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Manual page for DBX(5)

dbx - dbx symbol table information

DESCRIPTION

The compiler symbol information generated for dbx(1) uses the same structure as described in stab(5), with additional type and scope information appended to a symbol's name. The assembler directive used to describe symbol information has the following format:

stabs ``string'',kind,0,size,value

String contains the name, source language type, and scope of the symbol, kind specifies the memory class (e.g., external, static, parameter, local, register), and size specifies the byte size of the object, if relevant. The third field (0 above) is unused. For a global variable or a type, value is unused; for a local variable or parameter, it is the offset from the frame pointer, for a register variable, it is the associated register number.

The different kinds of stab entries are interpreted by dbx as follows:

N_GSYM: The symbol is a global variable (e.g., .comm variable). The variable's address can be found from the corresponding ld(1) symbol entry, thus the value field for N_GSYM symbols is ignored. For example, a global variable ``x'' will have both an N_GSYM entry and an ld(1) entry (e.g., N_BSS + N_EXT). See a.out(5) for details about these other entries. of
N_FUN: The symbol is a procedure or function. The size field contains the line number of the entry point. The value field contains the address of the entry point (in the text segment).
N_STSYM: The symbol is a statically allocated variable for which an initial value has been specified. The value field contains the address of the variable (in the data segment).
N_LCSYM: The symbol is statically allocated, but not initialized.
N_RSYM: The symbol is a register variable whose value is kept in the register denoted by the value field.
N_PSYM: The symbol is a parameter whose value is pushed on the stack before the call. The value field contains the offset from the argument base pointer.
N_LSYM: The symbol is a local variable whose value is stored in the most recently defined procedure's stack frame. The value is the (often negative) offset from the frame pointer.
N_PC, N_MOD2: The symbol defines separate compilation information for pre-linking checking for Berkeley Pascal and DEC Modula-2 programs respectively. For Pascal, the value field contains the line number that the symbol is defined on. The value field is not used for Modula-2.

Most of the source level information about a symbol is stored in the string field of the stab entry. Since strings are kept in a separate string table in the a.out file, they can be arbitrarily long. Thus there are no restrictions on the kind or length of information in the string field, and it was not necessary to modify the assembler or loader when extending or modifying the format of this information.

Below is a grammar describing the syntax of the symbol string. Except in the case of a constant whose value is a string, there are no blanks in a symbol string.


NAME:	[a-zA-Z_][a-zA-Z_0-9]*
INTEGER:	[-][0-9][0-9]*
REAL:	[+-][0-9]*(.[0-9][0-9]*|)([eE]([+-]|)[0-9][0-9]*|)
STRING:	``.*''
BSTRING:	.*

String:
    NAME `:' Class
    `:' Class

Class:
    `c' `=' Constant `;'
    Variable
    Procedure
    Parameter
    NamedType
    `X' ExportInfo	-- export or import information (for N_MOD2 only)

Constant:
    `i' INTEGER
    `r' REAL
    `c' OrdValue
    `b' OrdValue
    `s' STRING
    `e' TypeId `,' OrdValue
    `S' TypeId `,' NumElements `,' NumBits `,' BSTRING

OrdValue:
    INTEGER

NumElements:
    INTEGER

NumBits:
    INTEGER

Variable:
    TypeId	-- local variable of type TypeId
    `r' TypeId	-- register variable of type TypeId
    `S' TypeId	-- module variable of type TypeId (static global in C)
    `V' TypeId	-- own variable of type TypeId (static local in C)
    `G' TypeId	-- global variable of type TypeId

Procedure:
    Proc		-- top level procedure
    Proc `,' NAME `,' NAME	-- local to first NAME,
		-- second NAME is corresponding ld symbol

Proc:
    `P'	-- global procedure
    `Q'	-- local procedure (static in C)
    `I'	-- internal procedure (different calling sequence)
    `F' TypeId	-- function returning type TypeId
    `f' TypeId	-- local function
    `J' TypeId	-- internal function

Parameter:
    `p' TypeId	-- value parameter of type TypeId
    `v' TypeId	-- reference parameter of type TypeId

NamedType:
    `t' TypeId	-- type name for type TypeId
    `T' TypeId	-- C structure tag name for struct TypeId

TypeId:
    INTEGER		-- Unique (per compilation) number of type
    INTEGER `=' TypeDef	-- Definition of type number
    INTEGER `=' TypeAttrs TypeDef

--
-- Type attributes are extra information associated with a type,
-- such as alignment constraints or pointer checking semantics.
-- Dbx interprets some of these, but will ignore rather than complain
-- about any it does not recognize.  Therefore this is a way to add
-- extra information for pre-linking checking.
--
TypeAttrs:
    `@' TypeAttrList `;'

TypeAttrList:
    TypeAttrList `,' TypeAttr
    TypeAttr

TypeAttr:
    `a' INTEGER	-- align boundary
    `s' INTEGER	-- size in bits
    `p' INTEGER	-- pointer class (e.g., checking)
    BSTRING		-- something else

TypeDef:
    INTEGER
    Subrange
    Array
    Record
    `e' EnumList `;'	-- enumeration
    `*' TypeId		-- pointer to TypeId
    `S' TypeId		-- set of TypeId
    `d' TypeId		-- file of TypeId
    ProcedureType
    `i' NAME `:' NAME `;'	-- imported type ModuleName:Name
    `o' NAME `;'		-- opaque type
    `i' NAME `:' NAME `,' TypeId `;'
    `o' NAME `,' TypeId `;'

Subrange:
    `r' TypeId `;' INTEGER `;' INTEGER

Array:
    `a' TypeId `;' TypeId	-- array [TypeId] of TypeId
    `A' TypeId		-- open array of TypeId
    `D' INTEGER `,' TypeId	-- N-dim. dynamic array
    `E' INTEGER `,' TypeId	-- N-dim. subarray

ProcedureType:
    `f' TypeId `;'		-- C function type
    `f' TypeId `,' NumParams `;' TParamList `;'
    `p' NumParams `;' TParamList `;'

NumParams:
    INTEGER

Record:
    `s' ByteSize FieldList `;'	-- structure/record
    `u' ByteSize FieldList `;'	-- C union

ByteSize:
    INTEGER

FieldList :
    Field
    FieldList Field

Field:
    NAME `:' TypeId `,' BitOffset `,' BitSize `;'

BitSize:
    INTEGER

BitOffset:
    INTEGER

EnumList:
    Enum
    EnumList Enum

Enum:
    NAME `:' OrdValue `,'

ParamList:
    Param
    ParamList Param

Param:
    NAME `:' TypeId `,' PassBy `;'

PassBy:
    INTEGER

TParam:
    TypeId `,' PassBy `;'

TParamList :
    TParam
    TParamList TParam

Export:
    INTEGER ExportInfo

ExportInfo:
    `t' TypeId
    `f' TypeId `,' NumParams `;' ParamList `;'
    `p' NumParams `;' ParamList `;'
    `v' TypeId
    `c' `=' Constant

A `?' indicates that the symbol information is continued in the next stab entry. This directive can only occur where a `;' would otherwise separate the fields of a record or constants in an enumeration. It is useful when the number of elements in one of these lists is large.

dbx - dbx symbol table information

DESCRIPTION

SEE ALSO