fix(guest): allow guest functions with more than 11 parameters

CHANGELOG.md

@@ -19,6 +19,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 ### Fixed
 
 * Guest libc accepts null buffers for zero-length writes.
+* Fix calls to guest functions with more than 11 parameters. Registration accepts up to 32, but every call with more than 11 failed.
 
 ## [v0.18.0] - 2026-10-13
 

src/hyperlight_common/src/func/param_type.rs

@@ -66,6 +66,29 @@ macro_rules! impl_supported_param_type {
 for_each_param_type!(impl_supported_param_type);
 
 /// A trait to describe the tuple of parameters that a host function can take.
+///
+/// Functions take at most 32 parameters.
+///
+/// ```
+/// fn takes<T: hyperlight_common::func::ParameterTuple>() {}
+/// takes::<(
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+/// )>();
+/// ```
+///
+/// ```compile_fail
+/// fn takes<T: hyperlight_common::func::ParameterTuple>() {}
+/// takes::<(
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32, i32, i32, i32, i32, i32, i32, i32,
+///     i32,
+/// )>();
+/// ```
 pub trait ParameterTuple: Sized + Clone + Send + Sync + 'static {
     /// The number of parameters in the tuple
     const SIZE: usize;

src/hyperlight_guest_bin/src/guest_function/definition.rs

@@ -177,20 +177,6 @@ impl<F: Copy> GuestFunctionDefinition<F> {
 
     /// Verify that `self` has same signature as the provided `parameter_types`.
     pub fn verify_parameters(&self, parameter_types: &[ParameterType]) -> Result<()> {
-        // Verify that the function does not have more than `MAX_PARAMETERS` parameters.
-        const MAX_PARAMETERS: usize = 11;
-        if parameter_types.len() > MAX_PARAMETERS {
-            return Err(HyperlightGuestError::new(
-                ErrorCode::GuestError,
-                format!(
-                    "Function {} has too many parameters: {} (max allowed is {}).",
-                    self.function_name,
-                    parameter_types.len(),
-                    MAX_PARAMETERS
-                ),
-            ));
-        }
-
         if self.parameter_types.len() != parameter_types.len() {
             return Err(HyperlightGuestError::new(
                 ErrorCode::GuestFunctionIncorrecNoOfParameters,

src/hyperlight_guest_macro/src/lib.rs

@@ -37,7 +37,7 @@ impl Parse for NameArg {
 ///
 /// The function arguments must be supported parameter types, and the return type must be
 /// a supported return type or a `Result<T, HyperlightGuestError>` with T being a supported
-/// return type.
+/// return type. Guest functions take at most 32 parameters, the limit `ParameterTuple` sets.
 ///
 /// # Note
 /// The function will be registered with the host at program initialization regardless of

src/hyperlight_host/tests/sandbox_host_tests.rs

@@ -12,7 +12,7 @@ use hyperlight_testing::simple_guest_as_pathbuf;
 
 pub mod common; // pub to disable dead_code warning
 use crate::common::{
-    with_all_guests, with_all_sandboxes, with_c_sandbox, with_c_sandbox_from,
+    with_all_guests, with_all_sandboxes, with_c_sandbox, with_c_sandbox_from, with_rust_sandbox,
     with_rust_uninit_sandbox, with_rust_uninit_sandbox_cfg,
 };
 
@@ -200,6 +200,24 @@ fn multiple_parameters() {
     });
 }
 
+#[test]
+fn guest_function_with_thirty_two_parameters() {
+    with_rust_sandbox(|mut sandbox| {
+        let sum: i32 = sandbox
+            .call(
+                "SumThirtyTwoArgs",
+                (
+                    1_i32, 2_i32, 3_i32, 4_i32, 5_i32, 6_i32, 7_i32, 8_i32, 9_i32, 10_i32, 11_i32,
+                    12_i32, 13_i32, 14_i32, 15_i32, 16_i32, 17_i32, 18_i32, 19_i32, 20_i32, 21_i32,
+                    22_i32, 23_i32, 24_i32, 25_i32, 26_i32, 27_i32, 28_i32, 29_i32, 30_i32, 31_i32,
+                    32_i32,
+                ),
+            )
+            .unwrap();
+        assert_eq!(sum, (1..=32).sum::<i32>());
+    });
+}
+
 #[test]
 fn incorrect_parameter_type() {
     with_all_sandboxes(|mut sandbox| {

src/tests/rust_guests/simpleguest/src/main.rs

@@ -326,6 +326,13 @@ fn print_eleven_args(arg1: String, arg2: i32, arg3: i64, arg4: String, arg5: Str
     host_print(message)
 }
 
+#[rustfmt::skip]
+#[allow(clippy::too_many_arguments)]
+#[guest_function("SumThirtyTwoArgs")]
+fn sum_thirty_two_args(a1: i32, a2: i32, a3: i32, a4: i32, a5: i32, a6: i32, a7: i32, a8: i32, a9: i32, a10: i32, a11: i32, a12: i32, a13: i32, a14: i32, a15: i32, a16: i32, a17: i32, a18: i32, a19: i32, a20: i32, a21: i32, a22: i32, a23: i32, a24: i32, a25: i32, a26: i32, a27: i32, a28: i32, a29: i32, a30: i32, a31: i32, a32: i32) -> i32 {
+    a1 + a2 + a3 + a4 + a5 + a6 + a7 + a8 + a9 + a10 + a11 + a12 + a13 + a14 + a15 + a16 + a17 + a18 + a19 + a20 + a21 + a22 + a23 + a24 + a25 + a26 + a27 + a28 + a29 + a30 + a31 + a32
+}
+
 #[guest_function("BufferOverrun")]
 fn buffer_overrun(value: String) -> i32 {
     let c_str = value.as_str();