docs/overview.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Sun Jul 27 14:28:36 2008 +0000 (2008-07-27)
branch1.2
changeset 739 8ebf5ea601d8
parent 630 2789bdd1a950
child 767 fe5e42bf7bbc
permissions -rw-r--r--
Backport #876 from trunk:
Re-enable the restart functionality by removing some variables from the saved environment.

/branches/1.2/scripts/functions | 16 10 6 0 ++++++++++------
1 file changed, 10 insertions(+), 6 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   Contributed code
    18 Configuring crosstool-NG
    19   Interesting config options
    20   Re-building an existing toolchain
    21 Running crosstool-NG
    22   Stopping and restarting a build
    23   Testing all toolchains at once
    24   Overriding the number of // jobs
    25 Using the toolchain
    26 Toolchain types
    27 Internals
    28   Makefile front-end
    29   Kconfig parser
    30   Architecture-specific
    31   Adding a new version of a component
    32   Build scripts
    33 
    34 ________________
    35                /
    36 Introduction  /
    37 _____________/
    38 
    39 crosstool-NG aims at building toolchains. Toolchains are an essential component
    40 in a software development project. It will compile, assemble and link the code
    41 that is being developed. Some pieces of the toolchain will eventually end up
    42 in the resulting binary/ies: static libraries are but an example.
    43 
    44 So, a toolchain is a very sensitive piece of software, as any bug in one of the
    45 components, or a poorly configured component, can lead to execution problems,
    46 ranging from poor performance, to applications ending unexpectedly, to
    47 mis-behaving software (which more than often is hard to detect), to hardware
    48 damage, or even to human risks (which is more than regrettable).
    49 
    50 Toolchains are made of different piece of software, each being quite complex
    51 and requiring specially crafted options to build and work seamlessly. This
    52 is usually not that easy, even in the not-so-trivial case of native toolchains.
    53 The work reaches a higher degree of complexity when it comes to cross-
    54 compilation, where it can become quite a nightmare...
    55 
    56 Some cross-toolchains exist on the internet, and can be used for general
    57 development, but they have a number of limitations:
    58   - they can be general purpose, in that they are configured for the majority:
    59     no optimisation for your specific target,
    60   - they can be prepared for a specific target and thus are not easy to use,
    61     nor optimised for, or even supporting your target,
    62   - they often are using aging components (compiler, C library, etc...) not
    63     supporting special features of your shiny new processor;
    64 On the other side, these toolchain offer some advantages:
    65   - they are ready to use and quite easy to install and setup,
    66   - they are proven if used by a wide community.
    67 
    68 But once you want to get all the juice out of your specific hardware, you will
    69 want to build your own toolchain. This is where crosstool-NG comes into play.
    70 
    71 There are also a number of tools that build toolchains for specific needs,
    72 which are not really scalable. Examples are:
    73   - buildroot (buildroot.uclibc.org) whose main purpose is to build root file
    74     systems, hence the name. But once you have your toolchain with buildroot,
    75     part of it is installed in the root-to-be, so if you want to build a whole
    76     new root, you either have to save the existing one as a template and
    77     restore it later, or restart again from scratch. This is not convenient,
    78   - ptxdist (www.pengutronix.de/software/ptxdist), whose purpose is very
    79     similar to buildroot,
    80   - other projects (openembedded.org for example), which are again used to
    81     build root file systems.
    82 
    83 crosstool-NG is really targeted at building toolchains, and only toolchains.
    84 It is then up to you to use it the way you want.
    85 
    86 ___________
    87           /
    88 History  /
    89 ________/
    90 
    91 crosstool was first 'conceived' by Dan Kegel, who offered it to the community
    92 as a set of scripts, a repository of patches, and some pre-configured, general
    93 purpose setup files to be used to configure crosstool. This is available at
    94 http://www.kegel.com/crosstool, and the subversion repository is hosted on
    95 google at http://code.google.com/p/crosstool/.
