diff --git a/Makefile.vars b/Makefile.vars
index f38555b..a906a31 100755
--- a/Makefile.vars
+++ b/Makefile.vars
@@ -53,7 +53,6 @@
 
 # Web directory - where the HTML files will be put.
  HTMLDIR := ./html
-
 #******************************************************************************#
 # Object names, libs                                                           #
 #******************************************************************************#
@@ -64,7 +63,6 @@
 # Static library name
  ANAME := $(if $(FOR_WINDOWS),lib$(NAME).lib,lib$(NAME).a)
  ANAMES := lib$(NAME).lib lib$(NAME).a lib$(NAME).dll.a
-
 #******************************************************************************#
 # Binary utilities                                                             #
 #******************************************************************************#
@@ -78,7 +76,7 @@
 # - More flags (for profiling, ...)
 #CMOREFLAGS :=
 # - Check flags (for warnings)
- CWERROR := all extra no-unused-macros no-vla
+ CWERROR := all extra no-unused-macros no-vla no-nonnull-compare
 ifdef MORE_WARNINGS
  CWERROR += shadow write-strings redundant-decls format format-nonliteral \
 	format-security implicit-function-declaration \
diff --git a/include/libp7.h b/include/libp7.h
index 34822e2..5bd7067 100644
--- a/include/libp7.h
+++ b/include/libp7.h
@@ -83,12 +83,16 @@ extern const char *p7_error_strings[];
 /*  Random stuff                                                              */
 /* ************************************************************************** */
 /* Filename and dirname */
-extern int p7_validate_filename(const char *p7_arg_filename);
-extern int p7_validate_dirname(const char *p7_arg_dirname);
+extern int p7_validate_filename(const char *p7_arg_filename)
+	p7_attribute_THROW p7_attribute_wur p7_attribute_nonnull(1);
+extern int p7_validate_dirname(const char *p7_arg_dirname)
+	p7_attribute_THROW p7_attribute_wur p7_attribute_nonnull(1);
 
 /* Make settings out of a string */
-extern int p7_makesettings(p7_streamsettings_t *p7_arg_settings,
-	const char *p7_arg_s);
+# define p7_attrs_makesettings \
+	p7_attribute_THROW p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_makesettings, p7_attrs_makesettings,
+	p7_streamsettings_t *p7_arg_settings, const char *p7_arg_string)
 /* ************************************************************************** */
 /*  Core functions                                                            */
 /* ************************************************************************** */
@@ -109,137 +113,217 @@ extern int p7_makesettings(p7_streamsettings_t *p7_arg_settings,
 # define P7_TERM            p7_flag_term
 
 /* "Normal" initialization */
-extern int p7_init(p7_handle_t **p7_arg_handle, unsigned int p7_arg_flags);
-extern int p7_cominit(p7_handle_t **p7_arg_handle, unsigned int p7_arg_flags,
-	const char *p7_arg_path, const p7_streamsettings_t *p7_arg_settings);
-extern int p7_comlist(p7_list_device_t *p7_arg_callback, void *p7_arg_cookie);
+# define p7_attrs_init    p7_attribute_THROW
+p7_declare_func(p7_init, int, p7_attrs_init,
+	p7_handle_t **p7_arg_handle, unsigned int p7_arg_flags)
+# define p7_attrs_cominit p7_attribute_THROW p7_attribute_nonnull(3)
+p7_declare_func(p7_cominit, int, p7_attrs_cominit,
+	p7_handle_t **p7_arg_handle, unsigned int p7_arg_flags,
+	const char *p7_arg_path, const p7_streamsettings_t *p7_arg_settings)
 
-/* De-initialization */
-extern void p7_exit(p7_handle_t *p7_arg_handle);
+/* Deinitialization */
+# define p7_attrs_exit p7_attribute_nonnull(1)
+p7_declare_func(p7_exit, void, p7_attrs_exit,
+	p7_handle_t *p7_arg_handle)
+
+/* List serial devices */
+# define p7_attrs_comlist p7_attribute_nonnull(1)
+p7_declare_func(p7_comlist, int, p7_attrs_comlist,
+	p7_list_device_t *p7_arg_callback, void *p7_arg_cookie)
 /* ************************************************************************** */
 /*  MCS interaction                                                           */
 /* ************************************************************************** */
 /* List files */
-extern int p7_mcs_list(p7_handle_t *p7_arg_handle,
-	p7_mcslist_t *p7_arg_callback, void *p7_arg_cookie);
+# define p7_attrs_mcs_list p7_attribute_nonnull(1)
+p7_declare_ufunc(p7_mcs_list, p7_attrs_mcs_list,
+	p7_handle_t *p7_arg_handle,
+	p7_mcslist_t *p7_arg_callback, void *p7_arg_cookie)
 
 /* Send a file */
-extern int p7_mcs_send(p7_handle_t *p7_arg_handle, g1m_mcsfile_t *p7_arg_file,
-	int p7_arg_overwrite, p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp);
+# define p7_attrs_mcs_send p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_mcs_send, p7_attrs_mcs_send,
+	p7_handle_t *p7_arg_handle, g1m_mcsfile_t *p7_arg_file,
+	int p7_arg_overwrite, p7_confirm_t *p7_arg_confirm,
+	p7_disp_t *p7_arg_disp)
 
