File.........: overview.txt

Content......: Overview of how crosstool-NG works.

Copyrigth....: (C) 2007 Yann E. MORIN <yann.morin.1998@anciens.enib.fr>

License......: Creative Commons Attribution Share Alike (CC-by-sa), v2.5

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Table Of Content  /

_________________/

Introduction

History

Referring to crosstool-NG

Installing crosstool-NG

  Install method

  The hacker's way

  Preparing for packaging

  Shell completion

  Contributed code

Configuring crosstool-NG

  Interesting config options

  Re-building an existing toolchain

  Using as a backend for a build-system

Running crosstool-NG

  Stopping and restarting a build

  Testing all toolchains at once

  Overriding the number of // jobs

  Note on // jobs

  Tools wrapper

Using the toolchain

  The 'populate' script

Toolchain types

  Seemingly-native toolchains

Contributing

  Sending a bug report

  Sending patches

Internals

  Makefile front-end

  Kconfig parser

  Architecture-specific

  Adding a new version of a component

  Build scripts

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               /

Introduction  /

_____________/

crosstool-NG aims at building toolchains. Toolchains are an essential component

in a software development project. It will compile, assemble and link the code

that is being developed. Some pieces of the toolchain will eventually end up

in the resulting binary/ies: static libraries are but an example.

So, a toolchain is a very sensitive piece of software, as any bug in one of the

components, or a poorly configured component, can lead to execution problems,

ranging from poor performance, to applications ending unexpectedly, to

mis-behaving software (which more than often is hard to detect), to hardware

damage, or even to human risks (which is more than regrettable).

Toolchains are made of different piece of software, each being quite complex

and requiring specially crafted options to build and work seamlessly. This

is usually not that easy, even in the not-so-trivial case of native toolchains.

The work reaches a higher degree of complexity when it comes to cross-

compilation, where it can become quite a nightmare...

Some cross-toolchains exist on the internet, and can be used for general

development, but they have a number of limitations:

  - they can be general purpose, in that they are configured for the majority:

    no optimisation for your specific target,

  - they can be prepared for a specific target and thus are not easy to use,

    nor optimised for, or even supporting your target,

  - they often are using aging components (compiler, C library, etc...) not

    supporting special features of your shiny new processor;

On the other side, these toolchain offer some advantages:

  - they are ready to use and quite easy to install and setup,

  - they are proven if used by a wide community.

But once you want to get all the juice out of your specific hardware, you will

want to build your own toolchain. This is where crosstool-NG comes into play.

There are also a number of tools that build toolchains for specific needs,

which are not really scalable. Examples are:

  - buildroot (buildroot.uclibc.org) whose main purpose is to build root file

    systems, hence the name. But once you have your toolchain with buildroot,

    part of it is installed in the root-to-be, so if you want to build a whole

    new root, you either have to save the existing one as a template and

    restore it later, or restart again from scratch. This is not convenient,

  - ptxdist (www.pengutronix.de/software/ptxdist), whose purpose is very

    similar to buildroot,

  - other projects (openembedded.org for example), which are again used to

    build root file systems.

crosstool-NG is really targeted at building toolchains, and only toolchains.

It is then up to you to use it the way you want.

___________

          /

History  /

________/

crosstool was first 'conceived' by Dan Kegel, who offered it to the community

as a set of scripts, a repository of patches, and some pre-configured, general

purpose setup files to be used to configure crosstool. This is available at

http://www.kegel.com/crosstool, and the subversion repository is hosted on

google at http://code.google.com/p/crosstool/.

I once managed to add support for uClibc-based toolchains, but it did not make

into mainline, mostly because I didn't have time to port the patch forward to

the new versions, due in part to the big effort it was taking.

So I decided to clean up crosstool in the state it was, re-order the things

in place, add appropriate support for what I needed, that is uClibc support

and a menu-driven configuration, named the new implementation crosstool-NG,

(standing for crosstool Next Generation, as many other comunity projects do,

and as a wink at the TV series "Star Trek: The Next Generation" ;-) ) and

made it available to the community, in case it was of interest to any one.

_____________________________

                            /

Referring to crosstool-NG  /

__________________________/

The long name of the project is crosstool-NG:

  * no leading uppercase (except as first word in a sentence)

  * crosstool and NG separated with a hyphen (dash)

  * NG in uppercase

Crosstool-NG can also be referred to by its short name CT-NG:

  * all in uppercase

  * CT and NG separated with a hyphen (dash)

The long name is preferred over the short name, except in mail subjects, where

the short name is a better fit.

