A target is the execution environment occupied by your program.
Often, GDB runs in the same host environment as your program; in
that case, the debugging target is specified as a side effect when you
use the file or core commands. When you need more
flexibility--for example, running GDB on a physically separate
host, or controlling a standalone system over a serial port or a
realtime system over a TCP/IP connection--you
can use the target command to specify one of the target types
configured for GDB (see section Commands for managing targets).
There are three classes of targets: processes, core files, and executable files. GDB can work concurrently on up to three active targets, one in each class. This allows you to (for example) start a process and inspect its activity without abandoning your work on a core file.
For example, if you execute `gdb a.out', then the executable file
a.out is the only active target. If you designate a core file as
well--presumably from a prior run that crashed and coredumped--then
GDB has two active targets and uses them in tandem, looking
first in the corefile target, then in the executable file, to satisfy
requests for memory addresses. (Typically, these two classes of target
are complementary, since core files contain only a program's
read-write memory--variables and so on--plus machine status, while
executable files contain only the program text and initialized data.)
When you type run, your executable file becomes an active process
target as well. When a process target is active, all GDB commands
requesting memory addresses refer to that target; addresses in an
active core file or
executable file target are obscured while the process
target is active.
Use the core-file and exec-file commands to select a
new core file or executable target (see section Commands to specify files). To specify as a target a process that is already running, use
the attach command (see section Debugging an already-running process).
target type parameters
target command does not repeat if you press RET again
after executing the command.
help target
info target or info files
(see section Commands to specify files).
help target name
set gnutarget args
set gnutarget command. Unlike most target commands,
with gnutarget the target refers to a program, not a machine.
Warning: To specify a file format with set gnutarget,
you must know the actual BFD name.
See section Commands to specify files.
show gnutarget
show gnutarget command to display what file format
gnutarget is set to read. If you have not set gnutarget,
GDB will determine the file format for each file automatically
and show gnutarget displays The current BDF target is "auto".
Here are some common targets (available, or not, depending on the GDB configuration):
target exec program
target core filename
target remote dev
target remote
now supports the load command. This is only useful if you have
some other way of getting the stub to the target system, and you can put
it somewhere in memory where it won't get clobbered by the download.
target sim
target udi keyword
target amd-eb dev speed PROG
target remote;
speed allows you to specify the linespeed; and PROG is the
name of the program to be debugged, as it appears to DOS on the PC.
See section The EBMON protocol for AMD29K.
target hms dev
device and speed to control the serial
line and the communications speed used.
See section GDB and Hitachi microprocessors.
target nindy devicename
target st2000 dev speed
target vxworks machinename
target bug dev
target cpu32bug dev
target op50n dev
target w89k dev
target est dev
target rom68k dev
target array dev
target sparclite dev
Different targets are available on different configurations of GDB; your configuration may have more or fewer targets.
You can now choose which byte order to use with a target system.
Use the set endian big and set endian little commands.
Use the set endian auto command to instruct
GDB to use the byte order associated with the executable.
You can see the current setting for byte order with the show endian
command.
Warning: Currently, only embedded MIPS configurations support
dynamic selection of target byte order.
If you are trying to debug a program running on a machine that cannot run GDB in the usual way, it is often useful to use remote debugging. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger.
Some configurations of GDB have special serial or TCP/IP interfaces to make this work with particular debugging targets. In addition, GDB comes with a generic serial protocol (specific to GDB, but not specific to any particular target system) which you can use if you write the remote stubs--the code that runs on the remote system to communicate with GDB.
Other remote targets may be available in your
configuration of GDB; use help target to list them.
To debug a program running on another machine (the debugging target machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need:
The next step is to arrange for your program to use a serial port to communicate with the machine where GDB is running (the host machine). In general terms, the scheme looks like this:
gdbserver instead of linking a stub into your program.
See section Using the gdbserver program, for details.
The debugging stub is specific to the architecture of the remote machine; for example, use `sparc-stub.c' to debug programs on SPARC boards.
These working remote stubs are distributed with GDB:
i386-stub.c
m68k-stub.c
sh-stub.c
sparc-stub.c
sparcl-stub.c
The `README' file in the GDB distribution may list other recently added stubs.
