Before configuring, you should make sure you know
where you want the g77 and gcc
binaries to be installed after they're built,
because this information is given to the configuration
tool and used during the build itself.
A g77 installation normally includes installation of
a Fortran-aware version of gcc, so that the gcc
command recognizes Fortran source files and knows how to compile
them.
For this to work, the version of gcc that you will be building
as part of g77 must be installed as the "active"
version of gcc on the system.
Sometimes people make the mistake of installing gcc as
`/usr/local/bin/gcc',
leaving an older, non-Fortran-aware version in `/usr/bin/gcc'.
(Or, the opposite happens.)
This can result in gcc being unable to compile Fortran
source files,
because when the older version of gcc is invoked,
it complains that it does not
recognize the language, or the file name suffix.
So, determine whether gcc already is installed on your system,
and, if so, where it is installed, and prepare to configure the
new version of gcc you'll be building so that it installs
over the existing version of gcc.
You might want to back up your existing copy of `/usr/bin/gcc', and the entire `/usr/lib' directory, before you perform the actual installation (as described in this manual).
Existing gcc installations typically are
found in `/usr' or `/usr/local'.
(This means the commands are installed in `/usr/bin' or
`/usr/local/bin',
the libraries in `/usr/lib' or `/usr/local/lib',
and so on.)
If you aren't certain where the currently
installed version of gcc and its
related programs reside, look at the output
of this command:
gcc -v -o /tmp/delete-me -xc /dev/null -xnone
All sorts of interesting information on the locations of various
gcc-related programs and data files should be visible
in the output of the above command.
(The output also is likely to include a diagnostic from
the linker, since there's no `main_()' function.)
However, you do have to sift through it yourself; gcc
currently provides no easy way to ask it where it is installed
and where it looks for the various programs and data files it
calls on to do its work.
Just building g77 should not overwrite any installed
programs--but, usually, after you build g77, you will want
to install it, so backing up anything it might overwrite is
a good idea.
(This is true for any package, not just g77,
though in this case it is intentional that g77 overwrites
gcc if it is already installed--it is unusual that
the installation process for one distribution intentionally
overwrites a program or file installed by another distribution,
although, in this case, g77 is an augmentation of the
gcc distribution.)
Another reason to back up the existing version first,
or make sure you can restore it easily, is that it might be
an older version on which other users have come to depend
for certain behaviors.
However, even the new version of gcc you install
will offer users the ability to specify an older version of
the actual compilation programs if desired, and these
older versions need not include any g77 components.
See section `Specifying Target Machine and Compiler Version' in Using and Porting GNU CC, for information on the `-V'
option of gcc.
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