Initial integration of G77.

Please do a make cleandir before rebuilding gcc!

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+1996-03-05
+
+This directory contains the version 0.5.18 release of the GNU Fortran
+compiler.  The GNU Fortran compiler is free software.  See the file
+COPYING.g77 for copying permission.
+
+* IMPORTANT: Things you _must_ do are marked with a * at the beginning of
+  the line in this file!!!
+
+This README is for GNU Fortran, and describes the files in the f/
+directory.  The f/ directory is intended to be a subdirectory of a
+gcc source tree.  These directories are referred to below as gcc/,
+which is the top-level directory containing the gcc back end, the
+gcc C front end, and other non-Fortran files, and gcc/f/, which
+contains all of the Fortran files.
+
+* To build GNU Fortran, you must have a recent gcc distribution,
+  such as version 2.6.3 or 2.7.0.  Do not attempt to use any version
+  of gcc prior to 2.6.2 or at or beyond 2.8.0 (or 3.0, etc.), because
+  this version of g77 is designed to work only with gcc versions 2.6.x
+  and 2.7.x.
+
+* Note that you must have source copies of these gcc distributions!!
+  You cannot build g77 just using binaries of gcc.  Also, unless you
+  are an expert, avoid using any distribution of gcc not identical to
+  the one distributed by the FSF -- for example, using a special version
+  modified to produce better code for the Pentium (sometimes labeled
+  gcc-i2.6.3 -- note the `i') will not work with this distribution of g77.
+
+If you have just unpacked the g77 distribution, before proceeding,
+you must merge the contents of the g77 distribution with the appropriate
+gcc distribution on your system before proceeding.
+
+* Read and follow the instructions in g77-0.5.18/f/INSTALL that
+  explain how to merge a g77 source directory into a gcc source
+  directory.  You can use Info to read the same installation
+  instructions via:
+
+    info -f g77-0.5.18/f/g77.info -n Unpacking
+
+The resulting directory layout includes the following, where gcc/ might be
+a link to, for example, gcc-2.7.2/:
+
+    gcc/                    Non-Fortran files in gcc (not part of g77*.tar)
+    gcc/README.g77          This file
+    gcc/f/                  GNU Fortran front end
+    gcc/f/gbe/              Patches required for gcc back end versions
+    gcc/f/runtime/          libf2c configuration and f2c.h file generation
+    gcc/f/runtime/libF77/   Non-I/O portion of libf2c
+    gcc/f/runtime/libI77/   I/O portion of libf2c
+
+gcc/f/ as a whole contains the program GNU Fortran (g77), plus a portion
+of the separate program f2c, which is in gcc/f/runtime.  NOTE: The f2c
+code is not part of the program g77, just distributed with it.
+
+This directory is named gcc/f/ because it, along with its contents, is
+designed to be a subdirectory of a GNU CC (gcc) development directory.  I.e.
+when a gcc distribution is unpacked into a directory (named gcc/ for
+example), it typically contains subdirectories like gcc/config/ and
+gcc/cp/.  The latter is the subdirectory for the GNU C++ (g++) program.
+
+Similarly, the g77 directory f/ is designed to be placed in gcc/ so that
+it becomes the subdirectory gcc/f/.  g77 is distributed as g77-someversion/f/
+so that unpacking the g77 distribution is done in the normal GNU way,
+resulting in a directory having the version number in the name.  However,
+to build g77, the g77 distribution must be merged with an appropriate gcc
+distribution, normally in a gcc directory, before configuring, building,
+and installing g77.
+
+Applying g77 patches in the form of .diff files is done by typing
+"patch -p1 -d gcc" (where gcc/f/ is the active version).  That is,
+g77 patches are distributed in the same form, and at the same directory
+level, as patches to the gcc distribution.
+
+gcc/f/ has text files that document the Fortran compiler, source
+files for the GNU Fortran Front End (FFE), and some other stuff.
+
+gcc/f/gbe/ has patch files for various versions of gcc, primarily
+needed to patch the GNU compiler Back End (GBE) to fix and improve it
+for use with g77.  If a patch file exists for the version of gcc you
+want to build along with g77, you MUST apply the patch before building
+g77 with that version or g77 will not build or work properly.*
+
+* Read gcc/f/gbe/README for more information.
