Add the possibility to stop after a specified step.
Update the Makefile help and the documentation accordingly.
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
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.
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).
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...
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.
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.
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
52 - other projects (openembeded.org for example), which is again used to
53 build root file systems.
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.
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/.
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.
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.
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
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". ;-)
92 ct-ng is configured by a configurator presenting a menu-stuctured set of
93 options. These options let you specify the way you want your toolchain built,
94 where you want it installed, what architecture and specific processor it
95 will support, the version of the components you want to use, etc... The
96 value for those options are then stored in a configuration file.
98 To enter the menu, type:
101 To build the so-configured target, simply type:
104 This will use the above configuration to retrieve, extract and patch the
105 components, build, install and eventually test your newly built toolchain.
107 You are then free to add the toolchain /bin directory in your PATH to use
110 In any case, you can get some terse help. Just type:
114 Stoping and restarting a build |
115 -------------------------------*
117 If you want to stop the build after a step you are debugging, you can pass the
118 variable STOP to make:
121 Conversely, if you want to restart a build at a specific step you are
122 debugging, you can pass the RESTART variable to make:
123 make RESTART=some_step
125 The list of steps is, in order of appearence in the build process:
127 - kernel_check_config
138 ____________________________
140 Configuring crosstool-NG /
141 _________________________/
143 crosstool-NG is configured the same way you configure your Linux kernel: by
144 using a curses-based menu. It is assumed you now how to handle this.
146 Almost every config item has a help entry. Read it carefully.
148 String and number options can refer to environment variables. In such a case,
149 you must use the shell syntax: ${VAR}. No such option is ever needed by make.
150 You need to neither single- nor double-quote the string options.
152 There are three environment variablea that are computed by crosstool-NG, and
156 It represents the target triplet you are building for. You can use it for
157 example in the installation/prefix directory, such as:
158 /opt/x-tools/${CT_TARGET}
161 The top directory where crosstool-NG sits. You shouldn't need it in most
162 cases. There is one case where you may need it: if you have local patches
163 and you store them in your copy of crosstool-NG, you can refer to them
164 by using CT_TOP_DIR, such as:
165 ${CT_TOP_DIR}/patches.myproject
168 The version of crosstool-NG you are using. Not much help for you, but it's
169 there if you need it.
172 Interesting config options |
173 ---------------------------*
175 CT_LOCAL_TARBALLS_DIR:
176 If you already have sone tarballs in a direcotry, enter it here. That will
177 speed up the retrieving phase, where crosstool-ng would otherwise download
181 This is where the toolchain will be installed in (and for now, where it
185 The file where *all* log messages will go. Keep the default, in goes in
186 ${CT_PREFIX_DIR}/${CT_TARGET}.log
189 An identifier for your toolchain, will take place in the vendor part of the
190 target triplet. It shall *not* contain spaces or dashes. Usually, keep it
191 to a one-word string, or use underscores to separate words if you need.
192 Avoid dots, commas, and special characters.
195 An alias for the toolchian. It will be used as a prefix to the toolchain
196 tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
203 There are four kinds of toolchains you could encounter.
205 First off, you must understand the following: when it comes to compilers there
206 are up to four machines involved:
207 1) the machine configuring the toolchain components: the config machine
208 2) the machine building the toolchain components: the build machine
209 3) the machine running the toolchain: the host machine
210 4) the machine the toolchain is building for: the target machine
212 We can most of the time assume that the config machine and the build machine
213 are the same. Most of the time, this will be true. The only time it isn't
214 is if you're using distributed compilation (such as distcc). Let's forget
215 this for the sake of simplicity.
217 So we're left with three machines:
222 Any toolchain will involve those three machines. You can be as pretty sure of
223 this as "2 and 2 are 4". Here is how they come into play:
225 1) build == host == target
226 This is a plain native toolchain, targetting the exact same machine as the
227 one it is built on, and running again on this exact same machine. You have
228 to build such a toolchain when you want to use an updated component, such
229 as a newer gcc for example.
230 ct-ng calls it "native".
232 2) build == host != target
233 This is a classic cross-toolchain, which is expected to be run on the same
234 machine it is compiled on, and generate code to run on a second machine,
236 ct-ng calls it "cross".
238 3) build != host == target
239 Such a toolchain is also a native toolchain, as it targets the same machine
240 as it runs on. But it is build on another machine. You want such a
241 toolchain when porting to a new architecture, or if the build machine is
242 much faster than the host machine.
243 ct-ng calls it "cross-native".
245 4) build != host != target
246 This one is called a canadian-toolchain (*), and is tricky. The three
247 machines in play are different. You might want such a toolchain if you
248 have a fast build machine, but the users will use it on another machine,
249 and will produce code to run on a third machine.
250 ct-ng calls it "canadian".
252 ct-ng can build all these kinds of toolchains (or is aiming at it, anyway!)
254 (*) The term Canadian Cross came about because at the time that these issues
255 were all being hashed out, Canada had three national political parties.
256 http://en.wikipedia.org/wiki/Cross_compiler
263 Internally, crosstool-NG is script-based. To ease usage, the frontend is
269 The Makefile defines a set of rules to call each action. You can get the
270 list, along with some terse description, by typing "make help" in your
271 favourite command line.
273 The Makefile sets the version variable from the version file in ${CT_TOP_DIR}
274 which is then available to others in the CT_VERSION environment variable.
276 The kconfig language is a hacked version, vampirised from the toybox project
277 by Rob LANDLEY (http://www.landley.net/code/toybox/), adapted to my needs.