ABI EABI

http://bbs.chinaunix.net/thread-1950213-1-1.html

这个是友善之臂的linux内核移植里头提到的那篇文章，我以前也转载过，不过好像没找到这么全的出处。

ABI和API是不一样的，ABI是强调的是B，也就是二进制级别的兼容。P是编程。I是接口。

应该是关于I的设计问题，我不太理解，应该很深刻。想不到编译器竟然这么有学问。

1。什么是ABI

ABI，application binary interface (ABI)， 应用程序二进制接口。
既然是 接口，那就是某两种东西之间的沟通桥梁，此处有这些种情况：
A。 应用程序 <－> 操作系统；
B。应用程序 <－> （应用程序所用到的）库
C 。应用程序各个组件之间

类似于API的作用是使得程序的代码间的兼容，ABI目的是使得程序的二进制（级别）的兼容。

2。什么是OABI 和 EABI
OABI中的O，表示“Old”，“Lagacy”，旧的，过时的，OABI就是旧的/老的ABI。
EABI中的E，表示“Embedded”，是一种新的ABI。
EABI有时候也叫做GNU EABI。
OABI和EABI都是专门针对ARM的CPU来说的。

3。EABI的好处 ／ 为何要用EABI
A。支持 软件浮点和硬件实现浮点功能混用
B。 系统调用的效率更高
C。后今后的工具更兼容
D。软件浮点的情况下，EABI的软件浮点的效率要比OABI高很多。

4。OABI和EABI的区别
两种ABI在如下方面有区别：
A。调用规则（包括参数如何传递及如何获得返回值）
B。系统调用的数目以及应用程序应该如何去做系统调用
C。目标 文件的二进制格式，程序库等
D。结构体中的 填充（padding/packing）和对齐。
E。
OABI：
* ABI flags passed to binutils: -mabi=apcs-gnu -mfpu=fpa
* gcc -dumpmachine: arm-unknown- linux
* objdump -x for compiled binary:

private flags = 2: [APCS-32] [FPA float format] [has entry point]

* "file" on compiled Debian binary:

ELF 32-bit LSB executable, ARM, version 1 (ARM), for GNU/Linux 2.2.0, dynamically linked (uses shared libs), for GNU/Linux 2.2.0, stripped

* " readelf -h | grep Flags ""

Flags: 0x0

EABI：
* ABI flags passed by gcc to binutils: -mabi=aapcs-linux -mfloat-abi=soft -meabi=4
* gcc -dumpmachine: arm-unknown-linux-gnueabi
* objdump -x for compiled binary:

private flags = 4000002: [Version4 EABI] [has entry point]

* "file" on compiled binary (under Debian):

ELF 32-bit LSB executable, ARM, version 1 (SYSV), for GNU/Linux 2.4.17, dynamically linked (uses shared libs) , for GNU/Linux 2.4.17, stripped

* "readelf -h | grep Flags""

Flags: 0x4000002, has entry point, Version4 EABI

ARM kernel port created in 1998
Used GCC’s C calling convention for arm
Userspace to kernel syscall interface designed to pass 5 or
more arguments efficiently (via registers). Similar to
RISCOS conventions, without condition codes to indicate
errors.
Floating point was done with FP instruction set. Executed
by FPU if present, emulated if not.




FP solutions
Runtime Emulators (‘hard-float’):
Acorn FPE (binary module)
NWFPE, FastFPE
Compile-time functions (‘soft-float’)
GCC softfloat
Softfloat and Emulators incompatible due to different calling
conventions.
Real FPU/emulation: Calls use r0-r3 for 1st 4 arguments, stack for the rest.
floats can fill multiple registers, and be split across registers and stack.
Return value is put in Coprocessor register f0.
Softfloat: the return value is put in r0-r2 (depending on size)
Debian-arm uses hard-float, because it pre-dates the soft-float
concept.

