IS-DOS - "object module format *. obj IS-DOS assembly language."

Category "IS-DOS - programmers" No 3


            Prokopenko SV

        Ed. Eliseev, VA


    "The format object modules *. obj

           IS-DOS Assembler "
________________________________________


     This article discusses the object module format adopted in 
the IS-DOS and supported by IS-DOS assembler and linker object 
modules link.com. This format is an official standard IS-DOS. 
If you want to move to the IS-DOS finished object modules from 
other operating systems (such as CP / M 80), or write your own 
translator of any high-level language, we strongly

recommend that you stick with it
format that would allow the sharing of your developments with
IS-DOS Assembler and simplify the creation of
ready-made library of procedures for the IS-DOS.


     The article is written primarily
for professional programmers and software developers wishing to
create tools
Programming for the IS-DOS.

            ________________


     Files in the format *. obj created
IS-DOS Assembler and provide input
files for the linker link.com.


     The task is to create link.com
downloadable code module from *. com
one or more object modules
received broadcast program texts.


     Object file *. obj consists of
several regions, with lengths and relative displacements of the 
beginning of the file identified in its first 32 bytes (see 
Table 1): 


                            Table 1.

   Description of object files
--------------------------------------- Deposed. length value
---------------------------------------
  0,1 (2) - a reference to the area of global
               Ballroom Character Module -

               region [1] (the shift from

               beginning of the file)

  2,3 (2) - the length of the field


  4,5 (2) - a reference to the area of complex
               symmetric with respect to the expression
               stresses that determine the global
               Ballroom symbols of the module -

               region [2] (the shift from

               beginning of the file)

  6.7 (2) - the length of the field


  8.9 (2) - a reference to the area of
               programmatic area code

               [3] (offset from the beginning

               file)
10.11 (2) - the length of the field

12.13 (2) - a reference to the region of hell
               ests custom

               cell module and the remaining
               shihsya nevychislennymi in

               translation time expression
               stresses that determine the

               values of these cells

               region [4] (the shift from

               beginning of the file)
14.15 (2) - the length of the field

16-29 (14) - reserve

30-31 (2) - checksum lane
               Out of 30 bytes file.
--------------------------------------

     The checksum is considered the standard for IS-DOS way: a 
two-byte cell, summed up the values of individual bytes of a 
file. 


     Further, in the object module are listed above the field 
in the named order. Linker link.com important that followed the 
first area of global symbols (offset from the beginning of 
the file = 32). The order of the remaining areas are not 
important. 

            ________________


     Region 1. Global symbols

     defined in this module.


     All global symbols of the module are placed in this area 
as a 16 byte records in a format close to the format

Table of global symbols *. gtb. The differences relate only to 
character values and tag (*) these values. (See Table 2.)


-------------(*) Tag (English tag - a label ztiketka) -
Part of the data item (one or more bits of the word), which 
determines its type. (Editor's note.)

-------------
                          Table 2.
 The structure of global symbols.
---------------------------------------
  Offset. length value
---------------------------------------
   0,1 (2) - a reference to the previous

                  record

   2,3 (2) - a reference to the following

                  record

     4 (1) - number of characters in

                  the name of the symbol (N)

     5 (N) - marks the name of the symbol

                  (Symbols)

   5 + N (1) - the tag value of the symbol

   6 + N (2) - symbol value
---------------------------------------
 Possible tag values of the symbol:

 1 - a symbol defined in terms of external

     seekability expression that

     must be recorded in the 2

     object module. In this case,

     bytes at offset 6 and 6 + N + N +1 is not

     defined.


     In other cases, the actual value
 character is in a word at offset
 6 + N.

 % 10000000 - tag absolute value

     symbol.

 % 1 ******* - tag relative or

     complex relative importance

     symbol, where ******* - the degree of
     relativity (see description Assem
     Blair p.p.3.5.1, transferability when

     expression evaluation). Relative
     positive values are determined by relative
     relative to the beginning of the module.


     The degree of relativity here - it's
number of displacements, ie a number specifying how many times 
a unit address must be added or subtracted to / from the value

symbol when linking to a particular address. This number is 
defined as the 7-digit number with the sign bit in the bit 
number 6. 

     Here, bit 6 plays the same role that
and bit 7 in the 8-bit signed number.

     Thus, if 6 bits = 1, then
module address will not be added, and subtracted from the value 
of the symbol when linking. 


     For example, after defining in assembler $ MET EQU - $ 
($-a reference to the program counter) $ MET object file 
receive the tag value # FF, and the layout of the module 
address will be subtracted from the values $ MET once. 

            ________________


  Area 2. Outside of seekability

   expressions for the global symbols

     defined in this module.


