History of FP ABIs

The MIPS ABIs support a variety of different floating-point extensions where calling-convention and register sizes vary for floating-point data. The extensions exist to support a wide variety of optional architecture features. The resulting ABI variants are generally incompatible with each other and must be tracked carefully.

Traditionally the use of an explicit .gnu_attribute 4, n directive is used to indicate which ABI is in use by a specific module. It was then left to the user to ensure that command line options and the selected ABI were compatible with some potential for inconsistencies.