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20 <B>µ C l i b c</B>
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34 uClibc Frequently Asked Questions (FAQ)
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41 This is a collection of some of the frequently asked questions
42 about uClibc. Some of the questions even have answers. If you
43 have additions to this FAQ document, we would love to add them,
45 When you are done, <a href="http://uclibc.org/">you can click here to return
46 to the uClibc home page.</a>
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51 What platforms does uClibc run on?
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56 Currently uClibc runs on arm, i386, m68k, mipsel, powerpc, sh,
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63 Does uClibc support shared libraries?
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68 Yes. uClibc has shared library support on x86, arm, and powerpc.
69 Shared Libraries are _not_ currently supported on MMU-less systems.
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76 Why is it called uClibc?
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81 The letter 'u' is short for µ (the greek letter "mu"). µ is commonly used
82 as the abbreviation for the word "micro". The capital "C" is short for
83 "controller". So you uClibc is simply the microcontroller C library.
84 This is because uClibc was originaly created to support uClinux, a port of
85 Linux for MMU-less microcontrollers such as the Dragonball, Coldfire, and
86 ARM7TDMI. For simplicity, it is pronounced "yew-see-lib-see".
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93 Can I use it on my desktop x86 system?
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98 Sure! In fact, this can be very nice during development. By using it on
99 your development system, you can be sure that the code you are working on
100 will actually run when you deploy it your target system.
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107 Why are you doing this? Whats wrong with glibc?
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112 The inital reason, was that glibc does not support MMU-less systems. But
113 also because uClibc is so much smaller then the GNU C library. The GNU C
114 library has a different set of goals then uClibc. The GNU C library is a
115 great piece of software. It complies with just about every standard ever
116 created, and runs on just about every operating system as well -- no small
117 task! But there is a price to be paid for that. It is quite a large
118 library, and keeps getting larger with each release. It does not even
119 pretend to target embedded systems. To quote from Ulrich Drepper, the
120 maintainer of GNU libc: "...glibc is not the right thing for [an embedded
121 OS]. It is designed as a native library (as opposed to embedded). Many
122 functions (e.g., printf) contain functionality which is not wanted in
123 embedded systems." 24 May 1999
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130 So uClibc is smaller then glibc? Doesn't that mean it completely sucks?
131 How could it be smaller and not suck?
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136 uClibc has been designed from the ground up to be a C library for embedded
137 Linux. We don't need to worry about whether we support MS-DOS, or Cygwin,
138 or any other system. This lets us cut out lots of complexity, and very
139 carefully optimize for Linux. By very careful design, we can also take a
140 few shortcuts. For example, glibc contains an implementation of the
141 wordexp() function, in compliance with the Single Unix Specificaion,
142 version 2. Well, standards are important. But so is pragmatism. The
143 wordexp function is huge, and yet I am not aware of even one Linux
144 application that uses wordexp. So uClibc doesn't provide wordexp(). There
145 are many similar examples.
147 Glibc is a general purpose C library, and so as policy things are optimized
148 for speed. Most of uClibc's routines have been very carefuly written to
149 optimize them for size instead of speed.
151 The end result is a C library that will compile just about everything you
152 throw at it, that looks like glibc to application programs when you
153 compile, but is many times smaller.
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160 Why should I use uClibc?
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165 I don't know if you should use uClibc or not. It depends on your needs.
166 If you are building an embedded system, and you are tight on space, then
167 using uClibc instead if glibc should allow you to use your storage for
170 If you are trying to build a ultra fast fileserver for your company that
171 has 12 Terabytes of storage, then you probably want to use glibc...
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178 I want to create a closed source commercial application and I want to
179 protect my intellectual property. If I use uClibc, don't I have to
180 release all my source code for free?
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185 No, you do not need to give away your source code just because you use
186 uClibc and/or run on Linux.
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193 I want to create a closed source commercial application using uClibc.
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199 Yes. uClibc is licensed under the LGPL, just like GNU libc. If you are
200 using uClibc as a shared library, then your closed source application is
201 100% legal. Please consider sharing some of the money you make. :-)
203 If you are staticly linking your closed source commercial application with
204 uClibc, then you must take additional steps to comply with the uClibc
205 license. You can sell your application as usual, but you must also make
206 your closed source application available to your customers as an object
207 file which can then be linked with updated versions of uClibc. This will
208 (in theory) allow your customers to later link with updated versions of
209 uClibc. You do not need to make the application object file available to
210 everyone, just to those you gave the fully linked application.
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217 How do I compile stuff?
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222 The easiest way is to use the compiler wrapper built by uClibc. Instead of
223 using your usual compiler or cross compiler, you can use i386-uclibc-gcc,
224 (or whatever is appropriate for your architecture) and it will automagically
225 make your program link against uClibc.
