docs/overview.txt
author "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Sun Jul 01 19:04:20 2007 +0000 (2007-07-01)
changeset 182 223c84ec2d90
parent 181 ff64ca4ebe48
child 192 cea313af395e
permissions -rw-r--r--
Merge the build system to trunk: ct-ng is now installable:
- ./configure --prefix=/some/place
- make
- make install
- export PATH="${PATH}:/some/place/bin"
- ct-ng <action>
     1 File.........: overview.txt
     2 Content......: Overview of how ct-ng works.
     3 Copyrigth....: (C) 2007 Yann E. MORIN <yann.morin.1998@anciens.enib.fr>
     4 License......: see COPYING in the root of this package
     5 
     6 ________________
     7                /
     8 Introduction  /
     9 _____________/
    10 
    11 crosstool-NG aims at building toolchains. Toolchains are an essential component
    12 in a software development project. It will compile, assemble and link the code
    13 that is being developped. Some pieces of the toolchain will eventually end up
    14 in the resulting binary/ies: static libraries are but an example.
    15 
    16 So, a toolchain is a very sensitive piece of software, as any bug in one of the
    17 components, or a poorly configured component, can lead to execution problems,
    18 ranging from poor performance, to applications ending unexpectedly, to
    19 mis-behaving software (which more than often is hard to detect), to hardware
    20 damage, or even to human risks (which is more than regretable).
    21 
    22 Toolchains are made of different piece of software, each being quite complex
    23 and requiring specially crafted options to build and work seamlessly. This
    24 is usually not that easy, even in the not-so-trivial case of native toolchains.
    25 The work reaches a higher degree of complexity when it comes to cross-
    26 compilation, where it can become quite a nightmare...
    27 
    28 Some cross-toolchains exist on the internet, and can be used for general
    29 development, but they have a number of limitations:
    30   - they can be general purpose, in that they are configured for the majority:
    31     no optimisation for your specific target,
    32   - they can be prepared for a specific target and thus are not easy to use,
    33     nor optimised for, or even supporting your target,
    34   - they often are using ageing components (compiler, C library, etc...) not
    35     supporting special features of your shiny new processor;
    36 On the other side, these toolchain offer some advantages:
    37   - they are ready to use and quite easy to install and setup,
    38   - they are proven if used by a wide community.
    39 
    40 But once you want to get all the juice out of your specific hardware, you will
    41 want to build your own toolchain. This is where crosstool-ng comes into play.
    42 
    43 There are also a number of tools that builds toolchains for specific needs,
    44 which is not really scalable. Examples are:
    45   - buildroot (buildroot.uclibc.org) whose main puprpose is to build root file
    46     systems, hence the name. But once you have your toolchain with buildroot,
    47     part of it is installed in the root-to-be, so if you want to build a whole
    48     new root, you either have to save the existing one as a template and
    49     restore it later, or restart again from scratch. This is not convenient,
    50   - ptxdist (www.pengutronix.de/software/ptxdist), whose purpose is very
    51     similar to buildroot,
    52   - other projects (openembeded.org for example), which is again used to
    53     build root file systems.
    54 
    55 crosstool-NG is really targetted at building toolchains, and only toolchains.
    56 It is then up to you to use it the way you want.
    57 
    58 ___________
    59           /
    60 History  /
    61 ________/
    62 
    63 crosstool was first 'conceived' by Dan Kegel, which offered it to the community,
    64 as a set of scripts, a repository of patches, and some pre-configured, general
    65 purpose setup files to be used to configure crosstool. This is available at
    66 www.kegel.com/crosstool, and the subversion repository is hosted on google at
    67 http://code.google.com/p/crosstool/.
    68 
    69 At the time of writing, crosstool only supports building with one C library,
    70 namely glibc, and one C compiler, gcc; it is cripled with historical support
    71 for legacy components, and is some kind of a mess to upgrade. Also, submited
    72 patches take a looong time before they are integrated mainline.