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The ARM EABI port is now available. See ArmEabiHowto and ArmEabiTodo. 


Its progress towards inclusion in the Debian "lenny" release, scheduled for September 2008, is shown at armelLennyReleaseRecertification. 




Contents


In a nutshell
Terminology
GCC view
ARM floating points
GCC preprocessor macros for floating point
Struct packing and alignment
Stack alignment
64-bit data type alignment
Enum sizes
System call interface
Choice of minimum CPU
Thumb interworking suggests armv4t
Other scenarios
Why a new port
0. Not an option!
1. Rename all library packages
2. New arch
3. ABI: field in control file
4. conflicting libc packages
Roadmap
EABI status
Naming
Strategy
References


http://wiki.debian.org/ArmEabiPort

In a nutshell
EABI is the new "Embedded" ABI by ARM ltd. EABI is actually a family of ABI's and one of the "subABIs" is GNU EABI, for Linux. The effective changes for users are: 


Floating point performance, with or without an FPU is very much faster, and mixing soft and hardfloat code is possible 


Structure packing is not as painful as it used to be 
More compatibility with various tools (in future - currently linux-elf is well supported) 
A more efficient syscall convention 


At present (with gcc-4.1.1) it works with ARMv4t, ARMv5t processors and above, but supporting ARMv4 (e.g., StrongARM) requires toolchain modifications. See "Thumb interworking" below. 


Terminology
Strictly speaking, both the old and new ARM ABIs are subsets of the ARM EABI specification, but in everyday usage the term "EABI" is used to mean the new one described here and "OABI" or "old-ABI" to mean the old one. However, there are one or two programs that sometimes describe an old ABI binary as "EABI". 


To add to the confusion, powerpc has also had an ABI called "EABI" for some, which has nothing to do with this one. 




GCC view
New ABI is not only a new ABI field, it is also a new GCC target. 


Legacy ABI 


ABI flags passed to binutils: -mabi=apcs-gnu -mfpu=fpa 
gcc -dumpmachine: arm-unknown-linux 
objdump -x for compiled binary: 


private flags = 2: [APCS-32] [FPA float format] [has entry point]"file" on compiled Debian binary: 


ELF 32-bit LSB executable, ARM, version 1 (ARM), for GNU/Linux 2.2.0, dynamically linked (uses shared libs), for GNU/Linux 2.2.0, stripped"readelf -h | grep Flags"" 


Flags: 0x0Arm EABI: 


ABI flags passed by gcc to binutils: -mabi=aapcs-linux -mfloat-abi=soft -meabi=4 
gcc -dumpmachine: arm-unknown-linux-gnueabi 
objdump -x for compiled binary: 


private flags = 4000002: [Version4 EABI] [has entry point]"file" on compiled binary (under Debian): 


ELF 32-bit LSB executable, ARM, version 1 (SYSV), for GNU/Linux 2.4.17, dynamically linked (uses shared libs), for GNU/Linux 2.4.17, stripped"readelf -h | grep Flags"" 


Flags: 0x4000002, has entry point, Version4 EABIFurthermore, as well as the usual __arm__ and maybe also __thumb__ symbols, the C preprocessor symbol __ARM_EABI__ is also defined when compiling into EABI, while __ARMEL__ is predefined under both the new and old ABIs. 




ARM floating points
The current Debian port creates hardfloat FPA instructions. FPA comes from "Floating Point Accelerator". Since the FPA floating point unit was implemented only in very few ARM cores, these days FPA instructions are emulated in kernel via Illegal instruction faults. This is of course very inefficient: about 10 times slower that -msoft-float for a FIR test program. The FPA unit also has the peculiarity of having mixed-endian doubles, which is usually the biggest grief for ARM porters, along with structure packing issues. 


