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

 ____________________

                    /

 Table Of Content  /

 _________________/

 Introduction

 History

 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

 Running crosstool-NG

   Stopping and restarting a build

   Testing all toolchains at once

   Overriding the number of // jobs

 Using the toolchain

 Toolchain types

 Internals

   Makefile front-end

   Kconfig parser

   Architecture-specific

   Adding a new version of a component

   Build scripts

 ________________

                /

 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.

 ___________________________

                           /

 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

 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

 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 patches in the contrib/ sub-directory. These patches are

 to be applied to the source of crosstool-NG, prior to installing.

 An easy way to use contributed code is to pass the --with-contrib= option to

 ./configure. The possible values depend upon which contributions are packaged

 with your version, but you can get with it with passing one of those two

 special values:

   --with-contrib=list

     will list all available contributions

   --with-contrib=all

     will select all avalaible contributions

 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}-config

 This will dump the configuration to stdout, so to rebuild a toolchain with this

 configuration, the following is all you need to do:

   ${CT_TARGET}-config >.config

   ct-ng oldconfig

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

   ct-ng menuconfig

 ________________________

                        /

 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 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=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 STOP=libc_headers    and:    ct-ng 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...

 _______________________

                       /

 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.

 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 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

 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 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 (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.

 Adding a new version of a component |

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

 When a new component, such as the Linux kernel, gcc or any other is released,

 adding the new version to crosstool-NG is quite easy. There is a script that

 will do all that for you:

   scripts/addToolVersion.sh

 Run it with no option to get some help.

 Build scripts |

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

 To Be Written later...