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

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[ Upstream commit 31088f6f79 ]

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: a79ff731a1 ("netfilter: xtables: make XT_ALIGN() usable in exported headers by exporting __ALIGN_KERNEL()")
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Reported-by: Ruben Ayrapetyan <ruben.ayrapetyan@arm.com>
Tested-by: Ruben Ayrapetyan <ruben.ayrapetyan@arm.com>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Tested-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Kevin Brodsky 2023-04-11 10:27:47 +01:00 committed by Greg Kroah-Hartman
parent d1c4dedcd2
commit 397eb669da
1 changed files with 1 additions and 1 deletions
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2
include/uapi/linux/const.h
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@ -28,7 +28,7 @@
#define _BITUL(x) (_UL(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 __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))