[release/6.0] [mini] Use alloca for runtime_invoke retval buffer (#59006)

* [mini] Use alloca for runtime_invoke retval buffer

Fixes https://github.com/dotnet/runtime/issues/58957
Related to https://github.com/dotnet/runtime/pull/58215 which was attempting to
fix https://github.com/dotnet/runtime/issues/58190

* Set initial return buffer size to TARGET_SIZEOF_VOID_P

In the common case we use the return buffer just to hold a pointer to
the return value

Co-authored-by: Aleksey Kliger <alklig@microsoft.com>
Co-authored-by: Aleksey Kliger <aleksey@lambdageek.org>

diff --git a/src/mono/mono/mini/mini-runtime.c b/src/mono/mono/mini/mini-runtime.c
index 2abfe01..f3c9c9b 100644 (file)
--- a/src/mono/mono/mini/mini-runtime.c
+++ b/src/mono/mono/mini/mini-runtime.c
@@ -2999,7 +2999,7 @@ typedef struct {
        gpointer *wrapper_arg;
 } RuntimeInvokeInfo;
 
-#define MONO_SIZEOF_DYN_CALL_RET_BUF 256
+#define MONO_SIZEOF_DYN_CALL_RET_BUF TARGET_SIZEOF_VOID_P
 
 static RuntimeInvokeInfo*
 create_runtime_invoke_info (MonoMethod *method, gpointer compiled_method, gboolean callee_gsharedvt, gboolean use_interp, MonoError *error)
@@ -3159,9 +3159,8 @@ mono_llvmonly_runtime_invoke (MonoMethod *method, RuntimeInvokeInfo *info, void
 {
        MonoMethodSignature *sig = info->sig;
        MonoObject *(*runtime_invoke) (MonoObject *this_obj, void **params, MonoObject **exc, void* compiled_method);
-       gboolean retval_malloc = FALSE;
-       gpointer retval_ptr;
-       guint8 retval [MONO_SIZEOF_DYN_CALL_RET_BUF];
+       int32_t retval_size = MONO_SIZEOF_DYN_CALL_RET_BUF;
+       gpointer retval = NULL;
        int i, pindex;
 
        error_init (error);
@@ -3191,19 +3190,18 @@ mono_llvmonly_runtime_invoke (MonoMethod *method, RuntimeInvokeInfo *info, void
                if (info->ret_box_class && !sig->ret->byref &&
                    (sig->ret->type == MONO_TYPE_VALUETYPE ||
                     (sig->ret->type == MONO_TYPE_GENERICINST && !MONO_TYPE_IS_REFERENCE (sig->ret)))) {
-                       // if the return type is a struct and its too big for the stack buffer, malloc instead
+                       // if the return type is a struct, allocate enough stack space to hold it
                        MonoClass *ret_klass = mono_class_from_mono_type_internal (sig->ret);
                        g_assert (!mono_class_has_failure (ret_klass));
                        int32_t inst_size = mono_class_instance_size (ret_klass);
                        if (inst_size > MONO_SIZEOF_DYN_CALL_RET_BUF) {
-                               retval_malloc = TRUE;
-                               retval_ptr = g_new0 (guint8, inst_size);
-                               g_assert (retval_ptr);
+                               retval_size = inst_size;
                        }
                }
-               if (!retval_malloc)
-                       retval_ptr = &retval;
-               args [pindex ++] = &retval_ptr;
+       }
+       retval = g_alloca (retval_size);
+       if (sig->ret->type != MONO_TYPE_VOID) {
+               args [pindex ++] = &retval;
        }
        for (i = 0; i < sig->param_count; ++i) {
                MonoType *t = sig->params [i];
@@ -3252,9 +3250,7 @@ mono_llvmonly_runtime_invoke (MonoMethod *method, RuntimeInvokeInfo *info, void
                        if (sig->ret->byref) {
                                return mono_value_box_checked (info->ret_box_class, *(gpointer*)retval, error);
                        } else {
-                               MonoObject *ret = mono_value_box_checked (info->ret_box_class, retval_ptr, error);
-                               if (retval_malloc)
-                                       g_free (retval_ptr);
+                               MonoObject *ret = mono_value_box_checked (info->ret_box_class, retval, error);
                                return ret;
                        }
                } else {
@@ -3418,25 +3414,22 @@ mono_jit_runtime_invoke (MonoMethod *method, void *obj, void **params, MonoObjec
                gpointer *args;
                int i, pindex, buf_size;
                guint8 *buf;
-               guint8 retbuf [MONO_SIZEOF_DYN_CALL_RET_BUF];
-               guint8 *retval = &retbuf[0];
-               gboolean retval_malloc = FALSE;
+               int32_t retval_size = MONO_SIZEOF_DYN_CALL_RET_BUF;
+               guint8 *retval = NULL;
 
-               /* if the return value is too big, put it in a dynamically allocated temporary */
+               /* if the return type is a struct and it's too big, allocate more space for it */
                if (info->ret_box_class && !sig->ret->byref &&
                    (sig->ret->type == MONO_TYPE_VALUETYPE ||
                     (sig->ret->type == MONO_TYPE_GENERICINST && !MONO_TYPE_IS_REFERENCE (sig->ret)))) {
-                       // if the return type is a struct and its too big for the stack buffer, malloc instead
                        MonoClass *ret_klass = mono_class_from_mono_type_internal (sig->ret);
                        g_assert (!mono_class_has_failure (ret_klass));
                        int32_t inst_size = mono_class_instance_size (ret_klass);
                        if (inst_size > MONO_SIZEOF_DYN_CALL_RET_BUF) {
-                               retval_malloc = TRUE;
-                               retval = g_new0 (guint8, inst_size);
-                               g_assert (retval);
+                               retval_size = inst_size;
                        }
                }
 
+               retval = g_alloca (retval_size);
 
                /* Convert the arguments to the format expected by start_dyn_call () */
                args = (void **)g_alloca ((sig->param_count + sig->hasthis) * sizeof (gpointer));
@@ -3487,8 +3480,6 @@ mono_jit_runtime_invoke (MonoMethod *method, void *obj, void **params, MonoObjec
                                return mono_value_box_checked (info->ret_box_class, *(gpointer*)retval, error);
                        } else {
                                MonoObject *boxed_ret = mono_value_box_checked (info->ret_box_class, retval, error);
-                               if (retval_malloc)
-                                       g_free (retval);
                                return boxed_ret;
                        }
                } else {