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* Gdb-Internals: (gdbint).      The GNU debugger's internals.

END-INFO-DIR-ENTRY

   This file documents the internals of the GNU debugger GDB.

   Copyright 1990-1999 Free Software Foundation, Inc.  Contributed by

Cygnus Solutions.  Written by John Gilmore.  Second Edition by Stan

Shebs.

   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 or distribute modified versions of this

manual under the terms of the GPL (for which purpose this text may be

regarded as a program in the language TeX).

File: gdbint.info,  Node: Target Architecture Definition,  Next: Target Vector Definition,  Prev: Host Definition,  Up: Top

Target Architecture Definition

******************************

   GDB's target architecture defines what sort of machine-language

programs GDB can work with, and how it works with them.

   At present, the target architecture definition consists of a number

of C macros.

Registers and Memory

====================

   GDB's model of the target machine is rather simple.  GDB assumes the

machine includes a bank of registers and a block of memory.  Each

register may have a different size.

   GDB does not have a magical way to match up with the compiler's idea

of which registers are which; however, it is critical that they do

match up accurately.  The only way to make this work is to get accurate

information about the order that the compiler uses, and to reflect that

in the `REGISTER_NAME' and related macros.

   GDB can handle big-endian, little-endian, and bi-endian

architectures.

Using Different Register and Memory Data Representations

========================================================

   Some architectures use one representation for a value when it lives

in a register, but use a different representation when it lives in

memory.  In GDB's terminology, the "raw" representation is the one used

in the target registers, and the "virtual" representation is the one

used in memory, and within GDB `struct value' objects.

   For almost all data types on almost all architectures, the virtual

and raw representations are identical, and no special handling is

needed.  However, they do occasionally differ.  For example:

   * The x86 architecture supports an 80-bit long double type.

     However, when we store those values in memory, they occupy twelve

     bytes: the floating-point number occupies the first ten, and the

     final two bytes are unused.  This keeps the values aligned on

     four-byte boundaries, allowing more efficient access.  Thus, the

     x86 80-bit floating-point type is the raw representation, and the

     twelve-byte loosely-packed arrangement is the virtual

     representation.

   * Some 64-bit MIPS targets present 32-bit registers to GDB as 64-bit

     registers, with garbage in their upper bits.  GDB ignores the top

     32 bits.  Thus, the 64-bit form, with garbage in the upper 32

     bits, is the raw representation, and the trimmed 32-bit

     representation is the virtual representation.

   In general, the raw representation is determined by the

architecture, or GDB's interface to the architecture, while the virtual

representation can be chosen for GDB's convenience.  GDB's register

file, `registers', holds the register contents in raw format, and the

GDB remote protocol transmits register values in raw format.

   Your architecture may define the following macros to request raw /

virtual conversions:

 - Target Macro: int REGISTER_CONVERTIBLE (int REG)

     Return non-zero if register number REG's value needs different raw

     and virtual formats.

 - Target Macro: int REGISTER_RAW_SIZE (int REG)

     The size of register number REG's raw value.  This is the number

     of bytes the register will occupy in `registers', or in a GDB

     remote protocol packet.

 - Target Macro: int REGISTER_VIRTUAL_SIZE (int REG)

     The size of register number REG's value, in its virtual format.

     This is the size a `struct value''s buffer will have, holding that

     register's value.

 - Target Macro: struct type *REGISTER_VIRTUAL_TYPE (int REG)

     This is the type of the virtual representation of register number

     REG.  Note that there is no need for a macro giving a type for the

     register's raw form; once the register's value has been obtained,

     GDB always uses the virtual form.

 - Target Macro: void REGISTER_CONVERT_TO_VIRTUAL (int REG, struct type

          *TYPE, char *FROM, char *TO)

     Convert the value of register number REG to TYPE, which should

     always be `REGISTER_VIRTUAL_TYPE (REG)'.  The buffer at FROM holds

     the register's value in raw format; the macro should convert the

     value to virtual format, and place it at TO.

     Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW

     take their REG and TYPE arguments in different orders.

 - Target Macro: void REGISTER_CONVERT_TO_RAW (struct type *TYPE, int

          REG, char *FROM, char *TO)

     Convert the value of register number REG to TYPE, which should

     always be `REGISTER_VIRTUAL_TYPE (REG)'.  The buffer at FROM holds

     the register's value in raw format; the macro should convert the

     value to virtual format, and place it at TO.

     Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW

     take their REG and TYPE arguments in different orders.

Frame Interpretation

====================

Inferior Call Setup

===================

Compiler Characteristics

========================

Target Conditionals

===================

   This section describes the macros that you can use to define the

target machine.

`ADDITIONAL_OPTIONS'

`ADDITIONAL_OPTION_CASES'

`ADDITIONAL_OPTION_HANDLER'

`ADDITIONAL_OPTION_HELP'

     These are a set of macros that allow the addition of additional

     command line options to GDB.  They are currently used only for the

     unsupported i960 Nindy target, and should not be used in any other

     configuration.

`ADDR_BITS_REMOVE (addr)'

     If a raw machine instruction address includes any bits that are not

     really part of the address, then define this macro to expand into

     an expression that zeros those bits in ADDR.  This is only used for

     addresses of instructions, and even then not in all contexts.

     For example, the two low-order bits of the PC on the

     Hewlett-Packard PA 2.0 architecture contain the privilege level of

     the corresponding instruction.  Since instructions must always be

     aligned on four-byte boundaries, the processor masks out these

     bits to generate the actual address of the instruction.

     ADDR_BITS_REMOVE should filter out these bits with an expression

     such as `((addr) & ~3)'.

`BEFORE_MAIN_LOOP_HOOK'

     Define this to expand into any code that you want to execute

     before the main loop starts.  Although this is not, strictly

     speaking, a target conditional, that is how it is currently being

     used.  Note that if a configuration were to define it one way for

     a host and a different way for the target, GDB will probably not

     compile, let alone run correctly.  This is currently used only for

     the unsupported i960 Nindy target, and should not be used in any

     other configuration.

`BELIEVE_PCC_PROMOTION'

     Define if the compiler promotes a short or char parameter to an

     int, but still reports the parameter as its original type, rather

     than the promoted type.

`BELIEVE_PCC_PROMOTION_TYPE'

     Define this if GDB should believe the type of a short argument when

     compiled by pcc, but look within a full int space to get its value.

     Only defined for Sun-3 at present.

`BITS_BIG_ENDIAN'

     Define this if the numbering of bits in the targets does *not*

     match the endianness of the target byte order.  A value of 1 means

     that the bits are numbered in a big-endian order, 0 means

     little-endian.

`BREAKPOINT'

     This is the character array initializer for the bit pattern to put

     into memory where a breakpoint is set.  Although it's common to

     use a trap instruction for a breakpoint, it's not required; for

     instance, the bit pattern could be an invalid instruction.  The

     breakpoint must be no longer than the shortest instruction of the

     architecture.

     BREAKPOINT has been deprecated in favour of BREAKPOINT_FROM_PC.

`BIG_BREAKPOINT'

`LITTLE_BREAKPOINT'

     Similar to BREAKPOINT, but used for bi-endian targets.

     BIG_BREAKPOINT and LITTLE_BREAKPOINT have been deprecated in

     favour of BREAKPOINT_FROM_PC.

`REMOTE_BREAKPOINT'

`LITTLE_REMOTE_BREAKPOINT'

`BIG_REMOTE_BREAKPOINT'

     Similar to BREAKPOINT, but used for remote targets.

     BIG_REMOTE_BREAKPOINT and LITTLE_REMOTE_BREAKPOINT have been

     deprecated in favour of BREAKPOINT_FROM_PC.

`BREAKPOINT_FROM_PC (pcptr, lenptr)'

     Use the program counter to determine the contents and size of a

     breakpoint instruction.  It returns a pointer to a string of bytes

     that encode a breakpoint instruction, stores the length of the

     string to *lenptr, and adjusts pc (if necessary) to point to the

     actual memory location where the breakpoint should be inserted.

     Although it is common to use a trap instruction for a breakpoint,

     it's not required; for instance, the bit pattern could be an

     invalid instruction.  The breakpoint must be no longer than the

     shortest instruction of the architecture.

     Replaces all the other BREAKPOINT macros.

`MEMORY_INSERT_BREAKPOINT (addr, contents_cache)'

`MEMORY_REMOVE_BREAKPOINT (addr, contents_cache)'

     Insert or remove memory based breakpoints.  Reasonable defaults

     (`default_memory_insert_breakpoint' and

     `default_memory_remove_breakpoint' respectively) have been

     provided so that it is not necessary to define these for most

     architectures.  Architectures which may want to define

     MEMORY_INSERT_BREAKPOINT and MEMORY_REMOVE_BREAKPOINT will likely

     have instructions that are oddly sized or are not stored in a

     conventional manner.