When referring to a specific version of crosstool-NG, append the version number

either as:

  * crosstool-NG X.Y.Z

    - the long name, a space, and the version string

  * crosstool-ng-X.Y.Z

    - the long name in lowercase, a hyphen (dash), and the version string

    - this is used to name the release tarballs

  * crosstool-ng-X.Y.Z+hg_id

    - the long name in lowercase, a hyphen, the version string, and the Hg id

      (as returned by: ct-ng version)

    - this is used to differentiate between releases and snapshots

The frontend to crosstool-NG is the command ct-ng:

  * all in lowercase

  * ct and ng separated by a hyphen (dash)

___________________________

                          /

Installing crosstool-NG  /

________________________/

There are two ways you can use crosstool-NG:

 - build and install it, then get rid of the sources like you'd do for most

   programs,

 - or only build it and run from the source directory.

The former should be used if you got crosstool-NG from a packaged tarball, see

"Install method", below, while the latter is most useful for developpers that

use a clone of the repository, and want to submit patches, see "The Hacker's

way", below.

Install method |

---------------+

If you go for the install, then you just follow the classical, but yet easy

./configure way:

  ./configure --prefix=/some/place

  make

  make install

  export PATH="${PATH}:/some/place/bin"

You can then get rid of crosstool-NG source. Next create a directory to serve

as a working place, cd in there and run:

  ct-ng help

See below for complete usage.

The Hacker's way |

-----------------+

If you go the hacker's way, then the usage is a bit different, although very

simple:

  ./configure --local

  make

Now, *do not* remove crosstool-NG sources. They are needed to run crosstool-NG!

Stay in the directory holding the sources, and run:

  ./ct-ng help

See below for complete usage.

Now, provided you used a clone of the repository, you can send me your changes.

See the section titled CONTRIBUTING, below, for how to submit changees.

Preparing for packaging |

------------------------+

If you plan on packaging crosstool-NG, you surely don't want to install it

in your root file system. The install procedure of crosstool-NG honors the

DESTDIR variable:

  ./configure --prefix=/usr

  make

  make DESTDIR=/packaging/place install

Shell completion |

-----------------+

crosstool-NG comes with a shell script fragment that defines bash-compatible

completion. That shell fragment is currently not installed automatically, but

this is planned.

To install the shell script fragment, you have two options:

 - install system-wide, most probably by copying ct-ng.comp into

   /etc/bash_completion.d/

 - install for a single user, by copying ct-ng.comp into ${HOME}/ and

   sourcing this file from your ${HOME}/.bashrc

Contributed code |

-----------------+

Some people contibuted code that couldn't get merged for various reasons. This

code is available as lzma-compressed patches, in the contrib/ sub-directory.

These patches are to be applied to the source of crosstool-NG, prior to

installing, using something like the following:

  lzcat contrib/foobar.patch.lzma |patch -p1

There is no guarantee that a particuliar contribution applies to the current

version of crosstool-ng, or that it will work at all. Use contributions at

your own risk.

____________________________

                           /

Configuring crosstool-NG  /

_________________________/

crosstool-NG is configured with a configurator presenting a menu-stuctured set

of options. These options let you specify the way you want your toolchain

built, where you want it installed, what architecture and specific processor it

will support, the version of the components you want to use, etc... The

value for those options are then stored in a configuration file.

The configurator works the same way you configure your Linux kernel. It is

assumed you now how to handle this.

To enter the menu, type:

  ct-ng menuconfig

Almost every config item has a help entry. Read them carefully.

String and number options can refer to environment variables. In such a case,

you must use the shell syntax: ${VAR}. You shall neither single- nor double-

quote the string/number options.

There are three environment variables that are computed by crosstool-NG, and

that you can use:

CT_TARGET:

  It represents the target tuple you are building for. You can use it for

  example in the installation/prefix directory, such as:

    /opt/x-tools/${CT_TARGET}

CT_TOP_DIR:

  The top directory where crosstool-NG is running. You shouldn't need it in

  most cases. There is one case where you may need it: if you have local

  patches and you store them in your running directory, you can refer to them

  by using CT_TOP_DIR, such as:

    ${CT_TOP_DIR}/patches.myproject

CT_VERSION:

  The version of crosstool-NG you are using. Not much use for you, but it's

  there if you need it.

