From dcc48749e21d24b45b22f37734f0058138d71efc Mon Sep 17 00:00:00 2001
From: Folkert de Vries <folkert@folkertdev.nl>
Date: Wed, 7 May 2025 20:02:29 +0200
Subject: [PATCH] add `extern "custom"` functions

---
 src/abi/mod.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/abi/mod.rs b/src/abi/mod.rs
index fe5b220117f3..4c6fd9078154 100644
--- a/src/abi/mod.rs
+++ b/src/abi/mod.rs
@@ -51,6 +51,11 @@ pub(crate) fn conv_to_call_conv(
         CanonAbi::Rust | CanonAbi::C => default_call_conv,
         CanonAbi::RustCold => CallConv::Cold,
 
+        // Functions with this calling convention can only be called from assembly, but it is
+        // possible to declare an `extern "custom"` block, so the backend still needs a calling
+        // convention for declaring foreign functions.
+        CanonAbi::Custom => default_call_conv,
+
         CanonAbi::X86(x86_call) => match x86_call {
             X86Call::SysV64 => CallConv::SystemV,
             X86Call::Win64 => CallConv::WindowsFastcall,