docs/overview.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Sun Nov 16 22:19:57 2008 +0000 (2008-11-16)
changeset 1048 06521debb8ed
parent 1047 0c450efc5e3f
child 1095 a18b17c1ddc5
permissions -rw-r--r--
Get rid of the local-test in Makefile.

/trunk/Makefile.in | 30 19 11 0 +++++++++++++++++++-----------
/trunk/docs/overview.txt | 25 13 12 0 +++++++++++++------------
2 files changed, 32 insertions(+), 23 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   Preparing for packaging
    18   Shell completion
    19   Contributed code
    20 Configuring crosstool-NG
    21   Interesting config options
    22   Re-building an existing toolchain
    23 Running crosstool-NG
    24   Stopping and restarting a build
    25   Testing all toolchains at once
    26   Overriding the number of // jobs
    27 Using the toolchain
    28 Toolchain types
    29 Internals
    30   Makefile front-end
    31   Kconfig parser
    32   Architecture-specific
    33   Adding a new version of a component
    34   Build scripts
    35 
    36 ________________
    37                /
    38 Introduction  /
    39 _____________/
    40 
    41 crosstool-NG aims at building toolchains. Toolchains are an essential component
    42 in a software development project. It will compile, assemble and link the code
    43 that is being developed. Some pieces of the toolchain will eventually end up
    44 in the resulting binary/ies: static libraries are but an example.
    45 
    46 So, a toolchain is a very sensitive piece of software, as any bug in one of the
    47 components, or a poorly configured component, can lead to execution problems,
    48 ranging from poor performance, to applications ending unexpectedly, to
    49 mis-behaving software (which more than often is hard to detect), to hardware
    50 damage, or even to human risks (which is more than regrettable).
    51 
    52 Toolchains are made of different piece of software, each being quite complex
    53 and requiring specially crafted options to build and work seamlessly. This
    54 is usually not that easy, even in the not-so-trivial case of native toolchains.
    55 The work reaches a higher degree of complexity when it comes to cross-
    56 compilation, where it can become quite a nightmare...
    57 
    58 Some cross-toolchains exist on the internet, and can be used for general
    59 development, but they have a number of limitations:
    60   - they can be general purpose, in that they are configured for the majority:
    61     no optimisation for your specific target,
    62   - they can be prepared for a specific target and thus are not easy to use,
    63     nor optimised for, or even supporting your target,
    64   - they often are using aging components (compiler, C library, etc...) not
    65     supporting special features of your shiny new processor;
    66 On the other side, these toolchain offer some advantages:
    67   - they are ready to use and quite easy to install and setup,
    68   - they are proven if used by a wide community.
    69 
    70 But once you want to get all the juice out of your specific hardware, you will
    71 want to build your own toolchain. This is where crosstool-NG comes into play.
    72 
    73 There are also a number of tools that build toolchains for specific needs,
    74 which are not really scalable. Examples are:
    75   - buildroot (buildroot.uclibc.org) whose main purpose is to build root file
    76     systems, hence the name. But once you have your toolchain with buildroot,
    77     part of it is installed in the root-to-be, so if you want to build a whole
    78     new root, you either have to save the existing one as a template and
    79     restore it later, or restart again from scratch. This is not convenient,
    80   - ptxdist (www.pengutronix.de/software/ptxdist), whose purpose is very
    81     similar to buildroot,
    82   - other projects (openembedded.org for example), which are again used to
    83     build root file systems.
    84 
    85 crosstool-NG is really targeted at building toolchains, and only toolchains.
    86 It is then up to you to use it the way you want.
    87 
    88 ___________
    89           /
    90 History  /
    91 ________/
    92 
    93 crosstool was first 'conceived' by Dan Kegel, who offered it to the community
    94 as a set of scripts, a repository of patches, and some pre-configured, general
    95 purpose setup files to be used to configure crosstool. This is available at
    96 http://www.kegel.com/crosstool, and the subversion repository is hosted on
    97 google at http://code.google.com/p/crosstool/.
    98 
    99 I once managed to add support for uClibc-based toolchains, but it did not make
   100 into mainline, mostly because I didn't have time to port the patch forward to
   101 the new versions, due in part to the big effort it was taking.
