Add experimental `backtrace-trace-only` std feature #143910

ChrisDenton · 2025-07-13T22:57:00Z

This experimentally allows building std with backtrace but without symbolisation. It does not affect stable and requires build-std to use. This doesn't change the backtrace crate itself so relies on the optimizer to remove the unused parts.

Example usage:

# .cargo/config.toml
[unstable]
build-std = ["core", "alloc", "panic_unwind", "std"]
build-std-features = ["backtrace", "backtrace-trace-only", "panic-unwind"]

# Cargo.toml
[profile.release]
opt-level = 3
lto = "thin"
codegen-units = 1

Ideally we should split the backtrace feature into backtrace-trace and backtrace-symbolize (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users.

cc @joshtriplett

rustbot · 2025-07-13T22:57:04Z

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ChrisDenton · 2025-07-14T02:21:21Z

A quick test on an empty bin project does shows a fairly substantial difference in final binary size (exact numbers may vary of course):

platform	symbolize	trace only	diff
Linux	426 KiB	123 KiB	303 KiB
Windows	125 KiB	70 KiB	55 KiB

library/std/src/sys/backtrace.rs

library/std/Cargo.toml

tgross35 · 2025-07-14T04:27:34Z

Two comments then r=me

Ideally we should split the backtrace feature into backtrace-trace and backtrace-symbolize (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users.

Any idea why we don't have a default feature in std? If we did it would make this change a bit easier. I assume probably something related to bootstrap / config options.

bjorn3 · 2025-07-14T06:18:38Z

library/std/Cargo.toml

@@ -92,6 +92,7 @@ backtrace = [
    'object/rustc-dep-of-std',
    'miniz_oxide/rustc-dep-of-std',
 ]
+backtrace-trace-only = []


This will still compile addr2line, gimli and object. Maybe instead have a feature to enable just backtraces and then another feature which enables this feature and in addition enables backtrace symbolication.
Edit: You already suggested that in the PR description.

Yeah, doing this fully will require making changes to backtrace-rs, which I'm trying to avoid for the initial implementation. Also, although it's unstable, I don't want to break people currently using build-std-features just yet.

bjorn3 · 2025-07-14T06:26:04Z

library/std/src/sys/backtrace.rs

+            if cfg!(feature = "backtrace-trace-only") {
+                const HEX_WIDTH: usize = 2 + 2 * core::mem::size_of::<usize>();
+                let frame_ip = frame.ip();
+                res = writeln!(bt_fmt.formatter(), "{idx:4}: {frame_ip:HEX_WIDTH$?}");


To be able to actually symbolize the backtraces this would need to print both the path of the DSO (executable or dylib) and the offset within this DSO. It could be a dylib loaded at runtime and thanks to ASLR the exact location of DSOs can't be determined anymore after the fact unless we print it here.

This could take inspiration on what backtrace-rs does on Fuchsia which unconditionally does backtrace symbolication out of process.

How does this work normally when symbols aren't available? The backtrace is just unusable?

Yeah, I don't think the backtraces are all that usable without symbols when ASLR is disabled. I guess it still shows symbol names for system libraries.

Ok, I'm going to punt on doing the hard thing again 🙂. This is (arguably) a pre-existing issue and at least somewhat platform specific so would be much better fixed in backtrace-rs than std. This feature can then use whatever backtrace-rs has once that's written.

hanna-kruppe · 2025-07-14T08:28:21Z

cc #139209

ChrisDenton · 2025-07-14T11:58:49Z

Any idea why we don't have a default feature in std? If we did it would make this change a bit easier. I assume probably something related to bootstrap / config options.

I've no idea tbh.

I'd note that designing a build-std MVP suitable for stabilisation is now a project goal, which is likely to bring changes to how it all works. Another reason not to be too disruptive at this point.

ChrisDenton · 2025-07-14T13:13:22Z

@bors r=tgross35 rollup

bors · 2025-07-14T13:13:25Z

📌 Commit 9fd3886 has been approved by tgross35

It is now in the queue for this repository.

