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Configuration-Specific Information

While nearly all GDB commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations.

There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other.


This section describes details specific to particular native configurations.


On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, GDB searches for a user or system name first, before it searches for a convenience variable.

BSD libkvm Interface

BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory interface that provides a uniform interface for accessing kernel virtual memory images, including live systems and crash dumps. GDB uses this interface to allow you to debug live kernels and kernel crash dumps on many native BSD configurations. This is implemented as a special kvm debugging target. For debugging a live system, load the currently running kernel into GDB and connect to the kvm target:

(gdb) target kvm

For debugging crash dumps, provide the file name of the crash dump as an argument:

(gdb) target kvm /var/crash/bsd.0

Once connected to the kvm target, the following commands are available:

kvm pcb
Set current context from the Process Control Block (PCB) address.
kvm proc
Set current context from proc address. This command isn't available on modern FreeBSD systems.

SVR4 process information

Many versions of SVR4 and compatible systems provide a facility called `/proc' that can be used to examine the image of a running process using file-system subroutines. If GDB is configured for an operating system with this facility, the command info proc is available to report information about the process running your program, or about any process running on your system. info proc works only on SVR4 systems that include the procfs code. This includes, as of this writing, GNU/Linux, OSF/1 (Digital Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.

info proc
info proc process-id
Summarize available information about any running process. If a process ID is specified by process-id, display information about that process; otherwise display information about the program being debugged. The summary includes the debugged process ID, the command line used to invoke it, its current working directory, and its executable file's absolute file name. On some systems, process-id can be of the form `[pid]/tid' which specifies a certain thread ID within a process. If the optional pid part is missing, it means a thread from the process being debugged (the leading `/' still needs to be present, or else GDB will interpret the number as a process ID rather than a thread ID).
info proc mappings
Report the memory address space ranges accessible in the program, with information on whether the process has read, write, or execute access rights to each range. On GNU/Linux systems, each memory range includes the object file which is mapped to that range, instead of the memory access rights to that range.
info proc stat
info proc status
These subcommands are specific to GNU/Linux systems. They show the process-related information, including the user ID and group ID; how many threads are there in the process; its virtual memory usage; the signals that are pending, blocked, and ignored; its TTY; its consumption of system and user time; its stack size; its `nice' value; etc. For more information, see the `proc' man page (type man 5 proc from your shell prompt).
info proc all
Show all the information about the process described under all of the above info proc subcommands.
set procfs-trace
This command enables and disables tracing of procfs API calls.
show procfs-trace
Show the current state of procfs API call tracing.
set procfs-file file
Tell GDB to write procfs API trace to the named file. GDB appends the trace info to the previous contents of the file. The default is to display the trace on the standard output.
show procfs-file
Show the file to which procfs API trace is written.
These commands enable and disable tracing of entries into and exits from the syscall interface.
info pidlist
For QNX Neutrino only, this command displays the list of all the processes and all the threads within each process.
info meminfo
For QNX Neutrino only, this command displays the list of all mapinfos.

Features for Debugging DJGPP Programs

DJGPP is a port of the GNU development tools to MS-DOS and MS-Windows. DJGPP programs are 32-bit protected-mode programs that use the DPMI (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations.

GDB supports native debugging of DJGPP programs, and defines a few commands specific to the DJGPP port. This subsection describes those commands.

