Clang LTO Support Looks Like It Could Land For Linux 5.12

[FireBurn]

As someone who doens't use modules, I'm hoping this will just work for me when it lands

[AdelKS]

ms178 how do you avoid the objtool errors in practice ? I've been trying to x86_64 LTO for a while, at each new patch version, and the kernel compilation doesn't succeeded and I get a shit ton of objtool errors. I compile linux with the tkg patchset. Do I need to keep -02 or something ?

[Michael]

So GCC cannot do LTO on the Linux kernel yet?

Not on mainline yet.

[MastaG]

So GCC cannot do LTO on the Linux kernel yet?

[ms178]

For anyone who wants to try Clang LTO on x86-64, just download the Kernel from Sami's clang-lto Kernel branch: https://github.com/samitolvanen/linux/tree/clang-lto

Make sure to use make LLVM=1 LLVM_IAS=1 to get to see these options while configuring your Kernel. Also, some Kernel options are known to cause problems, Retpolines and trimming unused symbols will lead to objtool or modprobe errors. Only the latter are fatal for the build to finish.

I hope we will see this series land sooner rather than later, it would also be a first for LLVM/clang to support a major Kernel feature before GCC. And speaking of GCC, I hope Andi Kleen and the Microsoft guys will follow up on getting GCC LTO support eventually in a shape to merge in a not too distant future, too.

[phoronix]

Phoronix: Clang LTO Support Looks Like It Could Land For Linux 5.12

The support for Clang LTO of the Linux kernel for link-time optimizations when using that GCC alternative compiler looks like it will land with Linux 5.12...

http://www.phoronix.com/scan.php?page=news_item&px=Clang-LTO-Linux-Next-Queue