linux-kernel - Re: [PATCH v4 2/5] x86/alternative: add indirect call patching

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Message-ID: <20231114142733.GCZVOD1TvZ2qq536dg@fat_crate.local>
Date:   Tue, 14 Nov 2023 15:27:33 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v4 2/5] x86/alternative: add indirect call patching

On Tue, Nov 14, 2023 at 03:18:33PM +0100, Peter Zijlstra wrote:
> Well, a random absolute address isn't going to be any better or worse
> than 0. But perhaps adding the relocation as a comment helps?
> 
> 
>    ff 15 00 00 00 00       call   *0x0(%rip)  #  R_X86_64_PC32    pv_ops+0x4
> into:
>    e8 00 00 00 00 90	   call   +0          #  R_X86_64_PC32 *(pv_ops+0x04)

A bit better, yeah.

> ALT_FLAG_DEREFERENCE_INDIRECT_CALL ?
> 
> I'm going to already raise my hand and say that's too long ;-)

To your own suggestion? :-P

ALT_FLAG_DIRECT_CALL simply, I guess, along with an explanation.
Meaning, this flag tells the alternatives to produce a direct call.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette