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Further optimizations for LoadStoreErrorHandler

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This commit is contained in:
Alex Stewart 2015-09-21 22:13:14 -07:00
parent 9d62d09d3f
commit bcacfa426a
2 changed files with 268 additions and 200 deletions
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278
core/exception_vectors.S
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@ -26,7 +26,6 @@
.text
.section .vecbase.text, "x"
.global VecBase
.type VecBase, @function /* it's not really a function, but treat it like one */
.org 0
VecBase:
/* IMPORTANT: exception vector literals will go here, but we
@ -36,35 +35,38 @@ VecBase:
*/
.literal_position
.org 0x10
.type DebugExceptionVector, @function
DebugExceptionVector:
wsr.excsave2 a0
call0 sdk_user_fatal_exception_handler
rfi 2
.org 0x20
.type NMIExceptionVector, @function
NMIExceptionVector:
wsr.excsave3 a0
call0 CallNMIExceptionHandler
rfi 3 /* CallNMIExceptionHandler should call rfi itself */
.org 0x30
.type KernelExceptionVector, @function
KernelExceptionVector:
break 1, 0
call0 sdk_user_fatal_exception_handler
rfe
.org 0x50
.type UserExceptionVector, @function
UserExceptionVector:
wsr.excsave1 a0
rsr.exccause a0
beqi a0, CAUSE_LOADSTORE, UserExceptionLoadStoreHandler
beqi a0, CAUSE_LOADSTORE, LoadStoreErrorHandler
j UserExceptionHandler
.org 0x70
.type DoubleExceptionVector, @function
DoubleExceptionVector:
break 1, 4
rsr.exccause a0
beqi a0, CAUSE_LOADSTORE, DoubleExceptionLoadStoreHandler
call0 sdk_user_fatal_exception_handler
/* Reset vector would go here at offset 0x80 but should be unused,
@ -72,10 +74,260 @@ DoubleExceptionVector:
/***** end of exception vectors *****/
/* We include this here so UserExceptionLoadStoreHandler is within
the range of a 'beq' instruction jump.
/* Xtensa Exception unaligned load handler
Completes l8/l16 load instructions from Instruction address space,
for which the architecture only supports 32-bit reads.
Called from UserExceptionVector if EXCCAUSE is LoadStoreErrorCause
Fast path (no branches) is for l8ui.
*/
#include "exception_unaligned_load.S.inc"
.literal_position
.type LoadStoreErrorHandler, @function
LoadStoreErrorHandler:
# Note: we use a0 as our "stack pointer" here because it's already been
# saved in UserExceptionVector, and we never call out to other routines
# so we don't have to worry about it being clobbered. It would be
# preferable to use a1 instead, but this would require changes to other
# parts of UserExceptionHandler code which we haven't gotten around to
# yet.
# TODO: Eventually, switch everything over to saving a1 instead of a0
# in UserExceptionVector so we can use the more mnemonic SP for this.
# Note: registers are saved in the (regnum * 4) address so calculation
# is easier later on. This means we don't use the first two entries
# (since we don't save a0 or a1 here), so we just adjust the pointer in
# a0 to pretend we have two extra slots at the beginning.
movi a0, LoadStoreErrorHandlerStack - 8
s32i a2, a0, 0x08
s32i a3, a0, 0x0c
s32i a4, a0, 0x10
s32i a5, a0, 0x14
rsr.sar a5 # Save SAR in a5 to restore later
# Examine the opcode which generated the exception
# Note: Instructions are in this order to avoid pipeline stalls.
rsr.epc1 a2
movi a3, ~3
ssa8l a2 // sar is now correct shift for aligned read
and a2, a2, a3 // a2 now 4-byte aligned address of instruction
l32i a4, a2, 0
l32i a2, a2, 4
movi a3, 0x00700F // opcode mask for l8ui/l16si/l16ui
src a2, a2, a4 // a2 now instruction that failed
and a3, a2, a3
bnei a3, 0x000002, .LSE_check_l16
# Note: At this point, opcode could technically be one of two things:
# xx0xx2 (L8UI)
# xx8xx2 (Reserved (invalid) opcode)
# It is assumed that we'll never get to this point from an illegal
# opcode, so we don't bother to check for that case and presume this is
# always an L8UI.
/* a2 holds instruction */
movi a4, ~3
rsr.excvaddr a3 // read faulting address
and a4, a3, a4 /* a4 now word aligned read address */
l32i a4, a4, 0 /* perform the actual read */
ssa8l a3 /* sar is now shift to extract a3's byte */
srl a3, a4 /* shift right correct distance */
extui a4, a3, 0, 8 /* mask off bits we need for an l8 */
.LSE_post_fetch:
