Allow linking a prebuilt optimized compiler-rt builtins library #143689

pmur · 2025-07-09T15:40:39Z

Extend the .optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

rustbot · 2025-07-09T15:40:46Z

r? @Kobzol

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rustbot · 2025-07-09T15:40:48Z

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

This PR modifies bootstrap.example.toml.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

compiler-builtins is developed in its own repository. If possible, consider making this change to rust-lang/compiler-builtins instead.

cc @tgross35

Kobzol · 2025-07-09T19:22:53Z

I don't really know much about the optimized compiler-rt builtins. Maybe @tgross35 might know more?

Mark-Simulacrum · 2025-07-09T22:54:33Z

Can you say more about how much time this saves? Historically it's been my impression locally that building is basically free, this flag is more about whether it's possible to build (e.g., needs to be off if you're ad-hoc cross compiling). Though maybe I'm remembering wrong?

pmur · 2025-07-10T14:34:10Z

Can you say more about how much time this saves? Historically it's been my impression locally that building is basically free, this flag is more about whether it's possible to build (e.g., needs to be off if you're ad-hoc cross compiling). Though maybe I'm remembering wrong?

The goal is to enable optimized compiler-builtins in fedora packaging. There, rust is built using the distro provided llvm and resulting libraries. Some runtime features are absent if optimized compiler-builtins are not used. Notably, outlined aarch64 LSE atomic operations are not available without this support.

cuviper · 2025-07-10T16:40:26Z

Right, it's less about time and more about wanting to use our existing system LLVM packages.

pmur · 2025-07-22T22:07:21Z

Ping @tgross35. The intent here is to enable optimized-builtins in Fedora using the system's compiler-rt.builtins library.

tgross35

The changes to compiler-builtins lgtm with a possible rename of the var, assuming you have verified this works locally. Somebody more familiar with bootstrap (@Kobzol?) will need to review the changes there.

src/bootstrap/src/core/build_steps/compile.rs

library/compiler-builtins/compiler-builtins/build.rs

pmur · 2025-07-28T20:47:40Z

The changes to compiler-builtins lgtm with a possible rename of the var, assuming you have verified this works locally. Somebody more familiar with bootstrap (@Kobzol?) will need to review the changes there.

I did test builds with the fedora targets (excepting s390x, it lacks a libcompiler-rt.builtins library in rawhide right now). Likewise, I verified the LSE support linked in for aarch64 does work.

Is it a realistic case to consider something trying to link libgcc.a or libcompiler-rt.builtins.a when std already includes a copy of libcompiler-rt.builtins? That case I haven't tested.

tgross35 · 2025-08-01T06:29:30Z

library/compiler-builtins/compiler-builtins/build.rs

+            if let Some(dir) = rt_builtins_ext.parent() {
+                println!("cargo::rustc-link-search=native={}", dir.display());
+            }
+            println!(
+                "cargo::rustc-link-lib=static:+verbatim={}",
+                rt_builtins_ext.to_str().unwrap()
+            );


Does println!("cargo::rustc-link-arg={}", rt_builtins_ext.to_str().unwrap()) work to replace these by chance? I think passing the exact path to the linker should avoid needing to set both -l and -L.

That seems like it should work, but trying locally (x86-64-unknown-linux-gnu) didn't work as expected. The builtins library wasn't copied into the .rlib as is the case with the above or letting rust built them.

tgross35 · 2025-08-01T06:41:03Z

Is it a realistic case to consider something trying to link libgcc.a or libcompiler-rt.builtins.a when std already includes a copy of libcompiler-rt.builtins? That case I haven't tested.

I think this can happen in niche build setups, but no special handling should be needed; all three libraries make their builtin symbols weak, so conflicts aren't a problem.

bors · 2025-08-01T14:45:20Z

☔ The latest upstream changes (presumably #144773) made this pull request unmergeable. Please resolve the merge conflicts.

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? `@tgross35`

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? ``@tgross35``

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? ```@tgross35```

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? ````@tgross35````

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? `````@tgross35`````

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? ``````@tgross35``````

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled Add dynamic support for aarch64 LSE atomic ops on linux/gnu targets when optimized-compiler-builtins is not enabled. Enabling LSE is the primary motivator for rust-lang#143689, though extending the rust version doesn't seem too farfetched. Are there more details which I have overlooked which make this impractical? I've tested this on an aarch64 host with LSE. r? ```````@tgross35```````

Kobzol

Since this changes config options, you could also add a change entry to change_tracker.rs, but this is probably so niche that it's not even needed.

LGTM from my side.

pmur · 2025-08-20T20:34:22Z

Thanks. I also tried to improve the documentation in bootstrap.example.toml too.

bors · 2025-08-22T22:36:47Z

☔ The latest upstream changes (presumably #145352) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2025-08-25T20:54:37Z

☔ The latest upstream changes (presumably #145472) made this pull request unmergeable. Please resolve the merge conflicts.

Extend the <target>.optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

Create a dedicated enum to abstract the different ways compiler-builtins can be configured. This also relaxes build.optimized-compiler-builtins to accept the path of a library to match the behavior of <target>.optimized-compiler-builtins override.

rustbot · 2025-08-25T21:10:40Z

This PR was rebased onto a different master 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.

tgross35 · 2025-08-25T22:52:50Z

Thanks for the updates, LGTM as well
@bors r=Kobzol,tgross35

bors · 2025-08-25T22:52:52Z

📌 Commit 148a07c has been approved by Kobzol,tgross35

It is now in the queue for this repository.

