From: Aaron Conole <aconole@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
        Jason Baron <jbaron@akamai.com>, Joe Perches <joe@perches.com>
Subject: Re: [PATCH v2] printk: help pr_debug and pr_devel to optimize out arguments
References: <5661BFEE.1050103@akamai.com>
	<1449265902-21781-1-git-send-email-aconole@redhat.com>
	<1652262.soph10NRXK@wuerfel>
Date: Wed, 09 Dec 2015 10:13:26 -0500
In-Reply-To: <1652262.soph10NRXK@wuerfel> (Arnd Bergmann's message of "Wed, 09
	Dec 2015 12:52:38 +0100")
Message-ID: <f7tbn9zhcyx.fsf@aconole.bos.csb>
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Arnd Bergmann <arnd@arndb.de> writes:
> On Friday 04 December 2015 16:51:42 Aaron Conole wrote:
>> --- a/include/linux/printk.h
>> +++ b/include/linux/printk.h
>> @@ -106,13 +106,14 @@ struct va_format {
>>  
>>  /*
>>   * Dummy printk for disabled debugging statements to use whilst maintaining
>> - * gcc's format and side-effect checking.
>> + * gcc's format checking.
>>   */
>> -static inline __printf(1, 2)
>> -int no_printk(const char *fmt, ...)
>> -{
>> -       return 0;
>> -}
>> +#define no_printk(fmt, ...)                    \
>> +do {                                           \
>> +       if (0) {                                \
>> +               printk(fmt, ##__VA_ARGS__);     \
>> +       }                                       \
>> +} while (0)
>>  
>
> This change breaks compiling lib/842/, at least in some configurations:
>
> lib/842/842_decompress.c: In function '__do_index':
> lib/842/842_decompress.c:205:12422: error: implicit declaration of function 'no_printk'
>
> Using a gcc style vararg macro instead of the C99 style makes it work, but
> I don't know why the original version didn't work.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index cc3803a8f73e..4d1851a82254 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -108,10 +108,10 @@ struct va_format {
>   * Dummy printk for disabled debugging statements to use whilst maintaining
>   * gcc's format checking.
>   */
> -#define no_printk(fmt, ...)			\
> +#define no_printk(arg ...)			\
>  do {						\
>  	if (0) {				\
> -		printk(fmt, ##__VA_ARGS__);	\
> +		printk(arg);			\
>  	}					\
>  } while (0)
>  

Ugh. Sorry about this; I thought I had compiled everywhere but I guess not.
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