Linking rustc with custom linker is awkward

[karolzwolak]

Linking rustc with custom linker is awkward

There are two “easy” ways I can think of to use a custom linker:

1. Delegate to an existing linker/compiler
   Tell an existing linker or compiler to use your binary for the actual linking.
   For example:

   RUSTFLAGS="-Clinker=clang -Clink-arg=--ld-path=your-custom-linker"

   However, you can’t specify this for all builds in bootstrap.toml.
   You can set the linker explicitly — but not the -Clink-arg, since there’s no way to specify RUSTFLAGS or this flag directly there.

2. Symlink your custom linker to the linker rustc uses
   For example:

   • RUSTFLAGS="-Clinker-features=-lld" and symlinking the default system linker
   • RUSTFLAGS="-Clink-self-contained=-linker" and symlinking lld

   This should be possible to configure in bootstrap.toml, but I couldn’t get it working.
   Setting rust.bootstrap-override-lld = "external" in bootstrap.toml should roughly be equivalent to disabling self-contained linker, but it doesn’t seem to work.

Right now, to keep linking rustc with a custom linker, I have to always set the RUSTFLAGS variable, which is really cumbersome — and bootstrap.toml should offer a way to persist such settings.

Is there a reason why bootstrap.toml doesn’t support rustflags option like Cargo config.toml does?

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Proposed fixes

• Make rust.bootstrap-override-lld actually functional: fix: disable self-contained linker when bootstrap-override-lld is set #148709
• Add a way to specify linker arguments or general RUSTFLAGS in bootstrap.toml

[karolzwolak]

Persistently opting out of using lld isn't supported in `bootstrap.toml' too I think.