Messages in this thread |  | | Date | Mon, 9 Apr 2018 18:10:41 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] tools: restore READ_ONCE() C++ compatibility |
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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 >
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