    96 
    97 I once managed to add support for uClibc-based toolchains, but it did not make
    98 into mainline, mostly because I didn't have time to port the patch forward to
    99 the new versions, due in part to the big effort it was taking.
   100 
   101 So I decided to clean up crosstool in the state it was, re-order the things
   102 in place, add appropriate support for what I needed, that is uClibc support
   103 and a menu-driven configuration, named the new implementation crosstool-NG,
   104 (standing for crosstool Next Generation, as many other comunity projects do,
   105 and as a wink at the TV series "Star Trek: The Next Generation" ;-) ) and
   106 made it available to the community, in case it was of interest to any one.
   107 
   108 ___________________________
   109                           /
   110 Installing crosstool-NG  /
   111 ________________________/
   112 
   113 There are two ways you can use crosstool-NG:
   114  - build and install it, then get rid of the sources like you'd do for most
   115    programs,
   116  - or only build it and run from the source directory.
   117 
   118 The former should be used if you got crosstool-NG from a packaged tarball, see
   119 "Install method", below, while the latter is most useful for developpers that
   120 checked the code out from SVN, and want to submit patches, see "The Hacker's
   121 way", below.
   122 
   123 Install method |
   124 ---------------+
   125 
   126 If you go for the install, then you just follow the classical, but yet easy
   127 ./configure way:
   128   ./configure --prefix=/some/place
   129   make
   130   make install
   131   export PATH="${PATH}:/some/place/bin"
   132 
   133 You can then get rid of crosstool-NG source. Next create a directory to serve
   134 as a working place, cd in there and run:
   135   ct-ng help
   136 
   137 See below for complete usage.
   138 
   139 The Hacker's way |
   140 -----------------+
   141 
   142 If you go the hacker's way, then the usage is a bit different, although very
   143 simple:
   144   ./configure --local
   145   make
   146 
   147 Now, *do not* remove crosstool-NG sources. They are needed to run crosstool-NG!
   148 Stay in the directory holding the sources, and run:
   149   ./ct-ng help
   150 
   151 See below for complete usage.
   152 
   153 Now, provided you checked-out the code, you can send me your interesting changes
   154 by running:
   155   svn diff
   156 
   157 and mailing me the result! :-P
   158 
   159 Contributed code |
   160 -----------------+
   161 
   162 Some people contibuted code that couldn't get merged for various reasons. This
   163 code is available as patches in the contrib/ sub-directory. These patches are
   164 to be applied to the source of crosstool-NG, prior to installing.
   165 
   166 An easy way to use contributed code is to pass the --with-contrib= option to
   167 ./configure. The possible values depend upon which contributions are packaged
   168 with your version, but you can get with it with passing one of those two
   169 special values:
   170   --with-contrib=list
   171     will list all available contributions
   172 
   173   --with-contrib=all
   174     will select all avalaible contributions
   175 
   176 There is no guarantee that a particuliar contribution applies to the current
   177 version of crosstool-ng, or that it will work at all. Use contributions at
   178 your own risk.
   179 
   180 ____________________________
   181                            /
   182 Configuring crosstool-NG  /
   183 _________________________/
   184 
   185 crosstool-NG is configured with a configurator presenting a menu-stuctured set
   186 of options. These options let you specify the way you want your toolchain
   187 built, where you want it installed, what architecture and specific processor it
   188 will support, the version of the components you want to use, etc... The
   189 value for those options are then stored in a configuration file.
   190 
   191 The configurator works the same way you configure your Linux kernel. It is
   192 assumed you now how to handle this.
   193 
   194 To enter the menu, type:
   195   ct-ng menuconfig
   196 
   197 Almost every config item has a help entry. Read them carefully.
   198 
   199 String and number options can refer to environment variables. In such a case,
   200 you must use the shell syntax: ${VAR}. You shall neither single- nor double-
   201 quote the string/number options.