ARM has now introduced a new floating point unit, VFP (Vector Floating Points), which uses a different instruction set than FPA and stores floats in natural-endian IEEE-754 format. VFP is implemented in new some ARM9/10/11 cores, like in the new TI OMAP2 family. It seems likely that ARM cores without VFP will remain popular, as in many places ARM is used floats are unnecessary. 


To complicate thing further, ARM processors are being integrated with many other FPUs and DSPs, each of which adds its own set of instructions to the ARM set: 


Cirrus Logic's EP93XX series integrate an ARM920T core with a MaverickCrunch FPU. This also uses IEEE-754, though uses a different instruction set to VFP. Current ARM-Debian users cannot use their Maverick FPUs at all except by programming in assembler or using an alternative compiler. GCC has flags to generate Maverick FP instructions (-mfpu=maverick), but the .o files cannot be linked with the standard Debian GCC startup files or libraries. 


Intel's iWMMXt unit is used in their PXA270 processor with an XScale main core. This adds integer SIMD and some other instructions but there is currently no iWMMXt processor with hardware floating point capabilities. iWMMXt processors are incompatible with FPA due to opcode overlap, while they could have an VFP coprocessor in principal. That said, iWMMXt instructions should make soft-float fairly quick anyway. Again, GCC support exists (-march=iwmmxt) for this but is also currently unusable within standard Debian. 
Texas Instruments' OMAP, OMAP2, DaVinci DM644x series and numerous other products integrate a ARM9/ARM11 core with their own DSP core for multimedia acceleration and/or telecommunication signal processing, though it does fixed-point math and its DSP code is completely separate from the ARM code. In Linux DSP Gateway or proprietary solutions are used to load code for execution on the c55x/c6xx and provide a way to for ARM and DSP code to communicate. 


For a generic-purpose distribution like Debian, targeting binary compatibility, EABI lets us have the cake and eat it. We can make a soft-float distribution using IEEE-754 with FPU-specific versions of packages (linux-kernel-2.6.x-vfp, libc6-iwmmxt, mediaplayer-maverick, etc) where needed. This also enables individual packages to do runtime FPU detection and call code compiled for different FP scenarios (in liboil for example). 


The major FP variants worth support as alternative versions of FP-critical packages seem to be 


the current arm arch supporting armv3 with or without FPA and armv4 processors. 
EABI for generic ARM (>= armv4t) using IEEE soft-float 


EABI for lowest common denominator VFP (there are now more than one VFP "extended" variant) 
EABI for MaverickCrunch FPU 


EABI for iWMMXt using iWMMXt-specific soft-float 


GCC preprocessor macros for floating point
When porting code to ARM EABI, the following preprocessor macros are interesting: 


__VFP_FP__ means that the floating point format in use is that of the ARM VFP unit, which is native-endian IEEE-754. 


__MAVERICK__ means that the floating point format is that of the Cirrus Logic MaverickCrunch, which is also IEEE-754 and is always little-endian. 


__SOFTFP__ means that instead of floating point instructions, library calls are being generated for floating point math operations so that the code will run on a processor without an FPU. 


__VFP_FP__ and __MAVERICK__ are mutually exclusive. If neither is set, that means the floating point format in use is the old mixed-endian 45670123 format of the FPA unit. 


Note that __VFP_FP__ does not mean that VFP code generation has been selected. It only speaks of the floating point data format in use and is normally set when soft-float has been selected. The correct test for VFP code generation, for example around asm fragments containing VFP instructions, is 


#if (defined(__VFP_FP__) && !defined(__SOFTFP__))Paradoxically, the -mfloat-abi=softfp does not set the __SOFTFP___ macro, since it selects real floating point instructions using the soft-float ABI at function-call interfaces. 


By default in Debian armel, __VFP_FP__ && __SOFTFP__ are selected. 




Struct packing and alignment
With the new ABI, default structure packing changes, as do some default data sizes and alignment (which also have a knock-on effect on structure packing). In particular the minimum size and alignment of a structure was 4 bytes. Under the EABI there is no minimum and the alignment is determined by the types of the components it contains. This will break programs that know too much about the way structures are packed and can break code that writes binary files by dumping and reading structures. 




