/* SPDX-License-Identifier: GPL-2.0 */ /* * arch/alpha/lib/ev6-copy_user.S * * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> * * Copy to/from user space, handling exceptions as we go.. This * isn't exactly pretty. * * This is essentially the same as "memcpy()", but with a few twists. * Notably, we have to make sure that $0 is always up-to-date and * contains the right "bytes left to copy" value (and that it is updated * only _after_ a successful copy). There is also some rather minor * exception setup stuff.. * * 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 */ #include <linux/export.h> /* Allow an exception for an insn; exit if we get one. */ #define EXI(x,y...) \ 99: x,##y; \ .section __ex_table,"a"; \ .long 99b - .; \ lda $31, $exitin-99b($31); \ .previous #define EXO(x,y...) \ 99: x,##y; \ .section __ex_table,"a"; \ .long 99b - .; \ lda $31, $exitout-99b($31); \ .previous .set noat .align 4 .globl __copy_user .ent __copy_user # Pipeline info: Slotting & Comments __copy_user: .prologue 0 mov $18, $0 # .. .. .. E subq $18, 32, $1 # .. .. E. .. : Is this going to be a small copy? nop # .. E .. .. beq $18, $zerolength # U .. .. .. : U L U L and $16,7,$3 # .. .. .. E : is leading dest misalignment ble $1, $onebyteloop # .. .. U .. : 1st branch : small amount of data beq $3, $destaligned # .. U .. .. : 2nd (one cycle fetcher stall) subq $3, 8, $3 # E .. .. .. : L U U L : trip counter /* * The fetcher stall also hides the 1 cycle cross-cluster stall for $3 (L --> U) * This loop aligns the destination a byte at a time * We know we have at least one trip through this loop */ $aligndest: EXI( ldbu $1,0($17) ) # .. .. .. L : Keep loads separate from stores addq $16,1,$16 # .. .. E .. : Section 3.8 in the CWG addq $3,1,$3 # .. E .. .. : nop # E .. .. .. : U L U L /* * the -1 is to compensate for the inc($16) done in a previous quadpack * which allows us zero dependencies within either quadpack in the loop */ EXO( stb $1,-1($16) ) # .. .. .. L : addq $17,1,$17 # .. .. E .. : Section 3.8 in the CWG subq $0,1,$0 # .. E .. .. : bne $3, $aligndest # U .. .. .. : U L U L /* * If we fell through into here, we have a minimum of 33 - 7 bytes * If we arrived via branch, we have a minimum of 32 bytes */ $destaligned: and $17,7,$1 # .. .. .. E : Check _current_ source alignment bic $0,7,$4 # .. .. E .. : number bytes as a quadword loop EXI( ldq_u $3,0($17) ) # .. L .. .. : Forward fetch for fallthrough code beq $1,$quadaligned # U .. .. .. : U L U L /* * In the worst case, we've just executed an ldq_u here from 0($17) * and we'll repeat it once if we take the branch */ /* Misaligned quadword loop - not unrolled. Leave it that way. */ $misquad: EXI( ldq_u $2,8($17) ) # .. .. .. L : subq $4,8,$4 # .. .. E .. : extql $3,$17,$3 # .. U .. .. : extqh $2,$17,$1 # U .. .. .. : U U L L bis $3,$1,$1 # .. .. .. E : EXO( stq $1,0($16) ) # .. .. L .. : addq $17,8,$17 # .. E .. .. : subq $0,8,$0 # E .. .. .. : U L L U addq $16,8,$16 # .. .. .. E : bis $2,$2,$3 # .. .. E .. : nop # .. E .. .. : bne $4,$misquad # U .. .. .. : U L U L nop # .. .. .. E nop # .. .. E .. nop # .. E .. .. beq $0,$zerolength # U .. .. .. : U L U L /* We know we have at least one trip through the byte loop */ EXI ( ldbu $2,0($17) ) # .. .. .. L : No loads in the same quad addq $16,1,$16 # .. .. E .. : as the store (Section 3.8 in CWG) nop # .. E .. .. : br $31, $dirtyentry # L0 .. .. .. : L U U L /* Do the trailing byte loop load, then hop into the store part of the loop */ /* * A minimum of (33 - 7) bytes to do a quad at a time. * Based upon the usage context, it's worth the effort to unroll this loop * $0 - number of bytes to be moved * $4 - number of bytes to move as quadwords * $16 is current destination address * $17 is current source address */ $quadaligned: subq $4, 32, $2 # .. .. .. E : do not unroll for small stuff nop # .. .. E .. nop # .. E .. .. blt $2, $onequad # U .. .. .. : U L U L /* * There is a significant assumption here that the source and destination * addresses differ by more than 32 bytes. In this particular case, a * sparsity of registers further bounds this to be a minimum of 8 bytes. * But if this isn't met, then the output result will be incorrect. * Furthermore, due to a lack of available registers, we really can't * unroll this to be an 8x loop (which would enable us to use the wh64 * instruction memory hint instruction). */ $unroll4: EXI( ldq $1,0($17) ) # .. .. .. L EXI( ldq $2,8($17) ) # .. .. L .. subq $4,32,$4 # .. E .. .. nop # E .. .. .. : U U L L addq $17,16,$17 # .. .. .. E EXO( stq $1,0($16) ) # .. .. L .. EXO( stq $2,8($16) ) # .. L .. .. subq $0,16,$0 # E .. .. .. : U L L U addq $16,16,$16 # .. .. .. E EXI( ldq $1,0($17) ) # .. .. L .. EXI( ldq $2,8($17) ) # .. L .. .. subq $4, 32, $3 # E .. .. .. : U U L L : is there enough for another trip? EXO( stq $1,0($16) ) # .. .. .. L EXO( stq $2,8($16) ) # .. .. L .. subq $0,16,$0 # .. E .. .. addq $17,16,$17 # E .. .. .. : U L L U nop # .. .. .. E nop # .. .. E .. addq $16,16,$16 # .. E .. .. bgt $3,$unroll4 # U .. .. .. : U L U L nop nop nop beq $4, $noquads $onequad: EXI( ldq $1,0($17) ) subq $4,8,$4 addq $17,8,$17 nop EXO( stq $1,0($16) ) subq $0,8,$0 addq $16,8,$16 bne $4,$onequad $noquads: nop nop nop beq $0,$zerolength /* * For small copies (or the tail of a larger copy), do a very simple byte loop. * There's no point in doing a lot of complex alignment calculations to try to * to quadword stuff for a small amount of data. * $0 - remaining number of bytes left to copy * $16 - current dest addr * $17 - current source addr */ $onebyteloop: EXI ( ldbu $2,0($17) ) # .. .. .. L : No loads in the same quad addq $16,1,$16 # .. .. E .. : as the store (Section 3.8 in CWG) nop # .. E .. .. : nop # E .. .. .. : U L U L $dirtyentry: /* * the -1 is to compensate for the inc($16) done in a previous quadpack * which allows us zero dependencies within either quadpack in the loop */ EXO ( stb $2,-1($16) ) # .. .. .. L : addq $17,1,$17 # .. .. E .. : quadpack as the load subq $0,1,$0 # .. E .. .. : change count _after_ copy bgt $0,$onebyteloop # U .. .. .. : U L U L $zerolength: $exitin: $exitout: # Destination for exception recovery(?) nop # .. .. .. E nop # .. .. E .. nop # .. E .. .. ret $31,($26),1 # L0 .. .. .. : L U L U .end __copy_user EXPORT_SYMBOL(__copy_user)