   202 
   203 There are three environment variables that are computed by crosstool-NG, and
   204 that you can use:
   205 
   206 CT_TARGET:
   207   It represents the target tuple you are building for. You can use it for
   208   example in the installation/prefix directory, such as:
   209     /opt/x-tools/${CT_TARGET}
   210 
   211 CT_TOP_DIR:
   212   The top directory where crosstool-NG is running. You shouldn't need it in
   213   most cases. There is one case where you may need it: if you have local
   214   patches and you store them in your running directory, you can refer to them
   215   by using CT_TOP_DIR, such as:
   216     ${CT_TOP_DIR}/patches.myproject
   217 
   218 CT_VERSION:
   219   The version of crosstool-NG you are using. Not much use for you, but it's
   220   there if you need it.
   221 
   222 Interesting config options |
   223 ---------------------------+
   224 
   225 CT_LOCAL_TARBALLS_DIR:
   226   If you already have some tarballs in a direcotry, enter it here. That will
   227   speed up the retrieving phase, where crosstool-NG would otherwise download
   228   those tarballs.
   229 
   230 CT_PREFIX_DIR:
   231   This is where the toolchain will be installed in (and for now, where it
   232   will run from). Common use is to add the target tuple in the directory
   233   path, such as (see above):
   234     /opt/x-tools/${CT_TARGET}
   235 
   236 CT_TARGET_VENDOR:
   237   An identifier for your toolchain, will take place in the vendor part of the
   238   target tuple. It shall *not* contain spaces or dashes. Usually, keep it
   239   to a one-word string, or use underscores to separate words if you need.
   240   Avoid dots, commas, and special characters.
   241 
   242 CT_TARGET_ALIAS:
   243   An alias for the toolchian. It will be used as a prefix to the toolchain
   244   tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
   245 
   246 Also, if you think you don't see enough versions, you can try to enable one of
   247 those:
   248 
   249 CT_OBSOLETE:
   250   Show obsolete versions or tools. Most of the time, you don't want to base
   251   your toolchain on too old a version (of gcc, for example). But at times, it
   252   can come handy to use such an old version for regression tests. Those old
   253   versions are hidden behind CT_OBSOLETE.
   254 
   255 CT_EXPERIMENTAL:
   256   Show experimental versions or tools. Again, you might not want to base your
   257   toolchain on too recent tools (eg. gcc) for production. But if you need a
   258   feature present only in a recent version, or a new tool, you can find them
   259   hidden behind CT_EXPERIMENTAL.
   260 
   261 CT_BROKEN:
   262   Show broken versions or tools. Some usefull tools are currently broken: they
   263   won't compile, run, or worse, cause defects when running. But if you are
   264   brave enough, you can try and debug them. They are hidden behind CT_BROKEN,
   265   which itself is hidden behind CT_EXPERIMENTAL.
   266 
   267 Re-building an existing toolchain |
   268 ----------------------------------+
   269 
   270 If you have an existing toolchain, you can re-use the options used to build it
   271 to create a new toolchain. That needs a very little bit of effort on your side
   272 but is quite easy. The options to build a toolchain are saved in the build log
   273 file that is saved within the toolchain. crosstool-NG can extract those options
   274 to recreate a new configuration:
   275   ct-ng extractconfig </path/to/your/build.log >.config
   276 
   277 will extract those options, prompt you for the new ones, which you can later
   278 edit with menuconfig.
   279 
   280 Of course, if your build log was compressed, you'd have to use something like:
   281   bzcat /path/to/your/build.log.bz2 |ct-ng extractconfig >.config
   282 
   283 Then, once the configuration has been extracted, run:
   284   ct-ng oldconfig
   285 
   286 ________________________
   287                        /
   288 Running crosstool-NG  /
   289 _____________________/
   290 
   291 To build the toolchain, simply type:
   292   ct-ng build
   293 
   294 This will use the above configuration to retrieve, extract and patch the
   295 components, build, install and eventually test your newly built toolchain.