Stack alignment
The ARM EABI requires 8-byte stack alignment at public function entry points, compared to the previous 4-byte alignment. 




64-bit data type alignment
"One of the key differences between the traditional GNU/Linux ABI and the EABI is that 64-bit types (like long long) are aligned differently. In the traditional ABI, these types had 4-byte alignment; in the EABI they have 8-byte alignment. As a result, if you use the same structure definitions (in a header file) and include it in code used in both the kernel and in application code, you may find that the structure size and alignment differ." 


-- from the Codesourcery ARM GNU toolchain FAQ 




Enum sizes
The EABI defines an optional system for controlling the size of C enumerated types. For arm-linux it was decided to keep the existing behaviour (enums are at least the same size as an int) for consistency with other Linux systems. 


This is also reflected in the -mabi=aapcs or -mabi=aapcs-linux switches to GCC: aapcs defines enums to be a variable sized type, while with aapcs-linux they are always ints (4 bytes). 




System call interface
Two things change in the system call interface: alignment of 64-bit parameters passed in registers and the way the system call number itself is passed. 


With EABI, 64-bit function parameters passed in registers are aligned to an even-numbered register instead of using the next available pair. 


Here's an explanation from Russell King, 12 Jan 2006: 




We have r0 to r6 to pass 32-bit or 64-bit arguments. With EABI,
64-bit arguments will be aligned to an _even_ numbered register.
Hence:
long sys_foo(int a, long long b, int c, long long d);
will result in the following register layouts:
        EABI                            Current
r0      a                               a
r1      unused                          \_ b
r2      \_ b                            /
r3      /                               c
r4      c                               \_ d
r5                                      /
r6      ... out of space for 'd'        ... room for one other int.
r7      syscall numberSince this already causes an incompatible change in the system call interface, the opportunity has been taken to slip in a more efficient, totally incompatible way of doing system calls: instead of using the swi __NR_SYSCALL_BASE(==0x900000)+N instruction, where N is the number of the system call, swi 0 is always used with the system call number stashed in register r7. This is more efficient because the kernel no longer has to go and fish N out of the instruction stream(*), which used to have a negative impact on the efficiency of processors with separate text and data caches (i.e. most ARMs). 


Fortunately, the two schemes can coexist and EABI kernels have an option to support the old syscall interface (including old structure layout rules) for running old-EABI binaries. However some features (e.g., ALSA, MD (RAID) and system calls from Thumb mode) do not work correctly from old-ABI binaries. 


Some third party EABI toolchains (e.g., CodeSourcery 2005q3) use the old kernel interface via userspace shims in glibc. This is now obsolete and no longer supported by glibc. 


(*) This is only true if the old-ABI compatibility option is disabled. 


See this article for more details. 




Choice of minimum CPU


Thumb interworking suggests armv4t
The EABI includes thumb interworking, which means that 16-bit Thumb and normal 32-bit ARM instructions can be mixed at function-level granularity. 


Thumb interworking is mandatory according to the ARM EABI spec and requires every return and indirect function call to execute a BX instruction to set the core to the correct state, which is only present in armv4t cores and above. Gcc, too, only supports thumb interworking for armv4t and above. 


So Debian armel runs on a minimum CPU of ARMv4t and by default the Debian armel GCC generates code for armv4t (rather than the usual default ARM target of armv5t). 




Other scenarios
However a lower entry-level CPU is possible to do using different function return sequences which are of various speeds, and that work and/or allow Thumb interworking on different selections of the ARM architectures. 


0.  mov pc,lr  


Is what GCC currently emits for -march=armv4. It works on ARMv4 and above but is only Thumb interworking-safe from ARMv7. 


