linux-kernel - Re: [PATCH] MIPS: boot: Fix unaligned access with CONFIG_MIPS_RAW_APPENDED

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Message-ID: <20201228222532.GA24926@alpha.franken.de>
Date:   Mon, 28 Dec 2020 23:25:32 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>, od@...c.me,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, stable@...r.kernel.org
Subject: Re: [PATCH] MIPS: boot: Fix unaligned access with
 CONFIG_MIPS_RAW_APPENDED_DTB

On Wed, Dec 16, 2020 at 11:39:56PM +0000, Paul Cercueil wrote:
> The compressed payload is not necesarily 4-byte aligned, at least when
> compiling with Clang. In that case, the 4-byte value appended to the
> compressed payload that corresponds to the uncompressed kernel image
> size must be read using get_unaligned_le().
> 
> This fixes Clang-built kernels not booting on MIPS (tested on a Ingenic
> JZ4770 board).
> 
> Fixes: b8f54f2cde78 ("MIPS: ZBOOT: copy appended dtb to the end of the kernel")
> Cc: <stable@...r.kernel.org> # v4.7
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  arch/mips/boot/compressed/decompress.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
> index c61c641674e6..47c07990432b 100644
> --- a/arch/mips/boot/compressed/decompress.c
> +++ b/arch/mips/boot/compressed/decompress.c
> @@ -117,7 +117,7 @@ void decompress_kernel(unsigned long boot_heap_start)
>  		dtb_size = fdt_totalsize((void *)&__appended_dtb);
>  
>  		/* last four bytes is always image size in little endian */
> -		image_size = le32_to_cpup((void *)&__image_end - 4);
> +		image_size = get_unaligned_le32((void *)&__image_end - 4);

gives me following error

arch/mips/boot/compressed/decompress.c:120:16: error: implicit declaration of function ‘get_unaligned_le32’ [-Werror=implicit-function-declaration]
   image_size = get_unaligned_le32((void *)&__image_end - 4);

I've added

#include <asm/unaligned.h>

which fixes the compile error, but I'm wondering why the patch compiled
for you ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]