Rustc Basics

mohitmishra786/low-level-dev-skills/skills/rust/rustc-basics

作者 mohitmishra786bdc58472fa9f無授權條款253 個星標收錄於 2026年10月9日更新於 2026年10月9日儲存庫3 個月前更新

Rust compiler skill for systems programming. Use when selecting RUSTFLAGS, configuring Cargo profiles, tuning release builds, reading assembly or MIR output, understanding monomorphization, or diagnosing compilation errors. Activates on queries about rustc flags, Cargo.toml profiles, opt-level, LTO, codegen-units, target-cpu, emit asm, MIR, or Rust build performance.

僅含說明Software Development Learning & Education

AI 產生的概覽

指導 Rust 編譯器設定：RUSTFLAGS、Cargo 設定檔、建置調校，以及檢視 MIR 或組譯輸出。

功能: 提供呼叫 Rust 編譯器的操作說明，包括選擇建置模式、設定 Cargo.toml 的 release 與 dev 設定檔，以及設定 RUSTFLAGS。內容涵蓋檢視組譯、MIR 與 LLVM IR 輸出、理解單態化、縮減二進位檔體積，以及排查常見編譯錯誤。文中也引用了一份關於 RUSTFLAGS 與 Cargo 設定檔模式的配套文件。
適用情境: 適用於選擇 RUSTFLAGS、調校 release 建置、設定 Cargo 設定檔或診斷 Rust 編譯錯誤時。也適用於閱讀組譯或 MIR 輸出、研究單態化或縮減 Rust 二進位檔體積的情境。
執行需求: 不含指令碼，僅為說明性內容。執行所述命令需要 Rust 工具鏈（cargo、rustc）。部分選用步驟涉及第三方 cargo 子命令，如 cargo-show-asm、cargo-llvm-lines 和 cargo-bloat，需另行安裝。

rustc Basics

Purpose

Guide agents through Rust compiler invocation: RUSTFLAGS, Cargo profile configuration, build modes, MIR and assembly inspection, monomorphization, and common compilation error patterns.

Triggers

"How do I configure a release build in Rust for maximum performance?"
"How do I see the assembly output for a Rust function?"
"What is monomorphization and why is it making my compile slow?"
"How do I enable LTO in Rust?"
"My Rust binary is too large — how do I shrink it?"
"How do I read Rust MIR output?"

Workflow

1. Choose a build mode

bash

# Debug (default) — fast compile, no optimization, debug infocargo build
# Release — optimized, no debug info by defaultcargo build --release
# Check only (fastest, no codegen)cargo check
# Build for specific targetcargo build --release --target aarch64-unknown-linux-gnu

# Debug (default) — fast compile, no optimization, debug infocargo build
# Release — optimized, no debug info by defaultcargo build --release
# Check only (fastest, no codegen)cargo check
# Build for specific targetcargo build --release --target aarch64-unknown-linux-gnu

2. Cargo.toml profile configuration

toml

[profile.release]opt-level = 3          # 0-3, "s" (size), "z" (aggressive size)debug = false          # true = full, 1 = line tables only, 0 = nonelto = "thin"           # false | "thin" | true (fat LTO)codegen-units = 1      # 1 = max optimization, higher = faster compilepanic = "abort"        # "unwind" (default) | "abort" (smaller binary)strip = "symbols"      # "none" | "debuginfo" | "symbols"overflow-checks = false # default true in debug, false in release
[profile.release-with-debug]inherits = "release"debug = true           # release build with debug symbolsstrip = "none"
[profile.dev]opt-level = 1          # Speed up debug builds slightly

[profile.release]opt-level = 3          # 0-3, "s" (size), "z" (aggressive size)debug = false          # true = full, 1 = line tables only, 0 = nonelto = "thin"           # false | "thin" | true (fat LTO)codegen-units = 1      # 1 = max optimization, higher = faster compilepanic = "abort"        # "unwind" (default) | "abort" (smaller binary)strip = "symbols"      # "none" | "debuginfo" | "symbols"overflow-checks = false # default true in debug, false in release
[profile.release-with-debug]inherits = "release"debug = true           # release build with debug symbolsstrip = "none"
[profile.dev]opt-level = 1          # Speed up debug builds slightly

Setting	Impact
`lto = true` (fat)	Best optimization, slowest link
`lto = "thin"`	Good optimization, parallel link
`codegen-units = 1`	Best inlining, slower compile
`panic = "abort"`	Removes unwind tables, smaller binary
`opt-level = "z"`	Aggressive size reduction

3. RUSTFLAGS

bash

# Set for a single buildRUSTFLAGS="-C target-cpu=native" cargo build --release
# Enable all target CPU featuresRUSTFLAGS="-C target-cpu=native -C target-feature=+avx2,+bmi2" cargo build --release
# Control codegen at invocation levelRUSTFLAGS="-C opt-level=3 -C codegen-units=1 -C lto=on" cargo build --release

# Set for a single buildRUSTFLAGS="-C target-cpu=native" cargo build --release
# Enable all target CPU featuresRUSTFLAGS="-C target-cpu=native -C target-feature=+avx2,+bmi2" cargo build --release
# Control codegen at invocation levelRUSTFLAGS="-C opt-level=3 -C codegen-units=1 -C lto=on" cargo build --release

Persistent in .cargo/config.toml:

toml

[build]rustflags = ["-C", "target-cpu=native"]
[target.x86_64-unknown-linux-gnu]rustflags = ["-C", "target-cpu=native", "-C", "link-arg=-fuse-ld=lld"]

