linux-kernel - Re: arch/x86/entry/entry: RFC on recent kernels building error with llvm 11.0.2 internal assembler

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Date:   Sun, 8 May 2022 17:07:22 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Mauro Rossi <issor.oruam@...il.com>
Cc:     luto@...nel.org, Chih-Wei Huang <cwhuang@...roid-x86.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: arch/x86/entry/entry: RFC on recent kernels building error with
 llvm 11.0.2 internal assembler

On Sat, May 07, 2022 at 02:19:00PM +0200, Mauro Rossi wrote:
> > > Alternatively, you could apply the hack that Nick inserted into Android
> > > for this issue if upgrading your toolchain or turning off the integrated
> > > assembler is not possible:
> > >
> > > https://android.googlesource.com/kernel/common/+/e58f084735b8abf744d61083b92172ee23d45aae
> > >
> > > I really do not mean to sound dismissive or rude, I apologize if it
> > > comes off that way, but we have worked quite hard to avoid inserting
> > > unnecessary workarounds, as they are ultimately technical debt that can
> > > be hard to manage over the long term.
> > >
> > > Cheers,
> > > Nathan
> >
> > Thanks a lot Nathan
> >
> > It is definitely the clang version 11.0.x which is not updated in aosp
> > Android 11 production tags
> >
> > I will use Nick's workaround which works since only lsl %rax, %rax is
> > currently happening
> >
> > Many thanks, problem solved
> 
> Hello,
> I'm back again because I was assuming that Nick's workaround was working ok,
> but I have found that ARCH=x86_64 i.e. 64bit built kernel is causing
> an immediate hard reboot at initrd execution,
> just after hitting [ENTER] at grub/efi menu.

It looks like there was a follow up fix for that workaround, maybe that
resolves this issue as well?

https://android.googlesource.com/kernel/common/+/cc7f7a84191f5defc2ea4633eeea4acb4486b549

> ARCh=x86 i.e. 32bit kernel binary is not affected, but is Nick's
> workaround targeting 32 bit kernel builds?

No, the file that the build error originates from (entry_64.S) is only
built on x86_64.

> How do aosp android-mailine kernels avoid this instantaneous hard reboot issue?

That hack was reverted once the toolchain was upgraded:

https://android.googlesource.com/kernel/common/+/ff0216d09fd31802537f2d1702ec2f3e9be73aa3
https://android.googlesource.com/kernel/common/+/3c2c8d8f7f2639e319212d10cb8df5bd13098dae

Cheers,
Nathan