[PATCH] tools: mkimage: Allow changing U-Boot image magic

[Hauke Mehrtens]

On 1/23/23 19:49, Simon Glass wrote:
> Hi,
> 
> On Sun, 22 Jan 2023 at 07:20, Hauke Mehrtens <hauke at hauke-m.de> wrote:
>>
>> Extend mkimage with a new optional option -M to specify a special U-Boot
>> image magic number. OpenWrt ships images for about 30 different boards
>> with vendor boot loaders which are expecting the mkimage format, but
>> with a different image magic.
>>
>> OpenWrt includes this patch for mkimage more than 10 years.
>> It was added by Gabor Juhos in this commit:
>> https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=f3d2056b81b7a92d28402c22736534d84fe23cfe
>>
>> Cc: Gabor Juhos <j4g8y7 at gmail.com>
>> Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
>> ---
>>   tools/default_image.c |  4 ++--
>>   tools/imagetool.h     |  1 +
>>   tools/mkimage.c       | 14 ++++++++++++--
>>   3 files changed, 15 insertions(+), 4 deletions(-)
> 
> Strange...what is the different magic for?

I do not know really know why some vendors do this. With Openwrt we 
create images which user can install on their devices. We normally do 
not change the vendor bootloader and create an image which is compatible 
with the vendor boot loader.

I assume the vendors want to prevent users from installing "unsupported" 
images, but still want to use something close to the U-Boot image. With 
a different magic their boot loader (often vendor modified U-Boot) can 
prevent the user from installing "wrong" images.

I saw this on many devices sold by NetGear for example these devices:
NETGEAR WNDR4300
NETGEAR WNDR4500
NETGEAR WNR1000
NETGEAR WNR612 v2

I have also seen it from other vendors, probably some ODM or OEM does this.

Hauke