NAME

stab − symbol table types

SYNOPSIS

#include <stab.h>

DESCRIPTION

Stab.h defines some values of the n_type field of the symbol table of a.out(4) files. These are the types for permanent symbols (i.e. not local labels, etc.) used by the debugger dbx.  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.  As described in a.out, an element of the symbol table consists of the following structure:

/*

* Format of a symbol table entry.

*/
struct nlist {
union {
char*n_name;/* for use when in-core */
longn_strx;/* index into file string table */
} n_un;
unsigned charn_type;/* type flag */
charn_other;/* unused */
shortn_desc;/* see struct desc, below */
unsignedn_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.

*/
#defineN_UNDF0x0/* undefined */
#defineN_ABS0x2/* absolute */
#defineN_TEXT0x4/* text */
#defineN_DATA0x6/* data */
#defineN_BSS0x8/* bss */
 #defineN_EXT01/* 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>

*/
#defineN_STAB0xe0 /* 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 symbolic debugger, dbx, uses the following n_type values:

#defineN_GSYM0x20/* global symbol: name,,0,type,0 */
#defineN_FNAME0x22/* procedure name (f77 kludge): name,,0 */
#defineN_FUN0x24/* procedure: name,,0,linenumber,address */
#defineN_STSYM0x26/* static symbol: name,,0,type,address */
#defineN_LCSYM0x28/* .lcomm symbol: name,,0,type,address */
#defineN_RSYM0x40/* register sym: name,,0,type,register */
#defineN_SLINE0x44/* src line: 0,,0,linenumber,address */
#defineN_SSYM0x60/* structure elt: name,,0,type,struct_offset */
#defineN_SO0x64/* source file name: name,,0,0,address */
#defineN_LSYM0x80/* local sym: name,,0,type,offset */
#defineN_SOL0x84/* #included file name: name,,0,0,address */
#defineN_PSYM0xa0/* parameter: name,,0,type,offset */
#defineN_ENTRY0xa4/* alternate entry: name,linenumber,address */
#defineN_LBRAC0xc0/* left bracket: 0,,0,nesting level,address */
#defineN_RBRAC0xe0/* right bracket: 0,,0,nesting level,address */
#defineN_BCOMM0xe2/* begin common: name,, */
#defineN_ECOMM0xe4/* end common: name,, */
#defineN_ECOML0xe8/* end common (local name): ,,address */
#defineN_LENG0xfe/* second stab entry with length information */

where the comments give dbx conventional use for .stabs and the n_name, n_other, n_desc, and n_value fields of the given n_type. Dbx uses the n_desc field to hold a type specifier in the form used by the Portable C Compiler, cc(1), in which a base type is qualified in the following structure:

struct desc {
shortq6:2,
q5:2,
q4:2,
q3:2,
q2:2,
q1:2,
basic:4;
};

There are four qualifications, with q1 the most significant and q6 the least significant:

0none
1pointer
2function
3array

The sixteen basic types are assigned as follows:

0undefined
1function argument
2character
3short
4int
5long
6float
7double
8structure
9union
10enumeration
11member of enumeration
12unsigned character
13unsigned short
14unsigned int
15unsigned long

SEE ALSO

as(1), ld(1), dbx(1), a.out(4)

Version 2.3  —  July 04, 1985