target: semihosting: Drop gdb_hostio for hosted completely

* Drop all the function pointers from struct target_controller and its instance, gdb_controller;
* Hide the entirety of gdb_hostio.c behind PC_HOSTED macro,
  use `#endif /* PC_HOSTED */` style, like header guards, for long sections;
* Hide all the wrappers like tc_write();
* Hide parsing the F-packet reply from gdb_main_loop (as BMDA is not expected to emit F-requests)

src/gdb_hostio.c

@@ -24,6 +24,8 @@
 #include "gdb_hostio.h"
 #include "gdb_packet.h"
 
+#if PC_HOSTED == 0
+
 int hostio_reply(target_controller_s *const tc, char *const pbuf, const int len)
 {
 	(void)len;
@@ -149,3 +151,4 @@ int hostio_system(target_controller_s *tc, target_addr_t cmd, size_t cmd_len)
 	gdb_putpacket_f("Fsystem,%08X/%X", cmd, cmd_len);
 	return hostio_get_response(tc);
 }
+#endif /* PC_HOSTED */

src/gdb_main.c

@@ -116,6 +116,7 @@ target_controller_s gdb_controller = {
 	.destroy_callback = gdb_target_destroy_callback,
 	.printf = gdb_target_printf,
 
+#if PC_HOSTED == 0
 	.open = hostio_open,
 	.close = hostio_close,
 	.read = hostio_read,
@@ -128,12 +129,17 @@ target_controller_s gdb_controller = {
 	.gettimeofday = hostio_gettimeofday,
 	.isatty = hostio_isatty,
 	.system = hostio_system,
+#endif
 };
 
 /* execute gdb remote command stored in 'pbuf'. returns immediately, no busy waiting. */
 
 int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t size, bool in_syscall)
 {
+#if PC_HOSTED == 1
+	(void)tc;
+	(void)in_syscall;
+#endif
 	bool single_step = false;
 
 	/* GDB protocol main loop */
@@ -280,14 +286,16 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 		break;
 	}
 
-	case 'F': /* Semihosting call finished */
+#if PC_HOSTED == 0
+	case 'F': /* File-I/O call finished */
 		if (in_syscall)
 			return hostio_reply(tc, pbuf, size);
 		else {
 			DEBUG_GDB("*** F packet when not in syscall! '%s'\n", pbuf);
 			gdb_putpacketz("");
 		}
 		break;
+#endif
 
 	case '!': /* Enable Extended GDB Protocol. */
 		/*

src/include/target.h

@@ -159,6 +159,7 @@ struct target_controller {
 	void (*destroy_callback)(target_controller_s *, target_s *target);
 	void (*printf)(target_controller_s *, const char *fmt, va_list);
 
+#if PC_HOSTED == 0
 	/* Interface to host system calls */
 	int (*open)(target_controller_s *, target_addr_t path, size_t path_len, target_open_flags_e flags, mode_t mode);
 	int (*close)(target_controller_s *, int fd);
@@ -172,6 +173,7 @@ struct target_controller {
 	int (*gettimeofday)(target_controller_s *, target_addr_t tv, target_addr_t tz);
 	int (*isatty)(target_controller_s *, int fd);
 	int (*system)(target_controller_s *, target_addr_t cmd, size_t cmd_len);
+#endif
 	target_errno_e errno_;
 	bool interrupted;
 };

src/target/target.c

@@ -574,6 +574,7 @@ void tc_printf(target_s *t, const char *fmt, ...)
 	va_end(ap);
 }
 
+#if PC_HOSTED == 0
 /* Interface to host system calls */
 int tc_open(target_s *t, target_addr_t path, size_t plen, target_open_flags_e flags, mode_t mode)
 {
@@ -602,7 +603,7 @@ int tc_read(target_s *t, int fd, target_addr_t buf, unsigned int count)
 
 int tc_write(target_s *t, int fd, target_addr_t buf, unsigned int count)
 {
-#if PC_HOSTED == 0
+	/* BMP feature: redirect semihosting writes to debug_serial */
 	if (t->stdout_redirected && (fd == STDOUT_FILENO || fd == STDERR_FILENO)) {
 		while (count) {
 			uint8_t tmp[STDOUT_READ_BUF_SIZE];
@@ -616,8 +617,8 @@ int tc_write(target_s *t, int fd, target_addr_t buf, unsigned int count)
 		}
 		return 0;
 	}
-#endif
 
+	/* Delegate to gdb_hostio */
 	if (t->tc->write == NULL)
 		return 0;
 	return t->tc->write(t->tc, fd, buf, count);
@@ -688,3 +689,4 @@ int tc_system(target_s *t, target_addr_t cmd, size_t cmdlen)
 	}
 	return t->tc->system(t->tc, cmd, cmdlen);
 }
+#endif /* PC_HOSTED */