Re: [yocto] Regression in rust-cross-canadian-aarch64

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Tue, 2022-06-28 at 11:00 +0200, Peter Bergin wrote:
> When building rust-cross-canadian-aarch64 the file 
> 'tmp/work/x86_64-nativesdk-pokysdk-linux/rust-cross-canadian-aarch64/1.60.0-r0/targets/aarch64-poky-linux.json' 
> will be populated with the information '"llvm-target": 
> "x86_64-unknown-linux-gnu"'. This will lead to object files in wrong 
> format during 'Building stage2 std artifacts (x86_64-unknown-linux-gnu 
> -> aarch64-poky-linux)' in the do_compile step.
> 
> In 'meta/recipes-devtools/rust/rust-common.inc':
> 
>      # build tspec
>      tspec = {}
>      if bb.data.inherits_class('cross-canadian', d):
>          tspec['llvm-target'] = d.getVar('RUST_HOST_SYS', arch_abi)
>      else:
>          tspec['llvm-target'] = d.getVar('RUST_TARGET_SYS', arch_abi)
> 
> So for some reason it seems intentional to set 'llvm-target' to HOST_SYS 
> when 'cross-canadian'. The behavior has changed with this patch. Before 
> 'llvm-target' was set to RUST_TARGET_SYS for all target archs other than 
> x86_64 where it was set to RUST_HOST_SYS. I guess this change has to do 
> with the commit message 'This might even help cross-canadian work on 
> something which isn't x86-64.'? But unfortunately it seems to break the 
> case building on x86_64 for aarch64. It would be good to get some help 
> here to sort this out.

I've spent an age staring at this code this morning. I don't think
cross-canadian has ever worked properly. It might happen that some
combinations build but there are also some that don't and clearly never
have.

SDKMACHINE = "aarch64", MACHINE = "qemuarm64" certainly doesn't work.
It appears to be missing a ninja-native dependency and when that is
added, it can't find rust-llvm.

Looking at the do_configure from rust.inc, it considers BUILD triplets
and TARGET triplets but not HOST ones, which probably dooms cross-
canadian to failure since there, BUILD != HOST != TARGET.

Someone is going to have to step up and sort out the canadian cross
rust pieces properly. Whilst my patch probably did regress one config,
I think there are much deeper issues in there.

Cheers,

Richard