From f2048bca67b6dfa03b2972c3e6539d9ef79bb8c9 Mon Sep 17 00:00:00 2001
From: Aleksey Kliger <alklig@microsoft.com>
Date: Tue, 1 Mar 2022 10:36:06 -0500
Subject: [PATCH] [monoapi] Add mono_method_get_unmanaged_callers_only_ftnptr

Like `RuntimeMethodHandle.GetFunctionPointer`, but callable from native code
---
 src/mono/mono/metadata/external-only.c        | 23 +++++++++++++++++++
 src/mono/mono/metadata/icall.c                | 13 +++++++++++
 .../mono/metadata/mono-private-unstable.h     |  3 +++
 src/mono/mono/metadata/object-internals.h     |  3 +++
 4 files changed, 42 insertions(+)

diff --git a/src/mono/mono/metadata/external-only.c b/src/mono/mono/metadata/external-only.c
index 19999e384c7763..08d629dbf2dfc1 100644
--- a/src/mono/mono/metadata/external-only.c
+++ b/src/mono/mono/metadata/external-only.c
@@ -23,6 +23,7 @@
 #include "assembly-internals.h"
 #include "external-only.h"
 #include "threads.h"
+#include <mono/metadata/mono-private-unstable.h>
 #include "threads-types.h"
 #include "jit-info.h"
 
@@ -696,3 +697,25 @@ mono_domain_owns_vtable_slot (MonoDomain *domain, gpointer vtable_slot)
 {
 	return mono_mem_manager_mp_contains_addr (mono_mem_manager_get_ambient (), vtable_slot);
 }
+
+/**
+ * mono_method_get_unmanaged_callers_only_ftnptr:
+ * \param method method to generate a thunk for.
+ * \param error set on error
+ *
+ * Returns a function pointer for calling the given UnmanagedCallersOnly method from native code.
+ * The function pointer will use the calling convention specified on the UnmanagedCallersOnly
+ * attribute (or the default platform calling convention if omitted).
+ *
+ * Unlike \c mono_method_get_unmanaged_thunk, minimal marshaling is done to the method parameters in
+ * the wrapper. See
+ * https://docs.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.unmanagedcallersonlyattribute?view=net-6.0
+ * The method must be static and only use blittable argument types.  There is no exception out-argument.
+ *
+ *
+ */
+void*
+mono_method_get_unmanaged_callers_only_ftnptr (MonoMethod *method, MonoError *error)
+{
+ 	MONO_EXTERNAL_ONLY_GC_UNSAFE (gpointer, mono_method_get_unmanaged_wrapper_ftnptr_internal (method, TRUE, error));
+}
diff --git a/src/mono/mono/metadata/icall.c b/src/mono/mono/metadata/icall.c
index e471252ea6195b..b1e2d737f2246e 100644
--- a/src/mono/mono/metadata/icall.c
+++ b/src/mono/mono/metadata/icall.c
@@ -6600,6 +6600,19 @@ ves_icall_System_Environment_get_TickCount64 (void)
 gpointer
 ves_icall_RuntimeMethodHandle_GetFunctionPointer (MonoMethod *method, MonoError *error)
 {
+	return mono_method_get_unmanaged_wrapper_ftnptr_internal (method, FALSE, error);
+}
+
+void*
+mono_method_get_unmanaged_wrapper_ftnptr_internal (MonoMethod *method, gboolean only_unmanaged_callers_only, MonoError *error)
+{
+	/* WISH: we should do this in managed */
+	if (G_UNLIKELY (mono_method_has_unmanaged_callers_only_attribute (method))) {
+		method = mono_marshal_get_managed_wrapper  (method, NULL, (MonoGCHandle)0, error);
+		return_val_if_nok (error, NULL);
+	} else {
+		g_assert (!only_unmanaged_callers_only);
+	}
 	return mono_get_runtime_callbacks ()->get_ftnptr (method, error);
 }
 
diff --git a/src/mono/mono/metadata/mono-private-unstable.h b/src/mono/mono/metadata/mono-private-unstable.h
index 4618c8fe08bc92..72f0a912c5207b 100644
--- a/src/mono/mono/metadata/mono-private-unstable.h
+++ b/src/mono/mono/metadata/mono-private-unstable.h
@@ -42,4 +42,7 @@ mono_create_new_bundled_satellite_assembly (const char *name, const char *cultur
 
 typedef void * (*PInvokeOverrideFn) (const char *libraryName, const char *entrypointName);
 
+MONO_API MONO_RT_EXTERNAL_ONLY void*
+mono_method_get_unmanaged_callers_only_ftnptr (MonoMethod *method, MonoError *error);
+
 #endif /*__MONO_METADATA_MONO_PRIVATE_UNSTABLE_H__*/
diff --git a/src/mono/mono/metadata/object-internals.h b/src/mono/mono/metadata/object-internals.h
index 8f47c92ee86cdf..d5c69bbf2877f9 100644
--- a/src/mono/mono/metadata/object-internals.h
+++ b/src/mono/mono/metadata/object-internals.h
@@ -2097,4 +2097,7 @@ int
 mono_string_instance_is_interned (MonoString *str);
 #endif
 
+gpointer
+mono_method_get_unmanaged_wrapper_ftnptr_internal (MonoMethod *method, gboolean only_unmanaged_callers_only, MonoError *error);
+
 #endif /* __MONO_OBJECT_INTERNALS_H__ */