Interesting config options |

---------------------------+

CT_LOCAL_TARBALLS_DIR:

  If you already have some tarballs in a direcotry, enter it here. That will

  speed up the retrieving phase, where crosstool-NG would otherwise download

  those tarballs.

CT_PREFIX_DIR:

  This is where the toolchain will be installed in (and for now, where it

  will run from). Common use is to add the target tuple in the directory

  path, such as (see above):

    /opt/x-tools/${CT_TARGET}

CT_TARGET_VENDOR:

  An identifier for your toolchain, will take place in the vendor part of the

  target tuple. It shall *not* contain spaces or dashes. Usually, keep it

  to a one-word string, or use underscores to separate words if you need.

  Avoid dots, commas, and special characters.

CT_TARGET_ALIAS:

  An alias for the toolchian. It will be used as a prefix to the toolchain

  tools. For example, you will have ${CT_TARGET_ALIAS}-gcc

Also, if you think you don't see enough versions, you can try to enable one of

those:

CT_OBSOLETE:

  Show obsolete versions or tools. Most of the time, you don't want to base

  your toolchain on too old a version (of gcc, for example). But at times, it

  can come handy to use such an old version for regression tests. Those old

  versions are hidden behind CT_OBSOLETE. Those versions (or features) are so

  marked because maintaining support for those in crosstool-NG would be too

  costly, time-wise, and time is dear.

CT_EXPERIMENTAL:

  Show experimental versions or tools. Again, you might not want to base your

  toolchain on too recent tools (eg. gcc) for production. But if you need a

  feature present only in a recent version, or a new tool, you can find them

  hidden behind CT_EXPERIMENTAL. Those versions (or features) did not (yet)

  receive thorough testing in crosstool-NG, and/or are not mature enough to

  be blindly trusted.

Re-building an existing toolchain |

----------------------------------+

If you have an existing toolchain, you can re-use the options used to build it

to create a new toolchain. That needs a very little bit of effort on your side

but is quite easy. The options to build a toolchain are saved with the

toolchain, and you can retrieve this configuration by running:

  ${CT_TARGET}-ct-ng.config

An alternate method is to extract the configuration from a build.log file.

This will be necessary if your toolchain was build with crosstool-NG prior

to 1.4.0, but can be used with build.log files from any version:

  ct-ng extractconfig <build.log >.config

Or, if your build.log file is compressed (most probably!):

  bzcat build.log.bz2 |ct-ng extractconfig >.config

The above commands will dump the configuration to stdout, so to rebuild a

toolchain with this configuration, just redirect the output to the

.config file:

  ${CT_TARGET}-ct-ng.config >.config

  ct-ng oldconfig

Then, you can review and change the configuration by running:

  ct-ng menuconfig

Using as a backend for a build-system |

--------------------------------------+

Crosstool-NG can be used as a backend for an automated build-system. In this

case, some components that are expected to run on the target (eg. the native

gdb, ltrace, DUMA...) are not available in the menuconfig, and they are not

build either, as it is considered the responsibility of the build-system to

build its own versions of those tools.

If you want to use crosstool-NG as a backend to generate your toolchains for

your build-system, you have to set and export this environment variable:

  CT_IS_A_BACKEND=y

(case is not sensitive, you can say Y).

________________________

                       /

Running crosstool-NG  /

_____________________/

To build the toolchain, simply type:

  ct-ng build

This will use the above configuration to retrieve, extract and patch the

components, build, install and eventually test your newly built toolchain.

You are then free to add the toolchain /bin directory in your PATH to use

it at will.

In any case, you can get some terse help. Just type:

  ct-ng help

or:

  man 1 ct-ng

Stopping and restarting a build |

--------------------------------+

If you want to stop the build after a step you are debugging, you can pass the

variable STOP to make:

  ct-ng build STOP=some_step

Conversely, if you want to restart a build at a specific step you are

debugging, you can pass the RESTART variable to make:

  ct-ng build RESTART=some_step

Alternatively, you can call make with the name of a step to just do that step:

  ct-ng libc_headers

is equivalent to:

  ct-ng build RESTART=libc_headers STOP=libc_headers

The shortcuts +step_name and step_name+ allow to respectively stop or restart

at that step. Thus:

  ct-ng +libc_headers              and:    ct-ng libc_headers+

are equivalent to:

  ct-ng build STOP=libc_headers    and:    ct-ng build RESTART=libc_headers

To obtain the list of acceptable steps, please call:

  ct-ng list-steps

Note that in order to restart a build, you'll have to say 'Y' to the config

option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went

that far.