 /* Request a file */
-extern int p7_mcs_request(p7_handle_t *p7_arg_handle,
-	g1m_mcsfile_t **p7_arg_file, g1m_mcshead_t *p7_arg_head,
-	p7_disp_t *p7_arg_disp);
+# define p7_attrs_mcs_request \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) p7_attribute_nonnull(3)
+p7_declare_ufunc(p7_mcs_request, p7_attrs_mcs_request,
+	p7_handle_t *p7_arg_handle, g1m_mcsfile_t **p7_arg_file,
+	g1m_mcshead_t *p7_arg_head, p7_disp_t *p7_arg_disp)
 /* ************************************************************************** */
 /*  Storage memory interaction                                                */
 /* ************************************************************************** */
 /* Send a file using buffer */
-extern int p7_send(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer,
+# define p7_attrs_send \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) \
+	p7_attribute_nonnull(4) p7_attribute_nonnull(5)
+p7_declare_ufunc(p7_send, p7_attrs_send,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
 	const char *p7_arg_devname, int p7_arg_overwrite,
-	p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp);
+	p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp)
 
 /* Receive a file using buffer */
-extern int p7_request(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer,
+# define p7_attrs_request \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) \
+	p7_attribute_nonnull(4) p7_attribute_nonnull(5)
+p7_declare_ufunc(p7_request, p7_attrs_request,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
-	const char *p7_arg_devname, p7_disp_t *p7_arg_disp);
+	const char *p7_arg_devname, p7_disp_t *p7_arg_disp)
 
 /* FILE version of the two previous functions */
 # ifndef P7_DISABLED_FILE
-extern int p7_sendfile(p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
+#  define p7_attrs_sendfile \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) \
+	p7_attribute_nonnull(4) p7_attribute_nonnull(5)
+p7_declare_ufunc(p7_sendfile, p7_attrs_sendfile,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
 	const char *p7_arg_devname, int p7_arg_overwrite,
-	p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp);
-extern int p7_reqfile(p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
+	p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp)
+
+#  define p7_attrs_reqfile \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) \
+	p7_attribute_nonnull(4) p7_attribute_nonnull(5)
+p7_declare_ufunc(p7_reqfile, p7_attrs_reqfile,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
-	const char *p7_arg_devname, p7_disp_t *p7_arg_disp);
+	const char *p7_arg_devname, p7_disp_t *p7_arg_disp)
 # endif
 
 /* Memory version of the send function */
-extern int p7_sendmem(p7_handle_t *p7_arg_handle,
-	const void *p7_arg_mem, size_t p7_arg_size,
+# define p7_attrs_sendmem \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) \
+	p7_attribute_nonnull(5) p7_attribute_nonnull(6)
+p7_declare_ufunc(p7_sendmem, p7_attrs_sendmem,
+	p7_handle_t *p7_arg_handle, const void *p7_arg_mem, size_t p7_arg_size,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
-	const char *p7_arg_devname, int p7_arg_overwrite,
-	p7_confirm_t *p7_arg_confirm, p7_disp_t *p7_arg_disp);
+	const char *p7_arg_devname,
+	int p7_arg_overwrite, p7_confirm_t *p7_arg_confirm,
+	p7_disp_t *p7_arg_disp)
 
 /* Create a directory */
-extern int p7_createdir(p7_handle_t *p7_arg_handle,
-	const char *p7_arg_dirname, const char *p7_arg_devname);
+# define p7_attrs_createdir p7_attribute_nonnull(1) p7_attribute_nonnull(3)
+p7_declare_ufunc(p7_createdir, p7_attrs_createdir,
+	p7_handle_t *p7_arg_handle,
+	const char *p7_arg_dirname, const char *p7_arg_devname)
 
 /* Delete distant file */
-extern int p7_delete(p7_handle_t *p7_arg_handle,
-	const char *p7_arg_dirname, const char *p7_arg_filename,
-	const char *p7_arg_devname);
+# define p7_attrs_delete \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(3) p7_attribute_nonnull(4)
+p7_declare_ufunc(p7_delete, p7_attrs_delete,
+	p7_handle_t *p7_arg_handle, const char *p7_arg_dirname,
+	const char *p7_arg_filename, const char *p7_arg_devname)
 
 /* Copy file on distant device */
-extern int p7_copy(p7_handle_t *p7_arg_handle,
+# define p7_attrs_copy \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(3) \
+	p7_attribute_nonnull(5) p7_attribute_nonnull(6)
+p7_declare_ufunc(p7_copy, p7_attrs_copy,
+	p7_handle_t *p7_arg_handle,
 	const char *p7_arg_dirname, const char *p7_arg_filename,
 	const char *p7_arg_newdir, const char *p7_arg_newname,
-	const char *p7_arg_devname);
+	const char *p7_arg_devname)
 
 /* List files */
-extern int p7_list(p7_handle_t *p7_arg_handle, const char *p7_arg_devname,
-	p7_list_t *p7_arg_callback, void *p7_arg_cookie);
+# define p7_attrs_list p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_list, p7_attrs_list,
+	p7_handle_t *p7_arg_handle, const char *p7_arg_devname,
+	p7_list_t *p7_arg_callback, void *p7_arg_cookie)
 
 /* Get the free memory amount */
-extern int p7_getfreemem(p7_handle_t *p7_arg_handle, const char *p7_arg_devname,
-	p7uint_t *p7_arg_capacity);
+# define p7_attrs_getfreemem p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_getfreemem, p7_attrs_getfreemem,
+	p7_handle_t *p7_arg_handle, const char *p7_arg_devname,
+	p7uint_t *p7_arg_capacity)
 
