exceptions: optionally enforce c++ standards (#6333)

* exceptions: 3 choices: legacy, std::new never returns 0, or exceptions enabled
* arduino_new (doc, example, array)

cores/esp8266/abi.cpp

@@ -32,7 +32,7 @@ extern "C" void __cxa_pure_virtual(void) __attribute__ ((__noreturn__));
 extern "C" void __cxa_deleted_virtual(void) __attribute__ ((__noreturn__));
 
 
-#ifndef __cpp_exceptions
+#if !defined(__cpp_exceptions) && !defined(NEW_OOM_ABORT)
 void *operator new(size_t size)
 {
     void *ret = malloc(size);
@@ -52,7 +52,7 @@ void *operator new[](size_t size)
     }
     return ret;
 }
-#endif
+#endif // arduino's std::new legacy
 
 void __cxa_pure_virtual(void)
 {

cores/esp8266/core_esp8266_features.h

@@ -32,6 +32,37 @@
 
 #define WIFI_HAS_EVENT_CALLBACK
 
+#ifdef __cplusplus
+
+#include <stdlib.h> // malloc()
+#include <stddef.h> // size_t
+
+namespace arduino
+{
+    extern "C++"
+    template <typename T, typename ...TConstructorArgs>
+    T* new0 (size_t n, TConstructorArgs... TconstructorArgs)
+    {
+        // n==0: single allocation, otherwise it is an array
+        size_t offset = n? sizeof(size_t): 0;
+        size_t arraysize = n? n: 1;
+        T* ptr = (T*)malloc(offset + (arraysize * sizeof(T)));
+        if (ptr)
+        {
+            if (n)
+                *(size_t*)(ptr) = n;
+            for (size_t i = 0; i < arraysize; i++)
+                new (ptr + offset + i * sizeof(T)) T(TconstructorArgs...);
+            return ptr + offset;
+        }
+        return nullptr;
+    }
+}
+
+#define arduino_new(Type, ...) arduino::new0<Type>(0, ##__VA_ARGS__)
+#define arduino_newarray(Type, n, ...) arduino::new0<Type>(n, ##__VA_ARGS__)
+
+#endif // __cplusplus
 
 #ifndef __STRINGIFY
 #define __STRINGIFY(a) #a
@@ -61,4 +92,4 @@ inline uint32_t esp_get_cycle_count() {
 }
 #endif // not CORE_MOCK
 
-#endif
+#endif // CORE_ESP8266_FEATURES_H