From: Mark Rutland Date: Wed, 4 Apr 2018 16:34:45 +0000 (+0100) Subject: tools headers: Restore READ_ONCE() C++ compatibility X-Git-Tag: v4.17-rc2~6^2~4^2~15 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4d3b57da1593c66835d8e3a757e4751b35493fb8;p=thirdparty%2Fkernel%2Flinux.git tools headers: Restore READ_ONCE() C++ compatibility Our userspace defines READ_ONCE() in a way that clang doesn't like, as we have an anonymous union in which neither field is initialized. WRITE_ONCE() is fine since it initializes the __val field. For READ_ONCE() we can keep clang and GCC happy with a dummy initialization of the __c field, so let's do that. At the same time, let's split READ_ONCE() and WRITE_ONCE() over several lines for legibility, as we do in the in-kernel . Reported-by: Li Zhijian Reported-by: Sandipan Das Tested-by: Sandipan Das Signed-off-by: Mark Rutland Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()") Link: http://lkml.kernel.org/r/20180404163445.16492-1-mark.rutland@arm.com Signed-off-by: Arnaldo Carvalho de Melo --- diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index 04e32f965ad7f..1827c2f973f93 100644 --- a/tools/include/linux/compiler.h +++ b/tools/include/linux/compiler.h @@ -151,11 +151,21 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s * required ordering. */ -#define READ_ONCE(x) \ - ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) - -#define WRITE_ONCE(x, val) \ - ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) +#define READ_ONCE(x) \ +({ \ + union { typeof(x) __val; char __c[1]; } __u = \ + { .__c = { 0 } }; \ + __read_once_size(&(x), __u.__c, sizeof(x)); \ + __u.__val; \ +}) + +#define WRITE_ONCE(x, val) \ +({ \ + union { typeof(x) __val; char __c[1]; } __u = \ + { .__val = (val) }; \ + __write_once_size(&(x), __u.__c, sizeof(x)); \ + __u.__val; \ +}) #ifndef __fallthrough