info dos
This is a prefix of DJGPP-specific commands which print information about the target system and important OS structures.
info dos sysinfo
This command displays assorted information about the underlying platform: the CPU type and features, the OS version and flavor, the DPMI version, and the available conventional and DPMI memory.
info dos gdt
info dos ldt
info dos idt
These 3 commands display entries from, respectively, Global, Local, and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor tables are data structures which store a descriptor for each segment that is currently in use. The segment's selector is an index into a descriptor table; the table entry for that index holds the descriptor's base address and limit, and its attributes and access rights. A typical DJGPP program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment. These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment:
(gdb) info dos ldt $ds
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
This comes in handy when you want to see whether a pointer is outside the data segment's limit (i.e. garbled).
info dos pde
info dos pte
These two commands display entries from, respectively, the Page Directory and the Page Tables. Page Directories and Page Tables are data structures which control how virtual memory addresses are mapped into physical addresses. A Page Table includes an entry for every page of memory that is mapped into the program's address space; there may be several Page Tables, each one holding up to 4096 entries. A Page Directory has up to 4096 entries, one each for every Page Table that is currently in use. Without an argument, info dos pde displays the entire Page Directory, and info dos pte displays all the entries in all of the Page Tables. An argument, an integer expression, given to the info dos pde command means display only that entry from the Page Directory table. An argument given to the info dos pte command means display entries from a single Page Table, the one pointed to by the specified entry in the Page Directory. These commands are useful when your program uses DMA (Direct Memory Access), which needs physical addresses to program the DMA controller. These commands are supported only with some DPMI servers.
info dos address-pte addr
This command displays the Page Table entry for a specified linear address. The argument addr is a linear address which should already have the appropriate segment's base address added to it, because this command accepts addresses which may belong to any segment. For example, here's how to display the Page Table entry for the page where a variable i is stored:
(gdb) info dos address-pte __djgpp_base_address + (char *)&i
Page Table entry for address 0x11a00d30:
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
This says that i is stored at offset 0xd30 from the page whose physical base address is 0x02698000, and shows all the attributes of that page. Note that you must cast the addresses of variables to a char *, since otherwise the value of __djgpp_base_address, the base address of all variables and functions in a DJGPP program, will be added using the rules of C pointer arithmetics: if i is declared an int, GDB will add 4 times the value of __djgpp_base_address to the address of i. Here's another example, it displays the Page Table entry for the transfer buffer:
(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)
Page Table entry for address 0x29110:
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
(The + 3 offset is because the transfer buffer's address is the 3rd member of the _go32_info_block structure.) The output clearly shows that this DPMI server maps the addresses in conventional memory 1:1, i.e. the physical (0x00029000 + 0x110) and linear (0x29110) addresses are identical. This command is supported only with some DPMI servers.

In addition to native debugging, the DJGPP port supports remote debugging via a serial data link. The following commands are specific to remote serial debugging in the DJGPP port of GDB.

set com1base addr
This command sets the base I/O port address of the `COM1' serial port.
set com1irq irq
This command sets the Interrupt Request (IRQ) line to use for the `COM1' serial port. There are similar commands `set com2base', `set com3irq', etc. for setting the port address and the IRQ lines for the other 3 COM ports. The related commands `show com1base', `show com1irq' etc. display the current settings of the base address and the IRQ lines used by the COM ports.
info serial
This command prints the status of the 4 DOS serial ports. For each port, it prints whether it's active or not, its I/O base address and IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the counts of various errors encountered so far.

Features for Debugging MS Windows PE executables

GDB supports native debugging of MS Windows programs, including DLLs with and without symbolic debugging information. There are various additional Cygwin-specific commands, described in this subsection. The subsubsection see section Support for DLLs without debugging symbols describes working with DLLs that have no debugging symbols.

info w32
This is a prefix of MS Windows specific commands which print information about the target system and important OS structures.
info w32 selector
This command displays information returned by the Win32 API GetThreadSelectorEntry function. It takes an optional argument that is evaluated to a long value to give the information about this given selector. Without argument, this command displays information about the the six segment registers.
info dll
This is a Cygwin specific alias of info shared.
This command loads symbols from a dll similarly to add-sym command but without the need to specify a base address.
set new-console mode
If mode is on the debuggee will be started in a new console on next start. If mode is offi, the debuggee will be started in the same console as the debugger.
show new-console
Displays whether a new console is used when the debuggee is started.
set new-group mode
This boolean value controls whether the debuggee should start a new group or stay in the same group as the debugger. This affects the way the Windows OS handles Ctrl-C.
show new-group
Displays current value of new-group boolean.
set debugevents
This boolean value adds debug output concerning events seen by the debugger.
set debugexec
This boolean value adds debug output concerning execute events seen by the debugger.
set debugexceptions
This boolean value adds debug ouptut concerning exception events seen by the debugger.
set debugmemory
This boolean value adds debug ouptut concerning memory events seen by the debugger.
set shell
This boolean values specifies whether the debuggee is called via a shell or directly (default value is on).
show shell
Displays if the debuggee will be started with a shell.

Support for DLLs without debugging symbols

Very often on windows, some of the DLLs that your program relies on do not include symbolic debugging information (for example, `kernel32.dll'). When GDB doesn't recognize any debugging symbols in a DLL, it relies on the minimal amount of symbolic information contained in the DLL's export table. This subsubsection describes working with such symbols, known internally to GDB as "minimal symbols".

Note that before the debugged program has started execution, no DLLs will have been loaded. The easiest way around this problem is simply to start the program -- either by setting a breakpoint or letting the program run once to completion. It is also possible to force GDB to load a particular DLL before starting the executable --- see the shared library information in see section Commands to specify files or the dll-symbols command in see section Features for Debugging MS Windows PE executables. Currently, explicitly loading symbols from a DLL with no debugging information will cause the symbol names to be duplicated in GDB's lookup table, which may adversely affect symbol lookup performance.

