Fix linking statics on Arm64EC #140176

dpaoliello · 2025-04-22T22:21:37Z

Arm64EC builds recently started to fail due to the linker not finding a symbol:

symbols.o : error LNK2001: unresolved external symbol #_ZN3std9panicking11EMPTY_PANIC17hc8d2b903527827f1E (EC Symbol)
          C:\Code\hello-world\target\arm64ec-pc-windows-msvc\debug\deps\hello_world.exe : fatal error LNK1120: 1 unresolved externals

It turns out that EMPTY_PANIC is a new static variable that was being exported then imported from the standard library, but when exporting LLVM didn't prepend the name with # (as only functions are prefixed with this character), whereas Rust was prefixing with # when attempting to import it.

The fix is to have Rust not prefix statics with # when importing.

Adding tests discovered another issue: we need to correctly mark static exported from dylibs with DATA, otherwise MSVC's linker assumes they are functions and complains that there is no exit thunk for them.

CI found another bug: we only apply DllImport to non-local statics that aren't foreign items (i.e., in an extern block), that is we want to use DllImport for statics coming from other Rust crates. However, __rust_no_alloc_shim_is_unstable is a static generated by the Rust compiler if required, but downstream crates consider it a foreign item since it is declared in an extern "Rust" block, thus they do not apply DllImport to it and so fails to link if it is exported by the previous crate as DATA. The fix is to apply DllImport to foreign items that are marked with the rustc_std_internal_symbol attribute (i.e., we assume they aren't actually foreign and will be in some Rust crate).

Fixes #138541

try-job: dist-aarch64-msvc
try-job: dist-x86_64-msvc
try-job: x86_64-msvc-1
try-job: x86_64-msvc-2

rustbot · 2025-04-22T22:21:41Z

r? @Nadrieril

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rustbot · 2025-04-22T22:21:43Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

wesleywiser

Changes look good to me. Is it possible to write a regression test? (Either a full-scale integration test that links an exported static from one crate to another or a test that imports a static and dumps the symbol name or something?)

Nadrieril · 2025-04-23T23:21:45Z

r? @wesleywiser

wesleywiser · 2025-04-25T13:19:53Z

@rustbot author

rustbot · 2025-04-25T13:19:57Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rustbot · 2025-04-25T23:45:31Z

This PR modifies run-make tests.

cc @jieyouxu

dpaoliello · 2025-04-25T23:46:25Z

Changes look good to me. Is it possible to write a regression test? (Either a full-scale integration test that links an exported static from one crate to another or a test that imports a static and dumps the symbol name or something?)

Good call, found another bug: we need to correctly export variables as DATA otherwise the linker expects them to have thunks.

@rustbot ready

tests/run-make/crate-import-export-static/rmake.rs

wesleywiser · 2025-04-29T20:02:41Z

Thanks @dpaoliello!

@bors r+ rollup

Also nominating for potential beta backport as this fixes a serious issue for the Tier 2 aarch64-pc-windows-msvc.

bors · 2025-04-29T20:02:44Z

📌 Commit 7370c5c has been approved by wesleywiser

It is now in the queue for this repository.

Fix linking statics on Arm64EC Arm64EC builds recently started to fail due to the linker not finding a symbol: ``` symbols.o : error LNK2001: unresolved external symbol #_ZN3std9panicking11EMPTY_PANIC17hc8d2b903527827f1E (EC Symbol) C:\Code\hello-world\target\arm64ec-pc-windows-msvc\debug\deps\hello_world.exe : fatal error LNK1120: 1 unresolved externals ``` It turns out that `EMPTY_PANIC` is a new static variable that was being exported then imported from the standard library, but when exporting LLVM didn't prepend the name with `#` (as only functions are prefixed with this character), whereas Rust was prefixing with `#` when attempting to import it. The fix is to have Rust not prefix statics with `#` when importing. Adding tests discovered another issue: we need to correctly mark static exported from dylibs with `DATA`, otherwise MSVC's linker assumes they are functions and complains that there is no exit thunk for them. Fixes rust-lang#138541

…enton Rollup of 9 pull requests Successful merges: - rust-lang#139192 (mention provenance in the pointer::wrapping_offset docs) - rust-lang#140176 (Fix linking statics on Arm64EC) - rust-lang#140404 (rm `TypeVistable` impls for `Canonical`) - rust-lang#140437 (enable msa feature for mips in codegen tests) - rust-lang#140438 (Add `rust.debug-assertions-tools` option) - rust-lang#140446 (chore: fix some tests) - rust-lang#140470 (CI: rfl: move job forward to Linux v6.15-rc4) - rust-lang#140476 (chore: delete unused ui/auxiliary crates) - rust-lang#140481 (Require sanitizers be enabled for asan_odr_windows.rs) r? `@ghost` `@rustbot` modify labels: rollup

Zalathar · 2025-04-30T04:17:40Z

Possibly failed in rollup? #140495 (comment)

I'll kick off some try jobs to try to check whether this PR was the cause.

