xtensa: new fast_alloca handler
Instead of emulating movsp instruction in the kernel use window underflow handler to load missing register window and retry failed movsp. Signed-off-by: Max Filippov <jcmvbkbc@gmail.com> Signed-off-by: Chris Zankel <chris@zankel.net>
This commit is contained in:
Max Filippov
Chris Zankel
parent
99d5040ebc
commit
fff96d69f2
1 changed files with 40 additions and 152 deletions
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@ -31,7 +31,6 @@
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/* Unimplemented features. */
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#undef KERNEL_STACK_OVERFLOW_CHECK
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#undef ALLOCA_EXCEPTION_IN_IRAM
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/* Not well tested.
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*
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@ -819,11 +818,27 @@ ENDPROC(unrecoverable_exception)
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*
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* The ALLOCA handler is entered when user code executes the MOVSP
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* instruction and the caller's frame is not in the register file.
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* In this case, the caller frame's a0..a3 are on the stack just
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* below sp (a1), and this handler moves them.
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*
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* For "MOVSP <ar>,<as>" without destination register a1, this routine
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* simply moves the value from <as> to <ar> without moving the save area.
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* This algorithm was taken from the Ross Morley's RTOS Porting Layer:
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*
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* /home/ross/rtos/porting/XtensaRTOS-PortingLayer-20090507/xtensa_vectors.S
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*
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* It leverages the existing window spill/fill routines and their support for
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* double exceptions. The 'movsp' instruction will only cause an exception if
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* the next window needs to be loaded. In fact this ALLOCA exception may be
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* replaced at some point by changing the hardware to do a underflow exception
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* of the proper size instead.
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*
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* This algorithm simply backs out the register changes started by the user
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* excpetion handler, makes it appear that we have started a window underflow
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* by rotating the window back and then setting the old window base (OWB) in
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* the 'ps' register with the rolled back window base. The 'movsp' instruction
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* will be re-executed and this time since the next window frames is in the
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* active AR registers it won't cause an exception.
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*
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* If the WindowUnderflow code gets a TLB miss the page will get mapped
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* the the partial windeowUnderflow will be handeled in the double exception
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* handler.
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*
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* Entry condition:
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*
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@ -838,155 +853,28 @@ ENDPROC(unrecoverable_exception)
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* < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
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*/
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#if XCHAL_HAVE_BE
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#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 4, 4
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#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 0, 4
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#else
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#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 0, 4
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#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 4, 4
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#endif
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ENTRY(fast_alloca)
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rsr a0, windowbase
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rotw -1
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rsr a2, ps
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extui a3, a2, PS_OWB_SHIFT, PS_OWB_WIDTH
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xor a3, a3, a4
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l32i a4, a6, PT_AREG0
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l32i a1, a6, PT_DEPC
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rsr a6, depc
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wsr a1, depc
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slli a3, a3, PS_OWB_SHIFT
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xor a2, a2, a3
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wsr a2, ps
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rsync
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/* We shouldn't be in a double exception. */
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l32i a0, a2, PT_DEPC
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_bgeui a0, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lunhandled_double
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rsr a0, depc # get a2
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s32i a4, a2, PT_AREG4 # save a4 and
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s32i a3, a2, PT_AREG3
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s32i a0, a2, PT_AREG2 # a2 to stack
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/* Exit critical section. */
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movi a0, 0
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rsr a3, excsave1
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s32i a0, a3, EXC_TABLE_FIXUP
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rsr a4, epc1 # get exception address
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#ifdef ALLOCA_EXCEPTION_IN_IRAM
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#error iram not supported
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#else
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/* Note: l8ui not allowed in IRAM/IROM!! */
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l8ui a0, a4, 1 # read as(src) from MOVSP instruction
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#endif
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movi a3, .Lmovsp_src
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_EXTUI_MOVSP_SRC(a0) # extract source register number
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addx8 a3, a0, a3
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jx a3
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.Lunhandled_double:
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wsr a0, excsave1
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movi a0, unrecoverable_exception
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callx0 a0
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.align 8