DLL name prefixes

In keeping with the naming conventions used by the Microsoft debugging tools, DLL export symbols are made available with a prefix based on the DLL name, for instance KERNEL32!CreateFileA. The plain name is also entered into the symbol table, so CreateFileA is often sufficient. In some cases there will be name clashes within a program (particularly if the executable itself includes full debugging symbols) necessitating the use of the fully qualified name when referring to the contents of the DLL. Use single-quotes around the name to avoid the exclamation mark ("!") being interpreted as a language operator.

Note that the internal name of the DLL may be all upper-case, even though the file name of the DLL is lower-case, or vice-versa. Since symbols within GDB are case-sensitive this may cause some confusion. If in doubt, try the info functions and info variables commands or even maint print msymbols (see see section Examining the Symbol Table). Here's an example:

(gdb) info function CreateFileA
All functions matching regular expression "CreateFileA":

Non-debugging symbols:
0x77e885f4  CreateFileA
0x77e885f4  KERNEL32!CreateFileA
(gdb) info function !
All functions matching regular expression "!":

Non-debugging symbols:
0x6100114c  cygwin1!__assert
0x61004034  cygwin1!_dll_crt0@0
0x61004240  cygwin1!dll_crt0(per_process *)

Working with minimal symbols

Symbols extracted from a DLL's export table do not contain very much type information. All that GDB can do is guess whether a symbol refers to a function or variable depending on the linker section that contains the symbol. Also note that the actual contents of the memory contained in a DLL are not available unless the program is running. This means that you cannot examine the contents of a variable or disassemble a function within a DLL without a running program.

Variables are generally treated as pointers and dereferenced automatically. For this reason, it is often necessary to prefix a variable name with the address-of operator ("&") and provide explicit type information in the command. Here's an example of the type of problem:

(gdb) print 'cygwin1!__argv'
$1 = 268572168
(gdb) x 'cygwin1!__argv'
0x10021610:      "\230y\""

And two possible solutions:

(gdb) print ((char **)'cygwin1!__argv')[0]
$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
(gdb) x/2x &'cygwin1!__argv'
0x610c0aa8 <cygwin1!__argv>:    0x10021608      0x00000000
(gdb) x/x 0x10021608
0x10021608:     0x0022fd98
(gdb) x/s 0x0022fd98
0x22fd98:        "/cygdrive/c/mydirectory/myprogram"

Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, GDB can't examine the initial instructions of the function in order to skip the function's frame set-up code. You can work around this by using "*&" to set the breakpoint at a raw memory address:

(gdb) break *&'python22!PyOS_Readline'
Breakpoint 1 at 0x1e04eff0

The author of these extensions is not entirely convinced that setting a break point within a shared DLL like `kernel32.dll' is completely safe.

Commands specific to GNU Hurd systems

This subsection describes GDB commands specific to the GNU Hurd native debugging.

set signals
set sigs
This command toggles the state of inferior signal interception by GDB. Mach exceptions, such as breakpoint traps, are not affected by this command. sigs is a shorthand alias for signals.
show signals
show sigs
Show the current state of intercepting inferior's signals.
set signal-thread
set sigthread
This command tells GDB which thread is the libc signal thread. That thread is run when a signal is delivered to a running process. set sigthread is the shorthand alias of set signal-thread.
show signal-thread
show sigthread
These two commands show which thread will run when the inferior is delivered a signal.
set stopped
This commands tells GDB that the inferior process is stopped, as with the SIGSTOP signal. The stopped process can be continued by delivering a signal to it.
show stopped
This command shows whether GDB thinks the debuggee is stopped.
set exceptions
Use this command to turn off trapping of exceptions in the inferior. When exception trapping is off, neither breakpoints nor single-stepping will work. To restore the default, set exception trapping on.
show exceptions
Show the current state of trapping exceptions in the inferior.
set task pause
This command toggles task suspension when GDB has control. Setting it to on takes effect immediately, and the task is suspended whenever GDB gets control. Setting it to off will take effect the next time the inferior is continued. If this option is set to off, you can use set thread default pause on or set thread pause on (see below) to pause individual threads.
show task pause
Show the current state of task suspension.
set task detach-suspend-count
This command sets the suspend count the task will be left with when GDB detaches from it.
show task detach-suspend-count
Show the suspend count the task will be left with when detaching.
set task exception-port
set task excp
This command sets the task exception port to which GDB will forward exceptions. The argument should be the value of the send rights of the task. set task excp is a shorthand alias.
set noninvasive
This command switches GDB to a mode that is the least invasive as far as interfering with the inferior is concerned. This is the same as using set task pause, set exceptions, and set signals to values opposite to the defaults.
info send-rights
info receive-rights
info port-rights
info port-sets
info dead-names
info ports
info psets
These commands display information about, respectively, send rights, receive rights, port rights, port sets, and dead names of a task. There are also shorthand aliases: info ports for info port-rights and info psets for info port-sets.
set thread pause
This command toggles current thread suspension when GDB has control. Setting it to on takes effect immediately, and the current thread is suspended whenever GDB gets control. Setting it to off will take effect the next time the inferior is continued. Normally, this command has no effect, since when GDB has control, the whole task is suspended. However, if you used set task pause off (see above), this command comes in handy to suspend only the current thread.
show thread pause
This command shows the state of current thread suspension.
set thread run
This comamnd sets whether the current thread is allowed to run.
show thread run
Show whether the current thread is allowed to run.
set thread detach-suspend-count
This command sets the suspend count GDB will leave on a thread when detaching. This number is relative to the suspend count found by GDB when it notices the thread; use set thread takeover-suspend-count to force it to an absolute value.
show thread detach-suspend-count
Show the suspend count GDB will leave on the thread when detaching.
set thread exception-port
set thread excp
Set the thread exception port to which to forward exceptions. This overrides the port set by set task exception-port (see above). set thread excp is the shorthand alias.
set thread takeover-suspend-count
Normally, GDB's thread suspend counts are relative to the value GDB finds when it notices each thread. This command changes the suspend counts to be absolute instead.
set thread default
show thread default
Each of the above set thread commands has a set thread default counterpart (e.g., set thread default pause, set thread default exception-port, etc.). The thread default variety of commands sets the default thread properties for all threads; you can then change the properties of individual threads with the non-default commands.

