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.

Sami