ICE of SIGILL/STATUS_ILLEGAL_INSTRUCTION when compiling static variables with 2MB alignment targeting Windows

[chris-oo]

Static variables with alignment of 2MB when building for Windows crash with either SIGILL on Linux cross-comiling or STATUS_ILLEGAL_INSTRUCTION on Windows.

See https://godbolt.org/z/rvfM8M455.

Code

#[repr(C, align(0x200000))]
struct Foo(u8);
static FOO: Foo = Foo(0);
fn main() {}

Meta

rustc --version --verbose:

1.87
nightly

Error output

error: rustc interrupted by SIGILL, printing backtrace

Backtrace

error: rustc interrupted by SIGILL, printing backtrace

/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x39177df)[0x7959893177df]
/lib/x86_64-linux-gnu/libc.so.6(+0x42520)[0x795985642520]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm13WinCOFFWriter13defineSectionERKNS_11MCAssemblerERKNS_13MCSectionCOFFE+0x51c)[0x795981bb616c]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm13WinCOFFWriter24executePostLayoutBindingERNS_11MCAssemblerE+0xfd)[0x795981bb821d]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm19WinCOFFObjectWriter24executePostLayoutBindingERNS_11MCAssemblerE+0x13)[0x795981bb9613]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm11MCAssembler6layoutEv+0x1606)[0x795984144d06]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm16MCObjectStreamer10finishImplEv+0x63)[0x7959841435e3]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm10AsmPrinter14doFinalizationERNS_6ModuleE+0x35e)[0x7959839ebe5e]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm13FPPassManager14doFinalizationERNS_6ModuleE+0x2a)[0x79598382a0ea]
/opt/compiler-explorer/rust-1.87.0/lib/libLLVM.so.20.1-rust-1.87.0-stable(_ZN4llvm6legacy15PassManagerImpl3runERNS_6ModuleE+0x3ff)[0x795983e4a553]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f719c2)[0x79598b9719c2]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f71521)[0x79598b971521]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f6eb5b)[0x79598b96eb5b]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f6e834)[0x79598b96e834]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(_RINvNtNtCseJswNlh1fGO_3std3sys9backtrace28___rust_begin_short_backtraceNCINvXs0_Csj8izNYKuql0_18rustc_codegen_llvmNtB1g_18LlvmCodegenBackendNtNtNtCs2ZezlIswSFH_17rustc_codegen_ssa6traits7backend19ExtraBackendMethods18spawn_named_threadNCINvNtNtB2k_4back5write10spawn_workB1O_E0uE0uEB1g_+0x251)[0x79598b96cf91]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f6685c)[0x79598b96685c]
/opt/compiler-explorer/rust-1.87.0/lib/librustc_driver-9c23edfdcf82221e.so(+0x5f66bf7)[0x79598b966bf7]
/lib/x86_64-linux-gnu/libc.so.6(+0x94ac3)[0x795985694ac3]
/lib/x86_64-linux-gnu/libc.so.6(+0x126850)[0x795985726850]

note: we would appreciate a report at https://github.com/rust-lang/rust
Program terminated with signal: SIGILL
Execution build compiler returned: 132

[chris-oo]

Doing some cursory issue searching, I also saw #135752 and #70144, but I'm not sure if those are exactly the same or not.

[Fulgen301]

Static variables with alignment of 2MB when building for Windows

...are not supported. Both clang and MSVC reject it, and the maximum accepted value is documented to be 8192.

It shouldn't crash, but it shouldn't work either.

[chris-oo]

Right, the crash should probably be surfaced as some other kind of error.

[nthery]

@rustbot claim

[nthery]

The crash is caused by

  llvm_unreachable("unsupported section alignment");

in getAlignment() called from WinCOFFWriter::defineSection() in src\llvm-project\llvm\lib\MC\WinCOFFObjectWriter.cpp.

The Rust reference allows alignment up to 2^29 but, as explained in a previous comment, the Windows PE-COFF format supports only up to 8192.

So it seems to me that we should:

1. Change the Rust reference to something along the line of " The alignment value must be a power of two from 1 up to an target-specific value".
   Are there precedents in the reference for target-specific limits?
2. Add some error checking for Windows targets only. The error checking for repr(align) is implemented in compiler\rustc_attr_parsing\src\attributes\repr.rs.
   Is there infrastructure to perform target-specific error checking?

Thanks in advance

[nthery]

@rustbot label +O-Windows