about function attributes for functions returning a pointer

[Ian Lance Taylor]

Uwe Kleine-König <u.kleine-koenig@pengutronix.de> writes:

> in the linux kernel I defined a function as follows:
>
> 	static struct platform_device *__init __maybe_unused imx_add_imx_dma(void)
> 	{
> 		...
> 	}
>
> and the only used was #ifdefed out.
>
> With the following defines:
>
> 	#define __section(S) __attribute__ ((__section__(#S)))
> 	#define __cold __attribute__((__cold__))
> 	#define notrace __attribute__((no_instrument_function))
> 	#define __init	__section(.init.text) __cold notrace
> 	#define __maybe_unused                  __attribute__((unused))
>
> this still generated the "defined but unused" warning.
>
> Then after changing the definition to
>
> 	static struct platform_device __init __maybe_unused *imx_add_imx_dma(void)
>
> (i.e. move the * after the attribute stuff) the warning is gone.  In
> both cases (and when the function was used) it is put in the
> ".init.text" section though.  That is in the first case __init worked,
> but __maybe_unused did not.  Is this intended?  Do I something wrong?
> What is the most correct position for function attributes for functions
> returning a pointer?
>
> (I'm using gcc 4.3.2 for arm, OSELAS.Toolchain-1.99.3.6 here.  Could not
> reproduce with Debian's gcc 4.4.5 for x86 using a minimal example.)

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The syntax for attributes is documented at
http://gcc.gnu.org/onlinedocs/gcc-4.5.1/gcc/Attribute-Syntax.html .

I think the differences you are seeing are because some attributes can
apply to types and some can only apply to declarations.  Moving the
location of the __attribute__ affects which type it applies to.  In
particular __attribute__ ((unused)) may be used with a type, but
__attribute__ ((section (...))) may only be used with a declaration.

Ian