QNX Neutrino

GDB provides the following commands specific to the QNX Neutrino target:

set debug nto-debug
When set to on, enables debugging messages specific to the QNX Neutrino support.
show debug nto-debug
Show the current state of QNX Neutrino messages.

Embedded Operating Systems

This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures.

GDB includes the ability to debug programs running on various real-time operating systems.

Using GDB with VxWorks

target vxworks machinename
A VxWorks system, attached via TCP/IP. The argument machinename is the target system's machine name or IP address.

On VxWorks, load links filename dynamically on the current target system as well as adding its symbols in GDB.

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
All VxWorks-based targets now support the option 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:


Connecting to VxWorks

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.

VxWorks download

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"

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's data structures that reference the target system's symbol table.)

Running tasks

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.

Embedded Processors

This section goes into details specific to particular embedded configurations.

Whenever a specific embedded processor has a simulator, GDB allows to send an arbitrary command to the simulator.

sim command
Send an arbitrary command string to the simulator. Consult the documentation for the specific simulator in use for information about acceptable commands.


target rdi dev
ARM Angel monitor, via RDI library interface to ADP protocol. You may use this target to communicate with both boards running the Angel monitor, or with the EmbeddedICE JTAG debug device.
target rdp dev
ARM Demon monitor.

GDB provides the following ARM-specific commands:

set arm disassembler
This commands selects from a list of disassembly styles. The "std" style is the standard style.
show arm disassembler
Show the current disassembly style.
set arm apcs32
This command toggles ARM operation mode between 32-bit and 26-bit.
show arm apcs32
Display the current usage of the ARM 32-bit mode.
set arm fpu fputype
This command sets the ARM floating-point unit (FPU) type. The argument fputype can be one of these:
Determine the FPU type by querying the OS ABI.
Software FPU, with mixed-endian doubles on little-endian ARM processors.
GCC-compiled FPA co-processor.
Software FPU with pure-endian doubles.
VFP co-processor.
show arm fpu
Show the current type of the FPU.
set arm abi
This command forces GDB to use the specified ABI.
show arm abi
Show the currently used ABI.
set debug arm
Toggle whether to display ARM-specific debugging messages from the ARM target support subsystem.
show debug arm
Show whether ARM-specific debugging messages are enabled.

The following commands are available when an ARM target is debugged using the RDI interface:

rdilogfile [file]
Set the filename for the ADP (Angel Debugger Protocol) packet log. With an argument, sets the log file to the specified file. With no argument, show the current log file name. The default log file is `rdi.log'.
rdilogenable [arg]
Control logging of ADP packets. With an argument of 1 or "yes" enables logging, with an argument 0 or "no" disables it. With no arguments displays the current setting. When logging is enabled, ADP packets exchanged between GDB and the RDI target device are logged to a file.
set rdiromatzero
Tell GDB whether the target has ROM at address 0. If on, vector catching is disabled, so that zero address can be used. If off (the default), vector catching is enabled. For this command to take effect, it needs to be invoked prior to the target rdi command.
show rdiromatzero
Show the current setting of ROM at zero address.
set rdiheartbeat
Enable or disable RDI heartbeat packets. It is not recommended to turn on this option, since it confuses ARM and EPI JTAG interface, as well as the Angel monitor.
show rdiheartbeat
Show the setting of RDI heartbeat packets.

