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Message-ID: <a3faf6820b43cca25c3384d0248f494be7312598.camel@physik.fu-berlin.de>
Date: Sat, 05 Apr 2025 19:38:53 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Artur Rojek <contact@...ur-rojek.eu>, Yoshinori Sato
<ysato@...rs.sourceforge.jp>, Rich Felker <dalias@...c.org>, Daniel Lezcano
<daniel.lezcano@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Uros
Bizjak <ubizjak@...il.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>, "D . Jeff Dionne"
<jeff@...esemi.io>, Rob Landley <rob@...dley.net>,
linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sh: align .bss section padding to 8-byte boundary
Hi Artur,
On Sun, 2025-02-16 at 18:55 +0100, Artur Rojek wrote:
> J2 based devices expect to find a devicetree blob at the end of the bss
> section. As of a77725a9a3c5, libfdt enforces 8-byte alignment for the
> dtb, causing J2 devices to fail early in sh_fdt_init.
>
> As J2 loader firmware calculates the dtb location based on the kernel
> image .bss section size, rather than the __bss_stop symbol offset, the
> required alignment can't be enforced with BSS_SECTION(0, PAGE_SIZE, 8).
> Instead, inline modified version of the above macro, which grows .bss
> by the required size.
>
> While this change affects all existing SH boards, it should be benign on
> platforms which don't need this alignment.
>
> Signed-off-by: Artur Rojek <contact@...ur-rojek.eu>
> ---
> arch/sh/kernel/vmlinux.lds.S | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/sh/kernel/vmlinux.lds.S b/arch/sh/kernel/vmlinux.lds.S
> index 9644fe187a3f..008c30289eaa 100644
> --- a/arch/sh/kernel/vmlinux.lds.S
> +++ b/arch/sh/kernel/vmlinux.lds.S
> @@ -71,7 +71,20 @@ SECTIONS
>
> . = ALIGN(PAGE_SIZE);
> __init_end = .;
> - BSS_SECTION(0, PAGE_SIZE, 4)
> + __bss_start = .;
> + SBSS(0)
> + . = ALIGN(PAGE_SIZE);
> + .bss : AT(ADDR(.bss) - LOAD_OFFSET) {
> + BSS_FIRST_SECTIONS
> + . = ALIGN(PAGE_SIZE);
> + *(.bss..page_aligned)
> + . = ALIGN(PAGE_SIZE);
> + *(.dynbss)
> + *(BSS_MAIN)
> + *(COMMON)
> + . = ALIGN(8);
> + }
> + __bss_stop = .;
> _end = . ;
>
> STABS_DEBUG
I'll pick this up for now since Uros has confirmed that the compiler
won't just use SBSS without breaking the ABI, so I think to use this
fix for now.
If it breaks in the future, we can change it again.
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer
`. `' Physicist
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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