To build a program in ELF, use gcc as always. To build
in a.out, use gcc -b i486-linuxaout .
$ cat >hello.c
main() { printf("hello, world\n"); }
^D
$ gcc -o hello hello.c
$ file hello
hello: ELF 32-bit LSB executable i386 (386 and up) Version 1
$ ./hello
hello, world
This is perhaps an appropriate time to answer the question ``if a.out
compilers default to producing a program called a.out, what
name does an ELF compiler give its output?''. Still a.out,
is the answer. Boring boring boring ... :-)
To build libfoo.so as a shared library, the basic steps look
like this:
$ gcc -fPIC -c *.c
$ gcc -shared -Wl,-soname,libfoo.so.1 -o libfoo.so.1.0 *.o
$ ln -s libfoo.so.1.0 libfoo.so.1
$ ln -s libfoo.so.1 libfoo.so
$ export LD_LIBRARY_PATH=`pwd`:$LD_LIBRARY_PATH
This will generate a shared library called libfoo.so.1.0, and
the appropriate links for ld (libfoo.so) and the dynamic
linker (libfoo.so.1) to find it. To test, we add the current
directory to LD_LIBRARY_PATH.
When you're happpy that the library works, you'll have to move it to,
say, /usr/local/lib, and recreate the appropriate links.
Note that the libfoo.so link should point to
libfoo.so.1, so it doesn't need updating on every minor
version number change. The link from libfoo.so.1 to
libfoo.so.1.0 is kept up to date by ldconfig, which on
most systems is run as part of the boot process.
$ su
# cp libfoo.so.1.0 /usr/local/lib
# /sbin/ldconfig
# ( cd /usr/local/lib ; ln -s libfoo.so.1 libfoo.so )
You may have a need to continue to build programs in the old a.out
format. For `normal' programs all you need to do to use the a.out
compiler is specify the flag -b i486-linuxaout when you call
gcc, and -m i386linux when (if) you call ld. If you need to
build a.out DLL shared libraries still, you have my sympathy. To the
best of my knowledge, the short answer is that it doesn't work.
Please mail me if you know different.