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1.1 root 1: .\" Copyright (c) 1980 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)stab.5 6.3 (Berkeley) 5/19/86
6: .\"
7: .TH STAB 5 "May 19, 1986"
8: .UC 4
9: .SH NAME
10: stab \- symbol table types
11: .SH SYNOPSIS
12: .B "#include <stab.h>"
13: .SH DESCRIPTION
14: .I Stab.h
15: defines some values of the n_type field of the symbol table of a.out files.
16: These are the types for permanent symbols (i.e. not local labels, etc.)
17: used by the old debugger
18: .I sdb
19: and the Berkeley Pascal compiler
20: .IR pc (1).
21: Symbol table entries can be produced by the
22: .I .stabs
23: assembler directive.
24: This allows one to specify a double-quote delimited name, a symbol type,
25: one char and one short of information about the symbol, and an unsigned
26: long (usually an address).
27: To avoid having to produce an explicit label for the address field,
28: the
29: .I .stabd
30: directive can be used to implicitly address the current location.
31: If no name is needed, symbol table entries can be generated using the
32: .I .stabn
33: directive.
34: The loader promises to preserve the order of symbol table entries produced
35: by
36: .I .stab
37: directives.
38: As described in
39: .IR a.out (5),
40: an element of the symbol table
41: consists of the following structure:
42: .PP
43: .nf
44: /*
45: .ti +\w'/'u
46: * Format of a symbol table entry.
47: .ti +\w'/'u
48: */
49: .ta \w'#define\ 'u +\w'unsigned 'u +\w'char\ \ 'u +\w'n_name;\ \ 'u
50: struct nlist {
51: union {
52: char *n_name; /* for use when in-core */
53: long n_strx; /* index into file string table */
54: } n_un;
55: unsigned char n_type; /* type flag */
56: char n_other; /* unused */
57: short n_desc; /* see struct desc, below */
58: unsigned n_value; /* address or offset or line */
59: };
60: .fi
61: .DT
62: .PP
63: The low bits of the n_type field are used to place a symbol into
64: at most one segment, according to
65: the following masks, defined in
66: .RI < a.out.h >.
67: A symbol can be in none of these segments by having none of these segment
68: bits set.
69: .PP
70: .nf
71: /*
72: .ti +\w'/'u
73: * Simple values for n_type.
74: .ti +\w'/'u
75: */
76: .ta \w'#define\ 'u +\w'N_FNAME\ 'u +\w'0x0\ \ \ 'u
77: #define N_UNDF 0x0 /* undefined */
78: #define N_ABS 0x2 /* absolute */
79: #define N_TEXT 0x4 /* text */
80: #define N_DATA 0x6 /* data */
81: #define N_BSS 0x8 /* bss */
82:
83: #define N_EXT 01 /* external bit, or'ed in */
84: .DT
85: .fi
86: .PP
87: The n_value field of a symbol is relocated by the linker,
88: .IR ld (1)
89: as an address within the appropriate segment.
90: N_value fields of symbols not in any segment are unchanged by the linker.
91: In addition, the linker will discard certain symbols, according to rules
92: of its own, unless the n_type field has one of the following bits set:
93: .PP
94: .nf
95: /*
96: .ti +\w'/'u
97: * Other permanent symbol table entries have some of the N_STAB bits set.
98: .ti +\w'/'u
99: * These are given in <stab.h>
100: .ti +\w'/'u
101: */
102: .ta \w'#define\ 'u +\w'N_FNAME\ 'u +\w'0x0\ \ \ 'u
103: #define N_STAB 0xe0 /* if any of these bits set, don't discard */
104:
105: .DT
106: .fi
107: .PP
108: This allows up to 112 (7 \(** 16) symbol types, split between the various
109: segments.
110: Some of these have already been claimed.
111: The old symbolic debugger,
112: .IR sdb ,
113: uses the following n_type values:
114: .PP
115: .nf
116: .ta \w'#define\ 'u +\w'N_FNAME\ 'u +\w'0x0\ \ \ 'u
117: #define N_GSYM 0x20 /* global symbol: name,,0,type,0 */
118: #define N_FNAME 0x22 /* procedure name (f77 kludge): name,,0 */
119: #define N_FUN 0x24 /* procedure: name,,0,linenumber,address */
120: #define N_STSYM 0x26 /* static symbol: name,,0,type,address */
121: #define N_LCSYM 0x28 /* .lcomm symbol: name,,0,type,address */
122: #define N_RSYM 0x40 /* register sym: name,,0,type,register */
123: #define N_SLINE 0x44 /* src line: 0,,0,linenumber,address */
124: #define N_SSYM 0x60 /* structure elt: name,,0,type,struct_offset */
125: #define N_SO 0x64 /* source file name: name,,0,0,address */
126: #define N_LSYM 0x80 /* local sym: name,,0,type,offset */
127: #define N_SOL 0x84 /* #included file name: name,,0,0,address */
128: #define N_PSYM 0xa0 /* parameter: name,,0,type,offset */
129: #define N_ENTRY 0xa4 /* alternate entry: name,linenumber,address */
130: #define N_LBRAC 0xc0 /* left bracket: 0,,0,nesting level,address */
131: #define N_RBRAC 0xe0 /* right bracket: 0,,0,nesting level,address */
132: #define N_BCOMM 0xe2 /* begin common: name,, */
133: #define N_ECOMM 0xe4 /* end common: name,, */
134: #define N_ECOML 0xe8 /* end common (local name): ,,address */
135: #define N_LENG 0xfe /* second stab entry with length information */
136: .fi
137: .PP
138: where the comments give
139: .I sdb
140: conventional use for
141: .IR .stab s
142: and the n_name, n_other, n_desc, and n_value fields
143: of the given n_type.
144: .I Sdb
145: uses the n_desc field to hold a type specifier in the form used
146: by the Portable C Compiler,
147: .IR cc (1);
148: see the header file \fIpcc.h\fP
149: for details on the format of these type values.
150: .PP
151: The Berkeley Pascal compiler,
152: .IR pc (1),
153: uses the following n_type value:
154: .PP
155: .nf
156: #define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */
157: .fi
158: .PP
159: and uses the following subtypes to do type checking across separately
160: compiled files:
161: .nf
162: 1 source file name
163: 2 included file name
164: 3 global label
165: 4 global constant
166: 5 global type
167: 6 global variable
168: 7 global function
169: 8 global procedure
170: 9 external function
171: 10 external procedure
172: 11 library variable
173: 12 library routine
174: .fi
175: .SH "SEE ALSO"
176: as(1), ld(1), dbx(1), a.out(5)
177: .SH BUGS
178: .PP
179: More basic types are needed.
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