4BSD/usr/man/cat5/stab.5
STAB(5) UNIX Programmer's Manual STAB(5)
NAME
stab - symbol table types
SYNOPSIS
#include <stab.h>
DESCRIPTION
_S_t_a_b._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
_s_d_b(1) and the Berkeley Pascal compiler _p_c(1). Symbol table
entries can be produced by the ._s_t_a_b_s 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 ._s_t_a_b_d directive can be used to implicitly address the
current location. If no name is needed, symbol table
entries can be generated using the ._s_t_a_b_n directive. The
loader promises to preserve the order of symbol table
entries produced by ._s_t_a_b 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 seg-
ments 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 */
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STAB(5) UNIX Programmer's Manual STAB(5)
#define N_EXT 01 /* external bit, or'ed in */
The n_value field of a symbol is relocated by the linker,
_l_d(5) 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 sym-
bols, 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, _s_d_b(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 _s_d_b conventional use for ._s_t_a_bs
and the n_name, n_other, n_desc, and n_value fields of the
given n_type. _S_d_b uses the n_desc field to hold a type
specifier in the form used by the Portable C Compiler,
_c_c(1), in which a base type is qualified in the following
structure:
struct desc {
short q6:2,
q5:2,
q4:2,
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STAB(5) UNIX Programmer's Manual STAB(5)
q3:2,
q2:2,
q1:2,
basic:4;
};
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 Berkeley Pascal compiler, _p_c(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), sdb(1), a.out(5)
Printed 11/10/80 3
STAB(5) UNIX Programmer's Manual STAB(5)
BUGS
_S_d_b(1) assumes that a symbol of type N_GSYM with name _n_a_m_e
is located at address __n_a_m_e.
More basic types are needed.
Printed 11/10/80 4