Tue Aug 20 15:18:02 1991 Roland H. Pesch (pesch at cygint.cygnus.com)

[binutils.git] / gdb / README

		README for gdb-3.98 beta release
		John Gilmore	      31 July 91

This is GDB, the GNU source-level debugger, presently running under
un*x.  This is a beta test version of GDB version 4, and has not been
extensively tested.  It surely has some bugs, both bugs that were
present in version 3, and new bugs.  If your favorite bugfix is not
yet present here, I encourage you to port it into this version and
then send the diffs to [email protected].

A summary of features new since gdb-3.5 is in the file `WHATS.NEW'.


		Unpacking and Installation

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 gdb.  The idea is that a variety
of GNU tools can share a common copy of these things.

These generic files are packaged separately from GDB, in a tar file
called "bfd.ilrt-3.98.tar.Z".  ("ilrt" stands for include, libiberty,
readline, texinfo).  Unpack that tar file in the same directory in
which you unpacked the gdb-3.98.tar.Z file, so that for example the
'bfd' directory sits next to the 'gdb' directory.  The whole top-level
directory will look like this with `ls -F':

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

Once you have this stuff unpacked, and your current directory is here,
you can type:

	./configure HOSTNAME
	make

and all the libraries, as well as GDB will be configured and built.
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.  You
configure it this way by specifying `./configure host -target=target';
see below.


		More Documentation

The GDB manual is much expanded and improved.  For online browsing,
gdb/gdb.info is the main file, and there are gdb/gdb.info-1 through -6
files that can be installed into your main `info' tree.  If you want a
printed version of the manual, you can run, from the GDB source
directory,

	make gdb.dvi

to make the TeX device-independent output file.  This assumes you have
a running TeX on your system.  The source for the GDB manual is in
doc/gdb.texinfo (and a few other files it includes), provided with
this distribution.  The Makefile attempts to use the texinfo.tex
supplied as part of the BFD-and-libraries tar file, since the manual
uses Texinfo-2 which is not in common use yet.


		Configuration Details (extracted from gdb.texinfo)

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

   The `configure' script that's specific to GDB is distributed in
the main GDB source directory.  However, building GDB also requires
several other directories of source common to multiple GNU programs.
These directories (GNU libraries and includes) are distributed
separately, but their `configure' scripts and `Makefile's are
designed to work together.  To ensure that GDB's `Makefile' can find
all the pieces, you should make a single overall directory to hold
the directories of source for GNU libraries and includes, and you
should install the GDB source directory there too.  In this
Appendix, we refer to the directory of GNU source directories as GNUSRC.

   At a minimum, to build GDB you need the directories

`GNUSRC/gdb'
     the source specific to GDB itself

`GNUSRC/bfd'
     source for the Binary File Descriptor Library

`GNUSRC/include'
     GNU include files

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

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

Each of these directories has its own `configure' script.  GNUSRC has
an overall `configure' script, which is distributed with the GNU
libraries and includes.

   `configure' is designed to be called recursively, so it is most
convenient to run `configure' from the GNUSRC directory.  The
simplest way to configure and build GDB is the following:

     cd GNUSRC
     ./configure HOST
     make

where HOST is something like `sun4' or `vax', 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 build GDB for several host or target machines, and if your
`make' program handles the `VPATH' feature (GNU `make' does), it is
most convenient instead to build the different GDB configurations in
subdirectories (separate from the source).  `configure' does this
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 `+forcesubdirs' option
(abbreviated `+f').  For example, you can build GDB on a Sun 4 as
follows:

     cd GNUSRC
     ./configure +f sun4
     cd Host-sun4/Target-sun4
     make

   When `configure' uses subdirectories to build programs or
libraries, it creates nested directories `Host-HOST/Target-MACHINE'.
This is 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=MACHINE' option to `configure'.  Specifying
only hosts still gives you two levels of subdirectory for each host,
with the same machine-name suffix on both.  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-MACHINE' subdirectories, run `make' in those
subdirectories.

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

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

     cd GNUSRC
     configure sun4 +target=vx960

creates the following directories:

     GNUSRC/Host-sun4/Target-vx960
     GNUSRC/bfd/Host-sun4/Target-vx960
     GNUSRC/gdb/Host-sun4/Target-vx960
     GNUSRC/libiberty/Host-sun4/Target-vx960
     GNUSRC/readline/Host-sun4/Target-vx960

The `Makefile' in `GNUSRC/Host-sun4/Target-vx960' will `cd' to the
appropriate lower-level directories (such as
`GNUSRC/bfd/Host-sun4/Target-vx960'), 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.


		`configure' Options

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

     configure [+destdir=DIR] [+forcesubdirs] [+norecur] [+rm]
               [+target=MACHINE...] HOST...

You may introduce options with the character `-' rather than `+' if
you prefer; but options introduced with `+' may be truncated.

`+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'.

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

          Host-MACHINE/Target-MACHINE

     (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=MACHINE' 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 specified by other arguments.

`+target=MACHINE ...'
     Configure GDB for cross-debugging programs running on each
     specified MACHINE.  You may specify as many `+target' options
     as you wish.  To see a list of available targets, execute `ls
     tconfig' in the GDB source directory.  Without this option, GDB
     is configured to debug programs that run on the same machine
     (HOST) as GDB itself.

`HOST ...'
     Configure GDB to run on each specified HOST.  You may specify as
     many host names as you wish.  To see a list of available hosts,
     execute `ls xconfig' in the GDB source directory.

`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).
There is an effort to produce a GDB that works with Modula-2.  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
"[email protected]".  Please email all bugs to that address.

"mcheck.c", line 32, will produce a pointer conversion warning, which
can be ignored.

When gdb reads object files produced by the Sun bundled C compiler,
you will often get a "bad block start address patched" message.  You
can shut off such messages with the command `set complaint 0' (which
you can put in your ~/.gdbinit if you like).  Messages like this
during symbol reading indicate some mismatch between the object file
and GDB's symbol reading code (in this case, it's a mismatch
between the specs for the object file format, and what Sun's compiler
actually outputs).

If you port gdb to a new machine, please send the required changes
to [email protected].  If your changes are more than a few
lines, obtain and send in a copyright assignment from [email protected], 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 [email protected].

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 [email protected].  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.

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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