misc: fix char-subscripts warnings

src/gdb_main.c

@@ -596,16 +596,16 @@ static void handle_v_packet(char *packet, const size_t plen)
 		} else
 			gdb_putpacketz("E01");
 
-	} else if (!strncmp(packet, "vKill;", 6)) {
+	} else if (!strncmp(packet, "vKill;", 6U)) {
 		/* Kill the target - we don't actually care about the PID that follows "vKill;" */
 		handle_kill_target();
 		gdb_putpacketz("OK");
 
-	} else if (!strncmp(packet, "vRun", 4)) {
+	} else if (!strncmp(packet, "vRun", 4U)) {
 		/* Parse command line for get_cmdline semihosting call */
 		char cmdline[83];
 		char *pcmdline = cmdline;
-		char *tok = packet + 4;
+		char *tok = packet + 4U;
 		if (*tok == ';')
 			++tok;
 		cmdline[0] = '\0';
@@ -618,14 +618,15 @@ static void handle_v_packet(char *packet, const size_t plen)
 				tok++;
 				continue;
 			}
-			if (isxdigit(tok[0]) && isxdigit(tok[1])) {
-				unhexify(pcmdline, tok, 2);
+			/* isxdigit expects int, to handle EOF */
+			if (isxdigit((int8_t)tok[0U]) && isxdigit((int8_t)tok[1U])) {
+				unhexify(pcmdline, tok, 2U);
 				if ((*pcmdline == ' ') || (*pcmdline == '\\')) {
-					pcmdline[1] = *pcmdline;
+					pcmdline[1U] = *pcmdline;
 					*pcmdline++ = '\\';
 				}
 				pcmdline++;
-				tok += 2;
+				tok += 2U;
 				pcmdline[0] = '\0';
 				continue;
 			}

src/morse.c

@@ -21,10 +21,12 @@
 #include "morse.h"
 
 /* Morse code patterns and lengths */
-static const struct {
+typedef struct {
 	uint16_t code;
 	uint8_t bits;
-} morse_letter[] = {
+} morse_char_s;
+
+static const morse_char_s morse_char_lut[] = {
 	{0b0000000000011101, 8},  // 'A' .-
 	{0b0000000101010111, 12}, // 'B' -...
 	{0b0000010111010111, 14}, // 'C' -.-.
@@ -79,20 +81,20 @@ bool morse_update(void)
 		return false;
 
 	if (!bits) {
-		char c = morse_msg[msg_index++];
-		if (!c) {
+		char morse_char = morse_msg[msg_index++];
+		if (!morse_char) {
 			if (morse_repeat) {
-				c = morse_msg[0];
+				morse_char = morse_msg[0];
 				msg_index = 1U;
 			} else {
 				msg_index = SIZE_MAX;
 				return false;
 			}
 		}
-		if (c >= 'A' && c <= 'Z') {
-			c -= 'A';
-			code = morse_letter[c].code;
-			bits = morse_letter[c].bits;
+		if (morse_char >= 'A' && morse_char <= 'Z') {
+			const uint8_t morse_char_index = (uint8_t)morse_char - 'A';
+			code = morse_char_lut[morse_char_index].code;
+			bits = morse_char_lut[morse_char_index].bits;
 		} else {
 			code = 0U;
 			bits = 4U;