     It may also be desirable (from an efficiency standpoint) to define

     custom breakpoint insertion and removal routines if

     BREAKPOINT_FROM_PC needs to read the target's memory for some

     reason.

`CALL_DUMMY_P'

     A C expresson that is non-zero when the target suports inferior

     function calls.

`CALL_DUMMY_WORDS'

     Pointer to an array of LONGEST words of data containing

     host-byte-ordered REGISTER_BYTES sized values that partially

     specify the sequence of instructions needed for an inferior

     function call.

     Should be deprecated in favour of a macro that uses

     target-byte-ordered data.

`SIZEOF_CALL_DUMMY_WORDS'

     The size of CALL_DUMMY_WORDS.  When CALL_DUMMY_P this must return

     a positive value.  See also CALL_DUMMY_LENGTH.

`CALL_DUMMY'

     A static initializer for CALL_DUMMY_WORDS.  Deprecated.

`CALL_DUMMY_LOCATION'

     inferior.h

`CALL_DUMMY_STACK_ADJUST'

     Stack adjustment needed when performing an inferior function call.

     Should be deprecated in favor of something like STACK_ALIGN.

`CALL_DUMMY_STACK_ADJUST_P'

     Predicate for use of CALL_DUMMY_STACK_ADJUST.

     Should be deprecated in favor of something like STACK_ALIGN.

`CANNOT_FETCH_REGISTER (regno)'

     A C expression that should be nonzero if REGNO cannot be fetched

     from an inferior process.  This is only relevant if

     `FETCH_INFERIOR_REGISTERS' is not defined.

`CANNOT_STORE_REGISTER (regno)'

     A C expression that should be nonzero if REGNO should not be

     written to the target.  This is often the case for program

     counters, status words, and other special registers.  If this is

     not defined, GDB will assume that all registers may be written.

`DO_DEFERRED_STORES'

`CLEAR_DEFERRED_STORES'

     Define this to execute any deferred stores of registers into the

     inferior, and to cancel any deferred stores.

     Currently only implemented correctly for native Sparc

     configurations?

`COERCE_FLOAT_TO_DOUBLE (FORMAL, ACTUAL)'

     If we are calling a function by hand, and the function was declared

     (according to the debug info) without a prototype, should we

     automatically promote floats to doubles?  This macro must evaluate

     to non-zero if we should, or zero if we should leave the value

     alone.

     The argument ACTUAL is the type of the value we want to pass to

     the function.  The argument FORMAL is the type of this argument,

     as it appears in the function's definition.  Note that FORMAL may

     be zero if we have no debugging information for the function, or if

     we're passing more arguments than are officially declared (for

     example, varargs).  This macro is never invoked if the function

     definitely has a prototype.

     The default behavior is to promote only when we have no type

     information for the formal parameter.  This is different from the

     obvious behavior, which would be to promote whenever we have no

     prototype, just as the compiler does.  It's annoying, but some

     older targets rely on this.  If you want GDB to follow the typical

     compiler behavior -- to always promote when there is no prototype

     in scope -- your gdbarch init function can call

     `set_gdbarch_coerce_float_to_double' and select the

     `standard_coerce_float_to_double' function.

`CPLUS_MARKER'

     Define this to expand into the character that G++ uses to

     distinguish compiler-generated identifiers from

     programmer-specified identifiers.  By default, this expands into

     `'$''.  Most System V targets should define this to `'.''.

`DBX_PARM_SYMBOL_CLASS'

     Hook for the `SYMBOL_CLASS' of a parameter when decoding DBX symbol

     information.  In the i960, parameters can be stored as locals or as

     args, depending on the type of the debug record.

`DECR_PC_AFTER_BREAK'

     Define this to be the amount by which to decrement the PC after the

     program encounters a breakpoint.  This is often the number of

     bytes in BREAKPOINT, though not always.  For most targets this

     value will be 0.

`DECR_PC_AFTER_HW_BREAK'

     Similarly, for hardware breakpoints.

`DISABLE_UNSETTABLE_BREAK addr'

     If defined, this should evaluate to 1 if ADDR is in a shared

     library in which breakpoints cannot be set and so should be

     disabled.

`DO_REGISTERS_INFO'

     If defined, use this to print the value of a register or all

     registers.

`END_OF_TEXT_DEFAULT'

     This is an expression that should designate the end of the text

     section (? FIXME ?)

`EXTRACT_RETURN_VALUE(type,regbuf,valbuf)'

     Define this to extract a function's return value of type TYPE from

     the raw register state REGBUF and copy that, in virtual format,

     into VALBUF.

