path: root/gdb/README

		README for gdb-4.0 release
	John Gilmore	 		23 Aug 91

This is GDB, the GNU source-level debugger, presently running under un*x.
A summary of features new since gdb-3.5 is in the file `WHATS.NEW'.


Unpacking and Installation -- quick overview
==========================

This release moves the generic GNU include files, the BFD ("binary file
description") library, the getopt routines, obstacks, and the readline
library into the parent directory of the gdb source files.  The idea is
that a variety of GNU tools can share a common copy of these things.

These generic files are packaged together with the directory containing
the source code for GDB, for now.  When you unpack the gdb-4.0.tar.Z
file, you'll get a directory called `gdb-4.0', which contains:

  Makefile.in       bfd/              configure.in      libiberty/
  README            config.sub*       gdb/              readline/
  README.configure  configure*        include/          texinfo/

To build GDB, you can just do:

	cd gdb-4.0
	./configure HOSTNAME
	make
	cp gdb/gdb /usr/local/bin/gdb	(or wherever you want)

This will configure and build all the libraries as well as GDB.
If you get compiler warnings during this stage, see the `Reporting Bugs'
section below; there are a few known problems.

GDB can be used as a cross-debugger, running on a machine of one type
while debugging a program running on a machine of another type.  See below.


More Documentation
==================

   The GDB 4.0 release includes an already-formatted reference card, ready
for printing on a PostScript printer, as `gdb-4.0/gdb/refcard.ps'.  It
uses the most common PostScript fonts: the Times family, Courier,
and Symbol.  If you have a PostScript printer you can print the
reference card by just sending `refcard.ps' to the printer.

   The release also includes the online Info version of the manual
already formatted: the main Info file is `gdb-4.0/gdb/gdb.info', and
it refers to subordinate files matching `gdb.info*' in the same
directory.

   If you want to make these Info files yourself from the GDB
manual's source, you need the GNU `makeinfo' program.  Once you have
it, you can type

     cd gdb-4.0/gdb
     make gdb.info

to make the Info file.

   If you want to format and print copies of this manual, you need
several things:

   * TeX, the public domain typesetting program written by Donald
     Knuth, must be installed on your system and available through
     your execution path.

   * `gdb-4.0/texinfo': TeX macros defining the GNU Documentation
     Format.

   * *A DVI output program.*  TeX doesn't actually make marks on
     paper; it produces output files called DVI files.  If your
     system has TeX installed, chances are it has a program for
     printing out these files; one popular example is `dvips', which
     can print DVI files on PostScript printers.

Once you have these things, you can type

     cd gdb-4.0/gdb
     make gdb.dvi

to format the text of this manual, and print it with the usual output
method for TeX DVI files at your site.

   If you want to print the reference card, but don't have a PostScript
printer, or want to print using Computer Modern fonts instead, you can
still print it if you have TeX.  Format the reference card by typing

     cd gdb-4.0/gdb
     make refcard.dvi

The GDB reference card is designed to print in landscape mode on US
"letter" size paper; that is, on a sheet 11 inches wide by 8.5
inches high.  You will need to specify this form of printing as an
option to your DVI output program.


Installing GDB
==============

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

   The gdb distribution includes all the source code you need for gdb
in a single directory `gdb-4.0'.  That directory in turn contains:

`gdb-4.0/configure'
     Overall script for configuring GDB and all its supporting
     libraries.

`gdb-4.0/gdb'
     the source specific to GDB itself

`gdb-4.0/bfd'
     source for the Binary File Descriptor Library

`gdb-4.0/include'
     GNU include files

`gdb-4.0/libiberty'
     source for the `-liberty' free software library

`gdb-4.0/readline'
     source for the GNU command-line interface

Each of these directories has its own `configure' script, which are
used by the overall `configure' script in `gdb-4.0'.

