ARC: MWDT: get rid of MWDT startup libs

__cxa_atexit implementation provided by MWDT startup code calls
malloc which isn't supported right now. As we don't support
calling static destructors in Zephyr let's provide our own
__cxa_atexit stub and get rid of MWDT startup libs
entirely.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>

arch/arc/CMakeLists.txt

@@ -20,3 +20,7 @@ if(CONFIG_ISA_ARCV2)
 endif()
 
 add_subdirectory(core)
+
+if(COMPILER STREQUAL arcmwdt)
+  add_subdirectory(arcmwdt)
+endif()

arch/arc/arcmwdt/CMakeLists.txt

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+
+if(CONFIG_ARCMWDT_LIBC OR CONFIG_CPLUSPLUS)
+  zephyr_sources(arcmwdt-dtr-stubs.c)
+endif()

arch/arc/arcmwdt/arcmwdt-dtr-stubs.c

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021 Synopsys.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <toolchain.h>
+
+__weak void *__dso_handle;
+
+int __cxa_atexit(void (*destructor)(void *), void *objptr, void *dso)
+{
+	ARG_UNUSED(destructor);
+	ARG_UNUSED(objptr);
+	ARG_UNUSED(dso);
+	return 0;
+}
+
+int atexit(void (*function)(void))
+{
+	return 0;
+}

cmake/linker/arcmwdt/target.cmake

@@ -119,13 +119,9 @@ macro(toolchain_ld_baremetal)
     -Hhostlib=
     -Hheap=0
     -Hnoivt
+    -Hnocrt
   )
 
-  # We only use CPP initialization code from crt
-  if(NOT CONFIG_CPLUSPLUS)
-    zephyr_ld_options(-Hnocrt)
-  endif()
-
   # There are two options:
   # - We have full MWDT libc support and we link MWDT libc - this is default
   #   behavior and we don't need to do something for that.

include/arch/arc/v2/linker.ld

@@ -88,13 +88,6 @@ SECTIONS {
 #include <linker/kobject-text.ld>
 	} GROUP_LINK_IN(ROMABLE_REGION)
 
-#if defined(CONFIG_CPLUSPLUS) && !defined(CONFIG_CPP_STATIC_INIT_GNU) && defined(__MWDT_LINKER_CMD__)
-	/* .init section with code iterating over static objects constructors */
-	SECTION_PROLOGUE(.init,,ALIGN(4)) {
-		KEEP(*(.init*))
-	} GROUP_LINK_IN(ROMABLE_REGION)
-#endif /* CONFIG_CPLUSPLUS && !CONFIG_CPP_STATIC_INIT_GNU && __MWDT_LINKER_CMD__ */
-
 	__text_region_end = .;
 	__rodata_region_start = .;
 

subsys/cpp/cpp_init.c

@@ -20,11 +20,11 @@ void z_cpp_init_static(void)
 #else
 
 #ifdef __CCAC__
-void _init(void);
+void __do_global_ctors_aux(void);
 
 void z_cpp_init_static(void)
 {
-	_init();
+	__do_global_ctors_aux();
 }
 #endif /* __CCAC__ */