`EXTRACT_STRUCT_VALUE_ADDRESS(regbuf)'

     When EXTRACT_STRUCT_VALUE_ADDRESS_P this is used to to extract

     from an array REGBUF (containing the raw register state) the

     address in which a function should return its structure value, as a

     CORE_ADDR (or an expression that can be used as one).

`EXTRACT_STRUCT_VALUE_ADDRESS_P'

     Predicate for EXTRACT_STRUCT_VALUE_ADDRESS.

`FLOAT_INFO'

     If defined, then the `info float' command will print information

     about the processor's floating point unit.

`FP_REGNUM'

     If the virtual frame pointer is kept in a register, then define

     this macro to be the number (greater than or equal to zero) of

     that register.

     This should only need to be defined if `TARGET_READ_FP' and

     `TARGET_WRITE_FP' are not defined.

`FRAMELESS_FUNCTION_INVOCATION(fi)'

     Define this to an expression that returns 1 if the function

     invocation represented by FI does not have a stack frame

     associated with it.  Otherwise return 0.

`FRAME_ARGS_ADDRESS_CORRECT'

     stack.c

`FRAME_CHAIN(frame)'

     Given FRAME, return a pointer to the calling frame.

`FRAME_CHAIN_COMBINE(chain,frame)'

     Define this to take the frame chain pointer and the frame's nominal

     address and produce the nominal address of the caller's frame.

     Presently only defined for HP PA.

`FRAME_CHAIN_VALID(chain,thisframe)'

     Define this to be an expression that returns zero if the given

     frame is an outermost frame, with no caller, and nonzero

     otherwise.  Several common definitions are available.

     `file_frame_chain_valid' is nonzero if the chain pointer is nonzero

     and given frame's PC is not inside the startup file (such as

     `crt0.o').  `func_frame_chain_valid' is nonzero if the chain

     pointer is nonzero and the given frame's PC is not in `main()' or a

     known entry point function (such as `_start()').

     `generic_file_frame_chain_valid' and

     `generic_func_frame_chain_valid' are equivalent implementations for

     targets using generic dummy frames.

`FRAME_INIT_SAVED_REGS(frame)'

     See `frame.h'.  Determines the address of all registers in the

     current stack frame storing each in `frame->saved_regs'.  Space for

     `frame->saved_regs' shall be allocated by `FRAME_INIT_SAVED_REGS'

     using either `frame_saved_regs_zalloc' or `frame_obstack_alloc'.

     FRAME_FIND_SAVED_REGS and EXTRA_FRAME_INFO are deprecated.

`FRAME_NUM_ARGS (fi)'

     For the frame described by FI return the number of arguments that

     are being passed.  If the number of arguments is not known, return

     `-1'.

`FRAME_SAVED_PC(frame)'

     Given FRAME, return the pc saved there.  That is, the return

     address.

`FUNCTION_EPILOGUE_SIZE'

     For some COFF targets, the `x_sym.x_misc.x_fsize' field of the

     function end symbol is 0.  For such targets, you must define

     `FUNCTION_EPILOGUE_SIZE' to expand into the standard size of a

     function's epilogue.

`FUNCTION_START_OFFSET'

     An integer, giving the offset in bytes from a function's address

     (as used in the values of symbols, function pointers, etc.), and

     the function's first genuine instruction.

     This is zero on almost all machines: the function's address is

     usually the address of its first instruction.  However, on the

     VAX, for example, each function starts with two bytes containing a

     bitmask indicating which registers to save upon entry to the

     function.  The VAX `call' instructions check this value, and save

     the appropriate registers automatically.  Thus, since the offset

     from the function's address to its first instruction is two bytes,

     `FUNCTION_START_OFFSET' would be 2 on the VAX.

`GCC_COMPILED_FLAG_SYMBOL'

`GCC2_COMPILED_FLAG_SYMBOL'

     If defined, these are the names of the symbols that GDB will look

     for to detect that GCC compiled the file.  The default symbols are

     `gcc_compiled.' and `gcc2_compiled.', respectively. (Currently

     only defined for the Delta 68.)

`GDB_MULTI_ARCH'

     If defined and non-zero, enables suport for multiple architectures

     within GDB.

     The support can be enabled at two levels.  At level one, only

     definitions for previously undefined macros are provided; at level

     two, a multi-arch definition of all architecture dependant macros

     will be defined.

