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Date: Thu, 16 Nov 2017 18:47:15 +0000
From: Will Deacon <will.deacon@arm.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Alex Matveev <alxmtvv@gmail.com>, Andi Kleen <ak@linux.intel.com>,
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Subject: Re: [PATCH v2 10/18] arm64: add a workaround for GNU gold with
 ARM64_MODULE_PLTS
Message-ID: <20171116184714.GD21898@arm.com>
References: <20171116164101.GE94341@samitolvanen.mtv.corp.google.com>
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On Thu, Nov 16, 2017 at 08:41:01AM -0800, Sami Tolvanen wrote:
> On Thu, Nov 16, 2017 at 11:50:12AM +0000, Will Deacon wrote:
> > Why don't we just not do LTO if the toolchain is busted?
> 
> Because LTO can not only potentially improve performance, especially
> when combined with PGO (Profile Guided Optimization), but it also
> makes it possible to enable features like Control Flow Integrity that
> can make kernel vulnerabilities more difficult to exploit:
> 
>   https://clang.llvm.org/docs/ControlFlowIntegrity.html
> 
> > This feels like it will end up being a game of whack-a-mole as code
> > could be introduced that tickles known bugs on older toolchains.
> 
> I'm not sure this is much different from dealing with older versions
> of the existing toolchain. Otherwise, we wouldn't need cc-version or
> other similar macros, for example.

I think the big difference is that we have no compelling need to support
older versions of clang or gold.

Will