[PATCH v2] Makefile: fix generating environment file

[Rasmus Villemoes]

On 20/04/2021 23.10, Oleksandr Suvorov wrote:
> Hi Rasmus,
> 
> Thanks for your feedback!
> Yes, I noted that there were no possible situations with the trailing
> code != 0x00, but simply removing the additional trailing 0x00
> gives us an empty array default_environment[] for the empty defaultenv file.
> I need to test whether this case is handled in u-boot properly and
> then prepare the next patch version :P

No, I'm not suggesting removing the trailing nul byte, it very much has
to be there - the binary format of the environment is a sequence of
nul-terminated C strings of the key=value form, concatenated
back-to-back, terminated by an empty string.

What I'm suggesting is to take the input file

===
foo=bar

# Set our IP address
ip=1.2.3.4
===

do the comment- and empty-line stripping (the two first greps), and then
after that add an extra empty line

===
foo=bar
ip=1.2.3.4

===

and then feed that to the 'replace \n by nul bytes' | 'delete
backslash+nul+whitespace' | xxd pipe. That way there's always that
trailing nul on the input to xxd, i.e. in the example above, we would
feed foo=bar\0ip-1.2.3.4\0\0 into xxd, while with an initially empty
file xxd would just receive that single nul byte.

It's just that I think terminating the sequence of key=value lines by an
empty line more exactly matches the binary format.

Rasmus