1 files changed, 23 insertions, 6 deletions
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 4be363ca9a2..2eecf81a5d2 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -1708,15 +1708,32 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let mut cs_bx = Bx::build(self.cx, llbb);
             let cs = cs_bx.catch_switch(None, None, &[cp_llbb]);
 
-            // The "null" here is actually a RTTI type descriptor for the
-            // C++ personality function, but `catch (...)` has no type so
-            // it's null. The 64 here is actually a bitfield which
-            // represents that this is a catch-all block.
             bx = Bx::build(self.cx, cp_llbb);
             let null =
                 bx.const_null(bx.type_ptr_ext(bx.cx().data_layout().instruction_address_space));
-            let sixty_four = bx.const_i32(64);
-            funclet = Some(bx.catch_pad(cs, &[null, sixty_four, null]));
+
+            // The `null` in first argument here is actually a RTTI type
+            // descriptor for the C++ personality function, but `catch (...)`
+            // has no type so it's null.
+            let args = if base::wants_msvc_seh(self.cx.sess()) {
+                // This bitmask is a single `HT_IsStdDotDot` flag, which
+                // represents that this is a C++-style `catch (...)` block that
+                // only captures programmatic exceptions, not all SEH
+                // exceptions. The second `null` points to a non-existent
+                // `alloca` instruction, which an LLVM pass would inline into
+                // the initial SEH frame allocation.
+                let adjectives = bx.const_i32(0x40);
+                &[null, adjectives, null] as &[_]
+            } else {
+                // Specifying more arguments than necessary usually doesn't
+                // hurt, but the `WasmEHPrepare` LLVM pass does not recognize
+                // anything other than a single `null` as a `catch (...)` block,
+                // leading to problems down the line during instruction
+                // selection.
+                &[null] as &[_]
+            };
+
+            funclet = Some(bx.catch_pad(cs, args));
         } else {
             llbb = Bx::append_block(self.cx, self.llfn, "terminate");
             bx = Bx::build(self.cx, llbb);