1.  bx lr  


Is what GCC emits for -march=armv4t. It works on ARMv4t and above and Thumb interworking is possible on ARMv4t and above. Excludes armv4, the StrongARM which are very common and some armv5 users, but armv5 with no t seems a rare processor. CC needs modifying to implement any of the following choices. 


2.  tst lr, #1; moveq pc, lr; bx lr  


was suggested by Paul Brook as an alternative to BX. It works on ARMv4 and above and Thumb interworking is possible on ARMv4t and above, with the extra cost of two instructions per indirect call/function return, though in line with the run-on-minimum-hardware Debian way. 


Here is a patch by Richard K. Pixley which illustrates what is needed, but is not (April 2007) tested: http://lists.debian.org/debian-arm/2007/05/msg00015.html 


This is problematic because hand written assembly has to be manually fixed. 


3.  ldm/ldr  


Works on ARMv4 and above but Thumb interworking is only possible on ARMv5t and above, excluding ARMv4t users from using Thumb code with Debian. Gcc currently emits this for non-leaf functions on ARMv4 and ARMv5 (but not ARMv4t, where it uses BX, the only way to do interworking on v4t). Although a single instruction, this method may be slower than the three-instruction sequence because of the memory accesses it requires. 


4. Drop Thumb interworking 


A final option would be simply to compile the standard Debian repo --with-arch=armv4 --with-no-thumb-interwork. This would work on all processors without the dangers inherent in modifying GCC and, according to the GCC manual page, saves a slight size and speed overhead caused by being thumb-interworkable. 


There is significant discussion of the technical merits of these various schemes in the debian-arm mailing list thread Re: ARM EABI port: minimum CPU choice of which the above is a partial summary. 


5. tat says that simply compile for armv3 would work, though the code would be relatively slower on the most common, later CPUs. armv3 is fairly rare: Psion 5 


6. Kernel emulation traps 


It may be possible to catch illegal instruction in the kernel generated by the missing "BX" instruction, in the same way as missing hard floating point instructions can be emulated. It wouldn't be that fast on armv4 hardware (causing a context switch per function call/return) but such a kernel hack would allow the current repository to be used unmodified on armv4 hardware. 


7. Linker fixups 


The EABI provides mechanisms (R_ARM_V4BX relocations) for the linker to fixup bx instructions. Currently the linker only knows how to convert these to mov pc instructions, so you have to choose between armv4 or interworking at static link time. However the linker could be taught how to convert these into branches to a tst;moveq;bx stub. This has the advantage of also working for hand written assembly. It may be desirable to get the compiler to also generate this triplet inline for performance reasons. 


This is implemented in recent binutils. Code should be compiled with -march=armv4, and arrange for --fix-v4bx-interworking to be passed to the linker and --fix-v4bx to be passed to the assembler. A gcc patch may also need backporting to avoid and earlier sanity check. 


If you pass --fix-v4bx to the linker it will generate plain v4 binaries, which are not interworking safe, so should not be used on later cores (which may have Thumb libraries). --fix-v4bx-interworking generates code that works on armv4, and is also interworking safe on later hardware. 


The limitation of this option is that any bx instruction will clobber the condition codes. The ABI specifies that condition codes are normally call clobbered, so normally this is not a problem. AFAIK there is only one exception. The libgcc cfcmp* routines (gcc/config/arm/ieee-{sf,df}.S) need to preserve the C and Z flags. 


The linker fixup does introduce some additional overhead, so it may be desirable to also implement (2). Care should be taken to avoid double fixups. 




Why a new port
In Debian, we want to assure complete binary compatibility. Since the old ABI is not compatible with the new one, we can't allow packages built with old ABI to link against new-abi libs, or the other direction. So the options are: 




0. Not an option!
Under no circumstances distribute EABI binaries as .arm.deb depending on current library package names!!! 