@bors r-

Zalathar · 2025-04-30T04:20:41Z

@bors try

Fix linking statics on Arm64EC Arm64EC builds recently started to fail due to the linker not finding a symbol: ``` symbols.o : error LNK2001: unresolved external symbol #_ZN3std9panicking11EMPTY_PANIC17hc8d2b903527827f1E (EC Symbol) C:\Code\hello-world\target\arm64ec-pc-windows-msvc\debug\deps\hello_world.exe : fatal error LNK1120: 1 unresolved externals ``` It turns out that `EMPTY_PANIC` is a new static variable that was being exported then imported from the standard library, but when exporting LLVM didn't prepend the name with `#` (as only functions are prefixed with this character), whereas Rust was prefixing with `#` when attempting to import it. The fix is to have Rust not prefix statics with `#` when importing. Adding tests discovered another issue: we need to correctly mark static exported from dylibs with `DATA`, otherwise MSVC's linker assumes they are functions and complains that there is no exit thunk for them. Fixes rust-lang#138541 --- try-job: dist-aarch64-msvc try-job: dist-x86_64-msvc try-job: x86_64-msvc-1 try-job: x86_64-msvc-2

bors · 2025-04-30T04:21:51Z

⌛ Trying commit 7370c5c with merge fcf787f...

bors · 2025-04-30T05:09:42Z

💔 Test failed - checks-actions

jieyouxu · 2025-04-30T09:34:00Z

@bors rollup=iffy (linkage gaming)

dpaoliello · 2025-04-30T19:18:45Z

I can repro this locally, will investigate.

@rustbot author

bors · 2025-04-30T21:33:49Z

☔ The latest upstream changes (presumably #140520) made this pull request unmergeable. Please resolve the merge conflicts.

jieyouxu · 2025-05-01T14:10:30Z

This was discussed in today's compiler triage meeting. The team will revisit the backport decision once the PR merges.

wesleywiser · 2025-05-01T22:00:48Z

@bors try

Fix linking statics on Arm64EC Arm64EC builds recently started to fail due to the linker not finding a symbol: ``` symbols.o : error LNK2001: unresolved external symbol #_ZN3std9panicking11EMPTY_PANIC17hc8d2b903527827f1E (EC Symbol) C:\Code\hello-world\target\arm64ec-pc-windows-msvc\debug\deps\hello_world.exe : fatal error LNK1120: 1 unresolved externals ``` It turns out that `EMPTY_PANIC` is a new static variable that was being exported then imported from the standard library, but when exporting LLVM didn't prepend the name with `#` (as only functions are prefixed with this character), whereas Rust was prefixing with `#` when attempting to import it. The fix is to have Rust not prefix statics with `#` when importing. Adding tests discovered another issue: we need to correctly mark static exported from dylibs with `DATA`, otherwise MSVC's linker assumes they are functions and complains that there is no exit thunk for them. CI found another bug: we only apply `DllImport` to non-local statics that aren't foreign items (i.e., in an `extern` block), that is we want to use `DllImport` for statics coming from other Rust crates. However, `__rust_no_alloc_shim_is_unstable` is a static generated by the Rust compiler if required, but downstream crates consider it a foreign item since it is declared in an `extern "Rust"` block, thus they do not apply `DllImport` to it and so fails to link if it is exported by the previous crate as `DATA`. The fix is to apply `DllImport` to foreign items that are marked with the `rustc_std_internal_symbol` attribute (i.e., we assume they aren't actually foreign and will be in some Rust crate). Fixes rust-lang#138541 --- try-job: dist-aarch64-msvc try-job: dist-x86_64-msvc try-job: x86_64-msvc-1 try-job: x86_64-msvc-2

bors · 2025-05-01T22:01:59Z

⌛ Trying commit fc4135f with merge 7db0add...

rustbot assigned Nadrieril Apr 22, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 22, 2025

dpaoliello changed the title ~~[Arm64EC] Only decorate functions with #~~ [Arm64EC] Only decorate functions, not statics, with # Apr 22, 2025

wesleywiser approved these changes Apr 23, 2025

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rustbot assigned wesleywiser and unassigned Nadrieril Apr 23, 2025

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 25, 2025

dpaoliello force-pushed the arm64ecdec branch from 7b715cf to 60f35c8 Compare April 25, 2025 23:45

rustbot added the A-run-make Area: port run-make Makefiles to rmake.rs label Apr 25, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Apr 25, 2025

dpaoliello changed the title ~~[Arm64EC] Only decorate functions, not statics, with #~~ Fix linking statics on Arm64EC Apr 25, 2025

wesleywiser reviewed Apr 29, 2025

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tests/run-make/crate-import-export-static/rmake.rs Outdated Show resolved Hide resolved

dpaoliello force-pushed the arm64ecdec branch from 60f35c8 to b714161 Compare April 29, 2025 17:24

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dpaoliello force-pushed the arm64ecdec branch from b714161 to 7370c5c Compare April 29, 2025 18:12

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ChrisDenton mentioned this pull request Apr 30, 2025

Rollup of 9 pull requests #140495

Closed

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dpaoliello force-pushed the arm64ecdec branch from 7370c5c to b46aea9 Compare May 1, 2025 20:06

[Arm64EC] Only decorate functions with #

fc4135f

dpaoliello force-pushed the arm64ecdec branch from b46aea9 to fc4135f Compare May 1, 2025 20:14

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