Messages in this thread | | | Date | Tue, 20 Sep 2005 01:03:05 -0700 | From | Andrew Morton <> | Subject | Re: CONFIG_PRINTK doesn't makes size smaller |
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Vadim Lobanov <vlobanov@speakeasy.net> 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...? > > #define printk(...) ({ 0; }) >
You may find that when printk() is a static inline there are still copies of the control string in the generated kernel image:
printk("foo %d\n", bar());
must still evaluate bar() and may cause "foo %d\n" to turn up in vmlinux. IIRC later versions of gcc do remove the unreferenced string.
If printk is a macro, it all of course disappears. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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