`GDB_TARGET_IS_HPPA'

     This determines whether horrible kludge code in dbxread.c and

     partial-stab.h is used to mangle multiple-symbol-table files from

     HPPA's.  This should all be ripped out, and a scheme like elfread.c

     used.

`GET_LONGJMP_TARGET'

     For most machines, this is a target-dependent parameter.  On the

     DECstation and the Iris, this is a native-dependent parameter,

     since  is needed to define it.

     This macro determines the target PC address that longjmp() will

     jump to, assuming that we have just stopped at a longjmp

     breakpoint.  It takes a CORE_ADDR * as argument, and stores the

     target PC value through this pointer.  It examines the current

     state of the machine as needed.

`GET_SAVED_REGISTER'

     Define this if you need to supply your own definition for the

     function `get_saved_register'.

`HAVE_REGISTER_WINDOWS'

     Define this if the target has register windows.

`REGISTER_IN_WINDOW_P (regnum)'

     Define this to be an expression that is 1 if the given register is

     in the window.

`IBM6000_TARGET'

     Shows that we are configured for an IBM RS/6000 target.  This

     conditional should be eliminated (FIXME) and replaced by

     feature-specific macros.  It was introduced in haste and we are

     repenting at leisure.

`SYMBOLS_CAN_START_WITH_DOLLAR'

     Some systems have routines whose names start with `$'.  Giving this

     macro a non-zero value tells GDB's expression parser to check for

     such routines when parsing tokens that begin with `$'.

     On HP-UX, certain system routines (millicode) have names beginning

     with `$' or `$$'.  For example, `$$dyncall' is a millicode routine

     that handles inter-space procedure calls on PA-RISC.

`IEEE_FLOAT'

     Define this if the target system uses IEEE-format floating point

     numbers.

`INIT_EXTRA_FRAME_INFO (fromleaf, frame)'

     If additional information about the frame is required this should

     be stored in `frame->extra_info'.  Space for `frame->extra_info'

     is allocated using `frame_obstack_alloc'.

`INIT_FRAME_PC (fromleaf, prev)'

     This is a C statement that sets the pc of the frame pointed to by

     PREV.  [By default...]

`INNER_THAN (lhs,rhs)'

     Returns non-zero if stack address LHS is inner than (nearer to the

     stack top) stack address RHS. Define this as `lhs < rhs' if the

     target's stack grows downward in memory, or `lhs > rsh' if the

     stack grows upward.

`IN_SIGTRAMP (pc, name)'

     Define this to return true if the given PC and/or NAME indicates

     that the current function is a sigtramp.

`SIGTRAMP_START (pc)'

`SIGTRAMP_END (pc)'

     Define these to be the start and end address of the sigtramp for

     the given PC.  On machines where the address is just a compile time

     constant, the macro expansion will typically just ignore the

     supplied PC.

`IN_SOLIB_CALL_TRAMPOLINE pc name'

     Define this to evaluate to nonzero if the program is stopped in the

     trampoline that connects to a shared library.

`IN_SOLIB_RETURN_TRAMPOLINE pc name'

     Define this to evaluate to nonzero if the program is stopped in the

     trampoline that returns from a shared library.

`IN_SOLIB_DYNSYM_RESOLVE_CODE pc'

     Define this to evaluate to nonzero if the program is stopped in the

     dynamic linker.

`SKIP_SOLIB_RESOLVER pc'

     Define this to evaluate to the (nonzero) address at which execution

     should continue to get past the dynamic linker's symbol resolution

     function.  A zero value indicates that it is not important or

     necessary to set a breakpoint to get through the dynamic linker

     and that single stepping will suffice.

`IS_TRAPPED_INTERNALVAR (name)'

     This is an ugly hook to allow the specification of special actions

     that should occur as a side-effect of setting the value of a

     variable internal to GDB.  Currently only used by the h8500.  Note

     that this could be either a host or target conditional.

`NEED_TEXT_START_END'

     Define this if GDB should determine the start and end addresses of

     the text section.  (Seems dubious.)

`NO_HIF_SUPPORT'

     (Specific to the a29k.)

`REGISTER_CONVERTIBLE (REG)'

     Return non-zero if REG uses different raw and virtual formats.

     *Note Using Different Register and Memory Data Representations:

     Target Architecture Definition.

`REGISTER_RAW_SIZE (REG)'

     Return the raw size of REG.  *Note Using Different Register and

     Memory Data Representations: Target Architecture Definition.

`REGISTER_VIRTUAL_SIZE (REG)'

     Return the virtual size of REG.  *Note Using Different Register

     and Memory Data Representations: Target Architecture Definition.

