cross picking up wrong target options in cargos config.toml

[oliverbestmann]

I've added a [target.target.x86_64-unknown-linux-gnu] section to my $HOME/.cargo/config.toml. If i am now using cross to compile for a different target, say cross build --target aarch64-unknown-linux-gnu, the build picks up the config for x86_64-unknown-linux-gnu.

In my case, i've configured

oliver@machine ~> /bin/cat ~/.cargo/config.toml
[target.x86_64-unknown-linux-gnu]
linker = "/usr/bin/clang"
rustflags = [
  "-C", "target-cpu=native",
  "-C", "link-arg=-fuse-ld=/home/oliver/.local/bin/mold"
]

And the build fails with

oliver@machine ~> cross build --target aarch64-unknown-linux-gnu --release
info: syncing channel updates for '1.56.0-x86_64-unknown-linux-gnu'
  1.56.0-x86_64-unknown-linux-gnu unchanged - rustc 1.56.0 (09c42c458 2021-10-18)
error: linker `/usr/bin/clang` not found
  |
  = note: No such file or directory (os error 2)

doesn't work with rust 1.57.0 either.
cross version 0.2.1

[Emilgardis]

We shouldn't currently use that at all, instead you'd have to place the config in .cargo/config.tomlin the manifest root if you want it to go over to the cross builder

perhaps we should support this automatically, but currently you should be able to workaround it by mounting the .cargo folder inside the builder with https://github.com/rust-embedded/cross#mounting-volumes-into-the-build-environment to any of the supported paths

[Emilgardis]

Note that that feature is currently unreleased, you'd have to install from git

cargo install cross --git https://github.com/rust-embedded/cross

[oliverbestmann]

Thing is, I don't want cross to pick that file up at all. It currently contains only configuration related to my host machine and target. But when compiling with cross on x86_64 for target aarch64, it picks up the options for the x86_64 target.
Also still broken with the the current master version.

[kdar]

Thank you so much for this issue, as this was driving me up the wall why my cross compiling was failing. I'm a little confused as to why it was happening though. I was compiling a simple program, and it would compile until I added "libc" as a dependency. The failure was:

Compiling num-integer v0.1.44
error: linker `/usr/bin/clang` not found
  |
  = note: No such file or directory (os error 2)

This would happen because my ~/.cargo/config.toml contained:

[target.x86_64-unknown-linux-gnu]
linker = "/usr/bin/clang"
rustflags = ["-C", "link-arg=--ld-path=/usr/sbin/mold"]

The confusing thing to me is that I'm targetting aarch64-linux-android. Maybe I'm misunderstanding exactly what cross does, but why does it care about the x86_64-unknown-linux-gnu target when I'm compiling for android?

Anyway, this was surprising to me here and I agree with @oliverbestmann.

[oliverbestmann]

Any update on this @Emilgardis? The issue still exists in 7599e1a. cross still tries to use the target configuration of the host system, not the actual cross target system.
It even got worse as cross now exists with return code zero, indicating no error at all.

[Emilgardis]

I'll try to get in a fix for this. Not sure exactly what is happening but have an idea how to solve it.

[sadilekivan]

Just wanted to post an issue on this exact behavior. Any progress on it?

[Emilgardis]

I'd forgotten about this, this can be solved by us setting CARGO_TARGET_<triple>_LINKER in every image we provide, since env vars take priority over toml values. However, this still feels like a bad solution.

[Alexhuszagh]

I'm working on this now, since I'm also trying to support aliases. A simple solution is the one above, while also parsing the aliases (which we would have to do anyway). The complex solution, which I want to support, is below:

However, this would require using docker exec and then cleaning up the image ourselves if we write the concatenated config.toml to the file, and copying it in an initial step to the container. Unless if you know an environment variable we can set to locate where that config file would be, so we can store it in the target directory or something.

[sadilekivan]

I tried the environment variable solution, but if the config.toml is present, it still displays the same error. I think I'm using it correctly though, because if I set a non-existing linker it shows up as another error if my config.toml is gone.

I tried export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER="aarch64-linux-gnu-gcc" ; cross build --target aarch64-unknown-linux-gnu, It only works if my config.toml is not present.

[sadilekivan]

It does seem that way. For now I'm just renaming the config with a script. A pity though, an env variable fix would be less cumber some. Thanks for the fast feedback, I wasn't completely sure if that was the correct linker.

[Alexhuszagh]

Trying to find the best solution right now, and sorry for the convenience. Working on a few issues but this is pretty high on my priority list.

[Emilgardis]

I tried export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER="aarch64-linux-gnu-gcc" ; cross build --target aarch64-unknown-linux-gnu, It only works if my config.toml is not present.

This is correct, however you need to forward it to the container @sadilekivan

so in Cross.toml

[target.aarch64-unknown-linux-gnu.env]
passthrough = ["CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER=aarch64-linux-gnu-gcc"]