Re: CONFIG_PRINTK doesn't makes size smaller

[Vadim Lobanov]

On Tue, 20 Sep 2005, Andrey Panin wrote:

> On 263, 09 20, 2005 at 12:48:59AM -0700, Vadim Lobanov wrote:
> > On Tue, 20 Sep 2005, Andrey Panin wrote:
> >
> > > On 263, 09 20, 2005 at 02:14:55PM +0800, colin wrote:
> > > >
> > > > Hi there,
> > > > I tried to make kernel with CONFIG_PRINTK off. I considered it should become
> > > > smaller, but it didn't because it actually isn't an empty function, and
> > > > there are many copies of it in vmlinux, not just one. Here is its
> > > > definition:
> > > >     static inline int printk(const char *s, ...) { return 0; }
> > > >
> > > > I change the definition to this and it can greatly reduce the size by about
> > > > 5%:
> > > >     #define printk(...) do {} while (0)
> > > > However, this definition would lead to error in some situations. For
> > > > example:
> > > >     1. (printk)
> > > >     2. ret = printk
> > > >
> > > > I hope someone could suggest a better definition of printk that can both
> > > > make printk smaller and eliminate errors.
> > >
> > > What about the macro below ?
> > >
> > > #define printk(...) ({ do { } while(0); 0; })
> >
> > So what does the do-while loop give us in the above case? In other
> > words, why not just do the following...?
>
> do-while loop eliminates "statement with no effect" warnings from gcc4.
>
> > #define printk(...) ({ 0; })
> >

Funky: gcc3.3.4 seems to like it just fine. I am rather curious why gcc4
has different semantics in this case. But that is probably off-topic for
this list...

In either case, as Andrew Morton pointed out, function invokations as
arguments don't get expanded out in the case of it being a macro, so no
dice.

> --
> Andrey Panin		| Linux and UNIX system administrator
> pazke@xxxxxxxxx		| PGP key: wwwkeys.pgp.net
>

-VadimL
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