   102 
   103 So I decided to clean up crosstool in the state it was, re-order the things
   104 in place, add appropriate support for what I needed, that is uClibc support
   105 and a menu-driven configuration, named the new implementation crosstool-NG,
   106 (standing for crosstool Next Generation, as many other comunity projects do,
   107 and as a wink at the TV series "Star Trek: The Next Generation" ;-) ) and
   108 made it available to the community, in case it was of interest to any one.
   109 
   110 ___________________________
   111                           /
   112 Installing crosstool-NG  /
   113 ________________________/
   114 
   115 There are two ways you can use crosstool-NG:
   116  - build and install it, then get rid of the sources like you'd do for most
   117    programs,
   118  - or only build it and run from the source directory.
   119 
   120 The former should be used if you got crosstool-NG from a packaged tarball, see
   121 "Install method", below, while the latter is most useful for developpers that
   122 checked the code out from SVN, and want to submit patches, see "The Hacker's
   123 way", below.
   124 
   125 Install method |
   126 ---------------+
   127 
   128 If you go for the install, then you just follow the classical, but yet easy
   129 ./configure way:
   130   ./configure --prefix=/some/place
   131   make
   132   make install
   133   export PATH="${PATH}:/some/place/bin"
   134 
   135 You can then get rid of crosstool-NG source. Next create a directory to serve
   136 as a working place, cd in there and run:
   137   ct-ng help
   138 
   139 See below for complete usage.
   140 
   141 The Hacker's way |
   142 -----------------+
   143 
   144 If you go the hacker's way, then the usage is a bit different, although very
   145 simple:
   146   ./configure --local
   147   make
   148   make install
   149 
   150 Now, *do not* remove crosstool-NG sources. They are needed to run crosstool-NG!
   151 Stay in the directory holding the sources, and run:
   152   ./ct-ng help
   153 
   154 See below for complete usage.
   155 
   156 Now, provided you checked-out the code, you can send me your interesting changes
   157 by running:
   158   svn diff
   159 
   160 and mailing me the result! :-P
   161 
   162 Preparing for packaging |
   163 ------------------------+
   164 
   165 If you plan on packaging crosstool-NG, you surely don't want to install it
   166 in your root file system. The install procedure of crosstool-NG honors the
   167 DESTDIR variable:
   168 
   169   ./configure --prefix=/usr
   170   make
   171   make DESDTDIR=/packaging/place install
   172 
   173 Shell completion |
   174 -----------------+
   175 
   176 crosstool-NG comes with a shell script fragment that defines bash-compatible
   177 completion. That shell fragment is currently not installed automatically, but
   178 this is planned.
   179 
   180 To install the shell script fragment, you have two options:
   181  - install system-wide, most probably by copying ct-ng.comp into
   182    /etc/bash_completion.d/
   183  - install for a single user, by copying ct-ng.comp into ${HOME}/ and
   184    sourcing this file from your ${HOME}/.bashrc
   185 
   186 Contributed code |
   187 -----------------+
   188 
   189 Some people contibuted code that couldn't get merged for various reasons. This
   190 code is available as patches in the contrib/ sub-directory. These patches are
   191 to be applied to the source of crosstool-NG, prior to installing.
   192 
   193 An easy way to use contributed code is to pass the --with-contrib= option to
   194 ./configure. The possible values depend upon which contributions are packaged
   195 with your version, but you can get with it with passing one of those two
   196 special values:
   197   --with-contrib=list
   198     will list all available contributions
   199 
   200   --with-contrib=all
   201     will select all avalaible contributions
   202 
   203 There is no guarantee that a particuliar contribution applies to the current
   204 version of crosstool-ng, or that it will work at all. Use contributions at
   205 your own risk.
   206 
   207 ____________________________
   208                            /
   209 Configuring crosstool-NG  /
   210 _________________________/
   211 
   212 crosstool-NG is configured with a configurator presenting a menu-stuctured set
   213 of options. These options let you specify the way you want your toolchain
   214 built, where you want it installed, what architecture and specific processor it
   215 will support, the version of the components you want to use, etc... The
   216 value for those options are then stored in a configuration file.
