From: "H. Peter Anvin" <[email protected]>
To: Kanna Scarlet <[email protected]>, Joerg Roedel <[email protected]>
Cc: David Laight <[email protected]>,
Borislav Petkov <[email protected]>,
Thomas Gleixner <[email protected]>,
Ingo Molnar <[email protected]>,
Dave Hansen <[email protected]>,
"[email protected]" <[email protected]>,
Ard Biesheuvel <[email protected]>,
Bill Metzenthen <[email protected]>,
Brijesh Singh <[email protected]>,
Josh Poimboeuf <[email protected]>,
"Kirill A. Shutemov" <[email protected]>,
Mark Rutland <[email protected]>,
Michael Roth <[email protected]>,
Peter Zijlstra <[email protected]>,
Sean Christopherson <[email protected]>,
Steven Rostedt <[email protected]>,
Ammar Faizi <[email protected]>,
GNU/Weeb Mailing List <[email protected]>,
Linux Kernel Mailing List <[email protected]>
Subject: Re: [PATCH 1/1] x86: Change mov $0, %reg with xor %reg, %reg
Date: Mon, 8 Aug 2022 11:59:17 -0700 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On August 8, 2022 9:45:45 AM PDT, Kanna Scarlet <[email protected]>
wrote:
>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,
In some cases you can hoist the zeroing to avoid that (and sometimes
improve performance in the process), but be very careful in general when
messing with hand-optimized assembly code like crypto; for those pieces
of code benchmarking the change is mandatory.
next prev parent reply other threads:[~2022-08-08 19:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-04 15:26 [PATCH 0/1] x86 change mov 0, %reg to xor %reg, %reg Kanna Scarlet
2022-08-04 15:26 ` [PATCH 1/1] x86: Change mov $0, %reg with " Kanna Scarlet
2022-08-04 15:53 ` Borislav Petkov
2022-08-04 18:08 ` Kanna Scarlet
2022-08-05 9:26 ` David Laight
2022-08-05 9:42 ` Joerg Roedel
2022-08-08 16:45 ` Kanna Scarlet
2022-08-08 18:59 ` H. Peter Anvin [this message]
2022-08-08 16:38 ` Kanna Scarlet
2022-08-08 18:59 ` H. Peter Anvin
2022-08-09 7:38 ` David Laight
2022-08-05 9:54 ` Borislav Petkov
2022-08-08 16:57 ` Kanna Scarlet
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