Building all toolchains at once |

--------------------------------+

You can build all samples; simply call:

  ct-ng build-all

Overriding the number of // jobs |

---------------------------------+

If you want to override the number of jobs to run in // (the -j option to

make), you can either re-enter the menuconfig, or simply add it on the command

line, as such:

  ct-ng build.4

which tells crosstool-NG to override the number of // jobs to 4.

You can see the actions that support overriding the number of // jobs in

the help menu. Those are the ones with [.#] after them (eg. build[.#] or

build-all[.#], and so on...).

Note on // jobs |

----------------+

The crosstool-NG script 'ct-ng' is a Makefile-script. It does *not* execute

in parallel (there is not much to gain). When speaking of // jobs, we are

refering to the number of // jobs when making the *components*. That is, we

speak of the number of // jobs used to build gcc, glibc, and so on...

Tools wrapper |

--------------+

Starting with gcc-4.3 come two new dependencies: GMP and MPFR. With gcc-4.4,

come three new ones: GMP, PPL and CLooG/ppl. These are libraries that enable

advanced features to gcc. Additionally, some of the libraries can be used by

binutils and gdb. Unfortunately, not all systems on which crosstool-NG runs

have all of those libraries. And for those that do, the versions of those

libraries may be older than the version required by gcc.

This is why crosstool-NG builds its own set of libraries as part of the

toolchain.

The libraries are built as shared libraries, because building them as static

libraries has some short-comings. This poses no problem at build time, as

crosstool-NG correctly points gcc (and binutils and gdb) to the correct

place where our own version of the libraries are installed. But it poses

a problem when gcc et al. are run: the place where the libraries are is most

probably not known to the host dynamic linker. Still worse, if the host system

has its own versions, then ld.so would load the wrong library!

So we have to force the dynamic linker to load the correct version. We do this

by using the LD_LIBRARY_PATH variable, that informs the dynamic linker where

to look for shared libraries prior to searching its standard places. But we

can't impose that burden on all the system (because it'd be a nightmare to

configure, and because two toolchains on the same system may use different

versions of the libraries); so we have to do it on a per-toolchain basis.

So we rename all binaries of the toolchain (by adding a dot '.' as their first

character), and add a small program, the so-called "tools wrapper", that

correctly sets LD_LIBRARY_PATH prior to running the real tool.

First, the wrapper was written as a POSIX-compliant shell script. That shell

script is very simple, if not trivial, and works great. The only drawback is

that it does not work on host systems that lack a shell, for example the

MingW32 environment. To solve the issue, the wrapper has been re-written in C,

and compiled at build time. This C wrapper is much more complex than the shell

script, and although it sems to be working, it's been only lightly tested.

Some of the expected short-comings with this C wrapper are;

 - multi-byte file names may not be handled correctly

 - it's really big for what it does

So, the default wrapper installed with your toolchain is the shell script.

If you know that your system is missing a shell, then you shall use the C

wrapper (and report back whether it works, or does not work, for you).

_______________________

                      /

Using the toolchain  /

____________________/

Using the toolchain is as simple as adding the toolchain's bin directory in

your PATH, such as:

  export PATH="${PATH}:/your/toolchain/path/bin"

and then using the target tuple to tell the build systems to use your

toolchain:

  ./configure --target=your-target-tuple

or

  make CC=your-target-tuple-gcc

or

  make CROSS_COMPILE=your-target-tuple-

and so on...

It is strongly advised not to use the toolchain sys-root directory as an

install directory for your programs/packages. If you do so, you will not be

able to use your toolchain for another project. It is even strongly advised

that your toolchain is chmod-ed to read-only once successfully build, so that

you don't go polluting your toolchain with your programs/packages' files.

Thus, when you build a program/package, install it in a separate directory,

eg. /your/root. This directory is the /image/ of what would be in the root file

system of your target, and will contain all that your programs/packages have

installed.

The 'populate' script |

----------------------+

When your root directory is ready, it is still missing some important bits: the

toolchain's libraries. To populate your root directory with those libs, just

run:

  your-target-tuple-populate -s /your/root -d /your/root-populated

This will copy /your/root into /your/root-populated, and put the needed and only

the needed libraries there. Thus you don't polute /your/root with any cruft that

would no longer be needed should you have to remove stuff. /your/root always

contains only those things you install in it.

