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Date: Wed, 24 Jun 2020 16:51:44 -0700
From: Andi Kleen <ak@...ux.intel.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Will Deacon <will@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	clang-built-linux <clang-built-linux@...glegroups.com>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux ARM <linux-arm-kernel@...ts.infradead.org>,
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 17/22] arm64: vdso: disable LTO

On Wed, Jun 24, 2020 at 02:09:40PM -0700, Nick Desaulniers wrote:
> On Wed, Jun 24, 2020 at 1:58 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > On Wed, Jun 24, 2020 at 1:33 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> > >
> > > Filter out CC_FLAGS_LTO for the vDSO.
> >
> > Just curious about this patch (and the following one for x86's vdso),
> > do you happen to recall specifically what the issues with the vdso's
> > are?
> 
> + Andi (tangential, I actually have a bunch of tabs open with slides
> from http://halobates.de/ right now)
> 58edae3aac9f2
> 67424d5a22124
> $ git log -S DISABLE_LTO

I think I did it originally because the vDSO linker step didn't do
all the magic needed for gcc LTO. But it also doesn't seem to be
very useful for just a few functions that don't have complex
interactions, and somewhat risky for violating some assumptions.

-Andi

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