 /* Reset filesystem on a distant device */
-extern int p7_reset(p7_handle_t *p7_arg_handle, const char *p7_arg_devname);
+# define p7_attrs_reset p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_reset, p7_attrs_reset,
+	p7_handle_t *p7_arg_handle, const char *p7_arg_devname)
 
 /* Optimize distant device */
-extern int p7_optimize(p7_handle_t *p7_arg_handle, const char *p7_arg_devname);
+# define p7_attrs_optimize p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_optimize, p7_attrs_optimize,
+	p7_handle_t *p7_arg_handle, const char *p7_arg_devname)
 /* ************************************************************************** */
 /*  Miscallenous interactions                                                 */
 /* ************************************************************************** */
 /* Poke the calculator in order to keep it happy */
-extern int p7_poke(p7_handle_t *p7_arg_handle);
+# define p7_attrs_poke p7_attribute_nonnull(1)
+p7_declare_ufunc(p7_poke, p7_attrs_poke,
+	p7_handle_t *p7_arg_handle)
 
 /* Send an update.exe */
-extern int p7_sendexe(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer,
-	p7uint_t p7_arg_loadaddr, p7uint_t p7_arg_straddr, p7_disp_t *p7_arg_disp);
+# define p7_attrs_sendexe p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_sendexe, p7_attrs_sendexe,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
+	p7uint_t p7_arg_loadaddr, p7uint_t p7_arg_straddr, p7_disp_t *p7_arg_disp)
 
 /* Backup the flash ROM, bootcode and CASIOWIN entry */
-extern int p7_backup_rom(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer, p7_disp_t *p7_arg_disp);
-extern int p7_backup_ram(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer, p7_disp_t *p7_arg_disp);
-extern int p7_backup_boot(p7_handle_t *p7_arg_handle,
-	const p7_buffer_t *p7_arg_buffer, p7_disp_t *p7_arg_disp);
-extern int p7_backup_casiowin_entry(p7_handle_t *p7_arg_handle,
-	p7_casiowin_entry_t *p7_arg_entry);
+# define p7_attrs_backup_rom p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_rom, p7_attrs_backup_rom,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
+	p7_disp_t *p7_arg_disp)
+# define p7_attrs_backup_ram p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_ram, p7_attrs_backup_ram,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
+	p7_disp_t *p7_arg_disp)
+# define p7_attrs_backup_boot p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_boot, p7_attrs_backup_boot,
+	p7_handle_t *p7_arg_handle, const p7_buffer_t *p7_arg_buffer,
+	p7_disp_t *p7_arg_disp)
+# define p7_attrs_backup_casiowin_entry \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_casiowin_entry, p7_attrs_backup_casiowin_entry,
+	p7_handle_t *p7_arg_handle, p7_casiowin_entry_t *p7_arg_entry)
 
 /* set link settings */
-extern int p7_setlink(p7_handle_t *p7_arg_handle,
-	const p7_streamsettings_t *p7_arg_settings);
+# define p7_attrs_setlink p7_attribute_nonnull(1)
+p7_declare_ufunc(p7_setlink, p7_attrs_setlink,
+	p7_handle_t *p7_arg_handle, const p7_streamsettings_t *p7_arg_settings)
 
 /* FILE version of the previous functions */
 # ifndef P7_DISABLED_FILE
 /* Send an update.exe */
-extern int p7_sendexe_file(p7_handle_t *p7_arg_handle,
-	FILE *p7_arg_exe, p7uint_t p7_arg_loadaddr, p7uint_t p7_arg_straddr,
-	p7_disp_t *p7_arg_disp);
-extern int p7_backup_romfile(p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
-	p7_disp_t *p7_arg_disp);
-extern int p7_backup_ramfile(p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
-	p7_disp_t *p7_arg_disp);
-extern int p7_backup_bootfile(p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
-	p7_disp_t *p7_arg_disp);
+#  define p7_attrs_sendexe_file p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_sendexe_file, p7_attrs_sendexe_file,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_exe,
+	p7uint_t p7_arg_loadaddr, p7uint_t p7_arg_straddr,
+	p7_disp_t *p7_arg_disp)
+
+/* Backup things */
+#  define p7_attrs_backup_romfile \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_romfile, p7_attrs_backup_romfile,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
+	p7_disp_t *p7_arg_disp)
+#  define p7_attrs_backup_ramfile \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_ramfile, p7_attrs_backup_ramfile,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
+	p7_disp_t *p7_arg_disp)
+#  define p7_attrs_backup_bootfile \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_backup_bootfile, p7_attrs_backup_bootfile,
+	p7_handle_t *p7_arg_handle, FILE *p7_arg_file,
+	p7_disp_t *p7_arg_disp)
 # endif
 
 /* Memory version of the previous functions */
-extern int p7_sendexe_mem(p7_handle_t *p7_arg_handle,
-	const void *p7_arg_mem, size_t p7_arg_size, p7uint_t p7_arg_loadaddr,
-	p7uint_t p7_arg_straddr, p7_disp_t *p7_arg_disp);
+# define p7_attrs_sendexe_mem p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_sendexe_mem, p7_attrs_sendexe_mem,
+	p7_handle_t *p7_arg_handle, const void *p7_arg_mem, size_t p7_arg_size,
+	p7uint_t p7_arg_loadaddr, p7uint_t p7_arg_straddr,
+	p7_disp_t *p7_arg_disp)
 
