I have ubuntu x86_64 container and cargo build goes well.
But i need to build x86 library version too.
As far as I understand i need to add i686 toolchain and target.
rustup target add i686-unknown-linux-gnu done successful
rustup toolchain install stable-i686-unknown-linux-gnu finished with error
$ rustup toolchain install stable-i686-unknown-linux-gnu
info: syncing channel updates for 'stable-i686-unknown-linux-gnu'
info: latest update on 2018-11-08, rust version 1.30.1 (1433507eb 2018-11-07)
info: downloading component 'rustc'
info: downloading component 'rust-std'
info: downloading component 'cargo'
info: downloading component 'rust-docs'
info: installing component 'rustc'
info: installing component 'rust-std'
info: installing component 'cargo'
info: installing component 'rust-docs'
stable-i686-unknown-linux-gnu installed - (error reading rustc version)
and
$ rustup default stable-i686
info: using existing install for 'stable-i686-unknown-linux-gnu'
info: default toolchain set to 'stable-i686-unknown-linux-gnu'
stable-i686-unknown-linux-gnu unchanged - (error reading rustc version)
Do I missed something or took wrong approach?
Instead of changing your toolchain, you have to add the target to your current toolchain (make sure to switch back to your original toolchain first).
$ rustup target install i686-unknown-linux-gnu
$ cargo build --target=i686-unknown-linux-gnu
Of course, you need to install the 32-bit libraries on your system as well, e.g. on ubuntu you install them by
$ sudo apt install gcc-multilib
(for more information about that see How to Compile 32-bit Apps on 64-bit Ubuntu?)