xtensa: fix fast_syscall_spill_registers
The original implementation could clobber registers under certain conditions. The Xtensa processor architecture uses windowed registers and the original implementation was using a4 as a temporary register, which under certain conditions could be register a0 of the oldest window frame, and didn't always restore the content correctly. By moving the _spill_registers routine inside the fast system call, it frees up one more register (the return address is not required anymore) for the spill routine. Signed-off-by: Chris Zankel <chris@zankel.net>
This commit is contained in:
Chris Zankel
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3251f1e27a
commit
6b5a1f74e5
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@ -1081,34 +1081,202 @@ ENTRY(fast_syscall_spill_registers)
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rsr a0, sar
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s32i a3, a2, PT_AREG3
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s32i a0, a2, PT_SAR
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/* The spill routine might clobber a4, a7, a8, a11, a12, and a15. */
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s32i a4, a2, PT_AREG4
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s32i a0, a2, PT_AREG5 # store SAR to PT_AREG5
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/* The spill routine might clobber a7, a11, and a15. */
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s32i a7, a2, PT_AREG7
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s32i a8, a2, PT_AREG8
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s32i a11, a2, PT_AREG11
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s32i a12, a2, PT_AREG12
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s32i a15, a2, PT_AREG15
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call0 _spill_registers # destroys a3, a4, and SAR
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/*
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* Rotate ws so that the current windowbase is at bit 0.
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* Assume ws = xxxwww1yy (www1 current window frame).
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* Rotate ws right so that a4 = yyxxxwww1.
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*/
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rsr a0, windowbase
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rsr a3, windowstart # a3 = xxxwww1yy
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ssr a0 # holds WB
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slli a0, a3, WSBITS
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or a3, a3, a0 # a3 = xxxwww1yyxxxwww1yy
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srl a3, a3 # a3 = 00xxxwww1yyxxxwww1
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/* We are done if there are no more than the current register frame. */
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extui a3, a3, 1, WSBITS-1 # a3 = 0yyxxxwww
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movi a0, (1 << (WSBITS-1))
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_beqz a3, .Lnospill # only one active frame? jump
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/* We want 1 at the top, so that we return to the current windowbase */
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or a3, a3, a0 # 1yyxxxwww
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/* Skip empty frames - get 'oldest' WINDOWSTART-bit. */
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wsr a3, windowstart # save shifted windowstart
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neg a0, a3
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and a3, a0, a3 # first bit set from right: 000010000
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ffs_ws a0, a3 # a0: shifts to skip empty frames
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movi a3, WSBITS
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sub a0, a3, a0 # WSBITS-a0:number of 0-bits from right
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ssr a0 # save in SAR for later.
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rsr a3, windowbase
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add a3, a3, a0
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wsr a3, windowbase
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rsync
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rsr a3, windowstart
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srl a3, a3 # shift windowstart
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/* WB is now just one frame below the oldest frame in the register
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window. WS is shifted so the oldest frame is in bit 0, thus, WB
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and WS differ by one 4-register frame. */
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/* Save frames. Depending what call was used (call4, call8, call12),
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* we have to save 4,8. or 12 registers.
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*/
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.Lloop: _bbsi.l a3, 1, .Lc4
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_bbci.l a3, 2, .Lc12
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.Lc8: s32e a4, a13, -16
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l32e a4, a5, -12
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s32e a8, a4, -32
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s32e a5, a13, -12
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s32e a6, a13, -8
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s32e a7, a13, -4
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s32e a9, a4, -28
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s32e a10, a4, -24
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s32e a11, a4, -20
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srli a11, a3, 2 # shift windowbase by 2
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rotw 2
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_bnei a3, 1, .Lloop
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j .Lexit
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.Lc4: s32e a4, a9, -16
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s32e a5, a9, -12
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s32e a6, a9, -8
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s32e a7, a9, -4
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srli a7, a3, 1
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rotw 1
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_bnei a3, 1, .Lloop
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j .Lexit
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.Lc12: _bbci.l a3, 3, .Linvalid_mask # bit 2 shouldn't be zero!
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/* 12-register frame (call12) */
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l32e a0, a5, -12
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s32e a8, a0, -48
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mov a8, a0
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s32e a9, a8, -44
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s32e a10, a8, -40
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s32e a11, a8, -36
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s32e a12, a8, -32
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s32e a13, a8, -28
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s32e a14, a8, -24
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s32e a15, a8, -20
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srli a15, a3, 3
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/* The stack pointer for a4..a7 is out of reach, so we rotate the
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* window, grab the stackpointer, and rotate back.