[build]rustflags = ["-C", "target-cpu=native"]
[target.x86_64-unknown-linux-gnu]rustflags = ["-C", "target-cpu=native", "-C", "link-arg=-fuse-ld=lld"]

4. Inspect assembly output

bash

# Using cargo-show-asm (recommended)cargo install cargo-show-asmcargo asm --release 'myapp::module::function_name'
# Using rustc directlyrustc --emit=asm -C opt-level=3 -C target-cpu=native src/lib.rscat lib.s
# View MIR (mid-level IR, before codegen)rustc --emit=mir -C opt-level=3 src/lib.rscat lib.mir
# View LLVM IRrustc --emit=llvm-ir -C opt-level=3 src/lib.rscat lib.ll
# Use Compiler Explorer (Godbolt) patterns locallyRUSTFLAGS="--emit=asm" cargo build --releasefind target/ -name "*.s"

# Using cargo-show-asm (recommended)cargo install cargo-show-asmcargo asm --release 'myapp::module::function_name'
# Using rustc directlyrustc --emit=asm -C opt-level=3 -C target-cpu=native src/lib.rscat lib.s
# View MIR (mid-level IR, before codegen)rustc --emit=mir -C opt-level=3 src/lib.rscat lib.mir
# View LLVM IRrustc --emit=llvm-ir -C opt-level=3 src/lib.rscat lib.ll
# Use Compiler Explorer (Godbolt) patterns locallyRUSTFLAGS="--emit=asm" cargo build --releasefind target/ -name "*.s"

5. Understand monomorphization

Rust generics are monomorphized — each concrete type instantiation produces separate code. This causes:

Binary size bloat
Longer compile times
Potential i-cache pressure

bash

# Measure monomorphization bloatcargo install cargo-llvm-linescargo llvm-lines --release | head -30
# Shows: lines of LLVM IR per function (monomorphized copies visible)

# Measure monomorphization bloatcargo install cargo-llvm-linescargo llvm-lines --release | head -30
# Shows: lines of LLVM IR per function (monomorphized copies visible)

Mitigation strategies:

rust

// 1. Type erasure with dyn Trait (trades monomorphization for dispatch)fn process(iter: &mut dyn Iterator<Item = i32>) { ... }
// 2. Non-generic inner function patternfn my_generic<T: AsRef<str>>(s: T) {    fn inner(s: &str) { /* actual work */ }    inner(s.as_ref())  // monomorphization only in thin wrapper}

// 1. Type erasure with dyn Trait (trades monomorphization for dispatch)fn process(iter: &mut dyn Iterator<Item = i32>) { ... }
// 2. Non-generic inner function patternfn my_generic<T: AsRef<str>>(s: T) {    fn inner(s: &str) { /* actual work */ }    inner(s.as_ref())  // monomorphization only in thin wrapper}

6. Binary size reduction

bash

# Check binary size breakdowncargo install cargo-bloatcargo bloat --release --crates      # per-crate sizecargo bloat --release -n 20         # top 20 largest functions
# Compress executable (at cost of startup time)upx --best --lzma target/release/myapp

# Check binary size breakdowncargo install cargo-bloatcargo bloat --release --crates      # per-crate sizecargo bloat --release -n 20         # top 20 largest functions
# Compress executable (at cost of startup time)upx --best --lzma target/release/myapp

7. Common error triage

Error	Cause	Fix
`cannot find function in this scope`	Missing `use` or wrong module path	Add `use crate::module::fn_name`
`the trait X is not implemented for Y`	Missing impl or wrong generic bound	Implement trait or adjust bounds
`lifetime may not live long enough`	Borrow checker lifetime issue	Add explicit lifetime annotations
`cannot borrow as mutable because also borrowed as immutable`	Aliasing violation	Restructure borrows to not overlap
`use of moved value`	Value used after `move` into closure or function	Use `.clone()` or borrow instead
`mismatched types: expected &str found String`	String vs &str confusion	Use `.as_str()` or `&my_string`

8. Useful rustc flags

bash

# Show all enabled features at a given opt levelrustc -C opt-level=3 --print cfg
# List available targetsrustc --print target-list
# Show target-specific featuresrustc --print target-features --target x86_64-unknown-linux-gnu
# Explain an error coderustc --explain E0382

# Show all enabled features at a given opt levelrustc -C opt-level=3 --print cfg
# List available targetsrustc --print target-list
# Show target-specific featuresrustc --print target-features --target x86_64-unknown-linux-gnu
# Explain an error coderustc --explain E0382

For RUSTFLAGS reference and Cargo profile patterns, see references/rustflags-profiles.md [blocked].

Related skills

Use skills/rust/cargo-workflows for workspace management and Cargo tooling
Use skills/rust/rust-debugging for debugging Rust binaries with GDB/LLDB
Use skills/rust/rust-profiling for profiling and flamegraphs
Use skills/rust/rust-sanitizers-miri for memory safety validation

來源與署名

來源：mohitmishra786/low-level-dev-skills位於skills/rust/rustc-basics提交bdc5847

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Rustc Basics

rustc Basics

Purpose

Triggers

Workflow

1. Choose a build mode

2. Cargo.toml profile configuration

3. RUSTFLAGS

4. Inspect assembly output

5. Understand monomorphization

6. Binary size reduction

7. Common error triage

8. Useful rustc flags

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