    73 
    74 I once managed to add support for uClibc-based toolchains, but it did not make
    75 into mainline, mostly because I don't have time to port the patch forward to
    76 the new versions, due in part to the big effort it was taking.
    77 
    78 So I decided to clean up crosstool in the state it was, re-order the things
    79 in place, and add appropriate support for what I needed, that is uClibc
    80 support.
    81 
    82 The only option left to me was rewrite crosstool from scratch. I decided to go
    83 this way, and name the new implementation ct-ng, standing for crosstool Next
    84 Generation, as many other comunity projects do, and as a wink at the TV series
    85 "Star Trek: The Next Generation". ;-)
    86 
    87 ____________________________
    88                            /
    89 Configuring crosstool-NG  /
    90 _________________________/
    91 
    92 crosstool-NG is configured the same way you configure your Linux kernel: by
    93 using a curses-based menu. It is assumed you now how to handle this.
    94 
    95 To enter the menu, type:
    96   make menuconfig
    97 
    98 Almost every config item has a help entry. Read it carefully.
    99 
   100 String and number options can refer to environment variables. In such a case,
   101 you  must use the shell syntax: ${VAR}. No such option is ever needed by make.
   102 You need to neither single- nor double-quote the string options.
   103 
   104 There are three environment variablea that are computed by crosstool-NG, and
   105 that you can use:
   106 
   107 CT_TARGET:
   108   It represents the target triplet you are building for. You can use it for
   109   example in the installation/prefix directory, such as:
   110     /opt/x-tools/${CT_TARGET}
   111 
   112 CT_TOP_DIR:
   113   The top directory where crosstool-NG is running. You shouldn't need it in
   114   most cases. There is one case where you may need it: if you have local
   115   patches and you store them in your running directory, you can refer to them
   116   by using CT_TOP_DIR, such as:
   117     ${CT_TOP_DIR}/patches.myproject
   118 
   119 CT_VERSION:
   120   The version of crosstool-NG you are using. Not much help for you, but it's
   121   there if you need it.
   122 
   123 
   124 Interesting config options |
   125 ---------------------------*
   126 
   127 CT_LOCAL_TARBALLS_DIR:
   128   If you already have sone tarballs in a direcotry, enter it here. That will
   129   speed up the retrieving phase, where crosstool-ng would otherwise download
   130   those tarballs.
   131 
   132 CT_PREFIX_DIR:
   133   This is where the toolchain will be installed in (and for now, where it
   134   will run from).
   135 
   136 CT_TARGET_VENDOR:
   137   An identifier for your toolchain, will take place in the vendor part of the
   138   target triplet. It shall *not* contain spaces or dashes. Usually, keep it
   139   to a one-word string, or use underscores to separate words if you need.
   140   Avoid dots, commas, and special characters.
   141 
   142 CT_TARGET_ALIAS:
   143   An alias for the toolchian. It will be used as a prefix to the toolchain
   144   tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
   145 
   146 ________________________
   147                        /
   148 Running crosstool-NG  /
   149 _____________________/
   150 
   151 ct-ng is configured by a configurator presenting a menu-stuctured set of
   152 options. These options let you specify the way you want your toolchain built,
   153 where you want it installed, what architecture and specific processor it
   154 will support, the version of the components you want to use, etc... The
   155 value for those options are then stored in a configuration file.
   156 
   157 To build the toolchain, simply type:
   158   make
   159 
   160 This will use the above configuration to retrieve, extract and patch the
   161 components, build, install and eventually test your newly built toolchain.
   162 
   163 You are then free to add the toolchain /bin directory in your PATH to use
   164 it at will.
