Rust x86 without SSE2

This will allow you to use Rust on x86 i686 machines without SSE2. Rust calls this target i586 but it will work on a CHOST using i686.

32bit chroot

Create a 32bit chroot on a machine with sse2 using the correct tarball for your needs (I used stage3-i686-openrc).

You will need to install the following in your chroot:

root #emerge --ask sys-devel/clang dev-vcs/git dev-util/cmake eselect-rust

Rust

Repo

The git repo is used because the tag tarballs lack the needed submodules.

amd64 #git clone https://github.com/rust-lang/rust

amd64 #cd rust

amd64 #git checkout 1.64.0

amd64 #git submodule update --init --recursive

Build

Configure:

FILE config.toml

# Includes one of the default files in src/bootstrap/defaults
profile = "user"
changelog-seen = 2

[llvm]
cflags = "-lz -fcf-protection=none"
cxxflags = "-lz -fcf-protection=none"
ldflags = "-lz -fcf-protection=none"

Run the mono x.py build script:

amd64 #

PKG_CONFIG_ALLOW_CROSS=1 ./x.py dist --build i686-unknown-linux-gnu --host i586-unknown-linux-gnu --target i586-unknown-linux-gnu -j 4

All going well, when it terminates, there should be a fresh rustc binary:

amd64 #file build/i586-unknown-linux-gnu/stage2/bin/rustc

build/i586-unknown-linux-gnu/stage2/bin/rustc: ELF 32-bit LSB pie executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, not stripped

On the non sse2 machine

Install built Rust temporarily

Warning
Use a path like /usr/local where it's easy to delete the files afterwards and be sure nothing is lingering contaminating later builds. In fact, this whole procedure should be done in a clean chroot.

Copy the files over to the destination box (i686 in this case):

Copy over:
- build/dist/cargo-1.65.0-i586-unknown-linux-gnu.tar.xz
- build/dist/rust-std-1.65.0-dev-i586-unknown-linux-gnu.tar.xz
- build/dist/rustc-1.65.0-i686-unknown-linux-gnu.tar.xz
For each: on the other side, untar it to a temporary location, and run inside ./install.sh --prefix=/usr/local/lib/rust/1.65.0/

Ebuild editing

Copy the Rust ebuilds to a temporary location:

x86 #

mkdir -p /tmp/dev-lang/rust && cd /tmp/dev-lang/rust

x86 #cp -rv /var/db/repos/gentoo/dev-lang/rust/* .

Modify the relevant Rust ebuild corresponding to the current latest Rust release (must match the version built from git):

Add 'return' below `python-any-r1` in pkg_setup
Replace the rustc call in src_configure by just setting rust_stage0_root=/usr/local/lib/rust/1.65.0/
Comment out the [[ -d ${rust_stage0_root} ]] check
Remove the IUSE line for the sse2 check
Find the are with the three -fcf-protection=none and add -lz
`

Then try to emerge using it:

x86 #PKG_CONFIG_ALLOW_CROSS=1 RUSTFLAGS="-C opt-level=0" USE=system-bootstrap ebuild rust-1.65.0.ebuild clean merge

Once done, some manual fiddling may be needed to get LDPATH right initially and make eselect rust happy.

Run eselect rust update and placate any complaints it has if there's stale stuff left over from the /usr/local bits. Try env-update && . /etc/profile.

Remember to clean up /usr/local/{bin,lib/*}.

Now do it all again using a more vanilla ebuild:

x86 #rm -r /tmp/dev-lang/rust

x86 #mkdir -p /tmp/dev-lang/rust && cd /tmp/dev-lang/rust

x86 #cp -rv /var/db/repos/gentoo/dev-lang/rust/* .

Remove the IUSE check for SSE2 on x86.

x86 #USE=system-bootstrap ebuild rust-1.65.0.ebuild clean merge

With that you now have Rust working without the need of SSE2.