builder: add -trimpath support by jakebailey · Pull Request #5711 · tinygo-org/tinygo

jakebailey · 2026-09-19T17:47:03Z

Fixes #5275

With -no-debug, this doesn't really matter, but otherwise it does make binaries smaller and more reproducible.

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🟡 Changes recommended

CGo headers outside the package directory can still expose local paths and prevent reproducible cache keys.

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Map module root to rewrite external header paths and cache keys · New

What changed in this PR

Adds -trimpath support to remove local paths and improve binary reproducibility.

Changes:

Adds and propagates the -trimpath option.
Rewrites Go, CGo, library, and embedded-file paths.
Adds path-removal and reproducibility tests.

File	Description
`main.go`	Adds the CLI flag.
`main_test.go`	Tests the flag and output reproducibility.
`compileopts/options.go`	Stores the option.
`compileopts/config.go`	Configures path mapping and cache isolation.
`compiler/compiler.go`	Records mapped debug paths.
`loader/loader.go`	Maps package paths and flags.
`loader/loader_test.go`	Tests module path mapping.
`cgo/cgo.go`	Maps CGo source locations.
`cgo/cgo_test.go`	Updates the CGo call signature.
`builder/build.go`	Applies mapping during builds.
`builder/library.go`	Applies mapping to C libraries.
`testdata/trimpath/main.go`	Adds the integration test program.
`testdata/trimpath/main.c`	Adds test C code.
`testdata/trimpath/go.mod`	Defines the test module.
`testdata/trimpath/dependency/go.mod`	Defines the test dependency.
`testdata/trimpath/dependency/dependency.go`	Adds dependency code.
`testdata/trimpath/data.txt`	Adds embedded test data.

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Copilot

Copilot review overview

🟡 Changes recommended

Darwin cross-builds can fail on Windows because the linker preparation requires symbolic-link privileges.

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Fall back to copying when symbolic link creation fails · New

Resolved since last review (1)

Map module root to rewrite external header paths and cache keys

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Copilot review overview

🟡 Changes recommended

Module-less GOPATH packages can still retain absolute paths for shared C headers.

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Use PackageJSON.Root as the source root for GOPATH packages · New

Resolved since last review (1)

Fall back to copying when symbolic link creation fails

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Copilot review overview

🟡 Changes recommended

Synthetic GOROOT paths can still expose an absolute GOCACHE path.

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Map cached synthetic GOROOT to avoid absolute GOCACHE paths · New

Resolved since last review (1)

Use PackageJSON.Root as the source root for GOPATH packages

deadprogram · 2026-09-27T09:41:57Z

I know that this feature is wanted, for example #5275

Any update here?

jakebailey · 2026-09-27T15:39:26Z

Just dealing with copilot back and forth, will undraft when I feel like it's not missing any weird cases.

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Copilot review overview

🔵 Needs a closer look

Cross-platform CGo, DWARF, cache, and linker behavior warrants final human validation.

Review effort: Balanced
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Resolved since last review (1)

Map cached synthetic GOROOT to avoid absolute GOCACHE paths

deadprogram · 2026-09-28T13:23:22Z

@jakebailey please rebase and resolve merge conflicts. Thank you.

deadprogram · 2026-09-28T21:27:14Z

Thanks for all the work on this @jakebailey. I ran the tests on my local machine and took a good look. The following is edited from an automated review:

On targets that use automatic stack sizing, such as -target=pico2, a -trimpath build still contains the local TINYGOROOT/src path. It comes from the DWARF info for internal/task.stackSizes in transform/stacksize.go:86, which calls CreateFile("internal/task/task_stack.go", filepath.Join(goenv.Get("TINYGOROOT"), "src")) and is not changed in this PR. TestTrimPath runs on native, wasm and desktop targets, so it does not cover this path. Perhaps record it as internal/task/task_stack.go with an empty dir when trimming, and add a baremetal target to the test?
Some changes also apply when -trimpath is not set. C and assembly files are now compiled with -working-directory and passed by base name (builder/cc.go:140), CGo snippets get -working-directory=<tmpdir> (builder/build.go:477), CGo parsing always gets -Xclang -working-directory <pkgdir> (loader/loader.go:686), and the cgosnippet and embed object files now have fixed names instead of CreateTemp names. Is that intended for all builds? If so, should the PR description mention it?
Package.RecordedPath (loader/loader.go:435) loops over every package, and then every module dir, for each filename. It runs for each FileHashes entry, each CFlags path and each new DI file. Maybe build the dir to recorded dir table once per program? Seems like it could help on large programs maybe?

