linux-kernel - Re: [PATCH] x86/boot: Work around broken busybox truncate tool

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Message-ID: <cc549efcd078fdefafc12442b08ae7ceaa197eb9.camel@mailbox.org>
Date: Thu, 24 Apr 2025 12:22:32 +0200
From: Philipp Stanner <phasta@...lbox.org>
To: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, phasta@...nel.org
Subject: Re: [PATCH] x86/boot: Work around broken busybox truncate tool

Thank you very much for this fix :)

On Thu, 2025-04-24 at 12:19 +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> The GNU coreutils version of truncate, which is the original, accepts
> a
> % prefix for the -s size argument which means the file in question
> should be padded to a multiple of the given size. This is currently
> used
> to pad the setup block of bzImage to a multiple of 4k before
> appending
> the decompressor.
> 
> busybux reimplements truncate but does not support this idiom, and

typo, busybox.

> therefore fails the build since commit
> 
>   9c54baab4401 ("x86/boot: Drop CRC-32 checksum and the build tool
> that generates it")

Should this be marked as an official bug?

If so, I'd put this as a Fixes: tag below.

> 
> Work around this by avoiding truncate altogether, and relying on dd
> to
> perform the padding.
> 
> Reported-by: <phasta@...nel.org>

Tested-by: Philipp Stanner <phasta@...nel.org>


Thx,

P.

> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
> I personally think using a busybox environment for building the
> kernel
> is a terrible idea, and does not satisfy the build tool requirements
> listed in the documentation. But apparently, it used to work and now
> it
> doesn't, and the workaround is rather straight-forward.
> 
> IOW, I don't care whether this gets applied or not, so I will leave
> it
> to others to make the argument.
> 
>  arch/x86/boot/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> index 81f55da81967..640fcac3af74 100644
> --- a/arch/x86/boot/Makefile
> +++ b/arch/x86/boot/Makefile
> @@ -59,7 +59,7 @@ KBUILD_CFLAGS	+= $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
>  $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
>  
>  quiet_cmd_image = BUILD   $@
> -      cmd_image = cp $< $@; truncate -s %4K $@; cat
> $(obj)/vmlinux.bin >>$@
> +      cmd_image = (dd if=$< bs=4k conv=sync status=none; cat
> $(filter-out $<,$(real-prereqs))) >$@
>  
>  $(obj)/bzImage: $(obj)/setup.bin $(obj)/vmlinux.bin FORCE
>  	$(call if_changed,image)