Buildprof

Buildprof shows where the time went in a software build. It traces every process a Linux build launches and turns the recording into an interactive timeline you can explore in the browser.

It works below any individual build system, so the same view can include Cargo crates, Ninja jobs, compiler and linker invocations, shell scripts, code generators, file access, and arbitrary tools launched along the way.

Quick start

On the Linux machine that runs the build, put buildprof -- in front of your build command:*

# Or Homebrew, mise, packages: see Install below.
curl -fsSL https://buildprof.lalitm.com/install.sh | sh

buildprof -- make -j8

When the build finishes, the recording is saved as output.buildprof and opens in your browser. Allow the one-time prompt to access other apps and services on this device: that is the page fetching the recording from localhost. Nothing is ever uploaded.

To see the result without installing anything, open the pre-recorded ripgrep release build in the browser:

* Bazel, Gradle, Buck2, and other build systems with a daemon need a slightly different command; see Daemon build systems.

Investigating a slow build

The investigation guide walks through a recording step by step:

• find where the time goes and which commands are the expensive ones;
• spot low parallelism and long runs of many small commands;
• follow inputs back to the processes that produced them;
• look inside a compiler or linker invocation with compiler traces; and
• check whether a change actually helped.

For a worked example, follow the guided tour of the ripgrep recording above.

Why use Buildprof?

Build tools generally explain only the work they manage themselves. Cargo timings cannot break down an arbitrary build.rs script; Ninja cannot see inside commands it launches; compiler traces describe one compiler invocation rather than the build around it.

Buildprof follows the complete process tree instead. It lets you:

• see where wall-clock time went across the whole build;
• spot work which ran serially, overlapped, or started unexpectedly late;
• inspect full commands, working directories, lifetimes, and exit statuses;
• follow files from the process which produced them to processes which read them;
• use the same profiler with Make, Ninja, CMake, Meson, Cargo, Go, or wrapper scripts; and
• optionally add compiler-internal phases from Clang, LLD, and nightly Rust.

Install

Install on your Linux build machine using whichever method you prefer.

Shell installer:

curl -fsSL https://buildprof.lalitm.com/install.sh | sh

Homebrew:

brew install lalitmaganti/tap/buildprof

mise:

mise use -g github:LalitMaganti/buildprof

Cargo (builds from source; needs Rust 1.91 or newer):

cargo install --locked buildprof

Debian, Ubuntu, Fedora, and other .deb or .rpm distributions: download the package for your architecture from the latest release and install it with apt install ./buildprof_*.deb or dnf install ./buildprof-*.rpm.

Tarballs: the same release page carries prebuilt binaries for x86_64 and aarch64 Linux, both glibc and static musl.

Requirements

Recording builds is currently supported on Linux only. The kernel or container configuration must permit tracing child processes: Docker needs --cap-add SYS_PTRACE, kernel.yama.ptrace_scope must be below 3, and gVisor-style sandboxes cannot trace at all. Installing from source needs Rust 1.91 or newer.

Existing recordings can be viewed on any platform in the web UI, without installing Buildprof. Viewing a recording does not require the same operating system it was recorded on.

Usage

Recording a build

Put buildprof -- in front of the build command. Choose another output path or disable automatic opening when needed:

buildprof -o clean-build.buildprof --no-open -- ninja -C out

Opening recordings

Open an existing recording later with:

buildprof open clean-build.buildprof

buildprof.lalitm.com only delivers the UI itself. Your browser fetches the recording from localhost and processes it entirely in the page; no trace data leaves your machine.

Because the page comes from buildprof.lalitm.com and the recording from localhost, the browser asks once whether the site may access other apps and services on this device. Allow it. If you block it, the trace never loads. To recover, allow it again in the site settings next to the address bar, under "Apps on device" in Chrome or "Access this device" in Firefox, then run buildprof open again.

Recordings contain command lines and filesystem paths. Review them before sending them to anyone.

