target/riscv:Perform single step before resume if necessary

Two cases where single step is needed before resume:
1. ebreak used in software breakpoint;
2. a trigger that is taken just before the instruction
   that triggered it is retired.

Signed-off-by: Songhe Zhu <[email protected]> Co-developed-by: Fei Gao <[email protected]> Co-developed-by: xiatianyi <[email protected]>

src/target/riscv/riscv.c

@@ -623,12 +623,12 @@ static int find_first_trigger_by_id(struct target *target, int unique_id)
 
 static unsigned int count_trailing_ones(riscv_reg_t reg)
 {
-	assert(sizeof(riscv_reg_t) * 8 == 64);
-	for (unsigned int i = 0; i < 64; i++) {
+	const unsigned int riscv_reg_bits = sizeof(riscv_reg_t) * CHAR_BIT;
+	for (unsigned int i = 0; i < riscv_reg_bits; i++) {
 		if ((1 & (reg >> i)) == 0)
 			return i;
 	}
-	return 64;
+	return riscv_reg_bits;
 }
 
 static int set_trigger(struct target *target, unsigned int idx, riscv_reg_t tdata1, riscv_reg_t tdata2)
@@ -1576,6 +1576,7 @@ static int riscv_trigger_detect_hit_bits(struct target *target, int64_t *unique_
 
 	// FIXME: Add hit bits support detection and caching
 	RISCV_INFO(r);
+	r->need_single_step = false;
 
 	riscv_reg_t tselect;
 	if (riscv_reg_get(target, &tselect, GDB_REGNO_TSELECT) != ERROR_OK)
@@ -1601,9 +1602,17 @@ static int riscv_trigger_detect_hit_bits(struct target *target, int64_t *unique_
 				break;
 			case CSR_TDATA1_TYPE_MCONTROL:
 				hit_mask = CSR_MCONTROL_HIT;
+				if (get_field(tdata1, CSR_MCONTROL_TIMING) == CSR_MCONTROL_TIMING_BEFORE)
+					r->need_single_step = true;
 				break;
 			case CSR_TDATA1_TYPE_MCONTROL6:
 				hit_mask = CSR_MCONTROL6_HIT0 | CSR_MCONTROL6_HIT1;
+				int hit0 = get_field(tdata1, CSR_MCONTROL6_HIT0);
+				int hit1 = get_field(tdata1, CSR_MCONTROL6_HIT1);
+				int trigger_retired_info = (hit1 << 1) | hit0;
+				if (trigger_retired_info == CSR_MCONTROL6_HIT0_FALSE
+				    || trigger_retired_info == CSR_MCONTROL6_HIT0_BEFORE)
+					r->need_single_step = true;
 				break;
 			case CSR_TDATA1_TYPE_ICOUNT:
 				hit_mask = CSR_ICOUNT_HIT;
@@ -2547,16 +2556,29 @@ static int resume_prep(struct target *target, int current,
 	assert(target->state == TARGET_HALTED);
 	RISCV_INFO(r);
 
+	riscv_reg_t dcsr;
+	if (riscv_reg_get(target, &dcsr, GDB_REGNO_DCSR) != ERROR_OK)
+		return ERROR_FAIL;
+
 	if (!current && riscv_reg_set(target, GDB_REGNO_PC, address) != ERROR_OK)
 		return ERROR_FAIL;
 
 	if (handle_breakpoints) {
 		/* To be able to run off a trigger, we perform a step operation and then
 		 * resume. If handle_breakpoints is true then step temporarily disables
-		 * pending breakpoints so we can safely perform the step. */
-		if (old_or_new_riscv_step_impl(target, current, address, handle_breakpoints,
-				false /* callbacks are not called */) != ERROR_OK)
-			return ERROR_FAIL;
+		 * pending breakpoints so we can safely perform the step.
+		 *
+		 * Two cases where single step is needed before resuming:
+		 * 1. ebreak used in software breakpoint;
+		 * 2. a trigger that is taken just before the instruction that triggered it is retired.
+		 */
+		if (get_field(dcsr, CSR_DCSR_CAUSE) == CSR_DCSR_CAUSE_EBREAK
+		    || (get_field(dcsr, CSR_DCSR_CAUSE) == CSR_DCSR_CAUSE_TRIGGER
+			&& r->need_single_step)) {
+			if (old_or_new_riscv_step_impl(target, current, address, handle_breakpoints,
+					false /* callbacks are not called */) != ERROR_OK)
+				return ERROR_FAIL;
+		}
 	}
 
 	if (r->get_hart_state) {

src/target/riscv/riscv.h

@@ -152,6 +152,9 @@ struct riscv_info {
 	/* record the tinfo of each trigger */
 	unsigned int trigger_tinfo[RISCV_MAX_TRIGGERS];
 
+	/* record the dpc that triggered it is retired. */
+	bool need_single_step;
+
 	/* For each physical trigger contains:
 	 * -1: the hwbp is available
 	 * -4: The trigger is used by the itrigger command