RUST_BACKTRACE seems to be broken (as in PR 253557) on ppc64 elfv1. No idea why but it also does not seem worth fixing to me. It works fine on the other tested systems.

I have compilation issues on powerpc64le (related to the spec file) and am investigating this.

If powerpc64 elfv1 is the troublesome, I'd say it would be fine to ditch it, especially since 13.0 is going out soon anyway. Firefox doesn't work on elfv1 anyway.
I wouldn't be surprised if elfv1 support in Rust got broken anyway. AFAIK all the popular ppc64 Linux distros switched to elfv2.

lang/rust/files/powerpc64le/patch-compiler_rustc__target_src_spec_powerpc64le__unknown__freebsd.rs needs to be changed to:

--- compiler/rustc_target/src/spec/powerpc64le_unknown_freebsd.rs.orig  2021-01-07 03:05:53 UTC
+++ compiler/rustc_target/src/spec/powerpc64le_unknown_freebsd.rs
@@ -0,0 +1,16 @@
+use crate::spec::{LinkerFlavor, Target, TargetOptions};
+
+pub fn target() -> Target {
+    let mut base = super::freebsd_base::opts();
+    base.cpu = "ppc64le".to_string();
+    base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
+    base.max_atomic_width = Some(64);
+
+    Target {
+       llvm_target: "powerpc64le-unknown-freebsd".to_string(),
+       pointer_width: 64,
+       data_layout: "e-m:e-i64:64-n32:64".to_string(),
+       arch: "powerpc64".to_string(),
+       options: TargetOptions { mcount: "_mcount".to_string(), ..base },
+    }
+}

In D29425#659440, @pkubaj wrote:

I have compilation issues on powerpc64le (related to the spec file) and am investigating this.

If powerpc64 elfv1 is the troublesome, I'd say it would be fine to ditch it, especially since 13.0 is going out soon anyway. Firefox doesn't work on elfv1 anyway.
I wouldn't be surprised if elfv1 support in Rust got broken anyway. AFAIK all the popular ppc64 Linux distros switched to elfv2.

Well it is working now, so no reason to remove it just yet. There are more ports that use Rust too. For example librsvg2-rust which desktop ports depend on. We could switch elfv1 to use legacy librsvg if it ever came down to it though.

In the end as long as ports still support elfv1 I think we should keep elfv1 support in Rust on a best effort basis anyway.

lang/rust/files/powerpc64le/patch-compiler_rustctarget_src_spec_powerpc64leunknown__freebsd.rs needs to be changed to:

Done, but can somebody actually upstream the powerpc64le spec? I see that it was not done yet. You or maybe @bdragon?

https://github.com/rust-lang/rust/pull/83572

In D29425#659679, @pkubaj wrote:

https://github.com/rust-lang/rust/pull/83572

Thank you.

Can you also bump rust version in Mk/bsd.gecko.mk ?

In D29425#660356, @mikael wrote:

Can you also bump rust version in Mk/bsd.gecko.mk ?

Sure. I really should get around to create that USES=rust at some point...