You can then use /your/root-populated to build up your file system image, a

tarball, or to NFS-mount it from your target, or whatever you need.

The populate script accepts the following options:

 -s src_dir

    Use 'src_dir' as the un-populated root directory.

 -d dst_dir

    Put the populated root directory in 'dst_dir'.

 -l lib1 [...]

    Always add specified libraries.

 -L file

    Always add libraries listed in 'file'.

 -f

    Remove 'dst_dir' if it previously existed; continue even if any library

    specified with -l or -L is missing.

 -v

    Be verbose, and tell what's going on (you can see exactly where libs are

    coming from).

 -h

    Print the help.

See 'your-target-tuple-populate -h' for more information on the options.

Here is how populate works:

  1) performs some sanity checks:

     - src_dir and dst_dir are specified

     - src_dir exists

     - unless forced, dst_dir does not exist

     - src_dir != dst_dir

  2) copy src_dir to dst_dir

  3) add forced libraries to dst_dir

     - build the list from -l and -L options

     - get forced libraries from the sysroot (see below for heuristics)

       - abort on the first missing library, unless -f is specified

  4) add all missing libraries to dst_dir

     - scan dst_dir for every ELF files that are 'executable' or

       'shared object'

     - list the "NEEDED Shared library" fields

       - check if the library is already in dst_dir/lib or dst_dir/usr/lib

       - if not, get the library from the sysroot

         - if it's in sysroot/lib, copy it to dst_dir/lib

         - if it's in sysroot/usr/lib, copy it to dst_dir/usr/lib

         - in both cases, use the SONAME of the library to create the file

           in dst_dir

         - if it was not found in the sysroot, this is an error.

___________________

                  /

Toolchain types  /

________________/

There are four kinds of toolchains you could encounter.

First off, you must understand the following: when it comes to compilers there

are up to four machines involved:

  1) the machine configuring the toolchain components: the config machine

  2) the machine building the toolchain components:    the build machine

  3) the machine running the toolchain:                the host machine

  4) the machine the toolchain is generating code for: the target machine

We can most of the time assume that the config machine and the build machine

are the same. Most of the time, this will be true. The only time it isn't

is if you're using distributed compilation (such as distcc). Let's forget

this for the sake of simplicity.

So we're left with three machines:

 - build

 - host

 - target

Any toolchain will involve those three machines. You can be as pretty sure of

this as "2 and 2 are 4". Here is how they come into play:

1) build == host == target

    This is a plain native toolchain, targetting the exact same machine as the

    one it is built on, and running again on this exact same machine. You have

    to build such a toolchain when you want to use an updated component, such

    as a newer gcc for example.

    crosstool-NG calls it "native".

2) build == host != target

    This is a classic cross-toolchain, which is expected to be run on the same

    machine it is compiled on, and generate code to run on a second machine,

    the target.

    crosstool-NG calls it "cross".

3) build != host == target

    Such a toolchain is also a native toolchain, as it targets the same machine

    as it runs on. But it is build on another machine. You want such a

    toolchain when porting to a new architecture, or if the build machine is

    much faster than the host machine.

    crosstool-NG calls it "cross-native".

4) build != host != target

    This one is called a canadian-toolchain (*), and is tricky. The three

    machines in play are different. You might want such a toolchain if you

    have a fast build machine, but the users will use it on another machine,

    and will produce code to run on a third machine.

    crosstool-NG calls it "canadian".

crosstool-NG can build all these kinds of toolchains (or is aiming at it,

anyway!)

(*) The term Canadian Cross came about because at the time that these issues

    were all being hashed out, Canada had three national political parties.

    http://en.wikipedia.org/wiki/Cross_compiler

________________

               /

Contributing  /

_____________/

Sending a bug report |

---------------------+

If you need to send a bug report, please send a mail with subject

prefixed with "[CT_NG]" with to following destinations:

    TO: yann.morin.1998 (at) anciens.enib.fr

    CC: crossgcc (at) sourceware.org

Sending patches |

----------------+

If you want to enhance crosstool-NG, there's a to-do list in the TODO file.

Patches should come with the appropriate SoB line. A SoB line is typically

something like:

   Signed-off-by: John DOE <john.doe@somewhere.net>

The SoB line is clearly described in Documentation/SubmittingPatches , section

12, of your favourite Linux kernel source tree.

