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![Rob Gardner](/assets/img/avatar_default.png)
Short story: Exception handlers used by some copy_to_user() and copy_from_user() functions do not diligently clean up floating point register usage, and this can result in a user process seeing invalid values in floating point registers. This sometimes makes the process fail. Long story: Several cpu-specific (NG4, NG2, U1, U3) memcpy functions use floating point registers and VIS alignaddr/faligndata to accelerate data copying when source and dest addresses don't align well. Linux uses a lazy scheme for saving floating point registers; It is not done upon entering the kernel since it's a very expensive operation. Rather, it is done only when needed. If the kernel ends up not using FP regs during the course of some trap or system call, then it can return to user space without saving or restoring them. The various memcpy functions begin their FP code with VISEntry (or a variation thereof), which saves the FP regs. They conclude their FP code with VISExit (or a variation) which essentially marks the FP regs "clean", ie, they contain no unsaved values. fprs.FPRS_FEF is turned off so that a lazy restore will be triggered when/if the user process accesses floating point regs again. The bug is that the user copy variants of memcpy, copy_from_user() and copy_to_user(), employ an exception handling mechanism to detect faults when accessing user space addresses, and when this handler is invoked, an immediate return from the function is forced, and VISExit is not executed, thus leaving the fprs register in an indeterminate state, but often with fprs.FPRS_FEF set and one or more dirty bits. This results in a return to user space with invalid values in the FP regs, and since fprs.FPRS_FEF is on, no lazy restore occurs. This bug affects copy_to_user() and copy_from_user() for NG4, NG2, U3, and U1. All are fixed by using a new exception handler for those loads and stores that are done during the time between VISEnter and VISExit. n.b. In NG4memcpy, the problematic code can be triggered by a copy size greater than 128 bytes and an unaligned source address. This bug is known to be the cause of random user process memory corruptions while perf is running with the callgraph option (ie, perf record -g). This occurs because perf uses copy_from_user() to read user stacks, and may fault when it follows a stack frame pointer off to an invalid page. Validation checks on the stack address just obscure the underlying problem. Signed-off-by: Rob Gardner <rob.gardner@oracle.com> Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
381 lines
8.6 KiB
ArmAsm
381 lines
8.6 KiB
ArmAsm
/* NG4memcpy.S: Niagara-4 optimized memcpy.
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*
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* Copyright (C) 2012 David S. Miller (davem@davemloft.net)
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*/
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#ifdef __KERNEL__
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#include <asm/visasm.h>
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#include <asm/asi.h>
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#define GLOBAL_SPARE %g7
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#else
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#define ASI_BLK_INIT_QUAD_LDD_P 0xe2
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#define FPRS_FEF 0x04
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/* On T4 it is very expensive to access ASRs like %fprs and
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* %asi, avoiding a read or a write can save ~50 cycles.
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*/
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#define FPU_ENTER \
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rd %fprs, %o5; \
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andcc %o5, FPRS_FEF, %g0; \
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be,a,pn %icc, 999f; \
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wr %g0, FPRS_FEF, %fprs; \
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999:
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#ifdef MEMCPY_DEBUG
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#define VISEntryHalf FPU_ENTER; \
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clr %g1; clr %g2; clr %g3; clr %g5; subcc %g0, %g0, %g0;
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#define VISExitHalf and %o5, FPRS_FEF, %o5; wr %o5, 0x0, %fprs
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#else
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#define VISEntryHalf FPU_ENTER
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#define VISExitHalf and %o5, FPRS_FEF, %o5; wr %o5, 0x0, %fprs
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#endif
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#define GLOBAL_SPARE %g5
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#endif
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#ifndef STORE_ASI
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#ifndef SIMULATE_NIAGARA_ON_NON_NIAGARA
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#define STORE_ASI ASI_BLK_INIT_QUAD_LDD_P
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#else
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#define STORE_ASI 0x80 /* ASI_P */
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#endif
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#endif
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#if !defined(EX_LD) && !defined(EX_ST)
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#define NON_USER_COPY
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#endif
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#ifndef EX_LD
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#define EX_LD(x) x
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#endif
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#ifndef EX_LD_FP
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#define EX_LD_FP(x) x
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#endif
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#ifndef EX_ST
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#define EX_ST(x) x
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#endif
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#ifndef EX_ST_FP
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#define EX_ST_FP(x) x
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#endif
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#ifndef EX_RETVAL
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#define EX_RETVAL(x) x
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#endif
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#ifndef LOAD
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#define LOAD(type,addr,dest) type [addr], dest
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#endif
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#ifndef STORE
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#ifndef MEMCPY_DEBUG
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#define STORE(type,src,addr) type src, [addr]
