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xtensa: fix fast_syscall_spill_registers_fixup 

fast_syscall_spill_registers_fixup was not correctly updated by the
'keep a3 and excsave1 on entry to exception handlers' patch: it doesn't
preserve a3 that it gets on entry, breaking _spill_registers in case of
page fault on stack during register spilling, leading to unhandled
exception in kernel mode.

Preserve a3 by saving it in the original _spill_registers stack frame's
a3 during exception handling and restoring it afterwards.

Also fix comments and function bounds annotations.

Reported-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Tested-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Chris Zankel <chris@zankel.net>
This commit is contained in:
Max Filippov 2013-10-15 02:22:42 +04:00 committed by Chris Zankel
parent 61e6cfa80d
commit 244066f4be
1 changed files with 30 additions and 19 deletions
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49
arch/xtensa/kernel/entry.S
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@ -1122,7 +1122,7 @@ ENDPROC(fast_syscall_spill_registers)
* a3: exctable, original value in excsave1
*/
fast_syscall_spill_registers_fixup:
ENTRY(fast_syscall_spill_registers_fixup)
rsr a2, windowbase # get current windowbase (a2 is saved)
xsr a0, depc # restore depc and a0
@ -1134,22 +1134,26 @@ fast_syscall_spill_registers_fixup:
*/
xsr a3, excsave1 # get spill-mask
slli a2, a3, 1 # shift left by one
slli a3, a3, 1 # shift left by one
slli a3, a2, 32-WSBITS
src a2, a2, a3 # a1 = xxwww1yyxxxwww1yy......
slli a2, a3, 32-WSBITS
src a2, a3, a2 # a2 = xxwww1yyxxxwww1yy......
wsr a2, windowstart # set corrected windowstart
rsr a3, excsave1
l32i a2, a3, EXC_TABLE_DOUBLE_SAVE # restore a2
l32i a3, a3, EXC_TABLE_PARAM # original WB (in user task)
srli a3, a3, 1
rsr a2, excsave1
l32i a2, a2, EXC_TABLE_DOUBLE_SAVE # restore a2
xsr a2, excsave1
s32i a3, a2, EXC_TABLE_DOUBLE_SAVE # save a3
l32i a3, a2, EXC_TABLE_PARAM # original WB (in user task)
xsr a2, excsave1
/* Return to the original (user task) WINDOWBASE.
* We leave the following frame behind:
* a0, a1, a2 same
* a3: trashed (saved in excsave_1)
* a3: trashed (saved in EXC_TABLE_DOUBLE_SAVE)
* depc: depc (we have to return to that address)
* excsave_1: a3
* excsave_1: exctable
*/
wsr a3, windowbase
@ -1159,9 +1163,9 @@ fast_syscall_spill_registers_fixup:
* a0: return address
* a1: used, stack pointer
* a2: kernel stack pointer
* a3: available, saved in EXCSAVE_1
* a3: available
* depc: exception address
* excsave: a3
* excsave: exctable
* Note: This frame might be the same as above.
*/
@ -1181,9 +1185,12 @@ fast_syscall_spill_registers_fixup:
rsr a0, exccause
addx4 a0, a0, a3 # find entry in table
l32i a0, a0, EXC_TABLE_FAST_USER # load handler
l32i a3, a3, EXC_TABLE_DOUBLE_SAVE
jx a0
fast_syscall_spill_registers_fixup_return:
ENDPROC(fast_syscall_spill_registers_fixup)
ENTRY(fast_syscall_spill_registers_fixup_return)
/* When we return here, all registers have been restored (a2: DEPC) */
@ -1191,13 +1198,13 @@ fast_syscall_spill_registers_fixup_return:
/* Restore fixup handler. */
xsr a3, excsave1
movi a2, fast_syscall_spill_registers_fixup
s32i a2, a3, EXC_TABLE_FIXUP
s32i a0, a3, EXC_TABLE_DOUBLE_SAVE
rsr a2, windowbase
s32i a2, a3, EXC_TABLE_PARAM
l32i a2, a3, EXC_TABLE_KSTK
rsr a2, excsave1
s32i a3, a2, EXC_TABLE_DOUBLE_SAVE
movi a3, fast_syscall_spill_registers_fixup
s32i a3, a2, EXC_TABLE_FIXUP
rsr a3, windowbase
s32i a3, a2, EXC_TABLE_PARAM
l32i a2, a2, EXC_TABLE_KSTK
/* Load WB at the time the exception occurred. */
@ -1206,8 +1213,12 @@ fast_syscall_spill_registers_fixup_return:
wsr a3, windowbase
rsync
rsr a3, excsave1
l32i a3, a3, EXC_TABLE_DOUBLE_SAVE
rfde
ENDPROC(fast_syscall_spill_registers_fixup_return)
/*
* spill all registers.