linux-kernel - Re: [PATCH 1/1] x86: Change mov $0, %reg with xor %reg, %reg

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Date:   Mon, 8 Aug 2022 23:45:45 +0700
From:   Kanna Scarlet <knscarlet@...weeb.org>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     David Laight <David.Laight@...lab.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bill Metzenthen <billm@...bpc.org.au>,
        Brijesh Singh <brijesh.singh@....com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>,
        Michael Roth <michael.roth@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86: Change mov $0, %reg with xor %reg, %reg

On 8/5/22 4:42 PM, Joerg Roedel wrote:
> On Fri, Aug 05, 2022 at 09:26:02AM +0000, David Laight wrote:
>> Use "xor %rax,%rax" instead of "xor %eax,%eax" to save
>> the 'reg' prefix.
> 
> Also, some places explicitly use the mov variant to zero a register
> without touching rflags. Please be careful to not change those.

thank you for reminder, i will check again to make myself more sure
the patch doesn't break this %rflags dependency situation

Regards,
-- 
Kanna Scarlet