   It is most convenient to run `configure' from the `gdb-4.0'
directory.  The simplest way to configure and build GDB is the
following:

     cd gdb-4.0
     ./configure HOST
     make

where HOST is something like `sun4' or `decstation', that identifies
the platform where GDB will run.  This builds the three libraries
`bfd', `readline', and `libiberty', then `gdb' itself.  The
configured source files, and the binaries, are left in the
corresponding source directories.

   You can install `gdb' anywhere; it has no hardwired paths. 
However, you should make sure that the shell on your path (named by
the `SHELL' environment variable) is publicly readable; some systems
refuse to let GDB debug child processes whose programs are not
readable, and GDB uses the shell to start your program.

Configuration Subdirectories
============================

   If you want to run GDB versions for several host or target
machines, you'll need a different gdb 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.  If your `make' program handles the `VPATH' feature
(GNU `make' does), running `make' in each of these directories then
builds the gdb program specified there.

   `configure' creates these subdirectories for you when you
simultaneously specify several configurations; but it's a good habit
even for a single configuration.  You can specify the use of
subdirectories using the `+subdirs' option (abbreviated `+sub'). 
For example, you can build GDB on a Sun 4 as follows:

     cd gdb-4.0
     ./configure +sub sun4
     cd Host-sparc-sun-sunos4/Target-sparc-sun-sunos4
     make

   When `configure' uses subdirectories to build programs or
libraries, it creates nested directories `Host-HOST/Target-TARGET'. 
(As you see in the example, the names used for HOST and TARGET may
be expanded from your `configure' argument; *note Config Names::.).
`configure' uses these two directory levels because GDB can be
configured for cross-compiling: GDB can run on one machine (the
host) while debugging programs that run on another machine (the
target).  You specify cross-debugging targets by giving the
`+target=TARGET' option to `configure'.  Specifying only hosts still
gives you two levels of subdirectory for each host, with the same
configuration suffix on both; that is, if you give any number of
hosts but no targets, GDB will be configured for native debugging on
each host.  On the other hand, whenever you specify both hosts and
targets on the same command line, `configure' creates all
combinations of the hosts and targets you list.

   When you run `make' to build a program or library, you must run it
in a configured directory.  If you made a single configuration,
without subdirectories, run `make' in the source directory.  If you
have `Host-HOST/Target-TARGET' subdirectories, run `make' in those
subdirectories.

   Each `configure' and `Makefile' under each source directory runs
recursively, so that typing `make' in `gdb-4.0' (or in a
`gdb-4.0/Host-HOST/Target-TARGET' subdirectory) builds all the
required libraries, then GDB.

   If you run `configure' from a directory (such as `gdb-4.0') that
contains source directories for multiple libraries or programs,
`configure' creates the `Host-HOST/Target-TARGET' subdirectories in
each library or program's source directory.  For example, typing:

     cd gdb-4.0
     configure sun4 +target=vxworks960

creates the following directories:

     gdb-4.0/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
     gdb-4.0/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
     gdb-4.0/gdb/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
     gdb-4.0/libiberty/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks
     gdb-4.0/readline/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks

The `Makefile' in

     gdb-4.0/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks

will `cd' to the appropriate lower-level directories, for example:

     gdb-4.0/bfd/Host-sparc-sun-sunos4/Target-i960-wrs-vxworks

building each in turn.

   When you have multiple hosts or targets configured, 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, but the full name of that configuration
specifies that the architecture is `sparc', the vendor is `sun', and
the operating system is `sunos4'.

   The following table shows all the architectures, hosts, and OS
prefixes that `configure' recognizes in GDB 4.0.  Entries in the "OS
prefix"
column ending in a `*' may be followed by a release number.