`REGISTER_VIRTUAL_TYPE (REG)'

     Return the virtual type of REG.  *Note Using Different Register

     and Memory Data Representations: Target Architecture Definition.

`REGISTER_CONVERT_TO_VIRTUAL(REG, TYPE, FROM, TO)'

     Convert the value of register REG from its raw form to its virtual

     form.  *Note Using Different Register and Memory Data

     Representations: Target Architecture Definition.

`REGISTER_CONVERT_TO_RAW(TYPE, REG, FROM, TO)'

     Convert the value of register REG from its virtual form to its raw

     form.  *Note Using Different Register and Memory Data

     Representations: Target Architecture Definition.

`SOFTWARE_SINGLE_STEP_P'

     Define this as 1 if the target does not have a hardware single-step

     mechanism. The macro `SOFTWARE_SINGLE_STEP' must also be defined.

`SOFTWARE_SINGLE_STEP(signal,insert_breapoints_p)'

     A function that inserts or removes (dependant on

     INSERT_BREAPOINTS_P) breakpoints at each possible destinations of

     the next instruction. See `sparc-tdep.c' and `rs6000-tdep.c' for

     examples.

`SOFUN_ADDRESS_MAYBE_MISSING'

     Somebody clever observed that, the more actual addresses you have

     in the debug information, the more time the linker has to spend

     relocating them.  So whenever there's some other way the debugger

     could find the address it needs, you should omit it from the debug

     info, to make linking faster.

     `SOFUN_ADDRESS_MAYBE_MISSING' indicates that a particular set of

     hacks of this sort are in use, affecting `N_SO' and `N_FUN'

     entries in stabs-format debugging information.  `N_SO' stabs mark

     the beginning and ending addresses of compilation units in the text

     segment.  `N_FUN' stabs mark the starts and ends of functions.

     `SOFUN_ADDRESS_MAYBE_MISSING' means two things:

        * `N_FUN' stabs have an address of zero.  Instead, you should

          find the addresses where the function starts by taking the

          function name from the stab, and then looking that up in the

          minsyms (the linker/ assembler symbol table).  In other

          words, the stab has the name, and the linker / assembler

          symbol table is the only place that carries the address.

        * `N_SO' stabs have an address of zero, too.  You just look at

          the `N_FUN' stabs that appear before and after the `N_SO'

          stab, and guess the starting and ending addresses of the

          compilation unit from them.

`PCC_SOL_BROKEN'

     (Used only in the Convex target.)

`PC_IN_CALL_DUMMY'

     inferior.h

`PC_LOAD_SEGMENT'

     If defined, print information about the load segment for the

     program counter.  (Defined only for the RS/6000.)

`PC_REGNUM'

     If the program counter is kept in a register, then define this

     macro to be the number (greater than or equal to zero) of that

     register.

     This should only need to be defined if `TARGET_READ_PC' and

     `TARGET_WRITE_PC' are not defined.

`NPC_REGNUM'

     The number of the "next program counter" register, if defined.

`NNPC_REGNUM'

     The number of the "next next program counter" register, if defined.

     Currently, this is only defined for the Motorola 88K.

`PARM_BOUNDARY'

     If non-zero, round arguments to a boundary of this many bits before

     pushing them on the stack.

`PRINT_REGISTER_HOOK (regno)'

     If defined, this must be a function that prints the contents of the

     given register to standard output.

`PRINT_TYPELESS_INTEGER'

     This is an obscure substitute for `print_longest' that seems to

     have been defined for the Convex target.

`PROCESS_LINENUMBER_HOOK'

     A hook defined for XCOFF reading.

`PROLOGUE_FIRSTLINE_OVERLAP'

     (Only used in unsupported Convex configuration.)

`PS_REGNUM'

     If defined, this is the number of the processor status register.

     (This definition is only used in generic code when parsing "$ps".)

`POP_FRAME'

     Used in `call_function_by_hand' to remove an artificial stack

     frame.

`PUSH_ARGUMENTS (nargs, args, sp, struct_return, struct_addr)'

     Define this to push arguments onto the stack for inferior function

     call. Return the updated stack pointer value.

`PUSH_DUMMY_FRAME'

     Used in `call_function_by_hand' to create an artificial stack

     frame.

`REGISTER_BYTES'

     The total amount of space needed to store GDB's copy of the

     machine's register state.

`REGISTER_NAME(i)'

     Return the name of register I as a string.  May return NULL or NUL

     to indicate that register I is not valid.

