From: "Paul E. McKenney" <paulmck@kernel.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: 'Peter Zijlstra' <peterz@infradead.org>,
Marco Elver <elver@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Masahiro Yamada <masahiroy@kernel.org>,
Will Deacon <will@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Kees Cook <keescook@chromium.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
linux-arch <linux-arch@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>
Subject: Re: [PATCH 00/22] add support for Clang LTO
Date: Thu, 2 Jul 2020 11:00:42 -0700 [thread overview]
Message-ID: <20200702180042.GW9247@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <aeed740a4d86470d84ae7d5f1cf07951@AcuMS.aculab.com>
On Thu, Jul 02, 2020 at 09:37:26AM +0000, David Laight wrote:
> From: Paul E. McKenney
> > Sent: 01 July 2020 17:06
> ...
> > > Would an asm statement that uses the same 'register' for input and
> > > output but doesn't actually do anything help?
> > > It won't generate any code, but the compiler ought to assume that
> > > it might change the value - so can't do optimisations that track
> > > the value across the call.
> >
> > It might replace the volatile load, but there are optimizations that
> > apply to the downstream code as well.
> >
> > Or are you suggesting periodically pushing the dependent variable
> > through this asm? That might work, but it would be easier and
> > more maintainable to just mark the variable.
>
> Marking the variable requires compiler support.
> Although what 'volatile register int foo;' means might be interesting.
>
> So I was thinking that in the case mentioned earlier you do:
> ptr += LAUNDER(offset & 1);
> to ensure the compiler didn't convert to:
> if (offset & 1) ptr++;
> (Which is probably a pessimisation - the reverse is likely better.)
Indeed, Akshat's prototype follows the "volatile" qualifier in many
ways. https://github.com/AKG001/gcc/
Thanx, Paul
next prev parent reply other threads:[~2020-07-02 18:00 UTC|newest]
Thread overview: 184+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 20:31 [PATCH 00/22] add support for Clang LTO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 01/22] objtool: use sh_info to find the base for .rela sections Sami Tolvanen
2020-06-24 20:31 ` [PATCH 02/22] kbuild: add support for Clang LTO Sami Tolvanen
2020-06-24 20:53 ` Nick Desaulniers
2020-06-24 21:29 ` Sami Tolvanen
2020-06-25 2:26 ` Nathan Chancellor
2020-06-25 16:13 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 03/22] kbuild: lto: fix module versioning Sami Tolvanen
2020-06-24 20:31 ` [PATCH 04/22] kbuild: lto: fix recordmcount Sami Tolvanen
2020-06-24 21:27 ` Peter Zijlstra
2020-06-24 21:45 ` Sami Tolvanen
2020-06-25 7:45 ` Peter Zijlstra
2020-06-25 16:15 ` Sami Tolvanen
2020-06-25 20:02 ` [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Peter Zijlstra
2020-06-25 20:54 ` Nick Desaulniers
2020-06-25 22:40 ` Sami Tolvanen
2020-06-26 11:29 ` Peter Zijlstra
2020-06-26 11:42 ` Peter Zijlstra
[not found] ` <20200722135542.41127cc4@oasis.local.home>
[not found] ` <20200722184137.GP10769@hirez.programming.kicks-ass.net>
[not found] ` <20200722150943.53046592@oasis.local.home>
[not found] ` <20200722235620.GR10769@hirez.programming.kicks-ass.net>
[not found] ` <20200722200608.40ca9994@oasis.local.home>
2020-08-06 22:09 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 05/22] kbuild: lto: postpone objtool Sami Tolvanen
2020-06-24 21:19 ` Peter Zijlstra
2020-06-24 21:49 ` Sami Tolvanen
2020-06-25 7:47 ` Peter Zijlstra
2020-06-25 16:22 ` Sami Tolvanen
2020-06-25 18:33 ` Peter Zijlstra
2020-06-25 19:32 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 06/22] kbuild: lto: limit inlining Sami Tolvanen
2020-06-24 21:20 ` Peter Zijlstra
2020-06-24 23:37 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 07/22] kbuild: lto: merge module sections Sami Tolvanen
