Function Attributes

Give hints to the compiler and the reader of the code. More...

Macros
#define	__non_null
#define	__nonnull(params)
#define	__format(x, y)
#define	__format_arg(x)
#define	__packed
#define	__maybe_unused
#define	__deprecated
#define	__no_return
#define	__pure
#define	__const
#define	__cleanup(x)
#define	__returns_nonnull
#define	__warn_unused_res
#define	__fallthrough
#define	__cold
#define	__hot
#define	__nonstring

Detailed Description

These attributes are used to give the compiler and the user hints about the structures/functions/parameters for better static code analysis and understanding.

To avoid code duplication we define them here for all. Since we use features.h, all attributes are removed if the compiler cannot deal with it.

On the other hand we expect a GCC newer than the old 3.x days and all of these attributes should be understood by recent compilers. So, we define them here at most unconditionally.

Macro Definition Documentation

__non_null

#define __non_null

GCC function attribute: used to mark all arguments to be non-null

 void function(void *foo, void *bar) __non_null;

Note

This is a convenience macro only. The regular form is __nonnull() for this use case.

__nonnull

#define __nonnull

(

params

)

GCC function attribute: used to mark all or specific arguments to be non-null

 void function1(void *foo, void *bar) __nonnull(); // both arguments must be non-null
 void function2(void *foo, void *bar) __nonnull((2)); // the second argument must be non-null

Note

This macro is from compiler's features.h

__format

#define __format	(		x,
			y
	)

GCC function attribute: used to give the compiler a glue about the arguments and how to check them

Parameters

x	Parameter number of the format string (count starts with '1')
y	Parameter number of the first value string matching the format string (count starts with '1')

__format_arg

#define __format_arg

(

x

)

GCC function attribute: used to give the compiler a glue about the arguments and how to check them

Parameters

x

FIXME

__packed

#define __packed

GCC structure attribute: used to mark a structure to be non-aligned

__maybe_unused

#define __maybe_unused

GCC function/parameter attribute: used to mark a function or a parameter as maybe unused

__deprecated

#define __deprecated

GCC function attribute: used to mark a function as deprecated

__no_return

#define __no_return

GCC function attribute: mark a function which does not return

__pure

#define __pure

GCC function attribute: mark a function to be pure (refer __const), e.g. it returns a value based only on its parameters and global variables.

__const

#define __const

GCC function attribute: used to mark a function as const (refer __pure), e.g. it returns a value based only on its parameters.

__cleanup

#define __cleanup

(

x

)

GCC function attribute: define a cleanup function for an element

Parameters

x

FIXME

__returns_nonnull

#define __returns_nonnull

GCC function attribute: mark a function to never return a non-NULL value

__warn_unused_res

#define __warn_unused_res

GCC function attribute: warn if a caller does not use the returned value

__fallthrough

#define __fallthrough

GCC function attribute: do not warn if a switch/case fallthrough is intended

__cold

#define __cold

GCC function attribute: mark function for better branch prediction (here: the seldom chosen branch)

__hot

#define __hot

GCC function attribute: mark function for better branch prediction (here: the often chosen branch)

__nonstring

#define __nonstring

GCC variable attribute: mark an array as a non-string, e.g. no termination zero character available

 unsigned char pattern[100] __nonstring;