On LLVM clang compiled Linux kernel host, VirtualBox hard-freezes the host when launching a Virtual Machine.

[dreieck]

Ahoj,

I am on Linux, kernel version 6.8.8, VirtualBox version 7.0.16 (EDIT: also with version 7.0.18 as tested later, see follow-up comment).

Virtual Box host module compiled via DKMS for all installed kernels.

When I want to run any VortualBox virtual machine with a Linux kernel compiled using the LLVM clang compiler, the system freezes immediately, only a hard reset helps (also the Linux' SysRq does not work anymore). A dmesg -w running in parallel in another window does not show anything (before system freeze).

When I instead use a kernel compiled with GCC (otherwise same kernel configuration), VirtualBox virtual machine runs as expected.

Note that using LLVM clang is a supported compiler for Linux.

Compiler versions:

• clang --version:

  clang version 17.0.6
  Target: x86_64-pc-linux-gnu
  Thread model: posix
  InstalledDir: /usr/bin
  

• ld.lld --version: LLD 17.0.6 (compatible with GNU linkers)
• gcc --version | head -n1: gcc (GCC) 13.2.1 20240417

I attach the following files for background information:

• Kernel config of the GCC compiled kernel: config_6.8.8-gcc.gz (compressed),
• Kernel config of the LLVM clang compiled kernel: config_6.8.8-clang.gz (compressed),
• diff between those two kernel configurations: config-diff_6.8.8-gcc-clang.txt,
• dmesg output after booting the system with the GCC compiled kernel: dmesg_6.8.8-gcc.log,
• dmesg output after booting the system with the LLVM clang compiled kernel: dmesg_6.8.8-clang.log,
• hwinfo output (captured with the LLVM clang compiled kernel): hwinfo_6.8.8-clang.log.zstd (compressed),
• inxi -F output (captured with the LLVM clang compiled kernel): inxi_6.8.8-clang.log,
• lspci -vvv output (captured with the LLVM clang compiled kernel): lspci_6.8.8-clang.log,
• The VirtualBox-logfile of sucessfully running a Virtual Machine from the host booted with the GCC compiled kernel: VirtualBox-machine-log_CD boot-2024-05-04-19-58-26_6.8.8-gcc.log. *(All occurances of <censored> in those logs are censorings of my username.)*

Regards!

[dreieck]

Linux kernel configuration of the GCC compiled kernel

[dreieck]

Linux kernel config of the clang compiled kernel

[dreieck]

diff between the two kernel configs (GCC and clang compiled kernel)

[dreieck]

dmesg output after booting the system with the GCC compiled kernel

[dreieck]

dmesg output after booting the system with the clang compiled kernel

[dreieck]

hwinfo output (captured with the LLVM clang compiled kernel)

[dreieck]

inxi -F output (captured with the LLVM clang compiled kernel)

[dreieck]

lspci -vvv output (captured with the LLVM clang compiled kernel)

[dreieck]

The VirtualBox-logfile of sucessfully running a Virtual Machine from the host booted with the GCC compiled kernel

[dreieck]

Also happens with VirtualBox version 7.0.18, and with "Enable 3D Acceleration" switched off and with USB 1.1 instead of USB 3.0.

[galitsyn]

Hi dreieck,

Please update to version 7.0.18.

[dreieck]

Please update to version 7.0.18.

As I wrote in this follow-up comment (timestamp 2024-05-04T21:55:23+01:00) and in the edited post, I have updated to 7.0.18 and tested there; it also appears in 7.0.18.

[galitsyn]

Hi dreieck,

We do not officially support CLANG on Linux host (only GCC is supported). We also do not support DKMS anymore. I wonder if you are dealing with host modules which come with your Linux distribution?

[dreieck]

We do not officially support CLANG on Linux host (only GCC is supported).

That is sad. Since clang is a compiler supported by the Linux kernel I hereby feature request that VirtualBox host modules support it, too. Only with clang the linux kernel can be optimised by link time optimisation (LTO), which gives a performance gain.

This actually then will mean I prioritise moving my virtual machines away from VirtualBox to qemu/KVM/libvirt, since this does not have all those problems and seems more open; and going to stop using your software.

We also do not support DKMS anymore. I wonder if you are dealing with host modules which come with your Linux distribution?

Yes; virtualbox-host-dkms of Artix Linux: ​package, ​package recipe.

[galitsyn]

Hi dreieck,

Try to uninstall VirtualBox package which comes with your Linux distribution and install official one from Downloads page to see if the issue is still present.

[dreieck]

install official one from Downloads

You do not have Arch Linux packages.

And I _will not_ run a (possibly shady) ​shell script to install your software, maybe messing with my installation.

Do you have precompiled binaries available as e.g. a .tar.gz file, which are quite "relaxed" with regard to versioned dependencies/ statically compiled?, which perfectly can run out of /opt/?

---

What I am currently doing, going to test and then going to report back:

• Compiling vanilla Linux kernel with GCC and CLANG; and with CLANG
  • without LTO,
  • with ThinLTO,
  • with Full LTO.

[dreieck]

What I am currently doing, going to test and then going to report back:

• Compiling vanilla Linux kernel with GCC and CLANG; and with CLANG
  • without LTO,
  • with ThinLTO,
  • with Full LTO.

Already the clang-compiled linux kernel without LTO enabled -- based on the default configuration of my distribution (Artix) -- did lead to the freeze, whereas the same kernel based on the same configuration compiled with gcc did not.

So LTO is not the issue here.

So I still need to proof or disproof if this also happens with VirtualBox compiled "officially" by oracle.