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Load/store exception handler: handle re-entry via a NMI.

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The NMI can asynchronously interrupt the load/store exception handler. This
does occur frequently as the NMI handler code does invoke load/store
exceptions, and the load/store exception handler is heavly used. This was
corrupting the load/store exception handler saved state and thus randomly
corrupting registers a0 to a6 of the interruptee.
This commit is contained in:
Our Air Quality 2018-06-17 12:25:22 +10:00
parent d9c5f2eaa2
commit 8513e5de22
1 changed files with 78 additions and 34 deletions
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112
core/exception_vectors.S
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@ -23,7 +23,7 @@
#define CAUSE_LOADSTORE 3 #define CAUSE_LOADSTORE 3
#define CAUSE_LVL1INT 4 #define CAUSE_LVL1INT 4
.section .bss .section .data
/* Stack space for NMI handler /* Stack space for NMI handler
@ -37,13 +37,26 @@ NMIHandlerStack:
.skip 0x200 .skip 0x200
.NMIHandlerStackTop: .NMIHandlerStackTop:
/* The Load Store exception handler uses a separate stack to store the
* interruptee registers. It does not appear to be practical to use the
* interuptee stack, which must in invalid at some points? This exception is
* synchronouns and the handler does not call back into itself. However it may
* be interrupted by a NMI which in turn may re-enter this exception
* handler. The NMI is responsible for switching the stack pointer to be used by
* this exception handler. Room is allocated for up to 3 stack frames, a base
* and two NMI reentry frames, and each frame is 7 words wide.
*/
#define LoadStoreErrorHandlerStackFrameSize (5 * 4)
.balign 16 .balign 16
.global LoadStoreErrorHandlerStack
LoadStoreErrorHandlerStack: LoadStoreErrorHandlerStack:
.word 0 # a0 .skip LoadStoreErrorHandlerStackFrameSize * 3
.word 0 # (unused)
.word 0 # a2 .balign 4
.word 0 # a3 .global LoadStoreErrorHandlerStackPointer
.word 0 # a4 LoadStoreErrorHandlerStackPointer:
.word 0
.balign 4 .balign 4
.global debug_saved_ctx .global debug_saved_ctx
@ -131,10 +144,20 @@ DoubleExceptionVector:
LoadStoreErrorHandler: LoadStoreErrorHandler:
.type LoadStoreErrorHandler, @function .type LoadStoreErrorHandler, @function
/* Registers are saved in the address corresponding to their register /* Registers are saved in stack frame offsets corresponding to their
* number times 4. This allows a quick and easy mapping later on when * register number times 4. This allows a quick and easy mapping later
* needing to store the value to a particular register number. */ * on when needing to store the value to a particular register
movi sp, LoadStoreErrorHandlerStack * number.
*
* This handler may be interrupted asynchronously by the NMI. The NMI
* handler is responsible for switching the load/store handler stack
* pointer and that avoids that overhead here. This handler is
* synchronous so the NMI handler can modify and restore the load/store
* stack pointer safely.
*/
movi sp, LoadStoreErrorHandlerStackPointer
l32i sp, sp, 0
s32i a0, sp, 0 s32i a0, sp, 0
s32i a2, sp, 0x08 s32i a2, sp, 0x08
s32i a3, sp, 0x0c s32i a3, sp, 0x0c
@ -407,6 +430,12 @@ call_user_start:
.global call_user_start .global call_user_start
.type call_user_start, @function .type call_user_start, @function
/* Initialize the load/store error handler stack pointer. There are no
* load/store exceptions before this point. */
movi a2, LoadStoreErrorHandlerStackPointer
movi a3, LoadStoreErrorHandlerStack
s32i a3, a2, 0
movi a2, VecBase movi a2, VecBase
wsr a2, vecbase wsr a2, vecbase
call0 sdk_user_start call0 sdk_user_start
@ -422,7 +451,10 @@ call_user_start:
NMIExceptionHandler: NMIExceptionHandler:
.type NMIExceptionHandler, @function .type NMIExceptionHandler, @function
wsr sp, excsave3 # excsave3 holds user stack wsr sp, excsave3 # excsave3 holds user stack
/* Load the NMI handler stack pointer which is already offset by -0x40
* to create a frame to store the interruptee state. */
movi sp, .NMIHandlerStackTop - 0x40 movi sp, .NMIHandlerStackTop - 0x40
s32i a0, sp, 0x00 s32i a0, sp, 0x00
s32i a2, sp, 0x04 s32i a2, sp, 0x04
@ -449,39 +481,51 @@ NMIExceptionHandler:
wsr a0, ps wsr a0, ps
rsync rsync
/* mark the stack overflow point before we call the actual NMI handler */ /* Mark the stack overflow point before we call the actual NMI handler */
movi a0, NMIHandlerStack movi a0, NMIHandlerStack
movi a2, NMI_STACK_CANARY movi a2, NMI_STACK_CANARY
s32i a2, a0, 0x00 s32i a2, a0, 0x00
/* Switch the load/store error handler stack. */
movi a2, LoadStoreErrorHandlerStackPointer
l32i a3, a2, 0
addi a3, a3, LoadStoreErrorHandlerStackFrameSize
s32i a3, a2, 0
call0 sdk_wDev_ProcessFiq call0 sdk_wDev_ProcessFiq
/* verify we didn't overflow */ /* Verify we didn't overflow */
movi a0, NMIHandlerStack movi a0, NMIHandlerStack
l32i a3, a0, 0 l32i a3, a0, 0
movi a2, NMI_STACK_CANARY movi a2, NMI_STACK_CANARY
bne a3, a2, .NMIFatalStackOverflow bne a3, a2, .NMIFatalStackOverflow
l32i a0, sp, 0x3c /* Restore the load/store error handler stack. */
wsr a0, sar movi a2, LoadStoreErrorHandlerStackPointer
l32i a0, sp, 0x38 l32i a3, a2, 0
wsr a0, excvaddr addi a3, a3, -LoadStoreErrorHandlerStackFrameSize
l32i a0, sp, 0x34 s32i a3, a2, 0
wsr a0, excsave1
l32i a0, sp, 0x30 l32i a0, sp, 0x3c
wsr a0, exccause wsr a0, sar
l32i a0, sp, 0x2c l32i a0, sp, 0x38
wsr a0, epc1 wsr a0, excvaddr
l32i a11, sp, 0x28 l32i a0, sp, 0x34
l32i a10, sp, 0x24 wsr a0, excsave1
l32i a9, sp, 0x20 l32i a0, sp, 0x30
l32i a8, sp, 0x1c wsr a0, exccause
l32i a7, sp, 0x18 l32i a0, sp, 0x2c
l32i a6, sp, 0x14 wsr a0, epc1
l32i a5, sp, 0x10 l32i a11, sp, 0x28
l32i a4, sp, 0x0c l32i a10, sp, 0x24
l32i a3, sp, 0x08 l32i a9, sp, 0x20
movi a0, 0x33 # Reset PS l32i a8, sp, 0x1c
l32i a7, sp, 0x18
l32i a6, sp, 0x14
l32i a5, sp, 0x10
l32i a4, sp, 0x0c
l32i a3, sp, 0x08
movi a0, 0x33 # Reset PS
wsr a0, ps wsr a0, ps
rsync rsync
/* set dport nmi status to 1 (wDev_ProcessFiq clears bit 0 and verifies it /* set dport nmi status to 1 (wDev_ProcessFiq clears bit 0 and verifies it