linux-kernel - Re: [PATCH 1/3] kconfig: fix IS_ENABLED to not require all options to be defined

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Date:	Fri, 13 Apr 2012 10:31:54 -0000
From:	dick@...eefland.net (Dick Streefland)
To:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] kconfig: fix IS_ENABLED to not require all options to be defined

| +#define __ARG_PLACEHOLDER_1 0,
| +#define config_enabled(cfg) _config_enabled(cfg)
| +#define _config_enabled(value) __config_enabled(__ARG_PLACEHOLDER_##value)
| +#define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0)
| +#define ___config_enabled(__ignored, val, ...) val

The ISO C99 standard requires that the variable argument macro
___config_enabled() is expanded with at least three arguments. When
a CONFIG_* macro is not defined, there are only two arguments, and
gcc will issue a somewhat cryptic warning message when you compile
with the -pedantic option:

  "warning: ISO C99 requires rest arguments to be used"

Adding an additional dummy argument makes the code ISO C99 compliant,
and eliminates the warning:

diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index be342b9..eac65da 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -19,7 +19,7 @@
 #define __ARG_PLACEHOLDER_1 0,
 #define config_enabled(cfg) _config_enabled(cfg)
 #define _config_enabled(value) __config_enabled(__ARG_PLACEHOLDER_##value)
-#define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0)
+#define __config_enabled(arg1_or_junk) ___config_enabled(arg1_or_junk 1, 0, 0)
 #define ___config_enabled(__ignored, val, ...) val
 
 /*

Signed-off-by: Dick Streefland <dick@...eefland.net>

-- 
Dick

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