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

________________

               /

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 developped. 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 regretable).

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 ageing 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 builds toolchains for specific needs,

which is not really scalable. Examples are:

  - buildroot (buildroot.uclibc.org) whose main puprpose 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 (openembeded.org for example), which is again used to

    build root file systems.

crosstool-NG is really targetted 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, which 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/.

At the time of writing, crosstool only supports building with one C library,

namely glibc, and one C compiler, gcc; it is cripled with historical support

for legacy components, and is some kind of a mess to upgrade. Also, submited

patches take a loooong time before they are integrated mainline.

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

into mainline, mostly because I don'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, and add appropriate support for what I needed, that is uClibc

support. That was a disaster, as inclusion into mainline is slow as hell,

and the changes were so numerous.

The only option left to me was rewrite crosstool from scratch. I decided to go

this way, and name 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". ;-)

___________________________

                          /

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 usefull for developpers that

checked the code out from SVN, 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 checked-out the code, you can send me your interesting changes

by running:

  svn diff

and mailing me the result! :-P

____________________________

                           /

Configuring crosstool-NG  /

_________________________/

crosstool-NG is configured by 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 it 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.

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.

CT_BROKEN:

  Show broken versions or tools. Some usefull tools are currently broken: they

  won't compile, run, or worse, cause defects when running. But if you are

  brave enough, you can try and debug them. They are hidden behind CT_BROKEN,

  which itself is hidden behind EXPERIMENTAL.

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 in the build log

file that is saved within the toolchain. crosstool-NG can extract those options

to recreate a new configuration:

  ct-ng extractconfig </path/to/your/build.log

will extract those options, prompt you for the new ones, which you can later

edit with menuconfig.

Of course, if your build log was compressed, you'd have to use something like:

  bzcat /path/to/your/build.log.bz2 |ct-ng extractconfig

________________________

                       /

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

Stoping 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 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 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 RESTART=libs_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 STOP=libc_headers    and:    ct-ng RESTART=libc_headers

To obtain the list of acceptable steps, please call:

  ct-ng liststeps

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.

Testing all toolchains at once |

-------------------------------*

You can test-build all samples; simply call:

  ct-ng regtest

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

regtest[.#], and so on...).

_______________________

                      /

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...

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.

populate accepts the following options:

 -s [src_dir]

    Use 'src_dir' as the 'source', un-populated root directory

 -d [dst_dir]

    Put the 'destination', populated root directory in 'dst_dir'

 -f

    Remove 'dst_dir' if it previously existed

 -v

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

    coming from).

 -h

    Print the help

___________________

                  /

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

_____________

            /

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 search 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 toybox project

by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the

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

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 |

----------------------*

An architecture is defined by:

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

   The underscore is allowed. Eg.: arm, x86_64

 - a boolean kconfig option named after the architecture (in capital letters

   if possible) prefixed with "ARCH_". Eg.: ARCH_ARM, ARCH_x86_64

 - a directory in "arch/" named after the architecture, with the same letters

   as above. Eg.: arch/arm, arch/x86_64

   This directory contains:

   - a configuration file in kconfig syntax, named "config.in", which may be

     empty. Eg.: arch/arm/config.in

   - a function script in bash-3.0 syntax, named "functions", which shall

     follow the API defined below. Eg.: arch/arm/functions

The "functions" file API:

 > the function "CT_DoArchValues"

   + 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

     - contain:

       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 variable CT_KERNEL_ARCH

     - contains:

       the architecture name as understandable by the Linux kernel build

       system.

       Eg.: "arm" for an ARM

            "powerpc" for a PowerPC

            "i386" for an x86

     - defaults to:

       ${CT_ARCH}

   + provides:

     - optional

     - the environment variables to configure the cross-gcc

       - CT_ARCH_WITH_ARCH

       - CT_ARCH_WITH_ABI

       - CT_ARCH_WITH_CPU

       - CT_ARCH_WITH_TUNE

       - CT_ARCH_WITH_FPU

       - CT_ARCH_WITH_FLOAT

     - contain (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_ARCH}"        )

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

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

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

       - 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

       - CT_ARCH_ARCH_CFLAG

       - CT_ARCH_ABI_CFLAG

       - CT_ARCH_CPU_CFLAG

       - CT_ARCH_TUNE_CFLAG

       - CT_ARCH_FPU_CFLAG

       - CT_ARCH_FLOAT_CFLAG

       - CT_ARCH_ENDIAN_CFLAG

     - contain (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_AABI}"             )

       - 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.

Build scripts |

--------------*

To Be Written later...