g77install.texi

gcc-2.95.3 Linux下最常用的C编译器

in your system's documentation.

@node Always Flush Output
@subsection Always Flush Output
@cindex ALWAYS_FLUSH
@cindex synchronous write errors
@cindex disk full
@cindex flushing output
@cindex fflush()
@cindex I/O, flushing
@cindex output, flushing
@cindex writes, flushing
@cindex NFS
@cindex network file system

Some Fortran programs require output
(writes) to be flushed to the operating system (under UNIX,
via the @code{fflush()} library call) so that errors,
such as disk full, are immediately flagged via the relevant
@code{ERR=} and @code{IOSTAT=} mechanism, instead of such
errors being flagged later as subsequent writes occur, forcing
the previously written data to disk, or when the file is
closed.

Essentially, the difference can be viewed as synchronous error
reporting (immediate flagging of errors during writes) versus
asynchronous, or, more precisely, buffered error reporting
(detection of errors might be delayed).

@code{libg2c} supports flagging write errors immediately when
it is built with the @code{ALWAYS_FLUSH} macro defined.
This results in a @code{libg2c} that runs slower, sometimes
quite a bit slower, under certain circumstances---for example,
accessing files via the networked file system NFS---but the
effect can be more reliable, robust file I/O.

If you know that Fortran programs requiring this level of precision
of error reporting are to be compiled using the
version of @code{g77} you are building, you might wish to
modify the @code{g77} source tree so that the version of
@code{libg2c} is built with the @code{ALWAYS_FLUSH} macro
defined, enabling this behavior.

To do this, find this line in @file{@value{path-libf2c}/f2c.h} in
your @code{g77} source tree:

@example
/* #define ALWAYS_FLUSH */
@end example

Remove the leading @samp{/*@w{ }},
so the line begins with @samp{#define},
and the trailing @samp{@w{ }*/}.

Then build or rebuild @code{g77} as appropriate.

@node Maximum Stackable Size
@subsection Maximum Stackable Size
@vindex FFECOM_sizeMAXSTACKITEM
@cindex code, stack variables
@cindex maximum stackable size
@cindex stack, allocation
@cindex segmentation violation
@code{g77}, on most machines, puts many variables and arrays on the stack
where possible, and can be configured (by changing
@code{FFECOM_sizeMAXSTACKITEM} in @file{@value{path-g77}/com.c}) to force
smaller-sized entities into static storage (saving
on stack space) or permit larger-sized entities to be put on the
stack (which can improve run-time performance, as it presents
more opportunities for the GBE to optimize the generated code).

@emph{Note:} Putting more variables and arrays on the stack
might cause problems due to system-dependent limits on stack size.
Also, the value of @code{FFECOM_sizeMAXSTACKITEM} has no
effect on automatic variables and arrays.
@xref{But-bugs}, for more information.

@node Floating-point Bit Patterns
@subsection Floating-point Bit Patterns

@cindex cross-compiler, building
@cindex floating-point bit patterns
@cindex bit patterns
The @code{g77} build will crash if an attempt is made to build
it as a cross-compiler
for a target when @code{g77} cannot reliably determine the bit pattern of
floating-point constants for the target.
Planned improvements for version 0.6 of @code{g77}
will give it the capabilities it needs to not have to crash the build
but rather generate correct code for the target.
(Currently, @code{g77}
would generate bad code under such circumstances if it didn't crash
during the build, e.g. when compiling a source file that does
something like @samp{EQUIVALENCE (I,R)} and @samp{DATA R/9.43578/}.)

@node Large Initialization
@subsection Initialization of Large Aggregate Areas

@cindex speed, of compiler
@cindex slow compiler
@cindex memory utilization
@cindex large initialization
@cindex aggregate initialization
A warning message is issued when @code{g77} sees code that provides
initial values (e.g. via @code{DATA}) to an aggregate area (@code{COMMON}
or @code{EQUIVALENCE}, or even a large enough array or @code{CHARACTER}
variable)
that is large enough to increase @code{g77}'s compile time by roughly
a factor of 10.

This size currently is quite small, since @code{g77}
currently has a known bug requiring too much memory
and time to handle such cases.
In @file{@value{path-g77}/data.c}, the macro
@code{FFEDATA_sizeTOO_BIG_INIT_} is defined
to the minimum size for the warning to appear.
The size is specified in storage units,
which can be bytes, words, or whatever, on a case-by-case basis.

After changing this macro definition, you must
(of course) rebuild and reinstall @code{g77} for
the change to take effect.

