arch: arm: correct fault address logging

In ARMv7-M (and ARMv8-M) architecture it is
implementation defined whether separate MMFAR and BFAR are
implemented. This commit ensures that we always get the true
faulting address displayed in case of MemManage- or BusFault.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

arch/arm/core/fault.c

@@ -21,8 +21,10 @@
 #ifdef CONFIG_PRINTK
 #include <misc/printk.h>
 #define PR_EXC(...) printk(__VA_ARGS__)
+#define STORE_xFAR(reg_var, reg) u32_t reg_var = (u32_t)reg
 #else
 #define PR_EXC(...)
+#define STORE_xFAR(reg_var, reg)
 #endif /* CONFIG_PRINTK */
 
 #if (CONFIG_FAULT_DUMP > 0)
@@ -73,15 +75,26 @@ void _FaultDump(const NANO_ESF *esf, int fault)
 	PR_EXC("MMFSR: 0x%x, BFSR: 0x%x, UFSR: 0x%x\n",
 	       SCB_MMFSR, SCB_BFSR, SCB_MMFSR);
 
+	/* In a fault handler, to determine the true faulting address:
+	 * 1. Read and save the MMFAR or BFAR value.
+	 * 2. Read the MMARVALID bit in the MMFSR, or the BFARVALID bit in the
+	 * BFSR. The MMFAR or BFAR address is valid only if this bit is 1.
+	 *
+	 * Software must follow this sequence because another higher priority
+	 * exception might change the MMFAR or BFAR value.
+	 */
+	STORE_xFAR(mmfar, SCB->MMFAR);
+	STORE_xFAR(bfar, SCB->BFAR);
+
 	if (SCB->CFSR & CFSR_MMARVALID_Msk) {
-		PR_EXC("MMFAR: 0x%x\n", SCB->MMFAR);
+		PR_EXC("MMFAR: 0x%x\n", mmfar);
 		if (escalation) {
 			/* clear MMAR[VALID] to reset */
 			SCB->CFSR &= ~CFSR_MMARVALID_Msk;
 		}
 	}
 	if (SCB->CFSR & CFSR_BFARVALID_Msk) {
-		PR_EXC("BFAR: 0x%x\n", SCB->BFAR);
+		PR_EXC("BFAR: 0x%x\n", bfar);
 		if (escalation) {
 			/* clear CFSR_BFAR[VALID] to reset */
 			SCB->CFSR &= ~CFSR_BFARVALID_Msk;
@@ -136,8 +149,18 @@ static void _MpuFault(const NANO_ESF *esf, int fromHardFault)
 		PR_EXC("  Unstacking error\n");
 	} else if (SCB->CFSR & CFSR_DACCVIOL_Msk) {
 		PR_EXC("  Data Access Violation\n");
+		/* In a fault handler, to determine the true faulting address:
+		 * 1. Read and save the MMFAR value.
+		 * 2. Read the MMARVALID bit in the MMFSR.
+		 * The MMFAR address is valid only if this bit is 1.
+		 *
+		 * Software must follow this sequence because another higher
+		 * priority exception might change the MMFAR value.
+		 */
+		STORE_xFAR(mmfar, SCB->MMFAR);
+
 		if (SCB->CFSR & CFSR_MMARVALID_Msk) {
-			PR_EXC("  Address: 0x%x\n", (u32_t)SCB->MMFAR);
+			PR_EXC("  Address: 0x%x\n", mmfar);
 			if (fromHardFault) {
 				/* clear MMAR[VALID] to reset */
 				SCB->CFSR &= ~CFSR_MMARVALID_Msk;
@@ -168,8 +191,18 @@ static void _BusFault(const NANO_ESF *esf, int fromHardFault)
 		PR_EXC("  Unstacking error\n");
 	} else if (SCB->CFSR & CFSR_PRECISERR_Msk) {
 		PR_EXC("  Precise data bus error\n");
+		/* In a fault handler, to determine the true faulting address:
+		 * 1. Read and save the BFAR value.
+		 * 2. Read the BFARVALID bit in the BFSR.
+		 * The BFAR address is valid only if this bit is 1.
+		 *
+		 * Software must follow this sequence because another
+		 * higher priority exception might change the BFAR value.
+		 */
+		STORE_xFAR(bfar, SCB->BFAR);
+
 		if (SCB->CFSR & CFSR_BFARVALID_Msk) {
-			PR_EXC("  Address: 0x%x\n", (u32_t)SCB->BFAR);
+			PR_EXC("  Address: 0x%x\n", bfar);
 			if (fromHardFault) {
 				/* clear CFSR_BFAR[VALID] to reset */
 				SCB->CFSR &= ~CFSR_BFARVALID_Msk;