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Diffstat (limited to 'arch/ia64/lib/strlen.S')
| -rw-r--r-- | arch/ia64/lib/strlen.S | 195 |
1 files changed, 0 insertions, 195 deletions
diff --git a/arch/ia64/lib/strlen.S b/arch/ia64/lib/strlen.S deleted file mode 100644 index 1f4a46c151..0000000000 --- a/arch/ia64/lib/strlen.S +++ /dev/null @@ -1,195 +0,0 @@ -/* SPDX-License-Identifier: GPL-2.0 */ -/* - * - * Optimized version of the standard strlen() function - * - * - * Inputs: - * in0 address of string - * - * Outputs: - * ret0 the number of characters in the string (0 if empty string) - * does not count the \0 - * - * Copyright (C) 1999, 2001 Hewlett-Packard Co - * Stephane Eranian <eranian@hpl.hp.com> - * - * 09/24/99 S.Eranian add speculation recovery code - */ - -#include <linux/export.h> -#include <asm/asmmacro.h> - -// -// -// This is an enhanced version of the basic strlen. it includes a combination -// of compute zero index (czx), parallel comparisons, speculative loads and -// loop unroll using rotating registers. -// -// General Ideas about the algorithm: -// The goal is to look at the string in chunks of 8 bytes. -// so we need to do a few extra checks at the beginning because the -// string may not be 8-byte aligned. In this case we load the 8byte -// quantity which includes the start of the string and mask the unused -// bytes with 0xff to avoid confusing czx. -// We use speculative loads and software pipelining to hide memory -// latency and do read ahead safely. This way we defer any exception. -// -// Because we don't want the kernel to be relying on particular -// settings of the DCR register, we provide recovery code in case -// speculation fails. The recovery code is going to "redo" the work using -// only normal loads. If we still get a fault then we generate a -// kernel panic. Otherwise we return the strlen as usual. -// -// The fact that speculation may fail can be caused, for instance, by -// the DCR.dm bit being set. In this case TLB misses are deferred, i.e., -// a NaT bit will be set if the translation is not present. The normal -// load, on the other hand, will cause the translation to be inserted -// if the mapping exists. -// -// It should be noted that we execute recovery code only when we need -// to use the data that has been speculatively loaded: we don't execute -// recovery code on pure read ahead data. -// -// Remarks: -// - the cmp r0,r0 is used as a fast way to initialize a predicate -// register to 1. This is required to make sure that we get the parallel -// compare correct. -// -// - we don't use the epilogue counter to exit the loop but we need to set -// it to zero beforehand. -// -// - after the loop we must test for Nat values because neither the -// czx nor cmp instruction raise a NaT consumption fault. We must be -// careful not to look too far for a Nat for which we don't care. -// For instance we don't need to look at a NaT in val2 if the zero byte -// was in val1. -// -// - Clearly performance tuning is required. -// -// -// -#define saved_pfs r11 -#define tmp r10 -#define base r16 -#define orig r17 -#define saved_pr r18 -#define src r19 -#define mask r20 -#define val r21 -#define val1 r22 -#define val2 r23 - -GLOBAL_ENTRY(strlen) - .prologue - .save ar.pfs, saved_pfs - alloc saved_pfs=ar.pfs,11,0,0,8 // rotating must be multiple of 8 - - .rotr v[2], w[2] // declares our 4 aliases - - extr.u tmp=in0,0,3 // tmp=least significant 3 bits - mov orig=in0 // keep trackof initial byte address - dep src=0,in0,0,3 // src=8byte-aligned in0 address - .save pr, saved_pr - mov saved_pr=pr // preserve predicates (rotation) - ;; - - .body - - ld8 v[1]=[src],8 // must not speculate: can fail here - shl tmp=tmp,3 // multiply by 8bits/byte - mov mask=-1 // our mask - ;; - ld8.s w[1]=[src],8 // speculatively load next - cmp.eq p6,p0=r0,r0 // sets p6 to true for cmp.and - sub tmp=64,tmp // how many bits to shift our mask on the right - ;; - shr.u mask=mask,tmp // zero enough bits to hold v[1] valuable part - mov ar.ec=r0 // clear epilogue counter (saved in ar.pfs) - ;; - add base=-16,src // keep track of aligned base - or v[1]=v[1],mask // now we have a safe initial byte pattern - ;; -1: - ld8.s v[0]=[src],8 // speculatively load next - czx1.r val1=v[1] // search 0 byte from right - czx1.r val2=w[1] // search 0 byte from right following 8bytes - ;; - ld8.s w[0]=[src],8 // speculatively load next to next - cmp.eq.and p6,p0=8,val1 // p6 = p6 and val1==8 - cmp.eq.and p6,p0=8,val2 // p6 = p6 and mask==8 -(p6) br.wtop.dptk 1b // loop until p6 == 0 - ;; - // - // We must return try the recovery code iff - // val1_is_nat || (val1==8 && val2_is_nat) - // - // XXX Fixme - // - there must be a better way of doing the test - // - cmp.eq p8,p9=8,val1 // p6 = val1 had zero (disambiguate) - tnat.nz p6,p7=val1 // test NaT on val1 -(p6) br.cond.spnt .recover // jump to recovery if val1 is NaT - ;; - // - // if we come here p7 is true, i.e., initialized for // cmp - // - cmp.eq.and p7,p0=8,val1// val1==8? - tnat.nz.and p7,p0=val2 // test NaT if val2 -(p7) br.cond.spnt .recover // jump to recovery if val2 is NaT - ;; -(p8) mov val1=val2 // the other test got us out of the loop -(p8) adds src=-16,src // correct position when 3 ahead -(p9) adds src=-24,src // correct position when 4 ahead - ;; - sub ret0=src,orig // distance from base - sub tmp=8,val1 // which byte in word - mov pr=saved_pr,0xffffffffffff0000 - ;; - sub ret0=ret0,tmp // adjust - mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what - br.ret.sptk.many rp // end of normal execution - - // - // Outlined recovery code when speculation failed - // - // This time we don't use speculation and rely on the normal exception - // mechanism. that's why the loop is not as good as the previous one - // because read ahead is not possible - // - // IMPORTANT: - // Please note that in the case of strlen() as opposed to strlen_user() - // we don't use the exception mechanism, as this function is not - // supposed to fail. If that happens it means we have a bug and the - // code will cause of kernel fault. - // - // XXX Fixme - // - today we restart from the beginning of the string instead - // of trying to continue where we left off. - // -.recover: - ld8 val=[base],8 // will fail if unrecoverable fault - ;; - or val=val,mask // remask first bytes - cmp.eq p0,p6=r0,r0 // nullify first ld8 in loop - ;; - // - // ar.ec is still zero here - // -2: -(p6) ld8 val=[base],8 // will fail if unrecoverable fault - ;; - czx1.r val1=val // search 0 byte from right - ;; - cmp.eq p6,p0=8,val1 // val1==8 ? -(p6) br.wtop.dptk 2b // loop until p6 == 0 - ;; // (avoid WAW on p63) - sub ret0=base,orig // distance from base - sub tmp=8,val1 - mov pr=saved_pr,0xffffffffffff0000 - ;; - sub ret0=ret0,tmp // length=now - back -1 - mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what - br.ret.sptk.many rp // end of successful recovery code -END(strlen) -EXPORT_SYMBOL(strlen) |