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* Alternatively, we could also use the following approach, but that
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* makes the fixup routine much more complicated:
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* rotw 1
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* s32e a0, a13, -16
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* ...
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* rotw 2
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*/
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rotw 1
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mov a4, a13
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rotw -1
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s32e a4, a8, -16
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s32e a5, a8, -12
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s32e a6, a8, -8
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s32e a7, a8, -4
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rotw 3
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_beqi a3, 1, .Lexit
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j .Lloop
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.Lexit:
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/* Done. Do the final rotation and set WS */
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rotw 1
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rsr a3, windowbase
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ssl a3
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movi a3, 1
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sll a3, a3
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wsr a3, windowstart
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.Lnospill:
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/* Advance PC, restore registers and SAR, and return from exception. */
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l32i a3, a2, PT_AREG5
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l32i a4, a2, PT_AREG4
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l32i a3, a2, PT_SAR
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l32i a0, a2, PT_AREG0
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wsr a3, sar
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l32i a3, a2, PT_AREG3
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/* Restore clobbered registers. */
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l32i a4, a2, PT_AREG4
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l32i a7, a2, PT_AREG7
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l32i a8, a2, PT_AREG8
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l32i a11, a2, PT_AREG11
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l32i a12, a2, PT_AREG12
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l32i a15, a2, PT_AREG15
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movi a2, 0
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rfe
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.Linvalid_mask:
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/* We get here because of an unrecoverable error in the window
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* registers, so set up a dummy frame and kill the user application.
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* Note: We assume EXC_TABLE_KSTK contains a valid stack pointer.
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*/
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movi a0, 1
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movi a1, 0
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wsr a0, windowstart
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wsr a1, windowbase
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rsync
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movi a0, 0
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rsr a3, excsave1
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l32i a1, a3, EXC_TABLE_KSTK
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movi a4, (1 << PS_WOE_BIT) | LOCKLEVEL
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wsr a4, ps
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rsync
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movi a6, SIGSEGV
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movi a4, do_exit
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callx4 a4
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/* shouldn't return, so panic */
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wsr a0, excsave1
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movi a0, unrecoverable_exception
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callx0 a0 # should not return
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1: j 1b
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ENDPROC(fast_syscall_spill_registers)
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/* Fixup handler.
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@ -1232,209 +1400,6 @@ ENTRY(fast_syscall_spill_registers_fixup_return)
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ENDPROC(fast_syscall_spill_registers_fixup_return)
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/*
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* spill all registers.
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*
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* This is not a real function. The following conditions must be met:
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*
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* - must be called with call0.
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* - uses a3, a4 and SAR.
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* - the last 'valid' register of each frame are clobbered.
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* - the caller must have registered a fixup handler
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* (or be inside a critical section)
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* - PS_EXCM must be set (PS_WOE cleared?)
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*/
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ENTRY(_spill_registers)
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/*
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* Rotate ws so that the current windowbase is at bit 0.
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* Assume ws = xxxwww1yy (www1 current window frame).
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* Rotate ws right so that a4 = yyxxxwww1.
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*/
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rsr a4, windowbase
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rsr a3, windowstart # a3 = xxxwww1yy
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ssr a4 # holds WB
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slli a4, a3, WSBITS
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or a3, a3, a4 # a3 = xxxwww1yyxxxwww1yy
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srl a3, a3 # a3 = 00xxxwww1yyxxxwww1
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/* We are done if there are no more than the current register frame. */
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extui a3, a3, 1, WSBITS-1 # a3 = 0yyxxxwww
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movi a4, (1 << (WSBITS-1))
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_beqz a3, .Lnospill # only one active frame? jump
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/* We want 1 at the top, so that we return to the current windowbase */
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or a3, a3, a4 # 1yyxxxwww
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/* Skip empty frames - get 'oldest' WINDOWSTART-bit. */
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wsr a3, windowstart # save shifted windowstart
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neg a4, a3
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and a3, a4, a3 # first bit set from right: 000010000
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ffs_ws a4, a3 # a4: shifts to skip empty frames
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movi a3, WSBITS
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sub a4, a3, a4 # WSBITS-a4:number of 0-bits from right
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ssr a4 # save in SAR for later.
