error out when repr(align) exceeds COFF limit

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

Author: nthery

compiler/rustc_error_codes/src/error_codes/E0805.md

@@ -0,0 +1,11 @@
+The value of `N` that was specified for `repr(align(N))` was greater than the
+PE-COFF limit (8192 bytes).
+
+Erroneous code example:
+
+```compile_fail,E0805
+#[repr(align(16384))] // error: alignment must not be greater than 8192 bytes for COFF targets
+enum Foo {
+    Bar(u64),
+}
+```

compiler/rustc_error_codes/src/lib.rs

@@ -547,6 +547,7 @@ E0801: 0801,
 E0802: 0802,
 E0803: 0803,
 E0804: 0804,
+E0805: 0805,
         );
     )
 }

compiler/rustc_passes/messages.ftl

@@ -590,6 +590,9 @@ passes_repr_align_greater_than_target_max =
     alignment must not be greater than `isize::MAX` bytes
     .note = `isize::MAX` is {$size} for the current target
 
+passes_repr_align_greater_than_coff_max =
+    alignment must not be greater than 8192 bytes for COFF targets
+
 passes_repr_conflicting =
     conflicting representation hints
 

compiler/rustc_passes/src/check_attr.rs

@@ -36,13 +36,18 @@ use rustc_session::lint::builtin::{
 };
 use rustc_session::parse::feature_err;
 use rustc_span::{BytePos, DUMMY_SP, Span, Symbol, edition, sym};
+use rustc_target::spec::BinaryFormat;
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::infer::{TyCtxtInferExt, ValuePairs};
 use rustc_trait_selection::traits::ObligationCtxt;
 use tracing::debug;
 
 use crate::{errors, fluent_generated as fluent};
 
+// Max alignment supported for PE-COFF binary format.
+// See https://learn.microsoft.com/en-us/cpp/cpp/align-cpp?view=msvc-170
+const COFF_MAX_ALIGN_BYTES: usize = 0x2000;
+
 #[derive(LintDiagnostic)]
 #[diag(passes_diagnostic_diagnostic_on_unimplemented_only_for_traits)]
 struct DiagnosticOnUnimplementedOnlyForTraits;
@@ -2132,6 +2137,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     fn check_align_value(&self, align: Align, span: Span) {
+        if self.tcx.sess.target.binary_format == BinaryFormat::Coff {
+            if align.bytes() > COFF_MAX_ALIGN_BYTES {
+                self.dcx().emit_err(errors::InvalidReprAlignForCoff { span });
+            }
+        }
+
         if align.bytes() > 2_u64.pow(29) {
             // for values greater than 2^29, a different error will be emitted, make sure that happens
             self.dcx().span_delayed_bug(

compiler/rustc_passes/src/errors.rs

@@ -597,6 +597,13 @@ pub(crate) struct InvalidReprAlignForTarget {
     pub size: u64,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_repr_align_greater_than_coff_max, code = E0805)]
+pub(crate) struct InvalidReprAlignForCoff {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(LintDiagnostic)]
 #[diag(passes_repr_conflicting, code = E0566)]
 pub(crate) struct ReprConflictingLint;

tests/ui/repr/repr-align-max.rs

@@ -0,0 +1,12 @@
+//@ check-pass
+//@ ignore-windows
+
+#![allow(dead_code)]
+
+#[repr(align(536870912))] // ok: this is the largest accepted alignment
+struct S3(i32);
+
+#[repr(align(536870912))] // ok: this is the largest accepted alignment
+enum E3 { A, B }
+
+fn main() {}

tests/ui/repr/repr-align.rs

@@ -9,9 +9,6 @@ struct S1(i32);
 #[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 2^29
 struct S2(i32);
 
-#[repr(align(536870912))] // ok: this is the largest accepted alignment
-struct S3(i32);
-
 #[repr(align(0))] //~ ERROR: invalid `repr(align)` attribute: not a power of two
 struct S4(i32);
 
@@ -24,9 +21,6 @@ enum E1 { A, B }
 #[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 2^29
 enum E2 { A, B }
 
-#[repr(align(536870912))] // ok: this is the largest accepted alignment
-enum E3 { A, B }
-
 #[repr(align(0))] //~ ERROR: invalid `repr(align)` attribute: not a power of two
 enum E4 { A, B }
 

tests/ui/repr/repr-align.stderr

@@ -17,31 +17,31 @@ LL | #[repr(align(4294967296))]
    |              ^^^^^^^^^^
 
 error[E0589]: invalid `repr(align)` attribute: not a power of two
-  --> $DIR/repr-align.rs:15:14
+  --> $DIR/repr-align.rs:12:14
    |
 LL | #[repr(align(0))]
    |              ^
 
 error[E0589]: invalid `repr(align)` attribute: not an unsuffixed integer
-  --> $DIR/repr-align.rs:18:14
+  --> $DIR/repr-align.rs:15:14
    |
 LL | #[repr(align(16.0))]
    |              ^^^^
 
 error[E0589]: invalid `repr(align)` attribute: not a power of two
-  --> $DIR/repr-align.rs:21:14
+  --> $DIR/repr-align.rs:18:14
    |
 LL | #[repr(align(15))]
    |              ^^
 
 error[E0589]: invalid `repr(align)` attribute: larger than 2^29
-  --> $DIR/repr-align.rs:24:14
+  --> $DIR/repr-align.rs:21:14
    |
 LL | #[repr(align(4294967296))]
    |              ^^^^^^^^^^
 
 error[E0589]: invalid `repr(align)` attribute: not a power of two
-  --> $DIR/repr-align.rs:30:14
+  --> $DIR/repr-align.rs:24:14
    |
 LL | #[repr(align(0))]
    |              ^

tests/ui/repr/repr_align_greater_coff.rs

@@ -0,0 +1,11 @@
+//@ only-windows
+
+#![allow(dead_code)]
+
+#[repr(align(16384))]  //~ ERROR alignment must not be greater than 8192 bytes for COFF targets
+struct S1(i32);
+
+#[repr(align(16384))]  //~ ERROR alignment must not be greater than 8192 bytes for COFF targets
+enum E1 { A, B }
+
+fn main() {}

tests/ui/repr/repr_align_greater_coff.stderr

@@ -0,0 +1,15 @@
+error[E0805]: alignment must not be greater than 8192 bytes for COFF targets
+  --> $DIR/repr_align_greater_coff.rs:5:8
+   |
+LL | #[repr(align(16384))]
+   |        ^^^^^^^^^^^^
+
+error[E0805]: alignment must not be greater than 8192 bytes for COFF targets
+  --> $DIR/repr_align_greater_coff.rs:8:8
+   |
+LL | #[repr(align(16384))]
+   |        ^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0805`.