5.3. ABI Variables

On the ARM architecture, there are two major ABI types to choose from: EABI and OABI. There is also a Thumb ABI and an Intel IWMMX specific ABI but these are generally not recommended for most uses.

The EABI (Embedded ABI) is newer and supports additional features, faster software floating point operations, and Thumb interworking, but is only compatible with ARMv4t and newer cores. The EABI has sub-ABIs of: aapcs-linux and aapcs. aapcs-linux has standard Linux 4 byte enums while aapcs has variable length enums. aapcs-linux is recommended over aapcs.

The OABI (old ABI) is called apcs-gnu and supports ARMv4 and older cores. Generally the OABI is not used by modern ARM processors.

Setup for a Particular ABI:

export CLFS_ABI="[From Chart]"
echo export CLFS_ABI=\""${CLFS_ABI}\"" >> ~/.bashrc

The following table gives the entires for the different ABI's that CLFS Embedded supports. Make sure you select one for your build, this will ensure capatibilty of your build with your target architecture.

Table 5.1. List of Build Variables

aapcs-linux aapcs-linux Recommended for EABI. Standard Linux 32 bit (int) enums
apcs-gnu apcs-gnu Recommended for OABI
atpcs atpcs Thumb ABI
aapcs aapcs EABI w/ variable size enums
iwmmxt iwmmxt Supports Intel XScale MMX extensions