 /* Display streamed screen */
-extern int p7_getscreen(p7_handle_t *p7_arg_handle,
-	p7_screenfunc_t *p7_arg_callback);
+# define p7_attrs_getscreen p7_attribute_nonnull(1)
+p7_declare_ufunc(p7_getscreen, p7_attrs_getscreen,
+	p7_handle_t *p7_arg_handle, p7_screenfunc_t *p7_arg_callback)
 
 # ifdef __cplusplus
 }
diff --git a/include/libp7/cdefs.h b/include/libp7/cdefs.h
new file mode 100644
index 0000000..3c46a18
--- /dev/null
+++ b/include/libp7/cdefs.h
@@ -0,0 +1,120 @@
+/* *****************************************************************************
+ * libp7/cdefs.h -- libp7 C definitions.
+ * Copyright (C) 2016-2017 Thomas "Cakeisalie5" Touhey <thomas@touhey.fr>
+ *
+ * This file is part of libp7.
+ * libp7 is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 3.0 of the License,
+ * or (at your option) any later version.
+ *
+ * libp7 is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with libp7; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * The libp7 buffer interface is an abstraction layer between libp7 and files
+ * or data on disk in general.
+ * ************************************************************************** */
+#ifndef LIBP7_CDEFS_H
+# define LIBP7_CDEFS_H
+
+/* ************************************************************************** */
+/*  Important things                                                          */
+/* ************************************************************************** */
+/* Declare any function. */
+# ifdef  p7_declare_func
+#  undef p7_declare_func
+# endif
+# ifdef __STDC_VERSION__
+#  define p7_declare_func(P7_ARG_NAME, P7_ARG_RET, P7_ARG_ATTRS, ...) \
+extern P7_ARG_RET P7_ARG_NAME (__VA_ARGS__) P7_ARG_ATTRS;
+# else
+#  define p7_declare_func(P7_ARG_NAME, P7_ARG_RET, P7_ARG_ATTRS, ...) \
+extern P7_ARG_RET P7_ARG_NAME () P7_ARG_ATTRS;
+# endif
+
+/* Define any function (head). */
+# ifdef  p7_define_func
+#  undef p7_define_func
+# endif
+# if defined(_MSC_VER)
+#  define p7_define_func(P7_ARG_NAME, P7_ARG_RET, P7_ARG_ATTRS, ...) \
+P7_ARG_ATTRS P7_ARG_RET P7_ARG_NAME (__VA_ARGS__)
+# else
+#  define p7_define_func(P7_ARG_NAME, P7_ARG_RET, P7_ARG_ATTRS, ...) \
+P7_ARG_RET P7_ARG_NAME (__VA_ARGS__)
+# endif
+
+/* Declare an usage function.
+ * TODO: add the handle here? */
+# ifdef  p7_declare_ufunc
+#  undef p7_declare_ufunc
+# endif
+# define p7_declare_ufunc(P7_ARG_NAME, P7_ARG_ATTRS, ...) \
+	p7_declare_func(P7_ARG_NAME, int, P7_ARG_ATTRS p7_attribute_err, \
+		__VA_ARGS__)
+# define p7_define_ufunc(P7_ARG_NAME, P7_ARG_ATTRS, ...) \
+	p7_define_func(P7_ARG_NAME, int, P7_ARG_ATTRS p7_attribute_err, \
+		__VA_ARGS__)
+/* ************************************************************************** */
+/*  Attributes                                                                */
+/* ************************************************************************** */
+/* p7_attribute_THROW: optimize function calls for C++
+ * TODO: explain more */
+
+# ifdef  p7_attribute_THROW
+#  undef p7_attribute_THROW
+# endif
+# if defined(__cplusplus)
+#  define p7_attribute_THROW throw()
+# elif defined(__GNUC__)
+#  define p7_attribute_THROW __attribute__((nothrow))
+# elif defined(_MSC_VER)
+#  define p7_attribute_THROW __declspec(nothrow)
+# else
+#  define p7_attribute_THROW
+# endif
+
+/* p7_attribute_nonnull: require a pointer argument not to be NULL
+ * A warning shall be issued when a NULL value is passed as an argument that
+ * shouldn't be. The macro argument is the argument index, starting from 1. */
+
+# ifdef  p7_attribute_nonnull
+#  undef p7_attribute_nonnull
+# endif
+# if defined(__GNUC__)
+#  define p7_attribute_nonnull(P7_ARG_N) __attribute__((nonnull(P7_ARG_N)))
+# else
+#  define p7_attribute_nonnull(P7_ARG_N)
+# endif
+
+/* p7_attribute_wur: warn unused result
+ * A warning shall be issued if the result of the function isn't used.
+ * Note that __pure implies __wur, you don't need to put the two. */
+
+# ifdef  p7_attribute_wur
+#  undef p7_attribute_wur
+# endif
+# if defined(__GNUC__) && (__GNUC__ >= 4)
+#  define p7_attribute_wur __attribute__((warn_unused_result))
+# elif defined(_MSC_VER) && (_MSC_VER >= 1700)
+#  include <sal.h>
+#  define p7_attribute_wur _Check_return_
+# else
+#  define p7_attribute_wur
+# endif
+
+/* p7_attribute_err: return a libp7 error
+ * This is so the `wur` on functions returning an error is more easily
+ * tweakable. */
+
+# ifdef  p7_attribute_err
+#  undef p7_attribute_err
+# endif
+# define p7_attribute_err /* p7_attribute_wur */
+
+#endif /* LIBP7_CDEFS_H */
diff --git a/include/libp7/server.h b/include/libp7/server.h
index cb51c8f..da8ed31 100644
--- a/include/libp7/server.h
+++ b/include/libp7/server.h
@@ -31,13 +31,18 @@ extern "C" {
  *
  * Here is the function for serving directly: */
 
