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

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Message-ID: <CAEQFVGbmHAQ=zxMTr4cmb9oeCarwZgyhiJnnL-Lrwmjatuaa2Q@mail.gmail.com>
Date:   Sun, 29 May 2022 20:46:54 +0200
From:   Mauro Rossi <issor.oruam@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>
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 Mon, May 9, 2022 at 2:07 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> 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

Hello,

sorry i still have the issue when building with hack "ANDROID: x86:
entry: work around LLVM_IAS=1 bug in LSL"
I'd just like to understand why I get instant reboot in 64bit kernel
built with LLVM_IAS=1

I searched for the places where #include "calling.h" is used

utente@...nte-3TB:~/r-x86_kernel/kernel$ grep -r \#include\ \"calling
arch/x86/entry/thunk_64.S:#include "calling.h"
arch/x86/entry/entry_32.S:#include "calling.h"
arch/x86/entry/entry_64_compat.S:#include "calling.h"
arch/x86/entry/entry_64.S:#include "calling.h"

Probably the hardcoding done in the hack is impacting some other asm
target built in 64 bit kernel and causes a wrong X86 instruction , is
there a way to refine the #if defto avoid that problem while still
building with LLVM_IAS=1 ?

Thanks for the info
Mauro