The debugging stub for your architecture supplies these three subroutines:
set_debug_traps
handle_exception to run when your
program stops. You must call this subroutine explicitly near the
beginning of your program.
handle_exception
handle_exception to
run when a trap is triggered.
handle_exception takes control when your program stops during
execution (for example, on a breakpoint), and mediates communications
with GDB on the host machine. This is where the communications
protocol is implemented; handle_exception acts as the GDB
representative on the target machine; it begins by sending summary
information on the state of your program, then continues to execute,
retrieving and transmitting any information GDB needs, until you
execute a GDB command that makes your program resume; at that point,
handle_exception returns control to your own code on the target
machine.
breakpoint
handle_exception---in effect, to GDB. On some machines,
simply receiving characters on the serial port may also trigger a trap;
again, in that situation, you don't need to call breakpoint from
your own program--simply running `target remote' from the host
GDB session gets control.
Call breakpoint if none of these is true, or if you simply want
to make certain your program stops at a predetermined point for the
start of your debugging session.
The debugging stubs that come with GDB are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine.
First of all you need to tell the stub how to communicate with the serial port.
int getDebugChar()
getchar for your target system; a
different name is used to allow you to distinguish the two if you wish.
void putDebugChar(int)
putchar for your target system; a
different name is used to allow you to distinguish the two if you wish.
If you want GDB to be able to stop your program while it is
running, you need to use an interrupt-driven serial driver, and arrange
for it to stop when it receives a ^C (`\003', the control-C
character). That is the character which GDB uses to tell the
remote system to stop.
Getting the debugging target to return the proper status to GDB
probably requires changes to the standard stub; one quick and dirty way
is to just execute a breakpoint instruction (the "dirty" part is that
GDB reports a SIGTRAP instead of a SIGINT).
Other routines you need to supply are:
void exceptionHandler (int exception_number, void *exception_address)
exceptionHandler.
void flush_i_cache()
You must also make sure this library routine is available:
void *memset(void *, int, int)
memset that sets an area of
memory to a known value. If you have one of the free versions of
libc.a, memset can be found there; otherwise, you must
either obtain it from your hardware manufacturer, or write your own.
If you do not use the GNU C compiler, you may need other standard
library subroutines as well; this varies from one stub to another,
but in general the stubs are likely to use any of the common library
subroutines which gcc generates as inline code.
In summary, when your program is ready to debug, you must follow these steps.
getDebugChar,putDebugChar,flush_i_cache,memset,exceptionHandler.
set_debug_traps(); breakpoint();
exceptionHook. Normally you just use:
void (*exceptionHook)() = 0;but if before calling
set_debug_traps, you set it to point to a
function in your program, that function is called when
GDB continues after stopping on a trap (for example, bus
error). The function indicated by exceptionHook is called with
one parameter: an int which is the exception number.
target remote command.
Its argument specifies how to communicate with the target
machine--either via a devicename attached to a direct serial line, or a
TCP port (usually to a terminal server which in turn has a serial line
to the target). For example, to use a serial line connected to the
device named `/dev/ttyb':
target remote /dev/ttybTo use a TCP connection, use an argument of the form
host:port. For example, to connect to port 2828 on a
terminal server named manyfarms:
target remote manyfarms:2828
Now you can use all the usual commands to examine and change data and to step and continue the remote program.
To resume the remote program and stop debugging it, use the detach
command.
Whenever GDB is waiting for the remote program, if you type the interrupt character (often C-C), GDB attempts to stop the program. This may or may not succeed, depending in part on the hardware and the serial drivers the remote system uses. If you type the interrupt character once again, GDB displays this prompt:
Interrupted while waiting for the program. Give up (and stop debugging it)? (y or n)
If you type y, GDB abandons the remote debugging session. (If you decide you want to try again later, you can use `target remote' again to connect once more.) If you type n, GDB goes back to waiting.
The stub files provided with GDB implement the target side of the communication protocol, and the GDB side is implemented in the GDB source file `remote.c'. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. `sparc-stub.c' is the best organized, and therefore the easiest to read.)
However, there may be occasions when you need to know something about the protocol--for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for GDB.
All GDB commands and responses (other than acknowledgements, which are single characters) are sent as a packet which includes a checksum. A packet is introduced with the character `$', and ends with the character `#' followed by a two-digit checksum:
$packet info#checksum
checksum is computed as the modulo 256 sum of the packet info characters.
