linux-kernel - Re: [PATCH v2] x86: Avoid relocation information in final vmlinux

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Date:   Fri, 25 Nov 2022 17:41:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Petr Pavlu <petr.pavlu@...e.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, nicolas@...sle.eu,
        masahiroy@...nel.org, kirill.shutemov@...ux.intel.com,
        tony.luck@...el.com, michael.roth@....com, nathan@...nel.org,
        ndesaulniers@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: Avoid relocation information in final vmlinux

On Thu, Nov 24, 2022 at 04:41:11PM +0100, Borislav Petkov wrote:
> This is in both cases with your patch, once with RANDOMIZE_BASE=y and
> once with RANDOMIZE_BASE=n.
> 
> IOW, your patch actually makes my vmlinux bigger by 51K.
> 
> IOW, I cannot reproduce your
> 
> | Configuration      | With relocs | Stripped relocs |
> | x86_64_defconfig   |       70 MB |           43 MB |
> 
> claim, but not with a defconfig but with my specially tailored config.
> 
> I guess the next thing I'll try is without your patch.

Ok, I tried reproducing your defconfig numbers first:

defconfig:						vmlinux
- with patch: NEED_RELOCS=y				 48053656
- with patch, NEED_RELOCS=n, 				 48000696
- without patch, NEED_RELOCS=n, 			 48000696
- without patch: NEED_RELOCS=y				 83091744

So yes, I can reproduce your observation - defconfig *with* your patch
does slim down vmlinux, because, well, it is moving the reloc sections
into a separate file. Doh.

And with my .config too:

tailored config:
- with patch: 		NEED_RELOCS=y			377718768
- without patch, 	NEED_RELOCS=y			639952576

So I guess we can try it - let's see who complains.

Thx.

-- 
Regards/Gruss,
    Boris.

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