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. 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 /* alternative 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, 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),
gdb(1),
ld(1),
a.out(5)
HISTORY
The
stab file appeared in
4.0BSD.
BUGS
More basic types are needed.