2020-06-24 21:01 ` Nick Desaulniers
2020-06-24 21:31 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 08/22] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-06-24 21:13 ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 09/22] init: lto: ensure initcall ordering Sami Tolvanen
2020-06-24 20:31 ` [PATCH 10/22] init: lto: fix PREL32 relocations Sami Tolvanen
2020-06-24 20:31 ` [PATCH 11/22] pci: " Sami Tolvanen
2020-06-24 20:31 ` [PATCH 12/22] modpost: lto: strip .lto from module names Sami Tolvanen
2020-06-24 22:05 ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 13/22] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-06-24 20:57 ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 14/22] efi/libstub: disable LTO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 15/22] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-06-24 20:31 ` [PATCH 16/22] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen
2020-06-24 20:31 ` [PATCH 17/22] arm64: vdso: disable LTO Sami Tolvanen
2020-06-24 20:58 ` Nick Desaulniers
2020-06-24 21:09 ` Nick Desaulniers
2020-06-24 23:51 ` Andi Kleen
2020-06-24 21:52 ` Sami Tolvanen
2020-06-24 23:05 ` Nick Desaulniers
2020-06-24 23:39 ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 18/22] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 20:31 ` [PATCH 19/22] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 20/22] x86, ftrace: disable recordmcount for ftrace_make_nop Sami Tolvanen
2020-06-24 20:31 ` [PATCH 21/22] x86, relocs: Ignore L4_PAGE_OFFSET relocations Sami Tolvanen
2020-06-24 20:32 ` [PATCH 22/22] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 21:15 ` [PATCH 00/22] add support for Clang LTO Peter Zijlstra
2020-06-24 21:30 ` Sami Tolvanen
2020-06-25 8:27 ` Will Deacon
2020-06-24 21:31 ` Nick Desaulniers
2020-06-25 8:03 ` Peter Zijlstra
2020-06-25 8:24 ` Peter Zijlstra
2020-06-25 8:57 ` Peter Zijlstra
2020-06-30 19:19 ` Marco Elver
2020-06-30 20:12 ` Peter Zijlstra
2020-06-30 20:30 ` Paul E. McKenney
2020-07-01 9:10 ` Peter Zijlstra
2020-07-01 14:20 ` David Laight
2020-07-01 16:06 ` Paul E. McKenney
2020-07-02 9:37 ` David Laight
2020-07-02 18:00 ` Paul E. McKenney [this message]
2020-07-01 9:41 ` Marco Elver
2020-07-01 10:03 ` Will Deacon
2020-07-01 11:40 ` Peter Zijlstra
2020-07-01 14:06 ` Paul E. McKenney
2020-07-01 15:05 ` Peter Zijlstra
2020-07-01 16:03 ` Paul E. McKenney
2020-07-02 8:20 ` Peter Zijlstra
2020-07-02 17:59 ` Paul E. McKenney
2020-07-03 13:13 ` Peter Zijlstra
2020-07-03 13:25 ` Peter Zijlstra
2020-07-03 14:51 ` Paul E. McKenney
2020-07-03 14:42 ` Paul E. McKenney
2020-07-06 16:26 ` Paul E. McKenney
2020-07-06 18:29 ` Peter Zijlstra
2020-07-06 18:39 ` Paul E. McKenney
2020-07-06 19:40 ` Peter Zijlstra
2020-07-06 23:41 ` Paul E. McKenney
2020-06-28 16:56 ` Masahiro Yamada
2020-06-29 23:20 ` Sami Tolvanen
2020-07-07 15:51 ` Sami Tolvanen
2020-07-07 16:05 ` Sami Tolvanen
2020-07-07 16:56 ` Jakub Kicinski
2020-07-07 17:17 ` Nick Desaulniers
2020-07-07 17:30 ` Jakub Kicinski
2020-09-03 20:30 ` [PATCH v2 00/28] Add " Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 01/28] x86/boot/compressed: Disable relocation relaxation Sami Tolvanen
2020-09-03 21:44 ` Kees Cook
2020-09-03 23:42 ` Arvind Sankar
2020-09-04 7:14 ` Nathan Chancellor
2020-09-03 20:30 ` [PATCH v2 02/28] x86/asm: Replace __force_order with memory clobber Sami Tolvanen
2020-09-03 21:45 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 03/28] lib/string.c: implement stpcpy Sami Tolvanen
2020-09-03 21:47 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 04/28] RAS/CEC: Fix cec_init() prototype Sami Tolvanen
2020-09-03 21:50 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 05/28] objtool: Add a pass for generating __mcount_loc Sami Tolvanen
2020-09-03 21:51 ` Kees Cook
2020-09-03 22:03 ` Sami Tolvanen