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#else
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#define STORE(type,src,addr) type##a src, [addr] %asi
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#endif
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#endif
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#ifndef STORE_INIT
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#define STORE_INIT(src,addr) stxa src, [addr] STORE_ASI
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#endif
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#ifndef FUNC_NAME
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#define FUNC_NAME NG4memcpy
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#endif
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#ifndef PREAMBLE
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#define PREAMBLE
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#endif
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#ifndef XCC
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#define XCC xcc
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#endif
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.register %g2,#scratch
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.register %g3,#scratch
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.text
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.align 64
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.globl FUNC_NAME
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.type FUNC_NAME,#function
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FUNC_NAME: /* %o0=dst, %o1=src, %o2=len */
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#ifdef MEMCPY_DEBUG
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wr %g0, 0x80, %asi
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#endif
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srlx %o2, 31, %g2
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cmp %g2, 0
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tne %XCC, 5
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PREAMBLE
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mov %o0, %o3
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brz,pn %o2, .Lexit
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cmp %o2, 3
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ble,pn %icc, .Ltiny
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cmp %o2, 19
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ble,pn %icc, .Lsmall
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or %o0, %o1, %g2
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cmp %o2, 128
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bl,pn %icc, .Lmedium
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nop
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.Llarge:/* len >= 0x80 */
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/* First get dest 8 byte aligned. */
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sub %g0, %o0, %g1
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and %g1, 0x7, %g1
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brz,pt %g1, 51f
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sub %o2, %g1, %o2
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1: EX_LD(LOAD(ldub, %o1 + 0x00, %g2))
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add %o1, 1, %o1
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subcc %g1, 1, %g1
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add %o0, 1, %o0
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bne,pt %icc, 1b
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EX_ST(STORE(stb, %g2, %o0 - 0x01))
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51: LOAD(prefetch, %o1 + 0x040, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x080, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x0c0, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x100, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x140, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x180, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x1c0, #n_reads_strong)
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LOAD(prefetch, %o1 + 0x200, #n_reads_strong)
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/* Check if we can use the straight fully aligned
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* loop, or we require the alignaddr/faligndata variant.
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*/
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andcc %o1, 0x7, %o5
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bne,pn %icc, .Llarge_src_unaligned
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sub %g0, %o0, %g1
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/* Legitimize the use of initializing stores by getting dest
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* to be 64-byte aligned.
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*/
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and %g1, 0x3f, %g1
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brz,pt %g1, .Llarge_aligned
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sub %o2, %g1, %o2
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1: EX_LD(LOAD(ldx, %o1 + 0x00, %g2))
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add %o1, 8, %o1
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subcc %g1, 8, %g1
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add %o0, 8, %o0
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bne,pt %icc, 1b
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EX_ST(STORE(stx, %g2, %o0 - 0x08))
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.Llarge_aligned:
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/* len >= 0x80 && src 8-byte aligned && dest 8-byte aligned */
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andn %o2, 0x3f, %o4
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sub %o2, %o4, %o2
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1: EX_LD(LOAD(ldx, %o1 + 0x00, %g1))
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add %o1, 0x40, %o1
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EX_LD(LOAD(ldx, %o1 - 0x38, %g2))
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subcc %o4, 0x40, %o4
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EX_LD(LOAD(ldx, %o1 - 0x30, %g3))
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EX_LD(LOAD(ldx, %o1 - 0x28, GLOBAL_SPARE))
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EX_LD(LOAD(ldx, %o1 - 0x20, %o5))
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EX_ST(STORE_INIT(%g1, %o0))
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add %o0, 0x08, %o0
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EX_ST(STORE_INIT(%g2, %o0))
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add %o0, 0x08, %o0
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EX_LD(LOAD(ldx, %o1 - 0x18, %g2))
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EX_ST(STORE_INIT(%g3, %o0))
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add %o0, 0x08, %o0
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EX_LD(LOAD(ldx, %o1 - 0x10, %g3))
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EX_ST(STORE_INIT(GLOBAL_SPARE, %o0))
