bootstrap: use target's LLVM libdir when cross-compiling by heiher · Pull Request #162170 · rust-lang/rust

heiher · 2026-09-02T06:15:55Z

Cargo::cargo adds LLVM's library search path to rustflags for ToolRustcPrivate/Codegen so that tools linking against compiler libraries can find libLLVM. However, it always queried host_llvm_config(), which resolves to the host's llvm-config regardless of the requested target. When cross-compiling, this appends the host's LLVM libdir to the target's link flags, which can cause linking to fail.

Only use llvm-config --libdir when target is the host. Otherwise, ensure the Llvm step for target and derive the libdir from its root_dir() instead of invoking llvm-config, since the resulting binary may not be executable on the host if it was built for a different target.

rustbot · 2026-09-02T06:16:01Z

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Kobzol

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Kobzol · 2026-09-02T07:39:36Z

+                    .to_owned()
+            } else {
+                let llvm_output = self.ensure(Llvm { target });
+                llvm_output.root_dir().join("lib").to_string_lossy().into_owned()


Does this work also on macOS/Windows? That being said, it is surely better than passing the host LLVM libdir :)

It seems to work on macOS/Windows, but I don't have an environment to verify it. Could we test it on CI?

Not sure if we actually cross-compile LLVM on CI somewhere on macOS/Windows. Let's try it.

Wouldn't be hard if you want to try with something like https://github.com/rust-lang/rust/pull/148751/changes#diff-8291d819a8dc37b937e63c4e34dc5b27c59b1725e3ee677ffe0f970711d646df or windows-gnu.
This sounds like a recent-ish regression, as it seemed to work fine last year when gnullvm hosts were still cross-compiled from Linux.

rustbot · 2026-09-04T01:39:20Z

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.

`Cargo::cargo` adds LLVM's library search path to `rustflags` for `ToolRustcPrivate`/`Codegen` so that tools linking against compiler libraries can find `libLLVM`. However, it always queried `host_llvm_config()`, which resolves to the *host*'s `llvm-config` regardless of the requested `target`. When cross-compiling, this appends the host's LLVM libdir to the target's link flags, which can cause linking to fail. Only use `llvm-config --libdir` when `target` is the host. Otherwise, ensure the `Llvm` step for `target` and derive the libdir from its `root_dir()` instead of invoking `llvm-config`, since the resulting binary may not be executable on the host if it was built for a different target.

Kobzol · 2026-09-04T08:20:11Z

I think I was the directory also being named lib on Windows. Let's try it, thanks!

@bors r+ rollup=iffy

rust-bors · 2026-09-04T08:20:14Z

📌 Commit b1e1bc9 has been approved by Kobzol

It is now in the queue for this repository.

bootstrap: use target's LLVM libdir when cross-compiling `Cargo::cargo` adds LLVM's library search path to `rustflags` for `ToolRustcPrivate`/`Codegen` so that tools linking against compiler libraries can find `libLLVM`. However, it always queried `host_llvm_config()`, which resolves to the *host*'s `llvm-config` regardless of the requested `target`. When cross-compiling, this appends the host's LLVM libdir to the target's link flags, which can cause linking to fail. Only use `llvm-config --libdir` when `target` is the host. Otherwise, ensure the `Llvm` step for `target` and derive the libdir from its `root_dir()` instead of invoking `llvm-config`, since the resulting binary may not be executable on the host if it was built for a different target.

Rollup of 14 pull requests Successful merges: - #162324 (miri subtree update) - #162170 (bootstrap: use target's LLVM libdir when cross-compiling) - #158312 (Adds support for AArch64 SVE to inline assembly) - #159792 (A more readable debug map for IndexMaps) - #160745 (make closures act like MaybeDangling) - #161263 (break rustc_expand-rustc_middle dependency) - #161895 (std::sys::pal::sgx: fix mismatched alloc/free alignment) - #161940 (Promote `wasm32-wasip3` to a tier 2 target) - #161397 (coverage: Tidy tests and add some new ones) - #161616 (Report precondition violation for `<usize as SliceIndex>::get_unchecked` in const-eval) - #162248 (Add regression test for unsized const parameter default ICE) - #162250 (Fix hashing of span end columns in incremental compilation) - #162265 (cargotest: add lockfiles) - #162318 (bootstrap: Fix broken path for `./x doc compiler/rustc --open`)

Rollup merge of #162170 - heiher:fix-llvm-libdir, r=Kobzol bootstrap: use target's LLVM libdir when cross-compiling `Cargo::cargo` adds LLVM's library search path to `rustflags` for `ToolRustcPrivate`/`Codegen` so that tools linking against compiler libraries can find `libLLVM`. However, it always queried `host_llvm_config()`, which resolves to the *host*'s `llvm-config` regardless of the requested `target`. When cross-compiling, this appends the host's LLVM libdir to the target's link flags, which can cause linking to fail. Only use `llvm-config --libdir` when `target` is the host. Otherwise, ensure the `Llvm` step for `target` and derive the libdir from its `root_dir()` instead of invoking `llvm-config`, since the resulting binary may not be executable on the host if it was built for a different target.

Rollup of 14 pull requests Successful merges: - rust-lang/rust#162324 (miri subtree update) - rust-lang/rust#162170 (bootstrap: use target's LLVM libdir when cross-compiling) - rust-lang/rust#158312 (Adds support for AArch64 SVE to inline assembly) - rust-lang/rust#159792 (A more readable debug map for IndexMaps) - rust-lang/rust#160745 (make closures act like MaybeDangling) - rust-lang/rust#161263 (break rustc_expand-rustc_middle dependency) - rust-lang/rust#161895 (std::sys::pal::sgx: fix mismatched alloc/free alignment) - rust-lang/rust#161940 (Promote `wasm32-wasip3` to a tier 2 target) - rust-lang/rust#161397 (coverage: Tidy tests and add some new ones) - rust-lang/rust#161616 (Report precondition violation for `<usize as SliceIndex>::get_unchecked` in const-eval) - rust-lang/rust#162248 (Add regression test for unsized const parameter default ICE) - rust-lang/rust#162250 (Fix hashing of span end columns in incremental compilation) - rust-lang/rust#162265 (cargotest: add lockfiles) - rust-lang/rust#162318 (bootstrap: Fix broken path for `./x doc compiler/rustc --open`)

rustbot assigned Mark-Simulacrum Sep 2, 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 Sep 2, 2026

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rustbot assigned Kobzol and unassigned Mark-Simulacrum Sep 2, 2026

heiher force-pushed the fix-llvm-libdir branch from 6ef85c4 to b1e1bc9 Compare September 4, 2026 01:39

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 Sep 4, 2026

JonathanBrouwer mentioned this pull request Sep 4, 2026

Rollup of 13 pull requests #162293

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Zalathar mentioned this pull request Sep 5, 2026

Rollup of 20 pull requests #162317

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JonathanBrouwer mentioned this pull request Sep 5, 2026

Rollup of 14 pull requests #162327

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Zalathar mentioned this pull request Sep 5, 2026

Rollup of 14 pull requests #162333

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rust-bors Bot merged commit 9e9cc06 into rust-lang:main Sep 5, 2026
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rustbot added this to the 1.100.0 milestone Sep 5, 2026

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bootstrap: use target's LLVM libdir when cross-compiling - #162170

bootstrap: use target's LLVM libdir when cross-compiling#162170
rust-bors[bot] merged 1 commit into
rust-lang:mainfrom
heiher:fix-llvm-libdir

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