-extern int p7_serve_directly(p7_handle_t *p7_arg_handle,
-	p7_server_callback_t **p7_arg_callbacks, void *p7_arg_cookie);
+# define p7_attrs_serve_directly p7_attribute_nonnull(1) p7_attribute_nonnull(2)
+p7_declare_ufunc(p7_serve_directly, p7_attrs_serve_directly,
+	p7_handle_t *p7_arg_handle,
+	p7_server_callback_t **p7_arg_callbacks, void *p7_arg_cookie)
 
 /* And here is the function for serving a 'classical' server: */
 
-extern int p7_serve(p7_handle_t *p7_arg_handle, p7_server_t *p7_arg_info,
-	p7_filesystem_t *p7_arg_filesystems);
+# define p7_attrs_serve \
+	p7_attribute_nonnull(1) p7_attribute_nonnull(2) p7_attribute_nonnull(3)
+p7_declare_ufunc(p7_serve, p7_attrs_serve,
+	p7_handle_t *p7_arg_handle, p7_server_t *p7_arg_info,
+	p7_filesystem_t *p7_arg_filesystems)
 
 # ifdef __cplusplus
 }
diff --git a/include/libp7/types.h b/include/libp7/types.h
index 08ad948..825c088 100644
--- a/include/libp7/types.h
+++ b/include/libp7/types.h
@@ -34,6 +34,7 @@
 #  include <alloca.h>
 # endif
 # include <libg1m.h>
+# include <libp7/cdefs.h>
 # ifdef __cplusplus
 extern "C" {
 # endif
diff --git a/src/usage/backup.c b/src/usage/backup.c
index 92ef9cc..84d9b4e 100644
--- a/src/usage/backup.c
+++ b/src/usage/backup.c
@@ -88,7 +88,6 @@ static int decode_entry(p7_handle_t *handle, p7_casiowin_entry_t *entry,
 	/* no error */
 	return (0);
 }
-
 /* ************************************************************************** */
 /*  Get a CASIOWIN entry                                                      */
 /* ************************************************************************** */
@@ -101,7 +100,8 @@ static int decode_entry(p7_handle_t *handle, p7_casiowin_entry_t *entry,
  *	@return				the error code (0 if ok)
  */
 
-int p7_backup_casiowin_entry(p7_handle_t *handle, p7_casiowin_entry_t *entry)
+p7_define_ufunc(p7_backup_casiowin_entry, p7_attrs_backup_casiowin_entry,
+	p7_handle_t *handle, p7_casiowin_entry_t *entry)
 {
 	int err;
 
@@ -144,7 +144,6 @@ int p7_backup_casiowin_entry(p7_handle_t *handle, p7_casiowin_entry_t *entry)
 	/* decode and return */
 	return (decode_entry(handle, entry, &raw));
 }
-
 /* ************************************************************************** */
 /*  Backup the bootcode                                                       */
 /* ************************************************************************** */
@@ -165,8 +164,8 @@ int p7_backup_casiowin_entry(p7_handle_t *handle, p7_casiowin_entry_t *entry)
  */
 
 #define bootcode_size (0x10000)
-int p7_backup_boot(p7_handle_t *handle, const p7_buffer_t *buffer,
-	p7_disp_t disp)
+p7_define_ufunc(p7_backup_boot, p7_attrs_backup_boot,
+	p7_handle_t *handle, const p7_buffer_t *buffer, p7_disp_t *disp)
 {
 	int err;
 
@@ -219,7 +218,8 @@ int p7_backup_boot(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				the error code (0 if ok).
  */
 
-int p7_backup_bootfile(p7_handle_t *handle, FILE *file, p7_disp_t disp)
+p7_define_ufunc(p7_backup_bootfile, p7_attrs_backup_bootfile,
+	p7_handle_t *handle, FILE *file, p7_disp_t *disp)
 {
 	chk_iswrite(file);
 	p7_buffer_t buffer = {
@@ -244,8 +244,8 @@ int p7_backup_bootfile(p7_handle_t *handle, FILE *file, p7_disp_t disp)
  */
 
 #define rom_size (handle->_server.p7_server_flash_rom_capacity)
-int p7_backup_rom(p7_handle_t *handle, const p7_buffer_t *buffer,
-	p7_disp_t disp)
+p7_define_ufunc(p7_backup_rom, p7_attrs_backup_rom,
+	p7_handle_t *handle, const p7_buffer_t *buffer, p7_disp_t *disp)
 {
 	int err;
 
@@ -298,7 +298,8 @@ int p7_backup_rom(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				the error code (0 if ok).
  */
 
-int p7_backup_romfile(p7_handle_t *handle, FILE *file, p7_disp_t disp)
+p7_define_ufunc(p7_backup_romfile, p7_attrs_backup_romfile,
+	p7_handle_t *handle, FILE *file, p7_disp_t *disp)
 {
 	chk_iswrite(file);
 	p7_buffer_t buffer = {
@@ -323,8 +324,8 @@ int p7_backup_romfile(p7_handle_t *handle, FILE *file, p7_disp_t disp)
  */
 