     ARCHITECTURE  VENDOR        OS prefix
     ------------+-------------+-------------
                 |             |
      a29k       | altos       | aix*
      alliant    | aout        | aout
      arm        | apollo      | bout
      c1         | att         | bsd*
      c2         | bout        | coff
      i386       | coff        | ctix*
      i860       | convergent  | dynix*
      i960       | convex      | esix*
      m68000     | dec         | hpux*
      m68k       | encore      | isc*
      m88k       | gould       | mach*
      mips       | hp          | newsos*
      ns32k      | ibm         | nindy*
      pyramid    | intel       | none
      rs6000     | isi         | osf*
      rtpc       | little      | sco*    
      sparc      | mips        | sunos*  
      tahoe      | motorola    | sysv*   
      tron       | ncr         | ultrix* 
      vax        | next        | unos*   
                 | none        | v88r*   
                 | sco         | vms*    
                 | sequent     | vxworks*
                 | sgi         | 
                 | sony        |
                 | sun         |
                 | unicom      |
                 | utek        |
                 | wrs         |

     *Warning:* Many combinations of architecture, vendor, and OS are
     untested.

   The `configure' script accompanying GDB 4.0 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-sunos4
     % sh config.sub sun3
     m68k-sun-sunos4
     % sh config.sub decstation
     mips-dec-ultrix
     % sh config.sub hp300bsd
     m68k-hp-bsd
     % sh config.sub i386v
     i386-none-sysv
     % sh config.sub i486v
     *** No vendor: configuration `i486v' not recognized

`configure' Options
===================

   Here is a summary of all the `configure' options and arguments
that you might use for building GDB:

     configure [+destdir=DIR] [+subdirs] [+norecur] [+rm]
               [+target=TARGET...] HOST...

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

`+destdir=DIR'
     DIR is an installation directory *path prefix*.  After you
     configure with this option, `make install' will install GDB as
     `DIR/bin/gdb', and the libraries in `DIR/lib'.  If you specify
     `+destdir=/usr/local', for example, `make install' creates
     `/usr/local/bin/gdb'.

`+subdirs'
     Write configuration specific files in subdirectories of the form

          Host-HOST/Target-TARGET

     (and configure the `Makefile' to write binaries there too). 
     Without this option, if you specify only one configuration for
     GDB, `configure' will use the same directory for source,
     configured files, and binaries.  This option is used
     automatically if you specify more than one HOST or more than
     one
     `+target=TARGET' option on the `configure' command line.

`+norecur'
     Configure only the directory where `configure' is executed; do
     not propagate configuration to subdirectories.

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

`+target=TARGET ...'
     Configure GDB for cross-debugging programs running on each
     specified TARGET.  You may specify as many `+target' options as
     you wish.  Without this option, GDB is configured to debug
     programs that run on the same machine (HOST) as GDB itself.

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

`HOST ...'
     Configure GDB to run on each specified HOST.  You may specify as
     many host names as you wish.

     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 GDB or its supporting libraries.


		Languages other than C

C++ support has been integrated into gdb.  GDB should work with FORTRAN
programs.  (If you have problems, please send a bug report; you may
have to refer to some FORTRAN variables with a trailing underscore).
Andrew Beers has produced a GDB that works with Modula-2, which will
appear in gdb-4.1.  I am not aware of anyone who is working on getting
gdb to use the syntax of any other language.  Pascal programs which use
sets, subranges, file variables, or nested functions will not currently
work.


		Kernel debugging

I have't done this myself so I can't really offer any advice.
Remote debugging over serial lines works fine, but the kernel debugging
code in here has not been tested in years.  Van Jacobson claims to have
better kernel debugging, but won't release it for ordinary mortals.


		Remote debugging

The files m68k-stub.c and i386-stub.c contain two examples of remote
stubs to be used with remote.c.  They are designeded to run standalone
on a 68k or 386 cpu and communicate properly with the remote.c stub
over a serial line.

The file rem-multi.shar contains a general stub that can probably
run on various different flavors of unix to allow debugging over a
serial line from one machine to another.

The files remote-eb.c and remote-nindy.c are two examples of remote
interfaces for talking to existing ROM monitors (for the AMD 29000 and the
Intel 960 repsectively).