Renesas H8/300

target hms dev
A Renesas SH, H8/300, or H8/500 board, attached via serial line to your host. Use special commands device and speed to control the serial line and the communications speed used.
target e7000 dev
E7000 emulator for Renesas H8 and SH.
target sh3 dev
target sh3e dev
Renesas SH-3 and SH-3E target systems.

When you select remote debugging to a Renesas SH, H8/300, or H8/500 board, the load command downloads your program to the Renesas board and also opens it as the current executable target for GDB on your host (like the file command).

GDB needs to know these things to talk to your Renesas SH, H8/300, or H8/500:

  1. that you want to use `target hms', the remote debugging interface for Renesas microprocessors, or `target e7000', the in-circuit emulator for the Renesas SH and the Renesas 300H. (`target hms' is the default when GDB is configured specifically for the Renesas SH, H8/300, or H8/500.)
  2. what serial device connects your host to your Renesas board (the first serial device available on your host is the default).
  3. what speed to use over the serial device.

Connecting to Renesas boards

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 9600bps connection).

The `device' and `speed' commands are available only when you use a Unix host to debug your Renesas 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.

The following sample session illustrates the steps needed to start a program under GDB control on an H8/300. The example uses a sample H8/300 program called `t.x'. The procedure is the same for the Renesas SH and the H8/500.

First hook up your development board. In this example, we use a board attached to serial port COM2; if you use a different serial port, substitute its name in the argument of the mode command. When you call asynctsr, the auxiliary comms program used by the debugger, you give it just the numeric part of the serial port's name; for example, `asyncstr 2' below runs asyncstr on COM2.

C:\H8300\TEST> asynctsr 2
C:\H8300\TEST> mode com2:9600,n,8,1,p

Resident portion of MODE loaded

COM2: 9600, n, 8, 1, p

Warning: We have noticed a bug in PC-NFS that conflicts with asynctsr. If you also run PC-NFS on your DOS host, you may need to disable it, or even boot without it, to use asynctsr to control your development board.

Now that serial communications are set up, and the development board is connected, you can start up GDB. Call GDB with the name of your program as the argument. GDB prompts you, as usual, with the prompt `(gdb)'. Use two special commands to begin your debugging session: `target hms' to specify cross-debugging to the Renesas board, and the load command to download your program to the board. load displays the names of the program's sections, and a `*' for each 2K of data downloaded. (If you want to refresh GDB data on symbols or on the executable file without downloading, use the GDB commands file or symbol-file. These commands, and load itself, are described in section Commands to specify files.)

(eg-C:\H8300\TEST) gdb t.x
GDB is free software and you are welcome to distribute copies
 of it under certain conditions; type "show copying" to see
 the conditions.
There is absolutely no warranty for GDB; type "show warranty"
for details.
GDB, Copyright 1992 Free Software Foundation, Inc...
(gdb) target hms
Connected to remote H8/300 HMS system.
(gdb) load t.x
.text   : 0x8000 .. 0xabde ***********
.data   : 0xabde .. 0xad30 *
.stack  : 0xf000 .. 0xf014 *

At this point, you're ready to run or debug your program. From here on, you can use all the usual GDB commands. The break command sets breakpoints; the run command starts your program; print or x display data; the continue command resumes execution after stopping at a breakpoint. You can use the help command at any time to find out more about GDB commands.

Remember, however, that operating system facilities aren't available on your development board; for example, if your program hangs, you can't send an interrupt--but you can press the RESET switch!

Use the RESET button on the development board

In either case, GDB sees the effect of a RESET on the development board as a "normal exit" of your program.

Using the E7000 in-circuit emulator

You can use the E7000 in-circuit emulator to develop code for either the Renesas 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
Use this form if your E7000 is connected to a serial port. The port argument identifies what serial port to use (for example, `com2'). The third argument is the line speed in bits per second (for example, `9600').
target e7000 hostname
If your E7000 is installed as a host on a TCP/IP network, you can just specify its hostname; GDB uses telnet to connect.

The following special commands are available when debugging with the Renesas E7000 ICE:

e7000 command
This sends the specified command to the E7000 monitor.
ftplogin machine username password dir
This command records information for subsequent interface with the E7000 monitor via the FTP protocol: GDB will log into the named machine using specified username and password, and then chdir to the named directory dir.
ftpload file
This command uses credentials recorded by ftplogin to fetch and load the named file from the E7000 monitor.
This command drains any pending text buffers stored on the E7000.
set usehardbreakpoints
show usehardbreakpoints
These commands set and show the use of hardware breakpoints for all breakpoints. See section Setting breakpoints, for more information about using hardware breakpoints selectively.