Note that, as of version 0.5.18, improvements have
reduced the scope of the problem for @emph{sparse}
initialization of large arrays, especially those
with large, contiguous uninitialized areas.
However, the warning is issued at a point prior to
when @code{g77} knows whether the initialization is sparse,
and delaying the warning could mean it is produced
too late to be helpful.

Therefore, the macro definition should not be adjusted to
reflect sparse cases.
Instead, adjust it to generate the warning when densely
initialized arrays begin to cause responses noticeably slower
than linear performance would suggest.

@node Alpha Problems Fixed
@subsection Alpha Problems Fixed

@cindex Alpha, support
@cindex 64-bit systems
@code{g77} used to warn when it was used to compile Fortran code
for a target configuration that is not basically a 32-bit
machine (such as an Alpha, which is a 64-bit machine, especially
if it has a 64-bit operating system running on it).
That was because @code{g77} was known to not work
properly on such configurations.

As of version 0.5.20, @code{g77} is believed to work well
enough on such systems.
So, the warning is no longer needed or provided.

However, support for 64-bit systems, especially in
areas such as cross-compilation and handling of
intrinsics, is still incomplete.
The symptoms
are believed to be compile-time diagnostics rather
than the generation of bad code.
It is hoped that version 0.6 will completely support 64-bit
systems.

@node Quick Start
@section Quick Start
@cindex quick start

@ifset OMIT-FSF-G77
For users of the @value{which-g77} version of @code{g77},
this information is superceded by the
@value{which-gcc} installation instructions.
@end ifset

@ifclear OMIT-FSF-G77
This procedure configures, builds, and installs @code{g77}
``out of the box'' and works on most UNIX systems.
Each command is identified by a unique number,
used in the explanatory text that follows.
For the most part, the output of each command is not shown,
though indications of the types of responses are given in a
few cases.

To perform this procedure, the installer must be logged
in as user @code{root}.
Much of it can be done while not logged in as @code{root},
and users experienced with UNIX administration should be
able to modify the procedure properly to do so.

Following traditional UNIX conventions, it is assumed that
the source trees for @code{g77} and @code{gcc} will be
placed in @file{/usr/src}.
It also is assumed that the source distributions themselves
already reside in @file{/usr/FSF}, a naming convention
used by the author of @code{g77} on his own system:

@example
/usr/FSF/gcc-@value{version-gcc}.tar.gz
/usr/FSF/g77-@value{version-g77}.tar.gz
@end example

@c (You can use @file{gcc-2.7.2.1.tar.gz} instead, or
@c the equivalent of it obtained by applying the
@c patch distributed as @file{gcc-2.7.2-2.7.2.1.diff.gz}
@c to version 2.7.2 of @code{gcc},
@c if you remember to make the appropriate adjustments in the
@c instructions below.)

@c @cindex SunOS4
@c Users of the following systems should not blindly follow
@c these quick-start instructions, because of problems their
@c systems have coping with straightforward installation of
@c @code{g77}:
@c 
@c @itemize @bullet
@c @item
@c SunOS4
@c @end itemize
@c 
@c Instead, see @ref{Complete Installation}, for detailed information
@c on how to configure, build, and install @code{g77} for your
@c particular system.
@c Also, see @ref{Trouble,,Known Causes of Trouble with GNU Fortran},
@c for information on bugs and other problems known to afflict the
@c installation process, and how to report newly discovered ones.
@c 
@c If your system is @emph{not} on the above list, and @emph{is}
@c a UNIX system or one of its variants, you should be able to
@c follow the instructions below.

If you vary @emph{any} of the steps below, you might run into
trouble, including possibly breaking existing programs for
other users of your system.
Before doing so, it is wise to review the explanations of some
of the steps.
These explanations follow this list of steps.