 #define ram_size (0x10000)
-int p7_backup_ram(p7_handle_t *handle, const p7_buffer_t *buffer,
-	p7_disp_t disp)
+p7_define_ufunc(p7_backup_ram, p7_attrs_backup_ram,
+	p7_handle_t *handle, const p7_buffer_t *buffer, p7_disp_t *disp)
 {
 	int err;
 
@@ -377,7 +378,8 @@ int p7_backup_ram(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				the error code (0 if ok).
  */
 
-int p7_backup_ramfile(p7_handle_t *handle, FILE *file, p7_disp_t disp)
+p7_define_ufunc(p7_backup_ramfile, p7_attrs_backup_ramfile,
+	p7_handle_t *handle, FILE *file, p7_disp_t *disp)
 {
 	chk_iswrite(file);
 	p7_buffer_t buffer = {
diff --git a/src/usage/getscreen.c b/src/usage/getscreen.c
index 3b4fb13..368abc6 100644
--- a/src/usage/getscreen.c
+++ b/src/usage/getscreen.c
@@ -117,7 +117,8 @@ static void p7_getscreen_adapt(uint32_t **pixels, p7_packet_t *resp)
  *	@return				if it worked
  */
 
-int p7_getscreen(p7_handle_t *handle, int (*callback)(int, int, uint32_t**))
+p7_define_ufunc(p7_getscreen, p7_attrs_getscreen,
+	p7_handle_t *handle, p7_screenfunc_t *callback)
 {
 	int err;
 	/* make checks */
diff --git a/src/usage/mcs/list.c b/src/usage/mcs/list.c
index 5aef0b7..d2b3b3f 100644
--- a/src/usage/mcs/list.c
+++ b/src/usage/mcs/list.c
@@ -28,7 +28,8 @@
  *	@return				if it worked.
  */
 
-int p7_mcs_list(p7_handle_t *handle, p7_mcslist_t callback, void *cookie)
+p7_define_ufunc(p7_mcs_list, p7_attrs_mcs_list,
+	p7_handle_t *handle, p7_mcslist_t *callback, void *cookie)
 {
 	int err;
 
diff --git a/src/usage/mcs/request.c b/src/usage/mcs/request.c
index 3188254..4337022 100644
--- a/src/usage/mcs/request.c
+++ b/src/usage/mcs/request.c
@@ -29,11 +29,11 @@
  *	@return				the libp7 error (0 if ok)
  */
 
-int p7_mcs_request(p7_handle_t *handle, g1m_mcsfile_t **file,
-	g1m_mcshead_t *reqhead, p7_disp_t disp)
+p7_define_ufunc(p7_mcs_request, p7_attrs_mcs_request,
+	p7_handle_t *handle, g1m_mcsfile_t **file,
+	g1m_mcshead_t *head, p7_disp_t *disp)
 {
 	int err;
-
 	/* make checks */
 	chk_handle(handle);
 	chk_seven(handle);
diff --git a/src/usage/mcs/send.c b/src/usage/mcs/send.c
index eb93455..13b7d19 100644
--- a/src/usage/mcs/send.c
+++ b/src/usage/mcs/send.c
@@ -31,8 +31,9 @@
  *	@return				the libp7 error (0 if ok).
  */
 
-int p7_mcs_send(p7_handle_t *handle, g1m_mcsfile_t *file,
-	int overwrite, p7_confirm_t confirm, p7_disp_t disp)
+p7_define_ufunc(p7_mcs_send, p7_attrs_mcs_send,
+	p7_handle_t *handle, g1m_mcsfile_t *file,
+	int overwrite, p7_confirm_t *confirm, p7_disp_t *disp)
 {
 	int err;
 
diff --git a/src/usage/poke.c b/src/usage/poke.c
index e04bcad..1359378 100644
--- a/src/usage/poke.c
+++ b/src/usage/poke.c
@@ -26,7 +26,8 @@
  *	@return				if it worked.
  */
 
-int p7_poke(p7_handle_t *handle)
+p7_define_ufunc(p7_poke, p7_attrs_poke,
+	p7_handle_t *handle)
 {
 	int err;
 	/* make checks */
diff --git a/src/usage/sendexe.c b/src/usage/sendexe.c
index 4d5fad4..05e0160 100644
--- a/src/usage/sendexe.c
+++ b/src/usage/sendexe.c
@@ -30,8 +30,9 @@
  *	@return				0 if it worked, error code otherwise
  */
 
-int p7_sendexe(p7_handle_t *handle, const p7_buffer_t *buffer,
-	p7uint_t loadaddr, p7uint_t straddr, p7_disp_t disp)
+p7_define_ufunc(p7_sendexe, p7_attrs_sendexe,
+	p7_handle_t *handle, const p7_buffer_t *buffer,
+	p7uint_t loadaddr, p7uint_t straddr, p7_disp_t *disp)
 {
 	int err;
 
@@ -77,8 +78,9 @@ int p7_sendexe(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				the error code
  */
 
