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438 lines
14 KiB
TeX
438 lines
14 KiB
TeX
.bp odd
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.cs 5
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.he
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.mt 5
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.mb 6
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.pl 66
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.ll 65
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.po 10
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.hm 2
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.fm 2
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.ft All Information Presented Here is Proprietary to Digital Research
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.he
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.ce 2
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.tc 3 Command File Format
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.sh
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Section 3
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.qs
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.sp
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.sh
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Command File Format
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.qs
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.he CP/M-8000 Programmer's Guide 3.1 Command File Format
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.sp 2
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.pp 5
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This section describes the format of a command file.
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The linker processes one or more compiled or assembled files to
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produce an executable machine-readable file called a command
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file. By default, a command file has a filetype of 8000.
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.ix command file
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.ix symbol table
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.pp
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A command file always contains a header, two program segments
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(a text segment and an initialized data segment), and optionally
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contains a symbol table and relocation information. These components are
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described in the following sections.
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============ THE ENTIRE REMAINDER OF THIS SECTION MUST BE ==========
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============ RE-WRITTEN BASED ON INFORMATION IN X.OUT.H ==========
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.sp 2
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.tc 3.1 The Header and Program Segments
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.sh
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3.1 The Header and Program Segments
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.ix header
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.ix program segments
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.qs
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.pp
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The header, the first component in the file, specifies
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the size and starting address of the other components in the command
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file, which are listed below.
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.sp 2
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.in 5
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.ti -2
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o Program segments:
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.sp
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text: contains the program instructions.
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.sp
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.in 12
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.ti -7
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data: contains data initialized within the command file.
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.sp
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.ti -7
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block storage segment (bss):
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.sp 0
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specifies space for uninitialized data generated by the program during
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execution. Although space for the bss is specified in the source command
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file, the space is not allocated until the command file is loaded in memory.
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Therefore, the source command file on the disk contains no uninitialized data.
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.sp
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.in 5
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.ti -2
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o Symbol table: defines referenced symbols.
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.sp
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.ti -2
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o Relocation information:
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.sp 0
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.in 12
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specifies the relative relocation of
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each word within each program segment, if required.
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.in 0
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.sp
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.ix command file format
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.pp
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The command file format supports two types of headers. The size
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and content of each type differs. The contiguity of the program
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segments determines which type of header a command file contains.
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When the program segments must be contiguous, the file contains a
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14-word header in the format shown in Figure 3-1. When the
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program segments can be noncontiguous, the file contains an
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18-word header in the format shown in Figure 3-2. The first word
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of each header contains a hexadecimal integer that defines which
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type of header the file contains.
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.sp 3
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.po 5
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.nf
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Byte Sample Values Size Contents
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Offset
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1 Word Integer 601AH denotes text,
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0H 601AH data, and bss are contiguous
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2H 2376H 1 Longword Number of bytes in text segment
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6H 422H 1 Longword Number of bytes in data segment
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0AH 1806H 1 Longword Number of bytes in bss
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0EH 142H 1 Longword Number of bytes in symbol table
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12H 0000H 1 Longword Reserved; always zero
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16H 500H 1 Longword Beginning of text segment and
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of program execution
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1AH 00H
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1 Word Integer flag for relocation
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bits; if 0, relocation bits
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exist; if not 0, no relocation
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bits exist.
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.fi
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.po 10
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.ce
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.sh
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Figure 3-1. Header for Contiguous Program Segments
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.qs
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.sp 2
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.pp
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To create a file that can contain noncontiguous program segments,
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specify the -T, -D, and -B linker options described in
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Section 6 when you link the files. The header, identified by
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601BH denotes the size and location of each program
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segment. Note that this header indicates the program segments
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can be noncontiguous and does not imply the segments must be
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noncontiguous. See Figure 3-2.
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.sp 2
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.ne 32
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.nf
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.po 5
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Byte Sample Values Size Contents
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Offset
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1 Word Integer 601BH denotes text, data,
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0H 601BH and bss can be noncontiguous
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2H 57864H 1 Longword Number of bytes in text segment
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6H 446H 1 Longword Number of bytes in data segment
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0AH 2568H 1 Longword Number of bytes in bss
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0EH 69H 1 Longword Number of bytes in symbol table
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12H 0000H 1 Longword Reserved; always zero
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16H 500H 1 Longword Beginning of text segment
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1AH 00H
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1 Word Integer flag for relocation bits;
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if 0, relocation bits exist; if
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not 0, no relocation bits exist.