Builds on a remote machine

Over SSH there is no browser to launch, so Buildprof prints the port forward to run from your own machine instead and waits for the browser to fetch the trace:

ssh -L 9001:127.0.0.1:9001 user@buildhost

VS Code Remote and JetBrains Gateway forward the port automatically. The wait gives up after ten minutes; adjust it with --wait <SECONDS>, where 0 waits forever. Alternatively, copy the recording to your own machine and open it in the web UI. No local installation is needed for viewing.

Collection options

Process creation, commands, and timing are always recorded. File opens and renames are also recorded by default; to reduce overhead on builds with lots of filesystem activity, disable that layer:

buildprof --no-file-events -- make -j6

The process timeline remains available, but file lists and producer/consumer links are unavailable. This skips filesystem interception itself, rather than collecting and discarding events. The UI identifies recordings made this way.

Compiler details

Process timing is usually the right level for understanding a build. When a particular compiler or linker invocation needs a closer look, enable compiler tracing:

buildprof --compiler-traces -- cargo build

Buildprof currently imports Clang -ftime-trace, explicitly selected LLD --time-trace, and nightly Rust self-profile data. These events appear as a summary of active compiler threads with expandable per-thread phase tracks. Compiler tracing can be combined with process-only recording:

buildprof --no-file-events --compiler-traces -- ninja -C build

A build which invokes Clang through an absolute path currently bypasses compiler tracing. Buildprof will still record the compiler process, but its Clang and LLD internal phases will be absent.

Compiler tracing can also change compiler cache keys or turn cache hits into misses. Existing Rust compiler wrappers remain in the invocation chain, but cache preservation is not guaranteed in this mode.

Build systems

Buildprof follows the process tree, so it does not need to understand the build system. These are exercised by the conformance suite on every change:

• Make: compiles, archiving, linking, and renamed outputs.
• CMake with Ninja: the configure step and the Ninja build.
• Meson with Ninja: the setup step and the Ninja build.
• Cargo: rustc invocations and linking; nightly self-profile data with --compiler-traces.
• Go: compile, assemble, and link.

Anything else that runs as a child process is recorded the same way: shell scripts, code generators, wrapper scripts, and tools launched by the build.

Daemon build systems

Work handed to a daemon or a remote executor happens outside the process tree and is not visible. If the daemon is already running, the recording shows only the client; if the recorded command starts it, the recording continues until the daemon exits. Run without the daemon, or stop it before and after the build:

bazel shutdown && buildprof -- sh -c 'bazel build //... ; bazel shutdown'
buildprof -- ./gradlew --no-daemon build
buck2 kill && buildprof -- sh -c 'buck2 build //... ; buck2 kill'
sccache --stop-server && buildprof -- sh -c 'cargo build; sccache --stop-server'

How it works

On Linux, Buildprof launches the command under ptrace and follows process creation, execution, and exit through the complete descendant tree. A seccomp filter lets it stop only for the filesystem operations it records instead of paying the cost of intercepting every system call.

The recorder writes a Perfetto protobuf trace directly. Perfetto provides the storage format, query engine, and core timeline interactions; Buildprof adds the build-specific view on top, including process ancestry, command types, concurrency, file relationships, and optional compiler timing data.

Backwards compatibility

Before 1.0, the CLI and the UI move in lockstep at the minor version: a recording is meant to be viewed in a UI from the same 0.x series, and patch releases never change the trace format. Every UI version stays deployed under its own path, the CLI opens the one matching its version, and the UI links to the matching series when it is handed a recording from a different one, so nothing stops working, but the trace format may change between minor releases.

From 1.0 onward, the trace format is stable and compatibility is permanent: any recording opens in every later UI, and newer UIs simply add features on top of older recordings.

Self-hosting the UI

Each release attaches buildprof-ui-v<version>.tar.zst, the complete UI as static files. Serve its contents from any web server and point the CLI at it:

buildprof open --url https://ui.example.internal/v0.2.0 clean-build.buildprof

Development

See CONTRIBUTING.md for the layout and the UI workflow. Run the complete conformance suite in the Linux development container:

just bootstrap
just test

For a quick host-side check of formatting, lints, unit tests, and package contents:

just release-check

License

Licensed under the Apache License, Version 2.0. See LICENSE and AUTHORS.