update the documentation somewhat. Still not complete, though... :-(
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 You then simply run make. It will use this configuration file to retrieve,
99 extract and patch the components, build, install and test your newly built
102 You are then free to add the toolchain /bin directory in your PATH to use
105 ____________________________
107 Configuring crosstool-NG /
108 _________________________/
110 crosstool-NG is configured the same way you configure your Linux kernel: by
111 using a curses-based menu. It is assumed you now how to handle this.
113 Almost every config item has a help entry. Read it carefully.
115 String and number options can refer to environment variables. In such a case,
116 you must use the shell syntax: ${VAR}. No such option is ever needed by make.
117 You need to neither single- nor double-quote the string options.
119 There are three environment variablea that are computed by crosstool-NG, and
123 It represents the target triplet you are building for. You can use it for
124 example in the installation/prefix directory, such as:
125 /opt/x-tools/${CT_TARGET}
128 The top directory where crosstool-NG sits. You shouldn't need it in most
129 cases. There is one case where you may need it: if you have local patches
130 and you store them in your copy of crosstool-NG, you can refer to them
131 by using CT_TOP_DIR, such as:
132 ${CT_TOP_DIR}/patches.myproject
135 The version of crosstool-NG you are using. Not much help for you, but it's
136 there if you need it.
138 Interesting config options |
139 ---------------------------*
141 CT_LOCAL_TARBALLS_DIR:
142 If you already have sone tarballs in a direcotry, enter it here. That will
143 speed up the retrieving phase, where crosstool-ng would otherwise download
147 This is where the toolchain will be installed in (and for now, where it
151 The file where *all* log messages will go. Keep the default, in goes in
152 ${CT_PREFIX_DIR}/${CT_TARGET}.log
155 An identifier for your toolchain, will take place in the vendor part of the
156 target triplet. It shall *not* contain spaces or dashes. Usually, keep it
157 to a one-word string, or use underscores to separate words if you need.
158 Avoid dots, commas, and special characters.
161 An alias for the toolchian. It will be used as a prefix to the toolchain
162 tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
169 There are four kinds of toolchains you could encounter.
171 First off, you must understand the following: when it comes to compilers there
172 are up to four machines involved:
173 1) the machine configuring the toolchain components: the config machine
174 2) the machine building the toolchain components: the build machine
175 3) the machine running the toolchain: the host machine
176 4) the machine the toolchain is building for: the target machine
178 We can most of the time assume that the config machine and the build machine
179 are the same. Most of the time, this will be true. The only time it isn't
180 is if you're using distributed compilation (such as distcc). Let's forget
181 this for the sake of simplicity.
183 So we're left with three machines:
188 Any toolchain will involve those three machines. You can be as pretty sure of
189 this as "2 and 2 are 4". Here is how they come into play:
191 1) build == host == target
192 This is a plain native toolchain, targetting the exact same machine as the
193 one it is built on, and running again on this exact same machine. You have
194 to build such a toolchain when you want to use an updated component, such
195 as a newer gcc for example.
196 ct-ng calls it "native".
198 2) build == host != target
199 This is a classic cross-toolchain, which is expected to be run on the same
200 machine it is compiled on, and generate code to run on a second machine,
202 ct-ng calls it "cross".
204 3) build != host == target
205 Such a toolchain is also a native toolchain, as it targets the same machine
206 as it runs on. But it is build on another machine. You want such a
207 toolchain when porting to a new architecture, or if the build machine is
208 much faster than the host machine.
209 ct-ng calls it "cross-native".
211 4) build != host != target
212 This one is called a canadian-toolchain (*), and is tricky. The three
213 machines in play are different. You might want such a toolchain if you
214 have a fast build machine, but the users will use it on another machine,
215 and will produce code to run on a third machine.
216 ct-ng calls it "canadian".
218 ct-ng can build all these kinds of toolchains (or is aiming at it, anyway!)
220 (*) The term Canadian Cross came about because at the time that these issues
221 were all being hashed out, Canada had three national political parties.
222 http://en.wikipedia.org/wiki/Cross_compiler
229 Internally, crosstool-NG is script-based. To ease usage, the frontend is
235 The Makefile defines a set of rules to call each action. You can get the
236 list, along with some terse description, by typing "make help" in your
237 favourite command line.
239 The Makefile sets the version variable from the version file in ${CT_TOP_DIR}
240 which is then available to others in the CT_VERSION environment variable.
242 The kconfig language is a hacked version, vampirised from the toybox project
243 by Rob LANDLEY (http://www.landley.net/code/toybox/), adapted to my needs.