sys/new_delete: add malloc/free based new/delete implementation

[gschorcht]

Contribution description

This PR adds a module extracted from the Arduino core to provide C++ new and delete operators.

On some platforms libstdc++ is not used or not available, like on the AVR. Such platforms can use this module to implement the C++ new and delete operators using malloc and free respectively. However, to be thread-safe, a thread-safe implementation of malloc and free must be present.

The new_delete module is used by default by AVR if cpp module is used.

Testing procedure

Green CI. Module is compiled as part of C++ compilation of the arduino module for ATmega boards.

Issues/PRs references

Prerequesite for #17460 and #12518

[maribu]

I have some style suggestions and a question, see inline

[maribu]

I don't quite get this one. I cannot find an API doc, but the arguments do not seem to make much sense unless this expected to behave somewhat like realloc

[gschorcht]

According to https://www.cplusplus.com/reference/new/operator%20new/

void* operator new (std::size_t size, void* ptr) noexcept;

is the placement function which simply returns ptr and doesn't allocate storage:

ptr 
       A pointer to an already-allocated memory block of the proper size.
       If called by a new-expression, the object is initialized (or constructed) at this location.

[gschorcht]

The counterpart is

void operator delete (void* ptr, void* voidptr2) noexcept;

[gschorcht]

Found an good example how it could be used at cppreference.com

// within any block scope...
{
    alignas(T) unsigned char buf[sizeof(T)];
    // Statically allocate the storage with automatic storage duration
    // which is large enough for any object of type `T`.
    T* tptr = new(buf) T; // Construct a `T` object, placing it directly into your 
                          // pre-allocated storage at memory address `buf`.
    tptr->~T();           // You must **manually** call the object's destructor
                          // if its side effects is depended by the program.
}                         // Leaving this block scope automatically deallocates `buf`.

[gschorcht]

@maribu I didn't change anything, it's just the original code. Do you think it is necessary to bring it into RIOT style? The static tests are happy with the code as it is.

[gschorcht]

@maribu Fixed the style including indentation.

[gschorcht]

May I squash?

[gschorcht]

Compilation fails for AVR. It seems that avr-g++ (gcc 5.4.0) is not C++11 compatible. I can observe for ESP32.

[maribu]

Compilation fails for AVR. It seems that avr-g++ (gcc 5.4.0) is not C++11 compatible. I can observe for ESP32.

That old GCC does support C++11, if explicitly enabled. If I recall correctly it is just not the default back than (but it is for more recent toolchains).

We could fix that with just adding CXXFLAGS += -std=c++11 - which would be consistent with using C11.

Either way, please squash at will.

[gschorcht]

We could fix that with just adding CXXFLAGS += -std=c++11 - which would be consistent with using C11.

👍 Indeed, had to do the same for ESP's nvs flash modules.

Squashed.

[gschorcht]

Thanks for reviewing and merging.

With -std=c++14 we will get a compilation problem because not all possible operators are defined 😟

sys/cpp_new_delete/new_delete.cpp:34:6: error: the program should also define 'void operator delete(void*, unsigned int)' [-Werror=sized-deallocation]