When either the host or the target machine receives a packet, the first response expected is an acknowledgement: a single character, either `+' (to indicate the package was received correctly) or `-' (to request retransmission).
The host (GDB) sends commands, and the target (the debugging stub incorporated in your program) sends data in response. The target also sends data when your program stops.
Command packets are distinguished by their first character, which identifies the kind of command.
These are some of the commands currently supported (for a complete list of commands, look in `gdb/remote.c.'):
g
G
maddr,count
Maddr,count:...
c
caddr
s
saddr
k
?
T
If you have trouble with the serial connection, you can use the command
set remotedebug. This makes GDB report on all packets sent
back and forth across the serial line to the remote machine. The
packet-debugging information is printed on the GDB standard output
stream. set remotedebug off turns it off, and show
remotedebug shows you its current state.
gdbserver program
gdbserver is a control program for Unix-like systems, which
allows you to connect your program with a remote GDB via
target remote---but without linking in the usual debugging stub.
gdbserver is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that GDB itself does. In fact, a system that can run
gdbserver to connect to a remote GDB could also run
GDB locally! gdbserver is sometimes useful nevertheless,
because it is a much smaller program than GDB itself. It is
also easier to port than all of GDB, so you may be able to get
started more quickly on a new system by using gdbserver.
Finally, if you develop code for real-time systems, you may find that
the tradeoffs involved in real-time operation make it more convenient to
do as much development work as possible on another system, for example
by cross-compiling. You can use gdbserver to make a similar
choice for debugging.
GDB and gdbserver communicate via either a serial line
or a TCP connection, using the standard GDB remote serial
protocol.
gdbserver does not need your program's symbol table, so you can
strip the program if necessary to save space. GDB on the host
system does all the symbol handling.
To use the server, you must tell it how to communicate with GDB;
the name of your program; and the arguments for your program. The
syntax is:
target> gdbserver comm program [ args ... ]comm is either a device name (to use a serial line) or a TCP hostname and portnumber. For example, to debug Emacs with the argument `foo.txt' and communicate with GDB over the serial port `/dev/com1':
target> gdbserver /dev/com1 emacs foo.txt
gdbserver waits passively for the host GDB to communicate
with it.
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txtThe only difference from the previous example is the first argument, specifying that you are communicating with the host GDB via TCP. The `host:2345' argument means that
gdbserver is to
expect a TCP connection from machine `host' to local TCP port 2345.
(Currently, the `host' part is ignored.) You can choose any number
you want for the port number as long as it does not conflict with any
TCP ports already in use on the target system (for example, 23 is
reserved for telnet).(3) You must use the same port number with the host GDB
target remote command.
target
remote to establish communications with gdbserver. Its argument
is either a device name (usually a serial device, like
`/dev/ttyb'), or a TCP port descriptor in the form
host:PORT. For example:
(gdb) target remote /dev/ttybcommunicates with the server via serial line `/dev/ttyb', and
(gdb) target remote the-target:2345communicates via a TCP connection to port 2345 on host `the-target'. For TCP connections, you must start up
gdbserver prior to using
the target remote command. Otherwise you may get an error whose
text depends on the host system, but which usually looks something like
`Connection refused'.
gdbserve.nlm program
gdbserve.nlm is a control program for NetWare systems, which
allows you to connect your program with a remote GDB via
target remote.
GDB and gdbserve.nlm communicate via a serial line,
using the standard GDB remote serial protocol.
gdbserve.nlm does not need your program's symbol table, so you
can strip the program if necessary to save space. GDB on the
host system does all the symbol handling.
To use the server, you must tell it how to communicate with
GDB; the name of your program; and the arguments for your
program. The syntax is:
load gdbserve [ BOARD=board ] [ PORT=port ]
[ BAUD=baud ] program [ args ... ]
board and port specify the serial line; baud specifies
the baud rate used by the connection. port and node default
to 0, baud defaults to 9600 bps.
For example, to debug Emacs with the argument `foo.txt'and
communicate with GDB over serial port number 2 or board 1
using a 19200 bps connection:
load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
target
remote to establish communications with gdbserve.nlm. Its
argument is a device name (usually a serial device, like
`/dev/ttyb'). For example:
(gdb) target remote /dev/ttybcommunications with the server via serial line `/dev/ttyb'.
