docs/overview.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Sun Oct 05 15:32:00 2008 +0000 (2008-10-05)
changeset 903 9fb0f81b4416
parent 901 55fbab1b4f94
child 914 0b164a321177
permissions -rw-r--r--
Separate the architecture config file and function script.

/trunk/kconfig/kconfig.mk | 46 23 23 0 +++++++++++++++++++++++-----------------------
/trunk/scripts/crosstool.sh | 2 1 1 0 +-
/trunk/docs/overview.txt | 28 11 17 0 +++++++++++-----------------
3 files changed, 35 insertions(+), 41 deletions(-)
     1 File.........: overview.txt
     2 Content......: Overview of how crosstool-NG works.
     3 Copyrigth....: (C) 2007 Yann E. MORIN <yann.morin.1998@anciens.enib.fr>
     4 License......: Creative Commons Attribution Share Alike (CC-by-sa), v2.5
     5 
     6 ____________________
     7                    /
     8 Table Of Content  /
     9 _________________/
    10 
    11 
    12 Introduction
    13 History
    14 Installing crosstool-NG
    15   Install method
    16   The hacker's way
    17   Shell completion
    18   Contributed code
    19 Configuring crosstool-NG
    20   Interesting config options
    21   Re-building an existing toolchain
    22 Running crosstool-NG
    23   Stopping and restarting a build
    24   Testing all toolchains at once
    25   Overriding the number of // jobs
    26 Using the toolchain
    27 Toolchain types
    28 Internals
    29   Makefile front-end
    30   Kconfig parser
    31   Architecture-specific
    32   Adding a new version of a component
    33   Build scripts
    34 
    35 ________________
    36                /
    37 Introduction  /
    38 _____________/
    39 
    40 crosstool-NG aims at building toolchains. Toolchains are an essential component
    41 in a software development project. It will compile, assemble and link the code
    42 that is being developed. Some pieces of the toolchain will eventually end up
    43 in the resulting binary/ies: static libraries are but an example.
    44 
    45 So, a toolchain is a very sensitive piece of software, as any bug in one of the
    46 components, or a poorly configured component, can lead to execution problems,
    47 ranging from poor performance, to applications ending unexpectedly, to
    48 mis-behaving software (which more than often is hard to detect), to hardware
    49 damage, or even to human risks (which is more than regrettable).
    50 
    51 Toolchains are made of different piece of software, each being quite complex
    52 and requiring specially crafted options to build and work seamlessly. This
    53 is usually not that easy, even in the not-so-trivial case of native toolchains.
    54 The work reaches a higher degree of complexity when it comes to cross-
    55 compilation, where it can become quite a nightmare...
    56 
    57 Some cross-toolchains exist on the internet, and can be used for general
    58 development, but they have a number of limitations:
    59   - they can be general purpose, in that they are configured for the majority:
    60     no optimisation for your specific target,
    61   - they can be prepared for a specific target and thus are not easy to use,
    62     nor optimised for, or even supporting your target,
    63   - they often are using aging components (compiler, C library, etc...) not
    64     supporting special features of your shiny new processor;
    65 On the other side, these toolchain offer some advantages:
    66   - they are ready to use and quite easy to install and setup,
    67   - they are proven if used by a wide community.
    68 
    69 But once you want to get all the juice out of your specific hardware, you will
    70 want to build your own toolchain. This is where crosstool-NG comes into play.
    71 
    72 There are also a number of tools that build toolchains for specific needs,
    73 which are not really scalable. Examples are:
    74   - buildroot (buildroot.uclibc.org) whose main purpose is to build root file
    75     systems, hence the name. But once you have your toolchain with buildroot,
    76     part of it is installed in the root-to-be, so if you want to build a whole
    77     new root, you either have to save the existing one as a template and
    78     restore it later, or restart again from scratch. This is not convenient,
    79   - ptxdist (www.pengutronix.de/software/ptxdist), whose purpose is very
    80     similar to buildroot,
    81   - other projects (openembedded.org for example), which are again used to
    82     build root file systems.
    83 
    84 crosstool-NG is really targeted at building toolchains, and only toolchains.
