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.\" @(#)stab.5 8.1 (Berkeley) 6/5/93
.\" $FreeBSD$
.\"
.Dd June 10, 2010
.Dt STAB 5
.Os
.Sh NAME
.Nm stab
.Nd symbol table types
.Sh SYNOPSIS
.In stab.h
.Sh DESCRIPTION
The file
.In stab.h
defines some of the symbol table
.Fa 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
.Em sdb
and the Berkeley Pascal compiler
.Xr pc 1 .
Symbol table entries can be produced by the
.Pa .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
.Pa .stabd
directive can be used to implicitly address the current location.
If no name is needed, symbol table entries can be generated using the
.Pa .stabn
directive.
The loader promises to preserve the order of symbol table entries produced
by
.Pa .stab
directives.
As described in
.Xr a.out 5 ,
an element of the symbol table
consists of the following structure:
.Bd -literal
/*
* Format of a symbol table entry.
*/
struct nlist {
union {
const 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 */
};
.Ed
.Pp
The low bits of the
.Fa n_type
field are used to place a symbol into
at most one segment, according to
the following masks, defined in
.In a.out.h .
A symbol can be in none of these segments by having none of these segment
bits set.
.Bd -literal
/*
* 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 */
.Ed
.Pp
The
.Fa n_value
field of a symbol is relocated by the linker,
.Xr ld 1
as an address within the appropriate segment.
.Fa 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
.Fa n_type
field has one of the following bits set:
.Bd -literal
/*
* 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 */
.Ed
.Pp
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,
.Em sdb ,
uses the following n_type values:
.Bd -literal
#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 */
.Ed
.Pp
where the comments give
.Em sdb
conventional use for
.Pa .stab
.Fa s
and the
.Fa n_name ,
.Fa n_other ,
.Fa n_desc ,
and
.Fa n_value
fields
of the given
.Fa n_type .
.Em Sdb
uses the
.Fa n_desc
field to hold a type specifier in the form used
by the Portable C Compiler,
.Xr cc 1 ;
see the header file
.Pa pcc.h
for details on the format of these type values.
.Pp
The Berkeley Pascal compiler,
.Xr pc 1 ,
uses the following
.Fa n_type
value:
.Bd -literal
#define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */
.Ed
.Pp
and uses the following subtypes to do type checking across separately
compiled files:
.Bd -unfilled -offset indent
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
.Ed
.Sh SEE ALSO
.Xr as 1 ,
.Xr ld 1 ,
.Xr a.out 5
.Sh HISTORY
The
.Nm
file appeared in
.Bx 4.0 .
.Sh BUGS
More basic types are needed.