Nindy is a ROM Monitor program for Intel 960 target systems. When GDB is configured to control a remote Intel 960 using Nindy, you can tell GDB how to connect to the 960 in several ways:
target command at any point during your GDB
session. See section Commands for managing targets.
If you simply start gdb without using any command-line
options, you are prompted for what serial port to use, before you
reach the ordinary GDB prompt:
Attach /dev/ttyNN -- specify NN, or "quit" to quit:
Respond to the prompt with whatever suffix (after `/dev/tty')
identifies the serial port you want to use. You can, if you choose,
simply start up with no Nindy connection by responding to the prompt
with an empty line. If you do this and later wish to attach to Nindy,
use target (see section Commands for managing targets).
These are the startup options for beginning your GDB session with a Nindy-960 board attached:
-r port
tty (e.g. `-r a').
-O
Warning: if you specify `-O', but are actually trying to connect to a target system that expects the newer protocol, the connection fails, appearing to be a speed mismatch. GDB repeatedly attempts to reconnect at several different line speeds. You can abort this process with an interrupt.
-brk
BREAK signal to the target
system, in an attempt to reset it, before connecting to a Nindy target.
Warning: Many target systems do not have the hardware that this requires; it only works with a few boards.
The standard `-b' option controls the line speed used on the serial port.
reset
GDB supports AMD's UDI ("Universal Debugger Interface")
protocol for debugging the a29k processor family. To use this
configuration with AMD targets running the MiniMON monitor, you need the
program MONTIP, available from AMD at no charge. You can also
use GDB with the UDI-conformant a29k simulator program
ISSTIP, also available from AMD.
target udi keyword
AMD distributes a 29K development board meant to fit in a PC, together
with a DOS-hosted monitor program called EBMON. As a shorthand
term, this development system is called the "EB29K". To use
GDB from a Unix system to run programs on the EB29K board, you
must first connect a serial cable between the PC (which hosts the EB29K
board) and a serial port on the Unix system. In the following, we
assume you've hooked the cable between the PC's `COM1' port and
`/dev/ttya' on the Unix system.
The next step is to set up the PC's port, by doing something like this in DOS on the PC:
C:\> MODE com1:9600,n,8,1,none
This example--run on an MS DOS 4.0 system--sets the PC port to 9600 bps, no parity, eight data bits, one stop bit, and no "retry" action; you must match the communications parameters when establishing the Unix end of the connection as well.
To give control of the PC to the Unix side of the serial line, type the following at the DOS console:
C:\> CTTY com1
(Later, if you wish to return control to the DOS console, you can use
the command CTTY con---but you must send it over the device that
had control, in our example over the `COM1' serial line).
From the Unix host, use a communications program such as tip or
cu to communicate with the PC; for example,
cu -s 9600 -l /dev/ttya
The cu options shown specify, respectively, the linespeed and the
serial port to use. If you use tip instead, your command line
may look something like the following:
tip -9600 /dev/ttya
Your system may require a different name where we show
`/dev/ttya' as the argument to tip. The communications
parameters, including which port to use, are associated with the
tip argument in the "remote" descriptions file--normally the
system table `/etc/remote'.
Using the tip or cu connection, change the DOS working
directory to the directory containing a copy of your 29K program, then
start the PC program EBMON (an EB29K control program supplied
with your board by AMD). You should see an initial display from
EBMON similar to the one that follows, ending with the
EBMON prompt `#'---
C:\> G: G:\> CD \usr\joe\work29k G:\USR\JOE\WORK29K> EBMON Am29000 PC Coprocessor Board Monitor, version 3.0-18 Copyright 1990 Advanced Micro Devices, Inc. Written by Gibbons and Associates, Inc. Enter '?' or 'H' for help PC Coprocessor Type = EB29K I/O Base = 0x208 Memory Base = 0xd0000 Data Memory Size = 2048KB Available I-RAM Range = 0x8000 to 0x1fffff Available D-RAM Range = 0x80002000 to 0x801fffff PageSize = 0x400 Register Stack Size = 0x800 Memory Stack Size = 0x1800 CPU PRL = 0x3 Am29027 Available = No Byte Write Available = Yes # ~.