    85 It is then up to you to use it the way you want.
    86 
    87 ___________
    88           /
    89 History  /
    90 ________/
    91 
    92 crosstool was first 'conceived' by Dan Kegel, who offered it to the community
    93 as a set of scripts, a repository of patches, and some pre-configured, general
    94 purpose setup files to be used to configure crosstool. This is available at
    95 http://www.kegel.com/crosstool, and the subversion repository is hosted on
    96 google at http://code.google.com/p/crosstool/.
    97 
    98 I once managed to add support for uClibc-based toolchains, but it did not make
    99 into mainline, mostly because I didn't have time to port the patch forward to
   100 the new versions, due in part to the big effort it was taking.
   101 
   102 So I decided to clean up crosstool in the state it was, re-order the things
   103 in place, add appropriate support for what I needed, that is uClibc support
   104 and a menu-driven configuration, named the new implementation crosstool-NG,
   105 (standing for crosstool Next Generation, as many other comunity projects do,
   106 and as a wink at the TV series "Star Trek: The Next Generation" ;-) ) and
   107 made it available to the community, in case it was of interest to any one.
   108 
   109 ___________________________
   110                           /
   111 Installing crosstool-NG  /
   112 ________________________/
   113 
   114 There are two ways you can use crosstool-NG:
   115  - build and install it, then get rid of the sources like you'd do for most
   116    programs,
   117  - or only build it and run from the source directory.
   118 
   119 The former should be used if you got crosstool-NG from a packaged tarball, see
   120 "Install method", below, while the latter is most useful for developpers that
   121 checked the code out from SVN, and want to submit patches, see "The Hacker's
   122 way", below.
   123 
   124 Install method |
   125 ---------------+
   126 
   127 If you go for the install, then you just follow the classical, but yet easy
   128 ./configure way:
   129   ./configure --prefix=/some/place
   130   make
   131   make install
   132   export PATH="${PATH}:/some/place/bin"
   133 
   134 You can then get rid of crosstool-NG source. Next create a directory to serve
   135 as a working place, cd in there and run:
   136   ct-ng help
   137 
   138 See below for complete usage.
   139 
   140 The Hacker's way |
   141 -----------------+
   142 
   143 If you go the hacker's way, then the usage is a bit different, although very
   144 simple:
   145   ./configure --local
   146   make
   147 
   148 Now, *do not* remove crosstool-NG sources. They are needed to run crosstool-NG!
   149 Stay in the directory holding the sources, and run:
   150   ./ct-ng help
   151 
   152 See below for complete usage.
   153 
   154 Now, provided you checked-out the code, you can send me your interesting changes
   155 by running:
   156   svn diff
   157 
   158 and mailing me the result! :-P
   159 
   160 Shell completion |
   161 -----------------+
   162 
   163 crosstool-NG comes with a shell script fragment that defines bash-compatible
   164 completion. That shell fragment is currently not installed automatically, but
   165 this is planned.
   166 
   167 To install the shell script fragment, you have two options:
   168  - install system-wide, most probably by copying ct-ng.comp into
   169    /etc/bash_completion.d/
   170  - install for a single user, by copying ct-ng.comp into ${HOME}/ and
   171    sourcing this file from your ${HOME}/.bashrc
   172 
   173 Contributed code |
   174 -----------------+
   175 
   176 Some people contibuted code that couldn't get merged for various reasons. This
   177 code is available as patches in the contrib/ sub-directory. These patches are
   178 to be applied to the source of crosstool-NG, prior to installing.
   179 
   180 An easy way to use contributed code is to pass the --with-contrib= option to
   181 ./configure. The possible values depend upon which contributions are packaged
   182 with your version, but you can get with it with passing one of those two
   183 special values:
   184   --with-contrib=list
   185     will list all available contributions
   186 
   187   --with-contrib=all
   188     will select all avalaible contributions
   189 
   190 There is no guarantee that a particuliar contribution applies to the current
   191 version of crosstool-ng, or that it will work at all. Use contributions at
   192 your own risk.
