[PATCH v2] Makefile: fix generating environment file

[Rasmus Villemoes]

On 21/04/2021 17.21, Oleksandr Suvorov wrote:
> Hi Rasmus,
> 
> On Wed, Apr 21, 2021 at 12:34 AM Rasmus Villemoes
> <rasmus.villemoes at prevas.dk> wrote:
>>
>> 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.
> 
> (/me saying: never answer at night, never answer at night, never
> answer at night  :-D)
> 
>>
>> 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.
> 
> Sure, now I see. Your solution is more straight and clear.
> Unfortunately, it doesn't work :)

Yeah, I didn't really expect it to. Ah, it's because "set -e" is in
effect, so in

	( { grep -v '^#' | grep -v '^$$' ; echo '' ; } | \

the return value of the  grep -v '^#' | grep -v '^$$' pipeline is that
of the second grep, and when there's no input lines that match (such as,
with an empty input file), that's an EXIT_FAILURE. So the whole subshell
exits at that point, and nothing gets written to defaultenv_autogenerated.h.

Doing

define filechk_defaultenv.h
	( { grep -v '^#' | grep -v '^$$' || true ; echo '' ; } | \
	 tr '\n' '\0' | \
	 sed -e 's/\\\x0\s*//g' | \
	 xxd -i ; )
endef

seems to work.

Rasmus