   217 
   218 The configurator works the same way you configure your Linux kernel. It is
   219 assumed you now how to handle this.
   220 
   221 To enter the menu, type:
   222   ct-ng menuconfig
   223 
   224 Almost every config item has a help entry. Read them carefully.
   225 
   226 String and number options can refer to environment variables. In such a case,
   227 you must use the shell syntax: ${VAR}. You shall neither single- nor double-
   228 quote the string/number options.
   229 
   230 There are three environment variables that are computed by crosstool-NG, and
   231 that you can use:
   232 
   233 CT_TARGET:
   234   It represents the target tuple you are building for. You can use it for
   235   example in the installation/prefix directory, such as:
   236     /opt/x-tools/${CT_TARGET}
   237 
   238 CT_TOP_DIR:
   239   The top directory where crosstool-NG is running. You shouldn't need it in
   240   most cases. There is one case where you may need it: if you have local
   241   patches and you store them in your running directory, you can refer to them
   242   by using CT_TOP_DIR, such as:
   243     ${CT_TOP_DIR}/patches.myproject
   244 
   245 CT_VERSION:
   246   The version of crosstool-NG you are using. Not much use for you, but it's
   247   there if you need it.
   248 
   249 Interesting config options |
   250 ---------------------------+
   251 
   252 CT_LOCAL_TARBALLS_DIR:
   253   If you already have some tarballs in a direcotry, enter it here. That will
   254   speed up the retrieving phase, where crosstool-NG would otherwise download
   255   those tarballs.
   256 
   257 CT_PREFIX_DIR:
   258   This is where the toolchain will be installed in (and for now, where it
   259   will run from). Common use is to add the target tuple in the directory
   260   path, such as (see above):
   261     /opt/x-tools/${CT_TARGET}
   262 
   263 CT_TARGET_VENDOR:
   264   An identifier for your toolchain, will take place in the vendor part of the
   265   target tuple. It shall *not* contain spaces or dashes. Usually, keep it
   266   to a one-word string, or use underscores to separate words if you need.
   267   Avoid dots, commas, and special characters.
   268 
   269 CT_TARGET_ALIAS:
   270   An alias for the toolchian. It will be used as a prefix to the toolchain
   271   tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
   272 
   273 Also, if you think you don't see enough versions, you can try to enable one of
   274 those:
   275 
   276 CT_OBSOLETE:
   277   Show obsolete versions or tools. Most of the time, you don't want to base
   278   your toolchain on too old a version (of gcc, for example). But at times, it
   279   can come handy to use such an old version for regression tests. Those old
   280   versions are hidden behind CT_OBSOLETE.
   281 
   282 CT_EXPERIMENTAL:
   283   Show experimental versions or tools. Again, you might not want to base your
   284   toolchain on too recent tools (eg. gcc) for production. But if you need a
   285   feature present only in a recent version, or a new tool, you can find them
   286   hidden behind CT_EXPERIMENTAL.
   287 
   288 Re-building an existing toolchain |
   289 ----------------------------------+
   290 
   291 If you have an existing toolchain, you can re-use the options used to build it
   292 to create a new toolchain. That needs a very little bit of effort on your side
   293 but is quite easy. The options to build a toolchain are saved with the
   294 toolchain, and you can retrieve this configuration by running:
   295   ${CT_TARGET}-config
   296 
   297 This will dump the configuration to stdout, so to rebuild a toolchain with this
   298 configuration, the following is all you need to do:
   299   ${CT_TARGET}-config >.config
   300 
   301 Then, you can review and change the configuration by running:
   302   ct-ng menuconfig
   303 
   304 ________________________
   305                        /
   306 Running crosstool-NG  /
   307 _____________________/
   308 
   309 To build the toolchain, simply type:
   310   ct-ng build
   311 
   312 This will use the above configuration to retrieve, extract and patch the
   313 components, build, install and eventually test your newly built toolchain.
   314 
   315 You are then free to add the toolchain /bin directory in your PATH to use
   316 it at will.
