gdbint.texinfo

早期freebsd实现

\input texinfo
@setfilename gdbint.info
@c $Id: gdbint.texinfo,v 1.41 1992/10/21 21:11:55 gnu Exp $

@ifinfo
@format
START-INFO-DIR-ENTRY
* Gdb-Internals: (gdbint).	The GNU debugger's internals.
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@ifinfo
This file documents the internals of the GNU debugger GDB.

Copyright 1990, 1991, 1992 Free Software Foundation, Inc.
Contributed by Cygnus Support.  Written by John Gilmore.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy or distribute modified versions of this
manual under the terms of the GPL (for which purpose this text may be
regarded as a program in the language TeX).
@end ifinfo

@setchapternewpage off
@settitle GDB Internals
@titlepage
@title{Working in GDB}
@subtitle{A guide to the internals of the GNU debugger}
@author John Gilmore
@author Cygnus Support
@page
@tex
\def\$#1${{#1}}  % Kluge: collect RCS revision info without $...$
\xdef\manvers{\$Revision: 1.41 $}  % For use in headers, footers too
{\parskip=0pt
\hfill Cygnus Support\par
\hfill \manvers\par
\hfill \TeX{}info \texinfoversion\par
}
@end tex

@vskip 0pt plus 1filll
Copyright @copyright{} 1990, 1991, 1992 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@end titlepage

@node Top
@top
This documents the internals of the GNU debugger, GDB.  It is a
collection of miscellaneous information with little form at this point.
Mostly, it is a repository into which you can put information about
GDB as you discover it (or as you design changes to GDB).

@menu
* README::			The README File
* New Architectures::		Defining a New Host or Target Architecture
* Config::			Adding a New Configuration
* Host::			Adding a New Host
* Native::			Adding a New Native Configuration
* Target::			Adding a New Target
* Languages::			Defining New Source Languages
* Releases::			Configuring GDB for Release
* Partial Symbol Tables::	How GDB reads symbols quickly at startup
* BFD support for GDB::		How BFD and GDB interface
* Symbol Reading::		Defining New Symbol Readers
* Cleanups::			Cleanups
* Wrapping::			Wrapping Output Lines
* Frames::			Keeping track of function calls
* Coding Style::		Strunk and White for GDB maintainers
* Host Conditionals::		What features exist in the host
* Target Conditionals::		What features exist in the target
* Native Conditionals::		Conditionals for when host and target are same
* Obsolete Conditionals::	Conditionals that don't exist any more

@end menu

@node README
@chapter The @file{README} File

Check the @file{README} file, it often has useful information that does not
appear anywhere else in the directory.


@node New Architectures
@chapter Defining a New Host or Target Architecture

When building support for a new host and/or target, much of the work you
need to do is handled by specifying configuration files;
@pxref{Config,,Adding a New Configuration}.  Further work can be
divided into ``host-dependent'' (@pxref{Host,,Adding a New Host}) and
``target-dependent'' (@pxref{Target,,Adding a New Target}).  The
following discussion is meant to explain the difference between hosts
and targets.

@heading What is considered ``host-dependent'' versus ``target-dependent''?

@dfn{Host} refers to attributes of the system where GDB runs.
@dfn{Target} refers to the system where the program being debugged
executes.   In most cases they are the same machine, in which case
a third type of @dfn{Native} attributes come into play.

Defines and include files needed to build on the host are host support.
Examples are tty support, system defined types, host byte order, host
float format.

Defines and information needed to handle the target format are target
dependent.  Examples are the stack frame format, instruction set,
breakpoint instruction, registers, and how to set up and tear down the stack
to call a function.

Information that is only needed when the host and target are the same,
is native dependent.  One example is Unix child process support; if the
host and target are not the same, doing a fork to start the target
process is a bad idea.  The various macros needed for finding the
registers in the @code{upage}, running @code{ptrace}, and such are all in the
native-dependent files.

Another example of native-dependent code is support for features
that are really part of the target environment, but which require 
@code{#include} files that are only available on the host system.
Core file handling and @code{setjmp} handling are two common cases.

When you want to make GDB work ``native'' on a particular
machine, you have to include all three kinds of information.

The dependent information in GDB is organized into files by naming
conventions.  

