Problem with rustflags in .cargo/config

[lure23]

I'm placing my code on this template, and noticed one gotcha which I think you should know about.

The problem is, .cargo/configs of parent folders affect subprojects, and there's seemingly no way to cut this chord. In my case, a subproject does a "raw" (C to Rust) binding that the main project would then like to use.

So: what's the actual problem?

When doing cargo build in the subproject, I get a linkage error:

 note: /usr/bin/ld: cannot open linker script file defmt.x: No such file or directory

That subproject doesn't need defmt at all. It's very weird (imho) that the parent folder affects this way, but the ideology behind .cargo/config.toml seems to be that environment stuff goes there, not project specific stuff. I'm trying to find a way to move rustflags

rustflags = [
  "-C", "link-arg=-Tdefmt.x",
]

..away from there and into Cargo.toml - but there might not be such a way.

Work-around

Obviously, I can make the parent project into a sister folder, like main and raw. Currently, I am not aware of another means to bypass this. The issue on doing something about in cargo is open since Nov'19.

[jessebraham]

Thanks for opening the issue. I have found workspaces are often problematic in embedded projects and tend to avoid them when possible, so didn't consider others would use it like this.

I think I can probably just move the linker script configuration into a build script instead, which should I hope resolve the issue. Will take a look into it when I get a chance.

[jessebraham]

Well, I thought this should be simple. Unfortunately, it's seemingly impossible to pass the -Cforce-frame-pointers argument via a build script, even though the remaining RUSTFLAGS can all be set in this manner. So, due to limitations of Cargo, I'm not sure there's anything I can actually do about this for the foreseeable future.

If anybody has a solution to this I'm all ears, but at least from reading the documentation I'm not seeing a path forward.

All I can do is recommend avoiding workspaces for embedded projects. Hopefully one day Cargo is more flexible.

[lure23]

In my case, I wasn't really using workspaces. I had a cargo directory setup on the top level, and another one (for lower level C bindings) as a subdirectory. Have split this to two folders, so .cargo/config no longer bothers me.

btw. -Cforce-frame-pointers wouldn't be a problem. The "-C", "link-arg=-Tdefmt.x" is, since it would link in a library I don't want/need in the subdirectory. And those can be moved to build.rs.