   317 
   318 In any case, you can get some terse help. Just type:
   319   ct-ng help
   320 or:
   321   man 1 ct-ng
   322 
   323 Stopping and restarting a build |
   324 --------------------------------+
   325 
   326 If you want to stop the build after a step you are debugging, you can pass the
   327 variable STOP to make:
   328   ct-ng STOP=some_step
   329 
   330 Conversely, if you want to restart a build at a specific step you are
   331 debugging, you can pass the RESTART variable to make:
   332   ct-ng RESTART=some_step
   333 
   334 Alternatively, you can call make with the name of a step to just do that step:
   335   ct-ng libc_headers
   336 is equivalent to:
   337   ct-ng RESTART=libc_headers STOP=libc_headers
   338 
   339 The shortcuts +step_name and step_name+ allow to respectively stop or restart
   340 at that step. Thus:
   341   ct-ng +libc_headers        and:    ct-ng libc_headers+
   342 are equivalent to:
   343   ct-ng STOP=libc_headers    and:    ct-ng RESTART=libc_headers
   344 
   345 To obtain the list of acceptable steps, please call:
   346   ct-ng list-steps
   347 
   348 Note that in order to restart a build, you'll have to say 'Y' to the config
   349 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
   350 that far.
   351 
   352 Building all toolchains at once |
   353 --------------------------------+
   354 
   355 You can build all samples; simply call:
   356   ct-ng build-all
   357 
   358 Overriding the number of // jobs |
   359 ---------------------------------+
   360 
   361 If you want to override the number of jobs to run in // (the -j option to
   362 make), you can either re-enter the menuconfig, or simply add it on the command
   363 line, as such:
   364   ct-ng build.4
   365 
   366 which tells crosstool-NG to override the number of // jobs to 4.
   367 
   368 You can see the actions that support overriding the number of // jobs in
   369 the help menu. Those are the ones with [.#] after them (eg. build[.#] or
   370 build-all[.#], and so on...).
   371 
   372 Note on // jobs |
   373 ----------------+
   374 
   375 The crosstool-NG script 'ct-ng' is a Makefile-script. It does *not* execute
   376 in parallel (there is not much to gain). When speaking of // jobs, we are
   377 refering to the number of // jobs when making the *components*. That is, we
   378 speak of the number of // jobs used to build gcc, glibc, and so on...
   379 
   380 
   381 _______________________
   382                       /
   383 Using the toolchain  /
   384 ____________________/
   385 
   386 Using the toolchain is as simple as adding the toolchain's bin directory in
   387 your PATH, such as:
   388   export PATH="${PATH}:/your/toolchain/path/bin"
   389 
   390 and then using the target tuple to tell the build systems to use your
   391 toolchain:
   392   ./configure --target=your-target-tuple
   393 or
   394   make CC=your-target-tuple-gcc
   395 or
   396   make CROSS_COMPILE=your-target-tuple-
   397 and so on...
   398 
   399 It is strongly advised not to use the toolchain sys-root directory as an
   400 install directory for your programs/packages. If you do so, you will not be
   401 able to use your toolchain for another project. It is even strongly advised
   402 that your toolchain is chmod-ed to read-only once successfully build, so that
   403 you don't go polluting your toolchain with your programs/packages' files.
   404 
   405 Thus, when you build a program/package, install it in a separate directory,
   406 eg. /your/root. This directory is the /image/ of what would be in the root file
   407 system of your target, and will contain all that your programs/packages have
   408 installed.
   409 
   410 When your root directory is ready, it is still missing some important bits: the
   411 toolchain's libraries. To populate your root directory with those libs, just
   412 run:
   413   your-target-tuple-populate -s /your/root -d /your/root-populated
   414 
   415 This will copy /your/root into /your/root-populated, and put the needed and only
   416 the needed libraries there. Thus you don't polute /your/root with any cruft that
   417 would no longer be needed should you have to remove stuff. /your/root always
   418 contains only those things you install in it.
   419 
   420 You can then use /your/root-populated to build up your file system image, a
   421 tarball, or to NFS-mount it from your target, or whatever you need.
   422 
   423 populate accepts the following options:
   424 
   425  -s [src_dir]
   426     Use 'src_dir' as the 'source', un-populated root directory
   427 
   428  -d [dst_dir]
   429     Put the 'destination', populated root directory in 'dst_dir'
   430 
   431  -f
   432     Remove 'dst_dir' if it previously existed
   433 
   434  -v
   435     Be verbose, and tell what's going on (you can see exactly where libs are
   436     coming from).