Host-Dependent Files
@table @file
@item	config/*.mh
Sets Makefile parameters
@item	xm-*.h
Global #include's and #define's and definitions
@item	*-xdep.c
Global variables and functions
@end table

Native-Dependent Files
@table @file
@item	config/*.mh
Sets Makefile parameters (for @emph{both} host and native)
@item	nm-*.h
#include's and #define's and definitions.  This file
is only included by the small number of modules that need it,
so beware of doing feature-test #define's from its macros.
@item	*-nat.c
global variables and functions
@end table

Target-Dependent Files
@table @file
@item	config/*.mt
Sets Makefile parameters
@item	tm-*.h
Global #include's and #define's and definitions
@item	*-tdep.c
Global variables and functions
@end table

At this writing, most supported hosts have had their host and native
dependencies sorted out properly.  There are a few stragglers, which
can be recognized by the absence of NATDEPFILES lines in their
@file{config/*.mh}.

@node Config
@chapter Adding a New Configuration

Most of the work in making GDB compile on a new machine is in specifying
the configuration of the machine.  This is done in a dizzying variety of
header files and configuration scripts, which we hope to make more
sensible soon.  Let's say your new host is called an @var{xxx} (e.g.
@samp{sun4}), and its full three-part configuration name is
@code{@var{xarch}-@var{xvend}-@var{xos}} (e.g.  @samp{sparc-sun-sunos4}).  In
particular:

In the top level directory, edit @file{config.sub} and add @var{xarch},
@var{xvend}, and @var{xos} to the lists of supported architectures,
vendors, and operating systems near the bottom of the file.  Also, add
@var{xxx} as an alias that maps to
@code{@var{xarch}-@var{xvend}-@var{xos}}.  You can test your changes by
running

@example
./config.sub @var{xxx}
@end example
@noindent
and
@example
./config.sub @code{@var{xarch}-@var{xvend}-@var{xos}}
@end example
@noindent
which should both respond with @code{@var{xarch}-@var{xvend}-@var{xos}}
and no error messages.

Now, go to the @file{bfd} directory and 
create a new file @file{bfd/hosts/h-@var{xxx}.h}.  Examine the
other @file{h-*.h} files as templates, and create one that brings in the
right include files for your system, and defines any host-specific
macros needed by BFD, the Binutils, GNU LD, or the Opcodes directories.
(They all share the bfd @file{hosts} directory and the @file{configure.host}
file.)

Then edit @file{bfd/configure.host}.  Add a line to recognize your
@code{@var{xarch}-@var{xvend}-@var{xos}} configuration, and set
@code{my_host} to @var{xxx} when you recognize it.  This will cause your
file @file{h-@var{xxx}.h} to be linked to @file{sysdep.h} at configuration
time.  When creating the line that recognizes your configuration,
only match the fields that you really need to match; e.g. don't match
match the architecture or manufacturer if the OS is sufficient
to distinguish the configuration that your @file{h-@var{xxx}.h} file supports.
Don't match the manufacturer name unless you really need to.
This should make future ports easier.

Also, if this host requires any changes to the Makefile, create a file
@file{bfd/config/@var{xxx}.mh}, which includes the required lines.

It's possible that the @file{libiberty} and @file{readline} directories
won't need any changes for your configuration, but if they do, you can
change the @file{configure.in} file there to recognize your system and
map to an @file{mh-@var{xxx}} file.  Then add @file{mh-@var{xxx}}
to the @file{config/} subdirectory, to set any makefile variables you
need.  The only current options in there are things like @samp{-DSYSV}.
(This @file{mh-@var{xxx}} naming convention differs from elsewhere
in GDB, by historical accident.  It should be cleaned up so that all
such files are called @file{@var{xxx}.mh}.)

Aha!  Now to configure GDB itself!  Edit
@file{gdb/configure.in} to recognize your system and set @code{gdb_host}
to @var{xxx}, and (unless your desired target is already available) also
set @code{gdb_target} to something appropriate (for instance,
@var{xxx}).  To handle new hosts, modify the segment after the comment
@samp{# per-host}; to handle new targets, modify after @samp{#
per-target}.
@c Would it be simpler to just use different per-host and per-target
@c *scripts*, and call them from {configure} ?

Finally, you'll need to specify and define GDB's host-, native-, and
target-dependent @file{.h} and @file{.c} files used for your
configuration; the next two chapters discuss those.


