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32 .\" @(#)stab.5 8.1 (Berkeley) 6/5/93
33 .\" $FreeBSD: src/share/man/man5/stab.5,v 1.4.2.5 2001/12/17 11:30:15 ru Exp $
34 .\" $DragonFly: src/share/man/man5/stab.5,v 1.4 2006/05/26 19:39:40 swildner Exp $
35 .\"
36 .Dd June 5, 1993
37 .Dt STAB 5
38 .Os
39 .Sh NAME
40 .Nm stab
41 .Nd symbol table types
42 .Sh SYNOPSIS
43 .In stab.h
44 .Sh DESCRIPTION
45 The file
46 .In stab.h
47 defines some of the symbol table
48 .Fa n_type
49 field values for a.out files.
50 These are the types for permanent symbols (i.e. not local labels, etc.)
51 used by the old debugger
52 .Em sdb
53 and the Berkeley Pascal compiler
54 .Xr pc 1 .
55 Symbol table entries can be produced by the
56 .Pa .stabs
57 assembler directive.
58 This allows one to specify a double-quote delimited name, a symbol type,
59 one char and one short of information about the symbol, and an unsigned
60 long (usually an address).
61 To avoid having to produce an explicit label for the address field,
62 the
63 .Pa .stabd
64 directive can be used to implicitly address the current location.
65 If no name is needed, symbol table entries can be generated using the
66 .Pa .stabn
67 directive.
68 The loader promises to preserve the order of symbol table entries produced
69 by
70 .Pa .stab
71 directives.
72 As described in
73 .Xr a.out 5 ,
74 an element of the symbol table
75 consists of the following structure:
76 .Bd -literal
77 /*
78 * Format of a symbol table entry.
79 */
81 struct nlist {
82 union {
83 char *n_name; /* for use when in-core */
84 long n_strx; /* index into file string table */
85 } n_un;
86 unsigned char n_type; /* type flag */
87 char n_other; /* unused */
88 short n_desc; /* see struct desc, below */
89 unsigned n_value; /* address or offset or line */
90 };
91 .Ed
92 .Pp
93 The low bits of the
94 .Fa n_type
95 field are used to place a symbol into
96 at most one segment, according to
97 the following masks, defined in
98 .In a.out.h .
99 A symbol can be in none of these segments by having none of these segment
100 bits set.
101 .Bd -literal
102 /*
103 * Simple values for n_type.
104 */
106 #define N_UNDF 0x0 /* undefined */
107 #define N_ABS 0x2 /* absolute */
108 #define N_TEXT 0x4 /* text */
109 #define N_DATA 0x6 /* data */
110 #define N_BSS 0x8 /* bss */
112 #define N_EXT 01 /* external bit, or'ed in */
113 .Ed
114 .Pp
115 The
116 .Fa n_value
117 field of a symbol is relocated by the linker,
118 .Xr ld 1
119 as an address within the appropriate segment.
120 .Fa N_value
121 fields of symbols not in any segment are unchanged by the linker.
122 In addition, the linker will discard certain symbols, according to rules
123 of its own, unless the
124 .Fa n_type
125 field has one of the following bits set:
126 .Bd -literal
127 /*
128 * Other permanent symbol table entries have some of the N_STAB bits set.
129 * These are given in <stab.h>
130 */
132 #define N_STAB 0xe0 /* if any of these bits set, don't discard */
133 .Ed
134 .Pp
135 This allows up to 112 (7 \(** 16) symbol types, split between the various
136 segments.
137 Some of these have already been claimed.
138 The old symbolic debugger,
139 .Em sdb ,
140 uses the following n_type values:
141 .Bd -literal
142 #define N_GSYM 0x20 /* global symbol: name,,0,type,0 */
143 #define N_FNAME 0x22 /* procedure name (f77 kludge): name,,0 */
144 #define N_FUN 0x24 /* procedure: name,,0,linenumber,address */
145 #define N_STSYM 0x26 /* static symbol: name,,0,type,address */
146 #define N_LCSYM 0x28 /* .lcomm symbol: name,,0,type,address */
147 #define N_RSYM 0x40 /* register sym: name,,0,type,register */
148 #define N_SLINE 0x44 /* src line: 0,,0,linenumber,address */
149 #define N_SSYM 0x60 /* structure elt: name,,0,type,struct_offset */
150 #define N_SO 0x64 /* source file name: name,,0,0,address */
151 #define N_LSYM 0x80 /* local sym: name,,0,type,offset */
152 #define N_SOL 0x84 /* #included file name: name,,0,0,address */
153 #define N_PSYM 0xa0 /* parameter: name,,0,type,offset */
154 #define N_ENTRY 0xa4 /* alternate entry: name,linenumber,address */
155 #define N_LBRAC 0xc0 /* left bracket: 0,,0,nesting level,address */
156 #define N_RBRAC 0xe0 /* right bracket: 0,,0,nesting level,address */
157 #define N_BCOMM 0xe2 /* begin common: name,, */
158 #define N_ECOMM 0xe4 /* end common: name,, */
159 #define N_ECOML 0xe8 /* end common (local name): ,,address */
160 #define N_LENG 0xfe /* second stab entry with length information */
161 .Ed
162 .Pp
163 where the comments give
164 .Em sdb
165 conventional use for
166 .Pa .stab
167 .Fa s
168 and the
169 .Fa n_name ,
170 .Fa n_other ,
171 .Fa n_desc ,
172 and
173 .Fa n_value
174 fields
175 of the given
176 .Fa n_type .
177 .Em Sdb
178 uses the
179 .Fa n_desc
180 field to hold a type specifier in the form used
181 by the Portable C Compiler,
182 .Xr cc 1 ;
183 see the header file
184 .Pa pcc.h
185 for details on the format of these type values.
186 .Pp
187 The Berkeley Pascal compiler,
188 .Xr pc 1 ,
189 uses the following
190 .Fa n_type
191 value:
192 .Bd -literal
193 #define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */
194 .Ed
195 .Pp
196 and uses the following subtypes to do type checking across separately
197 compiled files:
198 .Bd -unfilled -offset indent
199 1 source file name
200 2 included file name
201 3 global label
202 4 global constant
203 5 global type
204 6 global variable
205 7 global function
206 8 global procedure
207 9 external function
208 10 external procedure
209 11 library variable
210 12 library routine
211 .Ed
212 .Sh SEE ALSO
213 .Xr as 1 ,
214 .Xr ld 1 ,
215 .Xr a.out 5
216 .Sh HISTORY
217 The
218 .Nm
219 file appeared in
220 .Bx 4.0 .
221 .Sh BUGS
222 More basic types are needed.