Introduce

1. Demo how to build rust application for router with mipsel CPU (MT7621)
2. Demo how to link libcurl built with uclibc lib. See src/main.rs and .cargo/config.toml (#[link (name="xxx")])
3. Demo how to call C function "curl_version" from libcurl.so and convert return c_char value into &str and print it out. See src/main.rs

Pre-request

1. Build Padavan firmware to getting all necessary native libraries for route os according to https://www.kiloleaf.com/posts/cross-compile-rust-for-openwrt/
   1. It's better to flash firmware built by yourself to avoid some version miss match issue
2. Build rustc toolchain for mipsel-unknown-linux-uclibc target according to https://www.kiloleaf.com/posts/cross-compile-rust-for-openwrt/
   1. I successfully built rust 1.55 for mipsel-unknown-linux-uclibc target
   2. See my config.toml file in rust source folder

Limitation

1. Since uclibc is not fully supported by rust. Most of 3rd part library won't be built such as

user@user-VirtualBox:~/rust_projects/hello$ cargo build --release --target=mipsel-unknown-linux-uclibc
    Updating crates.io index
  Downloaded openssl v0.9.24
  Downloaded lazy_static v0.2.11
  Downloaded bitflags v0.9.1
  Downloaded minihttp v0.1.9  <===== I add this one into Cargo.toml. But hit this issue. Will be appreciated if someone can help to resovle this failure
  Downloaded miniurl v0.1.3
  Downloaded minihttpse v0.1.6
  Downloaded native-tls v0.1.5
  Downloaded 7 crates (208.3 KB) in 3.33s
   Compiling pkg-config v0.3.20
   Compiling cc v1.0.70
   Compiling autocfg v1.0.1
   Compiling libc v0.2.102
error[E0463]: can't find crate for `std`

TODO

[ ] 1. Create a docker container to put all of them together to ease the life

Note

1. .cargo/config.toml -L (should have no space after -L otherwise rustc will not find any libraries)

link-arg=-L/opt/rt-n56u/toolchain-mipsel/toolchain-3.4.x/mipsel-linux-uclibc/sysroot/lib/

2. Ninja not found by CMake

ln -s /usr/bin/ninja /usr/sbin/ninja

3. Setup environment variables correctly before calling cargo build xxxx, suggest adding to ~/.bashrc

export PATH=$PATH:/opt/rt-n56u/toolchain-mipsel/toolchain-3.4.x/bin
export STAGING_DIR=/opt/rt-n56u/toolchain-mipsel/toolchain-3.4.x
export CC_mips_unknown_linux_uclibc=mipsel-linux-uclibc-gcc

4. How to debug if rustc find library specified by "-L" or "-l"

strace rustc 2>&1 | grep <lib name>

5. Check exported symbol list

readelf --symbols /opt/wsl/usr/local/lib/libc.so.1|grep dl_iterate_phdr

6. Git clone rust repo with all submodule otherwise you will get error when calling python ./x.py install

git clone https://github.com/rust-lang/rust.git
git submodule update --init --recursive

7. Resolve "error[E0463]: can't find crate for std"

rustup show
# optional
rustup default stable-x86_64-unknown-linux-gnu
export OPENSSL_LIB_DIR=/opt/rt-n56u/trunk/libs/libssl/openssl-1.1.1k
export OPENSSL_INCLUDE_DIR=/opt/rt-n56u/trunk/libs/libssl/openssl-1.1.1k/include
# this is really important otherwise unexpected error will occur
export PATH=/opt/wsl/usr/local/bin:$PATH
cargo build --release --target=mipsel-unknown-linux-uclibc -v

8. Resolve "Could not find directory of OpenSSL installation, and this -sys crate cannot"

export OPENSSL_LIB_DIR=/opt/rt-n56u/trunk/libs/libssl/openssl-1.1.1k
export OPENSSL_INCLUDE_DIR=/opt/rt-n56u/trunk/libs/libssl/openssl-1.1.1k/include

How to

1. Cross Build

cargo build --release --target=mipsel-unknown-linux-uclibc
# strip binary size
mipsel-linux-uclibc-strip ~/rust_projects/mips-uclibc-hello-rust/target/mipsel-unknown-linux-uclibc/release/mips-uclibc-hello-rust
# scp binary to route with mips MT7621
scp target/mipsel-unknown-linux-uclibc/release/mips-uclibc-hello-rust [email protected]:/tmp
# call the binary
/tmp/mips-uclibc-hello-rust

CPU info Example:
K2P:/tmp # cat /proc/cpuinfo
system type             : MediaTek MT7621 SoC
processor               : 0
cpu model               : MIPS 1004Kc V2.15

2. sccache - Shared Compilation Cache (rustc-wrapper = "/path/to/sccache") https://github.com/mozilla/sccache/

Reference

1. https://www.kiloleaf.com/posts/cross-compile-rust-for-openwrt/
2. https://github.com/hanwckf/rt-n56u
3. https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html
4. https://stackoverflow.com/questions/24145823/how-do-i-convert-a-c-string-into-a-rust-string-and-back-via-ffi
5. https://rustwiki.org/zh-CN/rust-by-example/hello/print/print_display.html - rust by example "Chinese version"
6. https://doc.rust-lang.org/nomicon/ownership.html - The Dark Arts of Unsafe Rust
7. https://doc.rust-lang.org/cargo/index.html - Cargo book
8. https://dhghomon.github.io/easy_rust/Chapter_1.html - Easy rust
9. https://doc.rust-lang.org/std/ - Rust std doc
10. https://cheats.rs/ - Rust cheats
11. https://rust-lang.github.io/async-book/01_getting_started/01_chapter.html - Rust Async
12. https://rustcc.gitbooks.io/rustprimer/content/intoborrow/cow.html - Rust Primer "Chinese version"
13. https://rust-lang-nursery.github.io/rust-cookbook/intro.html - Rust Cookbook
14. https://rust-lang-nursery.github.io/rust-cookbook/intro.html - Esy Rust
15. https://github.com/johnthagen/min-sized-rust - (important) How to reduce size of rust application

Useful tools

1. tmux
2. htop

Backup

1. May need to set up GW manually on rouer OS

ip ro add default via 192.168.1.1

2. To resolve

/opt/wsl/usr/local/bin/rustc --crate-name pkg_config /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/pkg-config-0.3.20/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debug-assertions=off -C metadata=1eb2583553d0fa50 -C extra-filename=-1eb2583553d0fa50 --out-dir /home/user/rust_projects/mips-uclibc-hello-rust/target/release/deps -L dependency=/home/user/rust_projects/mips-uclibc-hello-rust/target/release/deps --cap-lints allow -L /opt/wsl/usr/local/lib/rustlib/mipsel-unknown-linux-uclibc/lib/ --target=mipsel-unknown-linux-uclibc