gcc/README.g77

   1 1997-06-20
   2
   3 This directory contains the version 0.5.21 release of the GNU Fortran
   4 compiler.  The GNU Fortran compiler is free software.  See the file
   5 COPYING.g77 for copying permission.
   6
   7 * IMPORTANT: Things you _must_ do are marked with a * at the beginning of
   8   the line in this file!!!
   9
  10 This README is for GNU Fortran, and describes the files in the f/
  11 directory.  The f/ directory is intended to be a subdirectory of a
  12 gcc source tree.  These directories are referred to below as gcc/,
  13 which is the top-level directory containing the gcc back end, the
  14 gcc C front end, and other non-Fortran files, and gcc/f/, which
  15 contains all of the Fortran files.
  16
  17 * Note, if this is an egcs release, all the installation information
  18   which follows is not needed.  It is provided for historical reference
  19   only.
  20
  21 * To build GNU Fortran, you must have a source distribution of gcc
  22   version 2.7.2.2.  Do not attempt to use any other version
  23   of gcc, because this version of g77 is designed to work only with
  24   gcc version 2.7.2.2.
  25
  26 * Note that you must have source copies of these gcc distributions!!
  27   You cannot build g77 just using binaries of gcc.  Also, unless you
  28   are an expert, avoid using any distribution of gcc not identical to
  29   the one distributed by the FSF -- for example, using a special version
  30   modified to produce better code for the Pentium (sometimes labeled
  31   gcc-i2.6.3 -- note the `i') will not work with this distribution of g77.
  32
  33 If you have just unpacked the g77 distribution, before proceeding,
  34 you must merge the contents of the g77 distribution with the appropriate
  35 gcc distribution on your system before proceeding.
  36
  37 * Read and follow the instructions in g77-0.5.21/f/INSTALL that
  38   explain how to merge a g77 source directory into a gcc source
  39   directory.  You can use Info to read the same installation
  40   instructions via:
  41
  42     info -f g77-0.5.21/f/g77.info -n Unpacking
  43
  44 The resulting directory layout includes the following, where gcc/ might be
  45 a link to, for example, gcc-2.7.2.2/:
  46
  47     gcc/                    Non-Fortran files in gcc (not part of g77*.tar)
  48     gcc/README.g77          This file
  49     gcc/f/                  GNU Fortran front end
  50     gcc/f/gbe/              Patches required for gcc back end versions
  51     gcc/f/runtime/          libf2c configuration and f2c.h file generation
  52     gcc/f/runtime/libF77/   Non-I/O portion of libf2c
  53     gcc/f/runtime/libI77/   I/O portion of libf2c
  54     gcc/f/runtime/libU77/   Additional interfaces to libc for libf2c
  55
  56 gcc/f/ as a whole contains the program GNU Fortran (g77), plus a portion
  57 of the separate program f2c, which is in gcc/f/runtime.  NOTE: The f2c
  58 code is not part of the program g77, just distributed with it.
  59
  60 This directory is named gcc/f/ because it, along with its contents, is
  61 designed to be a subdirectory of a GNU CC (gcc) development directory.  I.e.
  62 when a gcc distribution is unpacked into a directory (named gcc/ for
  63 example), it typically contains subdirectories like gcc/config/ and
  64 gcc/cp/.  The latter is the subdirectory for the GNU C++ (g++) program.
  65
  66 Similarly, the g77 directory f/ is designed to be placed in gcc/ so that
  67 it becomes the subdirectory gcc/f/.  g77 is distributed as g77-someversion/f/
  68 so that unpacking the g77 distribution is done in the normal GNU way,
  69 resulting in a directory having the version number in the name.  However,
  70 to build g77, the g77 distribution must be merged with an appropriate gcc
  71 distribution, normally in a gcc directory, before configuring, building,
  72 and installing g77.
  73
  74 Applying g77 patches in the form of .diff files is done by typing
  75 "patch -p1 -d gcc" (where gcc/f/ is the active version).  That is,
  76 g77 patches are distributed in the same form, and at the same directory
  77 level, as patches to the gcc distribution.
  78
  79 gcc/f/ has text files that document the Fortran compiler, source
  80 files for the GNU Fortran Front End (FFE), and some other stuff.
  81
  82 gcc/f/gbe/ has patch files for various versions of gcc, primarily
  83 needed to patch the GNU compiler Back End (GBE) to fix and improve it
  84 for use with g77.  If a patch file exists for the version of gcc you
  85 want to build along with g77, you MUST apply the patch before building
  86 g77 with that version or g77 will not build or work properly.*
  87
  88 * Read gcc/f/gbe/README for more information.
