silence syscall-related compiiler warnings

Makefile

@@ -67,6 +67,7 @@ INCLUDES += \
 
 # Add your source files here.
 SRCS += \
+  ./dummy.c \
   ./littlefs/lfs.c \
   ./littlefs/lfs_util.c \
   ./filesystem/filesystem.c \

dummy.c

@@ -0,0 +1,50 @@
+// Joey did this but no copyright is claimed on these dummy functions.
+// We need these to silence linker warnings related to the -specs=nosys.specs flag.
+// Note that we do actually implement some syscalls, like _read and _write (which redirect IO to the USB CDC).
+// But these syscalls never get used, and as such they don't even take up space in the resulting binary.
+
+int _close(int fd);
+int _close(int fd) {
+    (void) fd;
+    return -1;
+}
+    
+int _fstat(int fd, void *buf);
+int _fstat(int fd, void *buf) {
+    (void) fd;
+    (void) buf;
+    return -1;
+}
+    
+int _getpid(void);
+int _getpid(void) {
+    return 0;
+}
+    
+int _isatty(int fd);
+int _isatty(int fd) {
+    (void) fd;
+    return 0;
+}
+    
+int _kill(int pid, int sig);
+int _kill(int pid, int sig) {
+    (void) pid;
+    (void) sig;
+    return -1;
+}
+    
+int _lseek(int fd, int offset, int whence);
+int _lseek(int fd, int offset, int whence) {
+    (void) fd;
+    (void) offset;
+    (void) whence;
+    return -1;
+}
+    
+int _open(const char *path, int flags);
+int _open(const char *path, int flags) {
+    (void) path;
+    (void) flags;
+    return -1;
+}