   193 
   194 ____________________________
   195                            /
   196 Configuring crosstool-NG  /
   197 _________________________/
   198 
   199 crosstool-NG is configured with a configurator presenting a menu-stuctured set
   200 of options. These options let you specify the way you want your toolchain
   201 built, where you want it installed, what architecture and specific processor it
   202 will support, the version of the components you want to use, etc... The
   203 value for those options are then stored in a configuration file.
   204 
   205 The configurator works the same way you configure your Linux kernel. It is
   206 assumed you now how to handle this.
   207 
   208 To enter the menu, type:
   209   ct-ng menuconfig
   210 
   211 Almost every config item has a help entry. Read them carefully.
   212 
   213 String and number options can refer to environment variables. In such a case,
   214 you must use the shell syntax: ${VAR}. You shall neither single- nor double-
   215 quote the string/number options.
   216 
   217 There are three environment variables that are computed by crosstool-NG, and
   218 that you can use:
   219 
   220 CT_TARGET:
   221   It represents the target tuple you are building for. You can use it for
   222   example in the installation/prefix directory, such as:
   223     /opt/x-tools/${CT_TARGET}
   224 
   225 CT_TOP_DIR:
   226   The top directory where crosstool-NG is running. You shouldn't need it in
   227   most cases. There is one case where you may need it: if you have local
   228   patches and you store them in your running directory, you can refer to them
   229   by using CT_TOP_DIR, such as:
   230     ${CT_TOP_DIR}/patches.myproject
   231 
   232 CT_VERSION:
   233   The version of crosstool-NG you are using. Not much use for you, but it's
   234   there if you need it.
   235 
   236 Interesting config options |
   237 ---------------------------+
   238 
   239 CT_LOCAL_TARBALLS_DIR:
   240   If you already have some tarballs in a direcotry, enter it here. That will
   241   speed up the retrieving phase, where crosstool-NG would otherwise download
   242   those tarballs.
   243 
   244 CT_PREFIX_DIR:
   245   This is where the toolchain will be installed in (and for now, where it
   246   will run from). Common use is to add the target tuple in the directory
   247   path, such as (see above):
   248     /opt/x-tools/${CT_TARGET}
   249 
   250 CT_TARGET_VENDOR:
   251   An identifier for your toolchain, will take place in the vendor part of the
   252   target tuple. It shall *not* contain spaces or dashes. Usually, keep it
   253   to a one-word string, or use underscores to separate words if you need.
   254   Avoid dots, commas, and special characters.
   255 
   256 CT_TARGET_ALIAS:
   257   An alias for the toolchian. It will be used as a prefix to the toolchain
   258   tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
   259 
   260 Also, if you think you don't see enough versions, you can try to enable one of
   261 those:
   262 
   263 CT_OBSOLETE:
   264   Show obsolete versions or tools. Most of the time, you don't want to base
   265   your toolchain on too old a version (of gcc, for example). But at times, it
   266   can come handy to use such an old version for regression tests. Those old
   267   versions are hidden behind CT_OBSOLETE.
   268 
   269 CT_EXPERIMENTAL:
   270   Show experimental versions or tools. Again, you might not want to base your
   271   toolchain on too recent tools (eg. gcc) for production. But if you need a
   272   feature present only in a recent version, or a new tool, you can find them
   273   hidden behind CT_EXPERIMENTAL.
   274 
   275 CT_BROKEN:
   276   Show broken versions or tools. Some usefull tools are currently broken: they
   277   won't compile, run, or worse, cause defects when running. But if you are
   278   brave enough, you can try and debug them. They are hidden behind CT_BROKEN,
   279   which itself is hidden behind CT_EXPERIMENTAL.
   280 
   281 Re-building an existing toolchain |
   282 ----------------------------------+
   283 
   284 If you have an existing toolchain, you can re-use the options used to build it
   285 to create a new toolchain. That needs a very little bit of effort on your side
   286 but is quite easy. The options to build a toolchain are saved with the
   287 toolchain, and you can retrieve this configuration by running:
   288   ${CT_TARGET}-config
   289 
   290 This will dump the configuration to stdout, so to rebuild a toolchain with this
   291 configuration, the following is all you need to do:
   292   ${CT_TARGET}-config >.config
   293 
   294 Then, you can review and change the configuration by running:
   295   ct-ng menuconfig
   296 
   297 ________________________
   298                        /
   299 Running crosstool-NG  /
   300 _____________________/
   301 
   302 To build the toolchain, simply type:
   303   ct-ng build
   304 
   305 This will use the above configuration to retrieve, extract and patch the
   306 components, build, install and eventually test your newly built toolchain.
