stab - symbol table types
#include <stab.h>
The <stab.h> file defines some of the symbol table n_type
field values
for a.out(5) 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, as well as
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 incore */
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, 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
as(1), gdb(1), ld(1), a.out(5)
The stab file appeared in 4.0BSD.
More basic types are needed.
OpenBSD 3.6 June 5, 1993
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