   296 
   297 You are then free to add the toolchain /bin directory in your PATH to use
   298 it at will.
   299 
   300 In any case, you can get some terse help. Just type:
   301   ct-ng help
   302 or:
   303   man 1 ct-ng
   304 
   305 Stopping and restarting a build |
   306 --------------------------------+
   307 
   308 If you want to stop the build after a step you are debugging, you can pass the
   309 variable STOP to make:
   310   ct-ng STOP=some_step
   311 
   312 Conversely, if you want to restart a build at a specific step you are
   313 debugging, you can pass the RESTART variable to make:
   314   ct-ng RESTART=some_step
   315 
   316 Alternatively, you can call make with the name of a step to just do that step:
   317   ct-ng libc_headers
   318 is equivalent to:
   319   ct-ng RESTART=libc_headers STOP=libc_headers
   320 
   321 The shortcuts +step_name and step_name+ allow to respectively stop or restart
   322 at that step. Thus:
   323   ct-ng +libc_headers        and:    ct-ng libc_headers+
   324 are equivalent to:
   325   ct-ng STOP=libc_headers    and:    ct-ng RESTART=libc_headers
   326 
   327 To obtain the list of acceptable steps, please call:
   328   ct-ng list-steps
   329 
   330 Note that in order to restart a build, you'll have to say 'Y' to the config
   331 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
   332 that far.
   333 
   334 Testing all toolchains at once |
   335 -------------------------------+
   336 
   337 You can test-build all samples; simply call:
   338   ct-ng regtest
   339 
   340 Overriding the number of // jobs |
   341 ---------------------------------+
   342 
   343 If you want to override the number of jobs to run in // (the -j option to
   344 make), you can either re-enter the menuconfig, or simply add it on the command
   345 line, as such:
   346   ct-ng build.4
   347 
   348 which tells crosstool-NG to override the number of // jobs to 4.
   349 
   350 You can see the actions that support overriding the number of // jobs in
   351 the help menu. Those are the ones with [.#] after them (eg. build[.#] or
   352 regtest[.#], and so on...).
   353 
   354 _______________________
   355                       /
   356 Using the toolchain  /
   357 ____________________/
   358 
   359 Using the toolchain is as simple as adding the toolchain's bin directory in
   360 your PATH, such as:
   361   export PATH="${PATH}:/your/toolchain/path/bin"
   362 
   363 and then using the target tuple to tell the build systems to use your
   364 toolchain:
   365   ./configure --target=your-target-tuple
   366 or
   367   make CC=your-target-tuple-gcc
   368 or
   369   make CROSS_COMPILE=your-target-tuple-
   370 and so on...
   371 
   372 It is strongly advised not to use the toolchain sys-root directory as an
   373 install directory for your programs/packages. If you do so, you will not be
   374 able to use your toolchain for another project. It is even strongly advised
   375 that your toolchain is chmod-ed to read-only once successfully build, so that
   376 you don't go polluting your toolchain with your programs/packages' files.
   377 
   378 Thus, when you build a program/package, install it in a separate directory,
   379 eg. /your/root. This directory is the /image/ of what would be in the root file
   380 system of your target, and will contain all that your programs/packages have
   381 installed.
   382 
   383 When your root directory is ready, it is still missing some important bits: the
   384 toolchain's libraries. To populate your root directory with those libs, just
   385 run:
   386   your-target-tuple-populate -s /your/root -d /your/root-populated
   387 
   388 This will copy /your/root into /your/root-populated, and put the needed and only
   389 the needed libraries there. Thus you don't polute /your/root with any cruft that
   390 would no longer be needed should you have to remove stuff. /your/root always
   391 contains only those things you install in it.
   392 
   393 You can then use /your/root-populated to build up your file system image, a
   394 tarball, or to NFS-mount it from your target, or whatever you need.
