From: Kevin Brodsky kevin.brodsky@arm.com
[ Upstream commit 31088f6f7906253ef4577f6a9b84e2d42447dba0 ]
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: a79ff731a1b2 ("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 --- include/uapi/linux/const.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/uapi/linux/const.h b/include/uapi/linux/const.h index af2a44c08683d..a429381e7ca50 100644 --- a/include/uapi/linux/const.h +++ b/include/uapi/linux/const.h @@ -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))