Re-order help entries in populate.
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 http://www.kegel.com/crosstool, and the subversion repository is hosted on
67 google at 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 loooong 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
80 support. That was a disaster, as inclusion into mainline is slow as hell,
81 and the changes were so numerous.
83 The only option left to me was rewrite crosstool from scratch. I decided to go
84 this way, and name the new implementation crosstool-NG, standing for crosstool
85 Next Generation, as many other comunity projects do, and as a wink at the TV
86 series "Star Trek: The Next Generation". ;-)
88 ____________________________
90 Configuring crosstool-NG /
91 _________________________/
93 crosstool-NG is configured the same way you configure your Linux kernel: by
94 using a curses-based menu. It is assumed you now how to handle this.
96 To enter the menu, type:
99 Almost every config item has a help entry. Read them carefully.
101 String and number options can refer to environment variables. In such a case,
102 you must use the shell syntax: ${VAR}. You shall neither single- nor double-
103 quote the string options.
105 There are three environment variables that are computed by crosstool-NG, and
109 It represents the target triplet you are building for. You can use it for
110 example in the installation/prefix directory, such as:
111 /opt/x-tools/${CT_TARGET}
114 The top directory where crosstool-NG is running. You shouldn't need it in
115 most cases. There is one case where you may need it: if you have local
116 patches and you store them in your running directory, you can refer to them
117 by using CT_TOP_DIR, such as:
118 ${CT_TOP_DIR}/patches.myproject
121 The version of crosstool-NG you are using. Not much use for you, but it's
122 there if you need it.
125 Interesting config options |
126 ---------------------------*
128 CT_LOCAL_TARBALLS_DIR:
129 If you already have sone tarballs in a direcotry, enter it here. That will
130 speed up the retrieving phase, where crosstool-NG would otherwise download
134 This is where the toolchain will be installed in (and for now, where it
138 An identifier for your toolchain, will take place in the vendor part of the
139 target triplet. It shall *not* contain spaces or dashes. Usually, keep it
140 to a one-word string, or use underscores to separate words if you need.
141 Avoid dots, commas, and special characters.
144 An alias for the toolchian. It will be used as a prefix to the toolchain
145 tools. For example, you will have ${CT_TARGET_ALIAS}-gcc
147 Also, if you think you don't see enough versions, you can try to enable one of
151 Show obsolete versions or tools. Most of the time, you don't want to base
152 your toolchain on too old a version (of gcc, for example). But at times, it
153 can come handy to use such an old version for regression tests. Those old
154 versions are hidden behind CT_BSOLETE.
157 Show experimental versions or tools. Again, you might not want to base your
158 toolchain on too recent tools (eg. gcc) for production. But if you need a
159 feature present only in a recent version, or a new tool, you can find them
160 hidden behind CT_EXPERIMENTAL.
163 Show broken versions or tools. Some usefull tools are currently broken: they
164 won't compile, run, or worse, cause defects when running. But if you are
165 brave enough, you can try and debug them. They are hidden behind CT_BROKEN,
166 which itself is hiddent behind EXPERIMENTAL.
168 ________________________
170 Running crosstool-NG /
171 _____________________/
173 crosstool-NG is configured by a configurator presenting a menu-stuctured set of
174 options. These options let you specify the way you want your toolchain built,
175 where you want it installed, what architecture and specific processor it
176 will support, the version of the components you want to use, etc... The
177 value for those options are then stored in a configuration file.
179 To build the toolchain, simply type:
182 This will use the above configuration to retrieve, extract and patch the
183 components, build, install and eventually test your newly built toolchain.
