* main.c: Move entire file except for #ifndef MAIN_OVERRIDE code

[binutils.git] / gas / README

-*- text -*-

		README for GAS 2.2.1 release
	  [cribbed largely from GDB's README file]

This is version 2.2.1 of the GNU assembler.

A number of things have changed and the wonderful world of gas looks very
different.  There's still a lot of irrelevant garbage lying around that will
be cleaned up in time.  Documentation is scarce, as are logs of the changes
made since the last gas release.  My apologies, and I'll try to get something
useful.

Unpacking and Installation - Summary
====================================

In this release, the GNU assembler ("gas") sources, the generic GNU include
files, the BFD ("binary file description") library, and other libraries all
have directories of their own underneath the gas-2.2.1 directory.  The idea is
that a variety of GNU tools can share a common copy of these things.
Configuration scripts and makefiles exist to cruise up and down this directory
tree and automatically build all the pieces in the right order.

When you unpack the gas-2.2.1.tar.z file, you'll find a directory called
`gas-2.2.1'.  To build GAS, you can just do:

	cd gas-2.2.1
	./configure
	make
	cp gas/as.new /usr/local/bin/as	(or whereever)

This will configure and build all the libraries as well as GAS.  If
`configure' can't determine your system type, specify one as its argument,
e.g., sun4 or decstation.

If you get compiler warnings during this stage, see the `Reporting Bugs'
section below; there are a few known problems.

GAS can be used as a cross-assembler, running on a machine of one type while
producing object files for a machine of another type.  See below.

Documentation
=============

The GAS release includes texinfo source for its manual, which can be processed
into `info' or `dvi' forms.

The DVI form is suitable for printing or displaying; the commands for doing
this vary from system to system.  On many systems, `lpr -d' will print a DVI
file.  On others, you may need to run a program such as `dvips' to convert the
DVI file into a form your system can print.

If you wish to build the DVI file, you will need to have TeX installed on your
system.  You can rebuild it by typing:

	cd gas-2.2.1/gas/doc
	make as.dvi

The Info form is viewable with the GNU Emacs `info' subsystem, or the
standalone `info' program, available as part of the GNU Texinfo distribution.
To build the info files, you will need the `makeinfo' program.  Type:

	cd gas-2.2.1/gas/doc
	make info

Installing GAS
==============

GAS comes with a `configure' script that automates the process of preparing
GAS for installation; you can then use `make' to build the program.

The GAS distribution includes all the source code you need for GAS in a single
directory, the name of which is usually composed by appending the version
number to `gas'.

The simplest way to configure and build GAS is to run `configure' from the
`gas-VERSION-NUMBER' source directory, which in this example is the `gas-2.2.1'
directory.

First switch to the `gas-VERSION-NUMBER' source directory if you are not
already in it; then run `configure'.  Pass the identifier for the platform on
which GAS will run as an argument.  For example:

	cd gas-2.2.1
	./configure HOST
	make

where HOST is an identifier such as `sun4' or `decstation', that identifies
the platform where GAS will run.

Running `configure HOST' followed by `make' builds the `bfd', `opcode', and
`libiberty' libraries, then `gas' itself.  (Exception: For VMS, the `bfd'
library is not used.)  The configured source files, and the binaries, are left
in the corresponding source directories.

The `configure' program is a Bourne-shell (`/bin/sh') script; if your system
does not recognize this automatically when you run a different shell, you may
need to run `sh' on it explicitly:

	sh configure HOST

If you run `configure' from a directory that contains source
directories for multiple libraries or programs, such as the `gas-2.2.1'
source directory for version 2.2.1, `configure' creates configuration
files for every directory level underneath (unless you tell it not to,
with the `--norecursion' option).

You can run the `configure' script from any of the subordinate directories in
the GAS distribution, if you only want to configure that subdirectory; but be
sure to specify a path to it.

For example, with version 2.2.1, type the following to configure only the `bfd'
subdirectory:

     cd gas-2.2.1/bfd
     ../configure HOST

Compiling GAS in another directory
==================================

   If you want to run GAS versions for several host or target machines,
you need a different `gas' compiled for each combination of host and
target.  `configure' is designed to make this easy by allowing you to
generate each configuration in a separate subdirectory, rather than in
the source directory.  If your `make' program handles the `VPATH'
feature (GNU `make' does), running `make' in each of these directories
builds the `gas' program specified there.

   To build `gas in a separate directory, run `configure' with the
`--srcdir' option to specify where to find the source. (You also need
to specify a path to find `configure' itself from your working
directory.  If the path to `configure' would be the same as the
argument to `--srcdir', you can leave out the `--srcdir' option; it
will be assumed.)

