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