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Annotation of researchv10dc/dist/man/v4/man5/a.out.5, revision 1.1

1.1     ! root        1: .th A.OUT V 9/9/73
        !             2: .sh NAME
        !             3: a.out \*- assembler and link editor output
        !             4: .sh DESCRIPTION
        !             5: .it A.out
        !             6: is the output file of the assembler
        !             7: .it as
        !             8: and the link editor
        !             9: .it ld.
        !            10: Both programs make
        !            11: .it a.out
        !            12: executable if there were no
        !            13: errors and no unresolved external references.
        !            14: .s3
        !            15: This file has four sections:
        !            16: a header, the program and data text, a symbol table, and relocation bits
        !            17: (in that order).
        !            18: The last two may be empty
        !            19: if the program was loaded
        !            20: with the ``\*-s'' option
        !            21: of
        !            22: .it ld
        !            23: or if the symbols and relocation have been
        !            24: removed by
        !            25: .it strip.
        !            26: .s3
        !            27: The header always contains 8 words:
        !            28: .s3
        !            29: .lp +5 3
        !            30: 1      A magic number (407 or 410(8))
        !            31: .lp +5 3
        !            32: 2      The size of the program text segment
        !            33: .lp +5 3
        !            34: 3      The size of the initialized portion of the data segment
        !            35: .lp +5 3
        !            36: 4      The size of the uninitialized (bss) portion of the data segment
        !            37: .lp +5 3
        !            38: 5      The size of the symbol table
        !            39: .lp +5 3
        !            40: 6      The entry location (always 0 at present)
        !            41: .lp +5 3
        !            42: 7      Unused
        !            43: .lp +5 3
        !            44: 8      A flag indicating relocation bits have been suppressed
        !            45: .s3
        !            46: .i0
        !            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: .s3
        !            50: When a file produced by the assembler or loader is
        !            51: loaded into core for execution, three logical segments are
        !            52: set up: the text segment, the data segment
        !            53: (with uninitialized data, which starts off as all 0, following
        !            54: initialized),
        !            55: and a stack.
        !            56: The text segment begins at 0
        !            57: in the core image; the header is not loaded.
        !            58: If the magic number (word 0) is 407, it indicates that the text
        !            59: segment is not to be write-protected and shared,
        !            60: so the data segment is immediately contiguous
        !            61: with the text segment.
        !            62: If the magic number is 410,
        !            63: the data segment begins at the first 0 mod 8K byte
        !            64: boundary following the text segment,
        !            65: and the text segment is not writable by the program;
        !            66: if other processes are executing the same file,
        !            67: they will share the text segment.
        !            68: .s3
        !            69: The stack will occupy the highest possible locations
        !            70: in the core image: from 177776(8) and growing downwards.
        !            71: The stack is automatically extended as required.
        !            72: The data segment is only extended as requested by
        !            73: the
        !            74: .it break
        !            75: system call.
        !            76: .s3
        !            77: The start of the text segment in the file is 20(8);
        !            78: the start of the data segment is 20+S\s6\dt\u\s10 (the size of the text)
        !            79: the start of the relocation information is
        !            80: 20+S\s6\dt\u\s10+S\s6\dd\u\s10;
        !            81: the start of the symbol table is
        !            82: 20+2(S\s6\dt\u\s10+S\s6\dd\u\s10)
        !            83: if the
        !            84: relocation information is present,
        !            85: 20+S\s6\dt\u\s10+S\s6\dd\u\s10
        !            86: if not.
        !            87: .s3
        !            88: The symbol table consists of 6-word entries.  The first
        !            89: four words contain the ASCII name of the symbol, null-padded.
        !            90: The next word is a flag indicating the type of symbol.
        !            91: The following values are possible:
        !            92: .s3
        !            93: .lp +6 3
        !            94: 00     undefined symbol
        !            95: .lp +6 3
        !            96: 01     absolute symbol
        !            97: .lp +6 3
        !            98: 02     text segment symbol
        !            99: .lp +6 3
        !           100: 03     data segment symbol
        !           101: .lp +6 3
        !           102: 37     file name symbol (produced by ld)
        !           103: .lp +6 3
        !           104: 04     bss segment symbol
        !           105: .lp +6 3
        !           106: 40     undefined external (.globl) symbol
        !           107: .lp +6 3
        !           108: 41     absolute external symbol
        !           109: .lp +6 3
        !           110: 42     text segment external symbol
        !           111: .lp +6 3
        !           112: 43     data segment external symbol
        !           113: .lp +6 3
        !           114: 44     bss segment external symbol
        !           115: .i0
        !           116: .s3
        !           117: Values other than those given above may
        !           118: occur if the user has defined some of his own instructions.
        !           119: .s3
        !           120: The last word of a symbol table entry contains the value of the symbol.
        !           121: .s3
        !           122: If the symbol's type is undefined external,
        !           123: and the value field is non-zero,
        !           124: the symbol is interpreted by the loader
        !           125: .it ld
        !           126: as
        !           127: the name of a common region
        !           128: whose size is indicated by the value of the
        !           129: symbol.
        !           130: .s3
        !           131: The value of a word in the text or data portions which is not
        !           132: a reference to an undefined external symbol
        !           133: is exactly that value which will appear in core
        !           134: when the file is executed.
        !           135: If a word in the text or data portion
        !           136: involves a reference to an undefined external symbol,
        !           137: as indicated by the relocation bits
        !           138: for that word,
        !           139: then the value of the word as stored in the file
        !           140: is an offset from the associated external symbol.
        !           141: When the file is processed by the
        !           142: link editor and the external symbol becomes
        !           143: defined, the value of the symbol will
        !           144: be added into the word in the file.
        !           145: .s3
        !           146: If relocation
        !           147: information is present, it amounts to one word per
        !           148: word of program text or initialized data.
        !           149: There is no relocation information if the ``suppress relocation''
        !           150: flag in the header is on.
        !           151: .s3
        !           152: Bits 3-1 of a relocation word indicate the segment referred
        !           153: to by the text or data word associated with the relocation
        !           154: word:
        !           155: .s3
        !           156: .lp +6 3
        !           157: 00     indicates the reference is absolute
        !           158: .lp +6 3
        !           159: 02     indicates the reference is to the text segment
        !           160: .lp +6 3
        !           161: 04     indicates the reference is to initialized data
        !           162: .lp +6 3
        !           163: 06     indicates the reference is to bss (uninitialized data)
        !           164: .lp +6 3
        !           165: 10     indicates the reference is to an undefined external symbol.
        !           166: .i0
        !           167: .s3
        !           168: Bit 0 of the relocation word indicates if
        !           169: .it on
        !           170: that the
        !           171: reference is relative to the pc (e.g. ``clr x'');
        !           172: if
        !           173: .it off,
        !           174: that
        !           175: the reference is to the actual symbol (e.g.,
        !           176: ``clr *$x'').
        !           177: .s3
        !           178: The remainder of the relocation word (bits 15-4)
        !           179: contains a symbol number in the case of external
        !           180: references, and is unused otherwise.
        !           181: The first symbol is numbered 0, the second 1, etc.
        !           182: .sh "SEE ALSO"
        !           183: as(I), ld(I), strip(I), nm(I)

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