On Saturday 05 July 2008 00:01, Andrew Morton wrote: > > > We also jump through hoops to print things like sector_t and > > > resource_size_t. They always need to be cast to `unsiged long long', > > > which generates additional stack space and text in some setups. > > > > The thing is that GCC checks types. So it's fine to add "print this > > pointer specially", but you can't in general add new printf arguments > > without also hacking GCC. Unless you use -Wno-format, and require > > sparse to check special kernel types. > > It would be excellent if gcc had an extension system so that you could > add new printf control chars and maybe even tell gcc how to check them. > But of course, if that were to happen, we couldn't use it for 4-5 years. > > What I had initially proposed was to abuse %S, which takes a wchar_t*. > gcc accepts `unsigned long *' for %S. > > Then, we put the kernel-specific control char after the S, so we can > print an inode (rofl) with > > struct inode *inode; > > printk("here is an inode: %Si\n", (unsigned long *)inode); > > Downsides are: > > - there's a cast, so you could accidentally do > > printk("here is an inode: %Si\n", (unsigned long *)dentry); > > - there's a cast, and they're ugly > > - gcc cannot of course check that the arg matches the control string > > Unfortunately (and this seems weird), gcc printf checking will not > accept a void* for %S: it _has_ to be wchar_t*, and the checker won't > permit void* substitution for that. Repeating myself here... We can add an alternative alias to printk: asmlinkage int printk(const char * fmt, ...) __attribute__ ((format (printf, 1, 2))) __cold; +asmlinkage int custom_printk(const char * fmt, ...) __cold asm ("printk"); custom_printk() is actually just printk(), that is, we won't need additional function, we need to teach *printk* about MAC addresses, NIPQUADs etc; and then use printk() if you use only standard %fmt (and have it checked by gcc), or use custom_printk() if you have non-standard %fmt in the format string. The only downside that in second case, you lose gcc checking. No big deal. -- vda -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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