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Date: Sun, 15 Apr 2018 23:41:33 -0700 From: tip-bot for Mark Rutland <tipbot@...or.com> To: linux-tip-commits@...r.kernel.org Cc: acme@...hat.com, lizhijian@...fujitsu.com, mingo@...nel.org, mark.rutland@....com, tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org, sandipan@...ux.vnet.ibm.com Subject: [tip:perf/urgent] tools headers: Restore READ_ONCE() C++ compatibility Commit-ID: 4d3b57da1593c66835d8e3a757e4751b35493fb8 Gitweb: https://git.kernel.org/tip/4d3b57da1593c66835d8e3a757e4751b35493fb8 Author: Mark Rutland <mark.rutland@....com> AuthorDate: Wed, 4 Apr 2018 17:34:45 +0100 Committer: Arnaldo Carvalho de Melo <acme@...hat.com> CommitDate: Thu, 12 Apr 2018 09:30:09 -0300 tools headers: Restore READ_ONCE() C++ compatibility Our userspace <linux/compiler.h> 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 <linux/compiler.h>. Reported-by: Li Zhijian <lizhijian@...fujitsu.com> Reported-by: Sandipan Das <sandipan@...ux.vnet.ibm.com> Tested-by: Sandipan Das <sandipan@...ux.vnet.ibm.com> Signed-off-by: Mark Rutland <mark.rutland@....com> 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 <acme@...hat.com> --- tools/include/linux/compiler.h | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h index 04e32f965ad7..1827c2f973f9 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
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