STAB(5) COMMAND REFERENCE 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 debugger
sdb(1) and the compilers. 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 */
Printed 3/13/89 1
STAB(5) COMMAND REFERENCE STAB(5)
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 symbolic debugger, sdb(1), 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 the 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 C Compiler, 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:4;
Printed 3/13/89 2
STAB(5) COMMAND REFERENCE STAB(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
The 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), sdb(1), and a.out(5).
Printed 3/13/89 3
%%index%%
na:240,77;
sy:317,273;
de:590,2559;3461,2884;6657,1304;
se:7961,151;
%%index%%000000000102