Commit 029c896c authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Andrew Morton
Browse files

kernel.h: move PTR_IF() and u64_to_user_ptr() to util_macros.h 

While the natural choice of PTR_IF() is kconfig.h, the latter is too broad
to include C code and actually the macro was moved out from there in the
past.  But kernel.h is neither a good choice for that.  Move it to
util_macros.h.  Do the same for u64_to_user_ptr().

While moving, add necessary documentation.

Link: https://lkml.kernel.org/r/20250324105228.775784-3-andriy.shevchenko@linux.intel.com


Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexandru Ardelean <aardelean@baylibre.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4ef5211e

include/linux/kernel.h

+1 −9
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include <linux/sprintf.h>

#include <linux/static_call_types.h>

#include <linux/instruction_pointer.h>

#include <linux/util_macros.h>

#include <linux/wordpart.h>



#include <asm/byteorder.h>
@@ -41,15 +42,6 @@ 


#define STACK_MAGIC	0xdeadbeef



#define PTR_IF(cond, ptr)	((cond) ? (ptr) : NULL)



#define u64_to_user_ptr(x) (		\

{					\

	typecheck(u64, (x));		\

	(void __user *)(uintptr_t)(x);	\

}					\

)



struct completion;

struct user;

include/linux/util_macros.h

+66 −0
Original line number Diff line number Diff line
@@ -79,6 +79,72 @@ 
	(__fc_i);							\

})



/**

 * PTR_IF - evaluate to @ptr if @cond is true, or to NULL otherwise.

 * @cond: A conditional, usually in a form of IS_ENABLED(CONFIG_FOO)

 * @ptr: A pointer to assign if @cond is true.

 *

 * PTR_IF(IS_ENABLED(CONFIG_FOO), ptr) evaluates to @ptr if CONFIG_FOO is set

 * to 'y' or 'm', or to NULL otherwise. The (ptr) argument must be a pointer.

 *

 * The macro can be very useful to help compiler dropping 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 configuration option is set.

 *

 * An alternative is to declare foo_suspend() always, but mark it

 * as __maybe_unused. 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 the macro it is possible to write the following:

 *

 *     static int foo_suspend(struct device *dev)

 *     {

 *        ...

 *     }

 *

 *     static struct pm_ops foo_ops = {

 *         .suspend = PTR_IF(IS_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.

 */

#define PTR_IF(cond, ptr)	((cond) ? (ptr) : NULL)



/**

 * to_user_ptr - cast a pointer passed as u64 from user space to void __user *

 * @x: The u64 value from user space, usually via IOCTL

 *

 * to_user_ptr() simply casts a pointer passed as u64 from user space to void

 * __user * correctly. Using this lets us get rid of all the tiresome casts.

 */

#define u64_to_user_ptr(x)		\

({					\

	typecheck(u64, (x));		\

	(void __user *)(uintptr_t)(x);	\

})



/**

 * is_insidevar - check if the @ptr points inside the @var memory range.

 * @ptr:	the pointer to a memory address.