@example
sh[ 1]# @kbd{cd /usr/src}
@set source-dir 1
sh[ 2]# @kbd{gunzip -c < /usr/FSF/gcc-@value{version-gcc}.tar.gz | tar xf -}
[Might say "Broken pipe"...that is normal on some systems.]
@set unpack-gcc 2
sh[ 3]# @kbd{gunzip -c < /usr/FSF/g77-@value{version-g77}.tar.gz | tar xf -}
["Broken pipe" again possible.]
@set unpack-g77 3
sh[ 4]# @kbd{ln -s gcc-@value{version-gcc} gcc}
@set link-gcc 4
sh[ 5]# @kbd{ln -s g77-@value{version-g77} g77}
@set link-g77 5
sh[ 6]# @kbd{mv -i g77/* gcc}
[No questions should be asked by mv here; or, you made a mistake.]
@set merge-g77 6
sh[ 7]# @kbd{cd gcc}
sh[ 8]# @kbd{./configure --prefix=/usr}
[Do not do the above if gcc is not installed in /usr/bin.
You might need a different @kbd{--prefix=@dots{}}, as
described below.]
@set configure-gcc 8
sh[ 9]# @kbd{make bootstrap}
[This takes a long time, and is where most problems occur.]
@set build-gcc 9
sh[10]# @kbd{make compare}
[This verifies that the compiler is `sane'.
If any files are printed, you have likely found a g77 bug.]
@set compare-gcc 10
sh[11]# @kbd{rm -fr stage1}
@set rm-stage1 11
sh[12]# @kbd{make -k install}
[The actual installation.]
@set install-g77 12
sh[13]# @kbd{g77 -v}
[Verify that g77 is installed, obtain version info.]
@set show-version 13
sh[14]#
@set end-procedure 14
@end example

@xref{Updating Documentation,,Updating Your Info Directory}, for
information on how to update your system's top-level @code{info}
directory to contain a reference to this manual, so that
users of @code{g77} can easily find documentation instead
of having to ask you for it.

Elaborations of many of the above steps follows:

@table @asis
@item Step @value{source-dir}: @kbd{cd /usr/src}
You can build @code{g77} pretty much anyplace.
By convention, this manual assumes @file{/usr/src}.
It might be helpful if other users on your system
knew where to look for the source code for the
installed version of @code{g77} and @code{gcc} in any case.

@c @item Step @value{unpack-gcc}: @kbd{gunzip -d @dots{}}
@c Here, you might wish to use @file{gcc-2.7.2.1.tar.gz}
@c instead, or apply @file{gcc-2.7.2-2.7.2.1.diff.gz} to achieve
@c similar results.

@item Step @value{unpack-g77}: @kbd{gunzip -d < /usr/FSF/g77-@value{version-g77}.tar.gz | tar xf -}
It is not always necessary to obtain the latest version of
@code{g77} as a complete @file{.tar.gz} file if you have
a complete, earlier distribution of @code{g77}.
If appropriate, you can unpack that earlier
version of @code{g77}, and then apply the appropriate patches
to achieve the same result---a source tree containing version
@value{version-g77} of @code{g77}.

@item Step @value{link-gcc}: @kbd{ln -s gcc-@value{version-gcc} gcc}
@item Step @value{link-g77}: @kbd{ln -s g77-@value{version-g77} g77}
These commands mainly help reduce typing,
and help reduce visual clutter in examples
in this manual showing what to type to install @code{g77}.

@c Of course, if appropriate, @kbd{ln -s gcc-2.7.2.1 gcc} or
@c similar.

@xref{Unpacking}, for information on
using distributions of @code{g77} made by organizations
other than the FSF.

@item Step @value{merge-g77}: @kbd{mv -i g77/* gcc}
After doing this, you can, if you like, type
@samp{rm g77} and @samp{rmdir g77-@value{version-g77}} to remove
the empty directory and the symbol link to it.
But, it might be helpful to leave them around as
quick reminders of which version(s) of @code{g77} are
installed on your system.

@xref{Unpacking}, for information
on the contents of the @file{g77} directory (as merged
into the @file{gcc} directory).

@item Step @value{configure-gcc}: @kbd{./configure --prefix=/usr}
This is where you specify that
the @file{g77} and @file{gcc} executables are to be
installed in @file{/usr/bin/},
the @code{g77} and @code{gcc} documentation is
to be installed in @file{/usr/info/} and @file{/usr/man/},
and so on.

You should ensure that any existing installation of the @file{gcc}
executable is in @file{/usr/bin/}.

However, if that existing version of @code{gcc} is not @value{version-gcc},
or if you simply wish to avoid risking overwriting it with a
newly built copy of the same version,
you can specify @samp{--prefix=/usr/local}
(which is the default)
or some other path,
and invoke the newly installed version
directly from that path's @file{bin} directory.

@xref{Where to Install,,Where in the World Does Fortran (and GNU CC) Go?},
for more information on determining where to install @code{g77}.
@xref{Configuring gcc}, for more information on the
configuration process triggered by invoking the @file{./configure}
script.

@item Step @value{build-gcc}: @kbd{make bootstrap}
@xref{Installation,,Installing GNU CC,
gcc,Using and Porting GNU CC}, for information
on the kinds of diagnostics you should expect during
this procedure.