diff options
author | Paul Cercueil <paul@crapouillou.net> | 2020-12-13 23:54:46 +0000 |
---|---|---|
committer | Linus Walleij <linus.walleij@linaro.org> | 2021-01-18 16:13:51 +0100 |
commit | 1b399bb04837183cecdc1b32ef1cfc7fcfa75d32 (patch) | |
tree | 1f10e4e0cd7d9621da2a129cc09cf95524522925 /include/linux/kconfig.h | |
parent | dbbdb8da424b97d1b7d08f5e8f0cad8a31934c58 (diff) | |
download | linux-stable-1b399bb04837183cecdc1b32ef1cfc7fcfa75d32.tar.gz linux-stable-1b399bb04837183cecdc1b32ef1cfc7fcfa75d32.tar.bz2 linux-stable-1b399bb04837183cecdc1b32ef1cfc7fcfa75d32.zip |
kconfig.h: Add IF_ENABLED() macro
IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y'
or 'm', NULL otherwise. The (ptr) argument must be a pointer.
The IF_ENABLED() macro can be very useful to help GCC drop dead code.
For instance, consider the following:
#ifdef CONFIG_FOO_SUSPEND
static int foo_suspend(struct device *dev)
{
...
}
#endif
static struct pm_ops foo_ops = {
#ifdef CONFIG_FOO_SUSPEND
.suspend = foo_suspend,
#endif
};
While this works, the foo_suspend() macro is compiled conditionally,
only when CONFIG_FOO_SUSPEND is set. This is problematic, as there could
be a build bug in this function, we wouldn't have a way to know unless
the config option is set.
An alternative is to declare foo_suspend() always, but mark it as maybe
unused:
static int __maybe_unused foo_suspend(struct device *dev)
{
...
}
static struct pm_ops foo_ops = {
#ifdef CONFIG_FOO_SUSPEND
.suspend = foo_suspend,
#endif
};
Again, this works, but the __maybe_unused attribute is required to
instruct the compiler that the function may not be referenced anywhere,
and is safe to remove without making a fuss about it. This makes the
programmer responsible for tagging the functions that can be
garbage-collected.
With this patch, it is now possible to write the following:
static int foo_suspend(struct device *dev)
{
...
}
static struct pm_ops foo_ops = {
.suspend = IF_ENABLED(CONFIG_FOO_SUSPEND, foo_suspend),
};
The foo_suspend() function will now be automatically dropped by the
compiler, and it does not require any specific attribute.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20201213235447.138271-1-paul@crapouillou.net
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'include/linux/kconfig.h')
-rw-r--r-- | include/linux/kconfig.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/kconfig.h b/include/linux/kconfig.h index 9d12c970f18f..e78e17a76dc9 100644 --- a/include/linux/kconfig.h +++ b/include/linux/kconfig.h @@ -72,4 +72,10 @@ */ #define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option)) +/* + * IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y' + * or 'm', NULL otherwise. + */ +#define IF_ENABLED(option, ptr) (IS_ENABLED(option) ? (ptr) : NULL) + #endif /* __LINUX_KCONFIG_H */ |