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1CH 57D64H 1 Longword Starting address of data segment
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20H 581AAH 1 Longword Starting address of bss
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.fi
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.po 10
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.sp 2
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.ce
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.sh
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Figure 3-2. Header for Noncontiguous Program Segments
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.sp
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.qs
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.he CP/M-8000 Programmer's Guide 3.2 The Symbol Table
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.sp
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.pp
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The linker computes the size of the segments in bytes. The result is always
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rounded up to an even number. For example, the linker adds a byte to a program
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segment that contains an odd number of bytes. The linker does not include the
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size of the header when it computes the size of the segments.
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.pp
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After a program is linked and loaded in memory, it contains three
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program segments:
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text, initialized data, and uninitialized data (bss).
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The BDOS Program Load Function (59) zeroes the
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bss when a program is loaded. A program begins
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execution at the beginning of the text segment. See Figures 3-1 and 3-2
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above.
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.sp 2
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.tc 3.2 The Symbol Table
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.he CP/M-8000 Programmer's Guide 3.2 The Symbol Table
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.sh
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3.2 The Symbol Table
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.qs
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.pp
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The symbol table lists all the symbols specified in a program.
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Each symbol in the table consists of a 7-word entry that describes the symbol
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name, type, and value. See Figure 3-3.
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.bp
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.ix symbol table
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.in 3
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.nf
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Field BYTE
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N A WORD
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M E
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Name
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Null Null
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Null Null
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Type A400H
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Value A6F0H
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.sp
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.fi
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.in 0
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.ce
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.sh
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Figure 3-3. Entry in Symbol Table
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.sp 2
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.pp
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The name
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field, the first four words, contains the ASCII name of the
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symbol. This field is padded with null characters when the ASCII
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name is less than eight characters. The fifth word contains the
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symbol type. Valid values are listed in Table 3-1.
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.sp 2
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.ce
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.sh
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Table 3-1. Values For Symbol Types
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.sp
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Type Value
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.sp
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.qs
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defined 8000H
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.sp
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equated 4000H
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.sp
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global 2000H
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.sp
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equated register 1000H
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.sp
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external reference 800H
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.sp
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data based relocatable 400H
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.sp
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text based relocatable 200H
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.sp
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bss based relocatable 100H
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.sp
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.pp
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When specifying a symbol type with multiple characteristics, the
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linker uses an OR instruction to combine several of the above
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values. For example, to specify a defined, global, data based,
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relocatable symbol, the linker combines the values of each
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characteristic for a value of A400H.
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.ix symbol type
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.pp
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The last field in an entry is the value field. It consists of a
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longword that contains the value of the symbol. The value can be
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an address, a register number, the value of an expression, or
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some other value. When the value field is nonzero and the type
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field contains an external symbol, the linker
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interprets the symbol to be a common region in which the size of
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the region equals the value of the symbol.
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.sp 2
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============= ALL PRINTING OF OBJECT FILE INFO DONE WITH XDUMP =========
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.ix symbol table, printing
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.tc 3.2.1 Printing The Symbol Table
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.sh
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3.2.1 Printing The Symbol Table
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.qs
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.pp
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Use the NM68 Utility to print the symbol table of an object or
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command file. To invoke this utility, specify
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the NM68 command and filename as shown below.
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.sp
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.ti 8
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NM68 filename.O [>filespec]
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.pp
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You must enter the filename of an object file or a command
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file. You can optionally redirect the NM68 output from your console to a
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file. To redirect the NM68 output to a file, specify a
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greater than sign (>) followed by a file specification after
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the filename and filetype of the file from which NM68 prints the
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symbol table.
