Re: [Buildroot] Overriding Kconfig Values from external br2

[Jesse Millwood <jesse_dev@fastmail.com>]

On Thu, 2022-01-06 at 18:09 +0100, Arnout Vandecappelle wrote:
> 
> 
> 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...
> 
I have it working actually. I had to patch my crosstool-ng toolchain to
add an extra default macro so that libunwind builds. 

> 
> > 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! I had to update some names of some things but I updated my
buildroot repo and was able to use the select method to enable
BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS. 

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