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1.1 root 1: .pa 1
2: .he 'A.OUT (V)'3/15/72'A.OUT (V)'
3: .ti 0
4: .nf
5: NAME a.out -- assembler and link editor output
6: .fi
7: .sp
8: .ti 0
9: DESCRIPTION
10: .br
11: .in 8
12: a.out_____
13: is the output file of the assembler as__ and the link editor ld__.
14: In both cases, a.out_____ may be executed provided there
15: were no errors and no unresolved external references.
16: .sp
17: This file has four sections:
18: a header, the program and data text, a symbol table, and relocation bits
19: (in that order).
20: The last two may be empty
21: if the program was loaded
22: with the "-s" option
23: of ld__ or if the symbols and relocation have been
24: removed by strip_____.
25:
26: The header always contains 8 words:
27:
28: .in +6
29: .ti -3
30: 1 A magic number (407(8))
31: .ti -3
32: 2 The size of the program text segment
33: .ti -3
34: 3 The size of the initialized data segment
35: .ti -3
36: 4 The size of the uninitialized (bss) segment
37: .ti -3
38: 5 The size of the symbol table
39: .ti -3
40: 6 The entry location (always 0 at present)
41: .ti -3
42: 7 The stack size required (0 at present)
43: .ti -3
44: 8 A flag indicating relocation bits have been suppressed
45:
46: .in -6
47: The sizes of each segment are in bytes but are even.
48: The size of the header is not included in any of the other sizes.
49:
50: When a file produced by the assembler or loader is
51: loaded into core for execution, three segments are
52: set up: the text segment, the data segment,
53: and the bss (uninitialized data) segment,
54: in that order.
55: The text segment begins at the lowest
56: location in the core image; the header is not loaded.
57: The data segment begins immediately after the text
58: segment, and the bss segment immediately after
59: the data segment.
60: The bss segment is initialized by 0's.
61: In the future the text segment will be write-protected
62: and shared.
63:
64: The start of the text segment in the file is 20(8);
65: the start of the data segment is 20+S9t8 (the size of the text)
66: the start of the relocation information is 20+S9t8+S9d8;
67: the start of the symbol table is 20+2(S9t8+S9d8) if the
68: relocation information is present, 20+S9t8+S9d8 if not.
69:
70: The symbol table consists of 6-word entries. The first
71: four contain the ASCII name of the symbol, null-padded.
72: The next word is a flag indicating the type of symbol.
73: The following values are possible:
74:
75: 00 undefined symbol
76: 01 absolute symbol
77: 02 text segment symbol
78: 03 data segment symbol
79: 04 bss segment symbol
80: 40 undefined external (.globl) symbol
81: 41 absolute external symbol
82: 42 text segment external symbol
83: 43 data segment external symbol
84: 44 bss segment external symbol
85:
86: Values other than those given above may
87: occur if the user has defined some of his own instructions.
88:
89: The last word of a symbol table entry contains the value of the symbol.
90:
91: If the symbol's type is undefined external,
92: and the value field is non-zero,
93: the symbol is interpreted by the loader ld__ as
94: the name of a common region
95: whose size is indicated by the value of the
96: symbol.
97:
98: The value of a word in the text or data portions which is not
99: a reference to an undefined external symbol
100: is exactly that value which will appear in core
101: when the file is executed.
102: If a word in the text or data portion
103: involves a reference to an undefined external symbol,
104: as indicated by the relocation bits
105: for that word,
106: then the value of the word as stored in the file
107: is an offset from the associated external symbol.
108: When the file is processed by the
109: link editor and the external symbol becomes
110: defined, the value of the symbol will
111: be added into the word in the file.
112:
113: If relocation
114: information is present, it amounts to one word per
115: word of program text or initialized data.
116: There is no relocation information if the "suppress relocation"
117: flag in the header is on.
118:
119: Bits 3-1 of a relocation word indicate the segment referred
120: to by the text or data word associated with the relocation
121: word:
122:
123: .in +6
124: .ti -4
125: 00 indicates the reference is absolute
126: .ti -4
127: 02 indicates the reference is to the text segment
128: .ti -4
129: 04 indicates the reference is to the data segment
130: .ti -4
131: 06 indicates the reference is to the bss segment
132: .ti -4
133: 10 indicates the reference is to an undefined external symbol.
134:
135: .in -6
136: Bit 0 of the relocation word indicates if on__ that the
137: reference is relative to the pc (e.g. "clr x");
138: if off___, the reference is to the actual symbol (e.g.,
139: "clr *$x").
140:
141: The remainder of the relocation word (bits 15-4)
142: contains a symbol number in the case of external
143: references, and is unused otherwise.
144: The first symbol is numbered 0, the second 1, etc.
145: .sp
146: .in 16
147: .ti 0
148: SEE ALSO as__,
149: .ul
150: ld, strip, nm, un(I)
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