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@@ -1,200 +0,0 @@
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-/*
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- * Optimized version of the strlen_user() function
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- *
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- * Inputs:
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- * in0 address of buffer
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- *
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- * Outputs:
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- * ret0 0 in case of fault, strlen(buffer)+1 otherwise
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- *
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- * Copyright (C) 1998, 1999, 2001 Hewlett-Packard Co
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- * David Mosberger-Tang <davidm@hpl.hp.com>
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- * Stephane Eranian <eranian@hpl.hp.com>
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- *
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- * 01/19/99 S.Eranian heavily enhanced version (see details below)
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- * 09/24/99 S.Eranian added speculation recovery code
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- */
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-
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-#include <asm/asmmacro.h>
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-#include <asm/export.h>
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-
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-//
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-// int strlen_user(char *)
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-// ------------------------
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-// Returns:
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-// - length of string + 1
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-// - 0 in case an exception is raised
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-//
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-// This is an enhanced version of the basic strlen_user. it includes a
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-// combination of compute zero index (czx), parallel comparisons, speculative
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-// loads and loop unroll using rotating registers.
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-//
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-// General Ideas about the algorithm:
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-// The goal is to look at the string in chunks of 8 bytes.
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-// so we need to do a few extra checks at the beginning because the
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-// string may not be 8-byte aligned. In this case we load the 8byte
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-// quantity which includes the start of the string and mask the unused
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-// bytes with 0xff to avoid confusing czx.
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-// We use speculative loads and software pipelining to hide memory
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-// latency and do read ahead safely. This way we defer any exception.
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-//
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-// Because we don't want the kernel to be relying on particular
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-// settings of the DCR register, we provide recovery code in case
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-// speculation fails. The recovery code is going to "redo" the work using
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-// only normal loads. If we still get a fault then we return an
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-// error (ret0=0). Otherwise we return the strlen+1 as usual.
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-// The fact that speculation may fail can be caused, for instance, by
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-// the DCR.dm bit being set. In this case TLB misses are deferred, i.e.,
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-// a NaT bit will be set if the translation is not present. The normal
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-// load, on the other hand, will cause the translation to be inserted
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-// if the mapping exists.
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-//
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-// It should be noted that we execute recovery code only when we need
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-// to use the data that has been speculatively loaded: we don't execute
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-// recovery code on pure read ahead data.
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-//
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-// Remarks:
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-// - the cmp r0,r0 is used as a fast way to initialize a predicate
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-// register to 1. This is required to make sure that we get the parallel
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-// compare correct.
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-//
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-// - we don't use the epilogue counter to exit the loop but we need to set
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-// it to zero beforehand.
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-//
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-// - after the loop we must test for Nat values because neither the
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-// czx nor cmp instruction raise a NaT consumption fault. We must be
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-// careful not to look too far for a Nat for which we don't care.
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-// For instance we don't need to look at a NaT in val2 if the zero byte
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-// was in val1.
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-//
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-// - Clearly performance tuning is required.
