| name | binary-size |
| description | Binary Size Optimization guidance for Fortress Rollback. Use when Reducing binary size, WASM size optimization, LTO configuration. |
Binary Size Optimization
Quick Profiles
Stable Rust -- Balanced
[profile.release]
opt-level = "z"
lto = true
codegen-units = 1
panic = "abort"
strip = true
Nightly -- Maximum Reduction
RUSTFLAGS="-Zlocation-detail=none -Zfmt-debug=none" cargo +nightly build \
-Z build-std=std,panic_abort \
-Z build-std-features="optimize_for_size" \
--target x86_64-unknown-linux-gnu --release
Techniques by Complexity
| Technique | Rust | Impact | Behavior Change |
|---|
| Release build | 1.0+ | 60-70% | No |
strip = true | 1.59+ | 50-80% | No |
opt-level = "z" or "s" | 1.28+ | 10-30% | No |
lto = true ("fat") | 1.0+ | 10-20% | No |
codegen-units = 1 | 1.0+ | 5-15% | No |
panic = "abort" | 1.10+ | 10-20% | Yes: no unwinding |
-Zlocation-detail=none | Nightly | 5-15% | No panic location |
-Zfmt-debug=none | Nightly | 5-15% | No {:?} output |
-Z build-std | Nightly | 20-50% | No |
-Cpanic=immediate-abort | Nightly | 10-30% | No panic message |
| UPX compression | Post | 50-70% | AV flags, startup |
#![no_std] | 1.30+ | ~10KB possible | Limited API |
Always try BOTH "s" and "z" -- depending on code, "s" can be smaller.
Dependency Optimization
Heavy vs Light Alternatives
| Category | Heavy | Lighter Alternative |
|---|
| CLI parsing | clap | lexopt, pico-args, argh |
| Serialization | serde | miniserde, nanoserde |
| HTTP | reqwest | ureq, minreq |
| Async runtime | tokio | smol, embassy |
| Regex | regex | regex-lite, memchr |
| Error handling | anyhow | thiserror only |
Minimize Features
serde = { version = "1.0", default-features = false, features = ["derive"] }
tokio = { version = "1.0", features = ["rt", "net"] }
Analysis Tools
cargo bloat --release --crates
cargo bloat --release -n 30
cargo llvm-lines --release | head -20
twiggy top -n 20 target/wasm32-unknown-unknown/release/my_lib.wasm
WASM-Specific
[profile.release]
opt-level = "z"
lto = true
codegen-units = 1
panic = "abort"
strip = true
cargo build --release --target wasm32-unknown-unknown
wasm-opt -Oz -o optimized.wasm target/wasm32-unknown-unknown/release/my_lib.wasm
Platform Notes
Windows: MSVC vs GNU
MSVC produces significantly smaller binaries (~10MB vs ~100MB for GNU/MinGW). Prefer MSVC for releases.
Linux: musl vs glibc
| Target | Trade-off |
|---|
*-linux-gnu | Smaller binary, needs glibc at runtime |
*-linux-musl | Larger binary, fully portable static |
Container Optimization
FROM rust:1.83-alpine AS builder
RUN apk add --no-cache musl-dev
WORKDIR /app
COPY . .
RUN cargo build --release --target x86_64-unknown-linux-musl && \
strip target/x86_64-unknown-linux-musl/release/myapp
FROM scratch
COPY --from=builder /app/target/x86_64-unknown-linux-musl/release/myapp /myapp
ENTRYPOINT ["/myapp"]
| Base Image | Size |
|---|
debian:bookworm | ~130 MB |
alpine:3 | ~7 MB |
distroless/static | ~2 MB |
scratch | 0 MB |
Checklist
Stable (No Behavior Changes)
Stable (With Behavior Changes)
Nightly
Dependencies
Post-Build
Example Journey
| Step | Size | Reduction |
|---|
| Debug build | 4.2 MB | -- |
| Release | 410 KB | 90% |
| + strip | 310 KB | 93% |
| + opt-level=z | 290 KB | 93% |
| + LTO | 250 KB | 94% |
| + codegen-units=1 | 240 KB | 94% |
| + panic=abort | 180 KB | 96% |
| + build-std (nightly) | 51 KB | 99% |
| + UPX | 24 KB | 99.4% |
Tools
| Tool | Purpose |
|---|
cargo-bloat | Find what takes space |
cargo-llvm-lines | Find generic bloat |
cargo-unused-features | Find unused features |
twiggy | WASM code size profiler |
wasm-opt | WASM binary optimizer |
| UPX | Executable packer |