   437 
   438  -h
   439     Print the help
   440 
   441 ___________________
   442                   /
   443 Toolchain types  /
   444 ________________/
   445 
   446 There are four kinds of toolchains you could encounter.
   447 
   448 First off, you must understand the following: when it comes to compilers there
   449 are up to four machines involved:
   450   1) the machine configuring the toolchain components: the config machine
   451   2) the machine building the toolchain components:    the build machine
   452   3) the machine running the toolchain:                the host machine
   453   4) the machine the toolchain is generating code for: the target machine
   454 
   455 We can most of the time assume that the config machine and the build machine
   456 are the same. Most of the time, this will be true. The only time it isn't
   457 is if you're using distributed compilation (such as distcc). Let's forget
   458 this for the sake of simplicity.
   459 
   460 So we're left with three machines:
   461  - build
   462  - host
   463  - target
   464 
   465 Any toolchain will involve those three machines. You can be as pretty sure of
   466 this as "2 and 2 are 4". Here is how they come into play:
   467 
   468 1) build == host == target
   469     This is a plain native toolchain, targetting the exact same machine as the
   470     one it is built on, and running again on this exact same machine. You have
   471     to build such a toolchain when you want to use an updated component, such
   472     as a newer gcc for example.
   473     crosstool-NG calls it "native".
   474 
   475 2) build == host != target
   476     This is a classic cross-toolchain, which is expected to be run on the same
   477     machine it is compiled on, and generate code to run on a second machine,
   478     the target.
   479     crosstool-NG calls it "cross".
   480 
   481 3) build != host == target
   482     Such a toolchain is also a native toolchain, as it targets the same machine
   483     as it runs on. But it is build on another machine. You want such a
   484     toolchain when porting to a new architecture, or if the build machine is
   485     much faster than the host machine.
   486     crosstool-NG calls it "cross-native".
   487 
   488 4) build != host != target
   489     This one is called a canadian-toolchain (*), and is tricky. The three
   490     machines in play are different. You might want such a toolchain if you
   491     have a fast build machine, but the users will use it on another machine,
   492     and will produce code to run on a third machine.
   493     crosstool-NG calls it "canadian".
   494 
   495 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
   496 anyway!)
   497 
   498 (*) The term Canadian Cross came about because at the time that these issues
   499     were all being hashed out, Canada had three national political parties.
   500     http://en.wikipedia.org/wiki/Cross_compiler
   501 
   502 _____________
   503             /
   504 Internals  /
   505 __________/
   506 
   507 Internally, crosstool-NG is script-based. To ease usage, the frontend is
   508 Makefile-based.
   509 
   510 Makefile front-end |
   511 -------------------+
   512 
   513 The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this
   514 script with an action will act exactly as if the Makefile was in the current
   515 working directory and make was called with the action as rule. Thus:
   516   ct-ng menuconfig
   517 
   518 is equivalent to having the Makefile in CWD, and calling:
   519   make menuconfig
   520 
   521 Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a
   522 traditional command.
   523 
   524 ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up
   525 at configuration time with ./configure.
   526 
   527 ct-ng also searches for config files, sub-tools, samples, scripts and patches in
   528 that library directory.
   529 
   530 Because of a stupid make behavior/bug I was unable to track down, implicit make
   531 rules are disabled: installing with --local would triger those rules, and mconf
   532 was unbuildable.
   533 
   534 Kconfig parser |
   535 ---------------+
   536 
   537 The kconfig language is a hacked version, vampirised from the Linux kernel
   538 (http://www.kernel.org/), and (heavily) adapted to my needs.
   539 
   540 The list of the most notable changes (at least the ones I remember) follows:
   541 - the CONFIG_ prefix has been replaced with CT_
   542 - a leading | in prompts is skipped, and subsequent leading spaces are not
   543   trimmed
   544 - otherwise leading spaces are silently trimmed
   545 
   546 The kconfig parsers (conf and mconf) are not installed pre-built, but as
   547 source files. Thus you can have the directory where crosstool-NG is installed,
   548 exported (via NFS or whatever) and have clients with different architectures
   549 use the same crosstool-NG installation, and most notably, the same set of
   550 patches.
