Fix: Clang fall-through warnings

src/gdb_main.c

@@ -195,7 +195,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 	}
 	case 's': /* 's [addr]': Single step [start at addr] */
 		single_step = true;
-		/* fall through */
+		BMD_FALLTHROUGH
 	case 'c': /* 'c [addr]': Continue [at addr] */
 	case 'C': /* 'C sig[;addr]': Continue with signal [at addr] */
 		if (!cur_target) {
@@ -205,7 +205,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 
 		target_halt_resume(cur_target, single_step);
 		SET_RUN_STATE(true);
-		/* fall through */
+		BMD_FALLTHROUGH
 	case '?': { /* '?': Request reason for target halt */
 		/*
 		 * This packet isn't documented as being mandatory,
@@ -714,7 +714,7 @@ static void handle_v_packet(char *packet, const size_t plen)
 		switch (packet[6]) {
 		case 's': /* 's': Single step */
 			single_step = true;
-			/* fall through */
+			BMD_FALLTHROUGH
 		case 'c': /* 'c': Continue */
 		case 'C': /* 'C sig': Continue with signal */
 			if (!cur_target) {

src/include/general.h

@@ -21,6 +21,10 @@
 #ifndef INCLUDE_GENERAL_H
 #define INCLUDE_GENERAL_H
 
+#if !defined(__cplusplus) && __STDC__ != 1
+#error "Black Magic Debug must be built in a standards compliant C mode"
+#endif
+
 #ifndef _GNU_SOURCE
 // NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
 #define _GNU_SOURCE
@@ -62,15 +66,6 @@
 
 #if PC_HOSTED == 0
 /*
- * XXX: This entire system needs replacing with something better thought out
- *
- * When built as firmware, if the target supports debugging, DEBUG_ERROR, DEBUG_WARN and
- * DEBUG_INFO get defined to a macro that turns them into printf() calls. The rest of the
- * levels turn into no-ops.
- *
- * When built as BMDA, the debug macros all turn into various kinds of console-printing
- * function, w/ gating for diagnostics other than warnings and info.
- *
  * XXX: This is not really the proper place for all this as this is too intrusive into
  * the rest of the code base. The correct way to do this would be to define a debug
  * logging layer and allow BMDA to override the default logging subsystem via
@@ -130,6 +125,25 @@ void debug_serial_send_stdout(const uint8_t *data, size_t len);
 #undef MAX
 #define MAX(x, y) (((x) > (y)) ? (x) : (y))
 
+/* Define this macro helper if the compiler doesn't for us */
+#ifndef __has_c_attribute
+#define __has_c_attribute(x) 0
+#endif
+
+/* If we're in C23 mode or newer, we can use the proper fallthrough attribute */
+#if __STDC_VERSION__ >= 202311L && __has_c_attribute(fallthrough)
+#define BMD_FALLTHROUGH [[fallthrough]];
+/* If we're on Clang, we can use the old style attribute on Clang 10 and newer */
+#elif defined(__clang__) && __clang_major__ >= 10
+#define BMD_FALLTHROUGH __attribute__((fallthrough));
+/* If we're on GCC then we have to be on at least GCC 7 for the attribute */
+#elif defined(__GNUC__) && __GNUC__ >= 7
+#define BMD_FALLTHROUGH __attribute__((fallthrough));
+/* If none of the above is true, make the annotation a no-op */
+#else
+#define BMD_FALLTHROUGH
+#endif
+
 #if defined(_MSC_VER) && !defined(__clang__)
 #define BMD_UNUSED
 #else

src/target/renesas_ra.c

@@ -702,6 +702,7 @@ static bool renesas_rv40_pe_mode(target_s *const target, const pe_mode_e pe_mode
 	case PNR_SERIES_RA6E2:
 	case PNR_SERIES_RA6T2:
 		has_fmeprot = true;
+		BMD_FALLTHROUGH
 	default:
 		break;
 	}

src/target/stm32f1.c

@@ -541,8 +541,8 @@ bool stm32f1_probe(target_s *target)
 	case 0x422U: /* STM32F30x */
 	case 0x446U: /* STM32F303xD/E and STM32F398xE */
 		target_add_ram(target, 0x10000000, 0x4000);
-		/* fall through */
 
+		BMD_FALLTHROUGH
 	case 0x432U: /* STM32F37x */
 	case 0x439U: /* STM32F302C8 */
 		target->driver = "STM32F3";

src/target/stm32f4.c

@@ -604,7 +604,7 @@ static bool optcr_mask(target_s *const t, uint32_t *const val)
 		break;
 	case ID_STM32F72X:
 		val[2] &= ~0x800000ffU;
-		/* Fall through*/
+		BMD_FALLTHROUGH
 	case ID_STM32F74X:
 		val[0] &= ~0x3f000000U;
 		break;