armv8m: make the debugger handle better faults through ICSR

src/target/cortexm.c

@@ -864,7 +864,21 @@ static target_halt_reason_e cortexm_halt_poll(target_s *target, target_addr64_t
 	priv->dcache_enabled = ccr & CORTEXM_CCR_DCACHE_ENABLE;
 	priv->icache_enabled = ccr & CORTEXM_CCR_ICACHE_ENABLE;
 
-	if ((dfsr & CORTEXM_DFSR_VCATCH) && cortexm_fault_unwind(target))
+	bool fault_state = false;
+	// the V8 may stop before actually executing the instruction
+	// so reading dfsr might not work.
+	// Instead, we check if there are pending faults on ICSR
+	// meaning we stopped while trying to execute a fault
+	// but maybe did not execute it
+	if ((target->target_options & CORTEXM_TOPT_FLAVOUR_V8M)) {
+		const uint32_t icsr = target_mem32_read32(target, CORTEXM_ICSR);
+		const uint32_t pending = CORTEXM_ICSR_VEC_PENDING(icsr);
+		//  catch all pending faults
+		if (pending > 0U && pending < 8U)
+			fault_state = true;
+	} else
+		fault_state = (dfsr & CORTEXM_DFSR_VCATCH) != 0U;
+	if (fault_state && cortexm_fault_unwind(target))
 		return TARGET_HALT_FAULT;
 
 	/* Remember if we stopped on a breakpoint */

src/target/cortexm.h

@@ -69,6 +69,9 @@ extern unsigned cortexm_wait_timeout;
 #define CORTEXM_DWT_MASK(i) (CORTEXM_DWT_BASE + 0x024U + (0x10U * (i)))
 #define CORTEXM_DWT_FUNC(i) (CORTEXM_DWT_BASE + 0x028U + (0x10U * (i)))
 
+/* ARMv8 External Debug Fault Status Register */
+#define CORTEXM_EDFSR (CORTEXM_SCS_BASE + 0xf98U)
+#define CORTEXM_ICSR  (CORTEXM_SCS_BASE + 0xd04U)
 /* Application Interrupt and Reset Control Register (AIRCR) */
 #define CORTEXM_AIRCR_VECTKEY (0x05faU << 16U)
 /* Bits 31:16 - Read as VECTKETSTAT, 0xfa05 */
@@ -188,6 +191,10 @@ extern unsigned cortexm_wait_timeout;
 #define CORTEXM_XPSR_THUMB          (1U << 24U)
 #define CORTEXM_XPSR_EXCEPTION_MASK 0x0000001fU
 
+/* ICSR for ARMv8-M, the exception are the same as IPSR */
+#define CORTEXM_ICSR_VEC_PENDING(x) (((x) >> 12U) & 0x1ffU)
+#define CORTEXM_ICSR_VEC_ACTIVE(x)  (((x) >> 0U) & 0x1ffU)
+
 bool cortexm_attach(target_s *target);
 void cortexm_detach(target_s *target);
 void cortexm_halt_resume(target_s *target, bool step);