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

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   This file documents the internals of the GNU debugger GDB.

Copyright 1990,1991,1992,1993,1994,1996,1998,1999,2000,2001    Free

Software Foundation, Inc.  Contributed by Cygnus Solutions.  Written by

John Gilmore.  Second Edition by Stan Shebs.

   Permission is granted to copy, distribute and/or modify this document

under the terms of the GNU Free Documentation License, Version 1.1 or

any later version published by the Free Software Foundation; with the

Invariant Sections being "Algorithms" and "Porting GDB", with the

Front-Cover texts being "A GNU Manual," and with the Back-Cover Texts

as in (a) below.

   (a) The FSF's Back-Cover Text is: "You have freedom to copy and

modify this GNU Manual, like GNU software.  Copies published by the Free

Software Foundation raise funds for GNU development."

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.

   The target architecture object is implemented as the C structure

`struct gdbarch *'.  The structure, and its methods, are generated

using the Bourn shell script `gdbarch.sh'.

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.

Pointers Are Not Always Addresses

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

   On almost all 32-bit architectures, the representation of a pointer

is indistinguishable from the representation of some fixed-length number

whose value is the byte address of the object pointed to.  On such

machines, the words "pointer" and "address" can be used interchangeably.

However, architectures with smaller word sizes are often cramped for

address space, so they may choose a pointer representation that breaks

this identity, and allows a larger code address space.

   For example, the Mitsubishi D10V is a 16-bit VLIW processor whose

instructions are 32 bits long(1).  If the D10V used ordinary byte

addresses to refer to code locations, then the processor would only be

able to address 64kb of instructions.  However, since instructions must

be aligned on four-byte boundaries, the low two bits of any valid

instruction's byte address are always zero--byte addresses waste two

bits.  So instead of byte addresses, the D10V uses word addresses--byte

addresses shifted right two bits--to refer to code.  Thus, the D10V can

use 16-bit words to address 256kb of code space.

   However, this means that code pointers and data pointers have

different forms on the D10V.  The 16-bit word `0xC020' refers to byte

address `0xC020' when used as a data address, but refers to byte address

`0x30080' when used as a code address.

   (The D10V also uses separate code and data address spaces, which also

affects the correspondence between pointers and addresses, but we're

going to ignore that here; this example is already too long.)

   To cope with architectures like this--the D10V is not the only

one!--GDB tries to distinguish between "addresses", which are byte

numbers, and "pointers", which are the target's representation of an

address of a particular type of data.  In the example above, `0xC020'

is the pointer, which refers to one of the addresses `0xC020' or

`0x30080', depending on the type imposed upon it.  GDB provides

functions for turning a pointer into an address and vice versa, in the

appropriate way for the current architecture.

   Unfortunately, since addresses and pointers are identical on almost

all processors, this distinction tends to bit-rot pretty quickly.  Thus,

each time you port GDB to an architecture which does distinguish

between pointers and addresses, you'll probably need to clean up some

architecture-independent code.

   Here are functions which convert between pointers and addresses:

 - Function: CORE_ADDR extract_typed_address (void *BUF, struct type

          *TYPE)

     Treat the bytes at BUF as a pointer or reference of type TYPE, and

     return the address it represents, in a manner appropriate for the

     current architecture.  This yields an address GDB can use to read

     target memory, disassemble, etc.  Note that BUF refers to a buffer

     in GDB's memory, not the inferior's.

     For example, if the current architecture is the Intel x86, this

     function extracts a little-endian integer of the appropriate

     length from BUF and returns it.  However, if the current

     architecture is the D10V, this function will return a 16-bit

     integer extracted from BUF, multiplied by four if TYPE is a

     pointer to a function.

     If TYPE is not a pointer or reference type, then this function

     will signal an internal error.

 - Function: CORE_ADDR store_typed_address (void *BUF, struct type

          *TYPE, CORE_ADDR ADDR)

     Store the address ADDR in BUF, in the proper format for a pointer

     of type TYPE in the current architecture.  Note that BUF refers to

     a buffer in GDB's memory, not the inferior's.

     For example, if the current architecture is the Intel x86, this

     function stores ADDR unmodified as a little-endian integer of the

     appropriate length in BUF.  However, if the current architecture

     is the D10V, this function divides ADDR by four if TYPE is a

     pointer to a function, and then stores it in BUF.

     If TYPE is not a pointer or reference type, then this function

     will signal an internal error.

 - Function: CORE_ADDR value_as_pointer (value_ptr VAL)

     Assuming that VAL is a pointer, return the address it represents,

     as appropriate for the current architecture.

     This function actually works on integral values, as well as

     pointers.  For pointers, it performs architecture-specific

     conversions as described above for `extract_typed_address'.

 - Function: CORE_ADDR value_from_pointer (struct type *TYPE, CORE_ADDR

          ADDR)

     Create and return a value representing a pointer of type TYPE to

     the address ADDR, as appropriate for the current architecture.

     This function performs architecture-specific conversions as

     described above for `store_typed_address'.

   GDB also provides functions that do the same tasks, but assume that

pointers are simply byte addresses; they aren't sensitive to the

current architecture, beyond knowing the appropriate endianness.

 - Function: CORE_ADDR extract_address (void *ADDR, int len)

     Extract a LEN-byte number from ADDR in the appropriate endianness

     for the current architecture, and return it.  Note that ADDR

     refers to GDB's memory, not the inferior's.

