On 11/28/2017 07:30 PM, Mark Rutland wrote:
Hi,
[Fixed acme's address and added more Ccs]
thanks
On Tue, Nov 28, 2017 at 02:13:42PM +0800, Li Zhijian wrote:
since 6aa7de0, we failed to build perf with C++(clang)
to fix the following compile errors
Sorry about this.
With llvm-config and libclang from the LLVM 5.0.0 release, I can
reproduce this.
--------------
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
So IIUC, g++ doesn't like the union aliasing trick that we use here, and
doesn't believe that __val has been initialised.
I haven't found a way around that yet. Ideally we'd just have a
non-const temporary (and a __builtin_memcpy) rather than a union, but I
can't find a way to strip const from typeof() prior to c++11.
...
--------------
Signed-off-by: Li Zhijian <lizhij...@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>
This is somewhat unfortunate, since we want to get rid of ACCESS_ONCE().
Got it
I'll see if I can come up with something to make the existing
{READ,WRITE}_ONCE() work, so that we can avoid issues with non-scalar
types.
That's great if we can bring up the existing code.
Thanks
Zhijian
Otherwise, could we please make these:
#define READ_ONCE(x) (*(volatile typeof(x) *)&(x))
#define WRITE_ONCE(x) (*(volatile typeof(x) *)&(x)) = (val)
Thanks,
Mark.
/*
@@ -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
--
2.7.4
