linux/arch/alpha/lib/ev6-strncpy_from_user.S

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/*
* 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 <asm/regdef.h>
/* Allow an exception for an insn; exit if we get one. */
#define EX(x,y...) \
99: x,##y; \
.section __ex_table,"a"; \
.long 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 0
.align 4
__strncpy_from_user:
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