`REGISTER_NAMES'

     Deprecated in favor of REGISTER_NAME.

`REG_STRUCT_HAS_ADDR (gcc_p, type)'

     Define this to return 1 if the given type will be passed by pointer

     rather than directly.

`SAVE_DUMMY_FRAME_TOS (sp)'

     Used in `call_function_by_hand' to notify the target dependent code

     of the top-of-stack value that will be passed to the the inferior

     code.  This is the value of the SP after both the dummy frame and

     space for parameters/results have been allocated on the stack.

`SDB_REG_TO_REGNUM'

     Define this to convert sdb register numbers into GDB regnums.  If

     not defined, no conversion will be done.

`SHIFT_INST_REGS'

     (Only used for m88k targets.)

`SKIP_PERMANENT_BREAKPOINT'

     Advance the inferior's PC past a permanent breakpoint.  GDB

     normally steps over a breakpoint by removing it, stepping one

     instruction, and re-inserting the breakpoint.  However, permanent

     breakpoints are hardwired into the inferior, and can't be removed,

     so this strategy doesn't work.  Calling SKIP_PERMANENT_BREAKPOINT

     adjusts the processor's state so that execution will resume just

     after the breakpoint.  This macro does the right thing even when

     the breakpoint is in the delay slot of a branch or jump.

`SKIP_PROLOGUE (pc)'

     A C expression that returns the address of the "real" code beyond

     the function entry prologue found at PC.

`SKIP_PROLOGUE_FRAMELESS_P'

     A C expression that should behave similarly, but that can stop as

     soon as the function is known to have a frame.  If not defined,

     `SKIP_PROLOGUE' will be used instead.

`SKIP_TRAMPOLINE_CODE (pc)'

     If the target machine has trampoline code that sits between

     callers and the functions being called, then define this macro to

     return a new PC that is at the start of the real function.

`SP_REGNUM'

     If the stack-pointer is kept in a register, then define this macro

     to be the number (greater than or equal to zero) of that register.

     This should only need to be defined if `TARGET_WRITE_SP' and

     `TARGET_WRITE_SP' are not defined.

`STAB_REG_TO_REGNUM'

     Define this to convert stab register numbers (as gotten from `r'

     declarations) into GDB regnums.  If not defined, no conversion

     will be done.

`STACK_ALIGN (addr)'

     Define this to adjust the address to the alignment required for the

     processor's stack.

`STEP_SKIPS_DELAY (addr)'

     Define this to return true if the address is of an instruction

     with a delay slot.  If a breakpoint has been placed in the

     instruction's delay slot, GDB will single-step over that

     instruction before resuming normally.  Currently only defined for

     the Mips.

`STORE_RETURN_VALUE (type, valbuf)'

     A C expression that stores a function return value of type TYPE,

     where VALBUF is the address of the value to be stored.

`SUN_FIXED_LBRAC_BUG'

     (Used only for Sun-3 and Sun-4 targets.)

`SYMBOL_RELOADING_DEFAULT'

     The default value of the `symbol-reloading' variable.  (Never

     defined in current sources.)

`TARGET_BYTE_ORDER_DEFAULT'

     The ordering of bytes in the target.  This must be either

     `BIG_ENDIAN' or `LITTLE_ENDIAN'.  This macro replaces

     TARGET_BYTE_ORDER which is deprecated.

`TARGET_BYTE_ORDER_SELECTABLE_P'

     Non-zero if the target has both `BIG_ENDIAN' and `LITTLE_ENDIAN'

     variants.  This macro replaces TARGET_BYTE_ORDER_SELECTABLE which

     is deprecated.

`TARGET_CHAR_BIT'

     Number of bits in a char; defaults to 8.

`TARGET_COMPLEX_BIT'

     Number of bits in a complex number; defaults to `2 *

     TARGET_FLOAT_BIT'.

     At present this macro is not used.

`TARGET_DOUBLE_BIT'

     Number of bits in a double float; defaults to `8 *

     TARGET_CHAR_BIT'.

`TARGET_DOUBLE_COMPLEX_BIT'

     Number of bits in a double complex; defaults to `2 *

     TARGET_DOUBLE_BIT'.

     At present this macro is not used.

`TARGET_FLOAT_BIT'

     Number of bits in a float; defaults to `4 * TARGET_CHAR_BIT'.

`TARGET_INT_BIT'

     Number of bits in an integer; defaults to `4 * TARGET_CHAR_BIT'.

