Commit 31088f6f authored by Kevin Brodsky's avatar Kevin Brodsky Committed by Andrew Morton

uapi/linux/const.h: prefer ISO-friendly __typeof__

typeof is (still) a GNU extension, which means that it cannot be used when
building ISO C (e.g.  -std=c99).  It should therefore be avoided in uapi
headers in favour of the ISO-friendly __typeof__.

Unfortunately this issue could not be detected by
CONFIG_UAPI_HEADER_TEST=y as the __ALIGN_KERNEL() macro is not expanded in
any uapi header.

This matters from a userspace perspective, not a kernel one. uapi
headers and their contents are expected to be usable in a variety of
situations, and in particular when building ISO C applications (with
-std=c99 or similar).

This particular problem can be reproduced by trying to use the
__ALIGN_KERNEL macro directly in application code, say:

#include <linux/const.h>

int align(int x, int a)
{
	return __KERNEL_ALIGN(x, a);
}
	
and trying to build that with -std=c99.	

Link: https://lkml.kernel.org/r/20230411092747.3759032-1-kevin.brodsky@arm.com
Fixes: a79ff731 ("netfilter: xtables: make XT_ALIGN() usable in exported headers by exporting __ALIGN_KERNEL()")
Signed-off-by: default avatarKevin Brodsky <kevin.brodsky@arm.com>
Reported-by: default avatarRuben Ayrapetyan <ruben.ayrapetyan@arm.com>
Tested-by: default avatarRuben Ayrapetyan <ruben.ayrapetyan@arm.com>
Reviewed-by: default avatarPetr Vorel <pvorel@suse.cz>
Tested-by: default avatarPetr Vorel <pvorel@suse.cz>
Reviewed-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a3b2aeac
...@@ -28,7 +28,7 @@ ...@@ -28,7 +28,7 @@
#define _BITUL(x) (_UL(1) << (x)) #define _BITUL(x) (_UL(1) << (x))
#define _BITULL(x) (_ULL(1) << (x)) #define _BITULL(x) (_ULL(1) << (x))
#define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1) #define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (__typeof__(x))(a) - 1)
#define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) #define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask))
#define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d)) #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
......
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