SDB(5)

NAME
sdb - symbol table types

SYNOPSIS
#include <sdb.h>

DESCRIPTION
Sdb.h defines some values of the n_type field of the symbol table of a.out files. These are the types for permanent symbols (i.e. not local labels, etc.) used by the 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.

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 <sdb.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 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 .stabs 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), in which a base type is qualified in the following structure:

struct desc {
	short	basic:4,
		q1:2,
		q2:2,
		q3:2,
		q4:2,
		q5:2,
		q6:2;
};

There are four qualifications, with q1 the most significant and q6 the least significant:
	0	none
	1	pointer
	2	function
	3	array
The sixteen basic types are assigned as follows:
	0	undefined
	1	function argument
	2	character
	3	short
	4	int
	5	long
	6	float
	7	double
	8	structure
	9	union
	10	enumeration
	11	member of enumeration
	12	unsigned character
	13	unsigned short
	14	unsigned int
	15	unsigned long

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

BUGS

Sdb assumes that a symbol of type N_GSYM with name name is located at address _name.

More basic types are needed.