@node Host
@chapter Adding a New Host

Once you have specified a new configuration for your host
(@pxref{Config,,Adding a New Configuration}), there are three remaining
pieces to making GDB work on a new machine.  First, you have to make it
host on the new machine (compile there, handle that machine's terminals
properly, etc).  If you will be cross-debugging to some other kind of
system that's already supported, you are done.

If you want to use GDB to debug programs that run on the new machine,
you have to get it to understand the machine's object files, symbol
files, and interfaces to processes; @pxref{Target,,Adding a New Target}
and @pxref{Native,,Adding a New Native Configuration}

Several files control GDB's configuration for host systems:

@table @file
@item gdb/config/mh-@var{xxx}
Specifies Makefile fragments needed when hosting on machine @var{xxx}.
In particular, this lists the required machine-dependent object files,
by defining @samp{XDEPFILES=@dots{}}.  Also
specifies the header file which describes host @var{xxx}, by defining
@samp{XM_FILE= xm-@var{xxx}.h}.  You can also define @samp{CC},
@samp{REGEX} and @samp{REGEX1}, @samp{SYSV_DEFINE}, @samp{XM_CFLAGS},
@samp{XM_ADD_FILES}, @samp{XM_CLIBS}, @samp{XM_CDEPS},
etc.; see @file{Makefile.in}.

@item gdb/xm-@var{xxx}.h
(@file{xm.h} is a link to this file, created by configure).
Contains C macro definitions describing the host system environment,
such as byte order, host C compiler and library, ptrace support,
and core file structure.  Crib from existing @file{xm-*.h} files
to create a new one.

@item gdb/@var{xxx}-xdep.c
Contains any miscellaneous C code required for this machine
as a host.  On many machines it doesn't exist at all.  If it does
exist, put @file{@var{xxx}-xdep.o} into the @code{XDEPFILES} line
in @file{gdb/config/mh-@var{xxx}}.
@end table

@subheading Generic Host Support Files

There are some ``generic'' versions of routines that can be used by
various systems.  These can be customized in various ways by macros
defined in your @file{xm-@var{xxx}.h} file.  If these routines work for
the @var{xxx} host, you can just include the generic file's name (with
@samp{.o}, not @samp{.c}) in @code{XDEPFILES}.  

Otherwise, if your machine needs custom support routines, you will need
to write routines that perform the same functions as the generic file.
Put them into @code{@var{xxx}-xdep.c}, and put @code{@var{xxx}-xdep.o}
into @code{XDEPFILES}.

@table @file
@item ser-bsd.c
This contains serial line support for Berkeley-derived Unix systems.

@item ser-go32.c
This contains serial line support for 32-bit programs running under DOS
using the GO32 execution environment.

@item ser-termios.c
This contains serial line support for System V-derived Unix systems.
@end table

Now, you are now ready to try configuring GDB to compile using your system
as its host.  From the top level (above @file{bfd}, @file{gdb}, etc), do:

@example
./configure @var{xxx} +target=vxworks960
@end example

This will configure your system to cross-compile for VxWorks on
the Intel 960, which is probably not what you really want, but it's
a test case that works at this stage.  (You haven't set up to be
able to debug programs that run @emph{on} @var{xxx} yet.)

If this succeeds, you can try building it all with:

@example
make
@end example

Repeat until the program configures, compiles, links, and runs.
When run, it won't be able to do much (unless you have a VxWorks/960
board on your network) but you will know that the host support is
pretty well done.

Good luck!  Comments and suggestions about this section are particularly
welcome; send them to @samp{bug-gdb@@prep.ai.mit.edu}.

@node Native
@chapter Adding a New Native Configuration

If you are making GDB run native on the @var{xxx} machine, you have
plenty more work to do.  Several files control GDB's configuration for
native support:

@table @file
@item gdb/config/@var{xxx}.mh
Specifies Makefile fragments needed when hosting @emph{or native}
on machine @var{xxx}.
In particular, this lists the required native-dependent object files,
by defining @samp{NATDEPFILES=@dots{}}.  Also
specifies the header file which describes native support on @var{xxx},
by defining @samp{NM_FILE= nm-@var{xxx}.h}.
You can also define @samp{NAT_CFLAGS},
@samp{NAT_ADD_FILES}, @samp{NAT_CLIBS}, @samp{NAT_CDEPS},
etc.; see @file{Makefile.in}.

