From 65042d6da3f7261b49d1e9be7eb8e0e1d3bdead1 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.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/abi.rs b/src/abi.rs
index 3d0c258f576d..08f3d2819040 100644
--- a/src/abi.rs
+++ b/src/abi.rs
@@ -239,12 +239,16 @@ impl<'gcc, 'tcx> FnAbiGccExt<'gcc, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 pub fn conv_to_fn_attribute<'gcc>(conv: CanonAbi, arch: &str) -> Option<FnAttribute<'gcc>> {
     let attribute = match conv {
         CanonAbi::C | CanonAbi::Rust => return None,
+        CanonAbi::RustCold => FnAttribute::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 => return None,
         CanonAbi::Arm(arm_call) => match arm_call {
             ArmCall::CCmseNonSecureCall => FnAttribute::ArmCmseNonsecureCall,
             ArmCall::CCmseNonSecureEntry => FnAttribute::ArmCmseNonsecureEntry,
             ArmCall::Aapcs => FnAttribute::ArmPcs("aapcs"),
         },
-        CanonAbi::RustCold => FnAttribute::Cold,
         CanonAbi::GpuKernel => {
             if arch == "amdgpu" {
                 FnAttribute::GcnAmdGpuHsaKernel