Remote-vx.c and the vx-share subdirectory contain a remote interface for the
VxWorks realtime kernel, which communicates over TCP using the Sun
RPC library.  This would be a useful starting point for other remote-
via-ethernet back ends.

[This section seems to be out of date, I have never seen the "rapp"
program, though I would like to.  FIXME.]
`rapp' runs under unix and acts as a remote stub (like rem-multi.shar
distributed with GDB version 3).  Currently it just works over UDP
(network), not over a serial line.  To get it running
* Compile GDB on the host machine as usual
* Compile rapp on the target machine, giving for both host and target
  the type of the target machine
* Install "gdb" in /etc/services on both machines.


		Reporting Bugs

The correct address for reporting bugs found in gdb is
"bug-gdb@prep.ai.mit.edu".  Please email all bugs to that address.

GDB can produce warnings about symbols that it does not understand.  By
default, these warnings are disabled.  You can enable them by executing
`set complaint 10' (which you can put in your ~/.gdbinit if you like).
I recommend doing this if you are working on a compiler, assembler,
linker, or gdb, since it will point out problems that you may be able
to fix.  Warnings produced during symbol reading indicate some mismatch
between the object file and GDB's symbol reading code (in many cases,
it's a mismatch between the specs for the object file format, and what
the compiler actually outputs or the debugger actually understands).

If you port gdb to a new machine, please send the required changes
to bug-gdb@prep.ai.mit.edu.  If your changes are more than a few
lines, obtain and send in a copyright assignment from gnu@prep.ai.mit.edu, as
described in the section `Writing Code for GDB'.


		X Windows versus GDB

xgdb is obsolete.  We are not doing any development or support of it.

There is an "xxgdb", which shows more promise, which was posted to
comp.sources.x.

For those intersted in auto display of source and the availability of
an editor while debugging I suggest trying gdb-mode in gnu-emacs
(Try typing M-x gdb RETURN).  Comments on this mode are welcome.


		About the machine-dependent files

tconfig/<machine>
This contains Makefile stuff for when the target system is <machine>.
It also specifies the name of the tm-XXX.h file for this machine.

xconfig/<machine>
This contains Makefile stuff for when the host system is <machine>.
It also specifies the name of the xm-XXX.h file for this machine.

tm-XXX.h (tm.h is a link to this file, created by configure).
This file contains macro definitions about the target machine's
registers, stack frame format and instructions.

xm-XXX.h (xm.h is a link to this file, created by configure).
This contains macro definitions describing the host system environment,
such as byte order, host C compiler and library, ptrace support,
and core file structure.

<machine>-opcode.h
<machine>-pinsn.c
These files contain the information necessary to print instructions
for your cpu type.  <machine>-opcode.h includes some large initialized
data structures, which is strange for a ".h" file, but it's OK since
it is only included in one place.  <machine>-opcode.h is shared
between the debugger and the assembler (if the GNU assembler has been
ported to that machine), whereas <machine>-pinsn.c is specific to GDB.

<machine>-tdep.c
This file contains any miscellaneous code required for this machine
as a target.  On some machines it doesn't exist at all.  Its existence
is specified in the tconfig/XXX file.

<machine>-xdep.c
This file contains any miscellaneous code required for this machine
as a host.  On some machines it doesn't exist at all.  Its existence
is specified in the xconfig/XXX file.

infptrace.c
This is the low level interface to inferior processes for systems
using the Unix ptrace call in a vanilla way.  Some systems have their
own routines in <machine>-xdep.c.  Whether or not it is used
is specified in the xconfig/XXX file.

coredep.c
Machine and system-dependent aspects of reading core files.  Some
machines use coredep.c; some have the routines in <machine>-xdep.c.
Whether or not it is used is specified in the xconfig/XXX file.
Now that BFD is used to read core files, virtually all machines should
use coredep.c and should just provide fetch_core_registers in
<machine>-xdep.c.

exec.c 
Machine and system-dependent aspects of reading executable files.
Some machines use exec.c; some have the routines in <machine>-tdep.c
Since BFD, virtually all machines should use exec.c.