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.Lmovsp_src:
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l32i a3, a2, PT_AREG0; _j 1f; .align 8
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mov a3, a1; _j 1f; .align 8
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l32i a3, a2, PT_AREG2; _j 1f; .align 8
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l32i a3, a2, PT_AREG3; _j 1f; .align 8
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l32i a3, a2, PT_AREG4; _j 1f; .align 8
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mov a3, a5; _j 1f; .align 8
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mov a3, a6; _j 1f; .align 8
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mov a3, a7; _j 1f; .align 8
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mov a3, a8; _j 1f; .align 8
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mov a3, a9; _j 1f; .align 8
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mov a3, a10; _j 1f; .align 8
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mov a3, a11; _j 1f; .align 8
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mov a3, a12; _j 1f; .align 8
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mov a3, a13; _j 1f; .align 8
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mov a3, a14; _j 1f; .align 8
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mov a3, a15; _j 1f; .align 8
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1:
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#ifdef ALLOCA_EXCEPTION_IN_IRAM
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#error iram not supported
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#else
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l8ui a0, a4, 0 # read ar(dst) from MOVSP instruction
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#endif
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addi a4, a4, 3 # step over movsp
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_EXTUI_MOVSP_DST(a0) # extract destination register
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wsr a4, epc1 # save new epc_1
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_bnei a0, 1, 1f # no 'movsp a1, ax': jump
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/* Move the save area. This implies the use of the L32E
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* and S32E instructions, because this move must be done with
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* the user's PS.RING privilege levels, not with ring 0
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* (kernel's) privileges currently active with PS.EXCM
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* set. Note that we have stil registered a fixup routine with the
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* double exception vector in case a double exception occurs.
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*/
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/* a0,a4:avail a1:old user stack a2:exc. stack a3:new user stack. */
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l32e a0, a1, -16
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l32e a4, a1, -12
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s32e a0, a3, -16
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s32e a4, a3, -12
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l32e a0, a1, -8
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l32e a4, a1, -4
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s32e a0, a3, -8
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s32e a4, a3, -4
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/* Restore stack-pointer and all the other saved registers. */
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mov a1, a3
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l32i a4, a2, PT_AREG4
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l32i a3, a2, PT_AREG3
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l32i a0, a2, PT_AREG0
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l32i a2, a2, PT_AREG2
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rfe
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/* MOVSP <at>,<as> was invoked with <at> != a1.
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* Because the stack pointer is not being modified,
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* we should be able to just modify the pointer
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* without moving any save area.
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* The processor only traps these occurrences if the
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* caller window isn't live, so unfortunately we can't
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* use this as an alternate trap mechanism.
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* So we just do the move. This requires that we
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* resolve the destination register, not just the source,
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* so there's some extra work.
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* (PERHAPS NOT REALLY NEEDED, BUT CLEANER...)
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*/
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/* a0 dst-reg, a1 user-stack, a2 stack, a3 value of src reg. */
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1: movi a4, .Lmovsp_dst
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addx8 a4, a0, a4
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jx a4
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.align 8
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.Lmovsp_dst:
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s32i a3, a2, PT_AREG0; _j 1f; .align 8
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mov a1, a3; _j 1f; .align 8
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s32i a3, a2, PT_AREG2; _j 1f; .align 8
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s32i a3, a2, PT_AREG3; _j 1f; .align 8
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s32i a3, a2, PT_AREG4; _j 1f; .align 8
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mov a5, a3; _j 1f; .align 8
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mov a6, a3; _j 1f; .align 8
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mov a7, a3; _j 1f; .align 8
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mov a8, a3; _j 1f; .align 8
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mov a9, a3; _j 1f; .align 8
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mov a10, a3; _j 1f; .align 8
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mov a11, a3; _j 1f; .align 8
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mov a12, a3; _j 1f; .align 8
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mov a13, a3; _j 1f; .align 8
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mov a14, a3; _j 1f; .align 8
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mov a15, a3; _j 1f; .align 8
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1: l32i a4, a2, PT_AREG4
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l32i a3, a2, PT_AREG3
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l32i a0, a2, PT_AREG0
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l32i a2, a2, PT_AREG2
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rfe
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_bbci.l a4, 31, 4f
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rotw -1
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_bbci.l a8, 30, 8f
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rotw -1
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j _WindowUnderflow12
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8: j _WindowUnderflow8
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4: j _WindowUnderflow4
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ENDPROC(fast_alloca)
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/*
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