Special GDB commands for Renesas micros

Some GDB commands are available only for the H8/300:

set machine h8300
set machine h8300h
Condition GDB for one of the two variants of the H8/300 architecture with `set machine'. You can use `show machine' to check which variant is currently in effect.


set memory mod
show memory
Specify which H8/500 memory model (mod) you are using with `set memory'; check which memory model is in effect with `show memory'. The accepted values for mod are small, big, medium, and compact.

Renesas M32R/D and M32R/SDI

target m32r dev
Renesas M32R/D ROM monitor.
target m32rsdi dev
Renesas M32R SDI server, connected via parallel port to the board.

The following GDB commands are specific to the M32R monitor:

set download-path path
Set the default path for finding donwloadable SREC files.
show download-path
Show the default path for downloadable SREC files.
set board-address addr
Set the IP address for the M32R-EVA target board.
show board-address
Show the current IP address of the target board.
set server-address addr
Set the IP address for the download server, which is the GDB's host machine.
show server-address
Display the IP address of the download server.
upload [file]
Upload the specified SREC file via the monitor's Ethernet upload capability. If no file argument is given, the current executable file is uploaded.
tload [file]
Test the upload command.

The following commands are available for M32R/SDI:

This command resets the SDI connection.
This command shows the SDI connection status.
Instructs the remote that M32R/Chaos debugging is to be used.
Instructs the remote to use the DEBUG_DMA method of accessing memory.
Instructs the remote to use the MON_CODE method of accessing memory.
Instructs the remote to set breakpoints by IB break.
Instructs the remote to set breakpoints by DBT.


The Motorola m68k configuration includes ColdFire support, and target command for the following ROM monitors.

target abug dev
ABug ROM monitor for M68K.
target cpu32bug dev
CPU32BUG monitor, running on a CPU32 (M68K) board.
target dbug dev
dBUG ROM monitor for Motorola ColdFire.
target est dev
EST-300 ICE monitor, running on a CPU32 (M68K) board.
target rom68k dev
ROM 68K monitor, running on an M68K IDP board.
target rombug dev
ROMBUG ROM monitor for OS/9000.

MIPS Embedded

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
To run a program on the board, start up 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
On some GDB host configurations, you can specify a TCP connection (for instance, to a serial line managed by a terminal concentrator) instead of a serial port, using the syntax `hostname:portnumber'.
target pmon port
PMON ROM monitor.
target ddb port
NEC's DDB variant of PMON for Vr4300.
target lsi port
LSI variant of PMON.
target r3900 dev
Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
target array dev
Array Tech LSI33K RAID controller board.

GDB also supports these special commands for MIPS targets:

set mipsfpu double
set mipsfpu single
set mipsfpu none
set mipsfpu auto
show mipsfpu
If your target board does not support the MIPS floating point coprocessor, you should use the command `set mipsfpu none' (if you need this, you may wish to put the command in your GDB init file). This tells GDB how to find the return value of functions which return floating point values. It also allows GDB to avoid saving the floating point registers when calling functions on the board. If you are using a floating point coprocessor with only single precision floating point support, as on the R4650 processor, use the command `set mipsfpu single'. The default double precision floating point coprocessor may be selected using `set mipsfpu double'. In previous versions the only choices were double precision or no floating point, so `set mipsfpu on' will select double precision and `set mipsfpu off' will select no floating point. As usual, you can inquire about the mipsfpu variable with `show mipsfpu'.
set timeout seconds
set retransmit-timeout seconds
show timeout
show retransmit-timeout
You can control the timeout used while waiting for a packet, in the MIPS remote protocol, with the 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.
set syn-garbage-limit num
Limit the maximum number of characters GDB should ignore when it tries to synchronize with the remote target. The default is 10 characters. Setting the limit to -1 means there's no limit.
show syn-garbage-limit
Show the current limit on the number of characters to ignore when trying to synchronize with the remote system.
set monitor-prompt prompt
Tell GDB to expect the specified prompt string from the remote monitor. The default depends on the target:
pmon target
ddb target
lsi target
show monitor-prompt
Show the current strings GDB expects as the prompt from the remote monitor.
set monitor-warnings
Enable or disable monitor warnings about hardware breakpoints. This has effect only for the lsi target. When on, GDB will display warning messages whose codes are returned by the lsi PMON monitor for breakpoint commands.
show monitor-warnings
Show the current setting of printing monitor warnings.
pmon command
This command allows sending an arbitrary command string to the monitor. The monitor must be in debug mode for this to work.

