Install LLVM DLL in the right place on Windows by mati865 · Pull Request #152609 · rust-lang/rust

mati865 · 2026-02-14T09:41:27Z

Continuation of #151795 towards #151774.

Unlike other systems, Windows requires runtime libraries to be present in PATH or right next to the binary.
So, we copy the library next to the binary as the easier solution.

Tested building rust-openssl in debug and release modes, but the difference is within noise margin.

rustbot · 2026-02-14T09:41:31Z

r? @Mark-Simulacrum

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bjorn3 · 2026-02-14T10:45:38Z

src/bootstrap/src/core/builder/mod.rs

+    /// compiler's sysroot.
+    ///
+    /// For example this returns `lib` on Unix and `bin` on Windows.
+    pub fn sysroot_runtime_libdir_relative(&self, compiler: Compiler) -> PathBuf {


What is the difference with relative_libdir? And if there is difference when should you choose this one over relative_libdir and vice versa?

To be honest, I have no idea what is the deal with stage == 0, but I thought leaving it there would be safer.

Also, libdir_relative doesn't "Windowsize" the path, so uncommenting install.libdir in bootstrap.toml will result in a broken Windows build because the DLLs would go to build/host/stage1/lib.
Although I don't know how much we should care about it since it doesn't work anyway. With this PR, libLLVM will correctly go to stage1/bin, but rustc_driver and std still go to stage1/lib.

Technically, all shared objects should be handled by sysroot_runtime_libdir_relative or similar function.

I can change this PR to use relative_libdir for installing LLVM, if we don't care about install.libdir case and stage0 is not a problem.

install.libdir is meant for the Unix world, not for Windows. Setting install.libdir on Windows probably already results in a broken build before this PR as rustc_driver.dll ends up in the wrong dir.

Fair enough, removed the new helper.

bjorn3 · 2026-02-14T14:45:08Z

src/bootstrap/src/core/build_steps/dist.rs

@@ -2533,7 +2533,7 @@ fn maybe_install_llvm(
    ),
 )]
 pub fn maybe_install_llvm_target(builder: &Builder<'_>, target: TargetSelection, sysroot: &Path) {
-    let dst_libdir = sysroot.join("lib/rustlib").join(target).join("lib");
+    let dst_libdir = sysroot.join("lib/rustlib").join(target).join(libdir(target));


Rustc probably expects it in lib when linking. I don't think this copy of the LLVM dylib is every used at runtime.

That wouldn't work well on Windows. With both GNU toolchains you can link to DLL directly, but it's a hit-or-miss situation. Linking via import library is the right way to do it.
With MSVC's link.exe and lld-link the situation is clearer - you cannot link DLL directly at all, the import library is the only way.

Maybe we don't need it at all and should bundle the import library instead on Windows?

This function should be installing both the DLL and the import library into the rustc linker path. Putting just the import library in rustlib and having a single copy of LLVM.dll in $(rustc --print sysroot)/bin would make sense to me. Doesn't have to be in the same PR IMO.

Currently it only installs the DLL. I'll revert this change when I'm back home.

Mark-Simulacrum · 2026-02-14T22:25:49Z

r? @bjorn3 perhaps? Seems like you have more context/knowledge here.

Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution.

bjorn3 · 2026-02-15T12:38:03Z

@bors try jobs=dist-x86_64-llvm-mingw

Please verify that the resulting toolchain can still build custom rustc drivers like miri. I don't have access to a Windows machine to check myself. r=me if that still works.

Install LLVM DLL in the right place on Windows try-job: dist-x86_64-llvm-mingw

rust-bors · 2026-02-15T14:38:40Z

☀️ Try build successful (CI)
Build commit: f0ea08a (f0ea08a0f2730b2678044d4dccd0ad5e0374f562, parent: ce0bf0b22b646bacf91f73393483f684a44848ca)

mati865 · 2026-02-15T16:18:01Z

It fails to find -lLLVM-22-rust-1.95.0-nightly because lib/rustlib/x86_64-pc-windows-gnullvm/lib (nor bin) is added to linker's search path. I'll look tomorrow why it's not being added.

@rustbot author

mati865 · 2026-02-15T16:39:12Z

@bors try jobs=dist-x86_64-llvm-mingw

Install LLVM DLL in the right place on Windows try-job: dist-x86_64-llvm-mingw

rust-bors · 2026-02-15T18:30:02Z

☀️ Try build successful (CI)
Build commit: 6faffc6 (6faffc66527e366ec8729ee8a6c91814460532c7, parent: 4c37f6d78c9c83e05caa0d1e43ce7d0c3f27538e)

mati865 · 2026-02-15T18:52:45Z

Looks like that was it.
This time ./miri build succeeded after a minute and ./miri test reports 13 passes and 73 ignored tests.

bjorn3 · 2026-02-15T19:23:39Z

@bors r+ rollup=iffy

rust-bors · 2026-02-15T19:23:42Z

📌 Commit 585297c has been approved by bjorn3

It is now in the queue for this repository.

