term% cat index.txt STAB(5) File Formats Manual STAB(5)
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 files. These are the types for permanent symbols (i.e. not local
labels, etc.) used by the compiler cc(1), the debugger pi(1) and the
Berkeley Pascal compiler pc(1). Symbol table entries can be produced
by the .stabs assembler directive. This allows one to specify a dou‐
ble-quote delimited name, a symbol type, one char and one short of in‐
formation 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 loca‐
tion. If no name is needed, symbol table entries can be generated us‐
ing 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 transcendental
debugger, pi(9.1), uses the following n_type values:
/*
* stabs for text symbols (must be 0x?4):
*/
#define N_BFUN 0x24 /* procedure: name,,0,lineno,address */
#define N_FUN 0x24
#define N_NARGS 0x34 /* function call: ,,0,nbytes,address */
#define N_SLINE 0x44 /* src line: ,,0,lineno,address */
#define N_SO 0x64 /* source file: name,,0,lineno,address */
#define N_SOL 0x84 /* #include file: name,,0,lineno,address */
#define N_ESO 0x94 /* end source file: name,,0,lineno,address */
#define N_ENTRY 0xa4 /* alternate entry: name,,0,lineno,address */
#define N_RFUN 0xb4 /* return from function: ,,0,lineno,address */
#define N_LBRAC 0xc4 /* left bracket: ,,0,level,address */
#define N_RBRAC 0xd4 /* right bracket: ,,0,level,address */
#define N_EFUN 0xf4 /* end of function: name,,0,lineno,address */
/*
* stabs for data symbols (must be 0x?6):
*/
#define N_STSYM 0x26 /* static symbol: name,,0,type,address */
/*
* stabs for bss symbols (must be 0x?8):
*/
#define N_LCSYM 0x28 /* .lcomm symbol: name,,0,type,address */
#define N_ECOML 0xe8 /* end common (local name): ,,address */
/*
* stabs for non-relocated stuff:
*/
#define N_GSYM 0x20 /* global symbol: name,,0,type,0 */
#define N_FNAME 0x22 /* procedure name (f77 kludge): name,,0 */
#define N_STFUN 0x32 /* static function: name,,0,type,0 */
#define N_RSYM 0x40 /* register sym: name,,0,type,register */
#define N_BSTR 0x5c /* begin structure: name,,0,type,length */
#define N_ESTR 0x5e /* end structure: name,,0,type,length */
#define N_SSYM 0x60 /* structure elt: name,,0,type,offset */
#define N_SFLD 0x70 /* structure field: name,,0,type,offset */
#define N_LSYM 0x80 /* local sym: name,,0,type,offset */
#define N_PSYM 0xa0 /* parameter: name,,0,type,offset */
#define N_BCOMM 0xe2 /* begin common: name,, */
#define N_ECOMM 0xe4 /* end common: name,, */
#define N_VER 0xf0 /* symbol table version number */
#define N_TYID 0xfa /* struct, union, or enum name */
#define N_DIM 0xfc /* dimension for arrays */
where the comments give the sdb conventional use for .stabs and the
n_name, n_other, n_desc, and n_value fields of the given n_type. Pi
uses the n_desc field to hold a type specifier in the form used by
cc(1), in which a base type is qualified in the following structure:
struct desc {
short q6:2,
q5:2,
q4:2,
q3:2,
q2:2,
q1:2,
basic:5;
};
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
16 void
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
SEE ALSO
as(1), ld(1), pi(1), a.out(5)
BUGS
The loader's relocation conventions limit the number of useful
n_type's.
More basic types are needed.
STAB(5)