OpenRISC 1000

See OR1k Architecture document (@uref{}) for more information about platform and commands.

target jtag jtag://host:port
Connects to remote JTAG server. JTAG remote server can be either an or1ksim or JTAG server, connected via parallel port to the board. Example: target jtag jtag://localhost:9999
or1ksim command
If connected to or1ksim OpenRISC 1000 Architectural Simulator, proprietary commands can be executed.
info or1k spr
Displays spr groups.
info or1k spr group
info or1k spr groupno
Displays register names in selected group.
info or1k spr group register
info or1k spr register
info or1k spr groupno registerno
info or1k spr registerno
Shows information about specified spr register.
spr group register value
spr register value
spr groupno registerno value
spr registerno value
Writes value to specified spr register.

Some implementations of OpenRISC 1000 Architecture also have hardware trace. It is very similar to GDB trace, except it does not interfere with normal program execution and is thus much faster. Hardware breakpoints/watchpoint triggers can be set using:

Load effective address/data
Store effective address/data
Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
Fetch data

When triggered, it can capture low level data, like: PC, LSEA, LDATA, SDATA, READSPR, WRITESPR, INSTR.

htrace commands:

hwatch conditional
Set hardware watchpoint on combination of Load/Store Effecive Address(es) or Data. For example: hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50) hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)
htrace info
Display information about current HW trace configuration.
htrace trigger conditional
Set starting criteria for HW trace.
htrace qualifier conditional
Set acquisition qualifier for HW trace.
htrace stop conditional
Set HW trace stopping criteria.
htrace record [data]*
Selects the data to be recorded, when qualifier is met and HW trace was triggered.
htrace enable
htrace disable
Enables/disables the HW trace.
htrace rewind [filename]
Clears currently recorded trace data. If filename is specified, new trace file is made and any newly collected data will be written there.
htrace print [start [len]]
Prints trace buffer, using current record configuration.
htrace mode continuous
Set continuous trace mode.
htrace mode suspend
Set suspend trace mode.


target dink32 dev
DINK32 ROM monitor.
target ppcbug dev
target ppcbug1 dev
PPCBUG ROM monitor for PowerPC.
target sds dev
SDS monitor, running on a PowerPC board (such as Motorola's ADS).

The following commands specifi to the SDS protocol are supported byGDB:

set sdstimeout nsec
Set the timeout for SDS protocol reads to be nsec seconds. The default is 2 seconds.
show sdstimeout
Show the current value of the SDS timeout.
sds command
Send the specified command string to the SDS monitor.

HP PA Embedded

target op50n dev
OP50N monitor, running on an OKI HPPA board.
target w89k dev
W89K monitor, running on a Winbond HPPA board.

Renesas SH

target hms dev
A Renesas SH board attached via serial line to your host. Use special commands device and speed to control the serial line and the communications speed used.
target e7000 dev
E7000 emulator for Renesas SH.
target sh3 dev
target sh3e dev
Renesas SH-3 and SH-3E target systems.

Tsqware Sparclet

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.

remotetimeout args
GDB supports the option 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. Example:

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:


Setting file to debug

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.

Connecting to Sparclet

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.

Sparclet download

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.

Running and debugging

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!";

Fujitsu Sparclite

target sparclite dev
Fujitsu sparclite boards, used only for the purpose of loading. You must use an additional command to debug the program. For example: target remote dev using GDB standard remote protocol.

Tandem ST2000

GDB may be used with a Tandem ST2000 phone switch, running Tandem's STDBUG protocol.

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
Send a command to the STDBUG monitor. See the manufacturer's manual for available commands.
Connect the controlling terminal to the STDBUG command monitor. When you are done interacting with STDBUG, typing either of two character sequences gets you back to the GDB command prompt: RET~. (Return, followed by tilde and period) or RET~C-d (Return, followed by tilde and control-D).

Zilog Z8000

When configured for debugging Zilog Z8000 targets, GDB includes a Z8000 simulator.

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 args
Debug programs on a simulated CPU. If the simulator supports setup options, specify them via args.

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 section Registers), the Z8000 simulator provides three additional items of information as specially named registers:

Counts clock-ticks in the simulator.
Counts instructions run in the simulator.
Execution time in 60ths of a second.

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.

Atmel AVR

When configured for debugging the Atmel AVR, GDB supports the following AVR-specific commands:

info io_registers
This command displays information about the AVR I/O registers. For each register, GDB prints its number and value.