   307 
   308 You are then free to add the toolchain /bin directory in your PATH to use
   309 it at will.
   310 
   311 In any case, you can get some terse help. Just type:
   312   ct-ng help
   313 or:
   314   man 1 ct-ng
   315 
   316 Stopping and restarting a build |
   317 --------------------------------+
   318 
   319 If you want to stop the build after a step you are debugging, you can pass the
   320 variable STOP to make:
   321   ct-ng STOP=some_step
   322 
   323 Conversely, if you want to restart a build at a specific step you are
   324 debugging, you can pass the RESTART variable to make:
   325   ct-ng RESTART=some_step
   326 
   327 Alternatively, you can call make with the name of a step to just do that step:
   328   ct-ng libc_headers
   329 is equivalent to:
   330   ct-ng RESTART=libc_headers STOP=libc_headers
   331 
   332 The shortcuts +step_name and step_name+ allow to respectively stop or restart
   333 at that step. Thus:
   334   ct-ng +libc_headers        and:    ct-ng libc_headers+
   335 are equivalent to:
   336   ct-ng STOP=libc_headers    and:    ct-ng RESTART=libc_headers
   337 
   338 To obtain the list of acceptable steps, please call:
   339   ct-ng list-steps
   340 
   341 Note that in order to restart a build, you'll have to say 'Y' to the config
   342 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
   343 that far.
   344 
   345 Testing all toolchains at once |
   346 -------------------------------+
   347 
   348 You can test-build all samples; simply call:
   349   ct-ng regtest
   350 
   351 Overriding the number of // jobs |
   352 ---------------------------------+
   353 
   354 If you want to override the number of jobs to run in // (the -j option to
   355 make), you can either re-enter the menuconfig, or simply add it on the command
   356 line, as such:
   357   ct-ng build.4
   358 
   359 which tells crosstool-NG to override the number of // jobs to 4.
   360 
   361 You can see the actions that support overriding the number of // jobs in
   362 the help menu. Those are the ones with [.#] after them (eg. build[.#] or
   363 regtest[.#], and so on...).
   364 
   365 _______________________
   366                       /
   367 Using the toolchain  /
   368 ____________________/
   369 
   370 Using the toolchain is as simple as adding the toolchain's bin directory in
   371 your PATH, such as:
   372   export PATH="${PATH}:/your/toolchain/path/bin"
   373 
   374 and then using the target tuple to tell the build systems to use your
   375 toolchain:
   376   ./configure --target=your-target-tuple
   377 or
   378   make CC=your-target-tuple-gcc
   379 or
   380   make CROSS_COMPILE=your-target-tuple-
   381 and so on...
   382 
   383 It is strongly advised not to use the toolchain sys-root directory as an
   384 install directory for your programs/packages. If you do so, you will not be
   385 able to use your toolchain for another project. It is even strongly advised
   386 that your toolchain is chmod-ed to read-only once successfully build, so that
   387 you don't go polluting your toolchain with your programs/packages' files.
   388 
   389 Thus, when you build a program/package, install it in a separate directory,
   390 eg. /your/root. This directory is the /image/ of what would be in the root file
   391 system of your target, and will contain all that your programs/packages have
   392 installed.
   393 
   394 When your root directory is ready, it is still missing some important bits: the
   395 toolchain's libraries. To populate your root directory with those libs, just
   396 run:
   397   your-target-tuple-populate -s /your/root -d /your/root-populated
   398 
   399 This will copy /your/root into /your/root-populated, and put the needed and only
   400 the needed libraries there. Thus you don't polute /your/root with any cruft that
   401 would no longer be needed should you have to remove stuff. /your/root always
   402 contains only those things you install in it.
