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researchv10 Dan Cross

.TH STAB 5
.CT 1 lib_obj
.SH NAME
stab \- symbol table types
.SH SYNOPSIS
.B "#include <stab.h>"
.SH DESCRIPTION
The include file
.L <stab.h>
defines some values of the
.L n_type
field of the symbol table of object files; see
.IR a.out (5).
These are the types for permanent symbols
used by the compilers
.IR cc (1)
and
.IR f77 (1)
and the debugger
.IR pi (9.1).
Symbol table entries are produced by assembler directives:
.TP \w'\f5.stabs\ \ \fP'u
.B .stabs
specifies a name in quotes \f5" "\fR, a symbol type
.RL ( n_type ),
one char
.RL ( n_other ),
one short 
.RL ( n_desc),
and an unsigned long 
.RL ( n_value ,
usually an address).
.PD 0
.TP
.B .stabd
the same, referring to the current location without an explicit
name.
.TP
.B .stabn
generates entries with no name.
.PD
.LP
The loader
.IR ld (1)
preserves the order of symbol table entries produced
by these directives.
.PP
The low bits of the
.L n_type
field place a symbol into
at most one segment, according to
the following masks, defined in
.BR <a.out.h> .
.PP
.EX
.ta \w'#define\ 'u +\w'N_FNAME\ 'u +\w'0x0\ \ \ 'u
#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	0x1	/* external bit, or'ed in */
.EE
.PP
The
.L n_value
field of a symbol is relocated by 
.I ld
as an address within the appropriate segment,
or is unchanged for a symbol not in any segment.
In addition, the loader will discard certain symbols, according to rules
of its own, unless the
.L n_type
field has one of the following bits set:
.PP
.L
#define	N_STAB	0xe0
.PP
This allows up to 112 symbol types, split among the various
segments.
Some of these have already been claimed.
Option 
.B -g
of
.I cc
uses the following values, all 4 mod 16, for text symbols.
Comments show the pertinent fields of the
.B .stabs
directive.
.PP
.EX
.ta \w'#define\ 'u +\w'N_ECOMM\ 'u +\w'0x0\ \ \ 'u +\n(wwu
#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 */
.EE
.PP
These values, all 8 mod 16, are used for data symbols:
.PP
.EX
#define	N_LCSYM	0x28	/* .lcomm symbol: name,,0,type,address */
#define	N_ECOML	0xe8	/* end common (local name): ,,address */
.EE
.PP
And these for non-relocated symbols:
.PP
.EX
#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 */
.EE
.PP
Field
.L n_desc
holds a type specifier in the form used by
.IR cc (1),
by up to 6 qualifiers, with
.B q1
most significant:
.PP
.EX
.ta \w'#define 'u +\w'short\ \ 'u
struct	desc	{
	short	q6:2, q5:2, q4:2, q3:2, q2:2, q1:2;
	short	basic:5;
};
.EE
.PP
The qualifiers are coded thus:
.2C
\f50\fR	none
\f51\fR	pointer
\f52\fR	function
\f53\fR	array
.1C
.PP
The basic types are coded thus:
.2C
\f50\fR	undefined
\f51\fR	function argument
\f52\fR	character
\f53\fR	short
\f54\fR	int
\f55\fR	long
\f56\fR	float
\f57\fR	double
\f58\fR	structure
\f59\fR	union
\f510\fR	enumeration
\f511\fR	member of enumeration
\f512\fR	unsigned character
\f513\fR	unsigned short
\f514\fR	unsigned int
\f515\fR	unsigned long
\f516\fR	void
.1C
.PP
The Pascal compiler,
.IR pc (A),
uses the following
.L n_type
value:
.PP
.L
#define	N_PC	0x30	/* global pascal symbol: name,,0,subtype,line */
.PP
and uses the following subtypes to do type checking across separately
compiled files:
.2C
\f51\fR	source file name
\f52\fR	included file name
\f53\fR	global label
\f54\fR	global constant
\f55\fR	global type
\f56\fR	global variable
\f57\fR	global function
\f58\fR	global procedure
\f59\fR	external function
\f510\fR	external procedure
.1C
.SH "SEE ALSO"
.IR a.out (5), 
.IR pi (9.1), 
.IR as (1), 
.IR ld (1)
.SH BUGS
.PP
The loader's relocation conventions limit the number of useful
.LR n_type
values.

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