cfg(target_arch) in build scripts for FFI still refer to the host rather than the target

[jguhlin]

Running

cross +nightly test --target aarch64-unknown-linux-gnu

Will trigger this part of the build script:

#[cfg(target_arch = "x86_64")]
fn target_specific(cc: &mut cc::Build) {
    println!("Building for x86_64");

Any ideas? I need to set up target specific optimizations or the software can get incredibly slow.

[Emilgardis]

cfg(target_arch) will always refer to the target the current crate is built for, and build scripts are always built for the host, not the target.

Instead, use the environment variable CARGO_CFG_TARGET_ARCH

as noted in the text, ensure that you actually retrieve the env var at runtime using env::var("CARGO_CFG_TARGET_ARCH")

note that this behaviour is not changed by cross, rather it's how cargo/rust works

[jguhlin]

Thanks, this is helpful!