When configured for debugging CRIS, GDB provides the following CRIS-specific commands:

set cris-version ver
Set the current CRIS version to ver, either `10' or `32'. The CRIS version affects register names and sizes. This command is useful in case autodetection of the CRIS version fails.
show cris-version
Show the current CRIS version.
set cris-dwarf2-cfi
Set the usage of DWARF-2 CFI for CRIS debugging. The default is `on'. Change to `off' when using gcc-cris whose version is below R59.
show cris-dwarf2-cfi
Show the current state of using DWARF-2 CFI.
set cris-mode mode
Set the current CRIS mode to mode. It should only be changed when debugging in guru mode, in which case it should be set to `guru' (the default is `normal').
show cris-mode
Show the current CRIS mode.

Renesas Super-H

For the Renesas Super-H processor, GDB provides these commands:

Show the values of all Super-H registers.

Windows CE

The following commands are available for Windows CE:

set remotedirectory dir
Tell GDB to upload files from the named directory dir. The default is `/gdb', i.e. the root directory on the current drive.
show remotedirectory
Show the current value of the upload directory.
set remoteupload method
Set the method used to upload files to remote device. Valid values for method are `always', `newer', and `never'. The default is `newer'.
show remoteupload
Show the current setting of the upload method.
set remoteaddhost
Tell GDB whether to add this host to the remote stub's arguments when you debug over a network.
show remoteaddhost
Show whether to add this host to remote stub's arguments when debugging over a network.


This section describes characteristics of architectures that affect all uses of GDB with the architecture, both native and cross.

x86 Architecture-specific issues.

set struct-convention mode
Set the convention used by the inferior to return structs and unions from functions to mode. Possible values of mode are "pcc", "reg", and "default" (the default). "default" or "pcc" means that structs are returned on the stack, while "reg" means that a struct or a union whose size is 1, 2, 4, or 8 bytes will be returned in a register.
show struct-convention
Show the current setting of the convention to return structs from functions.


set rstack_high_address address
On AMD 29000 family processors, registers are saved in a separate register stack. There is no way for GDB to determine the extent of this stack. Normally, GDB just assumes that the stack is "large enough". This may result in GDB referencing memory locations that do not exist. If necessary, you can get around this problem by specifying the ending address of the register stack with the set rstack_high_address command. The argument should be an address, which you probably want to precede with `0x' to specify in hexadecimal.
show rstack_high_address
Display the current limit of the register stack, on AMD 29000 family processors.


See the following section.


Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires GDB to search backward in the object code to find the beginning of a function.

To improve response time (especially for embedded applications, where GDB may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands:

set heuristic-fence-post limit
Restrict GDB to examining at most limit bytes in its search for the beginning of a function. A value of 0 (the default) means there is no limit. However, except for 0, the larger the limit the more bytes heuristic-fence-post must search and therefore the longer it takes to run. You should only need to use this command when debugging a stripped executable.
show heuristic-fence-post
Display the current limit.

These commands are available only when GDB is configured for debugging programs on Alpha or MIPS processors.

Several MIPS-specific commands are available when debugging MIPS programs:

set mips saved-gpreg-size size
Set the size of MIPS general-purpose registers saved on the stack. The argument size can be one of the following:
32-bit GP registers
64-bit GP registers
Use the target's default setting or autodetect the saved size from the information contained in the executable. This is the default
show mips saved-gpreg-size
Show the current size of MIPS GP registers on the stack.
set mips stack-arg-size size
Set the amount of stack space reserved for arguments to functions. The argument can be one of "32", "64" or "auto" (the default).
set mips abi arg
Tell GDB which MIPS ABI is used by the inferior. Possible values of arg are:
The default ABI associated with the current binary (this is the default).
show mips abi
Show the MIPS ABI used by GDB to debug the inferior.
set mipsfpu
show mipsfpu
See section MIPS Embedded.
set mips mask-address arg
This command determines whether the most-significant 32 bits of 64-bit MIPS addresses are masked off. The argument arg can be `on', `off', or `auto'. The latter is the default setting, which lets GDB determine the correct value.
show mips mask-address
Show whether the upper 32 bits of MIPS addresses are masked off or not.
set remote-mips64-transfers-32bit-regs
This command controls compatibility with 64-bit MIPS targets that transfer data in 32-bit quantities. If you have an old MIPS 64 target that transfers 32 bits for some registers, like SR and FSR, and 64 bits for other registers, set this option to `on'.
show remote-mips64-transfers-32bit-regs
Show the current setting of compatibility with older MIPS 64 targets.
set debug mips
This command turns on and off debugging messages for the MIPS-specific target code in GDB.
show debug mips
Show the current setting of MIPS debugging messages.


When GDB is debugging te HP PA architecture, it provides the following special commands:

set debug hppa
THis command determines whether HPPA architecture specific debugging messages are to be displayed.
show debug hppa
Show whether HPPA debugging messages are displayed.
maint print unwind address
This command displays the contents of the unwind table entry at the given address.

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