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Most Linux software is written in C and compiled with the GNU C compiler. GCC is a part of every Linux distribution. The latest compiler version, documentation, and patches are on ftp://ftp.gnu.org/pub/gnu/.
Programs that are written in C++ must be compiled with the GNU G++ compiler, which is also included in Linux distributions and available from the same place as GCC.
To build version 2.0.x kernels, you will need GCC version 2.7.2.x. Trying to build a Linux kernel with a different compiler, like GCC 2.8.x, EGCS, or PGCC, may cause problems until code dependencies of the 2.7.2.x compilers are fixed.
Information on the EGCS compiler is at htmlurl url="http://egcs.cygnus.com" name="http://egcs.cygnus.com">.
Note that at this time, the kernel developers are not answering bug requests for 2.0.x version kernels, but instead are concentrating on developing 2.1.x version kernels.
[J.H.M. Dassen]
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In general, Unix programs need very little porting. Simply follow the installation instructions. If you don't know--and don't know how to find out--the answers to some of the questions asked during the installation procedure, you can guess, but this tends to produce buggy programs. In this case, you're probably better off asking someone else to do the port.
If you have a BSD-ish program, you should try using
-I/usr/include/bsd and -lbsd on the appropriate
parts of the compilation lines.
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Ld.so is the dynamic library loader. Each binary using
shared libraries used to have about 3K of start-up code to find and
load the shared libraries. Now that code has been put in a special
shared library, /lib/ld.so, where all binaries can look for
it, so that it wastes less disk space, and can be upgraded more
easily.
Ld.so can be obtained from
tsx-11.mit.edu/pub/linux/packages/GCC/ and mirror sites. The
latest version at the time of writing is ld.so.1.9.5.tar.gz.
/lib/ld-linux.so.1 is the same thing for ELF (``
What's all this about ELF?
'') and comes in the same package as
the a.out loader.
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Note: You should always have a rescue disk set ready when you perform this procedure, in the likely event that something goes wrong!
This procedure is especially difficult if you're upgrading very old libraries like libc4. But you should be able to keep libc4 on the same system with libc5 libraries for the programs that still need them. The same holds true for upgrading from libc5 to the newer-yet glibc2 libraries.
The problem with upgrading dynamic libraries is that, the moment you remove the old libraries, the utilities that you need to upgrade to the new version of the libraries don't work. There are ways around around this. One is to temporarily place a spare copy of the run time libraries, which are in /lib/, in /usr/lib/, or /usr/local/lib/, or another directory that is listed in the /etc/ld.so.conf file.
For example, when upgrading libc5 libraries, the files in /lib/ might look something like:
libc.so.5 libc.so.5.4.33 libm.so.5 libm.so.5.0.9These are the C libraries and the math libraries. Copy them to another directory that is listed in /etc/ld.so.conf, like /usr/lib/.
cp -df /lib/libc.so.5* /usr/lib/ cp -df /lib/libm.so.5* /usr/lib/ ldconfigBe sure to run ldconfig to upgrade the library configuration.
The files libc.so.5 and libm.so.5 are symbolic links to the actual library files. When you upgrade, the new links will not be created if the old links are still there, unless you use the -f flag with cp. The -d flag to cp will copy the symbolic link itself, and not the file it points to.
If you need to overwrite the link to the library directly, use the -f flag with ln.
For example, to copy new libraries over the old ones, try this. Make a symbolic link to the new libraries first, then copy both the libraries and the links to /lib/, with the following commands.
ln -sf ./libm.so.5.0.48 libm.so.5 ln -sf ./libc.so.5.0.48 libc.so.5 cp -df libm.so.5* /lib cp -df libc.so.5* /libAgain, remember to run ldconfig after you copy the libraries.
If you are satisfied that everything is working correctly, you can remove the temporary copies of the old libraries from /usr/lib/ or wherever you copied them.
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First, look in the Linux Software Map--it's at sunsite.unc.edu/pub/Linux/docs/linux-software-map, and on the other FTP sites. A search engine is available on the World Wide Web at http://www.boutell.com/lsm/.
Check the FTP sites (``
Where can I get Linux material by FTP?
'') first--search the ls-lR or INDEX files
for appropriate strings.
Also look at the Linux Projects Map, ftp.ix.de/pub/ix/Linux/docs/Projects-Map.gz.
There's a search engine for Linux FTP archives at http://lfw.linuxhq.com/
Also check out the Freshmeat Web site http://www.freshmeat.org, which is really cool. (`` What online/free periodicals exist for Linux? ''
If you don't find anything, you could download the sources to
the program yourself and compile them. See ``
How do I port XXX to Linux?
'' If it's a large package that may require some
porting, post a message to comp.os.linux.development.apps.
If you compile a large-ish program, please upload it to one or more of
the FTP sites, and post a message to comp.os.linux.announce
(submit your posting to
linux-announce@news.ornl.gov).
