mirror of
https://github.com/adulau/aha.git
synced 2024-12-30 12:46:17 +00:00
1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
198 lines
6.5 KiB
ArmAsm
198 lines
6.5 KiB
ArmAsm
/*
|
|
* Optimized version of the strlen_user() function
|
|
*
|
|
* Inputs:
|
|
* in0 address of buffer
|
|
*
|
|
* Outputs:
|
|
* ret0 0 in case of fault, strlen(buffer)+1 otherwise
|
|
*
|
|
* Copyright (C) 1998, 1999, 2001 Hewlett-Packard Co
|
|
* David Mosberger-Tang <davidm@hpl.hp.com>
|
|
* Stephane Eranian <eranian@hpl.hp.com>
|
|
*
|
|
* 01/19/99 S.Eranian heavily enhanced version (see details below)
|
|
* 09/24/99 S.Eranian added speculation recovery code
|
|
*/
|
|
|
|
#include <asm/asmmacro.h>
|
|
|
|
//
|
|
// int strlen_user(char *)
|
|
// ------------------------
|
|
// Returns:
|
|
// - length of string + 1
|
|
// - 0 in case an exception is raised
|
|
//
|
|
// This is an enhanced version of the basic strlen_user. 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 return an
|
|
// error (ret0=0). Otherwise we return the strlen+1 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_user)
|
|
.prologue
|
|
.save ar.pfs, saved_pfs
|
|
alloc saved_pfs=ar.pfs,11,0,0,8
|
|
|
|
.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.s v[1]=[src],8 // load the initial 8bytes (must speculate)
|
|
shl tmp=tmp,3 // multiply by 8bits/byte
|
|
mov mask=-1 // our mask
|
|
;;
|
|
ld8.s w[1]=[src],8 // load next 8 bytes in 2nd pipeline
|
|
cmp.eq p6,p0=r0,r0 // sets p6 (required because of // 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
|
|
chk.s v[1], .recover // if already NaT, then directly skip to recover
|
|
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.few 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 // val2 contains the value
|
|
(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 origin
|
|
sub tmp=7,val1 // 7=8-1 because this strlen returns strlen+1
|
|
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 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
|
|
//
|
|
// XXX Fixme
|
|
// - today we restart from the beginning of the string instead
|
|
// of trying to continue where we left off.
|
|
//
|
|
.recover:
|
|
EX(.Lexit1, ld8 val=[base],8) // load the initial bytes
|
|
;;
|
|
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:
|
|
EX(.Lexit1, (p6) ld8 val=[base],8)
|
|
;;
|
|
czx1.r val1=val // search 0 byte from right
|
|
;;
|
|
cmp.eq p6,p0=8,val1 // val1==8 ?
|
|
(p6) br.wtop.dptk.few 2b // loop until p6 == 0
|
|
;;
|
|
sub ret0=base,orig // distance from base
|
|
sub tmp=7,val1 // 7=8-1 because this strlen returns strlen+1
|
|
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
|
|
|
|
//
|
|
// We failed even on the normal load (called from exception handler)
|
|
//
|
|
.Lexit1:
|
|
mov ret0=0
|
|
mov pr=saved_pr,0xffffffffffff0000
|
|
mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what
|
|
br.ret.sptk.many rp
|
|
END(__strlen_user)
|