Architecture-ABI

Introduction

There are currently many official and unofficial ABI -- Application Binary Interfaces -- in use within embedded Linux projects. The following is an attempt to lightly document what the individual architecture ABI consist of, without going into too many details..

Many of the following ABIs have grown organically based on specific processor designs and optimization levels. For the most part the processor optimizations are ignored in these descriptions, unless otherwise mentioned.

Additional references, CPU optimization compatibility and suggested canonical architecture namings may be provided.

ABI Summary

The following is a list of ABIs that are in common usage. Some of the ABIs discussed in the following sections will not appear in this table if they are legacy.

Arch	ABI	Endian	Compatibility
ARM	ARM EABI	Big Endian
ARM	ARM EABI	Little Endian

ARM

ABI

apcs-gnu a.k.a. OABI - The original ARM ABI.

It has two variants, an emulated hardware floating point, and a soft floating point variant. The legacy ABI should no longer be used in embedded projects and has more or less disappeared. The legacy ABI is not compatible with the EABI.

It can be detected by:

From: http://wiki.debian.org/ArmEabiPort

objdump -x contains [APCS-32]

The legacy abi can be enabled by using "-mabi=apcs-gnu"

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EABI - The new "Embedded" ABI by ARM ltd.

The new EABI specifies a single ABI that works in various hardware floating point and software floating point configurations as well as Thumb interworking. Overall structure packing is better, a more efficient syscall convention is provided.