Re: [Buildroot] Overriding Kconfig Values from external br2

[Arnout Vandecappelle <arnout@mind.be>]

On 06/01/2022 16:37, Jesse Millwood wrote:
> On Thu, 2022-01-06 at 10:45 +0100, Arnout Vandecappelle wrote:
>>
>>
>> On 05/01/2022 20:03, Jesse Millwood wrote:
>>> Hello,
>>>
>>> I have an external C/C++ toolchain that I've put together that uses
>>> MUSL. I've
>>> also built an external Rust toolchain that uses my MUSL toolchain.
>>>
>>> My issue is that there is a Rust Kconfig variable that specifies if
>>> a specific
>>> architecture supports Rust.
>>>
>>> The Kconfig variable in question is
>>> BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS
>>> in package/rustc/Config.in.host.
>>
>> [snip]
>>
>>> You may notice that I changed the libc depends line to be or'd with
>>> BR2_TOOLCHAIN_USES_MUSL. It seems that this does not get considered
>>> when I
>>> choose my external musl toolchain option. In the menuconfig when I
>>> search for
>>> the BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS variable with the
>>> "/" key it
>>> looks like it is only getting it from the original file. Does
>>> buildroot have a
>>> mechanism for overwriting this kind of setting and if not, does
>>> anyone have an
>>> idea of how I would accomplish what I am trying to do (make
>>> buildroot honor my
>>> external rust toolchain)?
>>
>>    No, there's no way to override the dependencies of an existing
>> Config.in
>> symbol in an external.
>>
>>    However, this was corrected in upstream Buildroot in commit
>> d69d40c029dc7d8199b745eaee759d92b66c5d17. So you can try to backport
>> that commit
>> instead, or just update Buildroot to something more recent.
> 
> Arnout, thanks for the pointer to the commit. That is a logical way to
> support other platforms. However, I have a powerpc musl rust toolchain
> that I've built externally.
> 
> With the changes in that commit can I set
> BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS to "y" in my external now

  Ah, no, you're right, powerpc-unknown-linux-musl is a Tier 3 platform and that 
patch only adds Tier 1 and 2. We could add a Tier 3 option as well (and disable 
the rust-bin option in that case).

  Note however that the stdlib status for this target is marked as "?" on [1], 
so I'm not sure it's ever going to work...


> that there is no depends expressions and it is all default logic? Or
> would I have to still add another expression that maybe defaults to "y"
> if a new variable is true like
> "BR2_EXTERNAL_RUSTC_TARGET_ARCH_SUPPORTS" that is defined in my
> external?

  No, that's not going to work.

  I think you can make a hack: add "select 
BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS" to your 
BR2_TOOLCHAIN_EXTERNAL_MY_MUSL definition. I think that works.

  Regards,
  Arnout


> 
> Thanks,
> Jesse
> 
>>
>>    Regards,
>>    Arnout
>>
>>
>>>
>>> Thanks,
>>> Jesse
>>>
>>> _______________________________________________
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>>> buildroot@buildroot.org
>>> https://lists.buildroot.org/mailman/listinfo/buildroot
>>>
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> 
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