   395 
   396 populate accepts the following options:
   397 
   398  -s [src_dir]
   399     Use 'src_dir' as the 'source', un-populated root directory
   400 
   401  -d [dst_dir]
   402     Put the 'destination', populated root directory in 'dst_dir'
   403 
   404  -f
   405     Remove 'dst_dir' if it previously existed
   406 
   407  -v
   408     Be verbose, and tell what's going on (you can see exactly where libs are
   409     coming from).
   410 
   411  -h
   412     Print the help
   413 
   414 ___________________
   415                   /
   416 Toolchain types  /
   417 ________________/
   418 
   419 There are four kinds of toolchains you could encounter.
   420 
   421 First off, you must understand the following: when it comes to compilers there
   422 are up to four machines involved:
   423   1) the machine configuring the toolchain components: the config machine
   424   2) the machine building the toolchain components:    the build machine
   425   3) the machine running the toolchain:                the host machine
   426   4) the machine the toolchain is generating code for: the target machine
   427 
   428 We can most of the time assume that the config machine and the build machine
   429 are the same. Most of the time, this will be true. The only time it isn't
   430 is if you're using distributed compilation (such as distcc). Let's forget
   431 this for the sake of simplicity.
   432 
   433 So we're left with three machines:
   434  - build
   435  - host
   436  - target
   437 
   438 Any toolchain will involve those three machines. You can be as pretty sure of
   439 this as "2 and 2 are 4". Here is how they come into play:
   440 
   441 1) build == host == target
   442     This is a plain native toolchain, targetting the exact same machine as the
   443     one it is built on, and running again on this exact same machine. You have
   444     to build such a toolchain when you want to use an updated component, such
   445     as a newer gcc for example.
   446     crosstool-NG calls it "native".
   447 
   448 2) build == host != target
   449     This is a classic cross-toolchain, which is expected to be run on the same
   450     machine it is compiled on, and generate code to run on a second machine,
   451     the target.
   452     crosstool-NG calls it "cross".
   453 
   454 3) build != host == target
   455     Such a toolchain is also a native toolchain, as it targets the same machine
   456     as it runs on. But it is build on another machine. You want such a
   457     toolchain when porting to a new architecture, or if the build machine is
   458     much faster than the host machine.
   459     crosstool-NG calls it "cross-native".
   460 
   461 4) build != host != target
   462     This one is called a canadian-toolchain (*), and is tricky. The three
   463     machines in play are different. You might want such a toolchain if you
   464     have a fast build machine, but the users will use it on another machine,
   465     and will produce code to run on a third machine.
   466     crosstool-NG calls it "canadian".
   467 
   468 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
   469 anyway!)
   470 
   471 (*) The term Canadian Cross came about because at the time that these issues
   472     were all being hashed out, Canada had three national political parties.
   473     http://en.wikipedia.org/wiki/Cross_compiler
   474 
   475 _____________
   476             /
   477 Internals  /
   478 __________/
   479 
   480 Internally, crosstool-NG is script-based. To ease usage, the frontend is
   481 Makefile-based.
   482 
   483 Makefile front-end |
   484 -------------------+
   485 
   486 The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this
   487 script with an action will act exactly as if the Makefile was in the current
   488 working directory and make was called with the action as rule. Thus:
   489   ct-ng menuconfig
   490 
   491 is equivalent to having the Makefile in CWD, and calling:
   492   make menuconfig
   493 
   494 Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a
   495 traditional command.
   496 
   497 ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up
   498 at configuration time with ./configure.
   499 
   500 ct-ng also searches for config files, sub-tools, samples, scripts and patches in
   501 that library directory.
   502 
   503 Because of a stupid make behavior/bug I was unable to track down, implicit make
   504 rules are disabled: installing with --local would triger those rules, and mconf
   505 was unbuildable.