   For example, with version 2.2.1, you can build GAS in a separate
directory for a Sun 4 like this:

     cd gas-2.2.1
     mkdir ../gas-sun4
     cd ../gas-sun4
     ../gas-2.2.1/configure sun4
     make

   When `configure' builds a configuration using a remote source
directory, it creates a tree for the binaries with the same structure
(and using the same names) as the tree under the source directory.  In
the example, you'd find the Sun 4 library `libiberty.a' in the
directory `gas-sun4/libiberty', and GAS itself in `gas-sun4/gas'.

   One popular reason to build several GAS configurations in separate
directories is to configure GAS for cross-compiling (where GAS runs on
one machine--the host--while debugging programs that run on another
machine--the target).  You specify a cross-debugging target by giving
the `--target=TARGET' option to `configure'.

   When you run `make' to build a program or library, you must run it
in a configured directory--whatever directory you were in when you
called `configure' (or one of its subdirectories).

   The `Makefile' that `configure' generates in each source directory
also runs recursively.  If you type `make' in a source directory such
as `gas-2.2.1' (or in a separate configured directory configured with
`--srcdir=PATH/gas-2.2.1'), you will build all the required libraries,
and then build GAS.

   When you have multiple hosts or targets configured in separate
directories, you can run `make' on them in parallel (for example, if
they are NFS-mounted on each of the hosts); they will not interfere
with each other.


Specifying names for hosts and targets
======================================

   The specifications used for hosts and targets in the `configure'
script are based on a three-part naming scheme, but some short
predefined aliases are also supported.  The full naming scheme encodes
three pieces of information in the following pattern:

     ARCHITECTURE-VENDOR-OS

   For example, you can use the alias `sun4' as a HOST argument or in a
`--target=TARGET' option.  The equivalent full name is
`sparc-sun-sunos4'.

   The `configure' script accompanying GAS does not provide any query
facility to list all supported host and target names or aliases. 
`configure' calls the Bourne shell script `config.sub' to map
abbreviations to full names; you can read the script, if you wish, or
you can use it to test your guesses on abbreviations--for example:

     % sh config.sub sun4
     sparc-sun-sunos411
     % sh config.sub sun3
     m68k-sun-sunos411
     % sh config.sub decstation
     mips-dec-ultrix42
     % sh config.sub hp300bsd
     m68k-hp-bsd
     % sh config.sub i386v
     i386-unknown-sysv
     % sh config.sub i786v
     Invalid configuration `i786v': machine `i786v' not recognized

`config.sub' is also distributed in the GAS source directory
(`gas-2.2.1', for version 2.2.1).


`configure' options
===================

   Here is a summary of the `configure' options and arguments that are
most often useful for building GAS.  `configure' also has several other
options not listed here.

     configure [--help]
               [--prefix=DIR]
               [--srcdir=PATH]
               [--norecursion] [--rm]
               [--target=TARGET] HOST
               [--with-OPTION]

You may introduce options with a single `-' rather than `--' if you
prefer; but you may abbreviate option names if you use `--'.

`--help'
     Display a quick summary of how to invoke `configure'.

`-prefix=DIR'
     Configure the source to install programs and files under directory
     `DIR'.

`--srcdir=PATH'
     *Warning: using this option requires GNU `make', or another `make'
     that implements the `VPATH' feature.*
     Use this option to make configurations in directories separate
     from the GAS source directories.  Among other things, you can use
     this to build (or maintain) several configurations simultaneously,
     in separate directories.  `configure' writes configuration
     specific files in the current directory, but arranges for them to
     use the source in the directory PATH.  `configure' will create
     directories under the working directory in parallel to the source
     directories below PATH.

`--norecursion'
     Configure only the directory level where `configure' is executed;
     do not propagate configuration to subdirectories.

`--rm'
     Remove the configuration that the other arguments specify.

`--target=TARGET'
     Configure GAS for cross-assembling programs for the specified
     TARGET.  Without this option, GAS is configured to assemble .o files
     that run on the same machine (HOST) as GAS itself.

     There is no convenient way to generate a list of all available
     targets.

`--with-OPTION'
     These flags tell the program or library being configured to assume the
     use of certain programs, or to otherwise configure themselves differently
     from the default for the specified host/target combination.  See below
     for a list of `--with' options recognized in the gas-2.2.1 distribution.

`HOST ...'
     Configure GAS to run on the specified HOST.

     There is no convenient way to generate a list of all available
     hosts.

`configure' accepts other options, for compatibility with configuring
other GNU tools recursively; but these are the only options that affect
GAS or its supporting libraries.

The `--with' options recognized by software in the gas-2.2.1 distribution are:

`--with-minimal-bfd'
     This causes the BFD library, if it is used by the assembler, to only link
     in support for the specified target; by default, support for all targets
     known to BFD is linked in, even though the assembler generally won't
     be able to use them.  This will probably be made a default, or replaced
     by a better mechanism, for gas-2.1.