185 You are then free to add the toolchain /bin directory in your PATH to use
188 In any case, you can get some terse help. Just type:
194 Stoping and restarting a build |
195 -------------------------------*
197 If you want to stop the build after a step you are debugging, you can pass the
198 variable STOP to make:
201 Conversely, if you want to restart a build at a specific step you are
202 debugging, you can pass the RESTART variable to make:
203 ct-ng RESTART=some_step
205 Alternatively, you can call make with the name of a step to just do that step:
208 ct-ng RESTART=libs_headers STOP=libc_headers
210 The shortcuts -step_name and step_name- allow to respectively stop or restart
212 ct-ng -libc_headers and: ct-ng libc_headers-
214 ct-ng STOP=libc_headers and: ct-ng RESTART=libc_headers
216 To obtain the list of acceptable steps, please call:
219 Note that in order to restart a build, you'll have to say 'Y' to the config
220 option CT_DEBUG_CT_SAVE_STEPS, and that the previous build effectively went
224 Testing all toolchains at once |
225 -------------------------------*
227 You can test-build all samples; simply call:
230 _______________________
232 Using the toolchain /
233 ____________________/
235 Using the toolchain is as simple as adding the toolchain's bin directory in
237 export PATH="${PATH}:/your/toolchain/path/bin"
239 and then using the target triplet to tell the build systems to use your
241 ./configure --target=your-target-triplet
242 make CC=your-target-triplet-gcc
243 make CROSS_COMPILE=your-target-triplet-
246 When your root directory is ready, it is still missing some important bits: the
247 toolchain's libraries. To populate your root directory with those libs, just
249 your-target-triplet-populate -s /your/root -d /your/root-populated
251 This will copy /your/root into /your/root-populated, and put the needed and only
252 the needed libraries there. Thus you don't polute /your/root with any cruft that
253 would no longer be needed should you have to remove stuff. /your/root always
254 contains only those things you install in it.
256 You can then use /your/root-populated to build up your file system image, a
257 tarball, or to NFS-mount it from your target, or whatever you need.
264 There are four kinds of toolchains you could encounter.
266 First off, you must understand the following: when it comes to compilers there
267 are up to four machines involved:
268 1) the machine configuring the toolchain components: the config machine
269 2) the machine building the toolchain components: the build machine
270 3) the machine running the toolchain: the host machine
271 4) the machine the toolchain is generating code for: the target machine
273 We can most of the time assume that the config machine and the build machine
274 are the same. Most of the time, this will be true. The only time it isn't
275 is if you're using distributed compilation (such as distcc). Let's forget
276 this for the sake of simplicity.
278 So we're left with three machines:
283 Any toolchain will involve those three machines. You can be as pretty sure of
284 this as "2 and 2 are 4". Here is how they come into play:
286 1) build == host == target
287 This is a plain native toolchain, targetting the exact same machine as the
288 one it is built on, and running again on this exact same machine. You have
289 to build such a toolchain when you want to use an updated component, such
290 as a newer gcc for example.
291 crosstool-NG calls it "native".
293 2) build == host != target
294 This is a classic cross-toolchain, which is expected to be run on the same
295 machine it is compiled on, and generate code to run on a second machine,
297 crosstool-NG calls it "cross".
299 3) build != host == target
300 Such a toolchain is also a native toolchain, as it targets the same machine
301 as it runs on. But it is build on another machine. You want such a
302 toolchain when porting to a new architecture, or if the build machine is
303 much faster than the host machine.
304 crosstool-NG calls it "cross-native".
306 4) build != host != target
307 This one is called a canadian-toolchain (*), and is tricky. The three
308 machines in play are different. You might want such a toolchain if you
309 have a fast build machine, but the users will use it on another machine,
310 and will produce code to run on a third machine.
311 crosstool-NG calls it "canadian".
313 crosstool-NG can build all these kinds of toolchains (or is aiming at it,
316 (*) The term Canadian Cross came about because at the time that these issues
317 were all being hashed out, Canada had three national political parties.
318 http://en.wikipedia.org/wiki/Cross_compiler
325 Internally, crosstool-NG is script-based. To ease usage, the frontend is
331 The entry point to crosstool-NG is the Makefile script "ct-ng". Calling this
332 script with an action will act exactly as if the Makefile was in the current
333 working directory and make was called with the action as rule. Thus:
335 is equivalent to having the Makefile in CWD, and calling:
338 Having ct-ng as it is avoids copying the Makefile everywhere, and acts as a
341 ct-ng loads sub- Makefiles from the library directory $(CT_LIB_DIR), as set up
342 at configuration time with ./configure.
344 ct-ng also search for config files, sub-tools, samples, scripts and patches in
345 that library directory.
350 The kconfig language is a hacked version, vampirised from the toybox project
351 by Rob LANDLEY (http://www.landley.net/code/toybox/), itself coming from the
352 Linux kernel (http://www.linux.org/ http://www.kernel.org/), and (heavily)
355 The kconfig parsers (conf and mconf) are not installed pre-built, but as
356 source files. Thus you can have the directory where crosstool-NG is installed,
357 exported (via NFS or whatever) and have clients with different architectures
358 use the same crosstool-NG installation, and most notably, the same set of
364 To Be Written later...