  89
  90 gcc/f/runtime/ contains the run-time libraries for the f2c program, also used
  91 by g77, and referred to as libf2c (though libf2c is really a combination of
  92 two distinct libraries, libF77 and libI77 -- in g77, this distinction is
  93 not made, and, further, Dave Love's implementation of libU77 is added
  94 to the mix).  This separate subdirectory is not part of the program g77, just
  95 distributed with it.  Some new files have been added to this subdirectory
  96 and some minor changes made to the files contained therein, to fix some
  97 bugs and facilitate automatic configuration, building, and installation of
  98 libf2c for use by g77 users.  See gcc/f/runtime/README for more information.
  99
 100 gcc/f/BUGS lists some important bugs known to be in g77.  Or:
 101
 102   info -f gcc/f/g77.info -n "Actual Bugs"
 103
 104 gcc/f/ChangeLog lists recent changes to g77 internals.
 105
 106 gcc/f/INSTALL describes how to build and install GNU Fortran.  Or:
 107
 108   info -f gcc/f/g77.info -n Installation
 109
 110 gcc/f/NEWS contains the per-release changes (not just user-visible ones
 111 seen in gcc/f/DOC) listed in the ~fortran/.plan file.  Or:
 112
 113   info -f gcc/f/g77.info -n News
 114
 115 * Read gcc/f/BUGS, gcc/f/INSTALL, and gcc/f/NEWS at the very least!
 116   All users of g77 (not just installers) should read gcc/f/g77.info*
 117   as well, using the "more" command if the "info" command is
 118   unavailable or they aren't accustomed to using it.
 119
 120 If you want to get into the FFE code, which lives entirely in gcc/f/, here
 121 are a few clues.  The file g77.c is the stand-alone source file for the
 122 `g77' command driver only -- this just invokes the `gcc' command, so it has
 123 nothing to do with the rest of the code in g77.  Most of the code
 124 ends up in an executable named `f771', which does the actual compiling,
 125 so it has the FFE merged with the gcc back end.
 126
 127 The file parse.c is the source file for main() for a stand-alone FFE and
 128 yyparse() for f771.  (Stand-alone building of the FFE doesn't work these days.)
 129 The file top.c contains the top-level FFE function ffe_file and it (along
 130 with top.h) define all ffe_[a-z].*, ffe[A-Z].*, and FFE_[A-Za-z].* symbols.
 131 The file fini.c is a main() program that is used when building the FFE to
 132 generate C header and source files for recognizing keywords.  The files
 133 malloc.c and malloc.h comprise a memory manager that defines all
 134 malloc_[a-z].*, malloc[A-Z].*, and MALLOC_[A-Za-z].* symbols.  All other
 135 modules named <xyz> are comprised of all files named <xyz>*.<ext> and
 136 define all ffe<xyz>_[a-z].*, ffe<xyz>[A-Z].*, and FFE<XYZ>_[A-Za-z].* symbols.
 137 If you understand all this, congratulations -- it's easier for me to remember
 138 how it works than to type in these grep patterns (such as they are).  But it
 139 does make it easy to find where a symbol is defined -- for example,
 140 the symbol "ffexyz_set_something" would be defined in xyz.h and implemented
 141 there (if it's a macro) or in xyz.c.
 142
 143 The "porting" files of note currently are: proj.h, which defines the
 144 "language" used by all the other source files (the language being
 145 Standard C plus some useful things like ARRAY_SIZE and such) -- change
 146 this file when you find your system doesn't properly define a Standard C
 147 macro or function, for example; target.h and target.c, which describe
 148 the target machine in terms of what data types are supported, how they are
 149 denoted (what C type does an INTEGER*8 map to, for example), how to convert
 150 between them, and so on (though as of 0.5.3, more and more of this information
 151 is being dynamically configured by ffecom_init_0); com.h and com.c, which
 152 interface to the target back end (currently only FFE stand-alone and the GBE);
 153 ste.c, which contains code for implementing recognized executable statements
 154 in the target back end (again currently either FFE or GBE); src.h and src.c,
 155 which describe information on the format(s) of source files (like whether
 156 they are never to be processed as case-insensitive with regard to Fortran
 157 keywords); and proj.c, which contains whatever code is needed to support
 158 the language defined by proj.h.
 159
 160 If you want to debug the f771 executable, for example if it crashes,
 161 note that the global variables "lineno" and "input_filename" are set
 162 to reflect the current line being read by the lexer during the first-pass
 163 analysis of a program unit and to reflect the current line being
 164 processed during the second-pass compilation of a program unit.  If
 165 an invocation of the function ffestd_exec_end() is on the stack,
 166 the compiler is in the second pass, otherwise it is in the first.
 167 (This information might help you reduce a test case and/or work around
 168 a bug in g77 until a fix is available.)
 169
 170 Any questions or comments on these topics, email egcs@cygnus.com