   506 
   507 Kconfig parser |
   508 ---------------+
   509 
   510 The kconfig language is a hacked version, vampirised from the toybox project
   511 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
   512 Linux kernel (http://www.kernel.org/), and (heavily) adapted to my needs.
   513 
   514 The kconfig parsers (conf and mconf) are not installed pre-built, but as
   515 source files. Thus you can have the directory where crosstool-NG is installed,
   516 exported (via NFS or whatever) and have clients with different architectures
   517 use the same crosstool-NG installation, and most notably, the same set of
   518 patches.
   519 
   520 Architecture-specific |
   521 ----------------------+
   522 
   523 Note: this chapter is not really well written, and might thus be a little bit
   524 complex to understand. To get a better grasp of what an architecture is, the
   525 reader is kindly encouraged to look at the "arch/" sub-directory, and to the
   526 existing architectures to see how things are laid out.
   527 
   528 An architecture is defined by:
   529 
   530  - a human-readable name, in lower case letters, with numbers as appropriate.
   531    The underscore is allowed; space and special characters are not.
   532      Eg.: arm, x86_64
   533  - a directory in "arch/" named after the architecture, with the same letters
   534    as above. Eg.: arch/arm, arch/x86_64
   535    This directory contains the following files, and only those files:
   536    - a configuration file in kconfig syntax, named "config.in", which shall
   537      follow the API defined below.
   538        Eg.: arch/arm/config.in
   539    - a function script in bash-3.0 syntax, named "functions", which shall
   540      follow the API defined below.
   541        Eg.: arch/arm/functions
   542    - an optional file, named "experimental" (in lower case!), which, if it
   543      is present, means that support for this architecture is EXPERIMENTAL.
   544        Eg.: arch/arm/experimental
   545 
   546 The "config.in" file API:
   547  > the config option "ARCH_%arch%" (where %arch% is to be replaced with the
   548    actual architecture name).
   549    That config option must have *neither* a type, *nor* a prompt! Also, it can
   550    *not* depend on any other config option (EXPERIMENTAL is managed as above).
   551      Eg.:
   552        config ARCH_arm
   553    + mandatory:
   554        defines a (terse) help entry for this architecture:
   555        Eg.:
   556          config ARCH_arm
   557            help
   558              The ARM architecture.
   559    + optional:
   560        selects adequate associated config options.
   561        Eg.:
   562          config ARCH_arm
   563            select ARCH_SUPPORTS_BOTH_ENDIAN
   564            select ARCH_DEFAULT_LE
   565            help
   566              The ARM architecture.
   567 
   568  > other target-specific options, at your discretion. Note however that to
   569    avoid name-clashing, such options shall be prefixed with "ARCH_%arch%",
   570    where %arch% is again replaced by the actual architecture name.
   571    (Note: due to historical reasons, and lack of time to clean up the code,
   572     I may have left some config options that do not completely conform to
   573     this, as the architecture name was written all upper case. However, the
   574     prefix is unique among architectures, and does not cause harm).
   575 
   576 The "functions" file API:
   577  > the function "CT_DoArchValues"
   578    + parameters: none
   579    + environment:
   580       - all variables from the ".config" file,
   581       - the two variables "target_endian_eb" and "target_endian_el" which are
   582         the endianness suffixes
   583    + return value: 0 upon success, !0 upon failure
   584    + provides:
   585      - mandatory
   586      - the environment variable CT_TARGET_ARCH
   587      - contains:
   588        the architecture part of the target tuple.
   589        Eg.: "armeb" for big endian ARM
   590             "i386" for an i386
   591    + provides:
   592      - optional
   593      - the environment variable CT_TARGET_SYS
   594      - contains:
   595        the sytem part of the target tuple.
   596        Eg.: "gnu" for glibc on most architectures
   597             "gnueabi" for glibc on an ARM EABI
   598      - defaults to:
   599        - for glibc-based toolchain: "gnu"
   600        - for uClibc-based toolchain: "uclibc"
   601    + provides:
   602      - optional
   603      - the environment variable CT_KERNEL_ARCH
   604      - contains:
   605        the architecture name as understandable by the Linux kernel build
   606        system.
