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Subject: Re: [PATCH v2] tools include: define READ_ONCE/WRITE_ONCE for C++
To:     linux-kernel@vger.kernel.org
Cc:     Li Zhijian <lizhijian@cn.fujitsu.com>, acme@redhat.com,
        philip.li@intel.com, mark.rutland@arm.com,
        paulmck@linux.vnet.ibm.com, mingo@kernel.org
References: <1512005772-27112-1-git-send-email-lizhijian@cn.fujitsu.com>
From:   Sandipan Das <sandipan@linux.vnet.ibm.com>
Date:   Wed, 4 Apr 2018 11:46:38 +0530
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Hi,

On 11/30/2017 07:06 AM, 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
> ...
> --------------
> 

I ran into the same problems while building perf with clang support.
If the solution proposed here is acceptable, can someone please pick
up this patch?

--
With Regards,
Sandipan