bsd-user: Implement do_freebsd_realpathat syscall

Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>

bsd-user/freebsd/os-stat.h

@@ -634,4 +634,30 @@ static inline abi_long do_freebsd_fcntl(abi_long arg1, abi_long arg2,
     return ret;
 }
 
+#if defined(__FreeBSD_version) && __FreeBSD_version >= 1300080
+extern int __realpathat(int fd, const char *path, char *buf, size_t size,
+        int flags);
+/* https://svnweb.freebsd.org/base?view=revision&revision=358172 */
+/* no man page */
+static inline abi_long do_freebsd_realpathat(abi_long arg1, abi_long arg2,
+        abi_long arg3, abi_long arg4, abi_long arg5)
+{
+    abi_long ret;
+    void *p, *b;
+
+    LOCK_PATH(p, arg2);
+    b = lock_user(VERIFY_WRITE, arg3, arg4, 0);
+    if (b == NULL) {
+        UNLOCK_PATH(p, arg2);
+        return -TARGET_EFAULT;
+    }
+
+    ret = get_errno(__realpathat(arg1, p, b, arg4, arg5));
+    UNLOCK_PATH(p, arg2);
+    unlock_user(b, arg3, ret);
+
+    return ret;
+}
+#endif
+
 #endif /* BSD_USER_FREEBSD_OS_STAT_H */