…ross35 Add experimental `backtrace-trace-only` std feature This experimentally allows building std with backtrace but without symbolisation. It does not affect stable and requires build-std to use. This doesn't change the backtrace crate itself so relies on the optimizer to remove the unused parts. Example usage: ```toml # .cargo/config.toml [unstable] build-std = ["core", "alloc", "panic_unwind", "std"] build-std-features = ["backtrace", "backtrace-trace-only", "panic-unwind"] ``` ```toml # Cargo.toml [profile.release] opt-level = 3 lto = "thin" codegen-units = 1 ``` Ideally we should split the backtrace feature into `backtrace-trace` and `backtrace-symbolize` (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users. cc `@joshtriplett`

…ross35 Add experimental `backtrace-trace-only` std feature This experimentally allows building std with backtrace but without symbolisation. It does not affect stable and requires build-std to use. This doesn't change the backtrace crate itself so relies on the optimizer to remove the unused parts. Example usage: ```toml # .cargo/config.toml [unstable] build-std = ["core", "alloc", "panic_unwind", "std"] build-std-features = ["backtrace", "backtrace-trace-only", "panic-unwind"] ``` ```toml # Cargo.toml [profile.release] opt-level = 3 lto = "thin" codegen-units = 1 ``` Ideally we should split the backtrace feature into `backtrace-trace` and `backtrace-symbolize` (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users. cc ``@joshtriplett``

Rollup of 16 pull requests Successful merges: - #142301 (tests: Fix duplicated-path-in-error fail with musl) - #142936 (rustdoc-json: Structured attributes) - #143355 (wrapping shift: remove first bitmask and table) - #143630 (Drop `./x suggest`) - #143738 (Move several float tests to floats/mod.rs) - #143752 (Don't panic if WASI_SDK_PATH not set when detecting compiler) - #143820 (Fixed a core crate compilation failure when enabling the `optimize_for_size` feature on some targets) - #143837 (Adjust `run_make_support::symbols` helpers) - #143878 (Port `#[pointee]` to the new attribute parsing infrastructure) - #143907 (core: make `str::split_at_unchecked()` inline) - #143910 (Add experimental `backtrace-trace-only` std feature) - #143927 (Preserve constness in trait objects up to hir ty lowering) - #143935 (rustc_type_ir/walk: move docstring to `TypeWalker` itself) - #143938 (Update books) - #143941 (update `cfg_select!` documentation) - #143948 (Update mdbook to 0.4.52) Failed merges: - #143926 (Remove deprecated fields in bootstrap) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 13 pull requests Successful merges: - #142301 (tests: Fix duplicated-path-in-error fail with musl) - #143630 (Drop `./x suggest`) - #143736 (Give all bytes of TypeId provenance) - #143752 (Don't panic if WASI_SDK_PATH not set when detecting compiler) - #143837 (Adjust `run_make_support::symbols` helpers) - #143878 (Port `#[pointee]` to the new attribute parsing infrastructure) - #143905 (Recover and suggest to use `;` to construct array type) - #143907 (core: make `str::split_at_unchecked()` inline) - #143910 (Add experimental `backtrace-trace-only` std feature) - #143927 (Preserve constness in trait objects up to hir ty lowering) - #143935 (rustc_type_ir/walk: move docstring to `TypeWalker` itself) - #143938 (Update books) - #143941 (update `cfg_select!` documentation) Failed merges: - #143926 (Remove deprecated fields in bootstrap) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143910 - ChrisDenton:no-symbolization, r=tgross35 Add experimental `backtrace-trace-only` std feature This experimentally allows building std with backtrace but without symbolisation. It does not affect stable and requires build-std to use. This doesn't change the backtrace crate itself so relies on the optimizer to remove the unused parts. Example usage: ```toml # .cargo/config.toml [unstable] build-std = ["core", "alloc", "panic_unwind", "std"] build-std-features = ["backtrace", "backtrace-trace-only", "panic-unwind"] ``` ```toml # Cargo.toml [profile.release] opt-level = 3 lto = "thin" codegen-units = 1 ``` Ideally we should split the backtrace feature into `backtrace-trace` and `backtrace-symbolize` (with the latter dependent on the former) because Cargo features tend to work better when they're positive rather than negative. But I'm keen for this experiment not to break existing users. cc ``@joshtriplett``

rustbot assigned tgross35 Jul 13, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jul 13, 2025

ChrisDenton force-pushed the no-symbolization branch 4 times, most recently from f7963bb to 1dccc65 Compare July 14, 2025 01:28

tgross35 reviewed Jul 14, 2025

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Add experimental backtrace-trace-only std feature

9fd3886

ChrisDenton force-pushed the no-symbolization branch from 1dccc65 to 9fd3886 Compare July 14, 2025 11:53

bors 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 Jul 14, 2025

Kobzol mentioned this pull request Jul 14, 2025

Rollup of 14 pull requests #143946

Closed

jhpratt mentioned this pull request Jul 15, 2025

Rollup of 16 pull requests #143951

Closed

samueltardieu mentioned this pull request Jul 15, 2025

Rollup of 13 pull requests #143958

Merged

bors merged commit 2e37e24 into rust-lang:master Jul 15, 2025
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rustbot added this to the 1.90.0 milestone Jul 15, 2025

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