diff options
Diffstat (limited to 'arch/alpha/lib/ev6-strncpy_from_user.S')
| -rw-r--r-- | arch/alpha/lib/ev6-strncpy_from_user.S | 424 |
1 files changed, 424 insertions, 0 deletions
diff --git a/arch/alpha/lib/ev6-strncpy_from_user.S b/arch/alpha/lib/ev6-strncpy_from_user.S new file mode 100644 index 000000000000..d2e28178cacc --- /dev/null +++ b/arch/alpha/lib/ev6-strncpy_from_user.S @@ -0,0 +1,424 @@ +/* + * 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 |