   551 
   552 Architecture-specific |
   553 ----------------------+
   554 
   555 Note: this chapter is not really well written, and might thus be a little bit
   556 complex to understand. To get a better grasp of what an architecture is, the
   557 reader is kindly encouraged to look at the "arch/" sub-directory, and to the
   558 existing architectures to see how things are laid out.
   559 
   560 An architecture is defined by:
   561 
   562  - a human-readable name, in lower case letters, with numbers as appropriate.
   563    The underscore is allowed; space and special characters are not.
   564      Eg.: arm, x86_64
   565  - a file in "config/arch/", named after the architecture's name, and suffixed
   566    with ".in".
   567      Eg.: config/arch/arm.in
   568  - a file in "scripts/build/arch/", named after the architecture's name, and
   569    suffixed with ".sh".
   570      Eg.: scripts/build/arch/arm.sh
   571 
   572 The architecture's ".in" file API:
   573  > the config option "ARCH_%arch%" (where %arch% is to be replaced with the
   574    actual architecture name).
   575    That config option must have *neither* a type, *nor* a prompt! Also, it can
   576    *not* depend on any other config option (EXPERIMENTAL is managed as above).
   577      Eg.:
   578        config ARCH_arm
   579    + mandatory:
   580        defines a (terse) help entry for this architecture:
   581        Eg.:
   582          config ARCH_arm
   583            help
   584              The ARM architecture.
   585    + optional:
   586        selects adequate associated config options.
   587        Note: 64-bit architectures *shall* select ARCH_64
   588        Eg.:
   589          config ARCH_arm
   590            select ARCH_SUPPORTS_BOTH_ENDIAN
   591            select ARCH_DEFAULT_LE
   592            help
   593              The ARM architecture.
   594        Eg.:
   595          config ARCH_x86_64
   596             select ARCH_64
   597             help
   598               The x86_64 architecture.
   599 
   600  > other target-specific options, at your discretion. Note however that to
   601    avoid name-clashing, such options shall be prefixed with "ARCH_%arch%",
   602    where %arch% is again replaced by the actual architecture name.
   603    (Note: due to historical reasons, and lack of time to clean up the code,
   604     I may have left some config options that do not completely conform to
   605     this, as the architecture name was written all upper case. However, the
   606     prefix is unique among architectures, and does not cause harm).
   607 
   608 The architecture's ".sh" file API:
   609  > the function "CT_DoArchTupleValues"
   610    + parameters: none
   611    + environment:
   612      - all variables from the ".config" file,
   613      - the two variables "target_endian_eb" and "target_endian_el" which are
   614        the endianness suffixes
   615    + return value: 0 upon success, !0 upon failure
   616    + provides:
   617      - mandatory
   618      - the environment variable CT_TARGET_ARCH
   619      - contains:
   620        the architecture part of the target tuple.
   621        Eg.: "armeb" for big endian ARM
   622             "i386" for an i386
   623    + provides:
   624      - optional
   625      - the environment variable CT_TARGET_SYS
   626      - contains:
   627        the sytem part of the target tuple.
   628        Eg.: "gnu" for glibc on most architectures
   629             "gnueabi" for glibc on an ARM EABI
   630      - defaults to:
   631        - for glibc-based toolchain: "gnu"
   632        - for uClibc-based toolchain: "uclibc"
   633    + provides:
   634      - optional
   635      - the environment variable CT_KERNEL_ARCH
   636      - contains:
   637        the architecture name as understandable by the Linux kernel build
   638        system.
   639        Eg.: "arm" for an ARM
   640             "powerpc" for a PowerPC
   641             "i386" for an x86
   642      - defaults to:
   643        ${CT_ARCH}
   644    + provides:
   645      - optional
   646      - the environment variables to configure the cross-gcc (defaults)
   647        - CT_ARCH_WITH_ARCH    : the gcc ./configure switch to select architecture level         ( "--with-arch=${CT_ARCH_ARCH}"   )
   648        - CT_ARCH_WITH_ABI     : the gcc ./configure switch to select ABI level                  ( "--with-abi=${CT_ARCH_ABI}"     )
   649        - CT_ARCH_WITH_CPU     : the gcc ./configure switch to select CPU instruction set        ( "--with-cpu=${CT_ARCH_CPU}"     )
   650        - CT_ARCH_WITH_TUNE    : the gcc ./configure switch to select scheduling                 ( "--with-tune=${CT_ARCH_TUNE}"   )
   651        - CT_ARCH_WITH_FPU     : the gcc ./configure switch to select FPU type                   ( "--with-fpu=${CT_ARCH_FPU}"     )
   652        - CT_ARCH_WITH_FLOAT   : the gcc ./configure switch to select floating point arithmetics ( "--with-float=soft" or /empty/  )
   653    + provides:
   654      - optional
   655      - the environment variables to pass to the cross-gcc to build target binaries (defaults)
   656        - CT_ARCH_ARCH_CFLAG   : the gcc switch to select architecture level                     ( "-march=${CT_ARCH_ARCH}"            )
   657        - CT_ARCH_ABI_CFLAG    : the gcc switch to select ABI level                              ( "-mabi=${CT_ARCH_ABI}"              )
   658        - CT_ARCH_CPU_CFLAG    : the gcc switch to select CPU instruction set                    ( "-mcpu=${CT_ARCH_CPU}"              )
   659        - CT_ARCH_TUNE_CFLAG   : the gcc switch to select scheduling                             ( "-mtune=${CT_ARCH_TUNE}"            )
   660        - CT_ARCH_FPU_CFLAG    : the gcc switch to select FPU type                               ( "-mfpu=${CT_ARCH_FPU}"              )
   661        - CT_ARCH_FLOAT_CFLAG  : the gcc switch to choose floating point arithmetics             ( "-msoft-float" or /empty/           )
   662        - CT_ARCH_ENDIAN_CFLAG : the gcc switch to choose big or little endian                   ( "-mbig-endian" or "-mlittle-endian" )
   663      - default to:
   664        see above.
   665    + provides:
   666      - optional
   667      - the environement variables to configure the core and final compiler, specific to this architecture:
   668        - CT_ARCH_CC_CORE_EXTRA_CONFIG   : additional, architecture specific core gcc ./configure flags
   669        - CT_ARCH_CC_EXTRA_CONFIG        : additional, architecture specific final gcc ./configure flags
   670      - default to:
   671        - all empty
   672    + provides:
   673      - optional
   674      - the architecture-specific CFLAGS and LDFLAGS:
   675        - CT_ARCH_TARGET_CLFAGS
   676        - CT_ARCH_TARGET_LDFLAGS
   677      - default to:
   678        - all empty
   679 
   680 You can have a look at "config/arch/arm.in" and "scripts/build/arch/arm.sh" for
   681 a quite complete example of what an actual architecture description looks like.
   682 
   683 Kernel specific |
   684 ----------------+
   685 
   686 A kernel is defined by:
   687 
   688  - a human-readable name, in lower case letters, with numbers as appropriate.
   689    The underscore is allowed; space and special characters are not (although
   690    they are internally replaced with underscores.
   691      Eg.: linux, bare-metal
   692  - a file in "config/kernel/", named after the kernel name, and suffixed with
   693    ".in".
   694      Eg.: config/kernel/linux.in, config/kernel/bare-metal.in
   695  - a file in "scripts/build/kernel/", named after the kernel name, and suffixed
   696    with ".sh".
   697      Eg.: scripts/build/kernel/linux.sh, scripts/build/kernel/bare-metal.sh
   698 
   699 The kernel's ".in" file must contain:
   700  > an optional lines containing exactly "# EXPERIMENTAL", starting on the
   701    first column, and without any following space or other character.
   702    If this line is present, then this kernel is considered EXPERIMENTAL,
   703    and correct dependency on EXPERIMENTAL will be set.
   704 
   705  > the config option "KERNEL_%kernel_name%" (where %kernel_name% is to be
   706    replaced with the actual kernel name, with all special characters and
   707    spaces replaced by underscores).
   708    That config option must have *neither* a type, *nor* a prompt! Also, it can
   709    *not* depends on EXPERIMENTAL.
   710      Eg.: KERNEL_linux, KERNEL_bare_metal
   711    + mandatory:
   712        defines a (terse) help entry for this kernel.
   713        Eg.:
   714          config KERNEL_bare_metal
   715            help
   716              Build a compiler for use without any kernel.
   717    + optional:
   718        selects adequate associated config options.
   719        Eg.:
   720          config KERNEL_bare_metal
   721            select BARE_METAL
   722            help
   723              Build a compiler for use without any kernel.
   724 
   725  > other kernel specific options, at your discretion. Note however that, to
   726    avoid name-clashing, such options should be prefixed with
   727    "KERNEL_%kernel_name%", where %kernel_name% is again tp be replaced with
   728    the actual kernel name.
   729    (Note: due to historical reasons, and lack of time to clean up the code,
   730     I may have left some config options that do not completely conform to
   731     this, as the kernel name was written all upper case. However, the prefix
   732     is unique among kernels, and does not cause harm).
   733 
   734 The kernel's ".sh" file API:
   735  > is a bash script fragment
   736 
   737  > defines the function CT_DoKernelTupleValues
   738    + see the architecture's CT_DoArchTupleValues, except for:
   739    + set the environment variable CT_TARGET_KERNEL, the kernel part of the
   740      target tuple
   741    + return value: ignored
   742 
   743  > defines the function "do_print_filename":
   744    + parameters: none
   745    + environment:
   746       - all variables from the ".config" file,
   747    + return value: ignored
   748    + behavior: output the kernel's tarball filename, with adequate suffix,
   749      on stdout.
   750        Eg.: linux-2.6.26.5.tar.bz2
   751 
   752  > defines the function "do_kernel_get":
   753    + parameters: none
   754    + environment:
   755       - all variables from the ".config" file.
   756    + return value: 0 for success, !0 for failure.
   757    + behavior: download the kernel's sources, and store the tarball into
   758      "${CT_TARBALLS_DIR}". To this end, a functions is available, that
   759      abstracts downloading tarballs:
   760      - CT_DoGet <tarball_base_name> <URL1 [URL...]>
   761        Eg.: CT_DoGet linux-2.6.26.5 ftp://ftp.kernel.org/pub/linux/kernel/v2.6
   762      Note: retrieving sources from svn, cvs, git and the likes is not supported
   763      by CT_DoGet. You'll have to do this by hand, as it is done for eglibc in
   764      "scripts/build/libc/eglibc.sh"
   765 
   766  > defines the function "do_kernel_extract":
   767    + parameters: none
   768    + environment:
   769       - all variables from the ".config" file,
   770    + return value: 0 for success, !0 for failure.
   771    + behavior: extract the kernel's tarball into "${CT_SRC_DIR}", and apply
   772      required patches. To this end, a function is available, that abstracts
   773      extracting tarballs:
   774      - CT_ExtractAndPatch <tarball_base_name>
   775        Eg.: CT_ExtractAndPatch linux-2.6.26.5
   776 
   777  > defines the function "do_kernel_headers":
   778    + parameters: none
   779    + environment:
   780       - all variables from the ".config" file,
   781    + return value: 0 for success, !0 for failure.
   782    + behavior: install the kernel headers (if any) in "${CT_SYSROOT_DIR}/usr/include"
   783 
   784  > defines any kernel-specific helper functions
   785    These functions, if any, must be prefixed with "do_kernel_%CT_KERNEL%_",
   786    where '%CT_KERNEL%' is to be replaced with the actual kernel name, to avoid
   787    any name-clashing.
   788 
   789 You can have a look at "config/kernel/linux.in" and "scripts/build/kernel/linux.sh"
   790 as an example of what a complex kernel description looks like.
   791 
   792 Adding a new version of a component |
   793 ------------------------------------+
   794 
   795 When a new component, such as the Linux kernel, gcc or any other is released,
   796 adding the new version to crosstool-NG is quite easy. There is a script that
   797 will do all that for you:
   798   tools/addToolVersion.sh
   799 
   800 Run it with no option to get some help.
   801 
   802 Build scripts |
   803 --------------+
   804 
   805 To Be Written later...