linux-kernel - Re: [PATCH -tip] x86/idle: Work around LLVM assembler bug with MONITOR and MWAIT insn

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Message-ID: <CAFULd4a49RRMKrSVh3Q5zpeK4EJVW61tm=fCN4aOWX8=x8rKnw@mail.gmail.com>
Date: Thu, 3 Apr 2025 11:06:02 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH -tip] x86/idle: Work around LLVM assembler bug with
 MONITOR and MWAIT insn

On Thu, Apr 3, 2025 at 10:25 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Apr 03, 2025 at 09:04:37AM +0200, Uros Bizjak wrote:
> > LLVM assembler is not able to assemble correct forms of MONITOR
> > and MWAIT instructions with explicit operands:
> >
> >   error: invalid operand for instruction
> >           monitor %rax,%ecx,%edx
> >                        ^~~~
> >
> > Use instruction mnemonics with implicit operands when LLVM assembler
> > is detected to work around this issue.
> >
> > Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Fixes: cd3b85b27542 ("x86/idle: Use MONITOR and MWAIT mnemonics in <asm/mwait.h>")
>
> No, you should whack that one - the toolchains are clearly not ready yet...

The least common denominator is an insn with implicit operands. I'll
post V2 that fixes it that way.

Uros.