Then you'll need to correctly configure Mercurial. There are two extensions

that you may find usefull:

  - mq        : http://mercurial.selenic.com/wiki/MqExtension

  - patchbomb : http://mercurial.selenic.com/wiki/PatchbombExtension

Commit messages should look like (without leading pipes):

 |component: short, one-line description

 |

 |optional longer description

 |on multiple lines if needed

Here is an example commit message (see revision a53a5e1d61db):

 |comp-libs/cloog: fix building

 |

 |For CLooG/PPL 0.15.3, the directory name was simply cloog-ppl.

 |For any later versions, the directory name does have the version, such as

 |cloog-ppl-0.15.4.

Here's a typical hacking session:

  hg clone http://ymorin.is-a-geek.org/hg/crosstool-ng crosstool-ng

  cd crosstool-ng

  hg qinit

  hg qnew -D -U -e my_first_patch

  *edit patch description*

  *hack* *hack* *check* *fails* *hack* *hack* *check* *works*

  hg qref -D -e

  *edit patch description, serving as commit message*

  hg qnew -D -U -e my_second_patch

  *edit patch description*

  *hack* *hack* *check* *fails* *hack* *hack* *check* *works*

  hg qref -D -e

  *edit patch description, serving as commit message*

  hg email --outgoing --intro   \

           --from '"Your Full NAME" <your.email (at) your.domain>'   \

           --to '"Yann E. MORIN" <yann.morin.1998 (at) anciens.enib.fr>'    \

           --cc 'crossgcc (at) sourceware.org'

  *edit introductory message*

  *wait for feedback*

  *re-send if no answer for a few days*

Note: replace '(at)' above with a plain '@'.

_____________

            /

Internals  /

__________/

Internally, crosstool-NG is script-based. To ease usage, the frontend is

Makefile-based.

Makefile front-end |

-------------------+

The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this

script with an action will act exactly as if the Makefile was in the current

working directory and make was called with the action as rule. Thus:

  ct-ng menuconfig

is equivalent to having the Makefile in CWD, and calling:

  make menuconfig

Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a

traditional command.

ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up

at configuration time with ./configure.

ct-ng also searches for config files, sub-tools, samples, scripts and patches in

that library directory.

Because of a stupid make behavior/bug I was unable to track down, implicit make

rules are disabled: installing with --local would triger those rules, and mconf

was unbuildable.

Kconfig parser |

---------------+

The kconfig language is a hacked version, vampirised from the Linux kernel

(http://www.kernel.org/), and (heavily) adapted to my needs.

The list of the most notable changes (at least the ones I remember) follows:

- the CONFIG_ prefix has been replaced with CT_

- a leading | in prompts is skipped, and subsequent leading spaces are not

  trimmed; otherwise leading spaces are silently trimmed

- removed the warning about undefined environment variable

The kconfig parsers (conf and mconf) are not installed pre-built, but as

source files. Thus you can have the directory where crosstool-NG is installed,

exported (via NFS or whatever) and have clients with different architectures

use the same crosstool-NG installation, and most notably, the same set of

patches.

Architecture-specific |

----------------------+

Note: this chapter is not really well written, and might thus be a little bit

complex to understand. To get a better grasp of what an architecture is, the

reader is kindly encouraged to look at the "arch/" sub-directory, and to the

existing architectures to see how things are laid out.

An architecture is defined by:

 - a human-readable name, in lower case letters, with numbers as appropriate.

   The underscore is allowed; space and special characters are not.

     Eg.: arm, x86_64

 - a file in "config/arch/", named after the architecture's name, and suffixed

   with ".in".

     Eg.: config/arch/arm.in

 - a file in "scripts/build/arch/", named after the architecture's name, and

   suffixed with ".sh".

     Eg.: scripts/build/arch/arm.sh

The architecture's ".in" file API:

 > the config option "ARCH_%arch%" (where %arch% is to be replaced with the

   actual architecture name).

   That config option must have *neither* a type, *nor* a prompt! Also, it can

   *not* depend on any other config option (EXPERIMENTAL is managed as above).

     Eg.:

       config ARCH_arm

   + mandatory:

       defines a (terse) help entry for this architecture:

       Eg.:

         config ARCH_arm

           help

             The ARM architecture.

