Add nightly-only support for Cargo unremap trim-paths files in `rust-gdb` by Urgau · Pull Request #160560 · rust-lang/rust

Urgau · 2026-08-05T11:36:33Z

This PR adds support in rust-gdb for the un-remapping file produced by Cargo with -Ztrim-paths (rust-lang/cargo#17303). This support is nightly-only, and only activated when RUST_GDB_TRIM_PATHS=unstable is set.

An example of the unremap file:

{"v":1}
{"rust_version":"1.96.0-nightly","workspace_root":"/home/me/app"}
{"from":"/cargo/build-dir","to":"/home/me/app/target"}
{"from":"/cargo/registry/6f17d22d3f0a95d1","to":"/home/me/.cargo/registry/src/index.crates.io-6f17d22d3f0a95d1"}
{"from":"/rustc/abc123","to":"/home/me/.rustup/toolchains/nightly/lib/rustlib/src/rust"}

Disclaimer: I used Gemini to figure out how to interact with GDB, GDB doc is not very discoverable, everything can be sourced to the docs (links in the source code).

cc @weihanglo

rustbot · 2026-08-05T11:36:39Z

r? @Mark-Simulacrum

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Owners of files modified in this PR: @Mark-Simulacrum

weihanglo · 2026-08-05T11:40:09Z

How should we test this? Do you have any manual steps to follow?

View changes since the review

Side note: I am adding tests in rust-lang/rust exercising the unremap file itself.

I tested it by manually modifying the rust-gdb script to point to my local gdb_trim_paths.py ("$GDB_PYTHON_MODULE_DIRECTORY/gdb_trim_paths.py" to "$YOUR_RUST_LOCAL_CHECKOUT/src/etc/gdb_trim_paths.py"), as otherwise you need to do x.py dist which annoying.

Then I created a dummy hello-world Cargo project, cargo build-it and manually added the hello-world.trim-paths.jsonl file (since the Cargo bump PR is not yet merged).

After that you can just execute rust-gdb as always:

rust-gdb target/debug/hello-world & run

or rust-gdb & file target/debug/hello-world & run

Tip: show substitute-path shows all the substitutions.

Mark-Simulacrum

I think only semi-blocking bits are the shellcheck + linking a tracking issue.

View changes since this review

Mark-Simulacrum · 2026-08-08T23:06:25Z

+
+
+def _load_trim_paths(filepath):
+    trim_paths_path = f"{filepath}.trim-paths.jsonl"


Not blocking (consider it just a thought out of curiosity) -- should this be looking up in some gdb facility for finding these? E.g., so that you can fetch this from debuginfod servers or look next to the debuginfo on disk rather than the actual binary?

That's a interesting idea.

I haven't looked it up much, but it seems like debuginfod works with some kind of "BuildID" to retrieve the debuginfo files. gdb automatically reads the "BuildID" and fetches from debuginfod.

What I haven't figure-out is how to access the fetched content, there doesn't seems to be an easy way for that. We could invoke debuginfod-find debuginfo to "force" the fetch and look inside the fetched content, but that seems a bit hacky.

Leaving a comment inside the script to look at it.

Mark-Simulacrum · 2026-08-08T23:08:26Z

+
+        # Try loading the header line, which contains the version (v) field
+        try:
+            header = json.loads(lines[0])


Not blocking, but it seems a little odd to me to include a version like this as a JSON blob. Maybe we should have magic starting bytes instead? E.g., specifically rust-trim-paths-v1\n?

I think header follow what Cargo also does for SBOM, @weihanglo you know more I think?

I guess my feeling is that if we're going to have a versioned header, I'd much rather treat it as a magic byte sequence than a JSON blob. That seems more reliable against future iteration (e.g., allows us to move away from JSON for it).

Good point, though I think fi we ever change the format, tools should just give up parsing

Sure, but it's generally noisy and more expensive to attempt to parse JSON than to look for a fixed string. Here it's not terrible, we have Python anyway, but if we were doing this in (say) C then that becomes much more gnarly. Of course, if the actual format is JSON then that's no big deal :)

Yeah. I meant we can always change the format in a new toolchain version. People anyway need to align with the parsing logic, so it doesn't matter if this version it is JSON and next becomes ad-hoc binary format.

rustbot · 2026-08-09T09:52:14Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Mark-Simulacrum · 2026-08-09T22:01:02Z

