
+
+	.set noat
+	.set noreorder
+	.text
+
+	.globl __strncpy_from_user
+	.ent __strncpy_from_user
+	.frame $30, 0, $26
+	.prologue 1
+
+	.align 4
+__strncpy_from_user:
+	ldgp	$29, 0($27)	# E E : becomes 2 instructions (for exceptions)
+	and	a0, 7, t3	# E : find dest misalignment
+	beq	a2, $zerolength	# U :
+
+	/* Are source and destination co-aligned?  */
+	mov	a0, v0		# E : save the string start
+	xor	a0, a1, t4	# E :
+	EX( ldq_u t1, 0(a1) )	# L : Latency=3 load first quadword
+	ldq_u	t0, 0(a0)	# L : load first (partial) aligned dest quadword
+
+	addq	a2, t3, a2	# E : bias count by dest misalignment
+	subq	a2, 1, a3	# E :
+	addq	zero, 1, t10	# E :
+	and	t4, 7, t4	# E : misalignment between the two
+
+	and	a3, 7, t6	# E : number of tail bytes
+	sll	t10, t6, t10	# E : t10 = bitmask of last count byte
+	bne	t4, $unaligned	# U :
+	lda	t2, -1		# E : build a mask against false zero
+
+	/*
+	 * We are co-aligned; take care of a partial first word.
+	 * On entry to this basic block:
+	 * t0 == the first destination word for masking back in
+	 * t1 == the first source word.
+	 */
+
+	srl	a3, 3, a2	# E : a2 = loop counter = (count - 1)/8
+	addq	a1, 8, a1	# E :
+	mskqh	t2, a1, t2	# U :   detection in the src word
+	nop
+
+	/* Create the 1st output word and detect 0's in the 1st input word.  */
+	mskqh	t1, a1, t3	# U :
+	mskql	t0, a1, t0	# U : assemble the first output word
+	ornot	t1, t2, t2	# E :
+	nop
+
+	cmpbge	zero, t2, t8	# E : bits set iff null found
+	or	t0, t3, t0	# E :
+	beq	a2, $a_eoc	# U :
+	bne	t8, $a_eos	# U : 2nd branch in a quad.  Bad.
+
+	/* On entry to this basic block:
+	 * t0 == a source quad not containing a null.
+	 * a0 - current aligned destination address
+	 * a1 - current aligned source address
+	 * a2 - count of quadwords to move.
+	 * NOTE: Loop improvement - unrolling this is going to be
+	 *	a huge win, since we're going to stall otherwise.
+	 *	Fix this later.  For _really_ large copies, look
+	 *	at using wh64 on a look-ahead basis.  See the code
+	 *	in clear_user.S and copy_user.S.
+	 * Presumably, since (a0) and (a1) do not overlap (by C definition)
+	 * Lots of nops here:
+	 *	- Separate loads from stores
+	 *	- Keep it to 1 branch/quadpack so the branch predictor
+	 *	  can train.
+	 */
+$a_loop:
+	stq_u	t0, 0(a0)	# L :
+	addq	a0, 8, a0	# E :
+	nop
+	subq	a2, 1, a2	# E :
+
+	EX( ldq_u t0, 0(a1) )	# L :
+	addq	a1, 8, a1	# E :
+	cmpbge	zero, t0, t8	# E : Stall 2 cycles on t0
+	beq	a2, $a_eoc      # U :
+
+	beq	t8, $a_loop	# U :
+	nop
+	nop
+	nop
+
+	/* Take care of the final (partial) word store.  At this point
+	 * the end-of-count bit is set in t8 iff it applies.
+	 *
+	 * On entry to this basic block we have:
+	 * t0 == the source word containing the null
+	 * t8 == the cmpbge mask that found it.