   403 
   404 You can then use /your/root-populated to build up your file system image, a
   405 tarball, or to NFS-mount it from your target, or whatever you need.
   406 
   407 populate accepts the following options:
   408 
   409  -s [src_dir]
   410     Use 'src_dir' as the 'source', un-populated root directory
   411 
   412  -d [dst_dir]
   413     Put the 'destination', populated root directory in 'dst_dir'
   414 
   415  -f
   416     Remove 'dst_dir' if it previously existed
   417 
   418  -v
   419     Be verbose, and tell what's going on (you can see exactly where libs are
   420     coming from).
   421 
   422  -h
   423     Print the help
   424 
   425 ___________________
   426                   /
   427 Toolchain types  /
   428 ________________/
   429 
   430 There are four kinds of toolchains you could encounter.
   431 
   432 First off, you must understand the following: when it comes to compilers there
   433 are up to four machines involved:
   434   1) the machine configuring the toolchain components: the config machine
   435   2) the machine building the toolchain components:    the build machine
   436   3) the machine running the toolchain:                the host machine
   437   4) the machine the toolchain is generating code for: the target machine
   438 
   439 We can most of the time assume that the config machine and the build machine
   440 are the same. Most of the time, this will be true. The only time it isn't
   441 is if you're using distributed compilation (such as distcc). Let's forget
   442 this for the sake of simplicity.
   443 
   444 So we're left with three machines:
   445  - build
   446  - host
   447  - target
   448 
   449 Any toolchain will involve those three machines. You can be as pretty sure of
   450 this as "2 and 2 are 4". Here is how they come into play:
   451 
   452 1) build == host == target
   453     This is a plain native toolchain, targetting the exact same machine as the
   454     one it is built on, and running again on this exact same machine. You have
   455     to build such a toolchain when you want to use an updated component, such
   456     as a newer gcc for example.
   457     crosstool-NG calls it "native".
   458 
   459 2) build == host != target
   460     This is a classic cross-toolchain, which is expected to be run on the same
   461     machine it is compiled on, and generate code to run on a second machine,
   462     the target.
   463     crosstool-NG calls it "cross".
   464 
   465 3) build != host == target
   466     Such a toolchain is also a native toolchain, as it targets the same machine
   467     as it runs on. But it is build on another machine. You want such a
   468     toolchain when porting to a new architecture, or if the build machine is
   469     much faster than the host machine.
   470     crosstool-NG calls it "cross-native".
   471 
   472 4) build != host != target
   473     This one is called a canadian-toolchain (*), and is tricky. The three
   474     machines in play are different. You might want such a toolchain if you
   475     have a fast build machine, but the users will use it on another machine,
   476     and will produce code to run on a third machine.
   477     crosstool-NG calls it "canadian".
   478 
   479 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
   480 anyway!)
   481 
   482 (*) The term Canadian Cross came about because at the time that these issues
   483     were all being hashed out, Canada had three national political parties.
   484     http://en.wikipedia.org/wiki/Cross_compiler
   485 
   486 _____________
   487             /
   488 Internals  /
   489 __________/
   490 
   491 Internally, crosstool-NG is script-based. To ease usage, the frontend is
   492 Makefile-based.
   493 
   494 Makefile front-end |
   495 -------------------+
   496 
   497 The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this
   498 script with an action will act exactly as if the Makefile was in the current
   499 working directory and make was called with the action as rule. Thus:
   500   ct-ng menuconfig
   501 
   502 is equivalent to having the Makefile in CWD, and calling:
   503   make menuconfig
   504 
   505 Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a
   506 traditional command.
   507 
   508 ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up
   509 at configuration time with ./configure.
   510 
   511 ct-ng also searches for config files, sub-tools, samples, scripts and patches in
   512 that library directory.
   513 
   514 Because of a stupid make behavior/bug I was unable to track down, implicit make
   515 rules are disabled: installing with --local would triger those rules, and mconf
   516 was unbuildable.