1. Rename all library packages
This is an ABI transition that affects all architectures, and it has been done before (aout -> elf, c++ ABI) 


+ apt-get dist-upgrade for users is possible 
- Requires insane amounts of work - every single library package needs to be renamed 
- Requires a very long transition period, in which unstable will be broken for all archs. 
c++ ABI transition takes about half an year, full transition could thus take around 2 years 
- Achieving Consensus for such transition on debian-devel would be very hard. 
Non-ARM developers will object doing such amount of work only for a minor arch. If arm gets dropped from Release Arch's, we can't even file RC bugs for the migration. 
- Very invasive change, affecting every user and developer of Debian. 


2. New arch
+ Technically, since we drop FPA instruction support, and gcc dumpmachine triplet is different, we can argue we have a new arch 
+ Does not affect non-ARM users 
+ we can target EABI for armv4(t?)+ while we can can keep oldabi port for ARMv3 (RiscPC) and maybe armv4 (StrongARM) users. 
+ Allows using new instructions (thumb) and drops the old FPU instruction set 
+ Can be done quickly, does not affect other arch's release cycle 
+ requires less archive space during migration 
- Current ARM users don't have a easy upgrade path 
For the last point, a statically compiled [ArchTakeover] tool could be created. This would also allow i386->amd64 style migrations. 




3. ABI: field in control file
This was suggested as part of Multiarch proposal. It is unknown if it would actually become part of Debian or not 


+ Reflects the packages ABI correctly, would help other transitions as well 
- no working implementation 
- no consensus on how to do it (apt developers want something more generic instead) 
- might be hard to fit into current archive infrastructure 
- make dependency resolving hard 
From these choices, we believe a new port is the best compromise. 




4. conflicting libc packages
In this scenario, we create a libc6-eabi(-dev) package that has eabi glibc and ld-linux.so.3. This package will conflict with libc6(-dev), and thus you can mix and match eabi and non-eabi binaries and libs. 


+ similar to the libc6.1 style packages on some archs 
+ requires modifying only glibc 
- ugly 
- most of ARM port will remain uninstallable for long time 
- apt-get dist-upgrade will still not work, since it gives up quickly when lots of packages conflict 
Let's not make perfect an enemy of good!! 




Roadmap
Armel (EABI) will be released with etch+1 as it should be in good shape by then. That release will thus contain arm and armel. Arm will be dropped in etch+2, assuming that the above gcc changes to support armv4 CPUs in armel prove practical. If we cannot support armv4 in armel then arm will remain around until we drop v4/StrongARM support, i.e. the port falls into general disuse. 




EABI status
The commercial ARM RealView C/C++ compiler was the first to support EABI, and usable EABI support came into GCC from version 4.1.0. 


CodeSourcery provide GNU ARM toolchains. The 2005Q3 release is a modified version of gcc-3.4.4 while 2006Q1 is from gcc-4.1.0. These toolchains produce EABI object code and the 2006Q1 release also uses the EABI Linux kernel interface. 


EABI is supported in the ARM Linux kernel from version 2.6.16 and there is an optional compatibility feature to allow the running of old-ABI binaries with an EABI kernel. The inverse mechanism, to run EABI binaries in an ABI kernel, is not implemented and is said to be non-trivial to do. 


Riku Voipio has built a booting EABI root filesystem up to X as proof of concept, which seems stable, built with codesourcery gcc 3.4 toolchain. 


Koen Kooi has used OpenEmbedded to build a pure EABI root filesystem including native toolchain, visible under http://dominion.kabel.utwente.nl/koen/cms/working-native-eabi-toolchain The compiler is gcc-4.1.1 with glibc-2.4: the exact versions we need. The system boots and runs fine on armv5t and the C compiler seems to work well. However the C++ compiler is not working because libstdc++ is not installed and perl does not execute because libperl.so.5 is not installed as well. Both problems can be solved by using ipkg to install them. 