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232 How do I make autoconf and automake behave?
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238 <pre>export PATH=/usr/i386-linux-uclibc/bin:$PATH</pre>
239 (or similar adjusted for your target architecture) then run you can simply
240 run autoconf/automake and it should _just work_.
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247 When I run 'ldd' to get a list of the library dependancies for a uClibc
248 binary, ldd segfaults! Or it runs my application? Anyways, it doesn't
249 work! What should I do?
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254 Use the ldd that is built by uClibc, not your system's one. When your
255 system's ldd looks for the library dependancies, it actually tries to
256 _execute_ that program. This works fine -- usually. I doesn't work at all
257 when you are cross compiling (thats why ldd segfaults). The ldd program
258 created by uClibc is cross platform and doesn't actually try to run the
259 target program like your system one does, so it should do the right thing,
260 and won't segfault, even when you are cross compiling.
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266 What is the history of uClibc? Where did it come from?
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271 This history and origin of uClibc is long and twisty.
272 In the beginning, there was <a href="http://www.gnu.org/software/libc/libc.html">GNU libc</a>. Then, libc4
273 (which later became linux libc 5) forked from GNU libc version 1.07.4, with
274 additions from 4.4BSD, in order to support Linux. Later, the <a
275 href="http://www.cix.co.uk/~mayday/">Linux-8086 C library</a>, which is part of
276 the <a href="http://www.elks.ecs.soton.ac.uk/">elks project</a>, was created,
277 which was, apparently, largely written from scratch but also borrowed code from
278 libc4, glibc, some Atari library code, with bits and pieces from about 20 other
279 places. Then uClibc forked off from the Linux-8086 C library in order to run
280 on <a href="http://www.uclinux.org">µClinux</a>.
283 I had for some time been despairing over the state of C libraries in Linux.
284 GNU libc, the standard, is very poorly suited to embedded systems (and it just
285 gets bigger with every release). I spent quite a bit of time looking over the
286 other Open Source C libraries that I knew of (listed below), and none of them really
287 impressed me. I felt there was a real vacancy in the embedded Linux ecology.
288 The closest library to what I imagined an embedded C library should be was
289 uClibc. But that had a lot of problems too -- not the least of which was that,
290 traditionally, uClibc had a complete source tree fork in order to support each
291 and every new platform, resulting in a big mess of twisty versions, all
292 different. I decided to fix it and the result is what you see here.
293 My source tree has now become the official uClibc source tree and it now lives
298 To start with, (with some initial help from <a
299 href="http://www.uclinux.org/developers/index.html">D. Jeff Dionne</a>), I
300 ported it to run on x86. I then grafted in the header files from glibc 2.1.3
301 and cleaned up the resulting breakage. This (plus some additional work) has
302 made it almost completely independant of kernel headers, a large departure from
303 its traditional tightly-coupled-to-the-kernel origins. I have written and/or
304 rewritten a number of things that were missing or broken, and sometimes grafted
305 in bits of code from the current glibc and libc5. I have also built a proper
306 platform abstraction layer, so now you can simply edit the file "Config" and
307 use that to decide which architecture you will be compiling for, and whether or
308 not your target has an MMU, and FPU, etc. I have also added a test suite,
309 which, though incomplete, is a good start. Several people have helped by
310 contributing ports to new architectures, and a lot of work has been done on
311 adding support for missing features.
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318 I need you to add <favorite feature> now! How come you don't answer all my
319 questions on the mailing list withing 5 minutes? I demand that you help me <em>Right Now</em>!
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324 You have not paid us a single cent and yet you still have the product of
325 over year and a half of work from Erik and Manuel and lots of other people.
326 How dare you treat us that way! We work on uClibc because we find it
327 interesting. If you go off flaming us, we will ignore you.
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334 I need you to add <favorite feature>! Are the uClibc developers willing to
335 be paid in order to add in <favorite feature>? Are you willing to provide
339 <TR><TD BGCOLOR="#eeeee0">
341 Sure! Now you have our attention! What you should do is contact <a
342 href="mailto:andersen@codepoet.org">Erik Andersen</a> of <a
343 href="http://codepoet-consulting.com/">CodePoet Consulting</a> to bid
344 on your project. If Erik is too busy to personally add your feature, there
345 are several other active uClibc contributors who may be able to help you out.
346 Erik can contact them and ask them about their availability.
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352 I think you guys are great and I want to help support your work!
355 <TR><TD BGCOLOR="#eeeee0">
357 Wow, that would be great! You can click here to help support uClibc and/or request features.
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379 Ok, I'm done reading all these questions.
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384 <a href="http://uclibc.org/">Well then, click here to return to the uClibc home page.</a>
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