   517 
   518 Kconfig parser |
   519 ---------------+
   520 
   521 The kconfig language is a hacked version, vampirised from the toybox project
   522 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
   523 Linux kernel (http://www.kernel.org/), and (heavily) adapted to my needs.
   524 
   525 The kconfig parsers (conf and mconf) are not installed pre-built, but as
   526 source files. Thus you can have the directory where crosstool-NG is installed,
   527 exported (via NFS or whatever) and have clients with different architectures
   528 use the same crosstool-NG installation, and most notably, the same set of
   529 patches.
   530 
   531 Architecture-specific |
   532 ----------------------+
   533 
   534 Note: this chapter is not really well written, and might thus be a little bit
   535 complex to understand. To get a better grasp of what an architecture is, the
   536 reader is kindly encouraged to look at the "arch/" sub-directory, and to the
   537 existing architectures to see how things are laid out.
   538 
   539 An architecture is defined by:
   540 
   541  - a human-readable name, in lower case letters, with numbers as appropriate.
   542    The underscore is allowed; space and special characters are not.
   543      Eg.: arm, x86_64
   544  - a file in "config/arch/", named after the architecture's name, and suffixed
   545    with ".in".
   546      Eg.: config/arch/arm.in
   547  - a file in "scripts/build/arch/", named after the architecture's name, and
   548    suffixed with ".sh".
   549      Eg.: scripts/build/arch/arm.sh
   550 
   551 The architecture's ".in" file API:
   552  > the config option "ARCH_%arch%" (where %arch% is to be replaced with the
   553    actual architecture name).
   554    That config option must have *neither* a type, *nor* a prompt! Also, it can
   555    *not* depend on any other config option (EXPERIMENTAL is managed as above).
   556      Eg.:
   557        config ARCH_arm
   558    + mandatory:
   559        defines a (terse) help entry for this architecture:
   560        Eg.:
   561          config ARCH_arm
   562            help
   563              The ARM architecture.
   564    + optional:
   565        selects adequate associated config options.
   566        Eg.:
   567          config ARCH_arm
   568            select ARCH_SUPPORTS_BOTH_ENDIAN
   569            select ARCH_DEFAULT_LE
   570            help
   571              The ARM architecture.
   572 
   573  > other target-specific options, at your discretion. Note however that to
   574    avoid name-clashing, such options shall be prefixed with "ARCH_%arch%",
   575    where %arch% is again replaced by the actual architecture name.
   576    (Note: due to historical reasons, and lack of time to clean up the code,
   577     I may have left some config options that do not completely conform to
   578     this, as the architecture name was written all upper case. However, the
   579     prefix is unique among architectures, and does not cause harm).
   580 
   581 The architecture's ".sh" file API:
   582  > the function "CT_DoArchValues"
   583    + parameters: none
   584    + environment:
   585      - all variables from the ".config" file,
   586      - the two variables "target_endian_eb" and "target_endian_el" which are
   587        the endianness suffixes
   588    + return value: 0 upon success, !0 upon failure
   589    + provides:
   590      - mandatory
   591      - the environment variable CT_TARGET_ARCH
   592      - contains:
   593        the architecture part of the target tuple.
   594        Eg.: "armeb" for big endian ARM
   595             "i386" for an i386
   596    + provides:
   597      - optional
   598      - the environment variable CT_TARGET_SYS
   599      - contains:
   600        the sytem part of the target tuple.
   601        Eg.: "gnu" for glibc on most architectures
   602             "gnueabi" for glibc on an ARM EABI
   603      - defaults to:
   604        - for glibc-based toolchain: "gnu"
   605        - for uClibc-based toolchain: "uclibc"
   606    + provides:
   607      - optional
   608      - the environment variable CT_KERNEL_ARCH
   609      - contains:
   610        the architecture name as understandable by the Linux kernel build
   611        system.