-int p7_sendexe_file(p7_handle_t *handle,
-	FILE *exe, p7uint_t loadaddr, p7uint_t straddr, p7_disp_t disp)
+p7_define_ufunc(p7_sendexe_file, p7_attrs_sendexe_file,
+	p7_handle_t *handle, FILE *exe,
+	p7uint_t loadaddr, p7uint_t straddr, p7_disp_t *disp)
 {
 	/* make checks */
 	chk_isread(exe);
@@ -117,9 +119,9 @@ int p7_sendexe_file(p7_handle_t *handle,
  *	@return				the error code.
  */
 
-int p7_sendexe_mem(p7_handle_t *handle,
-	const void *mem, size_t size, p7uint_t loadaddr, p7uint_t straddr,
-	p7_disp_t disp)
+p7_define_ufunc(p7_sendexe_mem, p7_attrs_sendexe_mem,
+	p7_handle_t *handle, const void *mem, size_t size,
+	p7uint_t loadaddr, p7uint_t straddr, p7_disp_t *disp)
 {
 	chk_mem(mem);
 	chk_filesize(size);
diff --git a/src/usage/server/classical.c b/src/usage/server/classical.c
index 6b43e09..00bbc4e 100644
--- a/src/usage/server/classical.c
+++ b/src/usage/server/classical.c
@@ -306,8 +306,8 @@ static int change_working_directory(p7_server_cookie_t *cookie,
  *	@return				the error code.
  */
 
-int p7_serve(p7_handle_t *handle, p7_server_t *info,
-	p7_filesystem_t *filesystems)
+p7_define_ufunc(p7_serve, p7_attrs_serve,
+	p7_handle_t *handle, p7_server_t *info, p7_filesystem_t *filesystems)
 {
 	/* make cookie and commands */
 	p7_server_cookie_t cookie = {
diff --git a/src/usage/server/direct.c b/src/usage/server/direct.c
index c3bbc88..a82ae15 100644
--- a/src/usage/server/direct.c
+++ b/src/usage/server/direct.c
@@ -28,8 +28,8 @@
  *	@return				the error.
  */
 
-int p7_serve_directly(p7_handle_t *handle, p7_server_callback_t **callbacks,
-	void *cookie)
+p7_define_ufunc(p7_serve_directly, p7_attrs_serve_directly,
+	p7_handle_t *handle, p7_server_callback_t **callbacks, void *cookie)
 {
 	int err;
 	/* make checks */
diff --git a/src/usage/setlink.c b/src/usage/setlink.c
index 05ddce8..05428b2 100644
--- a/src/usage/setlink.c
+++ b/src/usage/setlink.c
@@ -28,7 +28,8 @@
  *	@return				the error code.
  */
 
-int p7_setlink(p7_handle_t *handle, const p7_streamsettings_t *settings)
+p7_define_ufunc(p7_setlink, p7_attrs_setlink,
+	p7_handle_t *handle, const p7_streamsettings_t *settings)
 {
 	int err;
 
diff --git a/src/usage/storage/copy.c b/src/usage/storage/copy.c
index 67db01b..e6618c3 100644
--- a/src/usage/storage/copy.c
+++ b/src/usage/storage/copy.c
@@ -31,7 +31,8 @@
  *	@return				if it worked
  */
 
-int p7_copy(p7_handle_t *handle,
+p7_define_ufunc(p7_copy, p7_attrs_copy,
+	p7_handle_t *handle,
 	const char *dirname, const char *filename,
 	const char *newdir, const char *newname, const char *devname)
 {
diff --git a/src/usage/storage/createdir.c b/src/usage/storage/createdir.c
index 51291bd..b72a106 100644
--- a/src/usage/storage/createdir.c
+++ b/src/usage/storage/createdir.c
@@ -28,7 +28,8 @@
  *	@return				the error code (0 if ok)
  */
 
-int p7_createdir(p7_handle_t *handle, const char *dirname, const char *devname)
+p7_define_ufunc(p7_createdir, p7_attrs_createdir,
+	p7_handle_t *handle, const char *dirname, const char *devname)
 {
 	int err;
 
diff --git a/src/usage/storage/delete.c b/src/usage/storage/delete.c
index d4eba3d..b1f1c39 100644
--- a/src/usage/storage/delete.c
+++ b/src/usage/storage/delete.c
@@ -29,8 +29,9 @@
  *	@return				if it worked
  */
 
-int p7_delete(p7_handle_t *handle,
-	const char *dirname, const char *filename, const char *devname)
+p7_define_ufunc(p7_delete, p7_attrs_delete,
+	p7_handle_t *handle, const char *dirname,
+	const char *filename, const char *devname)
 {
 	int err;
 
diff --git a/src/usage/storage/getfreemem.c b/src/usage/storage/getfreemem.c
index 971f7e6..6218495 100644
--- a/src/usage/storage/getfreemem.c
+++ b/src/usage/storage/getfreemem.c
@@ -28,8 +28,8 @@
  *	@return				if there was an error.
  */
 
-int p7_getfreemem(p7_handle_t *handle, const char *devname,
-	p7uint_t *capacity)
+p7_define_ufunc(p7_getfreemem, p7_attrs_getfreemem,
+	p7_handle_t *handle, const char *devname, p7uint_t *capacity)
 {
 	int err;
 	/* make checks */
diff --git a/src/usage/storage/list.c b/src/usage/storage/list.c
index 592f9a8..8ec9c89 100644
--- a/src/usage/storage/list.c
+++ b/src/usage/storage/list.c
@@ -29,9 +29,9 @@
  *	@return				if it worked
  */
 