Then exit the cu or tip program (done in the example by
typing ~. at the EBMON prompt). EBMON keeps
running, ready for GDB to take over.
For this example, we've assumed what is probably the most convenient
way to make sure the same 29K program is on both the PC and the Unix
system: a PC/NFS connection that establishes "drive G:" on the
PC as a file system on the Unix host. If you do not have PC/NFS or
something similar connecting the two systems, you must arrange some
other way--perhaps floppy-disk transfer--of getting the 29K program
from the Unix system to the PC; GDB does not download it over the
serial line.
Finally, cd to the directory containing an image of your 29K
program on the Unix system, and start GDB---specifying as argument the
name of your 29K program:
cd /usr/joe/work29k gdb myfoo
Now you can use the target command:
target amd-eb /dev/ttya 9600 MYFOO
In this example, we've assumed your program is in a file called
`myfoo'. Note that the filename given as the last argument to
target amd-eb should be the name of the program as it appears to DOS.
In our example this is simply MYFOO, but in general it can include
a DOS path, and depending on your transfer mechanism may not resemble
the name on the Unix side.
At this point, you can set any breakpoints you wish; when you are ready
to see your program run on the 29K board, use the GDB command
run.
To stop debugging the remote program, use the GDB detach
command.
To return control of the PC to its console, use tip or cu
once again, after your GDB session has concluded, to attach to
EBMON. You can then type the command q to shut down
EBMON, returning control to the DOS command-line interpreter.
Type CTTY con to return command input to the main DOS console,
and type ~. to leave tip or cu.
The target amd-eb command creates a file `eb.log' in the
current working directory, to help debug problems with the connection.
`eb.log' records all the output from EBMON, including echoes
of the commands sent to it. Running `tail -f' on this file in
another window often helps to understand trouble with EBMON, or
unexpected events on the PC side of the connection.
To connect your ST2000 to the host system, see the manufacturer's manual. Once the ST2000 is physically attached, you can run:
target st2000 dev speed
to establish it as your debugging environment. dev is normally
the name of a serial device, such as `/dev/ttya', connected to the
ST2000 via a serial line. You can instead specify dev as a TCP
connection (for example, to a serial line attached via a terminal
concentrator) using the syntax hostname:portnumber.
The load and attach commands are not defined for
this target; you must load your program into the ST2000 as you normally
would for standalone operation. GDB reads debugging information
(such as symbols) from a separate, debugging version of the program
available on your host computer.
These auxiliary GDB commands are available to help you with the ST2000 environment:
st2000 command
connect
GDB enables developers to spawn and debug tasks running on networked
VxWorks targets from a Unix host. Already-running tasks spawned from
the VxWorks shell can also be debugged. GDB uses code that runs on
both the Unix host and on the VxWorks target. The program
gdb is installed and executed on the Unix host. (It may be
installed with the name vxgdb, to distinguish it from a
GDB for debugging programs on the host itself.)
VxWorks-timeout args
vxworks-timeout.
This option is set by the user, and args represents the number of
seconds GDB waits for responses to rpc's. You might use this if
your VxWorks target is a slow software simulator or is on the far side
of a thin network line.
The following information on connecting to VxWorks was current when this manual was produced; newer releases of VxWorks may use revised procedures.
To use GDB with VxWorks, you must rebuild your VxWorks kernel
to include the remote debugging interface routines in the VxWorks
library `rdb.a'. To do this, define INCLUDE_RDB in the
VxWorks configuration file `configAll.h' and rebuild your VxWorks
kernel. The resulting kernel contains `rdb.a', and spawns the
source debugging task tRdbTask when VxWorks is booted. For more
information on configuring and remaking VxWorks, see the manufacturer's
manual.
Once you have included `rdb.a' in your VxWorks system image and set
your Unix execution search path to find GDB, you are ready to
run GDB. From your Unix host, run gdb (or vxgdb,
depending on your installation).
GDB comes up showing the prompt:
(vxgdb)
The GDB command target lets you connect to a VxWorks target on the
network. To connect to a target whose host name is "tt", type:
(vxgdb) target vxworks tt
GDB displays messages like these:
Attaching remote machine across net... Connected to tt.
