added some useless shell commands

rocklibc/include/syscall.h

@@ -13,13 +13,14 @@
 #define SYS_FORK    21
 #define SYS_EXEC    22
 #define SYS_DUP2    23
+#define SYS_LSEEK    24
 
 int open(const char* path);
 int write(int fd, const void *buf, size_t count);
 int read(int fd, void *buf, size_t count);
 int close(int fd);
 
-size_t lseek(int fd, size_t offset, int whence);
+int lseek(int fd, size_t offset, int whence);
 
 void exit(int status) __attribute__((noreturn));
 

rocklibc/src/syscall.c

@@ -39,6 +39,10 @@ int read(int fd, void* buf, size_t cnt) {
     return syscall3(SYS_READ, (uint32_t)fd, (uint32_t)buf, (uint32_t)cnt);
 }
 
+int lseek(int fd, size_t offset, int whence) {
+    return syscall3(SYS_LSEEK, (uint32_t)fd, offset, whence);
+}
+
 int close(int fd) {
     return syscall1(SYS_CLOSE, fd);
 }