imx233: fix IRQ handler w.r.t unwinder

The IRQ handler saves registers on the IRQ stack, saves the old PC to imx233
HW_DIGCTL_SCRATCH0 register and switcht to SVC for the actual handling. The
old code had a problem in that if the unwinder is called during the IRQ (for
example by the watchdog), then __get_sp() will use SPSR_svc to discover the
previous mode, switch to it and recover SP. But SPSR_svc is invalid, it should
be SPSR_irq but we switch from IRQ to SVC mode. The new code copies SPSR_irq
to SPSR_svc in IRQ to fix this problem. It also saves/restore SCRATCH0 in
case I one day renable nested interrupts or use SCRATCH0 for other purposes.
I also changed the old watchdog code to call UIE directly instead of trying
to make the code crash with a SWI.

Change-Id: Id87462d410764b019bd2aa9adc71cb917ade32e3

1 files changed, 6 insertions, 5 deletions

diff --git a/firmware/target/arm/imx233/system-imx233.c b/firmware/target/arm/imx233/system-imx233.c
index 5fd162a1ca..c6f974b108 100644
--- a/firmware/target/arm/imx233/system-imx233.c
+++ b/firmware/target/arm/imx233/system-imx233.c
@@ -52,15 +52,16 @@
 #define WATCHDOG_HW_DELAY   (10 * HZ)
 #define WATCHDOG_SW_DELAY   (5 * HZ)
 
+void UIE(unsigned int pc, unsigned int num);
+
 static void woof_woof(void)
 {
-    /* stop hadrware watchdog, we catched the error */
+    /* stop hardware watchdog, we catched the error */
     imx233_rtc_enable_watchdog(false);
+    /* recover current PC and trigger abort, so in the hope to get a useful
+     * backtrace */
     uint32_t pc = HW_DIGCTL_SCRATCH0;
-    /* write a "SWI #0xdead" instruction at the faulty instruction so that it
-     * will trigger a proper backtrace */
-    *(uint32_t *)pc = 0xef00dead;
-    commit_discard_idcache();
+    UIE(pc, 4);
 }
 
 static void good_dog(void)