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STAB(5)			  FreeBSD File Formats Manual		       STAB(5)

NAME
     stab -- symbol table types

SYNOPSIS
     #include <stab.h>

DESCRIPTION
     The file <stab.h> defines some of the symbol table	n_type field values
     for a.out files.  These are the types for permanent symbols (i.e.,	not
     local labels, etc.)  used by the old debugger sdb and the Berkeley	Pascal
     compiler pc(1).  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 sym-
     bol, and an unsigned long (usually	an address).  To avoid having to pro-
     duce 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.	As described in	a.out(5), an element of	the symbol ta-
     ble consists of the following structure:

     /*
     * Format of a symbol table	entry.
     */

     struct nlist {
	     union {
		     const char	*n_name;     /*	for use	when in-core */
		     long    n_strx;	     /*	index into file	string table */
	     } n_un;
	     unsigned char   n_type;	     /*	type flag */
	     char	     n_other;	     /*	unused */
	     short	     n_desc;	     /*	see struct desc, below */
	     unsigned	     n_value;	     /*	address	or offset or line */
     };

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

     /*
     * Simple values for n_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(1) as	an
     address within the	appropriate segment.  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	n_type
     field has one of the following bits set:

     /*
     * Other permanent symbol table entries have some of the N_STAB bits set.
     * These are given in <stab.h>
     */

     #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
     segments.	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    /*	procedure name (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    /*	source file name: name,,0,0,address */
     #define N_LSYM  0x80    /*	local sym: name,,0,type,offset */
     #define N_SOL   0x84    /*	#included file name: 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,nesting level,address */
     #define N_RBRAC 0xe0    /*	right bracket: 0,,0,nesting level,address */
     #define N_BCOMM 0xe2    /*	begin common: name,, */
     #define N_ECOMM 0xe4    /*	end common: name,, */
     #define N_ECOML 0xe8    /*	end common (local name): ,,address */
     #define N_LENG  0xfe    /*	second stab entry with length information */

     where the comments	give sdb conventional use for .stab s and the n_name,
     n_other, n_desc, and n_value fields of the	given n_type.  Sdb uses	the
     n_desc field to hold a type specifier in the form used by the Portable C
     Compiler, cc(1); see the header file pcc.h	for details on the format of
     these type	values.

     The Berkeley Pascal compiler, pc(1), uses the following n_type value:

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

     and uses the following subtypes to	do type	checking across	separately
     compiled files:

	   1	   source file name
	   2	   included file name
	   3	   global label
	   4	   global constant
	   5	   global type
	   6	   global variable
	   7	   global function
	   8	   global procedure
	   9	   external function
	   10	   external procedure
	   11	   library variable
	   12	   library routine

SEE ALSO
     as(1), ld(1), a.out(5)

HISTORY
     The stab file appeared in 4.0BSD.

BUGS
     More basic	types are needed.

FreeBSD	9.2			 June 10, 2010			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | BUGS

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