On Mon, Jul 06, 2020 at 05:08:20PM +0100, Dave Martin wrote: > On Tue, Jun 30, 2020 at 06:37:34PM +0100, Will Deacon wrote: > > diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h > > new file mode 100644 > > index 000000000000..515e360b01a1 > > --- /dev/null > > +++ b/arch/arm64/include/asm/rwonce.h > > @@ -0,0 +1,63 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +/* > > + * Copyright (C) 2020 Google LLC. > > + */ > > +#ifndef __ASM_RWONCE_H > > +#define __ASM_RWONCE_H > > + > > +#ifdef CONFIG_CLANG_LTO > > + > > +#include <linux/compiler_types.h> > > +#include <asm/alternative-macros.h> > > + > > +#ifndef BUILD_VDSO > > + > > +#ifdef CONFIG_AS_HAS_LDAPR > > +#define __LOAD_RCPC(sfx, regs...) \ > > + ALTERNATIVE( \ > > + "ldar" #sfx "\t" #regs, \ > > ^ Should this be here? It seems that READ_ONCE() will actually read > twice... even if that doesn't actually conflict with the required > semantics of READ_ONCE(), it looks odd. It's patched at runtime, so it's either LDAR or LDAPR. > Making a direct link between LTO and the memory model also seems highly > spurious (as discussed in the other subthread) so can we have a comment > explaining the reasoning? Sure, although like I say, this is more about helping to progress that conversation. Will