GDB then attempts to read the symbol tables of any object modules loaded into the VxWorks target since it was last booted. GDB locates these files by searching the directories listed in the command search path (see section Your program's environment); if it fails to find an object file, it displays a message such as:
prog.o: No such file or directory.
When this happens, add the appropriate directory to the search path with
the GDB command path, and execute the target
command again.
If you have connected to the VxWorks target and you want to debug an
object that has not yet been loaded, you can use the GDB
load command to download a file from Unix to VxWorks
incrementally. The object file given as an argument to the load
command is actually opened twice: first by the VxWorks target in order
to download the code, then by GDB in order to read the symbol
table. This can lead to problems if the current working directories on
the two systems differ. If both systems have NFS mounted the same
filesystems, you can avoid these problems by using absolute paths.
Otherwise, it is simplest to set the working directory on both systems
to the directory in which the object file resides, and then to reference
the file by its name, without any path. For instance, a program
`prog.o' may reside in `vxpath/vw/demo/rdb' in VxWorks
and in `hostpath/vw/demo/rdb' on the host. To load this
program, type this on VxWorks:
-> cd "vxpath/vw/demo/rdb"
v Then, in GDB, type:
(vxgdb) cd hostpath/vw/demo/rdb (vxgdb) load prog.o
GDB displays a response similar to this:
Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
You can also use the load command to reload an object module
after editing and recompiling the corresponding source file. Note that
this makes GDB delete all currently-defined breakpoints,
auto-displays, and convenience variables, and to clear the value
history. (This is necessary in order to preserve the integrity of
debugger data structures that reference the target system's symbol
table.)
You can also attach to an existing task using the attach command as
follows:
(vxgdb) attach task
where task is the VxWorks hexadecimal task ID. The task can be running or suspended when you attach to it. Running tasks are suspended at the time of attachment.
GDB enables developers to debug tasks running on
Sparclet targets from a Unix host.
GDB uses code that runs on
both the Unix host and on the Sparclet target. The program
gdb is installed and executed on the Unix host.
timeout args
remotetimeout.
This option is set by the user, and args represents the number of
seconds GDB waits for responses.
When compiling for debugging, include the options "-g" to get debug information and "-Ttext" to relocate the program to where you wish to load it on the target. You may also want to add the options "-n" or "-N" in order to reduce the size of the sections.
sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
You can use objdump to verify that the addresses are what you intended.
sparclet-aout-objdump --headers --syms prog
Once you have set
your Unix execution search path to find GDB, you are ready to
run GDB. From your Unix host, run gdb
(or sparclet-aout-gdb, depending on your installation).
GDB comes up showing the prompt:
(gdbslet)
The GDB command file lets you choose with program to debug.
(gdbslet) file prog
GDB then attempts to read the symbol table of `prog'. GDB locates the file by searching the directories listed in the command search path. If the file was compiled with debug information (option "-g"), source files will be searched as well. GDB locates the source files by searching the directories listed in the directory search path (see section Your program's environment). If it fails to find a file, it displays a message such as:
prog: No such file or directory.
When this happens, add the appropriate directories to the search paths with
the GDB commands path and dir, and execute the
target command again.
The GDB command target lets you connect to a Sparclet target.
To connect to a target on serial port "ttya", type:
(gdbslet) target sparclet /dev/ttya Remote target sparclet connected to /dev/ttya main () at ../prog.c:3
GDB displays messages like these:
Connected to ttya.
Once connected to the Sparclet target,
you can use the GDB
load command to download the file from the host to the target.
The file name and load offset should be given as arguments to the load
command.
Since the file format is aout, the program must be loaded to the starting
address. You can use objdump to find out what this value is. The load
offset is an offset which is added to the VMA (virtual memory address)
of each of the file's sections.
For instance, if the program
`prog' was linked to text address 0x1201000, with data at 0x12010160
and bss at 0x12010170, in GDB, type:
(gdbslet) load prog 0x12010000 Loading section .text, size 0xdb0 vma 0x12010000
If the code is loaded at a different address then what the program was linked
to, you may need to use the section and add-symbol-file commands
to tell GDB where to map the symbol table.
You can now begin debugging the task using GDB's execution control
commands, b, step, run, etc. See the GDB
manual for the list of commands.