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add %o0, 0x08, %o0
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EX_LD(LOAD(ldx, %o1 - 0x08, GLOBAL_SPARE))
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EX_ST(STORE_INIT(%o5, %o0))
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add %o0, 0x08, %o0
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EX_ST(STORE_INIT(%g2, %o0))
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add %o0, 0x08, %o0
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EX_ST(STORE_INIT(%g3, %o0))
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add %o0, 0x08, %o0
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EX_ST(STORE_INIT(GLOBAL_SPARE, %o0))
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add %o0, 0x08, %o0
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bne,pt %icc, 1b
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LOAD(prefetch, %o1 + 0x200, #n_reads_strong)
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membar #StoreLoad | #StoreStore
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brz,pn %o2, .Lexit
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cmp %o2, 19
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ble,pn %icc, .Lsmall_unaligned
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nop
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ba,a,pt %icc, .Lmedium_noprefetch
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.Lexit: retl
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mov EX_RETVAL(%o3), %o0
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.Llarge_src_unaligned:
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#ifdef NON_USER_COPY
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VISEntryHalfFast(.Lmedium_vis_entry_fail)
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#else
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VISEntryHalf
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#endif
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andn %o2, 0x3f, %o4
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sub %o2, %o4, %o2
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alignaddr %o1, %g0, %g1
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add %o1, %o4, %o1
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EX_LD_FP(LOAD(ldd, %g1 + 0x00, %f0))
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1: EX_LD_FP(LOAD(ldd, %g1 + 0x08, %f2))
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subcc %o4, 0x40, %o4
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EX_LD_FP(LOAD(ldd, %g1 + 0x10, %f4))
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EX_LD_FP(LOAD(ldd, %g1 + 0x18, %f6))
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EX_LD_FP(LOAD(ldd, %g1 + 0x20, %f8))
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EX_LD_FP(LOAD(ldd, %g1 + 0x28, %f10))
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EX_LD_FP(LOAD(ldd, %g1 + 0x30, %f12))
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EX_LD_FP(LOAD(ldd, %g1 + 0x38, %f14))
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faligndata %f0, %f2, %f16
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EX_LD_FP(LOAD(ldd, %g1 + 0x40, %f0))
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faligndata %f2, %f4, %f18
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add %g1, 0x40, %g1
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faligndata %f4, %f6, %f20
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faligndata %f6, %f8, %f22
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faligndata %f8, %f10, %f24
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faligndata %f10, %f12, %f26
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faligndata %f12, %f14, %f28
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faligndata %f14, %f0, %f30
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EX_ST_FP(STORE(std, %f16, %o0 + 0x00))
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EX_ST_FP(STORE(std, %f18, %o0 + 0x08))
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EX_ST_FP(STORE(std, %f20, %o0 + 0x10))
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EX_ST_FP(STORE(std, %f22, %o0 + 0x18))
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EX_ST_FP(STORE(std, %f24, %o0 + 0x20))
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EX_ST_FP(STORE(std, %f26, %o0 + 0x28))
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EX_ST_FP(STORE(std, %f28, %o0 + 0x30))
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EX_ST_FP(STORE(std, %f30, %o0 + 0x38))
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add %o0, 0x40, %o0
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bne,pt %icc, 1b
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LOAD(prefetch, %g1 + 0x200, #n_reads_strong)
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#ifdef NON_USER_COPY
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VISExitHalfFast
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#else
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VISExitHalf
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#endif
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brz,pn %o2, .Lexit
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cmp %o2, 19
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ble,pn %icc, .Lsmall_unaligned
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nop
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ba,a,pt %icc, .Lmedium_unaligned
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#ifdef NON_USER_COPY
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.Lmedium_vis_entry_fail:
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or %o0, %o1, %g2
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#endif
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.Lmedium:
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LOAD(prefetch, %o1 + 0x40, #n_reads_strong)
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andcc %g2, 0x7, %g0
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bne,pn %icc, .Lmedium_unaligned
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nop
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.Lmedium_noprefetch:
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andncc %o2, 0x20 - 1, %o5
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be,pn %icc, 2f
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sub %o2, %o5, %o2
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1: EX_LD(LOAD(ldx, %o1 + 0x00, %g1))
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EX_LD(LOAD(ldx, %o1 + 0x08, %g2))
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EX_LD(LOAD(ldx, %o1 + 0x10, GLOBAL_SPARE))
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EX_LD(LOAD(ldx, %o1 + 0x18, %o4))
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add %o1, 0x20, %o1
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subcc %o5, 0x20, %o5
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EX_ST(STORE(stx, %g1, %o0 + 0x00))
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EX_ST(STORE(stx, %g2, %o0 + 0x08))
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EX_ST(STORE(stx, GLOBAL_SPARE, %o0 + 0x10))