		Writing Code for GDB

We appreciate having users contribute code that is of general use, but
for it to be included in future GDB releases it must be cleanly
written.  We do not want to include changes that will needlessly make
future maintainance difficult.  It is not much harder to do things
right, and in the long term it is worth it to the GNU project, and
probably to you individually as well.

Please code according to the GNU coding standards.  If you do not have
a copy, you can request one by sending mail to gnu@prep.ai.mit.edu.

If you make substantial changes, you'll have to file a copyright
assignment with the Free Software Foundation before we can produce a
release that includes your changes.  Send mail requesting the copyright
assignment to gnu@prep.ai.mit.edu.  Do this early, like before the
changes actually work, or even before you start them, because a manager
or lawyer on your end will probably make this a slow process.

Please try to avoid making machine-specific changes to
machine-independent files.  If this is unavoidable, put a hook in the
machine-independent file which calls a (possibly) machine-dependent
macro (for example, the IGNORE_SYMBOL macro can be used for any
symbols which need to be ignored on a specific machine.  Calling
IGNORE_SYMBOL in dbxread.c is a lot cleaner than a maze of #if
defined's).  The machine-independent code should do whatever "most"
machines want if the macro is not defined in param.h.  Using #if
defined can sometimes be OK (e.g. SET_STACK_LIMIT_HUGE) but should be
conditionalized on a specific feature of an operating system (set in
tm.h or xm.h) rather than something like #if defined(vax) or #if
defined(SYSV).  If you use an #ifdef on some symbol that is defined
in a header file (e.g. #ifdef TIOCSETP), *please* make sure that you
have #include'd the relevant header file in that module!

It is better to replace entire routines which may be system-specific,
rather than put in a whole bunch of hooks which are probably not going
to be helpful for any purpose other than your changes.  For example,
if you want to modify dbxread.c to deal with DBX debugging symbols
which are in COFF files rather than BSD a.out files, do something
along the lines of a macro GET_NEXT_SYMBOL, which could have
different definitions for COFF and a.out, rather than trying to put
the necessary changes throughout all the code in dbxread.c that
currently assumes BSD format.

Please avoid duplicating code.  For example, in GDB 3.x all the stuff
in infptrace.c was duplicated in *-dep.c, and so changing something
was very painful.  In GDB 4.x, these have all been consolidated
into infptrace.c.  infptrace.c can deal with variations between
systems the same way any system-independent file would (hooks, #if
defined, etc.), and machines which are radically different don't need
to use infptrace.c at all.  The same was true of core_file_command
and exec_file_command.


		Debugging gdb with itself

If gdb is limping on your machine, this is the preferred way to get it
fully functional.  Be warned that in some ancient Unix systems, like
Ultrix 4.0, a program can't be running in one process while it is being
debugged in another.  Rather than doing "./gdb ./gdb", which works on
Suns and such, you can copy gdb to gdb2 and then do "./gdb ./gdb2".

When you run gdb in this directory, it will read a ".gdbinit" file that
sets up some simple things to make debugging gdb easier.  The "info"
command, when executed without a subcommand in a gdb being debugged by
gdb, will pop you back up to the top level gdb.  See .gdbinit for details.

I strongly recommend printing out the reference card and using it.
Send reference-card suggestions to bug-gdb@prep.ai.mit.edu, just like bugs.

If you use emacs, you will probably want to do a "make TAGS" after you
configure your distribution; this will put the machine dependent
routines for your local machine where they will be accessed first by a
M-period.

Also, make sure that you've compiled gdb with your local cc or taken
appropriate precautions regarding ansification of include files.  See
the Makefile for more information.

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