…mpiler-builtins, r=Kobzol,tgross35 Allow linking a prebuilt optimized compiler-rt builtins library Extend the <target>.optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

Rollup of 13 pull requests Successful merges: - #143193 (Port `#[link]` to the new attribute parsing infrastructure ) - #143689 (Allow linking a prebuilt optimized compiler-rt builtins library) - #144885 (Implement some more checks in `ptr_guaranteed_cmp`. ) - #145535 (make rustdoc::invalid_html_tags more robust) - #145766 (test(rustfmt): Verify frontmatter is preserved) - #145811 (Fix some minor issues in comments) - #145814 (Handle unwinding fatal errors in codegen workers) - #145815 (Wait for DPkg frontend lock when trying to remove packages) - #145821 (compiletest: if a compiler fails, show its output) - #145845 (Make `x test distcheck` self-contained) - #145847 (Don't show warnings from xcrun with -Zverbose-internals) - #145856 (Update books) - #145858 (Update wasm-component-ld dependency) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 12 pull requests Successful merges: - #143689 (Allow linking a prebuilt optimized compiler-rt builtins library) - #144885 (Implement some more checks in `ptr_guaranteed_cmp`. ) - #145535 (make rustdoc::invalid_html_tags more robust) - #145766 (test(rustfmt): Verify frontmatter is preserved) - #145811 (Fix some minor issues in comments) - #145814 (Handle unwinding fatal errors in codegen workers) - #145815 (Wait for DPkg frontend lock when trying to remove packages) - #145821 (compiletest: if a compiler fails, show its output) - #145845 (Make `x test distcheck` self-contained) - #145847 (Don't show warnings from xcrun with -Zverbose-internals) - #145856 (Update books) - #145858 (Update wasm-component-ld dependency) r? `@ghost` `@rustbot` modify labels: rollup

…tins, r=Kobzol,tgross35 Allow linking a prebuilt optimized compiler-rt builtins library Extend the <target>.optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

bors · 2025-08-26T08:03:33Z

⌛ Testing commit 148a07c with merge 822f4de...

Zalathar · 2025-08-26T08:26:57Z

Yielding to enclosing rollup, which flaked out.

@bors retry

Rollup of 12 pull requests Successful merges: - #143689 (Allow linking a prebuilt optimized compiler-rt builtins library) - #144885 (Implement some more checks in `ptr_guaranteed_cmp`. ) - #145535 (make rustdoc::invalid_html_tags more robust) - #145766 (test(rustfmt): Verify frontmatter is preserved) - #145811 (Fix some minor issues in comments) - #145814 (Handle unwinding fatal errors in codegen workers) - #145815 (Wait for DPkg frontend lock when trying to remove packages) - #145821 (compiletest: if a compiler fails, show its output) - #145845 (Make `x test distcheck` self-contained) - #145847 (Don't show warnings from xcrun with -Zverbose-internals) - #145856 (Update books) - #145858 (Update wasm-component-ld dependency) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #143689 - pmur:murp/external-rt-optimized-compiler-builtins, r=Kobzol,tgross35 Allow linking a prebuilt optimized compiler-rt builtins library Extend the <target>.optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

rustbot assigned Kobzol Jul 9, 2025

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pmur force-pushed the murp/external-rt-optimized-compiler-builtins branch from 27fcb13 to 1ea1789 Compare July 9, 2025 18:29

tgross35 self-assigned this Jul 9, 2025

cuviper mentioned this pull request Jul 10, 2025

Don't panic if WASI_SDK_PATH not set when detecting compiler #143752

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pmur force-pushed the murp/external-rt-optimized-compiler-builtins branch from 1ea1789 to 8ce8e15 Compare July 24, 2025 16:20

pmur mentioned this pull request Jul 30, 2025

compiler-builtins: plumb LSE support for aarch64 on linux/gnu when optimized-compiler-builtins not enabled #144705

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pmur force-pushed the murp/external-rt-optimized-compiler-builtins branch from 8ce8e15 to f8de502 Compare August 4, 2025 21:23

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pmur force-pushed the murp/external-rt-optimized-compiler-builtins branch from 12172b6 to c1d67ef Compare August 25, 2025 14:54

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Paul Murphy and others added 2 commits August 25, 2025 16:08

Allow linking a prebuilt optimized compiler-rt builtins library

64cbe52

Extend the <target>.optimized-compiler-builtins bootstrap option to accept a path to a prebuilt compiler-rt builtins library, and update compiler-builtins to enable optimized builtins without building compiler-rt builtins.

pmur force-pushed the murp/external-rt-optimized-compiler-builtins branch from c1d67ef to 148a07c Compare August 25, 2025 21:10

tgross35 approved these changes Aug 25, 2025

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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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 25, 2025

Zalathar mentioned this pull request Aug 26, 2025

Rollup of 13 pull requests #145865

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Zalathar mentioned this pull request Aug 26, 2025

Rollup of 12 pull requests #145871

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bors merged commit 2741508 into rust-lang:master Aug 26, 2025
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rustbot added this to the 1.91.0 milestone Aug 26, 2025

Allow linking a prebuilt optimized compiler-rt builtins library #143689

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