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Measuring Rust Binary Bloat

Last Refreshed: 2019-09-03

Instructions for analyzing the binary size and composition of Rust programs on Fuchsia. The examples use the //src/diagnostics/archivist package.

Prerequisites

cargo-bloat

These instructions cover the installation and use of cargo-bloat, a tool for Rust projects inspired by Bloaty McBloatface.

To install:

cargo install cargo-bloat --features regex-filter [--force]

If you've installed a previous version or would like to add regex filtering support to an existing installation, you may need to add --force.

fargo

This example uses cargo subcommands from crates.io, so you must install fargo.

Run fx build

Consult the fx common tools documentation for information about including the correct binary target in your build args.

Next, run fx build within your Fuchsia source directory.

Create Cargo.toml

Follow the instructions to generate a Cargo.toml for your project.

Build with fargo

cargo-bloat doesn't currently support passing an arbitrary manifest path, you'll need to cd to the directory with the generated Cargo.toml:

cd $FUCHSIA_DIR/src/diagnostics/archivist

From that directory, ensure you can produce a release build with fargo:

fargo build --release

Run the release build from plain fargo first, as cargo-bloat will swallow any build errors.

Measure size contributions with cargo-bloat

Once we're sure that fargo can produce a release binary for our target, run cargo-bloat:

fargo cargo bloat -- --release -n 5
Compiling ...
Analyzing .../src/../out/cargo_target/x86_64-fuchsia/release/archivist

 File  .text     Size              Crate Name
 1.7%   4.5%  38.0KiB              regex <regex::exec::ExecNoSync as regex::re_trait::Regular...
 1.0%   2.5%  21.4KiB       regex_syntax regex_syntax::ast::parse::ParserI<P>::parse_with_comments
 0.8%   2.1%  17.7KiB fuchsia_component? <fuchsia_component::server::ServiceFs<ServiceObjTy> as...
 0.4%   0.9%   8.0KiB              regex regex::re_unicode::Regex::shortest_match_at
 0.4%   0.9%   7.8KiB                std _ZN9libunwind10CFI_ParserINS_17LocalAddressSpaceEE17paI...
33.8%  89.0% 751.9KiB                    And 6152 smaller methods. Use -n N to show more.
38.0% 100.0% 844.8KiB                    .text section size, the file size is 2.2MiB

It's important to measure binary size in release, as it can be difficult to predict the impact of changes on debug builds.

The -n 5 arguments limit output to 5 lines. Run cargo bloat --help for all options, and see below for several commonly used ones.

Group functions by crate

Use the --crates flag to group bloat analysis by an estimate of the source crate:

fargo cargo bloat -- --release -n 5 --crates
Compiling ...
Analyzing .../src/../out/cargo_target/x86_64-fuchsia/release/archivist

 File  .text     Size Crate
13.3%  34.9% 294.8KiB std
 6.3%  16.7% 141.0KiB regex
 5.0%  13.2% 111.3KiB regex_syntax
 2.1%   5.5%  46.1KiB fidl
 1.8%   4.7%  39.5KiB json5
 9.6%  25.1% 212.2KiB And 64 more crates. Use -n N to show more.
38.0% 100.0% 844.8KiB .text section size, the file size is 2.2MiB

Note: numbers above are a result of guesswork. They are not 100% correct and never will be.

Attributing generic functions to their originating crate is an error-prone heuristic analysis and you should drill down with filters and granular output to confirm any discoveries from crate-grouped output.

Filter functions

To drill down into the sources of bloat in a particular crate, you can filter by source crate name or regex over the function name (with the feature flag enabled) with the --filter flag:

fargo cargo bloat -- --release -n 5 --filter regex_syntax
Compiling ...
Analyzing .../src/../out/cargo_target/x86_64-fuchsia/release/archivist

File .text     Size        Crate Name
1.0%  2.5%  21.4KiB regex_syntax regex_syntax::ast::parse::ParserI<P>::parse_with_comments
0.3%  0.8%   6.4KiB regex_syntax regex_syntax::ast::parse::ParserI<P>::parse_escape
0.2%  0.5%   3.8KiB regex_syntax <regex_syntax::hir::translate::TranslatorI as regex_syntax::ast...
0.1%  0.2%   1.8KiB regex_syntax <regex_syntax::hir::translate::TranslatorI as regex_syntax::ast...
0.1%  0.2%   1.7KiB regex_syntax regex_syntax::unicode::class
3.4%  9.0%  76.2KiB              And 698 smaller methods. Use -n N to show more.
5.0% 13.2% 111.2KiB              filtered data size, the file size is 2.2MiB