What do you think of these?

jakebailey · 2026-09-28T22:15:25Z

Yeah, I think this is true, will look.
That's intentional to match upstream Go and the change isn't possible without it.
I'll see if this can be improved.

Generated CGo globals can share a source position. Break these ties by name so independent compilations produce the same bitcode and ThinLTO symbol names instead of depending on Go map iteration order.

Local source and cache paths make binaries depend on the build directory and expose the builder filesystem layout. Trim these paths from debug information and C __FILE__ strings, including with -no-debug. Leave the compiled-in runtime.GOROOT empty in trimmed builds, matching Go. Match Go's C compilation directories in both modes so trimpath does not change header lookup. Relative C flags now resolve from the source directory instead of the command's working directory. Keep source paths usable for debugger substitution and package-size reports. Compare independent builds with separate caches so cache reuse does not hide nondeterministic output. Fixes 5275

LLD 15 records ThinLTO cache paths and object timestamps in Mach-O outputs. These make trimmed binaries depend on cache location and build time even when their source paths have been removed. LLD 16 changed cached-object handling in https://reviews.llvm.org/D131624. Disable ThinLTO caching only for trimmed Darwin builds on LLVM 15, and suppress object timestamps. Other compilation caches remain enabled. Exercise Darwin trimpath builds in the oldest-toolchain compatibility job.

Some Clang builds record compiler arguments in debug information by default. Those arguments contain source, cache, and temporary paths that prefix maps do not rewrite. Even when the final binary omits that debug information, the paths affect ThinLTO symbol hashes. Disable command-line recording for trimmed C sources and libraries. The LLVM 18.1.8 Darwin regression reproduces this with independent builds.

Compiler-provided headers can live outside the TinyGo source tree when using a system LLVM installation. Their absolute paths remain in DWARF, as seen with __stddef_size_t.h in WASI test binaries on LLVM 18 and 19. Use the known Clang resource directory for trimmed builds so its headers can be recorded under a stable clang path. Apply this to both package compilation and cached libraries.

Trimmed path lookups repeatedly resolve every package and module root. This repeats filesystem work for synthetic GOROOT paths and visits the same module once per package. Build immutable directory mappings after loading the package graph and deduplicate shared roots. Keep package mappings ahead of module mappings, with the same longest-directory and lexical tie-breaking rules. Add lookup benchmarks for 10, 100, and 1000 packages and regression coverage for mapping precedence and path boundaries.

deadprogram

Thank you very much for everything on this @jakebailey now merging!

pjebs · 2026-10-03T02:34:27Z

@jakebailey Was this PR built with AI assistance?

jakebailey · 2026-10-03T02:40:46Z

To some extent, yes

pjebs · 2026-10-03T03:11:18Z

@jakebailey Which model did you use?

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jakebailey marked this pull request as draft September 19, 2026 17:52

jakebailey force-pushed the trimpath branch from 092c129 to 2659e1c Compare September 20, 2026 18:22

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jakebailey marked this pull request as ready for review September 27, 2026 20:12

jakebailey force-pushed the trimpath branch 2 times, most recently from 7080803 to 2f14a87 Compare September 28, 2026 19:28

compiler: make equal-position member ordering deterministic

c294437

Generated CGo globals can share a source position. Break these ties by name so independent compilations produce the same bitcode and ThinLTO symbol names instead of depending on Go map iteration order.

jakebailey added 5 commits September 28, 2026 15:26

jakebailey force-pushed the trimpath branch from 2f14a87 to 6bf41a8 Compare September 28, 2026 22:26

deadprogram approved these changes Sep 30, 2026

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deadprogram merged commit 2119e25 into tinygo-org:dev Sep 30, 2026
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jakebailey deleted the trimpath branch September 30, 2026 17:26

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