search for: clang_lto

...In future, for > > very aggressive non-LTO compilers even, one may then also select that > > if there is substantiated worry things do actually break. > > I agree, a separate config option would be better here. > > Also Will, the LTO patches use CONFIG_LTO_CLANG instead of CLANG_LTO. D'oh, sorry. I'll fix that (I had that #ifdef commented out for my testing). Will

On Tue, Jun 30, 2020 at 09:47:30PM +0200, Marco Elver wrote: > I do wonder, though, if there is some way to make the compiler do > something better for us. Clearly, implementing real > memory_order_consume hasn't worked out until today. But maybe the > compiler could promote dependent loads to acquires if it recognizes it > lost dependencies during optimizations. Just thinking

On Tue, Jun 30, 2020 at 09:47:30PM +0200, Marco Elver wrote: > On Tue, 30 Jun 2020 at 19:39, Will Deacon <will at kernel.org> wrote: > > > > When building with LTO, there is an increased risk of the compiler > > converting an address dependency headed by a READ_ONCE() invocation > > into a control dependency and consequently allowing for harmful > >

On Tue, Jun 30, 2020 at 09:25:03PM +0200, Arnd Bergmann wrote: > On Tue, Jun 30, 2020 at 7:39 PM Will Deacon <will at kernel.org> wrote: > > +#define __READ_ONCE(x) \ > > +({ \ > > + int atomic = 1; \

...> +++ 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( \ > &g...

On Mon, Jul 06, 2020 at 05:00:23PM +0100, Dave Martin wrote: > On Thu, Jul 02, 2020 at 08:23:02AM +0100, Will Deacon wrote: > > On Wed, Jul 01, 2020 at 06:07:25PM +0100, Dave P Martin wrote: > > > Also, can you illustrate code that can only be unsafe with Clang LTO? > > > > I don't have a concrete example, but it's an ongoing concern over on the LTO > >

...> +++ 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 > > Don't we have a generic option for LTO that's not specific to Clang. /me looks at the LTO series some more Oh yeah, there's CONFIG_LTO which is selected by CONFIG_LTO_CLANG, which is the non-typoed version of the above. I can switch this to CONFIG_LTO. > Also, can you i...

On Tue, Jun 30, 2020 at 7:39 PM Will Deacon <will at kernel.org> wrote: > +#define __READ_ONCE(x) \ > +({ \ > + int atomic = 1; \ > + union { __unqual_scalar_typeof(x) __val; char __c[1]; } __u; \ > +

On Tue, Jun 30, 2020 at 7:39 PM Will Deacon <will at kernel.org> wrote: > +#define __READ_ONCE(x) \ > +({ \ > + int atomic = 1; \ > + union { __unqual_scalar_typeof(x) __val; char __c[1]; } __u; \ > +

.../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, \ + ".arch_extension rcpc\n" \ +...

I'm trying to put together a Micro Conference for Linux Plumbers conference focused on "make LLVM slightly less shitty." Do you all plan on attending the conference? Would it be worthwhile to hold a session focused on discussing this (LTO and memory models) be worthwhile? On Tue, Jul 7, 2020 at 3:51 PM Paul E. McKenney <paulmck at kernel.org> wrote: > > On Tue, Jul 07,

...) arm64: Reduce the number of header files pulled into vmlinux.lds.S arm64: alternatives: Split up alternative.h arm64: cpufeatures: Add capability for LDAPR instruction arm64: alternatives: Remove READ_ONCE() usage during patch operation arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y .../RCU/Design/Requirements/Requirements.rst | 2 +- Documentation/memory-barriers.txt | 156 +--------- .../translations/ko_KR/memory-barriers.txt | 146 +-------- arch/alpha/include/asm/atomic.h | 16 +- arch/alpha/include/asm/barrier.h | 61 +---...

...) arm64: Reduce the number of header files pulled into vmlinux.lds.S arm64: alternatives: Split up alternative.h arm64: cpufeatures: Add capability for LDAPR instruction arm64: alternatives: Remove READ_ONCE() usage during patch operation arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y .../RCU/Design/Requirements/Requirements.rst | 2 +- Documentation/memory-barriers.txt | 156 +--------- .../translations/ko_KR/memory-barriers.txt | 146 +-------- arch/alpha/include/asm/atomic.h | 16 +- arch/alpha/include/asm/barrier.h | 61 +---...