Clang LTO Support Merged For Linux 5.12 Including ARM64 + x86_64

[phoronix]

Phoronix: Clang LTO Support Merged For Linux 5.12 Including ARM64 + x86_64

Pop open the champagne as the in-development Linux 5.12 kernel will be able to support link-time optimizations (LTO) in conjunction with the LLVM Clang compiler on not only AArch64 (64-bit ARM) but also x86_64...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-5.12-Clang-LTO-Merged

[FireBurn]

A very quick test of this and my Raven system didn't boot, it's an EFI stub kernel booted directly by UEFI without grub

[Space Heater]

A very quick test of this and my Raven system didn't boot, it's an EFI stub kernel booted directly by UEFI without grub

I'd strongly recommend reporting this upstream and providing any details you can.

[FireBurn]

I'll need to reboot my other machine

I've compiled it again on another and noticed these warnings:

vmlinux.o: warning: objtool: aesni_gcm_init_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_enc_update_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_dec_update_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_finalize_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_init_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_enc_update_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_dec_update_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_finalize_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha1_transform_avx2()+0xc: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha1_ni_transform()+0x7: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha256_transform_rorx()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_ssse3()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_avx()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_rorx()+0x7: unsupported stack pointer realignment
vmlinux.o: warning: objtool: crc_pcl()+0x87: sibling call from callable instruction with modified stack frame
vmlinux.o: warning: objtool: eb_relocate_parse_slow()+0x457: stack state mismatch: cfa1=7+128 cfa2=-1+0
vmlinux.o: warning: objtool: eb_copy_relocations()+0x1d5: stack state mismatch: cfa1=7+96 cfa2=-1+0

[FireBurn]

I'll play around with it some more in the morning and see if I can find the issue, hopefully it's just my local setup

[Alliancemd]

I tried to compile(without LTO) Linux 5.11.0 with Clang 12 on x86_64 and it cannot load my modules on boot...
I don't use a complicated config, it's basically Ubuntu's config.
Same kernel + config compiled and ran fine with GCC 10.2.0.

[ms178]

First, hooray for getting it merged! With an earlier version of the patchset wih x86_64, I had no issues on my system. But that was on 5.10 with Clang 11.0.1 and a Kernel config which was heavily stripped down for my setup. Some Kernel options are also known to be problematic, such as stripping of unneeded symbols or the option for hardening against spectre/meltdown. Please report any issues here with details of the kernel, used toolchain and your config file: https://github.com/ClangBuiltLinux/linux/issues

[FireBurn]

It's working fine on my main machine

[ 0.000000] Linux version 5.11.0-tip+ (root@axion) (clang version 11.1.0, LLD 11.1.0) #2606 SMP Wed Feb 24 03:26:27 GMT 2021

I'll reboot the Raven box manaully and see if it starts this time

[FireBurn]

Ah, I forgot about an AMDGPU fix I needed to apply for my RAVEN system

[ms178]

I'll need to reboot my other machine

I've compiled it again on another and noticed these warnings:

vmlinux.o: warning: objtool: aesni_gcm_init_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_enc_update_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_dec_update_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_finalize_avx_gen2()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_init_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_enc_update_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_dec_update_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: aesni_gcm_finalize_avx_gen4()+0x12: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha1_transform_avx2()+0xc: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha1_ni_transform()+0x7: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha256_transform_rorx()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_ssse3()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_avx()+0x13: unsupported stack pointer realignment
vmlinux.o: warning: objtool: sha512_transform_rorx()+0x7: unsupported stack pointer realignment
vmlinux.o: warning: objtool: crc_pcl()+0x87: sibling call from callable instruction with modified stack frame
vmlinux.o: warning: objtool: eb_relocate_parse_slow()+0x457: stack state mismatch: cfa1=7+128 cfa2=-1+0
vmlinux.o: warning: objtool: eb_copy_relocations()+0x1d5: stack state mismatch: cfa1=7+96 cfa2=-1+0

Could you please mention some details of your system where you see this issues on, such as some hardware details and the toolchain, config and kernel source used for reproducing these issues at this specific post: https://github.com/ClangBuiltLinux/linux/issues/977

If you are using custom compiler flags, that would also be of interest.

Thanks!