Sorry that size reduction was for a debug build. For a release build 6.5MB -> 1.6MB (with rocket, serde, wiringpi and pam-auth)
$ rm -f target/arm-unknown-linux-gnueabihf/release/rpitest; \
cargo build --target arm-unknown-linux-gnueabihf --release; \
mv target/arm-unknown-linux-gnueabihf/release/rpitest ./strip.off; \
rm -f target/arm-unknown-linux-gnueabihf/release/rpitest; \
cargo build --target arm-unknown-linux-gnueabihf --release; \
mv target/arm-unknown-linux-gnueabihf/release/rpitest ./strip.on; \
arm-none-eabi-strip strip.on; \
ls -lh strip.on strip.off
Compiling rpitest v0.1.0 (file:///Users/akos/projects/rust/tutorial)
Finished release [optimized] target(s) in 4.65 secs
Compiling rpitest v0.1.0 (file:///Users/akos/projects/rust/tutorial)
Finished release [optimized] target(s) in 4.44 secs
-rwxr-xr-x 1 akos staff 6.5M Mar 19 08:09 strip.off
-rwxr-xr-x 2 akos staff 1.6M Mar 19 08:09 strip.on