target/riscv:Perform single step before resume if necessary

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.

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

Author: zhusonghe

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)
@@ -668,6 +668,16 @@ static int set_trigger(struct target *target, unsigned int idx, riscv_reg_t tdat
 	const uint32_t type = get_field(tdata1, CSR_TDATA1_TYPE(riscv_xlen(target)));
 	const bool is_mcontrol = type == CSR_TDATA1_TYPE_MCONTROL;
 
+	if (type == CSR_TDATA1_TYPE_MCONTROL) {
+		if (get_field(tdata1_rb, CSR_MCONTROL_TIMING) == CSR_MCONTROL_TIMING_BEFORE)
+			r->halt_before_dpc = true;
+	} else if (type == CSR_TDATA1_TYPE_MCONTROL6) {
+		int hit0 = get_field(tdata1_rb, CSR_MCONTROL6_HIT0);
+		int hit1 = get_field(tdata1_rb, CSR_MCONTROL6_HIT1);
+		if (((hit1 << 1) | hit0) == CSR_MCONTROL6_HIT0_BEFORE)
+			r->halt_before_dpc = true;
+	}
+
 	/* Determine if tdata1 supports what we need.
 	 * For mcontrol triggers, we don't care about
 	 * the value in the read-only "maskmax" field.
@@ -2547,16 +2557,29 @@ 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->halt_before_dpc)) {
+			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 halt_before_dpc;
+
 	/* For each physical trigger contains:
 	 * -1: the hwbp is available
 	 * -4: The trigger is used by the itrigger command