   612        Eg.: "arm" for an ARM
   613             "powerpc" for a PowerPC
   614             "i386" for an x86
   615      - defaults to:
   616        ${CT_ARCH}
   617    + provides:
   618      - optional
   619      - the environment variables to configure the cross-gcc (defaults)
   620        - CT_ARCH_WITH_ARCH    : the gcc ./configure switch to select architecture level         ( "--with-arch=${CT_ARCH_ARCH}"   )
   621        - CT_ARCH_WITH_ABI     : the gcc ./configure switch to select ABI level                  ( "--with-abi=${CT_ARCH_ABI}"     )
   622        - CT_ARCH_WITH_CPU     : the gcc ./configure switch to select CPU instruction set        ( "--with-cpu=${CT_ARCH_CPU}"     )
   623        - CT_ARCH_WITH_TUNE    : the gcc ./configure switch to select scheduling                 ( "--with-tune=${CT_ARCH_TUNE}"   )
   624        - CT_ARCH_WITH_FPU     : the gcc ./configure switch to select FPU type                   ( "--with-fpu=${CT_ARCH_FPU}"     )
   625        - CT_ARCH_WITH_FLOAT   : the gcc ./configure switch to select floating point arithmetics ( "--with-float=soft" or /empty/  )
   626    + provides:
   627      - optional
   628      - the environment variables to pass to the cross-gcc to build target binaries (defaults)
   629        - CT_ARCH_ARCH_CFLAG   : the gcc switch to select architecture level                     ( "-march=${CT_ARCH_ARCH}"            )
   630        - CT_ARCH_ABI_CFLAG    : the gcc switch to select ABI level                              ( "-mabi=${CT_ARCH_ABI}"              )
   631        - CT_ARCH_CPU_CFLAG    : the gcc switch to select CPU instruction set                    ( "-mcpu=${CT_ARCH_CPU}"              )
   632        - CT_ARCH_TUNE_CFLAG   : the gcc switch to select scheduling                             ( "-mtune=${CT_ARCH_TUNE}"            )
   633        - CT_ARCH_FPU_CFLAG    : the gcc switch to select FPU type                               ( "-mfpu=${CT_ARCH_FPU}"              )
   634        - CT_ARCH_FLOAT_CFLAG  : the gcc switch to choose floating point arithmetics             ( "-msoft-float" or /empty/           )
   635        - CT_ARCH_ENDIAN_CFLAG : the gcc switch to choose big or little endian                   ( "-mbig-endian" or "-mlittle-endian" )
   636      - default to:
   637        see above.
   638    + provides:
   639      - optional
   640      - the environement variables to configure the core and final compiler, specific to this architecture:
   641        - CT_ARCH_CC_CORE_EXTRA_CONFIG   : additional, architecture specific core gcc ./configure flags
   642        - CT_ARCH_CC_EXTRA_CONFIG        : additional, architecture specific final gcc ./configure flags
   643      - default to:
   644        - all empty
   645    + provides:
   646      - optional
   647      - the architecture-specific CFLAGS and LDFLAGS:
   648        - CT_ARCH_TARGET_CLFAGS
   649        - CT_ARCH_TARGET_LDFLAGS
   650      - default to:
   651        - all empty
   652 
   653 You can have a look at "config/arch/arm.in" and "scripts/build/arch/arm.sh" for
   654 a quite complete example of what an actual architecture description looks like.
   655 
   656 Kernel specific |
   657 ----------------+
   658 
   659 A kernel is defined by:
   660 
   661  - a human-readable name, in lower case letters, with numbers as appropriate.
   662    The underscore is allowed; space and special characters are not (although
   663    they are internally replaced with underscores.
   664      Eg.: linux, bare-metal
   665  - a file in "config/kernel/", named after the kernel name, and suffixed with
   666    ".in".
   667      Eg.: config/kernel/linux.in, config/kernel/bare-metal.in
   668  - a file in "scripts/build/kernel/", named after the kernel name, and suffixed
   669    with ".sh".
   670      Eg.: scripts/build/kernel/linux.sh, scripts/build/kernel/bare-metal.sh
   671 
   672 The kernel's ".in" file must contain:
   673  > an optional lines containing exactly "# EXPERIMENTAL", starting on the
   674    first column, and without any following space or other character.
   675    If this line is present, then this kernel is considered EXPERIMENTAL,
   676    and correct dependency on EXPERIMENTAL will be set.