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EX_ST(STORE(stx, %o4, %o0 + 0x18))
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bne,pt %icc, 1b
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add %o0, 0x20, %o0
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2: andcc %o2, 0x18, %o5
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be,pt %icc, 3f
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sub %o2, %o5, %o2
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1: EX_LD(LOAD(ldx, %o1 + 0x00, %g1))
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add %o1, 0x08, %o1
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add %o0, 0x08, %o0
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subcc %o5, 0x08, %o5
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bne,pt %icc, 1b
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EX_ST(STORE(stx, %g1, %o0 - 0x08))
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3: brz,pt %o2, .Lexit
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cmp %o2, 0x04
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bl,pn %icc, .Ltiny
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nop
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EX_LD(LOAD(lduw, %o1 + 0x00, %g1))
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add %o1, 0x04, %o1
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add %o0, 0x04, %o0
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subcc %o2, 0x04, %o2
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bne,pn %icc, .Ltiny
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EX_ST(STORE(stw, %g1, %o0 - 0x04))
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ba,a,pt %icc, .Lexit
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.Lmedium_unaligned:
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/* First get dest 8 byte aligned. */
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sub %g0, %o0, %g1
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and %g1, 0x7, %g1
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brz,pt %g1, 2f
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sub %o2, %g1, %o2
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1: EX_LD(LOAD(ldub, %o1 + 0x00, %g2))
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add %o1, 1, %o1
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subcc %g1, 1, %g1
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add %o0, 1, %o0
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bne,pt %icc, 1b
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EX_ST(STORE(stb, %g2, %o0 - 0x01))
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2:
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and %o1, 0x7, %g1
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brz,pn %g1, .Lmedium_noprefetch
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sll %g1, 3, %g1
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mov 64, %g2
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sub %g2, %g1, %g2
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andn %o1, 0x7, %o1
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EX_LD(LOAD(ldx, %o1 + 0x00, %o4))
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sllx %o4, %g1, %o4
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andn %o2, 0x08 - 1, %o5
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sub %o2, %o5, %o2
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1: EX_LD(LOAD(ldx, %o1 + 0x08, %g3))
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add %o1, 0x08, %o1
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subcc %o5, 0x08, %o5
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srlx %g3, %g2, GLOBAL_SPARE
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or GLOBAL_SPARE, %o4, GLOBAL_SPARE
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EX_ST(STORE(stx, GLOBAL_SPARE, %o0 + 0x00))
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add %o0, 0x08, %o0
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bne,pt %icc, 1b
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sllx %g3, %g1, %o4
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srl %g1, 3, %g1
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add %o1, %g1, %o1
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brz,pn %o2, .Lexit
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nop
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ba,pt %icc, .Lsmall_unaligned
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.Ltiny:
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EX_LD(LOAD(ldub, %o1 + 0x00, %g1))
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subcc %o2, 1, %o2
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be,pn %icc, .Lexit
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EX_ST(STORE(stb, %g1, %o0 + 0x00))
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EX_LD(LOAD(ldub, %o1 + 0x01, %g1))
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subcc %o2, 1, %o2
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be,pn %icc, .Lexit
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EX_ST(STORE(stb, %g1, %o0 + 0x01))
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EX_LD(LOAD(ldub, %o1 + 0x02, %g1))
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ba,pt %icc, .Lexit
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EX_ST(STORE(stb, %g1, %o0 + 0x02))
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.Lsmall:
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andcc %g2, 0x3, %g0
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bne,pn %icc, .Lsmall_unaligned
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andn %o2, 0x4 - 1, %o5
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sub %o2, %o5, %o2
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1:
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EX_LD(LOAD(lduw, %o1 + 0x00, %g1))
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add %o1, 0x04, %o1
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subcc %o5, 0x04, %o5
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add %o0, 0x04, %o0
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bne,pt %icc, 1b
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EX_ST(STORE(stw, %g1, %o0 - 0x04))
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brz,pt %o2, .Lexit
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nop
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ba,a,pt %icc, .Ltiny
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.Lsmall_unaligned:
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1: EX_LD(LOAD(ldub, %o1 + 0x00, %g1))
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add %o1, 1, %o1
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add %o0, 1, %o0
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subcc %o2, 1, %o2
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bne,pt %icc, 1b
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EX_ST(STORE(stb, %g1, %o0 - 0x01))
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ba,a,pt %icc, .Lexit
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.size FUNC_NAME, .-FUNC_NAME
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