   607        Eg.: "arm" for an ARM
   608             "powerpc" for a PowerPC
   609             "i386" for an x86
   610      - defaults to:
   611        ${CT_ARCH}
   612    + provides:
   613      - optional
   614      - the environment variables to configure the cross-gcc
   615        - CT_ARCH_WITH_ARCH
   616        - CT_ARCH_WITH_ABI
   617        - CT_ARCH_WITH_CPU
   618        - CT_ARCH_WITH_TUNE
   619        - CT_ARCH_WITH_FPU
   620        - CT_ARCH_WITH_FLOAT
   621      - contain (defaults):
   622        - CT_ARCH_WITH_ARCH    : the gcc ./configure switch to select architecture level         ( "--with-arch=${CT_ARCH_ARCH}"       )
   623        - CT_ARCH_WITH_ABI     : the gcc ./configure switch to select ABI level                  ( "--with-abi=${CT_ARCH_ABI}"         )
   624        - CT_ARCH_WITH_CPU     : the gcc ./configure switch to select CPU instruction set        ( "--with-cpu=${CT_ARCH_CPU}"         )
   625        - CT_ARCH_WITH_TUNE    : the gcc ./configure switch to select scheduling                 ( "--with-tune=${CT_ARCH_TUNE}"       )
   626        - CT_ARCH_WITH_FPU     : the gcc ./configure switch to select FPU type                   ( "--with-fpu=${CT_ARCH_FPU}"         )
   627        - CT_ARCH_WITH_FLOAT   : the gcc ./configure switch to select floating point arithmetics ( "--with-float=soft" or /empty/      )
   628    + provides:
   629      - optional
   630      - the environment variables to pass to the cross-gcc to build target binaries
   631        - CT_ARCH_ARCH_CFLAG
   632        - CT_ARCH_ABI_CFLAG
   633        - CT_ARCH_CPU_CFLAG
   634        - CT_ARCH_TUNE_CFLAG
   635        - CT_ARCH_FPU_CFLAG
   636        - CT_ARCH_FLOAT_CFLAG
   637        - CT_ARCH_ENDIAN_CFLAG
   638      - contain (defaults):
   639        - CT_ARCH_ARCH_CFLAG   : the gcc switch to select architecture level                     ( "-march=${CT_ARCH_ARCH}"            )
   640        - CT_ARCH_ABI_CFLAG    : the gcc switch to select ABI level                              ( "-mabi=${CT_ARCH_ABI}"              )
   641        - CT_ARCH_CPU_CFLAG    : the gcc switch to select CPU instruction set                    ( "-mcpu=${CT_ARCH_CPU}"              )
   642        - CT_ARCH_TUNE_CFLAG   : the gcc switch to select scheduling                             ( "-mtune=${CT_ARCH_TUNE}"            )
   643        - CT_ARCH_FPU_CFLAG    : the gcc switch to select FPU type                               ( "-mfpu=${CT_ARCH_FPU}"              )
   644        - CT_ARCH_FLOAT_CFLAG  : the gcc switch to choose floating point arithmetics             ( "-msoft-float" or /empty/           )
   645        - CT_ARCH_ENDIAN_CFLAG : the gcc switch to choose big or little endian                   ( "-mbig-endian" or "-mlittle-endian" )
   646      - default to:
   647        see above.
   648 
   649 Adding a new version of a component |
   650 ------------------------------------+
   651 
   652 When a new component, such as the Linux kernel, gcc or any other is released,
   653 adding the new version to crosstool-NG is quite easy. There is a script that
   654 will do all that for you:
   655   tools/addToolVersion.sh
   656 
   657 Run it with no option to get some help.
   658 
   659 Build scripts |
   660 --------------+
   661 
   662 To Be Written later...