[XTENSA] Fix register corruption for certain processor configurations

For processor configurations that have optional registers
(compiler-used but non-coprocessor), user space registers
might get corrupted when there are only 4 registers in
the current window-frame, ie. register a4 belongs to the
oldest frame in the register file.

Signed-off-by: Chris Zankel <chris@zankel.net>

diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 24770b6a5e4c5694aa3a4af7f4cbb2e8236781bc..dfd35dcc1cb553cb9105f5f824250a3b388e40fb 100644 (file)
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -395,55 +395,49 @@ common_exception_return:
        /* Jump if we are returning from kernel exceptions. */
 
 1:     l32i    a3, a1, PT_PS
-       _bbsi.l a3, PS_UM_BIT, 2f
-       j       kernel_exception_exit
+       _bbci.l a3, PS_UM_BIT, 4f
 
        /* Specific to a user exception exit:
         * We need to check some flags for signal handling and rescheduling,
         * and have to restore WB and WS, extra states, and all registers
         * in the register file that were in use in the user task.
-        */
-
-2:     wsr     a3, PS          /* disable interrupts */
-
-       /* Check for signals (keep interrupts disabled while we read TI_FLAGS)
-        * Note: PS.INTLEVEL = 0, PS.EXCM = 1
+        * Note that we don't disable interrupts here. 
         */
 
        GET_THREAD_INFO(a2,a1)
        l32i    a4, a2, TI_FLAGS
 
-       /* Enable interrupts again.
-        * Note: When we get here, we certainly have handled any interrupts.
-        *       (Hint: There is only one user exception frame on stack)
-        */
-
-       movi    a3, 1 << PS_WOE_BIT
-
        _bbsi.l a4, TIF_NEED_RESCHED, 3f
        _bbci.l a4, TIF_SIGPENDING, 4f
 
        l32i    a4, a1, PT_DEPC
        bgeui   a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
-       /* Reenable interrupts and call do_signal() */
 
-       wsr     a3, PS
+       /* Call do_signal() */
+
        movi    a4, do_signal   # int do_signal(struct pt_regs*, sigset_t*)
        mov     a6, a1
        movi    a7, 0
        callx4  a4
        j       1b
 
-3:     /* Reenable interrupts and reschedule */
+3:     /* Reschedule */
 
-       wsr     a3, PS
        movi    a4, schedule    # void schedule (void)
        callx4  a4
        j       1b
 
-       /* Restore the state of the task and return from the exception. */
+4:     /* Restore optional registers. */
+
+       load_xtregs_opt a1 a2 a4 a5 a6 a7 PT_XTREGS_OPT
 
-4:     /* a2 holds GET_CURRENT(a2,a1)  */
+       wsr     a3, PS          /* disable interrupts */
+
+       _bbci.l a3, PS_UM_BIT, kernel_exception_exit
+
+user_exception_exit:
+
+       /* Restore the state of the task and return from the exception. */
 
        /* Switch to the user thread WINDOWBASE. Save SP temporarily in DEPC */
 
@@ -509,10 +503,6 @@ common_exception_return:
 
 kernel_exception_exit:
 
-       /* Disable interrupts (a3 holds PT_PS) */
-
-       wsr     a3, PS
-
 #ifdef PREEMPTIBLE_KERNEL
 
 #ifdef CONFIG_PREEMPT
@@ -591,10 +581,6 @@ kernel_exception_exit:
 
 common_exception_exit:
 
-       /* Restore optional registers. */
-
-       load_xtregs_opt a1 a3 a4 a5 a6 a7 PT_XTREGS_OPT
-
        /* Restore address registers. */
 
        _bbsi.l a2, 1, 1f