   + optional:

       selects adequate associated config options.

       Note: 64-bit architectures *shall* select ARCH_64

       Eg.:

         config ARCH_arm

           select ARCH_SUPPORTS_BOTH_ENDIAN

           select ARCH_DEFAULT_LE

           help

             The ARM architecture.

       Eg.:

         config ARCH_x86_64

            select ARCH_64

            help

              The x86_64 architecture.

 > other target-specific options, at your discretion. Note however that to

   avoid name-clashing, such options shall be prefixed with "ARCH_%arch%",

   where %arch% is again replaced by the actual architecture name.

   (Note: due to historical reasons, and lack of time to clean up the code,

    I may have left some config options that do not completely conform to

    this, as the architecture name was written all upper case. However, the

    prefix is unique among architectures, and does not cause harm).

The architecture's ".sh" file API:

 > the function "CT_DoArchTupleValues"

   + parameters: none

   + environment:

     - all variables from the ".config" file,

     - the two variables "target_endian_eb" and "target_endian_el" which are

       the endianness suffixes

   + return value: 0 upon success, !0 upon failure

   + provides:

     - mandatory

     - the environment variable CT_TARGET_ARCH

     - contains:

       the architecture part of the target tuple.

       Eg.: "armeb" for big endian ARM

            "i386" for an i386

   + provides:

     - optional

     - the environment variable CT_TARGET_SYS

     - contains:

       the sytem part of the target tuple.

       Eg.: "gnu" for glibc on most architectures

            "gnueabi" for glibc on an ARM EABI

     - defaults to:

       - for glibc-based toolchain: "gnu"

       - for uClibc-based toolchain: "uclibc"

   + provides:

     - optional

     - the environment variables to configure the cross-gcc (defaults)

       - CT_ARCH_WITH_ARCH    : the gcc ./configure switch to select architecture level         ( "--with-arch=${CT_ARCH_ARCH}"   )

       - CT_ARCH_WITH_ABI     : the gcc ./configure switch to select ABI level                  ( "--with-abi=${CT_ARCH_ABI}"     )

       - CT_ARCH_WITH_CPU     : the gcc ./configure switch to select CPU instruction set        ( "--with-cpu=${CT_ARCH_CPU}"     )

       - CT_ARCH_WITH_TUNE    : the gcc ./configure switch to select scheduling                 ( "--with-tune=${CT_ARCH_TUNE}"   )

       - CT_ARCH_WITH_FPU     : the gcc ./configure switch to select FPU type                   ( "--with-fpu=${CT_ARCH_FPU}"     )

       - CT_ARCH_WITH_FLOAT   : the gcc ./configure switch to select floating point arithmetics ( "--with-float=soft" or /empty/  )

   + provides:

     - optional

     - the environment variables to pass to the cross-gcc to build target binaries (defaults)

       - CT_ARCH_ARCH_CFLAG   : the gcc switch to select architecture level                     ( "-march=${CT_ARCH_ARCH}"            )

       - CT_ARCH_ABI_CFLAG    : the gcc switch to select ABI level                              ( "-mabi=${CT_ARCH_ABI}"              )

       - CT_ARCH_CPU_CFLAG    : the gcc switch to select CPU instruction set                    ( "-mcpu=${CT_ARCH_CPU}"              )

       - CT_ARCH_TUNE_CFLAG   : the gcc switch to select scheduling                             ( "-mtune=${CT_ARCH_TUNE}"            )

       - CT_ARCH_FPU_CFLAG    : the gcc switch to select FPU type                               ( "-mfpu=${CT_ARCH_FPU}"              )

       - CT_ARCH_FLOAT_CFLAG  : the gcc switch to choose floating point arithmetics             ( "-msoft-float" or /empty/           )

       - CT_ARCH_ENDIAN_CFLAG : the gcc switch to choose big or little endian                   ( "-mbig-endian" or "-mlittle-endian" )

     - default to:

       see above.

   + provides:

     - optional

     - the environement variables to configure the core and final compiler, specific to this architecture:

       - CT_ARCH_CC_CORE_EXTRA_CONFIG   : additional, architecture specific core gcc ./configure flags

       - CT_ARCH_CC_EXTRA_CONFIG        : additional, architecture specific final gcc ./configure flags

     - default to:

       - all empty

   + provides:

     - optional

     - the architecture-specific CFLAGS and LDFLAGS:

       - CT_ARCH_TARGET_CLFAGS

       - CT_ARCH_TARGET_LDFLAGS

     - default to:

       - all empty

You can have a look at "config/arch/arm.in" and "scripts/build/arch/arm.sh" for

a quite complete example of what an actual architecture description looks like.

