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Re: [PATCH v2 0/4] Introduce %rip-relative addressing to PER_CPU_VAR macro


  • To: Uros Bizjak <ubizjak@xxxxxxxxx>, x86@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
  • From: Dave Hansen <dave.hansen@xxxxxxxxx>
  • Date: Thu, 12 Oct 2023 13:53:47 -0700
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>
  • Delivery-date: Thu, 12 Oct 2023 20:54:18 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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?



 


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