Commit fe22cd9b authored Jan 15, 2016 by Aaron Conole Committed by Linus Torvalds Jan 16, 2016

printk: help pr_debug and pr_devel to optimize out arguments



Currently, pr_debug and pr_devel will not elide function call arguments
appearing in calls to the no_printk for these macros.  This is because
all side effects must be honored before proceeding to the 0-value
assignment in no_printk.

The behavior is contrary to documentation found in the CodingStyle and
the header file where these functions are declared.

This patch corrects that behavior by shunting out the call to no_printk
completely.  The format string is still checked by gcc for correctness,
but no code seems to be emitted in common cases.

[akpm@linux-foundation.org: remove braces, per Joe]
Fixes: 5264f2f7 ("include/linux/printk.h: use and neaten no_printk")
Signed-off-by: Aaron Conole <aconole@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Joe Perches <joe@perches.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 251c7234

include/linux/printk.h

+6 −6

Original line number	Diff line number	Diff line
		@@ -106,13 +106,13 @@ 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)

		#ifdef CONFIG_EARLY_PRINTK
		extern asmlinkage __printf(1, 2)

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