firmware-utils: mkmylofw broken since 9. Apr 2021

[Rafał Miłecki]

On 2021-04-13 08:39, Rafał Miłecki wrote:
> On 13.04.2021 00:46, Sven Roederer wrote:
>> since some days my master builds failing for ath79-generic. I was able 
>> to
>> narrow it to running "mkmylofw for compex_wpj344-16m".
>> The tool runs till the drive is full, currently my "compex_wpj344-16m-
>> squashfs-cpximg-6a08.bin.new" is 161GB and growing ...
>> 
>> Has anyone else seen this?
>> I'll check to see which of the relevant 6 commit trigger this during 
>> the next
>> days.
> 
> This is caused by the commit a2f66229450d ("firmware-utils: fix few
> random warnings").
> https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=a2f66229450dc2f7647c19ac83f3948e809406c2
> 
> Above change fixed C macro and affected following line of code:
> len = ALIGN(len,4) - block->size;
> 
> In compex_wpj344-16m case we have
> len: 0
> block->size: 5967872
> which results in len calculation as follows:
> len = ALIGN(0,4) - 5967872
> 
> Old macro resulted in:
> (0+(4-1))   &   ~(4-1) - 5967872
>                        ^ subtraction happens first
> 
> New macro results in:
> ((0+(4-1)) & ~(4-1))   -   5967872
>            ^ AND happens first
> 
> With new macro final len value is -5967872
> That results in write_out_padding() trying to write a lot of data.
> 
> So the old code was working accidentally. It resulted in calculating 
> len
> incorrectly but somehow that unexpected "0" value was working just 
> fine.
> 
> The original code comes from Florian from the 2007 commit 7b564bfdcbef
> ("Fix potential unligned access with MyLoader based devices, thanks
> Juhos")
> 
> https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=7b564bfdcbef05f68d8a658caf832c6832705e1f
> 
> Sven, Florian: any chance you know how that code:
> /* align next block on a 4 byte boundary */
> len = ALIGN(len,4) - block->size;
> 
> was meant to behave originally?

Please check commit d4f2c2914a65 ("firmware-utils: mkmylofw: fix blocks 
padding")
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=d4f2c2914a6547ef6067dd0968c4970e913f17f0