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>
diff --git a/arch/xtensa/kernel/vectors.S b/arch/xtensa/kernel/vectors.S
index cb8fd44..f9e1ec3 100644
--- a/arch/xtensa/kernel/vectors.S
+++ b/arch/xtensa/kernel/vectors.S
@@ -235,7 +235,7 @@
/* Check for overflow/underflow exception, jump if overflow. */
- _bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow
+ bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow
/*
* Restart window underflow exception.
