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 <[email protected]>
Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
Reported-by: Li Zhijian <[email protected]>
Reported-by: Sandipan Das <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
---
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
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
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.
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
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 <[email protected]>
> Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
> Reported-by: Li Zhijian <[email protected]>
> Reported-by: Sandipan Das <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
> ---
> 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
>
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 <[email protected]>
> > Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
> > Reported-by: Li Zhijian <[email protected]>
> > Reported-by: Sandipan Das <[email protected]>
> > Cc: Arnaldo Carvalho de Melo <[email protected]>
> > ---
> > 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
> >
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.
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
Commit-ID: 4d3b57da1593c66835d8e3a757e4751b35493fb8
Gitweb: https://git.kernel.org/tip/4d3b57da1593c66835d8e3a757e4751b35493fb8
Author: Mark Rutland <[email protected]>
AuthorDate: Wed, 4 Apr 2018 17:34:45 +0100
Committer: Arnaldo Carvalho de Melo <[email protected]>
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 <[email protected]>
Reported-by: Sandipan Das <[email protected]>
Tested-by: Sandipan Das <[email protected]>
Signed-off-by: Mark Rutland <[email protected]>
Fixes: 6aa7de059173a986 ("locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
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