path: root/include
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authorPaul Gortmaker <paul.gortmaker@windriver.com>2012-04-12 19:46:32 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-04-12 18:35:58 -0700
commit69349c2dc01c489eccaa4c472542c08e370c6d7e (patch)
tree2422ef07a511d51714e0e16da1ac65c7256e9add /include
parent7c427f45503f77f148cc2b66864e0684c60fa3a0 (diff)
kconfig: fix IS_ENABLED to not require all options to be defined
Using IS_ENABLED() within C (vs. within CPP #if statements) in its current form requires us to actually define every possible bool/tristate Kconfig option twice (__enabled_* and __enabled_*_MODULE variants). This results in a huge autoconf.h file, on the order of 16k lines for a x86_64 defconfig. Fixing IS_ENABLED to be able to work on the smaller subset of just things that we really have defined is step one to fixing this. Which means it has to not choke when fed non-enabled options, such as: include/linux/netdevice.h:964:1: warning: "__enabled_CONFIG_FCOE_MODULE" is not defined [-Wundef] The original prototype of how to implement a C and preprocessor compatible way of doing this came from the Google+ user "comex ." in response to Linus' crowdsourcing challenge for a possible improvement on his earlier C specific solution: #define config_enabled(x) (__stringify(x)[0] == '1') In this implementation, I've chosen variable names that hopefully make how it works more understandable. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
1 files changed, 18 insertions, 4 deletions
diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h
index 067eda0e4b32..be342b94c640 100644
--- a/include/linux/kconfig.h
+++ b/include/linux/kconfig.h
@@ -4,29 +4,43 @@
#include <generated/autoconf.h>
- * Helper macros to use CONFIG_ options in C expressions. Note that
+ * Helper macros to use CONFIG_ options in C/CPP expressions. Note that
* these only work with boolean and tristate options.
+ * Getting something that works in C and CPP for an arg that may or may
+ * not be defined is tricky. Here, if we have "#define CONFIG_BOOGER 1"
+ * we match on the placeholder define, insert the "0," for arg1 and generate
+ * the triplet (0, 1, 0). Then the last step cherry picks the 2nd arg (a one).
+ * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
+ * the last step cherry picks the 2nd arg, we get a zero.
+ */
+#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
* IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
* 0 otherwise.
#define IS_ENABLED(option) \
- (__enabled_ ## option || __enabled_ ## option ## _MODULE)
+ (config_enabled(option) || config_enabled(option##_MODULE))
* IS_BUILTIN(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y', 0
* otherwise. For boolean options, this is equivalent to
-#define IS_BUILTIN(option) __enabled_ ## option
+#define IS_BUILTIN(option) config_enabled(option)
* IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0
* otherwise.
-#define IS_MODULE(option) __enabled_ ## option ## _MODULE
+#define IS_MODULE(option) config_enabled(option##_MODULE)
#endif /* __LINUX_KCONFIG_H */