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Subject: Re: [PATCH] tools include: define READ_ONCE/WRITE_ONCE for C++
To:     <acme@redhat.com>
CC:     <linux-kernel@vger.kernel.org>, <philip.li@intel.com>,
        <mark.rutland@arm.com>
References: <1511849622-3683-1-git-send-email-lizhijian@cn.fujitsu.com>
From:   Li Zhijian <lizhijian@cn.fujitsu.com>
Message-ID: <bd627313-05b2-8a7b-e368-5a2b35b4fe86@cn.fujitsu.com>
Date:   Tue, 28 Nov 2017 14:16:07 +0800
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add Arnaldo Carvalho de Melo <acme@redhat.com>


On 11/28/2017 02:13 PM, Li Zhijian wrote:
> since 6aa7de0, we failed to build perf with C++(clang)
> to fix the following compile errors
> --------------
> lizhijian@haswell-OptiPlex-9020:~/lkp/linux/tools/perf$ make LLVM_CONFIG=/usr/bin/llvm-config-3.9 LIBCLANGLLVM=1
> ...
>    CC       util/probe-finder.o
> In file included from /home/lizj/linux/tools/perf/util/util.h:13:0,
>                   from /home/lizj/linux/tools/perf/util/util-cxx.h:20,
>                   from util/c++/clang-c.h:5,
>                   from util/c++/clang-test.cpp:2:
> /home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h: In function ‘int atomic_read(const atomic_t*)’:
> /home/lizj/linux/tools/include/linux/compiler.h:157:45: error: use of deleted function ‘atomic_read(const atomic_t*)::<anonymous union>::<constructor>()’
>    ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
>                                               ^
> /home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro ‘READ_ONCE’
>    return READ_ONCE((v)->counter);
>           ^
> /home/lizj/linux/tools/include/linux/compiler.h:157:11: note: ‘atomic_read(const atomic_t*)::<anonymous union>::<constructor>()’ is implicitly deleted because the default definition would be ill-formed:
>    ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
>             ^
> /home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro ‘READ_ONCE’
>    return READ_ONCE((v)->counter);
>           ^
> /home/lizj/linux/tools/include/linux/compiler.h:157:11: error: uninitialized const member in ‘union atomic_read(const atomic_t*)::<anonymous>’
>    ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
>             ^
> /home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro ‘READ_ONCE’
>    return READ_ONCE((v)->counter);
>           ^
> /home/lizj/linux/tools/include/linux/compiler.h:157:23: note: ‘const int atomic_read(const atomic_t*)::<anonymous union>::__val’ should be initialized
>    ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
>                         ^
> /home/lizj/linux/tools/include/asm/../../arch/x86/include/asm/atomic.h:28:9: note: in expansion of macro ‘READ_ONCE’
>    return READ_ONCE((v)->counter);
>           ^
>    LD       tests/perf-in.o
> ...
> --------------
>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> ---
>   tools/include/linux/compiler.h | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
> index 07fd03c..e4c8a0d 100644
> --- a/tools/include/linux/compiler.h
> +++ b/tools/include/linux/compiler.h
> @@ -86,6 +86,10 @@
>   
>   #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
>   
> +#ifdef __cplusplus
> +#define READ_ONCE(x) ACCESS_ONCE(x)
> +#define WRITE_ONCE(x, val) ACCESS_ONCE(x) = val
> +#else
>   #include <linux/types.h>
>   
>   /*
> @@ -160,6 +164,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>   #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; })
>   
> +#endif /* __cplusplus */
>   
>   #ifndef __fallthrough
>   # define __fallthrough


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