[BOLT] Optimizing Linux Kernel with BOLT but fail to boot

[hun-zi-shang-fen]

The Linux kernel fails to boot after applying BOLT optimization with the --split-functions option as described in the document （https://github.com/llvm/llvm-project/blob/main/bolt/docs/OptimizingLinux.md）. It gets stuck during the boot process at “Loading initial ramdisk...”

[maksfb]

Does it work without --split-functions? How is your kernel configured?

[hun-zi-shang-fen]

Does it work without --split-functions? How is your kernel configured?

yep, it work when I delete the --split-functions

[ptr1337]

Having same issue actually. Sadly till now no succes.

[MichaelDeets]

I'm still getting this problem with LLVM 20.1.7 (I did also try LLVM 21 from 2025/06/28) on Gentoo Linux using Kernel 6.16-rc4

Kernel configuration

This is after applying the first patch recommended from BOLT's Optimizing Linux guide inside arch/x86/kernel/vmlinux.lds.S.

Given it wasn't bootable, there wasn't any output, so I put the broken image through QEMU, and collected the output there instead.

Failed boot log w/ --split-functions

Not sure how helpful it would be, given it's not configured for the virtual environment.