linux-kernel - Re: [PATCH] arm64: remove special treatment for the link order of head.o

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Date:   Wed, 22 Mar 2023 15:51:52 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: remove special treatment for the link order of head.o

On Tue, 21 Mar 2023 at 23:26, Aurelien Jarno <aurelien@...el32.net> wrote:
>
> Hi,
>
> On 2022-10-13 08:35, Masahiro Yamada wrote:
> > In the previous discussion (see the Link tag), Ard pointed out that
> > arm/arm64/kernel/head.o does not need any special treatment - the only
> > piece that must appear right at the start of the binary image is the
> > image header which is emitted into .head.text.
> >
> > The linker script does the right thing to do. The build system does
> > not need to manipulate the link order of head.o.
> >
> > Link: https://lore.kernel.org/lkml/CAMj1kXH77Ja8bSsq2Qj8Ck9iSZKw=1F8Uy-uAWGVDm4-CG=EuA@mail.gmail.com/
> > Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  scripts/head-object-list.txt | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/scripts/head-object-list.txt b/scripts/head-object-list.txt
> > index b16326a92c45..f226e45e3b7b 100644
> > --- a/scripts/head-object-list.txt
> > +++ b/scripts/head-object-list.txt
> > @@ -15,7 +15,6 @@ arch/alpha/kernel/head.o
> >  arch/arc/kernel/head.o
> >  arch/arm/kernel/head-nommu.o
> >  arch/arm/kernel/head.o
> > -arch/arm64/kernel/head.o
> >  arch/csky/kernel/head.o
> >  arch/hexagon/kernel/head.o
> >  arch/ia64/kernel/head.o
>
> This patch causes a significant increase of the arch/arm64/boot/Image
> size. For instance the generic arm64 Debian kernel went from 31 to 39 MB
> after this patch has been applied to the 6.1 stable tree.
>
> In turn this causes issues with some bootloaders, for instance U-Boot on
> a Raspberry Pi limits the kernel size to 36 MB.
>

I cannot reproduce this with mainline

With the patch

$ size vmlinux
   text    data     bss     dec     hex filename
24567309 14752630 621680 39941619 26175f3 vmlinux

With the patch reverted

$ size vmlinux
   text    data     bss     dec     hex filename
24567309 14752694 621680 39941683 2617633 vmlinux

It would help to compare the resulting vmlinux ELF images from both
builds to see where the extra space is being allocated