@item gdb/nm-@var{xxx}.h
(@file{nm.h} is a link to this file, created by configure).
Contains C macro definitions describing the native system environment,
such as child process control and core file support.
Crib from existing @file{nm-*.h} files to create a new one.
Code that needs these definitions will have to @code{#include "nm.h"}
explicitly, since it is not included by @file{defs.h}.

@item gdb/@var{xxx}-nat.c
Contains any miscellaneous C code required for this native support
of this machine.  On some machines it doesn't exist at all.
@end table

@subheading Generic Native Support Files

There are some ``generic'' versions of routines that can be used by
various systems.  These can be customized in various ways by macros
defined in your @file{nm-@var{xxx}.h} file.  If these routines work for
the @var{xxx} host, you can just include the generic file's name (with
@samp{.o}, not @samp{.c}) in @code{NATDEPFILES}.  

Otherwise, if your machine needs custom support routines, you will need
to write routines that perform the same functions as the generic file.
Put them into @code{@var{xxx}-nat.c}, and put @code{@var{xxx}-nat.o}
into @code{NATDEPFILES}.  

@table @file

@item inftarg.c
This contains the @emph{target_ops vector} that supports Unix child
processes on systems which use ptrace and wait to control the child.

@item procfs.c
This contains the @emph{target_ops vector} that supports Unix child
processes on systems which use /proc to control the child.

@item fork-child.c
This does the low-level grunge that uses Unix system calls
to do a "fork and exec" to start up a child process.

@item infptrace.c
This is the low level interface to inferior processes for systems
using the Unix @code{ptrace} call in a vanilla way.

@item coredep.c::fetch_core_registers()
Support for reading registers out of a core file.  This routine calls
@code{register_addr()}, see below.
Now that BFD is used to read core files, virtually all machines should
use @code{coredep.c}, and should just provide @code{fetch_core_registers} in
@code{@var{xxx}-nat.c} (or @code{REGISTER_U_ADDR} in @code{nm-@var{xxx}.h}).

@item coredep.c::register_addr()
If your @code{nm-@var{xxx}.h} file defines the macro
@code{REGISTER_U_ADDR(addr, blockend, regno)}, it should be defined to
set @code{addr} to the offset within the @samp{user}
struct of GDB register number @code{regno}.  @code{blockend} is the
offset within the ``upage'' of @code{u.u_ar0}.
If @code{REGISTER_U_ADDR} is defined,
@file{coredep.c} will define the @code{register_addr()} function and use
the macro in it.  If you do not define @code{REGISTER_U_ADDR}, but you
are using the standard @code{fetch_core_registers()}, you will need to
define your own version of @code{register_addr()}, put it into your
@code{@var{xxx}-nat.c} file, and be sure @code{@var{xxx}-nat.o} is in
the @code{NATDEPFILES} list.  If you have your own
@code{fetch_core_registers()}, you may not need a separate
@code{register_addr()}.  Many custom @code{fetch_core_registers()}
implementations simply locate the registers themselves.@refill
@end table

When making GDB run native on a new operating system,
to make it possible to debug
core files, you will need to either write specific code for parsing your
OS's core files, or customize @file{bfd/trad-core.c}.  First, use
whatever @code{#include} files your machine uses to define the struct of
registers that is accessible (possibly in the u-area) in a core file
(rather than @file{machine/reg.h}), and an include file that defines whatever
header exists on a core file (e.g. the u-area or a @samp{struct core}).  Then
modify @code{trad_unix_core_file_p()} to use these values to set up the
section information for the data segment, stack segment, any other
segments in the core file (perhaps shared library contents or control
information), ``registers'' segment, and if there are two discontiguous
sets of registers (e.g.  integer and float), the ``reg2'' segment.  This
section information basically delimits areas in the core file in a
standard way, which the section-reading routines in BFD know how to seek
around in.

Then back in GDB, you need a matching routine called
@code{fetch_core_registers()}.  If you can use the generic one, it's in
@file{coredep.c}; if not, it's in your @file{@var{xxx}-nat.c} file.
It will be passed a char pointer to the entire ``registers'' segment,