+	 */
+$a_eos:
+	negq	t8, t12		# E : find low bit set
+	and	t8, t12, t12	# E : 
+
+	/* We're doing a partial word store and so need to combine
+	   our source and original destination words.  */
+	ldq_u	t1, 0(a0)	# L :
+	subq	t12, 1, t6	# E :
+
+	or	t12, t6, t8	# E :
+	zapnot	t0, t8, t0	# U : clear src bytes > null
+	zap	t1, t8, t1	# U : clear dst bytes <= null
+	or	t0, t1, t0	# E :
+
+	stq_u	t0, 0(a0)	# L :
+	br	$finish_up	# L0 :
+	nop
+	nop
+
+	/* Add the end-of-count bit to the eos detection bitmask.  */
+	.align 4
+$a_eoc:
+	or	t10, t8, t8
+	br	$a_eos
+	nop
+	nop
+
+
+/* The source and destination are not co-aligned.  Align the destination
+   and cope.  We have to be very careful about not reading too much and
+   causing a SEGV.  */
+
+	.align 4
+$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, unmasked
+	   t1 == the shifted low bits of the first source word
+	   t6 == bytemask that is -1 in dest word bytes */
+
+	EX( ldq_u t2, 8(a1) )	# L : load second src word
+	addq	a1, 8, a1	# E :
+	mskql	t0, a0, t0	# U : mask trailing garbage in dst
+	extqh	t2, a1, t4	# U :
+
+	or	t1, t4, t1	# E : first aligned src word complete
+	mskqh	t1, a0, t1	# U : mask leading garbage in src
+	or	t0, t1, t0	# E : first output word complete
+	or	t0, t6, t6	# E : mask original data for zero test
+
+	cmpbge	zero, t6, t8	# E :
+	beq	a2, $u_eocfin	# U :
+	bne	t8, $u_final	# U : bad news - 2nd branch in a quad
+	lda	t6, -1		# E : mask out the bits we have
+
+	mskql	t6, a1, t6	# U :   already seen
+	stq_u	t0, 0(a0)	# L : store first output word
+	or      t6, t2, t2	# E :
+	cmpbge	zero, t2, t8	# E : find nulls in second partial
+
+	addq	a0, 8, a0		# E :
+	subq	a2, 1, a2		# E :
+	bne	t8, $u_late_head_exit	# U :
+	nop
+
+	/* Finally, we've got all the stupid leading edge cases taken care
+	   of and we can set up to enter the main loop.  */
+
+	extql	t2, a1, t1	# U : position hi-bits of lo word
+	EX( ldq_u t2, 8(a1) )	# L : read next high-order source word
+	addq	a1, 8, a1	# E :
+	cmpbge	zero, t2, t8	# E :
+
+	beq	a2, $u_eoc	# U :
+	bne	t8, $u_eos	# U :
+	nop
+	nop
+
+	/* Unaligned copy main loop.  In order to avoid reading too much,
+	   the loop is structured to detect zeros in aligned source words.
+	   This has, unfortunately, effectively pulled half of a loop
+	   iteration out into the head and half into the tail, but it does
+	   prevent nastiness from accumulating in the very thing we want
+	   to run as fast as possible.
+
+	   On entry to this basic block:
+	   t1 == the shifted high-order bits from the previous source word
+	   t2 == the unshifted current source word
+
+	   We further know that t2 does not contain a null terminator.  */
+
+	/*
+	 * Extra nops here:
+	 *	separate load quads from store quads
+	 *	only one branch/quad to permit predictor training
+	 */
+
+	.align 4
+$u_loop:
+	extqh	t2, a1, t0	# U : extract high bits for current word
+	addq	a1, 8, a1	# E :
+	extql	t2, a1, t3	# U : extract low bits for next time
+	addq	a0, 8, a0	# E :
+
+	or	t0, t1, t0	# E : current dst word now complete
+	EX( ldq_u t2, 0(a1) )	# L : load high word for next time
+	subq	a2, 1, a2	# E :
+	nop
+
+	stq_u	t0, -8(a0)	# L : save the current word
+	mov	t3, t1		# E :
+	cmpbge	zero, t2, t8	# E : test new word for eos
+	beq	a2, $u_eoc	# U :
+
+	beq	t8, $u_loop	# U :
+	nop
+	nop
+	nop
+
+	/* We've found a zero somewhere in the source word we just read.
+	   If it resides in the lower half, we have one (probably partial)
+	   word to write out, and if it resides in the upper half, we
+	   have one full and one partial word left to write out.
+
+	   On entry to this basic block:
+	   t1 == the shifted high-order bits from the previous source word
+	   t2 == the unshifted current source word.  */
+	.align 4
+$u_eos:
+	extqh	t2, a1, t0	# U :
+	or	t0, t1, t0	# E : first (partial) source word complete
+	cmpbge	zero, t0, t8	# E : is the null in this first bit?
+	nop
+
+	bne	t8, $u_final	# U :
+	stq_u	t0, 0(a0)	# L : the null was in the high-order bits
+	addq	a0, 8, a0	# E :
+	subq	a2, 1, a2	# E :
+
+	.align 4
+$u_late_head_exit:
+	extql	t2, a1, t0	# U :
+	cmpbge	zero, t0, t8	# E :
+	or	t8, t10, t6	# E :
+	cmoveq	a2, t6, t8	# E :
+
+	/* Take care of a final (probably partial) result word.