@bors r+ rollup

rust-bors · 2026-08-09T22:01:06Z

📌 Commit 9755a34 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

…rk-Simulacrum Add nightly-only support for Cargo unremap trim-paths files in `rust-gdb` This PR adds support in `rust-gdb` for the un-remapping file produced by Cargo with `-Ztrim-paths` (rust-lang/cargo#17303). This support is nightly-only, and only activated when `RUST_GDB_TRIM_PATHS=unstable` is set. An example of the unremap file: ```json {"v":1} {"rust_version":"1.96.0-nightly","workspace_root":"/home/me/app"} {"from":"/cargo/build-dir","to":"/home/me/app/target"} {"from":"/cargo/registry/6f17d22d3f0a95d1","to":"/home/me/.cargo/registry/src/index.crates.io-6f17d22d3f0a95d1"} {"from":"/rustc/abc123","to":"/home/me/.rustup/toolchains/nightly/lib/rustlib/src/rust"} ```

Rollup of 7 pull requests Successful merges: - #160533 (dirfd dir operations (3/4)) - #160675 (bootstrap: Remove `PATH_REMAP` from command-line selector handling ) - #160807 (Update rustc crate rkyv to 0.8.18) - #160560 (Add nightly-only support for Cargo unremap trim-paths files in `rust-gdb`) - #160804 (Change .expect message on net/parser to follow precondition style) - #160805 (`extern "custom"`: add tests) - #160816 (Mark const ptr methods and free functions as inline(always) to match *mut)

Rollup of 11 pull requests Successful merges: - #160675 (bootstrap: Remove `PATH_REMAP` from command-line selector handling ) - #160807 (Update rustc crate rkyv to 0.8.18) - #159690 (Clarify `--remap-path-scope` impact on `rustc` metadata) - #160560 (Add nightly-only support for Cargo unremap trim-paths files in `rust-gdb`) - #160608 (normalization rework: clean up projection_ty_core) - #160785 (Get rid of LLM disclosure checkboxes) - #160804 (Change .expect message on net/parser to follow precondition style) - #160805 (`extern "custom"`: add tests) - #160816 (Mark const ptr methods and free functions as inline(always) to match *mut) - #160820 (Stabilize fs_set_times) - #160826 (Rename parse_delimited_token_tree in cfg_select)

Rollup merge of #160560 - Urgau:trim-paths-gdb-support, r=Mark-Simulacrum Add nightly-only support for Cargo unremap trim-paths files in `rust-gdb` This PR adds support in `rust-gdb` for the un-remapping file produced by Cargo with `-Ztrim-paths` (rust-lang/cargo#17303). This support is nightly-only, and only activated when `RUST_GDB_TRIM_PATHS=unstable` is set. An example of the unremap file: ```json {"v":1} {"rust_version":"1.96.0-nightly","workspace_root":"/home/me/app"} {"from":"/cargo/build-dir","to":"/home/me/app/target"} {"from":"/cargo/registry/6f17d22d3f0a95d1","to":"/home/me/.cargo/registry/src/index.crates.io-6f17d22d3f0a95d1"} {"from":"/rustc/abc123","to":"/home/me/.rustup/toolchains/nightly/lib/rustlib/src/rust"} ```

rustbot assigned Mark-Simulacrum Aug 5, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Aug 5, 2026

weihanglo reviewed Aug 5, 2026

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Urgau force-pushed the trim-paths-gdb-support branch 3 times, most recently from cb80619 to 410b8d8 Compare August 5, 2026 12:44

weihanglo reviewed Aug 5, 2026

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Comment thread src/etc/gdb_trim_paths.py

Mark-Simulacrum reviewed Aug 8, 2026

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Urgau force-pushed the trim-paths-gdb-support branch from 410b8d8 to 9274382 Compare August 9, 2026 09:52

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Add nightly-only support for Cargo unremap trim-paths files in rust-gdb

9755a34

Urgau force-pushed the trim-paths-gdb-support branch from 6a01cfa to 9755a34 Compare August 9, 2026 10:22

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 9, 2026

jhpratt mentioned this pull request Aug 9, 2026

Rollup of 7 pull requests #160823

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jhpratt mentioned this pull request Aug 10, 2026

Rollup of 11 pull requests #160830

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rust-bors Bot merged commit 7e7fc6f into rust-lang:main Aug 10, 2026
13 checks passed

rustbot added this to the 1.99.0 milestone Aug 10, 2026

Urgau mentioned this pull request Aug 10, 2026

Add nightly-only support for Cargo unremap trim-paths files in rust-lldb #160869

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		def _load_trim_paths(filepath):
		trim_paths_path = f"{filepath}.trim-paths.jsonl"

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