Use the .drectve section for exporting symbols from dlls on Windows by bjorn3 · Pull Request #142568 · rust-lang/rust (original) (raw)

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While it would be reasonable to expect the Windows linker to handle linker args in the .drectve section identical to cli arguments, as it turns out exporting weak symbols only works when the /EXPORT is in the .drectve section, not when it is a linker argument or when a .DEF file is used.

Necessary for and extracted out of #142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe!

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Jun 16, 2025

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Jun 16, 2025

Use the .drectve section for exporting symbols from dlls on Windows

Necessary for and extracted out of #142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe! try-job: x86_64-msvc-1 try-job: x86_64-msvc-2

@bors2 try jobs=x86_64-msvc-1,x86_64-msvc-2

⌛ Trying commit c353c7d with merge 3dadabc…

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Jun 16, 2025

Use the .drectve section for exporting symbols from dlls on Windows

Necessary for and extracted out of #142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe! try-job: x86_64-msvc-1 try-job: x86_64-msvc-2

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LGTM.

One overall design question: is it supported for folks to run the linker themselves AND specify their own def file? A couple of my changes broke the Chromium and Fuschia folks, so I'm a little paranoid now about changing anything to do with linking that may affect them.

One overall design question: is it supported for folks to run the linker themselves AND specify their own def file?

This PR on it's own has no effect at all on people running the linker themself. Both the .DEF file and the symbols.o file are only generated when rustc itself runs the linker.

As for a future PR that will use weak definitions, those symbols are not meant to be exported from a staticlib anyway. The only case that could break is if someone (Chromium) tries to link rlibs together into a dll and wants to export all symbols, which we don't officially support anyway. The Chromium people have had to adaot their build system for rustc changes anyway and I expect it to not all that hard to adapt to said future weak symbol usage too.

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Jun 17, 2025

Use the .drectve section for exporting symbols from dlls on Windows

Necessary for and extracted out of #142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe! try-job: x86_64-msvc-1 try-job: x86_64-msvc-2

☀️ Try build successful (CI)
Build commit: e97fbdf (e97fbdf63e618534ac0929eef0229de9fb477dad, parent: 55d436467c351b56253deeba209ae2553d1c243f)

Squashed everything and reverted some now unnecessary changes.

@rustbot ready

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Jun 17, 2025

📌 Commit 7539730 has been approved by wesleywiser

It is now in the queue for this repository.

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Jun 30, 2025

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Jul 1, 2025

…=wesleywiser

Use the .drectve section for exporting symbols from dlls on Windows

Necessary for and extracted out of rust-lang#142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe!

bors added a commit that referenced this pull request

Jul 2, 2025

Rollup of 12 pull requests

Successful merges:

#141829 (Specialize sleep_until implementation for unix (except mac))
#141847 (Explain TOCTOU on the top of std::fs, and reference it in functions)
#142138 (Add Vec::into_chunks)
#142321 (Expose elf abi on ppc64 targets)
#142568 (Use the .drectve section for exporting symbols from dlls on Windows)
#142886 (ci: aarch64-gnu: Stop skipping panic_abort_doc_tests)
#143038 (avoid suggesting traits from private dependencies)
#143194 (fix bitcast of single-element SIMD vectors)
#143206 (Align attr fixes)
#143258 (Don't recompute DisambiguatorState for every RPITIT in trait definition)
#143260 (Use the correct export kind for __rust_alloc_error_handler_should_panic)
#143274 (ci: support optional jobs)

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Jul 3, 2025

Use the .drectve section for exporting symbols from dlls on Windows

Necessary for and extracted out of #142366.

Thanks @dpaoliello for figuring out this weird quirk of link.exe! try-job: dist-i686-msvc

I think def files allow undecorated names, while /export needs the decorated name.

📌 Commit dda12ce has been approved by wesleywiser

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hey, I was wondering what the status of this was. I'm sorry if you've just had no time, that's completely understandable.

It seems that I need to implement symbol mangling for the symbol names that I pass as /export: in .drectve, which requires some refactors to thread through the necessary data like function calling convention and argument sizes to the symbols.o generation location. I haven't had time to work on this yet.

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