Commit fff96d69 authored by Max Filippov's avatar Max Filippov Committed by Chris Zankel

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
Signed-off-by: default avatarMax Filippov <>
Signed-off-by: default avatarChris Zankel <>
parent 99d5040e
......@@ -31,7 +31,6 @@
/* Unimplemented features. */
/* Not well tested.
......@@ -819,11 +818,27 @@ ENDPROC(unrecoverable_exception)
* The ALLOCA handler is entered when user code executes the MOVSP
* instruction and the caller's frame is not in the register file.
* In this case, the caller frame's a0..a3 are on the stack just
* below sp (a1), and this handler moves them.
* For "MOVSP <ar>,<as>" without destination register a1, this routine
* simply moves the value from <as> to <ar> without moving the save area.
* This algorithm was taken from the Ross Morley's RTOS Porting Layer:
* /home/ross/rtos/porting/XtensaRTOS-PortingLayer-20090507/xtensa_vectors.S
* It leverages the existing window spill/fill routines and their support for
* double exceptions. The 'movsp' instruction will only cause an exception if
* the next window needs to be loaded. In fact this ALLOCA exception may be
* replaced at some point by changing the hardware to do a underflow exception
* of the proper size instead.
* This algorithm simply backs out the register changes started by the user
* excpetion handler, makes it appear that we have started a window underflow
* by rotating the window back and then setting the old window base (OWB) in
* the 'ps' register with the rolled back window base. The 'movsp' instruction
* will be re-executed and this time since the next window frames is in the
* active AR registers it won't cause an exception.
* If the WindowUnderflow code gets a TLB miss the page will get mapped
* the the partial windeowUnderflow will be handeled in the double exception
* handler.
* Entry condition:
......@@ -838,155 +853,28 @@ ENDPROC(unrecoverable_exception)
#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 4, 4
#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 0, 4
#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 0, 4
#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 4, 4
rsr a0, windowbase
rotw -1
rsr a2, ps
extui a3, a2, PS_OWB_SHIFT, PS_OWB_WIDTH
xor a3, a3, a4
l32i a4, a6, PT_AREG0
l32i a1, a6, PT_DEPC
rsr a6, depc
wsr a1, depc
slli a3, a3, PS_OWB_SHIFT
xor a2, a2, a3
wsr a2, ps
/* We shouldn't be in a double exception. */
l32i a0, a2, PT_DEPC
_bgeui a0, VALID_DOUBLE_EXCEPTION_ADDRESS, .Lunhandled_double
rsr a0, depc # get a2
s32i a4, a2, PT_AREG4 # save a4 and
s32i a3, a2, PT_AREG3
s32i a0, a2, PT_AREG2 # a2 to stack
/* Exit critical section. */
movi a0, 0
rsr a3, excsave1
s32i a0, a3, EXC_TABLE_FIXUP
rsr a4, epc1 # get exception address
#error iram not supported
/* Note: l8ui not allowed in IRAM/IROM!! */
l8ui a0, a4, 1 # read as(src) from MOVSP instruction
movi a3, .Lmovsp_src
_EXTUI_MOVSP_SRC(a0) # extract source register number
addx8 a3, a0, a3
jx a3
wsr a0, excsave1
movi a0, unrecoverable_exception
callx0 a0
.align 8
l32i a3, a2, PT_AREG0; _j 1f; .align 8
mov a3, a1; _j 1f; .align 8
l32i a3, a2, PT_AREG2; _j 1f; .align 8
l32i a3, a2, PT_AREG3; _j 1f; .align 8
l32i a3, a2, PT_AREG4; _j 1f; .align 8
mov a3, a5; _j 1f; .align 8
mov a3, a6; _j 1f; .align 8
mov a3, a7; _j 1f; .align 8
mov a3, a8; _j 1f; .align 8
mov a3, a9; _j 1f; .align 8
mov a3, a10; _j 1f; .align 8
mov a3, a11; _j 1f; .align 8
mov a3, a12; _j 1f; .align 8
mov a3, a13; _j 1f; .align 8
mov a3, a14; _j 1f; .align 8
mov a3, a15; _j 1f; .align 8
#error iram not supported
l8ui a0, a4, 0 # read ar(dst) from MOVSP instruction
addi a4, a4, 3 # step over movsp
_EXTUI_MOVSP_DST(a0) # extract destination register
wsr a4, epc1 # save new epc_1
_bnei a0, 1, 1f # no 'movsp a1, ax': jump
/* Move the save area. This implies the use of the L32E
* and S32E instructions, because this move must be done with
* the user's PS.RING privilege levels, not with ring 0
* (kernel's) privileges currently active with PS.EXCM
* set. Note that we have stil registered a fixup routine with the
* double exception vector in case a double exception occurs.
/* a0,a4:avail a1:old user stack a2:exc. stack a3:new user stack. */
l32e a0, a1, -16
l32e a4, a1, -12
s32e a0, a3, -16
s32e a4, a3, -12
l32e a0, a1, -8
l32e a4, a1, -4
s32e a0, a3, -8
s32e a4, a3, -4
/* Restore stack-pointer and all the other saved registers. */
mov a1, a3
l32i a4, a2, PT_AREG4
l32i a3, a2, PT_AREG3
l32i a0, a2, PT_AREG0
l32i a2, a2, PT_AREG2
/* MOVSP <at>,<as> was invoked with <at> != a1.
* Because the stack pointer is not being modified,
* we should be able to just modify the pointer
* without moving any save area.
* The processor only traps these occurrences if the
* caller window isn't live, so unfortunately we can't
* use this as an alternate trap mechanism.
* So we just do the move. This requires that we
* resolve the destination register, not just the source,
* so there's some extra work.
/* a0 dst-reg, a1 user-stack, a2 stack, a3 value of src reg. */
1: movi a4, .Lmovsp_dst
addx8 a4, a0, a4
jx a4
.align 8
s32i a3, a2, PT_AREG0; _j 1f; .align 8
mov a1, a3; _j 1f; .align 8
s32i a3, a2, PT_AREG2; _j 1f; .align 8
s32i a3, a2, PT_AREG3; _j 1f; .align 8
s32i a3, a2, PT_AREG4; _j 1f; .align 8
mov a5, a3; _j 1f; .align 8
mov a6, a3; _j 1f; .align 8
mov a7, a3; _j 1f; .align 8
mov a8, a3; _j 1f; .align 8
mov a9, a3; _j 1f; .align 8
mov a10, a3; _j 1f; .align 8
mov a11, a3; _j 1f; .align 8
mov a12, a3; _j 1f; .align 8
mov a13, a3; _j 1f; .align 8
mov a14, a3; _j 1f; .align 8
mov a15, a3; _j 1f; .align 8
1: l32i a4, a2, PT_AREG4
l32i a3, a2, PT_AREG3
l32i a0, a2, PT_AREG0
l32i a2, a2, PT_AREG2
_bbci.l a4, 31, 4f
rotw -1
_bbci.l a8, 30, 8f
rotw -1
j _WindowUnderflow12
8: j _WindowUnderflow8
4: j _WindowUnderflow4
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