Date:   Tue, 31 May 2022 15:08:50 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Mauro Rossi <issor.oruam@...il.com>
Cc:     Nathan Chancellor <nathan@...nel.org>, 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>
Subject: Re: arch/x86/entry/entry: RFC on recent kernels building error with
 llvm 11.0.2 internal assembler

On Sun, May 29, 2022 at 10:52 AM Mauro Rossi <issor.oruam@...il.com> wrote:
>
>
>
> 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

As Nathan noted, I messed up the commit "ANDROID: x86: entry: work
around LLVM_IAS=1 bug in LSL". Please see:
https://android-review.googlesource.com/c/kernel/common/+/1521061
https://android-review.googlesource.com/c/kernel/common/+/1560152/

If you're using an older toolchain, you'll need just the first. If
you're using a newer toolchain, you'll need BOTH (or none, including
dropping "ANDROID: x86: entry: work around LLVM_IAS=1 bug in LSL").

>
> 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 to avoid that problem while still building with LLVM_IAS=1 ?
>
> Thanks for the info
> Mauro
>
>


-- 
Thanks,
~Nick Desaulniers

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