`--with-bfd-assembler'
     This causes the assembler to use the new code being merged into it to use
     BFD data structures internally, and use BFD for writing object files.
     For most targets, this isn't supported yet.  See `BFD CONVERSION' in the
     file `gas/NOTES'.

Supported platforms
===================

At this point I believe gas to be ansi only code for most target cpu's.  That
is, there should be relatively few, if any host system dependencies.  So
porting (as a cross-assembler) to hosts not yet supported should be fairly
easy.  Porting to a new target shouldn't be too tough if it's a variant of one
already supported.

Native assembling should work on:

	sun3
	sun4
	386bsd
	bsd/386?
	linux
	m68k hpux 8.0 (hpux 7.0 may be a problem)
	vax bsd, ultrix, vms
	hp9000s300
	decstation
	iris
	miniframe (m68k-sysv from Convergent Technologies)
	i386-aix (ps/2)

For cross-assemblers, I believe hosting to work on any of the machines listed
above, plus:

	rs6000
	sun386i
	at least some flavors of hpux (hpux 7.0 may be a problem)
	most flavors of sysV

I believe that gas as a cross-assembler can currently be targetted for:

	386bsd
	bsd/386?
	decstation-bsd (a.out format, to be used in BSD 4.4)
	ebmon29k
	go32 (DOS on i386, with DJGPP)
	h8/300, h8/500 (Hitachi)
	hp9000/300
	i386-aix (ps/2)
	i960-coff
	linux
	mips ecoff (decstation-ultrix, iris, mips magnum)
	nindy960
	sco386
	sun3
	sun4
	vax bsd or ultrix?
	vms
	vxworks68k
	vxworks960
	z8000 (Zilog)

MIPS ECOFF support has been added, but GAS will not run a C-style
preprocessor.  If you want that, rename your file to have a ".S" suffix, and
run gcc on it.

Support for ns32k, tahoe, i860, m88k may be suffering from bitrot.

Support for ELF is being worked on.  It should be available in version 2.2.

This version does not support the IBM RS/6000.  I am not aware of any work
being done to support it.  If you are interested in working on it, please
contact me.

This version does not support the HP PA/RISC running HP/UX.  A modified version
of gas 1.36 which does (well enough for gcc) is available by ftp from
jaguar.cs.utah.edu.

If you try out gas on some host or target not listed above, please let me know
the results, so I can update the list.

Compiler Support Hacks
======================

The assembler has been modified to support a feature that is potentially
useful when assembling compiler output, but which may confuse assembly
language programmers.  If assembler encounters a .word pseudo-op of the form
symbol1-symbol2 (the difference of two symbols), and the difference of those
two symbols will not fit in 16 bits, the assembler will create a branch around
a long jump to symbol1, and insert this into the output directly before the
next label: The .word will (instead of containing garbage, or giving an error
message) contain (the address of the long jump)-symbol2.  This allows the
assembler to assemble jump tables that jump to locations very far away into
code that works properly.  If the next label is more than 32K away from the
.word, you lose (silently); RMS claims this will never happen.  If the -K
option is given, you will get a warning message when this happens.


REPORTING BUGS IN GAS
=====================

Bugs in gas should be reported to [email protected].  They may be
cross-posted to bug-gcc if they affect the use of gas with gcc.  They should
not be reported just to bug-gcc, since I don't read that list, and therefore
wouldn't see them.

If you report a bug in GAS, please remember to include:

A description of exactly what went wrong, and exactly what should have
happened instead.

The type of machine (VAX, 68020, etc) and operating system (BSD, SunOS, DYNIX,
VMS, etc) GAS was running on.

The configuration name(s) given to the "configure" script.  The
"config.status" file should have this information.

The options given to GAS at run time.

The actual input file that caused the problem.

It is silly to report a bug in GAS without including an input file for GAS.
Don't ask us to generate the file just because you made it from files you
think we have access to.

1. You might be mistaken.
2. It might take us a lot of time to install things to regenerate that file.
3. We might get a different file from the one you got, and might not see any
bug.

To save us these delays and uncertainties, always send the input file for the
program that failed.  A smaller test case that demonstrates the problem is of
course preferable, but be sure it is a complete input file, and that it really
does demonstrate the problem; but if paring it down would cause large delays
in filing the bug report, don't bother.

If the input file is very large, and you are on the internet, you may want to
make it avaliable for anonymous FTP instead of mailing it.  If you do, include
instructions for FTP'ing it in your bug report.

If you expect to be contributing a large number of test cases, it would be
helpful if you would look at the test suite included in the release (based on
the Deja Gnu testing framework, available from the usual ftp sites) and write
test cases to fit into that framework.  This is certainly not required.