Re: [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y
From: Dave P Martin <dave.martin@arm.com>
Date: 2020-07-01 17:07:37
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linux-alpha, lkml, virtualization
On Tue, Jun 30, 2020 at 06:37:34PM +0100, Will Deacon wrote:
quoted hunk ↗ jump to hunk
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 reordering by the CPU. Ensure that such transformations are harmless by overriding the generic READ_ONCE() definition with one that provides acquire semantics when building with LTO. Signed-off-by: Will Deacon <will@kernel.org> --- arch/arm64/include/asm/rwonce.h | 63 +++++++++++++++++++++++++++++++ arch/arm64/kernel/vdso/Makefile | 2 +- arch/arm64/kernel/vdso32/Makefile | 2 +- 3 files changed, 65 insertions(+), 2 deletions(-) create mode 100644 arch/arm64/include/asm/rwonce.hdiff --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
Don't we have a generic option for LTO that's not specific to Clang. Also, can you illustrate code that can only be unsafe with Clang LTO? [...] Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel