docs/overview.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Tue Oct 14 20:06:37 2008 +0000 (2008-10-14)
changeset 934 e2f4be0feb9d
parent 903 9fb0f81b4416
child 965 45ddf096def1
permissions -rw-r--r--
Correctly auto-complete with start-steps as well.

/trunk/ct-ng.comp | 2 1 1 0 +-
1 file changed, 1 insertion(+), 1 deletion(-)
     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 Re-building an existing toolchain |
   276 ----------------------------------+
   277 
   278 If you have an existing toolchain, you can re-use the options used to build it
   279 to create a new toolchain. That needs a very little bit of effort on your side
   280 but is quite easy. The options to build a toolchain are saved with the
   281 toolchain, and you can retrieve this configuration by running:
   282   ${CT_TARGET}-config
   283 
   284 This will dump the configuration to stdout, so to rebuild a toolchain with this
   285 configuration, the following is all you need to do:
   286   ${CT_TARGET}-config >.config
   287 
   288 Then, you can review and change the configuration by running:
   289   ct-ng menuconfig
   290 
   291 ________________________
   292                        /
   293 Running crosstool-NG  /
   294 _____________________/
   295 
   296 To build the toolchain, simply type:
   297   ct-ng build
   298 
   299 This will use the above configuration to retrieve, extract and patch the
   300 components, build, install and eventually test your newly built toolchain.
   301 
   302 You are then free to add the toolchain /bin directory in your PATH to use
   303 it at will.
   304 
   305 In any case, you can get some terse help. Just type:
   306   ct-ng help
   307 or:
   308   man 1 ct-ng
   309 
   310 Stopping and restarting a build |
   311 --------------------------------+
   312 
   313 If you want to stop the build after a step you are debugging, you can pass the
   314 variable STOP to make:
   315   ct-ng STOP=some_step
   316 
   317 Conversely, if you want to restart a build at a specific step you are
   318 debugging, you can pass the RESTART variable to make:
   319   ct-ng RESTART=some_step
   320 
   321 Alternatively, you can call make with the name of a step to just do that step:
   322   ct-ng libc_headers
   323 is equivalent to:
   324   ct-ng RESTART=libc_headers STOP=libc_headers
   325 
   326 The shortcuts +step_name and step_name+ allow to respectively stop or restart
   327 at that step. Thus:
   328   ct-ng +libc_headers        and:    ct-ng libc_headers+
   329 are equivalent to:
   330   ct-ng STOP=libc_headers    and:    ct-ng RESTART=libc_headers
   331 
   332 To obtain the list of acceptable steps, please call:
   333   ct-ng list-steps
   334 
   335 Note that in order to restart a build, you'll have to say 'Y' to the config
   336 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
   337 that far.
   338 
   339 Testing all toolchains at once |
   340 -------------------------------+
   341 
   342 You can test-build all samples; simply call:
   343   ct-ng regtest
   344 
   345 Overriding the number of // jobs |
   346 ---------------------------------+
   347 
   348 If you want to override the number of jobs to run in // (the -j option to
   349 make), you can either re-enter the menuconfig, or simply add it on the command
   350 line, as such:
   351   ct-ng build.4
   352 
   353 which tells crosstool-NG to override the number of // jobs to 4.
   354 
   355 You can see the actions that support overriding the number of // jobs in
   356 the help menu. Those are the ones with [.#] after them (eg. build[.#] or
   357 regtest[.#], and so on...).
   358 
   359 _______________________
   360                       /
   361 Using the toolchain  /
   362 ____________________/
   363 
   364 Using the toolchain is as simple as adding the toolchain's bin directory in
   365 your PATH, such as:
   366   export PATH="${PATH}:/your/toolchain/path/bin"
   367 
   368 and then using the target tuple to tell the build systems to use your
   369 toolchain:
   370   ./configure --target=your-target-tuple
   371 or
   372   make CC=your-target-tuple-gcc
   373 or
   374   make CROSS_COMPILE=your-target-tuple-
   375 and so on...
   376 
   377 It is strongly advised not to use the toolchain sys-root directory as an
   378 install directory for your programs/packages. If you do so, you will not be
   379 able to use your toolchain for another project. It is even strongly advised
   380 that your toolchain is chmod-ed to read-only once successfully build, so that
   381 you don't go polluting your toolchain with your programs/packages' files.
   382 
   383 Thus, when you build a program/package, install it in a separate directory,
   384 eg. /your/root. This directory is the /image/ of what would be in the root file
   385 system of your target, and will contain all that your programs/packages have
   386 installed.
   387 
   388 When your root directory is ready, it is still missing some important bits: the
   389 toolchain's libraries. To populate your root directory with those libs, just
   390 run:
   391   your-target-tuple-populate -s /your/root -d /your/root-populated
   392 
   393 This will copy /your/root into /your/root-populated, and put the needed and only
   394 the needed libraries there. Thus you don't polute /your/root with any cruft that
   395 would no longer be needed should you have to remove stuff. /your/root always
   396 contains only those things you install in it.
   397 
   398 You can then use /your/root-populated to build up your file system image, a
   399 tarball, or to NFS-mount it from your target, or whatever you need.
   400 
   401 populate accepts the following options:
   402 
   403  -s [src_dir]
   404     Use 'src_dir' as the 'source', un-populated root directory
   405 
   406  -d [dst_dir]
   407     Put the 'destination', populated root directory in 'dst_dir'
   408 
   409  -f
   410     Remove 'dst_dir' if it previously existed
   411 
   412  -v
   413     Be verbose, and tell what's going on (you can see exactly where libs are
   414     coming from).
   415 
   416  -h
   417     Print the help
   418 
   419 ___________________
   420                   /
   421 Toolchain types  /
   422 ________________/
   423 
   424 There are four kinds of toolchains you could encounter.
   425 
   426 First off, you must understand the following: when it comes to compilers there
   427 are up to four machines involved:
   428   1) the machine configuring the toolchain components: the config machine
   429   2) the machine building the toolchain components:    the build machine
   430   3) the machine running the toolchain:                the host machine
   431   4) the machine the toolchain is generating code for: the target machine
   432 
   433 We can most of the time assume that the config machine and the build machine
   434 are the same. Most of the time, this will be true. The only time it isn't
   435 is if you're using distributed compilation (such as distcc). Let's forget
   436 this for the sake of simplicity.
   437 
   438 So we're left with three machines:
   439  - build
   440  - host
   441  - target
   442 
   443 Any toolchain will involve those three machines. You can be as pretty sure of
   444 this as "2 and 2 are 4". Here is how they come into play:
   445 
   446 1) build == host == target
   447     This is a plain native toolchain, targetting the exact same machine as the
   448     one it is built on, and running again on this exact same machine. You have
   449     to build such a toolchain when you want to use an updated component, such
   450     as a newer gcc for example.
   451     crosstool-NG calls it "native".
   452 
   453 2) build == host != target
   454     This is a classic cross-toolchain, which is expected to be run on the same
   455     machine it is compiled on, and generate code to run on a second machine,
   456     the target.
   457     crosstool-NG calls it "cross".
   458 
   459 3) build != host == target
   460     Such a toolchain is also a native toolchain, as it targets the same machine
   461     as it runs on. But it is build on another machine. You want such a
   462     toolchain when porting to a new architecture, or if the build machine is
   463     much faster than the host machine.
   464     crosstool-NG calls it "cross-native".
   465 
   466 4) build != host != target
   467     This one is called a canadian-toolchain (*), and is tricky. The three
   468     machines in play are different. You might want such a toolchain if you
   469     have a fast build machine, but the users will use it on another machine,
   470     and will produce code to run on a third machine.
   471     crosstool-NG calls it "canadian".
   472 
   473 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
   474 anyway!)
   475 
   476 (*) The term Canadian Cross came about because at the time that these issues
   477     were all being hashed out, Canada had three national political parties.
   478     http://en.wikipedia.org/wiki/Cross_compiler
   479 
   480 _____________
   481             /
   482 Internals  /
   483 __________/
   484 
   485 Internally, crosstool-NG is script-based. To ease usage, the frontend is
   486 Makefile-based.
   487 
   488 Makefile front-end |
   489 -------------------+
   490 
   491 The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this
   492 script with an action will act exactly as if the Makefile was in the current
   493 working directory and make was called with the action as rule. Thus:
   494   ct-ng menuconfig
   495 
   496 is equivalent to having the Makefile in CWD, and calling:
   497   make menuconfig
   498 
   499 Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a
   500 traditional command.
   501 
   502 ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up
   503 at configuration time with ./configure.
   504 
   505 ct-ng also searches for config files, sub-tools, samples, scripts and patches in
   506 that library directory.
   507 
   508 Because of a stupid make behavior/bug I was unable to track down, implicit make
   509 rules are disabled: installing with --local would triger those rules, and mconf
   510 was unbuildable.
   511 
   512 Kconfig parser |
   513 ---------------+
   514 
   515 The kconfig language is a hacked version, vampirised from the toybox project
   516 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
   517 Linux kernel (http://www.kernel.org/), and (heavily) adapted to my needs.
   518 
   519 The kconfig parsers (conf and mconf) are not installed pre-built, but as
   520 source files. Thus you can have the directory where crosstool-NG is installed,
   521 exported (via NFS or whatever) and have clients with different architectures
   522 use the same crosstool-NG installation, and most notably, the same set of
   523 patches.
   524 
   525 Architecture-specific |
   526 ----------------------+
   527 
   528 Note: this chapter is not really well written, and might thus be a little bit
   529 complex to understand. To get a better grasp of what an architecture is, the
   530 reader is kindly encouraged to look at the "arch/" sub-directory, and to the
   531 existing architectures to see how things are laid out.
   532 
   533 An architecture is defined by:
   534 
   535  - a human-readable name, in lower case letters, with numbers as appropriate.
   536    The underscore is allowed; space and special characters are not.
   537      Eg.: arm, x86_64
   538  - a file in "config/arch/", named after the architecture's name, and suffixed
   539    with ".in".
   540      Eg.: config/arch/arm.in
   541  - a file in "scripts/build/arch/", named after the architecture's name, and
   542    suffixed with ".sh".
   543      Eg.: scripts/build/arch/arm.sh
   544 
   545 The architecture's ".in" file API:
   546  > the config option "ARCH_%arch%" (where %arch% is to be replaced with the
   547    actual architecture name).
   548    That config option must have *neither* a type, *nor* a prompt! Also, it can
   549    *not* depend on any other config option (EXPERIMENTAL is managed as above).
   550      Eg.:
   551        config ARCH_arm
   552    + mandatory:
   553        defines a (terse) help entry for this architecture:
   554        Eg.:
   555          config ARCH_arm
   556            help
   557              The ARM architecture.
   558    + optional:
   559        selects adequate associated config options.
   560        Eg.:
   561          config ARCH_arm
   562            select ARCH_SUPPORTS_BOTH_ENDIAN
   563            select ARCH_DEFAULT_LE
   564            help
   565              The ARM architecture.
   566 
   567  > other target-specific options, at your discretion. Note however that to
   568    avoid name-clashing, such options shall be prefixed with "ARCH_%arch%",
   569    where %arch% is again replaced by the actual architecture name.
   570    (Note: due to historical reasons, and lack of time to clean up the code,
   571     I may have left some config options that do not completely conform to
   572     this, as the architecture name was written all upper case. However, the
   573     prefix is unique among architectures, and does not cause harm).
   574 
   575 The architecture's ".sh" file API:
   576  > the function "CT_DoArchValues"
   577    + parameters: none
   578    + environment:
   579      - all variables from the ".config" file,
   580      - the two variables "target_endian_eb" and "target_endian_el" which are
   581        the endianness suffixes
   582    + return value: 0 upon success, !0 upon failure
   583    + provides:
   584      - mandatory
   585      - the environment variable CT_TARGET_ARCH
   586      - contains:
   587        the architecture part of the target tuple.
   588        Eg.: "armeb" for big endian ARM
   589             "i386" for an i386
   590    + provides:
   591      - optional
   592      - the environment variable CT_TARGET_SYS
   593      - contains:
   594        the sytem part of the target tuple.
   595        Eg.: "gnu" for glibc on most architectures
   596             "gnueabi" for glibc on an ARM EABI
   597      - defaults to:
   598        - for glibc-based toolchain: "gnu"
   599        - for uClibc-based toolchain: "uclibc"
   600    + provides:
   601      - optional
   602      - the environment variable CT_KERNEL_ARCH
   603      - contains:
   604        the architecture name as understandable by the Linux kernel build
   605        system.
   606        Eg.: "arm" for an ARM
   607             "powerpc" for a PowerPC
   608             "i386" for an x86
   609      - defaults to:
   610        ${CT_ARCH}
   611    + provides:
   612      - optional
   613      - the environment variables to configure the cross-gcc (defaults)
   614        - CT_ARCH_WITH_ARCH    : the gcc ./configure switch to select architecture level         ( "--with-arch=${CT_ARCH_ARCH}"   )
   615        - CT_ARCH_WITH_ABI     : the gcc ./configure switch to select ABI level                  ( "--with-abi=${CT_ARCH_ABI}"     )
   616        - CT_ARCH_WITH_CPU     : the gcc ./configure switch to select CPU instruction set        ( "--with-cpu=${CT_ARCH_CPU}"     )
   617        - CT_ARCH_WITH_TUNE    : the gcc ./configure switch to select scheduling                 ( "--with-tune=${CT_ARCH_TUNE}"   )
   618        - CT_ARCH_WITH_FPU     : the gcc ./configure switch to select FPU type                   ( "--with-fpu=${CT_ARCH_FPU}"     )
   619        - CT_ARCH_WITH_FLOAT   : the gcc ./configure switch to select floating point arithmetics ( "--with-float=soft" or /empty/  )
   620    + provides:
   621      - optional
   622      - the environment variables to pass to the cross-gcc to build target binaries (defaults)
   623        - CT_ARCH_ARCH_CFLAG   : the gcc switch to select architecture level                     ( "-march=${CT_ARCH_ARCH}"            )
   624        - CT_ARCH_ABI_CFLAG    : the gcc switch to select ABI level                              ( "-mabi=${CT_ARCH_ABI}"              )
   625        - CT_ARCH_CPU_CFLAG    : the gcc switch to select CPU instruction set                    ( "-mcpu=${CT_ARCH_CPU}"              )
   626        - CT_ARCH_TUNE_CFLAG   : the gcc switch to select scheduling                             ( "-mtune=${CT_ARCH_TUNE}"            )
   627        - CT_ARCH_FPU_CFLAG    : the gcc switch to select FPU type                               ( "-mfpu=${CT_ARCH_FPU}"              )
   628        - CT_ARCH_FLOAT_CFLAG  : the gcc switch to choose floating point arithmetics             ( "-msoft-float" or /empty/           )
   629        - CT_ARCH_ENDIAN_CFLAG : the gcc switch to choose big or little endian                   ( "-mbig-endian" or "-mlittle-endian" )
   630      - default to:
   631        see above.
   632    + provides:
   633      - optional
   634      - the environement variables to configure the core and final compiler, specific to this architecture:
   635        - CT_ARCH_CC_CORE_EXTRA_CONFIG   : additional, architecture specific core gcc ./configure flags
   636        - CT_ARCH_CC_EXTRA_CONFIG        : additional, architecture specific final gcc ./configure flags
   637      - default to:
   638        - all empty
   639    + provides:
   640      - optional
   641      - the architecture-specific CFLAGS and LDFLAGS:
   642        - CT_ARCH_TARGET_CLFAGS
   643        - CT_ARCH_TARGET_LDFLAGS
   644      - default to:
   645        - all empty
   646 
   647 You can have a look at "config/arch/arm.in" and "scripts/build/arch/arm.sh" for
   648 a quite complete example of what an actual architecture description looks like.
   649 
   650 Kernel specific |
   651 ----------------+
   652 
   653 A kernel is defined by:
   654 
   655  - a human-readable name, in lower case letters, with numbers as appropriate.
   656    The underscore is allowed; space and special characters are not (although
   657    they are internally replaced with underscores.
   658      Eg.: linux, bare-metal
   659  - a file in "config/kernel/", named after the kernel name, and suffixed with
   660    ".in".
   661      Eg.: config/kernel/linux.in, config/kernel/bare-metal.in
   662  - a file in "scripts/build/kernel/", named after the kernel name, and suffixed
   663    with ".sh".
   664      Eg.: scripts/build/kernel/linux.sh, scripts/build/kernel/bare-metal.sh
   665 
   666 The kernel's ".in" file must contain:
   667  > an optional lines containing exactly "# EXPERIMENTAL", starting on the
   668    first column, and without any following space or other character.