Kernel specific |

----------------+

A kernel is defined by:

 - a human-readable name, in lower case letters, with numbers as appropriate.

   The underscore is allowed; space and special characters are not (although

   they are internally replaced with underscores.

     Eg.: linux, bare-metal

 - a file in "config/kernel/", named after the kernel name, and suffixed with

   ".in".

     Eg.: config/kernel/linux.in, config/kernel/bare-metal.in

 - a file in "scripts/build/kernel/", named after the kernel name, and suffixed

   with ".sh".

     Eg.: scripts/build/kernel/linux.sh, scripts/build/kernel/bare-metal.sh

The kernel's ".in" file must contain:

 > an optional lines containing exactly "# EXPERIMENTAL", starting on the

   first column, and without any following space or other character.

   If this line is present, then this kernel is considered EXPERIMENTAL,

   and correct dependency on EXPERIMENTAL will be set.

 > the config option "KERNEL_%kernel_name%" (where %kernel_name% is to be

   replaced with the actual kernel name, with all special characters and

   spaces replaced by underscores).

   That config option must have *neither* a type, *nor* a prompt! Also, it can

   *not* depends on EXPERIMENTAL.

     Eg.: KERNEL_linux, KERNEL_bare_metal

   + mandatory:

       defines a (terse) help entry for this kernel.

       Eg.:

         config KERNEL_bare_metal

           help

             Build a compiler for use without any kernel.

   + optional:

       selects adequate associated config options.

       Eg.:

         config KERNEL_bare_metal

           select BARE_METAL

           help

             Build a compiler for use without any kernel.

 > other kernel specific options, at your discretion. Note however that, to

   avoid name-clashing, such options should be prefixed with

   "KERNEL_%kernel_name%", where %kernel_name% is again tp be replaced with

   the actual kernel name.

   (Note: due to historical reasons, and lack of time to clean up the code,

    I may have left some config options that do not completely conform to

    this, as the kernel name was written all upper case. However, the prefix

    is unique among kernels, and does not cause harm).

The kernel's ".sh" file API:

 > is a bash script fragment

 > defines the function CT_DoKernelTupleValues

   + see the architecture's CT_DoArchTupleValues, except for:

   + set the environment variable CT_TARGET_KERNEL, the kernel part of the

     target tuple

   + return value: ignored

 > defines the function "do_kernel_get":

   + parameters: none

   + environment:

      - all variables from the ".config" file.

   + return value: 0 for success, !0 for failure.

   + behavior: download the kernel's sources, and store the tarball into

     "${CT_TARBALLS_DIR}". To this end, a functions is available, that

     abstracts downloading tarballs:

     - CT_DoGet <tarball_base_name> <URL1 [URL...]>

       Eg.: CT_DoGet linux-2.6.26.5 ftp://ftp.kernel.org/pub/linux/kernel/v2.6

     Note: retrieving sources from svn, cvs, git and the likes is not supported

     by CT_DoGet. You'll have to do this by hand, as it is done for eglibc in

     "scripts/build/libc/eglibc.sh"

 > defines the function "do_kernel_extract":

   + parameters: none

   + environment:

      - all variables from the ".config" file,

   + return value: 0 for success, !0 for failure.

   + behavior: extract the kernel's tarball into "${CT_SRC_DIR}", and apply

     required patches. To this end, a function is available, that abstracts

     extracting tarballs:

     - CT_ExtractAndPatch <tarball_base_name>

       Eg.: CT_ExtractAndPatch linux-2.6.26.5

 > defines the function "do_kernel_headers":

   + parameters: none

   + environment:

      - all variables from the ".config" file,

   + return value: 0 for success, !0 for failure.

   + behavior: install the kernel headers (if any) in "${CT_SYSROOT_DIR}/usr/include"

 > defines any kernel-specific helper functions

   These functions, if any, must be prefixed with "do_kernel_%CT_KERNEL%_",

   where '%CT_KERNEL%' is to be replaced with the actual kernel name, to avoid

   any name-clashing.

You can have a look at "config/kernel/linux.in" and "scripts/build/kernel/linux.sh"

as an example of what a complex kernel description looks like.