/* Unimplemented features. */
#undef KERNEL_STACK_OVERFLOW_CHECK
-#undef ALLOCA_EXCEPTION_IN_IRAM
/* Not well tested.
*
*
* 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:
*
* < VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
*/
-#if XCHAL_HAVE_BE
-#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 4, 4
-#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 0, 4
-#else
-#define _EXTUI_MOVSP_SRC(ar) extui ar, ar, 0, 4
-#define _EXTUI_MOVSP_DST(ar) extui ar, ar, 4, 4
-#endif
-
ENTRY(fast_alloca)
+ 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
+ rsync
- /* 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
-
-#ifdef ALLOCA_EXCEPTION_IN_IRAM
-#error iram not supported
-#else
- /* Note: l8ui not allowed in IRAM/IROM!! */
- l8ui a0, a4, 1 # read as(src) from MOVSP instruction
-#endif
- movi a3, .Lmovsp_src
- _EXTUI_MOVSP_SRC(a0) # extract source register number
- addx8 a3, a0, a3
- jx a3
-
-.Lunhandled_double:
- wsr a0, excsave1
- movi a0, unrecoverable_exception
- callx0 a0
-
- .align 8
-.Lmovsp_src:
- 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
-
-1:
-
-#ifdef ALLOCA_EXCEPTION_IN_IRAM
-#error iram not supported
-#else
- l8ui a0, a4, 0 # read ar(dst) from MOVSP instruction
-#endif
- 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
- rfe
-
- /* 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.
- * (PERHAPS NOT REALLY NEEDED, BUT CLEANER...)
- */
-
- /* 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
-.Lmovsp_dst:
- 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
- rfe
-
+ _bbci.l a4, 31, 4f
+ rotw -1
+ _bbci.l a8, 30, 8f
+ rotw -1
+ j _WindowUnderflow12
+8: j _WindowUnderflow8
+4: j _WindowUnderflow4
ENDPROC(fast_alloca)
/*
projects / karo-tx-linux.git / commitdiff