[jkrishnanjanappa]

rustc_target: Add support of Openembedded/Yocto Linux ppc64 and ppc64le targets

While building Rust standard libraries in Yocto, these targets use Openembedded-specific target triplets which are absent in the supported target list. Due to which Rust standard libraries build fails in Yocto.

The Openembedded-specific target triplets of ppc64 and ppc64le use linker and other settings similar to existing ppc64 and ppc64le Linux GNU targets respectively. So, add Openembedded-specific target triplets for ppc64 and ppc64le to build Rust libraries in Yocto.

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[rustbot]

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[oli-obk]

hmm... if you're building your own libstd anyway, can't you use the custom target scheme to add your targets?

Do you have some links to where you're using this?

[jkrishnanjanappa]

hmm... if you're building your own libstd anyway, can't you use the custom target scheme to add your targets?

I am building libstd-rs, which is a part of a distribution image using the Yocto project.
The recipe that builds libstd-rs is at
https://git.openembedded.org/openembedded-core/tree/meta/recipes-devtools/rust/libstd-rs_1.98.1.bb?id=4ded97c2905d1c4ec7911d904cad3a5fce98255f

The steps to build libstd-rs can be found at,
https://docs.yoctoproject.org/dev-manual/poky-manual-setup.html#use-git-to-clone-the-layers
https://docs.yoctoproject.org/dev-manual/poky-manual-setup.html#building-your-image

Do you have some links to where you're using this?

The libstd build failed without this change for ppc64 and ppc64le. On debugging, I found other OE (openembedded) supported targets
https://github.com/search?q=repo%3Arust-lang%2Frust+oe_linux&type=code already present in the code. So I thought of adding similar change for ppc64 and ppc64le.

Regards,
Jagadeesh

[jkrishnanjanappa]

@rustbot ready

[oli-obk]

r? @davidtwco who seems to actually understand what is happening here 😅

#157650 (comment)

[jkrishnanjanappa]

While building libstd-rs recipe ( https://git.openembedded.org/openembedded-core/tree/meta/recipes-devtools/rust/libstd-rs_1.98.1.bb?id=4ded97c2905d1c4ec7911d904cad3a5fce98255f ) for powerpc64 using Openembedded/Yocto project, the following error is observed as there are no powerpc64-oe-linux-gnu target.

  error: error loading target specification: invalid PowerPC64 big-endian ABI name and `cfg(target_abi)`    combination:
         ABI name: elfv1
         cfg(target_abi):
    |
    = help: run `rustc --print target-list` for a list of built-in targets
    = help: did you mean `powerpc64-unknown-linux-gnu`?

If we specify "--target powerpc64-unknown-linux-gnu" to workaround the missing target, the build again fails with the following error. The rust built-in powerpc64-unknown-linux-gnu target use "cc" as linker where as openembedded/Yocto cross-compilation toolchain use custom powerpc64-oe-linux-gcc as linker.

error: linker `cc` not found
  |
  = note: No such file or directory (os error 2)

error: could not compile `std` (lib) due to 1 previous error

The same behavior is true for powerpc64le using openembedded/Yocto cross-compilation toolchain.

This PR solves both the errors.

The discussions at #157650 and https://rust-lang.zulipchat.com/#narrow/channel/557100-yocto/topic/custom.20targets/near/594790061 helped me to understand the linker selection between powerpc64-unknown-linux-gnu and powerpc64-oe-linux-gnu.

Thanks,
Jagadeesh