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 <zhusonghe@eswincomputing.com> Co-developed-by: Fei Gao <gaofei@eswincomputing.com> Co-developed-by: xiatianyi <xiatianyi@eswincomputing.com>

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)
@@ -1561,6 +1561,59 @@ int riscv_remove_watchpoint(struct target *target,
 	return ERROR_OK;
 }
 
+static bool mcontrol_hit_supported(struct target *target, riscv_reg_t tdata1,
+				uint64_t hit_mask)
+{
+	/* Check if mcontrol.hit is implemented */
+	bool local_mcontrol_hit_not_supported = false;
+	const riscv_reg_t tdata1_test = set_field(tdata1, CSR_MCONTROL_HIT, 1);
+	riscv_reg_t tdata1_test_rb;
+	riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_test);
+	riscv_reg_get(target, &tdata1_test_rb, GDB_REGNO_TDATA1);
+	int tdata1_test_hit = get_field(tdata1_test, CSR_MCONTROL_HIT);
+	int tdata1_test_rb_hit = get_field(tdata1_test_rb, CSR_MCONTROL_HIT);
+	if (tdata1_test_hit != tdata1_test_rb_hit) {
+		local_mcontrol_hit_not_supported = true;
+	} else {
+		/* mcontrol.hit is implemented, but not fired. */
+		riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_test & ~hit_mask);
+	}
+	return local_mcontrol_hit_not_supported;
+}
+
+static bool mcontrol6_hit_supported(struct target *target, riscv_reg_t tdata1,
+				uint64_t hit_mask, int trigger_hit_info)
+{
+	bool local_mcontrol6_hit_not_supported = false;
+	/* Check if mcontrol6.hit0[1] is implemented. */
+	riscv_reg_t tdata1_hit0_test, tdata1_hit1_test, tdata1_test_rb;
+	tdata1_hit0_test = set_field(tdata1, CSR_MCONTROL6_HIT0, 1);
+	tdata1_hit1_test = set_field(tdata1, CSR_MCONTROL6_HIT1, 1);
+
+	/* Check timing "before" support. */
+	riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_hit0_test);
+	riscv_reg_get(target, &tdata1_test_rb, GDB_REGNO_TDATA1);
+	if (tdata1_test_rb != tdata1_hit0_test) {
+		local_mcontrol6_hit_not_supported = true;
+	} else {
+		riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_test_rb & ~hit_mask);
+		goto done;
+	}
+
+	/* Check timing "after" support. */
+	riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_hit1_test);
+	riscv_reg_get(target, &tdata1_test_rb, GDB_REGNO_TDATA1);
+	if (tdata1_test_rb != tdata1_hit1_test) {
+		local_mcontrol6_hit_not_supported = true;
+	} else {
+		local_mcontrol6_hit_not_supported = false;
+		riscv_reg_set(target, GDB_REGNO_TDATA1, tdata1_test_rb & ~hit_mask);
+	}
+	/* Ignore checking timing "imm after" support. */
+done:
+	return local_mcontrol6_hit_not_supported;
+}
+
 /**
  * Look at the trigger hit bits to find out which trigger is the reason we're
  * halted.  Sets *unique_id to the unique ID of that trigger. If *unique_id is
@@ -1576,6 +1629,7 @@ 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 +1655,26 @@ static int riscv_trigger_detect_hit_bits(struct target *target, int64_t *unique_
 				break;
 			case CSR_TDATA1_TYPE_MCONTROL:
 				hit_mask = CSR_MCONTROL_HIT;
+				bool mcontrol_hit_not_supported = false;
+				if ((tdata1 & hit_mask) == 0)
+					mcontrol_hit_not_supported = mcontrol_hit_supported(target, tdata1, hit_mask);
+				if (get_field(tdata1, CSR_MCONTROL_TIMING) == CSR_MCONTROL_TIMING_BEFORE
+				    && (mcontrol_hit_not_supported || (tdata1 & hit_mask)))
+					r->need_single_step = true;
 				break;
 			case CSR_TDATA1_TYPE_MCONTROL6:
 				hit_mask = CSR_MCONTROL6_HIT0 | CSR_MCONTROL6_HIT1;
+				bool mcontrol6_hit_not_supported = false;
+				int hit0 = get_field(tdata1, CSR_MCONTROL6_HIT0);
+				int hit1 = get_field(tdata1, CSR_MCONTROL6_HIT1);
+				int trigger_hit_info = (hit1 << 1) | hit0;
+				if (trigger_hit_info == CSR_MCONTROL6_HIT0_FALSE) {
+					mcontrol6_hit_not_supported = mcontrol6_hit_supported(target, tdata1,
+					hit_mask, trigger_hit_info);
+				}
+				if (mcontrol6_hit_not_supported
+					|| trigger_hit_info == CSR_MCONTROL6_HIT0_BEFORE)
+					r->need_single_step = true;
 				break;
 			case CSR_TDATA1_TYPE_ICOUNT:
 				hit_mask = CSR_ICOUNT_HIT;
@@ -2553,10 +2624,19 @@ static int resume_prep(struct target *target, int current,
 	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 (target->debug_reason == DBG_REASON_BREAKPOINT
+		    || (target->debug_reason == DBG_REASON_WATCHPOINT
+			&& 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