binary-size

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"        # Optimize for size (try "s" too -- sometimes smaller)
lto = true             # Link-time optimization
codegen-units = 1      # Better optimization
panic = "abort"        # Remove unwinding machinery
strip = true           # Strip symbols

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"] }  # Not "full"

Analysis Tools

cargo bloat --release --crates     # Size by crate
cargo bloat --release -n 30         # Top 30 functions
cargo llvm-lines --release | head -20  # Generic bloat
# WASM
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)

• Build with --release
• strip = true
• Try both opt-level = "z" and "s"
• lto = true
• codegen-units = 1

Stable (With Behavior Changes)

• panic = "abort" (if unwinding not needed)

Nightly

• -Zlocation-detail=none
• -Zfmt-debug=none
• -Z build-std=std,panic_abort
• -Z build-std-features="optimize_for_size"

Dependencies

• cargo bloat --crates to audit heavy deps
• Disable default features
• Consider lighter alternatives
• cargo unused-features analyze

Post-Build

• UPX compression (if appropriate)
• Verify binary runs correctly

---

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