error out when repr(align) exceeds COFF limit

[nthery]

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The PE-COFF binary format limits section alignment to 8192 bytes. Emit error when alignment exceeds this limit to avoid crash in llvm.

Closes #142386.

Reference PR:

• document COFF alignment limit reference#2081

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[rustbot]

Some changes occurred in diagnostic error codes

cc @GuillaumeGomez

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann

[workingjubilee]

It only needs to error if we generate a static based on this.

[folkertdev]

Could you include testing alignment on functions here in this PR (if relevant, but I suspect it is). I think you can just add it to the test files you already modify.

#![feature(fn_align)]

// ...

// and then you can annotate a function with `#[repr(align(N))]`
#[repr(align(16))]
fn foo() {}

[workingjubilee]

@nthery This simple version that rejects repr(align(0x4000)) will need to be cratered. Nonetheless please finish writing up the PR so we can do so.

[workingjubilee]

...wait, we can't crater for Windows.

[workingjubilee]

fbbth.

[bors]

☔ The latest upstream changes (presumably #138165) made this pull request unmergeable. Please resolve the merge conflicts.

[nthery]

Could you include testing alignment on functions here in this PR (if relevant, but I suspect it is). I think you can just add it to the test files you already modify.

#![feature(fn_align)]

// ...

// and then you can annotate a function with `#[repr(align(N))]`
#[repr(align(16))]
fn foo() {}

It is relevant indeed. I reproduced the original bug with a function alignment exceeding 0x2000 bytes. Thanks for spotting this. I will add some test points.

[nthery]

We should document this in the Reference, in:

• https://doc.rust-lang.org/1.90.0/reference/type-layout.html#r-layout.repr.alignment

@nthery, would you perhaps be interested in putting up a PR for that?

Here is the PR: rust-lang/reference#2081.

[traviscross]

Thanks for that.

@rfcbot reviewed

cc @rust-lang/fls

[rust-rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[workingjubilee]

I suspect we'll get such feedback soon enough, but I also think that the fastest way to find out is the old "throw it over the wall and see who screams" tactic, so!

@bors r+

[bors]

📌 Commit a8fc845 has been approved by workingjubilee

It is now in the queue for this repository.

[bors]

⌛ Testing commit a8fc845 with merge dcd6fb3...

[rust-log-analyzer]

The job aarch64-msvc-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [ui] tests\ui\structs-enums\align-struct.rs stdout ----

