Enable 32-bit x86 guest support (#1085)

* Gate hyperlight-guest-tracing to x86_64 only

Move hyperlight-guest-tracing dependency to target-specific section for
x86_64 architecture only. This allows i686 and other architectures to
build without x86_64-specific tracing functionality.

Signed-off-by: danbugs <danilochiarlone@gmail.com>

* ci: verify hyperlight-guest builds for 32-bit x86

Add CI check to ensure hyperlight-guest library builds for 32-bit x86
architecture (i686-unknown-linux-gnu) to maintain compatibility with
Nanvix's custom 32-bit x86 target.

Signed-off-by: danbugs <danilochiarlone@gmail.com>

---------

Signed-off-by: danbugs <danilochiarlone@gmail.com>

Author: danbugs

.github/workflows/dep_rust.yml

@@ -93,6 +93,12 @@ jobs:
       - name: Verify MSRV
         run: ./dev/verify-msrv.sh hyperlight-host hyperlight-guest hyperlight-guest-bin hyperlight-common
 
+      - name: Check hyperlight-guest builds for 32-bit (Nanvix compatibility)
+        if: ${{ runner.os == 'Linux' }}
+        run: |
+          rustup target add i686-unknown-linux-gnu
+          just check-guest-i686 ${{ inputs.config }}
+
   build:
     if: ${{ inputs.docs_only == 'false' }}
     timeout-minutes: 60

Justfile

@@ -198,6 +198,10 @@ test-rust-tracing target=default-target features="":
     {{ cargo-cmd }} test -p hyperlight-common -F trace_guest --profile={{ if target == "debug" { "dev" } else { target } }} {{ target-triple-flag }}
     {{ cargo-cmd }} test -p hyperlight-host --profile={{ if target == "debug" { "dev" } else { target } }} {{ if features =="" {'--features trace_guest'} else { "--features trace_guest," + features } }} {{ target-triple-flag }}
 
+# verify hyperlight-guest builds for 32-bit (for Nanvix compatibility - uses i686 as proxy for Nanvix's custom 32-bit x86 target)
+check-guest-i686 target=default-target:
+    cargo check -p hyperlight-guest --target i686-unknown-linux-gnu --profile={{ if target == "debug" { "dev" } else { target } }}
+
     # Build the tracing guest to ensure it builds with the tracing feature
     just build-rust-guests {{ target }} trace_guest
     just move-rust-guests {{ target }}

src/hyperlight_guest/Cargo.toml

@@ -15,10 +15,12 @@ Provides only the essential building blocks for interacting with the host enviro
 anyhow = { version = "1.0.100", default-features = false }
 serde_json = { version = "1.0", default-features = false, features = ["alloc"] }
 hyperlight-common = { workspace = true, default-features = false }
-hyperlight-guest-tracing = { workspace = true, default-features = false }
 flatbuffers = { version= "25.9.23", default-features = false }
 tracing = { version = "0.1.43", default-features = false, features = ["attributes"] }
 
+[target.'cfg(target_arch = "x86_64")'.dependencies]
+hyperlight-guest-tracing = { workspace = true, default-features = false, optional = true }
+
 [features]
 default = []
-trace_guest = ["hyperlight-guest-tracing/trace"]
+trace_guest = ["dep:hyperlight-guest-tracing", "hyperlight-guest-tracing?/trace"]

src/hyperlight_guest/src/exit.rs

@@ -27,7 +27,7 @@ use tracing::instrument;
 #[inline(never)]
 #[instrument(skip_all, level = "Trace")]
 pub fn halt() {
-    #[cfg(feature = "trace_guest")]
+    #[cfg(all(feature = "trace_guest", target_arch = "x86_64"))]
     {
         // Send data before halting
         // If there is no data, this doesn't do anything
@@ -49,7 +49,7 @@ pub extern "C" fn abort() -> ! {
 /// Exits the VM with an Abort OUT action and a specific code.
 pub fn abort_with_code(code: &[u8]) -> ! {
     // End any ongoing trace before aborting
-    #[cfg(feature = "trace_guest")]
+    #[cfg(all(feature = "trace_guest", target_arch = "x86_64"))]
     hyperlight_guest_tracing::end_trace();
     outb(OutBAction::Abort as u16, code);
     outb(OutBAction::Abort as u16, &[0xFF]); // send abort terminator (if not included in code)
@@ -62,7 +62,7 @@ pub fn abort_with_code(code: &[u8]) -> ! {
 /// This function is unsafe because it dereferences a raw pointer.
 pub unsafe fn abort_with_code_and_message(code: &[u8], message_ptr: *const c_char) -> ! {
     // End any ongoing trace before aborting
-    #[cfg(feature = "trace_guest")]
+    #[cfg(all(feature = "trace_guest", target_arch = "x86_64"))]
     hyperlight_guest_tracing::end_trace();
     unsafe {
         // Step 1: Send abort code (typically 1 byte, but `code` allows flexibility)
@@ -116,7 +116,7 @@ pub(crate) fn outb(port: u16, data: &[u8]) {
 /// in exception contexts. Because if the trace state is already locked, trying to create a span
 /// would cause a panic, which is undesirable in exception handling.
 pub(crate) unsafe fn out32(port: u16, val: u32) {
-    #[cfg(feature = "trace_guest")]
+    #[cfg(all(feature = "trace_guest", target_arch = "x86_64"))]
     {
         if let Some((ptr, len)) = hyperlight_guest_tracing::serialized_data() {
             // If tracing is enabled and there is data to send, send it along with the OUT action
@@ -142,7 +142,7 @@ pub(crate) unsafe fn out32(port: u16, val: u32) {
             };
         }
     }
-    #[cfg(not(feature = "trace_guest"))]
+    #[cfg(not(all(feature = "trace_guest", target_arch = "x86_64")))]
     unsafe {
         asm!("out dx, eax", in("dx") port, in("eax") val, options(preserves_flags, nomem, nostack));
     }

src/hyperlight_guest/src/guest_handle/host_comm.rs

@@ -179,7 +179,7 @@ impl GuestHandle {
         line: u32,
     ) {
         // Closure to send log message to host
-        let send_to_host = || {
+        let _send_to_host = || {
             let guest_log_data = GuestLogData::new(
                 message.to_string(),
                 source.to_string(),
@@ -201,7 +201,7 @@ impl GuestHandle {
             }
         };
 
-        #[cfg(feature = "trace_guest")]
+        #[cfg(all(feature = "trace_guest", target_arch = "x86_64"))]
         if hyperlight_guest_tracing::is_trace_enabled() {
             // If the "trace_guest" feature is enabled and tracing is initialized, log using tracing
             tracing::trace!(
@@ -213,11 +213,11 @@ impl GuestHandle {
                 code.lineno = line,
             );
         } else {
-            send_to_host();
+            _send_to_host();
         }
-        #[cfg(not(feature = "trace_guest"))]
+        #[cfg(not(all(feature = "trace_guest", target_arch = "x86_64")))]
         {
-            send_to_host();
+            _send_to_host();
         }
     }
 }

src/hyperlight_guest/src/lib.rs

@@ -15,7 +15,8 @@ limitations under the License.
 */
 
 #![no_std]
-// Deps
+#[cfg(all(feature = "trace_guest", not(target_arch = "x86_64")))]
+compile_error!("trace_guest feature is only supported on x86_64 architecture");
 
 extern crate alloc;