Hello Ian,
On Mon, Oct 04, 2010 at 11:23:45AM -0700, Ian Lance Taylor wrote:
> Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> 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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oops, ok, sorry.
> The syntax for attributes is documented at
> http://gcc.gnu.org/onlinedocs/gcc-4.5.1/gcc/Attribute-Syntax.html .
This is heavy reading. And though I'd claim not to be a novice C
programmer I don't understand it.
For me
static struct platform_device *__init __maybe_unused imx_add_imx_dma(void)
makes most sense, because the * belongs to struct platform_device and
it's imx_add_imx_dma() that is unused and should live in .init.text, not
*imx_add_imx_dma().
> 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.
As far as I got it both section() and unused are variable/function
attributes and not type attributes. So I think this explanation doesn't
match, does it?
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
