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
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 crosstool-NG, standing for crosstool
84 Next Generation, as many other comunity projects do, and as a wink at the TV
85 series "Star Trek: The Next Generation". ;-)
87 ____________________________
89 Configuring crosstool-NG /
90 _________________________/
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.
95 To enter the menu, type:
98 Almost every config item has a help entry. Read it carefully.
100 String and number options can refer to environment variables. In such a case,
101 you must use the shell syntax: ${VAR}. You shall neither single- nor double-
102 quote the string options.
104 There are three environment variables that are computed by crosstool-NG, and
108 It represents the target triplet you are building for. You can use it for
109 example in the installation/prefix directory, such as:
110 /opt/x-tools/${CT_TARGET}
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
120 The version of crosstool-NG you are using. Not much use for you, but it's
121 there if you need it.
124 Interesting config options |
125 ---------------------------*
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
133 This is where the toolchain will be installed in (and for now, where it
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.
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
146 ________________________
148 Running crosstool-NG /
149 _____________________/
151 crosstool-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.
157 To build the toolchain, simply type:
160 This will use the above configuration to retrieve, extract and patch the
161 components, build, install and eventually test your newly built toolchain.
163 You are then free to add the toolchain /bin directory in your PATH to use
166 In any case, you can get some terse help. Just type:
170 Stoping and restarting a build |
171 -------------------------------*
173 If you want to stop the build after a step you are debugging, you can pass the
174 variable STOP to make:
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 ct-ng RESTART=some_step
181 Alternatively, you can call make with the name of a step to just do that step:
184 ct-ng RESTART=libs_headers STOP=libc_headers
186 The shortcuts -step_name and step_name- allow to respectively stop or restart
188 ct-ng -libc_headers and: ct-ng libc_headers-
190 ct-ng STOP=libc_headers and: ct-ng RESTART=libc_headers
192 To obtain the list of acceptable steps, please call:
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
200 Testing all toolchains at once |
201 -------------------------------*
203 You can test-build all samples; simply call:
211 There are four kinds of toolchains you could encounter.
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
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.
225 So we're left with three machines:
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:
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 crosstool-NG calls it "native".
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,
244 crosstool-NG calls it "cross".
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 crosstool-NG calls it "cross-native".
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 crosstool-NG calls it "canadian".
260 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
263 (*) The term Canadian Cross came about because at the time that these issues
264 were all being hashed out, Canada had three national political parties.
265 http://en.wikipedia.org/wiki/Cross_compiler
272 Internally, crosstool-NG is script-based. To ease usage, the frontend is
278 To Be Written later...
283 The kconfig language is a hacked version, vampirised from the toybox project
284 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
285 Linux kernel (http://www.linux.org/ http://www.kernel.org/), and (heavily)