   165 
   166 In any case, you can get some terse help. Just type:
   167   make help
   168 
   169 
   170 Stoping and restarting a build |
   171 -------------------------------*
   172 
   173 If you want to stop the build after a step you are debugging, you can pass the
   174 variable STOP to make:
   175   make STOP=some_step
   176 
   177 Conversely, if you want to restart a build at a specific step you are
   178 debugging, you can pass the RESTART variable to make:
   179   make RESTART=some_step
   180 
   181 Alternatively, you can call make with the name of a step to just do that step:
   182   make libc_headers
   183 is equivalent to:
   184   make RESTART=libs_headers STOP=libc_headers
   185 
   186 The shortcuts -step_name and step_name- allow to respectively stop or restart
   187 at that step. Thus:
   188   make -libc_headers        and:    make libc_headers-
   189 are equivalent to:
   190   make STOP=libc_headers    and:    make RESTART=libc_headers
   191 
   192 To obtain the list of acceptable steps, please call:
   193   make liststeps
   194 
   195 Note that in order to restart a build, you'll have to say 'Y' to the config
   196 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
   197 that far.
   198 
   199 
   200 Testing all toolchains at once |
   201 -------------------------------*
   202 
   203 You can test-build all samples; simply call:
   204   make regtest
   205 
   206 ___________________
   207                   /
   208 Toolchain types  /
   209 ________________/
   210 
   211 There are four kinds of toolchains you could encounter.
   212 
   213 First off, you must understand the following: when it comes to compilers there
   214 are up to four machines involved:
   215   1) the machine configuring the toolchain components: the config machine
   216   2) the machine building the toolchain components:    the build machine
   217   3) the machine running the toolchain:                the host machine
   218   4) the machine the toolchain is building for:        the target machine
   219 
   220 We can most of the time assume that the config machine and the build machine
   221 are the same. Most of the time, this will be true. The only time it isn't
   222 is if you're using distributed compilation (such as distcc). Let's forget
   223 this for the sake of simplicity.
   224 
   225 So we're left with three machines:
   226  - build
   227  - host
   228  - target
   229 
   230 Any toolchain will involve those three machines. You can be as pretty sure of
   231 this as "2 and 2 are 4". Here is how they come into play:
   232 
   233 1) build == host == target
   234     This is a plain native toolchain, targetting the exact same machine as the
   235     one it is built on, and running again on this exact same machine. You have
   236     to build such a toolchain when you want to use an updated component, such
   237     as a newer gcc for example.
   238     ct-ng calls it "native".
   239 
   240 2) build == host != target
   241     This is a classic cross-toolchain, which is expected to be run on the same
   242     machine it is compiled on, and generate code to run on a second machine,
   243     the target.
   244     ct-ng calls it "cross".
   245 
   246 3) build != host == target
   247     Such a toolchain is also a native toolchain, as it targets the same machine
   248     as it runs on. But it is build on another machine. You want such a
   249     toolchain when porting to a new architecture, or if the build machine is
   250     much faster than the host machine.
   251     ct-ng calls it "cross-native".
   252 
   253 4) build != host != target
   254     This one is called a canadian-toolchain (*), and is tricky. The three
   255     machines in play are different. You might want such a toolchain if you
   256     have a fast build machine, but the users will use it on another machine,
   257     and will produce code to run on a third machine.
   258     ct-ng calls it "canadian".
   259 
   260 ct-ng can build all these kinds of toolchains (or is aiming at it, anyway!)
   261 
   262 (*) The term Canadian Cross came about because at the time that these issues
   263     were all being hashed out, Canada had three national political parties.
   264     http://en.wikipedia.org/wiki/Cross_compiler
   265 
   266 _____________
   267             /
   268 Internals  /
   269 __________/
   270 
   271 Internally, crosstool-NG is script-based. To ease usage, the frontend is
   272 Makefile-based.
   273 
   274 Makefile front-end |
   275 -------------------*
   276 
   277 To Be Written later...
   278 
   279 Kconfig parser |
   280 ---------------*
   281 
   282 The kconfig language is a hacked version, vampirised from the toybox project
   283 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
   284 Linux kernel (http://www.linux.org/ http://www.kernel.org/), and (heavily)
   285 adapted to my needs.
   286