feat: add aarch64 arch stubs for guest crates

Add aarch64 arch modules with unimplemented!() stubs:
- hyperlight-guest: layout, prim_alloc, exit modules
- hyperlight-guest-bin: dispatch and entrypoint stubs

Update cfg_attr paths in layout.rs and prim_alloc.rs to
include aarch64. All stubs panic at runtime — no aarch64
guest functionality is implemented yet.

Signed-off-by: Ludvig Liljenberg <4257730+ludfjig@users.noreply.github.com>

Author: ludfjig

src/hyperlight_guest/src/arch/aarch64/exit.rs

@@ -0,0 +1,22 @@
+/*
+Copyright 2025  The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+ */
+
+// TODO(aarch64): implement VM exit mechanism (e.g. hvc instruction)
+
+/// Trigger a VM exit sending a 32-bit value to the host on the given port.
+pub(crate) unsafe fn out32(_port: u16, _val: u32) {
+    unimplemented!("aarch64 out32")
+}

src/hyperlight_guest/src/arch/aarch64/layout.rs

@@ -0,0 +1,31 @@
+/*
+Copyright 2025  The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+ */
+
+// TODO(aarch64): these values are placeholders copied from amd64
+pub const MAIN_STACK_TOP_GVA: u64 = 0xffff_ff00_0000_0000;
+pub const MAIN_STACK_LIMIT_GVA: u64 = 0xffff_fe00_0000_0000;
+
+pub fn scratch_size() -> u64 {
+    unimplemented!("aarch64 scratch_size")
+}
+
+pub fn scratch_base_gpa() -> u64 {
+    unimplemented!("aarch64 scratch_base_gpa")
+}
+
+pub fn scratch_base_gva() -> u64 {
+    unimplemented!("aarch64 scratch_base_gva")
+}

src/hyperlight_guest/src/arch/aarch64/prim_alloc.rs

@@ -0,0 +1,25 @@
+/*
+Copyright 2025  The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+ */
+
+// TODO(aarch64): implement real aarch64 page allocator
+
+// There are no notable architecture-specific safety considerations
+// here, and the general conditions are documented in the
+// architecture-independent re-export in prim_alloc.rs
+#[allow(clippy::missing_safety_doc)]
+pub unsafe fn alloc_phys_pages(_n: u64) -> u64 {
+    unimplemented!("aarch64 alloc_phys_pages")
+}

src/hyperlight_guest/src/layout.rs

@@ -16,6 +16,7 @@ limitations under the License.
 
 #[cfg_attr(target_arch = "x86_64", path = "arch/amd64/layout.rs")]
 #[cfg_attr(target_arch = "x86", path = "arch/i686/layout.rs")]
+#[cfg_attr(target_arch = "aarch64", path = "arch/aarch64/layout.rs")]
 mod arch;
 
 pub use arch::{MAIN_STACK_LIMIT_GVA, MAIN_STACK_TOP_GVA};

src/hyperlight_guest/src/prim_alloc.rs

@@ -16,6 +16,7 @@ limitations under the License.
 
 #[cfg_attr(target_arch = "x86_64", path = "arch/amd64/prim_alloc.rs")]
 #[cfg_attr(target_arch = "x86", path = "arch/i686/prim_alloc.rs")]
+#[cfg_attr(target_arch = "aarch64", path = "arch/aarch64/prim_alloc.rs")]
 mod arch;
 
 /// Allocate n contiguous physical pages and return the physical

src/hyperlight_guest_bin/src/arch/aarch64/mod.rs

@@ -0,0 +1,35 @@
+/*
+Copyright 2025  The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+ */
+
+// TODO(aarch64): implement aarch64 guest runtime
+
+pub mod dispatch {
+    /// Dispatch function pointer — set during initialisation and called
+    /// by the host for each guest function invocation.
+    #[unsafe(no_mangle)]
+    pub extern "C" fn dispatch_function() {
+        unimplemented!("aarch64 dispatch_function")
+    }
+}
+
+/// The entrypoint for the guest binary — called by the hypervisor.
+///
+/// On aarch64 this is a stub that will be implemented when the
+/// aarch64 hypervisor backend is ready.
+#[unsafe(no_mangle)]
+pub extern "C" fn entrypoint() -> ! {
+    unimplemented!("aarch64 entrypoint")
+}