On Sat, Aug 19, 2017 at 03:34:01PM +0200, Arnd Bergmann wrote: > On Sat, Aug 19, 2017 at 2:51 PM, Arnd Bergmann <[email protected]> wrote: > > >> --- a/include/linux/completion.h > >> +++ b/include/linux/completion.h > >> @@ -74,7 +74,7 @@ static inline void complete_release_commit(struct > >> completion *x) {} > >> #endif > >> > >> #define COMPLETION_INITIALIZER_ONSTACK(work) \ > >> - ({ init_completion(&work); work; }) > >> + (*({ init_completion(&work); &work; })) > >> > >> /** > >> * DECLARE_COMPLETION - declare and initialize a completion structure > > > > Nice hack. Any idea why that's different to the compiler? > >
So I find this link:
https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
it says:
"In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression. "
I think this is why the temporary variable is constructed(or at least
allocated). Lemme put this in my commit log.
> > I've applied that one to my test tree now, and reverted my own patch,
> > will let you know if anything else shows up. I think we probably want
> > to merge both patches to mainline.
>
> There is apparently one user of COMPLETION_INITIALIZER_ONSTACK
> that causes a regression with the patch above:
>
> drivers/acpi/nfit/core.c: In function 'acpi_nfit_flush_probe':
> include/linux/completion.h:77:3: error: value computed is not used
> [-Werror=unused-value]
> (*({ init_completion(&work); &work; }))
>
> It would be trivial to convert to init_completion(), which seems to be
> what was intended there.
>
Thanks. Will send the conversion as a separate patch along with my
patch.
Regards,
Boqun
> Arnd
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