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.pp
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The NM68 utility does not sort the symbols; it prints them in the order in
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which they appear in the file. Each symbol name is printed, followed by its
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value and one or more of the type descriptors listed below:
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.sp 2
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.nf
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.in 3
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o equ (equated)
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o global
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o equreg (equated register)
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o external
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o data
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o text
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o bss
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o abs (absolute)
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.fi
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.in 0
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.sp 2
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.he CP/M-8000 Programmer's Guide 3.3 Relocation Information
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.tc 3.3 Relocation Information
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.sh
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3.3 Relocation Information
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.qs
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.ix relocation information
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.pp
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Relocation information is optional. The header relocation word,
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the last word in the header, indicates whether relocation
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information exists. When its value is zero, relocation
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information exists. None exists when the its value is nonzero.
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.pp
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Relocation information specifies the relocation of words in program
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segments. One word of relocation information, called a relocation word,
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exists for each word in each of the program segments. The assembler and
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compiler generate relocation words for external symbols and address
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constants referenced in the text and data program segments. The linker and
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sometimes the BDOS Program Load Function (59) use these relocation words as
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described below.
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.pp
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The linker resolves external symbols when
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linking files by modifying bits 0 through 2 of each relocation
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word that references an external symbol.
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After being modified, the relocation word indicates the program
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segment that the symbol references. Therefore, instead
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of referencing an external symbol, the relocation word references
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a word located in one of the program segments. Because the
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linker only modifies relocation words that refer to external
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symbols, relocation words that do not reference this type of
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symbol have the same value in the source file input to the linker
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and the
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executable file output by the linker.
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.ix relocation words
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.pp
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================= RELOCATION ON LOADING IS NOT SUPPORTED =============
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The BDOS Program Load Function uses relocation words when it
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loads a program in a location other than the one at which it was
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linked. The Program Load Parameter Block (LPB) used by the
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Program Load Function specifies where the program is loaded. When
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the LPB specifies a location other than the linked location, the
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BDOS computes a bias (the difference between where a program
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segment is linked and where it will be loaded in memory). When
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loading the program, the BDOS adds the bias as indicated by the
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relocation words to the address of the relocatable words in the
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text and/or data segments. However, when the BDOS loads the
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program in the memory locations at which it was linked, the BDOS
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does not use the relocation words.
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.ix Program Load Parameter Block (LPB)
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.sp 2
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.tc 3.3.1 The Format of A Relocation Word
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.sh
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3.3.1 The Format Of A Relocation Word
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.qs
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.pp
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A relocation word is a 16-bit quantity. Bits 0 through 2 in each
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relocation word indicate the type of address referenced and, if
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applicable, designate the segment to which the relocation word
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refers. Values for these bits are described in Table 3-2.
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.sp 2
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.sh
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.ce
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Table 3-2. Relocation Word Values (bits 0 through 2)
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.sp
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.in 5
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.ll 60
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Value Description
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.in 12
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.ti -5
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.sp
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00 no relocation information required; the reference is absolute
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.sp
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.ti -5
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01 reference relative to the base address of the data segment
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.sp
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.ti -5
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02 reference relative to the base address of the text segment
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.sp
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.ti -5
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03 reference relative to the base address of the bss
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.sp
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.ti -5
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04 references an undefined symbol
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.sp
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.ti -5
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05 references the upper word of a longword; the next relocation word
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contains the value determining whether the reference is absolute or
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dependent on the base address of the text or data segments, or the bss.
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.bp
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.in 0
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.ll 65
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.sh
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.ce
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Table 3-2. (continued)
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.sp
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.in 5
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.ll 60
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Value Description
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.in 12
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.sp
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.ti -5
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06 16-bit PC-relative reference
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.sp
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.ti -5
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07 indicates the first word of an instruction, which does not
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require relocation information.
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.in 0
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.ll 65
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.mb 6
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.fm 2
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.pp
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The remaining bits, 3 through 15, are not used unless the program
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references an external symbol. In that case, these bits contain
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an index to the symbol table. The index specifies the entry
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number of the symbol listed in the symbol table. Entry numbers in the
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symbol table are numbered sequentially starting with zero.
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.he CP/M-8000 Programmer's Guide 3.3 Relocation Words
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.sp 2
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.ce
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End of Section 3
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.bp
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.he CP/M-8000 Programmer's Guide End of Section 3
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.sp 50
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.nx four
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