[PATCH] tools: restore READ_ONCE() C++ compatibility

[PATCH] tools: restore READ_ONCE() C++ compatibility

[Mark Rutland]

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>.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
Reported-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Reported-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/include/linux/compiler.h | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

Hi,

This is fallout from my automated ACCESS_ONCE() removal, and I'm not that
familiar with using clang for perf.

In local testing, this fixes READ_ONCE() when compiling with clang, but I
subsequently hit some other issues which I believe are down to LLVM API
changes.

Zhijian, Sandipan, does this patch work for you?

Thanks,
Mark.

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
-- 
2.11.0

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Sandipan Das]

Hi Mark,

On 04/04/2018 10:04 PM, Mark Rutland wrote:
> 
> Zhijian, Sandipan, does this patch work for you?
> 

Yes it does. Thanks for the fix.

- Sandipan

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Mark Rutland]

On Wed, Apr 04, 2018 at 10:43:16PM +0530, Sandipan Das wrote:
> Hi Mark,
> 
> On 04/04/2018 10:04 PM, Mark Rutland wrote:
> > 
> > Zhijian, Sandipan, does this patch work for you?
> > 
> 
> Yes it does. Thanks for the fix.

Great! Can I take that as a Tested-by?

Thanks,
Mark.

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Sandipan Das]

On 04/04/2018 10:48 PM, Mark Rutland wrote:
> On Wed, Apr 04, 2018 at 10:43:16PM +0530, Sandipan Das wrote:
>> Hi Mark,
>>
>> On 04/04/2018 10:04 PM, Mark Rutland wrote:
>>>
>>> Zhijian, Sandipan, does this patch work for you?
>>>
>>
>> Yes it does. Thanks for the fix.
> 
> Great! Can I take that as a Tested-by?
> 

Sure.

- Sandipan

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Mark Rutland]

Hi Arnaldo,

As Sandipan gave a Tested-by for this, are you happy to pick it up as a
fix for v4.17?

Or would you prefer that I resend this?

Thanks,
Mark.

On Wed, Apr 04, 2018 at 05:34:45PM +0100, Mark Rutland wrote:
> 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>.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
> Reported-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> Reported-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  tools/include/linux/compiler.h | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> Hi,
> 
> This is fallout from my automated ACCESS_ONCE() removal, and I'm not that
> familiar with using clang for perf.
> 
> In local testing, this fixes READ_ONCE() when compiling with clang, but I
> subsequently hit some other issues which I believe are down to LLVM API
> changes.
> 
> Zhijian, Sandipan, does this patch work for you?
> 
> Thanks,
> Mark.
> 
> 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
> -- 
> 2.11.0
> 

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Arnaldo Carvalho de Melo]

Em Mon, Apr 09, 2018 at 06:10:41PM +0100, Mark Rutland escreveu:
> Hi Arnaldo,
> 
> As Sandipan gave a Tested-by for this, are you happy to pick it up as a
> fix for v4.17?
> 
> Or would you prefer that I resend this?

I forgot about this fix, but was exposed to it while processing
Sandipan's patches for fixing up builtin clang support, so I ended up
adding the following patch:

https://git.kernel.org/acme/c/ad0902e0c400

This sidesteps this issue by removing the sequence of includes that ends
up including the compiler.h from a C++ file.

Now 'make LIBCLANGLLVM=1 -C tools/perf' works, but I'll look at the
patch below, probably it will save some time in the future if we get to
include compiler.h from C++ code again...

Take a look at my perf/urgent branch, that I just asked Ingo to pull.

- Arnaldo
 
> Thanks,
> Mark.
> 
> On Wed, Apr 04, 2018 at 05:34:45PM +0100, Mark Rutland wrote:
> > 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>.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
> > Reported-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> > Reported-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > ---
> >  tools/include/linux/compiler.h | 20 +++++++++++++++-----
> >  1 file changed, 15 insertions(+), 5 deletions(-)
> > 
> > Hi,
> > 
> > This is fallout from my automated ACCESS_ONCE() removal, and I'm not that
> > familiar with using clang for perf.
> > 
> > In local testing, this fixes READ_ONCE() when compiling with clang, but I
> > subsequently hit some other issues which I believe are down to LLVM API
> > changes.
> > 
> > Zhijian, Sandipan, does this patch work for you?
> > 
> > Thanks,
> > Mark.
> > 
> > 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
> > -- 
> > 2.11.0
> > 

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Mark Rutland]

On Mon, Apr 09, 2018 at 04:40:32PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 09, 2018 at 06:10:41PM +0100, Mark Rutland escreveu:
> > Hi Arnaldo,
> > 
> > As Sandipan gave a Tested-by for this, are you happy to pick it up as a
> > fix for v4.17?
> > 
> > Or would you prefer that I resend this?
> 
> I forgot about this fix, but was exposed to it while processing
> Sandipan's patches for fixing up builtin clang support, so I ended up
> adding the following patch:
> 
> https://git.kernel.org/acme/c/ad0902e0c400
> 
> This sidesteps this issue by removing the sequence of includes that ends
> up including the compiler.h from a C++ file.
> 
> Now 'make LIBCLANGLLVM=1 -C tools/perf' works, but I'll look at the
> patch below, probably it will save some time in the future if we get to
> include compiler.h from C++ code again...
> 
> Take a look at my perf/urgent branch, that I just asked Ingo to pull.

Ah, that's great.

Sorry for the noise!

Mark.

Re: [PATCH] tools: restore READ_ONCE() C++ compatibility

[Arnaldo Carvalho de Melo]

Em Tue, Apr 10, 2018 at 11:55:15AM +0100, Mark Rutland escreveu:
> On Mon, Apr 09, 2018 at 04:40:32PM -0300, Arnaldo Carvalho de Melo wrote:
> > Now 'make LIBCLANGLLVM=1 -C tools/perf' works, but I'll look at the
> > patch below, probably it will save some time in the future if we get to
> > include compiler.h from C++ code again...

> > Take a look at my perf/urgent branch, that I just asked Ingo to pull.
 
> Ah, that's great.
 
> Sorry for the noise!

No noise at all, your patch is valid and I'm applying it. At some point
some code will include compiler.h at some include chain from a C++ file
and clang will explode once more, better fix it now :-)

- Arnaldo

[tip:perf/urgent] tools headers: Restore READ_ONCE() C++ compatibility

[tip-bot for Mark Rutland]

Commit-ID:  4d3b57da1593c66835d8e3a757e4751b35493fb8
Gitweb:     https://git.kernel.org/tip/4d3b57da1593c66835d8e3a757e4751b35493fb8
Author:     Mark Rutland <mark.rutland@arm.com>
AuthorDate: Wed, 4 Apr 2018 17:34:45 +0100
Committer:  Arnaldo Carvalho de Melo <acme@redhat.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@cn.fujitsu.com>
Reported-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Tested-by: Sandipan Das <sandipan@linux.vnet.ibm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.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@redhat.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