-int p7_list(p7_handle_t *handle, const char *devname,
-	void (*callback)(void*, const char*, const char*, p7uint_t),
-	void *cookie)
+p7_define_ufunc(p7_list, p7_attrs_list,
+	p7_handle_t *handle, const char *devname,
+	p7_list_t *callback, void *cookie)
 {
 	int err;
 
@@ -79,7 +79,8 @@ int p7_list(p7_handle_t *handle, const char *devname,
 			/* device root should not be sent */
 			if (!dir && !filename) continue;
 			/* call callback */
-			(*callback)(cookie, dir, filename, fs);
+			if (callback)
+				(*callback)(cookie, dir, filename, fs);
 			break;
 
 		default:
diff --git a/src/usage/storage/optimize.c b/src/usage/storage/optimize.c
index 92b97c0..b6b1db1 100644
--- a/src/usage/storage/optimize.c
+++ b/src/usage/storage/optimize.c
@@ -27,7 +27,8 @@
  *	@return				if it worked
  */
 
-int p7_optimize(p7_handle_t *handle, const char *devname)
+p7_define_ufunc(p7_optimize, p7_attrs_optimize,
+	p7_handle_t *handle, const char *devname)
 {
 	int err;
 
diff --git a/src/usage/storage/request.c b/src/usage/storage/request.c
index e7dbe08..801eb89 100644
--- a/src/usage/storage/request.c
+++ b/src/usage/storage/request.c
@@ -31,9 +31,10 @@
  *	@return				if it worked
  */
 
-int p7_request(p7_handle_t *handle, const p7_buffer_t *buffer,
-	const char *dirname, const char *filename, const char *devname,
-	p7_disp_t disp)
+p7_define_ufunc(p7_request, p7_attrs_request,
+	p7_handle_t *handle, const p7_buffer_t *buffer,
+	const char *dirname, const char *filename,
+	const char *devname, p7_disp_t *disp)
 {
 	int err;
 
@@ -101,9 +102,10 @@ int p7_request(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				the error code (0 if ok).
  */
 
-int p7_reqfile(p7_handle_t *handle, FILE *file,
-	const char *dirname, const char *filename, const char *devname,
-	p7_disp_t disp)
+p7_define_ufunc(p7_reqfile, p7_attrs_reqfile,
+	p7_handle_t *handle, FILE *file,
+	const char *dirname, const char *filename,
+	const char *devname, p7_disp_t *disp)
 {
 	chk_iswrite(file);
 	p7_buffer_t buffer = {
@@ -113,5 +115,4 @@ int p7_reqfile(p7_handle_t *handle, FILE *file,
 
 	return (p7_request(handle, &buffer, dirname, filename, devname, disp));
 }
-
 #endif
diff --git a/src/usage/storage/reset.c b/src/usage/storage/reset.c
index 10a11de..65bc9f1 100644
--- a/src/usage/storage/reset.c
+++ b/src/usage/storage/reset.c
@@ -27,7 +27,8 @@
  *	@return				if it worked
  */
 
-int p7_reset(p7_handle_t *handle, const char *devname)
+p7_define_ufunc(p7_reset, p7_attrs_reset,
+	p7_handle_t *handle, const char *devname)
 {
 	int err;
 
diff --git a/src/usage/storage/send.c b/src/usage/storage/send.c
index 45a5e06..2fe40e1 100644
--- a/src/usage/storage/send.c
+++ b/src/usage/storage/send.c
@@ -34,9 +34,11 @@
  *	@return				if it worked
  */
 
-int p7_send(p7_handle_t *handle, const p7_buffer_t *buffer,
-	const char *dirname, const char *filename, const char *devname,
-	int overwrite, p7_confirm_t confirm, p7_disp_t disp)
+p7_define_ufunc(p7_send, p7_attrs_send,
+	p7_handle_t *handle, const p7_buffer_t *buffer,
+	const char *dirname, const char *filename,
+	const char *devname, int overwrite,
+	p7_confirm_t *confirm, p7_disp_t *disp)
 {
 	int err;
 
@@ -139,9 +141,11 @@ int p7_send(p7_handle_t *handle, const p7_buffer_t *buffer,
  *	@return				if it worked
  */
 
-int p7_sendfile(p7_handle_t *handle,
-	FILE *file, const char *dirname, const char *filename,
-	const char *devname, int overwrite, p7_confirm_t confirm, p7_disp_t disp)
+p7_define_ufunc(p7_sendfile, p7_attrs_sendfile,
+	p7_handle_t *handle, FILE *file,
+	const char *dirname, const char *filename,
+	const char *devname, int overwrite,
+	p7_confirm_t *confirm, p7_disp_t *disp)
 {
 	chk_isread(file);
 
@@ -187,9 +191,11 @@ int p7_sendfile(p7_handle_t *handle,
  *	@return				if it worked
  */
 
-int p7_sendmem(p7_handle_t *handle, const void *mem, size_t size,
-	const char *dirname, const char *filename, const char *devname,
-	int overwrite, p7_confirm_t confirm, p7_disp_t disp)
+p7_define_ufunc(p7_sendmem, p7_attrs_sendmem,
+	p7_handle_t *handle, const void *mem, size_t size,
+	const char *dirname, const char *filename,
+	const char *devname, int overwrite, p7_confirm_t *confirm,
+	p7_disp_t *disp)
 {
 	chk_mem(mem);
 	chk_filesize(size);