Choose the option --fpu vfpv2 to have the compiler generate ARM code only for functions containing floating-point operations.

When the option --fpu vfpv2 is selected, the compiler generates ARM code for any function containing floating-point operations, regardless of whether the compiler is compiling for ARM or compiling for Thumb.

Functions containing floating-point operations and that are compiled for Thumb are compiled to ARM code, because Thumb code cannot contain VFP instructions or access VFP registers. This uses hardware VFP linkage.

When compiling for ARM only, use --fpu=vfp and not --fpu=softvfp+vfp. Software linkage adds an overhead in transfer values between VFP and ARM that slows down the transfers and requires additional instructions.

Choose the option --fpu softvfp+vfpv2 to have the compiler generate mixed ARM/Thumb code.

When the option --fpu softvfp+vfpv2 is selected, all functions are compiled using software floating-point linkage. This means that floating-point arguments are passed to and returned from functions in integer registers.

The Thumb instruction set does not contain VFP instructions and therefore cannot access VFP registers. Therefore, for Thumb code, when --fpu=softvfp+vfpv2 is used, the compiler generates calls to library functions to perform the VFP operations. These library functions have to use software linkage because the Thumb code cannot access the VFP registers that are required to use hardware linkage.

The RVCT libraries include versions of the software floating point functions that are compiled for ARM, and use VFP instructions to be used with --fpu=softvfp+vfpv2. These library functions give improved performance and reduced code size compared to the full software floating point functions.

Choose the option --fpu softvfp+vfpv3 to have the compiler generate mixed ARM/Thumb code.

When the option --fpu softvfp+vfpv3 is selected, all functions are compiled using software floating-point linkage. This means that floating-point arguments are passed to and returned from functions in ARM integer registers.

Software floating-point linkage enables you to link with generic libraries and legacy code that are themselves built with software floating-point linkage.

Choose the options --arm --fpu vfpv3 to have the compiler generate ARM code only. This uses hardware VFP linkage.

Choose the options --thumb --fpu vfpv3 to have the compiler generate Thumb-2 code only for your entire program. Thumb-2 supports VFP instructions. Therefore, there is no need to switch to ARM state to perform VFP operations. This uses hardware VFP linkage.