Documentation | Rust Documentation: Hello World on SPARC error "does not handle f128" since 2024-Nov-14 (#56)

[Frank Kuehndel (@frank_k)]

Frank Kuehndel created an issue: https://gitlab.rtems.org/rtems/docs/rtems-docs/-/issues/56



## Summary

Executing the exact instructions from the [rtems user manual](https://docs.rtems.org/branches/master/user/rust/bare-metal.html#bare-metal-rust-with-rtems) results in error message `rustc-LLVM ERROR: SPARCv8 does not handle f128 in calls; pass indirectly` when Rust attempts to compile `core (lib)`. The output looks like:

```
+ cargo +nightly build --target=sparc-unknown-none-elf
    Updating crates.io index
 Downloading crates ...
  Downloaded getopts v0.2.21
  Downloaded allocator-api2 v0.2.18
  Downloaded cfg-if v1.0.0
  Downloaded addr2line v0.22.0
  Downloaded adler v1.0.2
  Downloaded rustc-demangle v0.1.24
  Downloaded miniz_oxide v0.7.4
  Downloaded memchr v2.7.4
  Downloaded hashbrown v0.15.0
  Downloaded compiler_builtins v0.1.138
  Downloaded unicode-width v0.1.14
  Downloaded gimli v0.29.0
  Downloaded object v0.36.5
  Downloaded libc v0.2.161
   Compiling compiler_builtins v0.1.138
   Compiling core v0.0.0 (/home/ferris/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling rustc-std-workspace-core v1.99.0 (/home/ferris/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
rustc-LLVM ERROR: SPARCv8 does not handle f128 in calls; pass indirectly
error: could not compile `core` (lib)
Caused by:
  process didn't exit successfully: `/home/ferris/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name core --edition=2021 /home/ferris/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --warn=unexpected_cfgs --check-cfg 'cfg(bootstrap)' --check-cfg 'cfg(no_fp_fmt_parse)' --check-cfg 'cfg(stdarch_intel_sde)' --check-cfg 'cfg(target_os, values("rtems"))' --check-cfg 'cfg(feature, values(any()))' --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values("debug_refcell", "optimize_for_size", "panic_immediate_abort"))' -C metadata=f5f91e83da362cb6 -C extra-filename=-f5f91e83da362cb6 --out-dir /home/ferris/example-rust/hello-rtems/target/sparc-unknown-none-elf/debug/deps --target sparc-unknown-none-elf -C linker=sparc-rtems6-gcc -Z force-unstable-if-unmarked -L dependency=/home/ferris/example-rust/hello-rtems/target/sparc-unknown-none-elf/debug/deps -L dependency=/home/ferris/example-rust/hello-rtems/target/debug/deps --cap-lints allow -Ctarget-cpu=leon3 -Clinker-flavor=gcc -Clink-arg=-mcpu=leon3 -Clink-arg=-latomic` (exit status: 101)
```

The first known buggy build was:

| | Version/Commmit |
| ------ | ------ |
|Date: |2024-11-14T02:33:12+01:00 |
|rtems-docs: |9e8141cb5ec9d1244ecb1e5f0fdb73fc6f02ce51 |
|rtems-source-builder: |d82e3f433ba1441dc97e9d3c78eb0eb93212ed16 |
|rtems: |f7b04e72f86e6c26028f774c85beacb1e063c87e |
|cargo: |1.82.0 (8f40fc59f 2024-08-21) |
|rustc: |1.84.0-nightly (8adb4b30f 2024-11-13) |

The last known good build was:

| | Version/Commmit |
| ------ | ------ |
|Date: |2024-11-13T02:33:13+01:00 |
|rtems-docs: |4d2c0048e536648c4f6d9346f01868c1e7463ed3 |
|rtems-source-builder: |d82e3f433ba1441dc97e9d3c78eb0eb93212ed16 |
|rtems: |30fc123f8d65310772a07926acb7b0413e28b624 |
|cargo: |1.82.0 (8f40fc59f 2024-08-21) |
|rustc: |1.84.0-nightly (f7273e004 2024-11-12) |

I assume this is a new bug in Rust *nigthly*.

By the way, the build of hello world for Risc V (which is also part of the RTEMS user manual instructions) is not affected and works fine. It uses the *standard* `rustc` and not the *nightly* one.

## Steps to reproduce

Follow the instructions in [Bare Metal Rust with RTEMS](https://docs.rtems.org/branches/master/user/rust/bare-metal.html#bare-metal-rust-with-rtems)

### Pre-set options

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/docs/rtems-docs/-/issues/56
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