[int_19h]

Looking at the code, a great deal of this is non-portable and/or U.B, so I would hesitate to call it C. And I'm not talking about some hypothetical problems, but stuff that should surface quite soon. For example, this is how stack allocations are made:

    #define alloc_stack(T) ((struct T*)header_init( \
      (char[sizeof(struct Header) + sizeof(struct T)]){0}, T, AllocStack))

So far as I can see, there are basically no alignment guarantees here - the returned pointer to the char array is not guaranteed to be aligned properly for Header (which is a struct of a single void* field), nor is there any attempt to align T inside the array. If things get misaligned, on x86 and x64, it'll work (but possibly much slower than normal), but on e.g. ARM you'll get all kinds of weird things happening.

[ant6n]

Apparently ARM allows unaligned loads now (permitted in ARMv6, default in ARMv7). There seem to be some instructions that don't support it, like STM. Also, afaik code needs to be aligned properly, and function pointers need to be aligned properly lest you will switch between arm and thumb mode. Apparently you can tell the ARM compiler to assume all memory accesses are unaligned.

Under ARMv8, I think alignment is less of an issue.

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc....