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INFO-DIR-SECTION Programming & development tools.
START-INFO-DIR-ENTRY
* Gdb: (gdb).                     The GNU debugger.
END-INFO-DIR-ENTRY

   This file documents the GNU debugger GDB.

   This is the Eighth Edition, March 2000, of `Debugging with GDB: the
GNU Source-Level Debugger' for GDB Version 5.0.

   Copyright (C) 1988-2000 Free Software Foundation, Inc.

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

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the entire resulting derived work is distributed under the terms
of a permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.


File: gdb.info,  Node: Bootstrapping,  Next: Debug Session,  Prev: Stub Contents,  Up: Remote Serial

What you must do for the stub
.............................

   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()'
     Write this subroutine to read a single character from the serial
     port.  It may be identical to `getchar' for your target system; a
     different name is used to allow you to distinguish the two if you
     wish.

`void putDebugChar(int)'
     Write this subroutine to write a single character to the serial
     port.  It may be identical to `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)'
     Write this function to install EXCEPTION_ADDRESS in the exception
     handling tables.  You need to do this because the stub does not
     have any way of knowing what the exception handling tables on your
     target system are like (for example, the processor's table might
     be in ROM, containing entries which point to a table in RAM).
     EXCEPTION_NUMBER is the exception number which should be changed;
     its meaning is architecture-dependent (for example, different
     numbers might represent divide by zero, misaligned access, etc).
     When this exception occurs, control should be transferred directly
     to EXCEPTION_ADDRESS, and the processor state (stack, registers,
     and so on) should be just as it is when a processor exception
     occurs.  So if you want to use a jump instruction to reach
     EXCEPTION_ADDRESS, it should be a simple jump, not a jump to
     subroutine.

     For the 386, EXCEPTION_ADDRESS should be installed as an interrupt
     gate so that interrupts are masked while the handler runs.  The
     gate should be at privilege level 0 (the most privileged level).
     The SPARC and 68k stubs are able to mask interrupts themselves
     without help from `exceptionHandler'.

`void flush_i_cache()'
     On SPARC and SPARCLITE only, write this subroutine to flush the
     instruction cache, if any, on your target machine.  If there is no
     instruction cache, this subroutine may be a no-op.

     On target machines that have instruction caches, GDB requires this
     function to make certain that the state of your program is stable.

You must also make sure this library routine is available:

`void *memset(void *, int, int)'
     This is the standard library function `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.


File: gdb.info,  Node: Debug Session,  Next: Protocol,  Prev: Bootstrapping,  Up: Remote Serial

Putting it all together
.......................

   In summary, when your program is ready to debug, you must follow
these steps.

  1. Make sure you have defined the supporting low-level routines
     (*note What you must do for the stub: Bootstrapping.):
          `getDebugChar', `putDebugChar',
          `flush_i_cache', `memset', `exceptionHandler'.

  2. Insert these lines near the top of your program:

          set_debug_traps();
          breakpoint();

  3. For the 680x0 stub only, you need to provide a variable called
     `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.

  4. Compile and link together: your program, the GDB debugging stub for
     your target architecture, and the supporting subroutines.

  5. Make sure you have a serial connection between your target machine
     and the GDB host, and identify the serial port on the host.

  6. Download your program to your target machine (or get it there by
     whatever means the manufacturer provides), and start it.

  7. To start remote debugging, run GDB on the host machine, and specify
     as an executable file the program that is running in the remote
     machine.  This tells GDB how to find your program's symbols and
     the contents of its pure text.

  8. Establish communication using the `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/ttyb

     To 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.


File: gdb.info,  Node: Protocol,  Next: Server,  Prev: Debug Session,  Up: Remote Serial

Communication protocol
......................

   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.

   In the examples below, `<-' and `->' are used to indicate
transmitted and received data respectfully.

   All GDB commands and responses (other than acknowledgments) are sent
as a PACKET.  A PACKET is introduced with the character `$', the actual
PACKET-DATA, and the terminating character `#' followed by a two-digit
CHECKSUM:

     `$'PACKET-DATA`#'CHECKSUM

The two-digit CHECKSUM is computed as the modulo 256 sum of all
characters between the leading `$' and the trailing `#' (an eight bit
unsigned checksum).

   Implementors should note that prior to GDB 5.0 the protocol
specification also included an optional two-digit SEQUENCE-ID:

     `$'SEQUENCE-ID`:'PACKET-DATA`#'CHECKSUM

That SEQUENCE-ID was appended to the acknowledgment.  GDB has never
output SEQUENCE-IDs.  Stubs that handle packets added since GDB 5.0
must not accept SEQUENCE-ID.

   When either the host or the target machine receives a packet, the
first response expected is an acknowledgment: either `+' (to indicate
the package was received correctly) or `-' (to request retransmission):

     <- `$'PACKET-DATA`#'CHECKSUM
     -> `+'

The host (GDB) sends COMMANDs, and the target (the debugging stub
incorporated in your program) sends a RESPONSE.  In the case of step
and continue COMMANDs, the response is only sent when the operation has
completed (the target has again stopped).

   PACKET-DATA consists of a sequence of characters with the exception
of `#' and `$' (see `X' packet for additional exceptions).

   Fields within the packet should be separated using `,' `;' or `:'.
Except where otherwise noted all numbers are represented in HEX with
leading zeros suppressed.

   Implementors should note that prior to GDB 5.0, the character `:'
could not appear as the third character in a packet (as it would
potentially conflict with the SEQUENCE-ID).

   Response DATA can be run-length encoded to save space.  A `*' means
that the next character is an ASCII encoding giving a repeat count
which stands for that many repetitions of the character preceding the
`*'.  The encoding is `n+29', yielding a printable character where `n
>=3' (which is where rle starts to win).  The printable characters `$',
`#', `+' and `-' or with a numeric value greater than 126 should not be
used.

   Some remote systems have used a different run-length encoding
mechanism loosely refered to as the cisco encoding.  Following the `*'
character are two hex digits that indicate the size of the packet.

   So:
     "`0* '"

means the same as "0000".

   The error response returned for some packets includes a two character
error number.  That number is not well defined.

   For any COMMAND not supported by the stub, an empty response
(`$#00') should be returned.  That way it is possible to extend the
protocol.  A newer GDB can tell if a packet is supported based on that
response.

   A stub is required to support the `g', `G', `m', `M', `c', and `s'
COMMANDs.  All other COMMANDs are optional.

   Below is a complete list of all currently defined COMMANDs and their
corresponding response DATA:

Packet                 Request                Description
extended ops           `!'                    Use the extended remote
                                              protocol.  Sticky--only
                                              needs to be set once.  The
                                              extended remote protocol
                                              supports the `R' packet.
                       reply `'               Stubs that support the
                                              extended remote protocol
                                              return `' which,
                                              unfortunately, is identical
                                              to the response returned by
                                              stubs that do not support
                                              protocol extensions.
last signal            `?'                    Indicate the reason the
                                              target halted.  The reply is
                                              the same as for step and
                                              continue.
                       reply                  see below
reserved               `a'                    Reserved for future use
set program arguments  `A'ARGLEN`,'ARGNUM`,'ARG`,...'
*(reserved)*                                  
                                              Initialized `argv[]' array
                                              passed into program. ARGLEN
                                              specifies the number of
                                              bytes in the hex encoded
                                              byte stream ARG.  See
                                              `gdbserver' for more details.
                       reply `OK'             
                       reply `E'NN            
set baud               `b'BAUD                Change the serial line speed
*(deprecated)*                                to BAUD.  JTC: _When does the
                                              transport layer state
                                              change?  When it's received,
                                              or after the ACK is
                                              transmitted.  In either
                                              case, there are problems if
                                              the command or the
                                              acknowledgment packet is
                                              dropped._ Stan: _If people
                                              really wanted to add
                                              something like this, and get
                                              it working for the first
                                              time, they ought to modify
                                              ser-unix.c to send some kind
                                              of out-of-band message to a
                                              specially-setup stub and
                                              have the switch happen "in
                                              between" packets, so that
                                              from remote protocol's point
                                              of view, nothing actually
                                              happened._
set breakpoint         `B'ADDR,MODE           Set (MODE is `S') or clear
*(deprecated)*                                (MODE is `C') a breakpoint
                                              at ADDR.  _This has been
                                              replaced by the `Z' and `z'
                                              packets._
continue               `c'ADDR                ADDR is address to resume.
                                              If ADDR is omitted, resume at
                                              current address.
                       reply                  see below
continue with signal   `C'SIG`;'ADDR          Continue with signal SIG
                                              (hex signal number).  If
                                              `;'ADDR is omitted, resume
                                              at same address.
                       reply                  see below
toggle debug           `d'                    toggle debug flag.
*(deprecated)*                                
detach                 `D'                    Detach GDB from the remote
                                              system.  Sent to the remote
                                              target before GDB
                                              disconnects.
                       reply _no response_    GDB does not check for any
                                              response after sending this
                                              packet.
reserved               `e'                    Reserved for future use
reserved               `E'                    Reserved for future use
reserved               `f'                    Reserved for future use
reserved               `F'                    Reserved for future use
read registers         `g'                    Read general registers.
                       reply XX...            Each byte of register data
                                              is described by two hex
                                              digits.  The bytes with the
                                              register are transmitted in
                                              target byte order.  The size
                                              of each register and their
                                              position within the `g'
                                              PACKET are determined by the
                                              GDB internal macros
                                              REGISTER_RAW_SIZE and
                                              REGISTER_NAME macros.  The
                                              specification of several
                                              standard `g' packets is
                                              specified below.
                       `E'NN                  for an error.
write regs             `G'XX...               See `g' for a description of
                                              the XX... data.
                       reply `OK'             for success
                       reply `E'NN            for an error
reserved               `h'                    Reserved for future use
set thread             `H'CT...               Set thread for subsequent
                                              operations (`m', `M', `g',
                                              `G', et.al.).  C = `c' for
                                              thread used in step and
                                              continue; T... can be -1 for
                                              all threads.  C = `g' for
                                              thread used in other
                                              operations.  If zero, pick a
                                              thread, any thread.
                       reply `OK'             for success
                       reply `E'NN            for an error
cycle step *(draft)*   `i'ADDR`,'NNN          Step the remote target by a
                                              single clock cycle.  If
                                              `,'NNN is present, cycle
                                              step NNN cycles.  If ADDR is
                                              present, cycle step starting
                                              at that address.
signal then cycle      `I'                    See `i' and `S' for likely
step *(reserved)*                             syntax and semantics.
reserved               `j'                    Reserved for future use
reserved               `J'                    Reserved for future use
kill request           `k'                    FIXME: _There is no
                                              description of how operate
                                              when a specific thread
                                              context has been selected
                                              (ie. does 'k' kill only that
                                              thread?)_.
reserved               `l'                    Reserved for future use
reserved               `L'                    Reserved for future use
read memory            `m'ADDR`,'LENGTH       Read LENGTH bytes of memory
                                              starting at address ADDR.
                                              Neither GDB nor the stub
                                              assume that sized memory
                                              transfers are assumed using
                                              word alligned accesses.
                                              FIXME: _A word aligned memory
                                              transfer mechanism is
                                              needed._
                       reply XX...            XX... is mem contents. Can
                                              be fewer bytes than
                                              requested if able to read
                                              only part of the data.
                                              Neither GDB nor the stub
                                              assume that sized memory
                                              transfers are assumed using
                                              word alligned accesses.
                                              FIXME: _A word aligned
                                              memory transfer mechanism is
                                              needed._
                       reply `E'NN            NN is errno
write mem              `M'ADDR,LENGTH`:'XX... Write LENGTH bytes of memory
                                              starting at address ADDR.
                                              XX... is the data.
                       reply `OK'             for success
                       reply `E'NN            for an error (this includes
                                              the case where only part of
                                              the data was written).
reserved               `n'                    Reserved for future use
reserved               `N'                    Reserved for future use
reserved               `o'                    Reserved for future use
reserved               `O'                    Reserved for future use
read reg *(reserved)*  `p'N...                See write register.
                       return R....           The hex encoded value of the
                                              register in target byte
                                              order.
write reg              `P'N...`='R...         Write register N... with
                                              value R..., which contains
                                              two hex digits for each byte
                                              in the register (target byte
                                              order).
                       reply `OK'             for success
                       reply `E'NN            for an error
general query          `q'QUERY               Request info about QUERY.
                                              In general GDB queries have
                                              a leading upper case letter.
                                              Custom vendor queries
                                              should use a company prefix
                                              (in lower case) ex:
                                              `qfsf.var'.  QUERY may
                                              optionally be followed by a
                                              `,' or `;' separated list.
                                              Stubs must ensure that they
                                              match the full QUERY name.
                       reply `XX...'          Hex encoded data from query.
                                              The reply can not be empty.
                       reply `E'NN            error reply
                       reply `'               Indicating an unrecognized
                                              QUERY.
general set            `Q'VAR`='VAL           Set value of VAR to VAL.
                                              See `q' for a discussing of
                                              naming conventions.
reset *(deprecated)*   `r'                    Reset the entire system.
remote restart         `R'XX                  Restart the remote server.
                                              XX while needed has no clear
                                              definition.  FIXME: _An
                                              example interaction
                                              explaining how this packet
                                              is used in extended-remote
                                              mode is needed_.
step                   `s'ADDR                ADDR is address to resume.
                                              If ADDR is omitted, resume at
                                              same address.
                       reply                  see below
step with signal       `S'SIG`;'ADDR          Like `C' but step not
                                              continue.
                       reply                  see below
search                 `t'ADDR`:'PP`,'MM      Search backwards starting at
                                              address ADDR for a match
                                              with pattern PP and mask MM.
                                              PP and MM are 4 bytes.
                                              ADDR must be at least 3
                                              digits.
thread alive           `T'XX                  Find out if the thread XX is
                                              alive.
                       reply `OK'             thread is still alive
                       reply `E'NN            thread is dead
reserved               `u'                    Reserved for future use
reserved               `U'                    Reserved for future use
reserved               `v'                    Reserved for future use
reserved               `V'                    Reserved for future use
reserved               `w'                    Reserved for future use
reserved               `W'                    Reserved for future use
reserved               `x'                    Reserved for future use
write mem (binary)     `X'ADDR`,'LENGTH:XX... ADDR is address, LENGTH is
                                              number of bytes, XX... is
                                              binary data.  The characters
                                              `$', `#', and `0x7d' are
                                              escaped using `0x7d'.
                       reply `OK'             for success
                       reply `E'NN            for an error
reserved               `y'                    Reserved for future use
reserved               `Y'                    Reserved for future use
remove break or        `z'T`,'ADDR`,'LENGTH   See `Z'.
watchpoint *(draft)*                          
insert break or        `Z'T`,'ADDR`,'LENGTH   T is type: `0' - software
watchpoint *(draft)*                          breakpoint, `1' - hardware
                                              breakpoint, `2' - write
                                              watchpoint, `3' - read
                                              watchpoint, `4' - access
                                              watchpoint; ADDR is address;
                                              LENGTH is in bytes.  For a
                                              software breakpoint, LENGTH
                                              specifies the size of the
                                              instruction to be patched.
                                              For hardware breakpoints and
                                              watchpoints LENGTH specifies
                                              the memory region to be
                                              monitored.  To avoid
                                              potential problems with
                                              duplicate packets, the
                                              operations should be
                                              implemented in an idempotent
                                              way.
                       reply `E'NN            for an error
                       reply `OK'             for success
                       `'                     If not supported.
reserved               <other>                Reserved for future use

   The `C', `c', `S', `s' and `?' packets can receive any of the below
as a reply.  In the case of the `C', `c', `S' and `s' packets, that
reply is only returned when the target halts.  In the below the exact
meaning of `signal number' is poorly defined.  In general one of the
UNIX signal numbering conventions is used.

`S'AA                         AA is the signal number
`T'AAN...`:'R...`;'N...`:'R...`;'N...`:'R...`;'AA = two hex digit signal number; N... =
                              register number (hex), R...  = target byte
                              ordered register contents, size defined by
                              `REGISTER_RAW_SIZE'; N... = `thread', R...
                              = thread process ID, this is a hex
                              integer; N... = other string not starting
                              with valid hex digit.  GDB should ignore
                              this N..., R... pair and go on to the
                              next.  This way we can extend the protocol.
`W'AA                         The process exited, and AA is the exit
                              status.  This is only applicable for
                              certains sorts of targets.
`X'AA                         The process terminated with signal AA.
`N'AA`;'T...`;'D...`;'B...    AA = signal number; T... = address of
*(obsolete)*                  symbol "_start"; D... = base of data
                              section; B... = base of bss section.
                              _Note: only used by Cisco Systems targets.
                              The difference between this reply and the
                              "qOffsets" query is that the 'N' packet
                              may arrive spontaneously whereas the
                              'qOffsets' is a query initiated by the host
                              debugger._
`O'XX...                      XX... is hex encoding of ASCII data.  This
                              can happen at any time while the program
                              is running and the debugger should
                              continue to wait for 'W', 'T', etc.

   The following set and query packets have already been defined.

current thread `q'`C'         Return the current thread id.
               reply `QC'PID  Where PID is a HEX encoded 16 bit process
                              id.
               reply *        Any other reply implies the old pid.
all thread ids `q'`fThreadInfo'
               `q'`sThreadInfo'Obtain a list of active thread ids from
                              the target (OS).  Since there may be too
                              many active threads to fit into one reply
                              packet, this query works iteratively: it
                              may require more than one query/reply
                              sequence to obtain the entire list of
                              threads.  The first query of the sequence
                              will be the `qf'`ThreadInfo' query;
                              subsequent queries in the sequence will be
                              the `qs'`ThreadInfo' query.
                              NOTE: replaces the `qL' query (see below).
               reply `m'<ID>  A single thread id
               reply          a comma-separated list of thread ids
               `m'<ID>,<ID>...
               reply `l'      (lower case 'el') denotes end of list.
                              In response to each query, the target will
                              reply with a list of one or more thread
                              ids, in big-endian hex, separated by
                              commas.  GDB will respond to each reply
                              with a request for more thread ids (using
                              the `qs' form of the query), until the
                              target responds with `l' (lower-case el,
                              for `'last'').
extra thread   `q'`ThreadExtraInfo'`,'ID
info                          
                              Where <ID> is a thread-id in big-endian
                              hex.  Obtain a printable string
                              description of a thread's attributes from
                              the target OS.  This string may contain
                              anything that the target OS thinks is
                              interesting for GDB to tell the user about
                              the thread.  The string is displayed in
                              GDB's `info threads' display.  Some
                              examples of possible thread extra info
                              strings are "Runnable", or "Blocked on
                              Mutex".
               reply XX...    Where XX... is a hex encoding of ASCII
                              data, comprising the printable string
                              containing the extra information about the
                              thread's attributes.
query LIST or  `q'`L'STARTFLAGTHREADCOUNTNEXTTHREAD
THREADLIST                    
*(deprecated)*                
                              Obtain thread information from RTOS.
                              Where: STARTFLAG (one hex digit) is one to
                              indicate the first query and zero to
                              indicate a subsequent query; THREADCOUNT
                              (two hex digits) is the maximum number of
                              threads the response packet can contain;
                              and NEXTTHREAD (eight hex digits), for
                              subsequent queries (STARTFLAG is zero), is
                              returned in the response as ARGTHREAD.
                              NOTE: this query is replaced by the
                              `q'`fThreadInfo' query (see above).
               reply          
               `q'`M'COUNTDONEARGTHREADTHREAD...
                              Where: COUNT (two hex digits) is the
                              number of threads being returned; DONE
                              (one hex digit) is zero to indicate more
                              threads and one indicates no further
                              threads; ARGTHREADID (eight hex digits) is
                              NEXTTHREAD from the request packet;
                              THREAD... is a sequence of thread IDs from
                              the target.  THREADID (eight hex digits).
                              See `remote.c:parse_threadlist_response()'.
compute CRC    `q'`CRC:'ADDR`,'LENGTH
of memory                     
block                         
               reply `E'NN    An error (such as memory fault)
               reply `C'CRC32 A 32 bit cyclic redundancy check of the
                              specified memory region.
query sect     `q'`Offsets'   Get section offsets that the target used
offs                          when re-locating the downloaded image.
                              _Note: while a `Bss' offset is included in
                              the response, GDB ignores this and instead
                              applies the `Data' offset to the `Bss'
                              section._
               reply          
               `Text='XXX`;Data='YYY`;Bss='ZZZ
thread info    `q'`P'MODETHREADID
request                       
                              Returns information on THREADID.  Where:
                              MODE is a hex encoded 32 bit mode;
                              THREADID is a hex encoded 64 bit thread ID.
               reply *        See
                              `remote.c:remote_unpack_thread_info_response()'.
remote command `q'`Rcmd,'COMMAND
                              COMMAND (hex encoded) is passed to the
                              local interpreter for execution.  Invalid
                              commands should be reported using the
                              output string.  Before the final result
                              packet, the target may also respond with a
                              number of intermediate `O'OUTPUT console
                              output packets.  _Implementors should note
                              that providing access to a stubs's
                              interpreter may have security
                              implications_.
               reply `OK'     A command response with no output.
               reply OUTPUT   A command response with the hex encoded
                              output string OUTPUT.
               reply `E'NN    Indicate a badly formed request.
               reply `'       When `q'`Rcmd' is not recognized.

   The following `g'/`G' packets have previously been defined.  In the
below, some thirty-two bit registers are transferred as sixty-four
bits.  Those registers should be zero/sign extended (which?) to fill the
space allocated.  Register bytes are transfered in target byte order.
The two nibbles within a register byte are transfered most-significant -
least-significant.

MIPS32                               All registers are transfered as
                                     thirty-two bit quantities in the
                                     order: 32 general-purpose; sr; lo;
                                     hi; bad; cause; pc; 32
                                     floating-point registers; fsr; fir;
                                     fp.
MIPS64                               All registers are transfered as
                                     sixty-four bit quantities (including
                                     thirty-two bit registers such as
                                     `sr').  The ordering is the same as
                                     `MIPS32'.

   Example sequence of a target being re-started.  Notice how the
restart does not get any direct output:

     <- `R00'
     -> `+'
     _target restarts_
     <- `?'
     -> `+'
     -> `T001:1234123412341234'
     <- `+'

   Example sequence of a target being stepped by a single instruction:

     <- `G1445...'
     -> `+'
     <- `s'
     -> `+'
     _time passes_
     -> `T001:1234123412341234'
     <- `+'
     <- `g'
     -> `+'
     -> `1455...'
     <- `+'


File: gdb.info,  Node: Server,  Next: NetWare,  Prev: Protocol,  Up: Remote Serial

Using the `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.

_On the target machine,_
     you need to have a copy of the program you want to debug.
     `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.txt

     The 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').(1)  You must use the same port
     number with the host GDB `target remote' command.

_On the GDB host machine,_
     you need an unstripped copy of your program, since GDB needs
     symbols and debugging information.  Start up GDB as usual, using
     the name of the local copy of your program as the first argument.
     (You may also need the `--baud' option if the serial line is
     running at anything other than 9600bps.)  After that, use `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/ttyb

     communicates with the server via serial line `/dev/ttyb', and

          (gdb) target remote the-target:2345

     communicates 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'.

   ---------- Footnotes ----------

   (1) If you choose a port number that conflicts with another service,
`gdbserver' prints an error message and exits.


File: gdb.info,  Node: NetWare,  Prev: Server,  Up: Remote Serial

Using the `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.

_On the target machine,_
     you need to have a copy of the program you want to debug.
     `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 9600bps.

     For example, to debug Emacs with the argument `foo.txt'and
     communicate with GDB over serial port number 2 or board 1 using a
     19200bps connection:

          load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt

_On the GDB host machine,_
     you need an unstripped copy of your program, since GDB needs
     symbols and debugging information.  Start up GDB as usual, using
     the name of the local copy of your program as the first argument.
     (You may also need the `--baud' option if the serial line is
     running at anything other than 9600bps.  After that, use `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/ttyb

     communications with the server via serial line `/dev/ttyb'.


File: gdb.info,  Node: KOD,  Prev: Remote,  Up: Targets

Kernel Object Display
=====================

   Some targets support kernel object display.  Using this facility,
GDB communicates specially with the underlying operating system and can
display information about operating system-level objects such as
mutexes and other synchronization objects.  Exactly which objects can be
displayed is determined on a per-OS basis.

   Use the `set os' command to set the operating system.  This tells
GDB which kernel object display module to initialize:

     (gdb) set os cisco

   If `set os' succeeds, GDB will display some information about the
operating system, and will create a new `info' command which can be
used to query the target.  The `info' command is named after the
operating system:

     (gdb) info cisco
     List of Cisco Kernel Objects
     Object     Description
     any        Any and all objects

   Further subcommands can be used to query about particular objects
known by the kernel.

   There is currently no way to determine whether a given operating
system is supported other than to try it.


File: gdb.info,  Node: Configurations,  Next: Controlling GDB,  Prev: Targets,  Up: Top

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.

* Menu:

* Native::
* Embedded OS::
* Embedded Processors::
* Architectures::


File: gdb.info,  Node: Native,  Next: Embedded OS,  Up: Configurations

Native
======

   This section describes details specific to particular native
configurations.

* Menu:

* HP-UX::                       HP-UX
* SVR4 Process Information::    SVR4 process information


File: gdb.info,  Node: HP-UX,  Next: SVR4 Process Information,  Up: Native

HP-UX
-----

   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.


File: gdb.info,  Node: SVR4 Process Information,  Prev: HP-UX,  Up: Native

SVR4 process information
------------------------

   Many versions of SVR4 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 on several
kinds of information about the process running your program.  `info
proc' works only on SVR4 systems that include the `procfs' code.  This
includes OSF/1 (Digital Unix), Solaris, Irix, and Unixware, but not
HP-UX or Linux, for example.

`info proc'
     Summarize available information about the process.

`info proc mappings'
     Report on the address ranges accessible in the program, with
     information on whether your program may read, write, or execute
     each range.

`info proc times'
     Starting time, user CPU time, and system CPU time for your program
     and its children.

`info proc id'
     Report on the process IDs related to your program: its own process
     ID, the ID of its parent, the process group ID, and the session ID.

`info proc status'
     General information on the state of the process.  If the process is
     stopped, this report includes the reason for stopping, and any
     signal received.

`info proc all'
     Show all the above information about the process.


File: gdb.info,  Node: Embedded OS,  Next: Embedded Processors,  Prev: Native,  Up: Configurations

Embedded Operating Systems
==========================

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

* Menu:

* VxWorks::                     Using GDB with VxWorks

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