operator new: no exception without need for std::nothrow

[d-a-v]

CLOSED

https://stackoverflow.com/questions/6049563/with-fno-exceptions-what-happens-with-new-t
operator new will never return nullptr.
Either we get an exception, or if everything is compiled with -fno-exception, abort() is called.

(was:)

Overloads operator new so it can return nullptr instead of throwing an exception without need for (std::nothrow).

Requirement: <Arduino.h> must be included prior to any c++ header file

addresses #6269 @mcspr @mhightower83

[earlephilhower]

Interesting solution to the problem.

The standard libraries do not ever check the return value of new() != nullptr, they use a catch or they expect their code to stop and your upper lever code to have that catch(). There has been more than one bug where we find std::shared_ptr or some other compound type (which has elements that are new()ed) crashes with a stack trace after doing a new and trying to use the returned object.

Theoretically, it seems like this would let the std:: libs abort() on the failed new (since they should use the base new() and it will throw), and let user code use the broken nothrow new().

[earlephilhower]

Needs to set the last alloc addr/size on failure to help us debug crashes.

I'll try it out later today on some test cases, too, with and w/o exceptions...

[earlephilhower]

Please check out the old new() and new override, it sets the last-failed-alloc address which this needs to do as well:

Arduino/cores/esp8266/abi.cpp

Lines 31 to 49 in bb28d4a

	void *operator new(size_t size)
	{
	void *ret = malloc(size);
	if (0 != size && 0 == ret) {
	umm_last_fail_alloc_addr = __builtin_return_address(0);
	umm_last_fail_alloc_size = size;
	}
	return ret;
	}
	void *operator new[](size_t size)
	{
	void *ret = malloc(size);
	if (0 != size && 0 == ret) {
	umm_last_fail_alloc_addr = __builtin_return_address(0);
	umm_last_fail_alloc_size = size;
	}
	return ret;
	}

[d-a-v]

This is a hack.

Remove noexcept or move #include <new> before these definitions, and constructors will be called no matter what.

[earlephilhower]

For reference the prior new override was handled here:
https://github.com/esp8266/Arduino/blob/2.4.2/cores/esp8266/abi.cpp