On Tuesday 17 November 2015 17:12:37 Will Deacon wrote:
> On Tue, Nov 17, 2015 at 06:03:40PM +0100, Arnd Bergmann wrote:
> > On Tuesday 17 November 2015 16:44:53 Will Deacon wrote:
> > > > 8<----
> > > > Subject: ARM64: make smp_load_acquire() work with const arguments
> > > >
> > > > smp_load_acquire() uses typeof() to declare a local variable for temporarily
> > > > storing the output of the memory access. This fails when the argument is
> > > > constant, because the assembler complains about using a constant register
> > > > as output:
> > > >
> > > > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1'
> > > > used as 'asm' output
> > >
> > > Do you know the usage in the kernel causing this warning?
> >
> > A newly introduced function in include/net/sock.h:
> >
> > static inline int sk_state_load(const struct sock *sk)
> > {
> > return smp_load_acquire(&sk->sk_state);
> > }
>
> Hmm, maybe we could play a similar trick to READ_ONCE by declaring an
> anonymous union and writing through the non-const member?
Yes, I think that would work, if you think we need to care about the
case where we read into a structure.
Can you come up with a patch for that?
Arnd
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