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stab(4)								      stab(4)



NAME
  stab - Symbol	table types

SYNOPSIS

  #include <&lt;stab.h>&gt;

DESCRIPTION
  The stab.h header file defines some values of	the n_type field of the	sym-
  bol table of a.out files.  These are the types for permanent symbols (that
  is, not local	labels,	etc.) used by the old debugger sdb.  Symbol table
  entries can be produced by the .stabs	assembler directive.  This allows one
  to specify a double-quote delimited name, a symbol type, one char and	one
  short	of information about the symbol, and an	unsigned long (usually an
  address).  To	avoid having to	produce	an explicit label for the address
  field, the .stabd directive can be used to implicitly	address	the current
  location.  If	no name	is needed, symbol table	entries	can be generated
  using	the .stabn directive.  The loader promises to preserve the order of
  symbol table entries produced	by .stab directives.  An element of the	sym-
  bol table consists of	the following structure:

       /* SYMBOL INFORMATION ENTRY * This is used for defined symbols,
       imports and stabs.  The type (kind) * of	the associated symbols load
       command determines which.  typedef struct symbol_info_t {
	       union   {mo_offset_t    symbol_name;
			mo_ptr_t       symbol_nameP;
	     } si_name;
	       mo_short_t	       si_package_index;
	       mo_short_t	       si_type;
	       mo_short_t	       si_flags;
	       mo_byte_t	       si_reserved byte;
	       mo_byte_t	       si_sc_type;
	       union   {mo_addr_t      def_val;	       /* defined section,
       offset */
			mo_long_t      imp_val;	       /* index	in import
       list */
			mo_long_t      lit_val;	       /* literal value	*/
			mo_vm_addr_t   abs_val;	       /* absolute value */
	     } si_value;
       } symbol_info_t;

  The low bits of the si_sc_type field are used	to place a symbol into at
  most one segment, according to the following masks.  A symbol	can be in
  none of these	segments by having none	of these segment bits set.

       * Simple	values for si_sc_type.
       */ #define N_UNDF  0x0	  /* undefined */
       #define N_ABS   0x2     /* absolute */
       #define N_TEXT  0x4     /* text */
       #define N_DATA  0x6     /* data */
       #define N_BSS   0x8     /* bss */
       #define N_EXT   01      /* external bit,	or'ed in */

  The n_value field of a symbol	is relocated by	the linker, ld,	as an address
  within the appropriate segment.  The n_value fields of symbols not in	any
  segment are unchanged	by the linker.	In addition, the linker	will discard
  certain symbols, according to	rules of its own, unless the si_sc_type	field
  has one of the following bits	set:

       #define N_STAB  0xe0    /* if any of these bits set, don't discard */

  This allows up to 112	(7 * 16) symbol	types, split between the various seg-
  ments.  Some of these	have already been claimed.  The	old symbolic
  debugger, sdb, uses the following n_type values:

  #define N_GSYM 0x20	 /* global symbol: name,,0,type,0 */

  #define N_FNAME
		 0x22	 /* procedurename(f77 kludge): name,,0 */

  #define N_FUN	 0x24	 /* procedure: name,,0,linenumber,address */

  #define N_STSYM
		 0x26	 /* static symbol: name,,0,type,address	*/

  #define N_LCSYM
		 0x28	 /* .lcomm symbol: name,,0,type,address	*/

  #define N_RSYM 0x40	 /* register sym: name,,0,type,register	*/

  #define N_SLINE
		 0x44	 /* src	line: 0,,0,linenumber,address */

  #define N_SSYM 0x60	 /* structure elt: name,,0,type,struct_offset */

  #define N_SO	 0x64	 /* sourcefilename: name,,0,0,address */

  #define N_LSYM 0x80	 /* local sym: name,,0,type,offset */

  #define N_SOL	 0x84	 /* #includedfilename: name,,0,0,address */

  #define N_PSYM 0xa0	 /* parameter: name,,0,type,offset */

  #define N_ENTRY
		 0xa4	 /* alternate entry: name,,linenumber,address */

  #define N_LBRAC
		 0xc0	 /* left bracket: 0,,0,nestinglevel,address */

  #define N_RBRAC
		 0xe0	 /* right bracket: 0,,0,nestinglevel,address */

  #define N_BCOMM
		 0xe2	 /* begincommon: name,,	*/

  #define N_ECOMM
		 0xe4	 /* endcommon: name,, */

  #define N_ECOML
		 0xe8	 /* endcommon(local name): ,,address */

  #define N_LENG 0xfe	 /* secondstabentrywithlengthinformation */

  The comments give sdb	conventional use for .stabs and	the n_name, n_other,
  n_desc, and n_value fields of	the given n_type.  The sdb debugger uses the
  n_desc field to hold a type specifier	in the form used by the	Portable C
  Compiler, cc.


  The Berkeley Pascal compiler,	pc, uses the following si_sc_type value:

       #define	N_PC  0x30  /* global pascal symbol: name,,0,subtype,line */

  and uses the following subtypes to do	type checking across separately	com-
  piled	files:

    +  Source filename

    +  Included	filename

    +  Global label

    +  Global constant

    +  Global type

    +  Global variable

    +  Global function

    +  Global procedure

    +  External	function

    +  External	procedure

    +  Library variable

    +  "12" Library routine

RELATED	INFORMATION

  Commands: as(1), ld(1)