     This function should only be used in architecture-specific code; it

     doesn't have enough information to turn bits into a true address

     in the appropriate way for the current architecture.  If you can,

     use `extract_typed_address' instead.

 - Function: void store_address (void *ADDR, int LEN, LONGEST VAL)

     Store VAL at ADDR as a LEN-byte integer, in the appropriate

     endianness for the current architecture.  Note that ADDR refers to

     a buffer in GDB's memory, not the inferior's.

     This function should only be used in architecture-specific code; it

     doesn't have enough information to turn a true address into bits

     in the appropriate way for the current architecture.  If you can,

     use `store_typed_address' instead.

   Here are some macros which architectures can define to indicate the

relationship between pointers and addresses.  These have default

definitions, appropriate for architectures on which all pointers are

simple byte addresses.

 - Target Macro: CORE_ADDR POINTER_TO_ADDRESS (struct type *TYPE, char

          *BUF)

     Assume that BUF holds a pointer of type TYPE, in the appropriate

     format for the current architecture.  Return the byte address the

     pointer refers to.

     This function may safely assume that TYPE is either a pointer or a

     C++ reference type.

 - Target Macro: void ADDRESS_TO_POINTER (struct type *TYPE, char *BUF,

          CORE_ADDR ADDR)

     Store in BUF a pointer of type TYPE representing the address ADDR,

     in the appropriate format for the current architecture.

     This function may safely assume that TYPE is either a pointer or a

     C++ reference type.

Using Different Register and Memory Data Representations

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

   _Maintainer's note: The way GDB manipulates registers is undergoing

significant change.  Many of the macros and functions refered to in the

sections below are likely to be made obsolete.  See the file `TODO' for

more up-to-date information._

   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

conversions between the raw and virtual format:

 - Target Macro: int REGISTER_CONVERTIBLE (int REG)

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

     and virtual formats.

     You should not use `REGISTER_CONVERT_TO_VIRTUAL' for a register

     unless this macro returns a non-zero value for that register.

 - 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.

     You should only use `REGISTER_CONVERT_TO_VIRTUAL' with registers

     for which the `REGISTER_CONVERTIBLE' macro returns a non-zero

     value.

 - 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 zeroes 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)'.

`ADDRESS_TO_POINTER (TYPE, BUF, ADDR)'

     Store in BUF a pointer of type TYPE representing the address ADDR,

     in the appropriate format for the current architecture.  This

     macro may safely assume that TYPE is either a pointer or a C++

     reference type.  *Note Pointers Are Not Always Addresses: Target

     Architecture Definition.

`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 macro 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 bit 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 favor 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

     favor 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 favor 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 favor 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'

     See the file `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 `float's to `double's?  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.

`DWARF_REG_TO_REGNUM'

     Convert DWARF register number into GDB regnum.  If not defined, no

     conversion will be performed.

`DWARF2_REG_TO_REGNUM'

     Convert DWARF2 register number into GDB regnum.  If not defined,

     no conversion will be performed.

`ECOFF_REG_TO_REGNUM'

     Convert ECOFF register number into GDB regnum.  If not defined, no

     conversion will be performed.

`END_OF_TEXT_DEFAULT'

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

     section.

`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 defined, extract from the array REGBUF (containing the raw

     register state) the `CORE_ADDR' at which a function should return

     its structure value.

     If not defined, `EXTRACT_RETURN_VALUE' is used.

`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'

     See `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.  This 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.

     This 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 instead.

`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 trhe header file `setjmp.h' 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 a haste and we are

     repenting at leisure.

`I386_USE_GENERIC_WATCHPOINTS'

     An x86-based target can define this to use the generic x86

     watchpoint support; see *Note I386_USE_GENERIC_WATCHPOINTS:

     Algorithms.

`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 non-zero 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.)

`POINTER_TO_ADDRESS (TYPE, BUF)'

     Assume that BUF holds a pointer of type TYPE, in the appropriate

     format for the current architecture.  Return the byte address the

     pointer refers to.  *Note Pointers Are Not Always Addresses:

     Target Architecture Definition.

`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.

`RETURN_VALUE_ON_STACK(TYPE)'

     Return non-zero if values of type TYPE are returned on the stack,

     using the "struct convention" (i.e., the caller provides a pointer

     to a buffer in which the callee should store the return value).

     This controls how the `finish' command finds a function's return

     value, and whether an inferior function call reserves space on the

     stack for the return value.

     The full logic GDB uses here is kind of odd.

        * If the type being returned by value is not a structure,

          union, or array, and `RETURN_VALUE_ON_STACK' returns zero,

          then GDB concludes the value is not returned using the struct

          convention.

        * Otherwise, GDB calls `USE_STRUCT_CONVENTION' (see below).  If

          that returns non-zero, GDB assumes the struct convention is

          in use.

     In other words, to indicate that a given type is returned by value

     using the struct convention, that type must be either a struct,

     union, array, or something `RETURN_VALUE_ON_STACK' likes, _and_

     something that `USE_STRUCT_CONVENTION' likes.

     Note that, in C and C++, arrays are never returned by value.  In

     those languages, these predicates will always see a pointer type,

     never an array type.  All the references above to arrays being

     returned by value apply only to other languages.

`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 (depending 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'

     See `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 and in `return_command' to remove a real stack frame.

`PUSH_ARGUMENTS (NARGS, ARGS, SP, STRUCT_RETURN, STRUCT_ADDR)'

     Define this to push arguments onto the stack for inferior function

     call.  Returns 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.