https://www.virtualbox.org/ticket/20904

--- VirtualBox-6.1.34/Config.kmk
+++ VirtualBox-6.1.34/Config.kmk
@@ -4502,11 +4502,14 @@
 TEMPLATE_VBoxR0_TOOL                = $(VBOX_GCC_TOOL)
 TEMPLATE_VBoxR0_CFLAGS              = -fno-pie -nostdinc -g $(VBOX_GCC_pipe) $(VBOX_GCC_WERR) $(VBOX_GCC_PEDANTIC_C) \
 	$(VBOX_GCC_Wno-variadic-macros) $(VBOX_GCC_R0_OPT) $(VBOX_GCC_R0_FP) -fno-strict-aliasing -fno-exceptions \
-	$(VBOX_GCC_fno-stack-protector) -fno-common $(VBOX_GCC_fvisibility-hidden) -std=gnu99 $(VBOX_GCC_IPRT_FMT_CHECK)
+	$(VBOX_GCC_fno-stack-protector) -fno-common -ffreestanding $(VBOX_GCC_fvisibility-hidden) -std=gnu99 $(VBOX_GCC_IPRT_FMT_CHECK)
 TEMPLATE_VBoxR0_CXXFLAGS            = -fno-pie -nostdinc -g $(VBOX_GCC_pipe) $(VBOX_GCC_WERR) $(VBOX_GCC_PEDANTIC_CXX) \
 	$(VBOX_GCC_Wno-variadic-macros) $(VBOX_GCC_R0_OPT) $(VBOX_GCC_R0_FP) -fno-strict-aliasing -fno-exceptions \
 	$(VBOX_GCC_fno-stack-protector) -fno-common $(VBOX_GCC_fvisibility-inlines-hidden) $(VBOX_GCC_fvisibility-hidden) \
 	-fno-rtti $(VBOX_GCC_IPRT_FMT_CHECK)
+ if $(VBOX_GCC_VERSION_CC) >= 40500 # 4.1.2 complains, 4.5.2 is okay, didn't check which version inbetween made it okay with g++.
+TEMPLATE_VBoxR0_CXXFLAGS           += -ffreestanding
+ endif
 TEMPLATE_VBoxR0_CFLAGS.amd64        = -m64 -mno-red-zone -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -fasynchronous-unwind-tables -ffreestanding
 TEMPLATE_VBoxR0_CXXFLAGS.amd64      = -m64 -mno-red-zone -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -fasynchronous-unwind-tables
 TEMPLATE_VBoxR0_CXXFLAGS.freebsd    = -ffreestanding