Install LLVM DLL in the right place on Windows Continuation of rust-lang#151795 towards rust-lang#151774. Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution. Tested building `rust-openssl` in debug and release modes, but the difference is within noise margin.

mati865 · 2026-02-15T19:34:57Z

@bors r-

I need to reword that wip commit.

@JonathanBrouwer could you cancel the rollup? Sorry for the trouble.

rust-bors · 2026-02-15T19:35:03Z

Commit 585297c has been unapproved.

This PR was contained in a rollup (#152678), which was also unapproved.

JonathanBrouwer · 2026-02-15T19:56:02Z

With new bors the rollup is automatically unapproved if you r- :)

mati865 · 2026-02-16T14:51:42Z

Only updated the comments, so it probably doesn't require re-review.

@bors r=bjorn3

With new bors the rollup is automatically unapproved if you r- :)

Yeah, that's a great feature. I didn't know about it before bors reply.

rust-bors · 2026-02-16T14:51:45Z

📌 Commit 1d1280a has been approved by bjorn3

It is now in the queue for this repository.

Install LLVM DLL in the right place on Windows Continuation of rust-lang#151795 towards rust-lang#151774. Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution. Tested building `rust-openssl` in debug and release modes, but the difference is within noise margin.

…uwer Rollup of 6 pull requests Successful merges: - #152700 (miri subtree update) - #152715 (`rust-analyzer` subtree update) - #152609 (Install LLVM DLL in the right place on Windows) - #152206 (misc doc improvements) - #152664 (Fix mis-constructed `file_span` when generating scraped examples) - #152698 (Suppress unstable-trait notes under `-Zforce-unstable-if-unmarked`)

JonathanBrouwer · 2026-02-17T08:54:04Z

Since the rest of #152718 (comment) has been merged now, the failure there is either this PR or spurious
I'm expecting it to be spurious but will try to be sure
@bors try jobs=x86_64-msvc-1

Install LLVM DLL in the right place on Windows try-job: x86_64-msvc-1

rust-bors · 2026-02-17T11:43:59Z

☀️ Try build successful (CI)
Build commit: 907dd07 (907dd0769a3f21c240a2e795974b1752b1b3566f, parent: d1a11b670b617f1370f7b1cdf86e225a4e070f15)

Install LLVM DLL in the right place on Windows Continuation of rust-lang#151795 towards rust-lang#151774. Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution. Tested building `rust-openssl` in debug and release modes, but the difference is within noise margin.

Rollup of 6 pull requests Successful merges: - #152609 (Install LLVM DLL in the right place on Windows) - #149904 (`-Znext-solver` Remove the forced ambiguity hack from search graph) - #152704 (Remove `QueryCtxt` and trait `HasDepContext`) - #152746 (remove `#![allow(stable_features)]` from most tests) - #152675 (Improve `VaList` stdlib docs) - #152748 (Update `sysinfo` version to `0.38.2`)

Rollup merge of #152609 - mati865:gnullvm-llvm-dll, r=bjorn3 Install LLVM DLL in the right place on Windows Continuation of #151795 towards #151774. Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution. Tested building `rust-openssl` in debug and release modes, but the difference is within noise margin.

ZuseZ4 · 2026-02-17T17:51:54Z

Thanks again!

rustbot assigned Mark-Simulacrum Feb 14, 2026

mati865 mentioned this pull request Feb 14, 2026

[Proof of concept] Build shared LLVM lib for gnullvm #151795

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bjorn3 reviewed Feb 14, 2026

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mati865 force-pushed the gnullvm-llvm-dll branch from 6707f87 to 425ec35 Compare February 14, 2026 13:59

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rustbot assigned bjorn3 and unassigned Mark-Simulacrum Feb 14, 2026

Install LLVM DLL in the right place on Windows

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Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary. So, we copy the library next to the binary as the easier solution.

mati865 force-pushed the gnullvm-llvm-dll branch from 425ec35 to c91c21b Compare February 15, 2026 12:31

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Auto merge of #152609 - mati865:gnullvm-llvm-dll, r=<try>

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Install LLVM DLL in the right place on Windows try-job: dist-x86_64-llvm-mingw

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Auto merge of #152609 - mati865:gnullvm-llvm-dll, r=<try>

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Install LLVM DLL in the right place on Windows try-job: dist-x86_64-llvm-mingw

JonathanBrouwer mentioned this pull request Feb 15, 2026

Rollup of 2 pull requests #152678

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mati865 added 2 commits February 16, 2026 14:26

Add LLVM lib location to the linker search paths

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Build shared LLVM lib for windows-gnullvm

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mati865 force-pushed the gnullvm-llvm-dll branch from 585297c to 1d1280a Compare February 16, 2026 14:22

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Rollup of 6 pull requests #152718

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Auto merge of #152609 - mati865:gnullvm-llvm-dll, r=<try>

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Install LLVM DLL in the right place on Windows try-job: x86_64-msvc-1

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Rollup of 6 pull requests #152754

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Rollup of 6 pull requests #152755

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rust-bors bot merged commit 485f76b into rust-lang:main Feb 17, 2026
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