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rsr a3, windowbase
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add a3, a3, a4
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wsr a3, windowbase
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rsync
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rsr a3, windowstart
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srl a3, a3 # shift windowstart
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/* WB is now just one frame below the oldest frame in the register
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window. WS is shifted so the oldest frame is in bit 0, thus, WB
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and WS differ by one 4-register frame. */
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/* Save frames. Depending what call was used (call4, call8, call12),
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* we have to save 4,8. or 12 registers.
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*/
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_bbsi.l a3, 1, .Lc4
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_bbsi.l a3, 2, .Lc8
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/* Special case: we have a call12-frame starting at a4. */
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_bbci.l a3, 3, .Lc12 # bit 3 shouldn't be zero! (Jump to Lc12 first)
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s32e a4, a1, -16 # a1 is valid with an empty spill area
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l32e a4, a5, -12
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s32e a8, a4, -48
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mov a8, a4
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l32e a4, a1, -16
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j .Lc12c
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.Lnospill:
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ret
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.Lloop: _bbsi.l a3, 1, .Lc4
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_bbci.l a3, 2, .Lc12
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.Lc8: s32e a4, a13, -16
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l32e a4, a5, -12
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s32e a8, a4, -32
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s32e a5, a13, -12
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s32e a6, a13, -8
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s32e a7, a13, -4
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s32e a9, a4, -28
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s32e a10, a4, -24
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s32e a11, a4, -20
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srli a11, a3, 2 # shift windowbase by 2
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rotw 2
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_bnei a3, 1, .Lloop
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.Lexit: /* Done. Do the final rotation, set WS, and return. */
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rotw 1
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rsr a3, windowbase
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ssl a3
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movi a3, 1
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sll a3, a3
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wsr a3, windowstart
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ret
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.Lc4: s32e a4, a9, -16
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s32e a5, a9, -12
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s32e a6, a9, -8
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s32e a7, a9, -4
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srli a7, a3, 1
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rotw 1
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_bnei a3, 1, .Lloop
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j .Lexit
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.Lc12: _bbci.l a3, 3, .Linvalid_mask # bit 2 shouldn't be zero!
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/* 12-register frame (call12) */
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l32e a2, a5, -12
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s32e a8, a2, -48
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mov a8, a2
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.Lc12c: s32e a9, a8, -44
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s32e a10, a8, -40
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s32e a11, a8, -36
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s32e a12, a8, -32
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s32e a13, a8, -28
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s32e a14, a8, -24
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s32e a15, a8, -20
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srli a15, a3, 3
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/* The stack pointer for a4..a7 is out of reach, so we rotate the
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* window, grab the stackpointer, and rotate back.
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* Alternatively, we could also use the following approach, but that
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* makes the fixup routine much more complicated:
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* rotw 1
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* s32e a0, a13, -16
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* ...
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* rotw 2
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*/
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rotw 1
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mov a5, a13
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rotw -1
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s32e a4, a9, -16
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s32e a5, a9, -12
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s32e a6, a9, -8
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s32e a7, a9, -4
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rotw 3
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_beqi a3, 1, .Lexit
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j .Lloop
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.Linvalid_mask:
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/* We get here because of an unrecoverable error in the window
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* registers. If we are in user space, we kill the application,
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* however, this condition is unrecoverable in kernel space.
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*/
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rsr a0, ps
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_bbci.l a0, PS_UM_BIT, 1f
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/* User space: Setup a dummy frame and kill application.
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* Note: We assume EXC_TABLE_KSTK contains a valid stack pointer.
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*/
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movi a0, 1
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movi a1, 0
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wsr a0, windowstart
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wsr a1, windowbase
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rsync
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movi a0, 0
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rsr a3, excsave1
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l32i a1, a3, EXC_TABLE_KSTK
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movi a4, (1 << PS_WOE_BIT) | LOCKLEVEL
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wsr a4, ps
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rsync
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movi a6, SIGSEGV
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movi a4, do_exit
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callx4 a4
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1: /* Kernel space: PANIC! */
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wsr a0, excsave1
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movi a0, unrecoverable_exception
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callx0 a0 # should not return
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1: j 1b
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ENDPROC(_spill_registers)
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#ifdef CONFIG_MMU
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/*
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* We should never get here. Bail out!
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