2020-09-04 9:31 ` peterz
2020-09-10 18:29 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 06/28] objtool: Don't autodetect vmlinux.o Sami Tolvanen
2020-09-03 21:52 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 07/28] kbuild: add support for objtool mcount Sami Tolvanen
2020-09-03 21:56 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 08/28] x86, build: use " Sami Tolvanen
2020-09-03 21:58 ` Kees Cook
2020-09-03 22:11 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 09/28] kbuild: add support for Clang LTO Sami Tolvanen
2020-09-03 22:08 ` Kees Cook
2020-09-08 17:02 ` Sami Tolvanen
2020-09-05 19:36 ` Masahiro Yamada
2020-09-08 17:10 ` Sami Tolvanen
2020-09-05 20:17 ` Masahiro Yamada
2020-09-08 17:14 ` Sami Tolvanen
2020-09-07 15:30 ` Masahiro Yamada
2020-09-08 17:30 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 10/28] kbuild: lto: fix module versioning Sami Tolvanen
2020-09-03 22:11 ` Kees Cook
2020-09-08 18:23 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 11/28] kbuild: lto: postpone objtool Sami Tolvanen
2020-09-03 22:19 ` Kees Cook
2020-09-08 20:56 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 12/28] kbuild: lto: limit inlining Sami Tolvanen
2020-09-03 22:20 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 13/28] kbuild: lto: merge module sections Sami Tolvanen
2020-09-03 22:23 ` Kees Cook
2020-09-07 15:25 ` Masahiro Yamada
2020-09-08 21:07 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 14/28] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-09-03 22:29 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 15/28] init: lto: ensure initcall ordering Sami Tolvanen
2020-09-03 22:40 ` Kees Cook
2020-09-08 21:16 ` Sami Tolvanen
2020-09-10 9:25 ` David Woodhouse
2020-09-10 15:07 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 16/28] init: lto: fix PREL32 relocations Sami Tolvanen
2020-09-03 22:41 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 17/28] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-09-03 22:42 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 18/28] modpost: lto: strip .lto from module names Sami Tolvanen
2020-09-03 22:42 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 19/28] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-09-03 22:43 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 20/28] efi/libstub: disable LTO Sami Tolvanen
2020-09-03 22:43 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 21/28] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 22/28] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen
2020-09-03 22:44 ` Kees Cook
2020-09-08 21:23 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 23/28] arm64: vdso: disable LTO Sami Tolvanen
2020-09-03 22:45 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 24/28] KVM: arm64: disable LTO for the nVHE directory Sami Tolvanen
2020-09-03 22:45 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 25/28] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-09-03 22:45 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 26/28] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-09-03 22:46 ` Kees Cook
2020-09-03 20:30 ` [PATCH v2 27/28] x86, relocs: Ignore L4_PAGE_OFFSET relocations Sami Tolvanen
2020-09-03 22:47 ` Kees Cook
2020-09-08 23:28 ` Sami Tolvanen
2020-09-03 20:30 ` [PATCH v2 28/28] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-09-03 22:48 ` Kees Cook
2020-09-03 23:34 ` [PATCH v2 00/28] Add support for Clang LTO Kees Cook
2020-09-04 4:45 ` Nathan Chancellor
2020-09-03 23:38 ` Kees Cook
2020-09-04 7:53 ` Sedat Dilek
2020-09-04 8:55 ` peterz
2020-09-04 9:08 ` Sedat Dilek
2020-09-06 0:24 ` Masahiro Yamada
2020-09-08 23:46 ` Sami Tolvanen
2020-09-10 1:18 ` Masahiro Yamada
2020-09-10 15:17 ` Sami Tolvanen
2020-09-10 18:18 ` Kees Cook
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