mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-12 13:55:32 +00:00
1b399bb048
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>
81 lines
2.7 KiB
C
81 lines
2.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#ifndef __LINUX_KCONFIG_H
|
|
#define __LINUX_KCONFIG_H
|
|
|
|
/* CONFIG_CC_VERSION_TEXT (Do not delete this comment. See help in Kconfig) */
|
|
|
|
#include <generated/autoconf.h>
|
|
|
|
#ifdef CONFIG_CPU_BIG_ENDIAN
|
|
#define __BIG_ENDIAN 4321
|
|
#else
|
|
#define __LITTLE_ENDIAN 1234
|
|
#endif
|
|
|
|
#define __ARG_PLACEHOLDER_1 0,
|
|
#define __take_second_arg(__ignored, val, ...) val
|
|
|
|
/*
|
|
* The use of "&&" / "||" is limited in certain expressions.
|
|
* The following enable to calculate "and" / "or" with macro expansion only.
|
|
*/
|
|
#define __and(x, y) ___and(x, y)
|
|
#define ___and(x, y) ____and(__ARG_PLACEHOLDER_##x, y)
|
|
#define ____and(arg1_or_junk, y) __take_second_arg(arg1_or_junk y, 0)
|
|
|
|
#define __or(x, y) ___or(x, y)
|
|
#define ___or(x, y) ____or(__ARG_PLACEHOLDER_##x, y)
|
|
#define ____or(arg1_or_junk, y) __take_second_arg(arg1_or_junk 1, y)
|
|
|
|
/*
|
|
* 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 __is_defined(x) ___is_defined(x)
|
|
#define ___is_defined(val) ____is_defined(__ARG_PLACEHOLDER_##val)
|
|
#define ____is_defined(arg1_or_junk) __take_second_arg(arg1_or_junk 1, 0)
|
|
|
|
/*
|
|
* IS_BUILTIN(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y', 0
|
|
* otherwise. For boolean options, this is equivalent to
|
|
* IS_ENABLED(CONFIG_FOO).
|
|
*/
|
|
#define IS_BUILTIN(option) __is_defined(option)
|
|
|
|
/*
|
|
* IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0
|
|
* otherwise.
|
|
*/
|
|
#define IS_MODULE(option) __is_defined(option##_MODULE)
|
|
|
|
/*
|
|
* IS_REACHABLE(CONFIG_FOO) evaluates to 1 if the currently compiled
|
|
* code can call a function defined in code compiled based on CONFIG_FOO.
|
|
* This is similar to IS_ENABLED(), but returns false when invoked from
|
|
* built-in code when CONFIG_FOO is set to 'm'.
|
|
*/
|
|
#define IS_REACHABLE(option) __or(IS_BUILTIN(option), \
|
|
__and(IS_MODULE(option), __is_defined(MODULE)))
|
|
|
|
/*
|
|
* IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
|
|
* 0 otherwise.
|
|
*/
|
|
#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 */
|