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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>
36 lines
1,006 B
C
36 lines
1,006 B
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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/* const.h: Macros for dealing with constants. */
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#ifndef _UAPI_LINUX_CONST_H
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#define _UAPI_LINUX_CONST_H
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/* Some constant macros are used in both assembler and
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* C code. Therefore we cannot annotate them always with
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* 'UL' and other type specifiers unilaterally. We
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* use the following macros to deal with this.
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*
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* Similarly, _AT() will cast an expression with a type in C, but
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* leave it unchanged in asm.
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*/
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#ifdef __ASSEMBLY__
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#define _AC(X,Y) X
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#define _AT(T,X) X
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#else
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#define __AC(X,Y) (X##Y)
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#define _AC(X,Y) __AC(X,Y)
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#define _AT(T,X) ((T)(X))
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#endif
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#define _UL(x) (_AC(x, UL))
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#define _ULL(x) (_AC(x, ULL))
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#define _BITUL(x) (_UL(1) << (x))
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#define _BITULL(x) (_ULL(1) << (x))
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#define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (__typeof__(x))(a) - 1)
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#define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask))
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#define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
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#endif /* _UAPI_LINUX_CONST_H */
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