   677 
   678  > the config option "KERNEL_%kernel_name%" (where %kernel_name% is to be
   679    replaced with the actual kernel name, with all special characters and
   680    spaces replaced by underscores).
   681    That config option must have *neither* a type, *nor* a prompt! Also, it can
   682    *not* depends on EXPERIMENTAL.
   683      Eg.: KERNEL_linux, KERNEL_bare_metal
   684    + mandatory:
   685        defines a (terse) help entry for this kernel.
   686        Eg.:
   687          config KERNEL_bare_metal
   688            help
   689              Build a compiler for use without any kernel.
   690    + optional:
   691        selects adequate associated config options.
   692        Eg.:
   693          config KERNEL_bare_metal
   694            select BARE_METAL
   695            help
   696              Build a compiler for use without any kernel.
   697 
   698  > other kernel specific options, at your discretion. Note however that, to
   699    avoid name-clashing, such options should be prefixed with
   700    "KERNEL_%kernel_name%", where %kernel_name% is again tp be replaced with
   701    the actual kernel name.
   702    (Note: due to historical reasons, and lack of time to clean up the code,
   703     I may have left some config options that do not completely conform to
   704     this, as the kernel name was written all upper case. However, the prefix
   705     is unique among kernels, and does not cause harm).
   706 
   707 The kernel's ".sh" file API:
   708  > is a bash script fragment
   709 
   710  > defines the function "do_print_filename":
   711    + parameters: none
   712    + environment:
   713       - all variables from the ".config" file,
   714    + return value: ignored
   715    + behavior: output the kernel's tarball filename, with adequate suffix,
   716      on stdout.
   717        Eg.: linux-2.6.26.5.tar.bz2
   718 
   719  > defines the function "do_kernel_get":
   720    + parameters: none
   721    + environment:
   722       - all variables from the ".config" file.
   723    + return value: 0 for success, !0 for failure.
   724    + behavior: download the kernel's sources, and store the tarball into
   725      "${CT_TARBALLS_DIR}". To this end, a functions is available, that
   726      abstracts downloading tarballs:
   727      - CT_DoGet <tarball_base_name> <URL1 [URL...]>
   728        Eg.: CT_DoGet linux-2.6.26.5 ftp://ftp.kernel.org/pub/linux/kernel/v2.6
   729      Note: retrieving sources from svn, cvs, git and the likes is not supported
   730      by CT_DoGet. You'll have to do this by hand, as it is done for eglibc in
   731      "scripts/build/libc/eglibc.sh"
   732 
   733  > defines the function "do_kernel_extract":
   734    + parameters: none
   735    + environment:
   736       - all variables from the ".config" file,
   737    + return value: 0 for success, !0 for failure.
   738    + behavior: extract the kernel's tarball into "${CT_SRC_DIR}", and apply
   739      required patches. To this end, a function is available, that abstracts
   740      extracting tarballs:
   741      - CT_ExtractAndPatch <tarball_base_name>
   742        Eg.: CT_ExtractAndPatch linux-2.6.26.5
   743 
   744  > defines the function "do_kernel_headers":
   745    + parameters: none
   746    + environment:
   747       - all variables from the ".config" file,
   748    + return value: 0 for success, !0 for failure.
   749    + behavior: install the kernel headers (if any) in "${CT_SYSROOT_DIR}/usr/include"
   750 
   751  > defines any kernel-specific helper functions
   752    These functions, if any, must be prefixed with "do_kernel_%CT_KERNEL%_",
   753    where '%CT_KERNEL%' is to be replaced with the actual kernel name, to avoid
   754    any name-clashing.
   755 
   756 You can have a look at "config/kernel/linux.in" and "scripts/build/kernel/linux.sh"
   757 as an example of what a complex kernel description looks like.
   758 
   759 Adding a new version of a component |
   760 ------------------------------------+
   761 
   762 When a new component, such as the Linux kernel, gcc or any other is released,
   763 adding the new version to crosstool-NG is quite easy. There is a script that
   764 will do all that for you:
   765   tools/addToolVersion.sh
   766 
   767 Run it with no option to get some help.
   768 
   769 Build scripts |
   770 --------------+
   771 
   772 To Be Written later...