+
+gcc/f/runtime/ contains the run-time libraries for the f2c program, also used
+by g77, and referred to as libf2c (though libf2c is really a combination of
+two distinct libraries, libF77 and libI77 -- in g77, this distinction is
+not made).  This separate subdirectory is not part of the program g77, just
+distributed with it.  Some new files have been added to this subdirectory
+and some minor changes made to the files contained therein, to fix some
+bugs and facilitate automatic configuration, building, and installation of
+libf2c for use by g77 users.  See gcc/f/runtime/README for more information.
+
+gcc/f/BUGS lists some important bugs known to be in g77.  Or:
+
+  info -f gcc/f/g77.info -n "Actual Bugs"
+
+gcc/f/ChangeLog lists recent changes to g77 internals.
+
+gcc/f/INSTALL describes how to build and install GNU Fortran.  Or:
+
+  info -f gcc/f/g77.info -n Installation
+
+gcc/f/NEWS contains the per-release changes (not just user-visible ones
+seen in gcc/f/DOC) listed in the ~fortran/.plan file.  Or:
+
+  info -f gcc/f/g77.info -n News
+
+* Read gcc/f/BUGS, gcc/f/INSTALL, and gcc/f/NEWS at the very least!
+  All users of g77 (not just installers) should read gcc/f/g77.info*
+  as well, using the "more" command if the "info" command is
+  unavailable or they aren't used to using it.
+
+If you want to get into the FFE code, which lives entirely in gcc/f/, here
+are a few clues.  The file g77.c is the stand-alone source file for the
+`g77' command driver only -- this just invokes the `gcc' command, so it has
+nothing to do with the rest of the code in g77.  Most of the code
+ends up in an executable named `f771', which does the actual compiling,
+so it has the FFE merged with the gcc back end.
+
+The file parse.c is the source file for main() for a stand-alone FFE and
+yyparse() for f771.  (Stand-alone building of the FFE doesn't work these days.)
+The file top.c contains the top-level FFE function ffe_file and it (along
+with top.h) define all ffe_[a-z].*, ffe[A-Z].*, and FFE_[A-Za-z].* symbols.
+The file fini.c is a main() program that is used when building the FFE to
+generate C header and source files for recognizing keywords.  The files
+malloc.c and malloc.h comprise a memory manager that defines all
+malloc_[a-z].*, malloc[A-Z].*, and MALLOC_[A-Za-z].* symbols.  All other
+modules named <xyz> are comprised of all files named <xyz>*.<ext> and
+define all ffe<xyz>_[a-z].*, ffe<xyz>[A-Z].*, and FFE<XYZ>_[A-Za-z].* symbols.
+If you understand all this, congratulations -- it's easier for me to remember
+how it works than to type in these grep patterns (such as they are).  But it
+does make it easy to find where a symbol is defined -- for example,
+the symbol "ffexyz_set_something" would be defined in xyz.h and implemented
+there (if it's a macro) or in xyz.c.
+
+The "porting" files of note currently are: proj.h, which defines the
+"language" used by all the other source files (the language being
+Standard C plus some useful things like ARRAY_SIZE and such) -- change
+this file when you find your system doesn't properly define a Standard C
+macro or function, for example; target.h and target.c, which describe
+the target machine in terms of what data types are supported, how they are
+denoted (what C type does an INTEGER*8 map to, for example), how to convert
+between them, and so on (though as of 0.5.3, more and more of this information
+is being dynamically configured by ffecom_init_0); com.h and com.c, which
+interface to the target back end (currently only FFE stand-alone and the GBE);
+ste.c, which contains code for implementing recognized executable statements
+in the target back end (again currently either FFE or GBE); src.h and src.c,
+which describe information on the format(s) of source files (like whether
+they are never to be processed as case-insensitive with regard to Fortran
+keywords); and proj.c, which contains whatever code is needed to support
+the language defined by proj.h.
+
+If you want to debug the f771 executable, for example if it crashes,
+note that the global variables "lineno" and "input_filename" are set
+to reflect the current line being read by the lexer during the first-pass
+analysis of a program unit and to reflect the current line being
+processed during the second-pass compilation of a program unit.  If
+an invocation of the function ffestd_exec_end() is on the stack,
+the compiler is in the second pass, otherwise it is in the first.
+(This information might help you reduce a test case and/or work around
+a bug in g77 until a fix is available.)
+
+Any questions or comments on these topics, email fortran@gnu.ai.mit.edu.