(gdbslet) b main Breakpoint 1 at 0x12010000: file prog.c, line 3. (gdbslet) run Starting program: prog Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3 3 char *symarg = 0; (gdbslet) step 4 char *execarg = "hello!"; (gdbslet)
GDB needs to know these things to talk to your Hitachi SH, H8/300, or H8/500:
Use the special gdb command `device port' if you
need to explicitly set the serial device. The default port is the
first available port on your host. This is only necessary on Unix
hosts, where it is typically something like `/dev/ttya'.
gdb has another special command to set the communications
speed: `speed bps'. This command also is only used from Unix
hosts; on DOS hosts, set the line speed as usual from outside GDB with
the DOS mode command (for instance, `mode
com2:9600,n,8,1,p' for a 9600 bps connection).
The `device' and `speed' commands are available only when you
use a Unix host to debug your Hitachi microprocessor programs. If you
use a DOS host,
GDB depends on an auxiliary terminate-and-stay-resident program
called asynctsr to communicate with the development board
through a PC serial port. You must also use the DOS mode command
to set up the serial port on the DOS side.
You can use the E7000 in-circuit emulator to develop code for either the Hitachi SH or the H8/300H. Use one of these forms of the `target e7000' command to connect GDB to your E7000:
target e7000 port speed
target e7000 hostname
telnet to connect.
Some GDB commands are available only on the H8/300 or the H8/500 configurations:
set machine h8300
set machine h8300h
set memory mod
show memory
small,
big, medium, and compact.
GDB can use the MIPS remote debugging protocol to talk to a MIPS board attached to a serial line. This is available when you configure GDB with `--target=mips-idt-ecoff'.
Use these GDB commands to specify the connection to your target board:
target mips port
gdb with the
name of your program as the argument. To connect to the board, use the
command `target mips port', where port is the name of
the serial port connected to the board. If the program has not already
been downloaded to the board, you may use the load command to
download it. You can then use all the usual GDB commands.
For example, this sequence connects to the target board through a serial
port, and loads and runs a program called prog through the
debugger:
host$ gdb prog GDB is free software and ... (gdb) target mips /dev/ttyb (gdb) load prog (gdb) run
target mips hostname:portnumber
target pmon port
target ddb port
target lsi port
GDB also supports these special commands for MIPS targets:
set processor args
show processor
set processor command to set the type of MIPS
processor when you want to access processor-type-specific registers.
For example, set processor r3041 tells GDB
to use the CPO registers appropriate for the 3041 chip.
Use the show processor command to see what MIPS processor GDB
is using. Use the info reg command to see what registers
GDB is using.
set mipsfpu double
set mipsfpu single
set mipsfpu none
show mipsfpu
mipsfpu variable with
`show mipsfpu'.
set remotedebug n
show remotedebug
remotedebug variable. If you set it to 1 using
`set remotedebug 1', every packet is displayed. If you set it
to 2, every character is displayed. You can check the current value
at any time with the command `show remotedebug'.
set timeout seconds
set retransmit-timeout seconds
show timeout
show retransmit-timeout
set timeout seconds command. The
default is 5 seconds. Similarly, you can control the timeout used while
waiting for an acknowledgement of a packet with the set
retransmit-timeout seconds command. The default is 3 seconds.
You can inspect both values with show timeout and show
retransmit-timeout. (These commands are only available when
GDB is configured for `--target=mips-idt-ecoff'.)
The timeout set by set timeout does not apply when GDB
is waiting for your program to stop. In that case, GDB waits
forever because it has no way of knowing how long the program is going
to run before stopping.
For some configurations, GDB includes a CPU simulator that you can use instead of a hardware CPU to debug your programs. Currently, a simulator is available when GDB is configured to debug Zilog Z8000 or Hitachi microprocessor targets.
For the Z8000 family, `target sim' simulates either the Z8002 (the unsegmented variant of the Z8000 architecture) or the Z8001 (the segmented variant). The simulator recognizes which architecture is appropriate by inspecting the object code.
target sim
After specifying this target, you can debug programs for the simulated
CPU in the same style as programs for your host computer; use the
file command to load a new program image, the run command
to run your program, and so on.
As well as making available all the usual machine registers (see
info reg), this debugging target provides three additional items
of information as specially named registers:
cycles
insts
time
You can refer to these values in GDB expressions with the usual conventions; for example, `b fputc if $cycles>5000' sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks.
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