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:   Fri, 3 Jun 2022 15:13:32 -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 Wed, Jun 1, 2022 at 5:57 AM Mauro Rossi <issor.oruam@...il.com> wrote:
>
> On Wed, Jun 1, 2022 at 12:09 AM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > 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").
>
> Thanks Nick,
>
> I had already applied the squashed commit composed of  "ANDROID: x86:
> entry: work around LLVM_IAS=1 bug in LSL" (the one using .quad) and
> "ANDROID: x86: entry: fix LSL open coding", so I have already:
>
> .macro LOAD_CPU_AND_NODE_SEG_LIMIT reg:req
> movq $__CPUNODE_SEG, \reg
> +#ifdef __clang__
> +.long 0xc0030f48

LGTM

> +#else
> lsl \reg, \reg
> +#endif
> .endm
>
>
> So in principle my kernel image should boot when built with LLVM_IAS=1
> but to my surprise all my systems (Sony VAIO i7, Intel NUC DN2820FYKH
> with Celeron D2830, Athlon 200GE) are affected by hard reboot when
> executing the kernel image

Might need more info.  Do they boot when LLVM_IAS=0 is explicitly set
with your command line invocation of make? i.e. `make LLVM=1
LLVM_IAS=0 ...`?  Can you launch these kernels in qemu?

>
> I'm trying to understand how to build (and boot) with LLVM_IAS=1 and
> using clang 11.0.2 shipped with AOSP Android 11

I think this combo should work; we are testing x86_64 with mainline
https://github.com/ClangBuiltLinux/continuous-integration2/blob/95b9a12cad31675118d61c26d0b541fa4e3c8f09/generator.yml#L1694

Could be something in your .config files though.
-- 
Thanks,
~Nick Desaulniers