`TARGET_LONG_BIT'

     Number of bits in a long integer; defaults to `4 *

     TARGET_CHAR_BIT'.

`TARGET_LONG_DOUBLE_BIT'

     Number of bits in a long double float; defaults to `2 *

     TARGET_DOUBLE_BIT'.

`TARGET_LONG_LONG_BIT'

     Number of bits in a long long integer; defaults to `2 *

     TARGET_LONG_BIT'.

`TARGET_PTR_BIT'

     Number of bits in a pointer; defaults to `TARGET_INT_BIT'.

`TARGET_SHORT_BIT'

     Number of bits in a short integer; defaults to `2 *

     TARGET_CHAR_BIT'.

`TARGET_READ_PC'

`TARGET_WRITE_PC (val, pid)'

`TARGET_READ_SP'

`TARGET_WRITE_SP'

`TARGET_READ_FP'

`TARGET_WRITE_FP'

     These change the behavior of `read_pc', `write_pc', `read_sp',

     `write_sp', `read_fp' and `write_fp'.  For most targets, these may

     be left undefined.  GDB will call the read and write register

     functions with the relevant `_REGNUM' argument.

     These macros are useful when a target keeps one of these registers

     in a hard to get at place; for example, part in a segment register

     and part in an ordinary register.

`TARGET_VIRTUAL_FRAME_POINTER(pc,regp,offsetp)'

     Returns a `(register, offset)' pair representing the virtual frame

     pointer in use at the code address `"pc"'.  If virtual frame

     pointers are not used, a default definition simply returns

     `FP_REGNUM', with an offset of zero.

`USE_STRUCT_CONVENTION (gcc_p, type)'

     If defined, this must be an expression that is nonzero if a value

     of the given TYPE being returned from a function must have space

     allocated for it on the stack.  GCC_P is true if the function

     being considered is known to have been compiled by GCC; this is

     helpful for systems where GCC is known to use different calling

     convention than other compilers.

`VARIABLES_INSIDE_BLOCK (desc, gcc_p)'

     For dbx-style debugging information, if the compiler puts variable

     declarations inside LBRAC/RBRAC blocks, this should be defined to

     be nonzero.  DESC is the value of `n_desc' from the `N_RBRAC'

     symbol, and GCC_P is true if GDB has noticed the presence of

     either the `GCC_COMPILED_SYMBOL' or the `GCC2_COMPILED_SYMBOL'.

     By default, this is 0.

`OS9K_VARIABLES_INSIDE_BLOCK (desc, gcc_p)'

     Similarly, for OS/9000.  Defaults to 1.

   Motorola M68K target conditionals.

`BPT_VECTOR'

     Define this to be the 4-bit location of the breakpoint trap

     vector.  If not defined, it will default to `0xf'.

`REMOTE_BPT_VECTOR'

     Defaults to `1'.

Adding a New Target

===================

   The following files define a target to GDB:

`gdb/config/ARCH/TTT.mt'

     Contains a Makefile fragment specific to this target.  Specifies

     what object files are needed for target TTT, by defining

     `TDEPFILES=...' and `TDEPLIBS=...'.  Also specifies the header

     file which describes TTT, by defining `TM_FILE= tm-TTT.h'.

     You can also define `TM_CFLAGS', `TM_CLIBS', `TM_CDEPS', but these

     are now deprecated, replaced by autoconf, and may go away in

     future versions of GDB.

`gdb/config/ARCH/tm-TTT.h'

     (`tm.h' is a link to this file, created by configure).  Contains

     macro definitions about the target machine's registers, stack frame

     format and instructions.

`gdb/TTT-tdep.c'

     Contains any miscellaneous code required for this target machine.

     On some machines it doesn't exist at all.  Sometimes the macros in

     `tm-TTT.h' become very complicated, so they are implemented as

     functions here instead, and the macro is simply defined to call the

     function.  This is vastly preferable, since it is easier to

     understand and debug.

`gdb/config/ARCH/tm-ARCH.h'

     This often exists to describe the basic layout of the target

     machine's processor chip (registers, stack, etc).  If used, it is

     included by `tm-TTT.h'.  It can be shared among many targets that

     use the same processor.

`gdb/ARCH-tdep.c'

     Similarly, there are often common subroutines that are shared by

     all target machines that use this particular architecture.

   If you are adding a new operating system for an existing CPU chip,

add a `config/tm-OS.h' file that describes the operating system

facilities that are unusual (extra symbol table info; the breakpoint

instruction needed; etc).  Then write a `ARCH/tm-OS.h' that just