+	   On entry to this basic block:
+	   t0 == assembled source word
+	   t8 == cmpbge mask that found the null.  */
+	.align 4
+$u_final:
+	negq	t8, t6		# E : isolate low bit set
+	and	t6, t8, t12	# E :
+	ldq_u	t1, 0(a0)	# L :
+	subq	t12, 1, t6	# E :
+
+	or	t6, t12, t8	# E :
+	zapnot	t0, t8, t0	# U : kill source bytes > null
+	zap	t1, t8, t1	# U : kill dest bytes <= null
+	or	t0, t1, t0	# E :
+
+	stq_u	t0, 0(a0)	# E :
+	br	$finish_up	# U :
+	nop
+	nop
+
+	.align 4
+$u_eoc:				# end-of-count
+	extqh	t2, a1, t0	# U :
+	or	t0, t1, t0	# E :
+	cmpbge	zero, t0, t8	# E :
+	nop
+
+	.align 4
+$u_eocfin:			# end-of-count, final word
+	or	t10, t8, t8	# E :
+	br	$u_final	# U :
+	nop
+	nop
+
+	/* Unaligned copy entry point.  */
+	.align 4
+$unaligned:
+
+	srl	a3, 3, a2	# U : a2 = loop counter = (count - 1)/8
+	and	a0, 7, t4	# E : find dest misalignment
+	and	a1, 7, t5	# E : find src misalignment
+	mov	zero, t0	# E :
+
+	/* Conditionally load the first destination word and a bytemask
+	   with 0xff indicating that the destination byte is sacrosanct.  */
+
+	mov	zero, t6	# E :
+	beq	t4, 1f		# U :
+	ldq_u	t0, 0(a0)	# L :
+	lda	t6, -1		# E :
+
+	mskql	t6, a0, t6	# E :
+	nop
+	nop
+	nop
+
+	.align 4
+1:
+	subq	a1, t4, a1	# E : 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	# E :
+	extql	t1, a1, t1	# U : shift src into place
+	lda	t2, -1		# E : for creating masks later
+
+	beq	t12, $u_head	# U :
+	mskqh	t2, t5, t2	# U : begin src byte validity mask
+	cmpbge	zero, t1, t8	# E : is there a zero?
+	nop
+
+	extql	t2, a1, t2	# U :
+	or	t8, t10, t5	# E : test for end-of-count too
+	cmpbge	zero, t2, t3	# E :
+	cmoveq	a2, t5, t8	# E : Latency=2, extra map slot
+
+	nop			# E : goes with cmov
+	andnot	t8, t3, t8	# E :
+	beq	t8, $u_head	# U :
+	nop
+
+	/* At this point we've found a zero in the first partial word of
+	   the source.  We need to isolate the valid source data and mask
+	   it into the original destination data.  (Incidentally, we know
+	   that we'll need at least one byte of that original dest word.) */
+
+	ldq_u	t0, 0(a0)	# L :
+	negq	t8, t6		# E : build bitmask of bytes <= zero
+	mskqh	t1, t4, t1	# U :
+	and	t6, t8, t12	# E :
+
+	subq	t12, 1, t6	# E :
+	or	t6, t12, t8	# E :
+	zapnot	t2, t8, t2	# U : prepare source word; mirror changes
+	zapnot	t1, t8, t1	# U : to source validity mask
+
+	andnot	t0, t2, t0	# E : zero place for source to reside
+	or	t0, t1, t0	# E : and put it there
+	stq_u	t0, 0(a0)	# L :
+	nop
+
+	.align 4
+$finish_up:
+	zapnot	t0, t12, t4	# U : was last byte written null?
+	and	t12, 0xf0, t3	# E : binary search for the address of the
+	cmovne	t4, 1, t4	# E : Latency=2, extra map slot
+	nop			# E : with cmovne
+
+	and	t12, 0xcc, t2	# E : last byte written
+	and	t12, 0xaa, t1	# E :
+	cmovne	t3, 4, t3	# E : Latency=2, extra map slot
+	nop			# E : with cmovne
+
+	bic	a0, 7, t0
+	cmovne	t2, 2, t2	# E : Latency=2, extra map slot
+	nop			# E : with cmovne
+	nop
+
+	cmovne	t1, 1, t1	# E : Latency=2, extra map slot
+	nop			# E : with cmovne
+	addq	t0, t3, t0	# E :
+	addq	t1, t2, t1	# E :
+
+	addq	t0, t1, t0	# E :
+	addq	t0, t4, t0	# add one if we filled the buffer
+	subq	t0, v0, v0	# find string length
+	ret			# L0 :
+
+	.align 4
+$zerolength:
+	nop
+	nop
+	nop
+	clr	v0
+
+$exception:
+	nop
+	nop
+	nop
+	ret
+
+	.end __strncpy_from_user