RISC-V Semihosting 3 of 3: Warn if encountered but disabled

If semihosting is disabled but there is a semihosting request
encountered in the program, provide a clear hint to the user
what happened and what can be done about it.

Change-Id: I8fa7b821ca9a853cbc884f38d138fa5c8946c84c
Signed-off-by: Jan Matyas <[email protected]>

src/target/riscv/riscv_semihosting.c

@@ -104,28 +104,37 @@ enum semihosting_result riscv_semihosting(struct target *target, int *retval)
 	struct semihosting *semihosting = target->semihosting;
 	assert(semihosting);
 
-	if (!semihosting->is_active) {
-		LOG_TARGET_DEBUG(target, "   -> NONE (!semihosting->is_active)");
-		return SEMIHOSTING_NONE;
-	}
-
 	riscv_reg_t pc;
 	int result = riscv_reg_get(target, &pc, GDB_REGNO_PC);
 	if (result != ERROR_OK)
 		return SEMIHOSTING_ERROR;
 
-	bool sequence_found;
+	bool sequence_found = false;
 	*retval = riscv_semihosting_detect_magic_sequence(target, pc, &sequence_found);
 	if (*retval != ERROR_OK)
 		return SEMIHOSTING_ERROR;
 
+	if (!semihosting->is_active) {
+		if (sequence_found) {
+			// If semihositing is encountered but disabled, provide an additional hint to the user.
+			LOG_TARGET_WARNING(target, "RISC-V semihosting call encountered in the program "
+				"but semihosting is disabled!");
+			LOG_TARGET_WARNING(target, "The target will remain halted (PC = 0x%" TARGET_PRIxADDR ").", pc);
+			LOG_TARGET_WARNING(target, "Hint: Restart your debug session and enable semihosting "
+				"by command 'arm semihosting enable'.");
+		}
+
+		LOG_TARGET_DEBUG(target, "   -> NONE (!semihosting->is_active)");
+		return SEMIHOSTING_NONE;
+	}
+
 	if (!sequence_found) {
 		LOG_TARGET_DEBUG(target, "   -> NONE (no magic)");
 		return SEMIHOSTING_NONE;
 	}
 
 	/* Otherwise we have a semihosting call (and semihosting is enabled).
-	 * Proceed with the semihosting. */
+	 * Proceed with the handling of semihosting. */
 
 	/*
 	 * Perform semihosting call if we are not waiting on a fileio