If you're looking for an application program, the chances are that
someone has already written a free version. The
comp.sources.wanted FAQ has instructions for finding the
source code.
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Yes, unless it's the kernel.
The -m486 option to GCC, which is used to compile binaries for x486 machines, merely changes certain optimizations. This makes for slightly larger binaries that run somewhat faster on a 486. They still work fine on a 386, though, with a small performance hit.
However, from version 1.3.35 the kernel uses 486 or Pentium-specific instructions if configured for a 486 or Pentium, thus making it unusable on a 386.
GCC can be configured for a 386 or 486; the only difference is that configuring it for a 386 makes -m386 the default and configuring for a 486 makes -m486 the default. In either case, these can be overridden on a per-compilation basis or by editing /usr/lib/gcc-lib/i*-linux/n.n.n/specs.
There is an Alpha version of GCC which knows how to do optimization well for the 586, but it is quite unreliable, especially at high optimization settings. The Pentium GCC can be found on tsx-11.mit.edu in /pub/linux/ALPHA/pentium-gcc. I'd recommend using the ordinary 486 GCC instead; word has it that using -m386 produces code that's better for the Pentium, or at least slightly smaller.
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Currently, the same as -O2 (GCC 2.5) or -O3 (GCC 2.6, 2.7). Any number greater than that does the same thing. The Makefiles of newer kernels use -O2, and you should probably do the same.
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The files /usr/include/linux/ and
/usr/include/asm/ are often soft links to the
directories where the kernel headers are. They are usually under
/usr/src/kernel*/.
If you don't have the kernel sources, download them--see, `` How do I upgrade/recompile my kernel? ''
Then, use rm to remove any garbage, and ln to create
the links:
rm -rf /usr/include/linux /usr/include/asm ln -sf /usr/src/linux/include/linux /usr/include/linux ln -sf /usr/src/linux/include/asm /usr/include/asm
/usr/src/linux/include/asm/ is a symbolic link to an
architecture-specific asm directory--if you have a freshly
unpacked kernel source tree, you must make symlinks. You'll also find
that you may need to do `make config' in a newly-unpacked kernel source
tree, to create linux/autoconf.h.
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See the previous question regarding the header files.
Remember that when you apply a patch to the kernel, you must use the
-p0 or -p1 option: otherwise, the patch may be
misapplied. See the patch manual page for details.
``ld: unrecognized option `-qmagic''' means that
you should get a
newer linker, from
ftp://tsx-11.mit.edu/pub/linux/packages/GCC/, in the file
binutils-2.8.1.0.1.bin.tar.gz.
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For ELF,
gcc -fPIC -c *.c gcc -shared -Wl,-soname,libfoo.so.1 -o libfoo.so.1.0 *.oFor
a.out, get tools-n.nn.tar.gz from tsx-11.mit.edu, in
/pub/linux/packages/GCC/src/. It comes with documentation that will
tell you what to do. Note that a.out shared libraries are a
very tricky business. Consider upgrading your libraries to ELF
shared libraries. See the ELF HOWTO, at
sunsite.unc.edu/pub/Linux/docs/HOWTO/
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With an ELF compiler (`` What's all this about ELF? ''), the most common cause of large executables is the lack of an appropriate .so library link for one of the libraries you're using. There should be a link like libc.so for every library like libc.so.5.2.18.
With an a.out compiler the most common cause of large
executables is the -g linker (compiler) flag. This produces
(as well as debugging information in the output file) a program which
is statically linked--one which includes a copy of the C library
instead of a dynamically linked copy.
Other things worth investigating are -O and -O2,
which enable optimization (check the GCC documentation), and
-s (or the strip command) which strip the symbol information
from the resulting binary (making debugging totally impossible).
You may wish to use -N on very small executables (less than
8K with the -N), but you shouldn't do this unless you
understand its performance implications, and definitely never with
daemons.
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As well as the Unix multiprocessing model involving heavyweight processes, which is of course part of the standard Linux kernel, there are several implementations of lightweight processes or threads. Recent kernels implement a thread model, kthreads. In addition, there are the following packages available for Linux.
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Roughly equivalent functionality is built into GCC. Use the -Wall option to turn on most of the useful extra warnings. See the GCC manual for more details (type control-h followed by i in Emacs and select the entry for GCC).
There is a freely available program called `lclint' that does much the same thing as traditional lint. The announcement and source code are available at on larch.lcs.mit.edu in /pub/Larch/lclint/; on the World Wide Web, look at http://larch-www.lcs.mit.edu:8001/larch/lclint.html.
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Kermit is distributed under a non-GPL copyright that makes its terms of distribution somewhat different. The sources and some binaries are available on kermit.columbia.edu.
The WWW Home Page of the Columbia University Kermit project is http://www.columbia.edu/kermit/.
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