What is EABI?
GNU EABI is a new application binary interface (ABI) for Linux. It is part of a new family of ABI's from ARMŽ Ltd. known in the arm-linux community as EABI (or sometimes Embedded ABI).
How do I use EABI?
To use EABI, you'll need:- A linux kernel that supports EABI. All BitsyG5 kernels and boards that run the latest 2.6 kernel are configured with EABI support enabled. You can boot these kernels from an ATA flash card or on-board flash just as you would our regular kernels.
- An EABI root file system based on ADS' new Debian port which is available for download here.
You can install this root on an NFS server or harddrive, just as you would our regular full Debian distribution.
The root file system includes an arm-linux-gnueabi toolchain which you can use to recompile your own source code.
Why switch to EABI?
According to Debian Wiki the new EABI:- Allows mixing softfloat and hardfloat code.
- Uses a more efficient syscall convention.
- Will be more compatible with future tools.
Furthermore, the GCC default for EABI will be to use softfloat instructions for floating point arithmetic.
Traditionally, GCC used hardfloat FPA [1] instructions in arm-linux software. Unfortunately, most ARM processors lack support for FPA and instead rely on the kernel for floating point emulation (FPE). They do this through illegal instruction faults which are rather inefficient. Emulating floating point instructions using softfloat is significantly faster than the standard NWFPE used in most arm-linux kernels and appreciably faster than the FastFPE we use in our kernels.
Like most root file systems for ARM computers, Debian uses GCC's default for floating point operations. Prior to the introduction of EABI, the only way to use softfloat was to recompile the entire root file system with softfloat enabled. Now, with an EABI root file system, softfloat instructions will be used by default and you'll be able to mix hard and soft float executables.
In the absence of FPA hardware, the switch to softfloat alone will offer appreciable performance improvement. Additionaly, if your system has some non-FPA floating point hardware, you can recompile critical software with the appropriate hardfloat instructions for an even greater improvement in performance and still be able to run it alongside software that uses softfloat.
Besides FPA, what other intruction sets are there ?
We have or will have systems that use VFP (Vector Floating Points), Maverick Crunch (Cirrus Logic), and iWMMXt (Intel) instructions. (The iWMMXt instructions are actually integer SIMD instructions but their opcodes overlap those for FPA).
[1] FPA is a specific kind of floating point acceleration. Many ARM processors have floating point acceleration, just not the FPA variety.
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What is EABI and how do I use it?
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Posted - 11 Jan 2007 : 13:55:58
