linux-kernel - Re: [PATCH v2 0/4] Introduce %rip-relative addressing to PER_CPU

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Message-ID: <3af8dcec-66ec-4bd4-b7bf-4bc6f5f3c70f@intel.com>
Date:   Thu, 12 Oct 2023 13:53:47 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Uros Bizjak <ubizjak@...il.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 0/4] Introduce %rip-relative addressing to PER_CPU_VAR
 macro

On 10/12/23 13:12, Uros Bizjak wrote:
> The last patch introduces (%rip) suffix and uses it for x86_64 target,
> resulting in a small code size decrease: text data bss dec hex filename
> 25510677 4386685 808388 30705750 1d48856 vmlinux-new.o 25510629 4386685
> 808388 30705702 1d48826 vmlinux-old.o

I feel like I'm missing some of the motivation here.

50 bytes is great and all, but it isn't without the cost of changing
some rules and introducing potential PER_CPU_ARG() vs. PER_CPU_VAR()
confusion.

Are there some other side benefits?  What else does this enable?