# We jump back here after either the L8UI or the L16*I routines do the
# necessary work to read the value from memory.
# At this point, a2 holds the faulting instruction and a4 holds the
# correctly read value.
# Restore original SAR value (saved in a5) and update EPC so we'll
# return back to the instruction following the one we just emulated
# Note: Instructions are in this order to avoid pipeline stalls
rsr.epc1 a3
wsr.sar a5
addi a3, a3, 0x3
wsr.epc1 a3
# Stupid opcode tricks: The jumptable we use later on needs 16 bytes
# per entry (so we can avoid a second jump by just doing a RFE inside
# each entry). Unfortunately, however, Xtensa doesn't have an addx16
# operation to make that easy for us. Luckily, all of the faulting
# opcodes we're processing are guaranteed to have bit 3 be zero, which
# means if we just shift the register bits of the opcode down by 3
# instead of 4, we will get the register number multiplied by 2. This
# combined with an addx8 will give us an effective addx16 without
# needing any extra shift operations.
extui a2, a2, 3, 5 /* a2 now destination register 0-15 times 2 */
bgei a2, 12, .LSE_assign_reg # a6..a15 use jumptable
blti a2, 4, .LSE_assign_reg # a0..a1 use jumptable
# We're storing into a2..a5, which are all saved in our "stack" area.
# Calculate the correct address and stick the value in there, then just
# do our normal restore and RFE (no jumps required, which actually
# makes a2..a5 substantially faster).
addx2 a2, a2, a0
s32i a4, a2, 0
# Restore all regs and return
l32i a2, a0, 0x08
l32i a3, a0, 0x0c
l32i a4, a0, 0x10
l32i a5, a0, 0x14
rsr.excsave1 a0 # restore a0 saved by UserExceptionVector
rfe
.LSE_assign_reg:
# At this point, a2 contains the register number times 2, a4 is the
# read value.
movi a3, .LSE_assign_jumptable
addx8 a2, a2, a3 # a2 is now the address to jump to
# Restore everything except a2 and a4
l32i a3, a0, 0x0c
l32i a5, a0, 0x14
jx a2
/* Check the load instruction a2 for an l16si/16ui instruction
a2 is the instruction, a3 is masked instruction */
.balign 4
.LSE_check_l16:
movi a4, 0x001002 /* l16si or l16ui opcode after masking */
bne a3, a4, .LSE_wrong_opcode
# Note: At this point, the opcode could be one of two things:
# xx1xx2 (L16UI)
# xx9xx2 (L16SI)
# Both of these we can handle.
movi a4, ~3
rsr.excvaddr a3 // read faulting address
and a4, a3, a4 /* a4 now word aligned read address */
l32i a4, a4, 0 /* perform the actual read */
ssa8l a3 /* sar is now shift to extract a3's byte */
srl a3, a4 /* shift right correct distance */
extui a4, a3, 0, 16 /* mask off bits we need for an l16 */
bbci a2, 15, .LSE_post_fetch # Not a signed op
bbci a4, 15, .LSE_post_fetch # Value does not require sign-extension
movi a3, 0xFFFF0000
or a4, a3, a4 /* set 32-bit sign bits */
j .LSE_post_fetch
/* If we got here it's not an opcode we can try to fix, so bomb out */
.LSE_wrong_opcode:
# Restore registers so any dump the fatal exception routine produces
# will have correct values
wsr.sar a5 # Restore SAR saved in a5
l32i a2, a0, 0x08
l32i a3, a0, 0x0c
l32i a4, a0, 0x10
l32i a5, a0, 0x14
call0 sdk_user_fatal_exception_handler
.balign 4
.LSE_assign_jumptable:
.org .LSE_assign_jumptable + (16 * 0)
# a0 is saved in excsave1, so just update that with the value
wsr.excsave1 a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 1)
mov a1, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
# NOTE: Opcodes a2 .. a5 are not handled by the jumptable routines
# (they're taken care of directly in .LSE_post_fetch above)
# This leaves 64 bytes of wasted space here. We could fill it with
# other things, but that would just make it harder to understand what's
# going on, and that's bad enough with this routine already. Even on
# the ESP8266, 64 bytes of IRAM wasted aren't the end of the world..
.org .LSE_assign_jumptable + (16 * 6)
mov a6, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 7)
mov a7, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 8)
mov a8, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 9)
mov a9, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 10)
mov a10, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 11)
mov a11, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 12)
mov a12, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 13)
mov a13, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 14)
mov a14, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
.org .LSE_assign_jumptable + (16 * 15)
mov a15, a4
l32i a2, a0, 0x08
l32i a4, a0, 0x10
rsr.excsave1 a0
rfe
/* End of LoadStoreErrorHandler */
.section .bss
NMIHandlerStack: /* stack space for NMI handler */
@ -84,6 +336,12 @@ NMIHandlerStack: /* stack space for NMI handler */
NMIRegisterSaved: /* register space for saving NMI registers */
.skip 4*(16 + 6)
LoadStoreErrorHandlerStack:
.word 0 # a2
.word 0 # a3
.word 0 # a4
.word 0 # a5
/* Save register relative to a0 */
.macro SAVE_REG register, regnum
s32i \register, a0, (0x20 + 4 * \regnum)
@ -181,7 +439,7 @@ CallNMIExceptionHandler:
.type UserExceptionHandler, @function
UserExceptionHandler:
mov a0, sp /* a0 was saved in UserExceptionVector */
mov a0, sp /* a0 was saved by UserExceptionVector */
addi sp, sp, -0x50
s32i a0, sp, 0x10
rsr.ps a0
@ -214,7 +472,7 @@ UserHandleTimer:
and a3, a2, a3 /* a3 = a2 & 0xFFBF, ie remove 0x40 from a2 if set */
bnez a3, UserTimerDone /* bits other than 0x40 are set */
movi a3, 0x40
sub a12, a2, a3 /* a12 - a2 - 0x40 - I think a12 _must_ be zero here? */
sub a12, a2, a3 /* a12 = a2 - 0x40 -- Will be zero if bit 6 set */
call0 sdk__xt_timer_int /* tick timer interrupt */
mov a2, a12 /* restore a2 from a12, ie zero */
beqz a2, UserIntDone
@ -226,7 +484,7 @@ UserIntDone:
break 1, 1 /* non-zero remnant in a2 means fail */
call0 sdk_user_fatal_exception_handler
UserIntExit:
call0 sdk__xt_int_exit /* calls rfi */
call0 sdk__xt_int_exit /* jumps to _xt_user_exit. Never returns here */
/* _xt_user_exit is used to exit interrupt context.
TODO: Find a better place for this to live.