linux-kernel - Re: [PATCH -tip v2] x86/idle: Work around LLVM assembler bug with MONITOR and MWAIT insn

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Message-ID: <Z-5vAThgDL9gts35@gmail.com>
Date: Thu, 3 Apr 2025 13:20:33 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH -tip v2] x86/idle: Work around LLVM assembler bug with
 MONITOR and MWAIT insn


* Uros Bizjak <ubizjak@...il.com> 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 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>")
> Reported-by: kernel test robot <lkp@...el.com>

So I've zapped cd3b85b27542 instead - let's re-try it again and
see if there's any code generation tradeoffs vs. the byte encodings?

Thanks,

	Ingo