error: test compilation failed although it shouldn't!
status: exit code: 1
command: PATH="C:\a\rust\rust\build\aarch64-pc-windows-msvc\stage2\bin;C:\Program Files (x86)\Windows Kits\10\bin\arm64;C:\Program Files (x86)\Windows Kits\10\bin\10.0.26100.0\arm64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\bin\HostARM64\arm64;C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\bin\HostARM64\arm64;C:\a\rust\rust\build\aarch64-pc-windows-msvc\bootstrap-tools\aarch64-pc-windows-msvc\release\deps;C:\Program Files\Git\clangarm64\bin;C:\Program Files\Git\usr\bin;C:\Users\runneradmin\bin;C:\a\rust\rust\ninja;C:\a\rust\rust\citools\clang-rust\bin;C:\a\rust\rust\sccache;C:\aliyun-cli;C:\vcpkg;C:\Program Files (x86)\NSIS;C:\Program Files\Mercurial;C:\hostedtoolcache\windows\stack\3.7.1\x64;C:\mingw64\bin;C:\Program Files\dotnet;C:\Program Files\MySQL\MySQL Server 8.0\bin;C:\Program Files (x86)\R\R-4.5.1\bin\x64;C:\SeleniumWebDrivers\GeckoDriver;C:\SeleniumWebDrivers\EdgeDriver;C:\SeleniumWebDrivers\ChromeDriver;C:\Program Files (x86)\sbt\bin;C:\Program Files (x86)\GitHub CLI;C:\Program Files\Git\usr\bin;C:\Program Files (x86)\pipx_bin;C:\npm\prefix;C:\hostedtoolcache\windows\go\1.24.9\arm64\bin;C:\hostedtoolcache\windows\Python\3.12.10\arm64\Scripts;C:\hostedtoolcache\windows\Python\3.12.10\arm64;C:\hostedtoolcache\windows\Ruby\3.4.7\aarch64\bin;C:\Program Files\OpenSSL\bin;C:\tools\kotlinc\bin;C:\hostedtoolcache\windows\Java_Temurin-Hotspot_jdk\21.0.8-9.0\aarch64\bin;C:\Program Files (x86)\ImageMagick-7.1.2-Q16-HDRI;C:\Program Files\Microsoft SDKs\Azure\CLI2\wbin;C:\ProgramData\kind;C:\ProgramData\Chocolatey\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Windows\System32\OpenSSH;C:\Program Files\PowerShell\7;C:\Program Files\Microsoft\Web Platform Installer;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn;C:\Program Files\Microsoft SQL Server\150\Tools\Binn;C:\Program Files\dotnet;C:\Program Files (x86)\Windows Kits\10\Windows Performance Toolkit;C:\Program Files\Microsoft SQL Server\130\DTS\Binn;C:\Program Files\Microsoft SQL Server\140\DTS\Binn;C:\Program Files\Microsoft SQL Server\150\DTS\Binn;C:\Program Files\Microsoft SQL Server\160\DTS\Binn;C:\Program Files\Microsoft SQL Server\170\DTS\Binn;C:\Strawberry\c\bin;C:\Strawberry\perl\site\bin;C:\Strawberry\perl\bin;C:\ProgramData\chocolatey\lib\pulumi\tools\Pulumi\bin;C:\Program Files\CMake\bin;C:\Tools\Ninja;C:\ProgramData\chocolatey\lib\maven\apache-maven-3.9.11\bin;C:\Program Files\LLVM\bin;C:\Program Files\nodejs;C:\Program Files\Git\cmd;C:\Program Files\Git\clangarm64\bin;C:\Program Files\Git\usr\bin;C:\Program Files\GitHub CLI;C:\tools\php;C:\Program Files (x86)\sbt\bin;C:\Program Files\Amazon\AWSCLIV2;C:\Program Files\Amazon\SessionManagerPlugin\bin;C:\Program Files\Amazon\AWSSAMCLI\bin;C:\Program Files\Microsoft SQL Server\130\Tools\Binn;C:\Users\runneradmin\.dotnet\tools;C:\Users\runneradmin\.cargo\bin;C:\Users\runneradmin\AppData\Local\Microsoft\WindowsApps" "C:\\a\\rust\\rust\\build\\aarch64-pc-windows-msvc\\stage2\\bin\\rustc.exe" "C:\\a\\rust\\rust\\tests\\ui\\structs-enums\\align-struct.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\Users\\runneradmin\\.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\a\\rust\\rust\\vendor" "--sysroot" "C:\\a\\rust\\rust\\build\\aarch64-pc-windows-msvc\\stage2" "--target=aarch64-pc-windows-msvc" "--check-cfg" "cfg(test,FALSE)" "-O" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "C:\\a\\rust\\rust\\build\\aarch64-pc-windows-msvc\\test\\ui\\structs-enums\\align-struct\\a.exe" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=C:\\a\\rust\\rust\\build\\aarch64-pc-windows-msvc\\native\\rust-test-helpers"
stdout: none
--- stderr -------------------------------
error[E0806]: alignment must not be greater than 8192 bytes for COFF targets
##[error]  --> C:\a\rust\rust\tests\ui\structs-enums\align-struct.rs:67:8
   |
LL | #[repr(align(0x10000))]
   |        ^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0806`.
---

Some tests failed in compiletest suite=ui mode=ui host=aarch64-pc-windows-msvc target=aarch64-pc-windows-msvc
Bootstrap failed while executing `test --stage 2 --skip=compiler --skip=src`
Build completed unsuccessfully in 1:09:00
make: *** [Makefile:112: ci-msvc-py] Error 1
  local time: Sat Nov 15 20:39:53 CUT 2025
  network time: Sat, 15 Nov 2025 20:39:54 GMT
##[error]Process completed with exit code 2.
##[group]Run echo "disk usage:"
echo "disk usage:"

[bors]

💔 Test failed - checks-actions

[workingjubilee]

Ah, needs other tests fixed.

@rustbot author

[rustbot]

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

[bors]

☔ The latest upstream changes (presumably #149645) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC]

@nthery any updates on this? thanks