The Angstrom distro of OpenEmbedded has a public repository of ARM EABI ipackages compiled for armv5te and visible under http://angstrom-distribution.org/unstable/feed/ 


Lennert Buytenhek and ADS have built an EABI root filesystem, and some ten thousand (probably many more by now) packages. For download locations and other details, see the announcement 


QEMU 0.8.1 can run ARM EABI systems, though when running with the 2.6.16 kernel it is mind-bogglingly slow on x86 processors of a few hundred megahertz. Using 2.6.17-rc3 or later fixes this anomaly. To run a single ARM EABI executable in qemu-user mode, some patches are required, though these are not complete yet. 


Minimum versions of components with the first working EABI support are: 


binutils - from 2.16.92 - already in Debian 
gcc - gcc 4.1.0 (Thumb interworking on armv4t needs 4.1.1) 
glibc - fully upstream in 2.4. Will also be in 2.3.7 
Earlier glibcs (2.3.6?) support EABI userspace but had old-style syscalls to work with older kernels (2.6.8-2.6.13ish). 
kernel - eabi support is present from 2.6.16. 
dpkg, apt - patches will be submitted when port name consensus is achieved 


Naming
At the Extremadura emdebian meeting, 12-16 April 2006, the name "armel" was chosen. If a bigendian arm EABI port will be created, it will be called "armeb", and it will replace the previous oldabi-based "armeb" port effort. 




Strategy
The ultimate根本的 aim is a new standalone独立的 architecture, composed of three concrete具体的 components: 


At least two online repositories of precompiled binary packages 
At least two online buildd's: native ARM EABI machines that will compile Debian packages from source into ARM EABI packages automatically. See Autobuilder network and Setting up a buildd 


Debian installer support for the new arch. 




--------------------------------------------------------------------------------




The following is outdated but left here for historical interest. Lennert Buytenhek booted his Debian EABI port from the Angstrom distribution of OpenEmbedded. 


The chronological steps to bootstrap the new arch seem to be: 


1) Make Debian packages of a cross-compiler targeting ARM EABI. This means gcc-4.1, glibc-2.4+glibc-ports-2.4, binutils-2.17 and linux-2.6.16. This can be compiled using crosstool-0.42 and the patches and control files at http://freaknet.org/martin/crosstool, and packaged with the scripts at the same location. 


2) Make a package for the existing Debian experimental ARM arch of the Linux kernel compiled to use EABI internally, with run-old-ABI-binaries enabled, and test it with existing old-ABI Debian userland. 


3) Cross-build essential and required EABI userland packages using dpkg-cross. A parallel effort is the slind project, which is busy improving dpkg-cross support within the Emdebian framework. 


4) Make the Debian installer debootstrap work for the new arch. 


5) Populate the new-arch repository(-ies) with the rest of the Debian packages. 


Is there a "HOWTO Create a New Debian Arch" document? No. 


On the crossgcc list, Michael K. Edwards says of the procedure to bootstrap a new Debian arch by doing all building in a QEMU chroot on a fast host: 


You build your crosstools, you build your minimal chroot and a Canadian cross, then you qemu-chroot in and build a fully native toolchain. Instantiate a dpkg database with the host's dpkg and use equivs to fake up dpkg entries for your toolchain. Build your Required packages and real packages for build-essential, then construct a fresh qemu-chroot, this time with debootstrap and your pile o' packages. If you're paranoid, rebuild all your packages in this chroot and debootstrap afresh -- it's your first chance to test that your glibc built the Debian Way really works. Then start layering on applications, without worrying about whether they cross-compile easily. 


References
Definition of EABI: ARM Architecture Procedure Call Standard plus CodeSourcery's ARM GNU/Linux Application Binary Interface Supplement 


ELF for the ARM Architecture (PDF by ARM Ltd) 


GNU Toolchain for ARM FAQ by CodeSourcery 






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ArmEabiPort (last edited 2011-05-08 19:49:15 by MartinGuy)


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