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-//
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-
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-#define saved_pfs r11
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-#define tmp r10
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-#define base r16
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-#define orig r17
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-#define saved_pr r18
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-#define src r19
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-#define mask r20
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-#define val r21
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-#define val1 r22
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-#define val2 r23
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-
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-GLOBAL_ENTRY(__strlen_user)
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- .prologue
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- .save ar.pfs, saved_pfs
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- alloc saved_pfs=ar.pfs,11,0,0,8
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-
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- .rotr v[2], w[2] // declares our 4 aliases
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-
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- extr.u tmp=in0,0,3 // tmp=least significant 3 bits
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- mov orig=in0 // keep trackof initial byte address
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- dep src=0,in0,0,3 // src=8byte-aligned in0 address
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- .save pr, saved_pr
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- mov saved_pr=pr // preserve predicates (rotation)
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- ;;
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-
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- .body
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-
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- ld8.s v[1]=[src],8 // load the initial 8bytes (must speculate)
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- shl tmp=tmp,3 // multiply by 8bits/byte
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- mov mask=-1 // our mask
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- ;;
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- ld8.s w[1]=[src],8 // load next 8 bytes in 2nd pipeline
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- cmp.eq p6,p0=r0,r0 // sets p6 (required because of // cmp.and)
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- sub tmp=64,tmp // how many bits to shift our mask on the right
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- ;;
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- shr.u mask=mask,tmp // zero enough bits to hold v[1] valuable part
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- mov ar.ec=r0 // clear epilogue counter (saved in ar.pfs)
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- ;;
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- add base=-16,src // keep track of aligned base
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- chk.s v[1], .recover // if already NaT, then directly skip to recover
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- or v[1]=v[1],mask // now we have a safe initial byte pattern
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- ;;
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-1:
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- ld8.s v[0]=[src],8 // speculatively load next
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- czx1.r val1=v[1] // search 0 byte from right
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- czx1.r val2=w[1] // search 0 byte from right following 8bytes
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- ;;
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- ld8.s w[0]=[src],8 // speculatively load next to next
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- cmp.eq.and p6,p0=8,val1 // p6 = p6 and val1==8
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- cmp.eq.and p6,p0=8,val2 // p6 = p6 and mask==8
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-(p6) br.wtop.dptk.few 1b // loop until p6 == 0
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- ;;
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- //
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- // We must return try the recovery code iff
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- // val1_is_nat || (val1==8 && val2_is_nat)
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- //
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- // XXX Fixme
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- // - there must be a better way of doing the test
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- //
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- cmp.eq p8,p9=8,val1 // p6 = val1 had zero (disambiguate)
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- tnat.nz p6,p7=val1 // test NaT on val1
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-(p6) br.cond.spnt .recover // jump to recovery if val1 is NaT
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- ;;
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- //
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- // if we come here p7 is true, i.e., initialized for // cmp
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- //
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- cmp.eq.and p7,p0=8,val1// val1==8?
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- tnat.nz.and p7,p0=val2 // test NaT if val2
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-(p7) br.cond.spnt .recover // jump to recovery if val2 is NaT
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- ;;
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-(p8) mov val1=val2 // val2 contains the value
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-(p8) adds src=-16,src // correct position when 3 ahead
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-(p9) adds src=-24,src // correct position when 4 ahead
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- ;;
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- sub ret0=src,orig // distance from origin
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- sub tmp=7,val1 // 7=8-1 because this strlen returns strlen+1
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- mov pr=saved_pr,0xffffffffffff0000
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- ;;
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- sub ret0=ret0,tmp // length=now - back -1
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- mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what
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- br.ret.sptk.many rp // end of normal execution
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-
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- //
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- // Outlined recovery code when speculation failed
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- //
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- // This time we don't use speculation and rely on the normal exception
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- // mechanism. that's why the loop is not as good as the previous one
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- // because read ahead is not possible
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- //
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- // XXX Fixme
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- // - today we restart from the beginning of the string instead
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- // of trying to continue where we left off.
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- //
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-.recover:
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- EX(.Lexit1, ld8 val=[base],8) // load the initial bytes
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- ;;
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- or val=val,mask // remask first bytes
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- cmp.eq p0,p6=r0,r0 // nullify first ld8 in loop
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- ;;
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- //
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- // ar.ec is still zero here
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- //
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-2:
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- EX(.Lexit1, (p6) ld8 val=[base],8)
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- ;;
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- czx1.r val1=val // search 0 byte from right
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- ;;
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- cmp.eq p6,p0=8,val1 // val1==8 ?
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-(p6) br.wtop.dptk.few 2b // loop until p6 == 0
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- ;;
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- sub ret0=base,orig // distance from base
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- sub tmp=7,val1 // 7=8-1 because this strlen returns strlen+1
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- mov pr=saved_pr,0xffffffffffff0000
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- ;;
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- sub ret0=ret0,tmp // length=now - back -1
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- mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what
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- br.ret.sptk.many rp // end of successful recovery code
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-
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- //
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- // We failed even on the normal load (called from exception handler)
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- //
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-.Lexit1:
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- mov ret0=0
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- mov pr=saved_pr,0xffffffffffff0000
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- mov ar.pfs=saved_pfs // because of ar.ec, restore no matter what
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- br.ret.sptk.many rp
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-END(__strlen_user)
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-EXPORT_SYMBOL(__strlen_user)
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