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List:       busybox
Subject:    Re: [PATCH] buildsys: resurrect PLATFORM_LINUX and depend on it for linux-specific applets
From:       Michael Tokarev <mjt () tls ! msk ! ru>
Date:       2022-11-07 5:38:16
Message-ID: 4d236173-3eed-4341-68a3-7565c428e9d5 () msgid ! tls ! msk ! ru
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07.11.2022 08:25, Kang-Che Sung wrote:
> On Sat, Nov 5, 2022 at 12:55 AM Michael Tokarev <mjt@tls.msk.ru> wrote:
> 
>> diff --git a/Makefile b/Makefile

>> +.platform.in:
>> +       $(Q)printf '#ifndef __linux__\nplatform_is_not_linux\n#endif' \
>> +           | $(CPP) - | grep -s platform_is_not_linux \
>> +         && linux=n || linux=y; \
>> +       printf "config PLATFORM_LINUX\n\tbool\n\tdefault $$linux\n" > $@

> What is the reason for preferring #ifndef check rather than #ifdef?
> I mean, that would make PLATFORM_LINUX defaults to y if the compiler fails,
> and I would expect n in that case.

That's exactly the goal, - to make linux the default, that's the reason
I changed from ifdef linux to ifndef.  The idea is to bring as few burden
to the main authors as possible, - if this doesn't work, their favorite
platform wont be affected.  See the email I referred to in other message -
http://lists.busybox.net/pipermail/busybox/2011-February/074954.html -
from 11 years ago, - this is when "depends on LINUX" were (mistakenly)
changed to "select LINUX" in the first place, making it effectively
impossible to build busybox on non-linux.

> And I'm curious. Does Busybox's kconfig system supports macros as described in
> <https://www.kernel.org/doc/html/latest/kbuild/kconfig-macro-language.html> ?
> If the system supports macros, we can put this in the Kconfig file and simplify
> a lot of things:
> 
> config PLATFORM_LINUX
> <tab>bool
> <tab>default $(shell, { printf '#ifndef __linux__\n#error \n#endif\n' \
>      | $(CPP) - -o /dev/null; } >/dev/null 2>&1 && echo y || echo n)

No, - busybox's kconfig is much simpler than that, as far as I can see,
it is a fork off a much earlier kconfig language.

Thanks,

/mjt
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