Remove default linker flags in Rust

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Is there a way to remove problematic linker flags in the cargo build command? I'm trying to cross-compile a binary on windows for x86_64-unknown-linux-gnu but linking fails with the message: ld unrecognized option: --eh-frame-hdr. Is there a way to remove this argument from the linking stage without having to create a custom target specification for linux builds?

I only found the rustflags key in config.toml, but as far as I know it only allows you to add additional flags and not to strip existing ones.

rust-cargo rust cross-compiling
1 Answers

Start by making sure that you are passing the right linker-flavor. rustc might have misidentified what linker you are using, and specifying that might help. Also ensure you are using the right linker. But if you really want to remove that argument, it is possible using some unstable features.

There isn't a general way to remove individual linker arguments. The eh_frame_header target attribute indicates if the linker should insert a EH (exception handling) frame header. Unstable rustc does have support for changing individual target options, but it is a bit complicated and can only handle #![no_std] binaries on some platforms. You might want to consider just calling the linker manually.

First, dump the JSON target metadata (using a nightly compiler) for the target you are compiling to, replacing [target] with a target triple like thumbv7neon-unknown-linux-musleabihf:

$ rustc -Z unstable-options --print target-spec-json --target [target] > target.json

target.json now has target-specific compilation information. On some targets (such as WASM), EH frame headers are disabled by default. If you see a line like this in target.json, you are already done (and shouldn't be getting that error):

  "eh-frame-header": false,

If you don't see that line, then add it to target.json right after opening brace, like

{
  "eh-frame-header": false,
  ...

You can now specify the path to target.json wherever a target triple would normally be. However, you now need to recompile the standard libraries (such as core and std) with the new target information. Otherwise, the compiler will tell you that the `target-17676080659170949227` target may not be installed. On unstable Cargo, you can use -Z build-std to do that:

$ cargo +nightly run -Z build-std=core --target target.json

It will take a bit longer than normal, since it needs to recompile the core standard library. Not all platforms support compiling the fuller std library this way, but you can change the build-std=core to just build-std if you want to try to build the whole std standard library as well.

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