   669    If this line is present, then this kernel is considered EXPERIMENTAL,
   670    and correct dependency on EXPERIMENTAL will be set.
   671 
   672  > the config option "KERNEL_%kernel_name%" (where %kernel_name% is to be
   673    replaced with the actual kernel name, with all special characters and
   674    spaces replaced by underscores).
   675    That config option must have *neither* a type, *nor* a prompt! Also, it can
   676    *not* depends on EXPERIMENTAL.
   677      Eg.: KERNEL_linux, KERNEL_bare_metal
   678    + mandatory:
   679        defines a (terse) help entry for this kernel.
   680        Eg.:
   681          config KERNEL_bare_metal
   682            help
   683              Build a compiler for use without any kernel.
   684    + optional:
   685        selects adequate associated config options.
   686        Eg.:
   687          config KERNEL_bare_metal
   688            select BARE_METAL
   689            help
   690              Build a compiler for use without any kernel.
   691 
   692  > other kernel specific options, at your discretion. Note however that, to
   693    avoid name-clashing, such options should be prefixed with
   694    "KERNEL_%kernel_name%", where %kernel_name% is again tp be replaced with
   695    the actual kernel name.
   696    (Note: due to historical reasons, and lack of time to clean up the code,
   697     I may have left some config options that do not completely conform to
   698     this, as the kernel name was written all upper case. However, the prefix
   699     is unique among kernels, and does not cause harm).
   700 
   701 The kernel's ".sh" file API:
   702  > is a bash script fragment
   703 
   704  > defines the function "do_print_filename":
   705    + parameters: none
   706    + environment:
   707       - all variables from the ".config" file,
   708    + return value: ignored
   709    + behavior: output the kernel's tarball filename, with adequate suffix,
   710      on stdout.
   711        Eg.: linux-2.6.26.5.tar.bz2
   712 
   713  > defines the function "do_kernel_get":
   714    + parameters: none
   715    + environment:
   716       - all variables from the ".config" file.
   717    + return value: 0 for success, !0 for failure.
   718    + behavior: download the kernel's sources, and store the tarball into
   719      "${CT_TARBALLS_DIR}". To this end, a functions is available, that
   720      abstracts downloading tarballs:
   721      - CT_DoGet <tarball_base_name> <URL1 [URL...]>
   722        Eg.: CT_DoGet linux-2.6.26.5 ftp://ftp.kernel.org/pub/linux/kernel/v2.6
   723      Note: retrieving sources from svn, cvs, git and the likes is not supported
   724      by CT_DoGet. You'll have to do this by hand, as it is done for eglibc in
   725      "scripts/build/libc/eglibc.sh"
   726 
   727  > defines the function "do_kernel_extract":
   728    + parameters: none
   729    + environment:
   730       - all variables from the ".config" file,
   731    + return value: 0 for success, !0 for failure.
   732    + behavior: extract the kernel's tarball into "${CT_SRC_DIR}", and apply
   733      required patches. To this end, a function is available, that abstracts
   734      extracting tarballs:
   735      - CT_ExtractAndPatch <tarball_base_name>
   736        Eg.: CT_ExtractAndPatch linux-2.6.26.5
   737 
   738  > defines the function "do_kernel_headers":
   739    + parameters: none
   740    + environment:
   741       - all variables from the ".config" file,
   742    + return value: 0 for success, !0 for failure.
   743    + behavior: install the kernel headers (if any) in "${CT_SYSROOT_DIR}/usr/include"
   744 
   745  > defines any kernel-specific helper functions
   746    These functions, if any, must be prefixed with "do_kernel_%CT_KERNEL%_",
   747    where '%CT_KERNEL%' is to be replaced with the actual kernel name, to avoid
   748    any name-clashing.
   749 
   750 You can have a look at "config/kernel/linux.in" and "scripts/build/kernel/linux.sh"
   751 as an example of what a complex kernel description looks like.
   752 
   753 Adding a new version of a component |
   754 ------------------------------------+
   755 
   756 When a new component, such as the Linux kernel, gcc or any other is released,
   757 adding the new version to crosstool-NG is quite easy. There is a script that
   758 will do all that for you:
   759   tools/addToolVersion.sh
   760 
   761 Run it with no option to get some help.
   762 
   763 Build scripts |
   764 --------------+
   765 
   766 To Be Written later...