README: when and how to use this crate

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Jorge Aparicio 2016-08-23 20:35:30 -05:00
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@ -12,6 +12,27 @@ See [rust-lang/rust#35437][0].
[0]: https://github.com/rust-lang/rust/issues/35437
## When and how to use this crate?
If you are working with a target that doesn't have binary releases of std available via rustup (this
probably means you are building the core crate yourself) and need compiler-rt intrinsics (i.e. you
are probably getting linker errors when building an executable: "undefined reference to
__aeabi_memcpy"), you can use this crate to get those intrinsics and solve the linker errors. To do
that, simply add this crate as a Cargo dependency (it doesn't matter where in the dependency graph
this crate ends up, as long as it's there):
``` toml
[dependencies]
rustc-builtins = { git = "https://github.com/japaric/rustc-builtins" }
```
If you still get an "undefined reference to $INTRINSIC" error after that change, that means that we
haven't ported `$INTRINSIC` to Rust yet! Please open [an issue] with the name of the intrinsic and
the LLVM triple (e.g. thumbv7m-none-eabi) of the target you are using. That way we can prioritize
porting that particular intrinsic.
[an issue]: https://github.com/japaric/rustc-builtins/issues
## Contributing
1. Pick one or more intrinsics from the [pending list][#progress].