STAB(5) MidnightBSD 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 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(5), 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 */

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.

MidnightBSD 0.3 June 5, 1993 MidnightBSD 0.3