xtensa: keep exception/interrupt stack continuous
Restore original a0 in the kernel exception stack frame. This way it
looks like the frame that got interrupt/exception did alloca (copy a0 and
a1 spilled under old stack to the new location as well) to save registers
and then did a call to handler.
The point where interrupt/exception was taken is not in the stack chain,
only in pt_regs (call4 from that address can be simulated to keep it in
the stack trace).
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 51e9877..e955f60 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -122,6 +122,7 @@
/* Save SAR and turn off single stepping */
movi a2, 0
+ wsr a2, depc # terminate user stack trace with 0
rsr a3, sar
xsr a2, icountlevel
s32i a3, a1, PT_SAR
@@ -301,7 +302,18 @@
s32i a14, a1, PT_AREG14
s32i a15, a1, PT_AREG15
+ _bnei a2, 1, 1f
+
+ /* Copy spill slots of a0 and a1 to imitate movsp
+ * in order to keep exception stack continuous
+ */
+ l32i a3, a1, PT_SIZE
+ l32i a0, a1, PT_SIZE + 4
+ s32e a3, a1, -16
+ s32e a0, a1, -12
1:
+ l32i a0, a1, PT_AREG0 # restore saved a0
+ wsr a0, depc
#ifdef KERNEL_STACK_OVERFLOW_CHECK
@@ -346,12 +358,12 @@
s32i a0, a1, PT_EXCCAUSE
s32i a3, a2, EXC_TABLE_FIXUP
- /* All unrecoverable states are saved on stack, now, and a1 is valid,
- * so we can allow exceptions and interrupts (*) again.
- * Set PS(EXCM = 0, UM = 0, RING = 0, OWB = 0, WOE = 1, INTLEVEL = X)
+ /* All unrecoverable states are saved on stack, now, and a1 is valid.
+ * Now we can allow exceptions again. In case we've got an interrupt
+ * PS.INTLEVEL is set to LOCKLEVEL disabling furhter interrupts,
+ * otherwise it's left unchanged.
*
- * (*) We only allow interrupts if they were previously enabled and
- * we're not handling an IRQ
+ * Set PS(EXCM = 0, UM = 0, RING = 0, OWB = 0, WOE = 1, INTLEVEL = X)
*/
rsr a3, ps
@@ -362,28 +374,30 @@
moveqz a3, a2, a0 # a3 = LOCKLEVEL iff interrupt
movi a2, 1 << PS_WOE_BIT
or a3, a3, a2
- rsr a0, exccause
+ rsr a2, exccause
+ /* restore return address (or 0 if return to userspace) */
+ rsr a0, depc
xsr a3, ps
s32i a3, a1, PT_PS # save ps
/* Save lbeg, lend */
- rsr a2, lbeg
+ rsr a4, lbeg
rsr a3, lend
- s32i a2, a1, PT_LBEG
+ s32i a4, a1, PT_LBEG
s32i a3, a1, PT_LEND
/* Save SCOMPARE1 */
#if XCHAL_HAVE_S32C1I
- rsr a2, scompare1
- s32i a2, a1, PT_SCOMPARE1
+ rsr a3, scompare1
+ s32i a3, a1, PT_SCOMPARE1
#endif
/* Save optional registers. */
- save_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
+ save_xtregs_opt a1 a3 a4 a5 a6 a7 PT_XTREGS_OPT
#ifdef CONFIG_TRACE_IRQFLAGS
l32i a4, a1, PT_DEPC
@@ -391,8 +405,7 @@
* while PS.EXCM was set, i.e. interrupts disabled.
*/
bgeui a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 1f
- l32i a4, a1, PT_EXCCAUSE
- bnei a4, EXCCAUSE_LEVEL1_INTERRUPT, 1f
+ bnei a2, EXCCAUSE_LEVEL1_INTERRUPT, 1f
/* We came here with an interrupt means interrupts were enabled
* and we've just disabled them.
*/
@@ -407,8 +420,8 @@
rsr a4, excsave1
mov a6, a1 # pass stack frame
- mov a7, a0 # pass EXCCAUSE
- addx4 a4, a0, a4
+ mov a7, a2 # pass EXCCAUSE
+ addx4 a4, a2, a4
l32i a4, a4, EXC_TABLE_DEFAULT # load handler
/* Call the second-level handler */