Re: [PATCH v2] tools include: define READ_ONCE/WRITE_ONCE for C++

From: Li Zhijian
Date: Thu Dec 14 2017 - 20:20:51 EST


ping


On 11/30/2017 09:36 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 âint atomic_read(const atomic_t*)â:
/home/lizj/linux/tools/include/linux/compiler.h:157:45: error: use of deleted function âatomic_read(const atomic_t*)::<anonymous union>::<constructor>()â
({ 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 âREAD_ONCEâ
return READ_ONCE((v)->counter);
^
/home/lizj/linux/tools/include/linux/compiler.h:157:11: note: âatomic_read(const atomic_t*)::<anonymous union>::<constructor>()â 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 âREAD_ONCEâ
return READ_ONCE((v)->counter);
^
/home/lizj/linux/tools/include/linux/compiler.h:157:11: error: uninitialized const member in âunion atomic_read(const atomic_t*)::<anonymous>â
({ 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 âREAD_ONCEâ
return READ_ONCE((v)->counter);
^
/home/lizj/linux/tools/include/linux/compiler.h:157:23: note: âconst int atomic_read(const atomic_t*)::<anonymous union>::__valâ 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 âREAD_ONCEâ
return READ_ONCE((v)->counter);
^
LD tests/perf-in.o
...
--------------

Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>
---
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..d6675c5 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) (*(volatile typeof(x) *)&(x))
+#define WRITE_ONCE(x, val) (*(volatile typeof(x) *)&(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

--
Best regards.
Li Zhijian (8528)