     Expressions must be written in
postfix (*) form, separated
from another source 9 and lie in the same manner as that of the 
global symbols related to these expressions. 

-------------(*) Postfix form of the expressions -
a form in which the operands are first written, and then - 
Operators for example 2 instead of 4 + 2 + 4. (Editor's note.)

-------------

     Operands are written in standard form (see Table. 4 in the 
section "Format of the expressions"). As an example of such an 
expression can be reduced as follows: 

     Let MET - label offset from
beginning of the module # 33.

     For the global label $ met EQU
MET/256 in the object file will be placed
such expression in region 2 (hex format):

 80 33 00 80 00 01 2F.

    # 33256 /

            ________________


   Area 3. The code module.


     The area should contain the code of the processor up to a 
configurable value of bytes and words. And everything must be 
defined relative 2-byte values. Bytes, not defined in the 
module, or certain as external, complex relative, and

also relative, but not 2-byte
length can be any value (assembler writes back 0).

            ________________


      Area 4. Addresses and values

      custom cell module.


     The region consists of the records (two types), and should 
okanchivaetsya 4 bytes # FF.



             Types:


     1.Adresa 2-byte cells with a relative value.


     For example, in a fragment of MET: LD
HL, MET value at MET +1 will be
simple relative (to the register is loaded label value) and, 
therefore, address MET +1 should be written in 4 areas

as a record type 1. This address is an offset from the beginning
area code object module to a custom cell. In this case, the 
relative importance of the custom will be lie on the address in 
the code module. Therefore, to set up 2-byte cell is enough to 
know its address. This, practically, the most common type of 
custom values for layout modules.



     2. All other addresses of cells whose values are not 
determined until the end during the broadcast (along with the 
expressions that define these values). Format this record is as 
follows (see Table 3) 


                          Table 3

  Address format custom cells.
--------------------------------------- Deposed. length value
---------------------------------------
  0.1 (2) - # FFFF - sign of the beginning
              la record to distinguish it from

              record type 1.

  2 (1) - tag is determined by the value
              notation:

              0 - 2-byte word

              1 - 1 - byte cell

              2 - cell - the argument

                short transition teams
                of the type

                JR AAA; JR CC, AAA; where

                CC-condition for the transition.

              3 - number of bits (for any

                command of bit operations)

              4 - type of interruption (the argument
                ment teams IM)

              5 - number of restarts (the argument
                ment team RST)


  3,4 (2) - address is set

              cell (the same as that

              in the case record type 1)

  5 -... ... - An expression in postfix

              form (for details see

              below under the heading "Four
              Math Expressions ").

   ... (1) - Code 9 - a sign of the end

              expression.
---------------------------------------


           Format expressions.


     To speed up computation
expressions when linking them is usually written in postfix 
form, ie when the operators come after their arguments. 

Recognizes the following operators:

Binary:

+ 2B addition
- 2D subtraction
* 2A multiplication
/ 2F division
'& 26 bitwise logical "and".
@ 40 bitwise logical "or".
! 21 bitwise logical exclusion
      sponding to "or".
? 3F MOD operator

Unary:

, 2C minus sign (the sign of number)
^ 5E squaring (2 ^)


  The recording format of the arguments following
(See Table 4).


                           Table 4.

     The format of the operands in expressions.
---------------------------------------
  Offset. length value
---------------------------------------
   0 1 - Tag value of the argument.

   1 2 - Numeric value argument
                ment.

      or

   1 N - Symbolic value

                argument length in the N values
                Cove, is used to

                inclusion in the expression

                undefined in the module

                characters. N can be

                1 to 6.
---------------------------------------
Types of tags:

 If the high bit - 1, then the argument

     has a numeric value.

 % 10000000 - the argument ab
     absolutely

 % 1 ******* - relative or complex

     the relative value of the argument

     ******* degree (see the description of the degree of
     description of the area 1).

 If the high bit - 0, then the argument NEs
     us to undefined symbol in module
     ox, and the tag determines the number of settlement
     leduyuschih him symbol characters.


     For example, the tag% 00000 *** asterisks indicate the 
number of characters in the symbol. This number can be from 1 
to 6. 


       Examples of records of expressions:

Expression


            <MET+1> / 256 '& amp2 ^ 3,

where MET - mark with a relative shift in the module # 10, will 
appear in object module as the next line in the

hex format:

81 10 00 80 01 00 80 00 01 2B 2F

  MET 1 + 256 /

80 03 00 5E 26

   March 2 ~ '&

81 - tag relative importance of degree 1 (for the label MET).

80 - the tag of the absolute values for the numbers
1, 256 and 3.

Expression


               2 * <MET+1>,

where MET - not defined in the module symbol will appear in the 
object module as the following string in hex format:


80 02 00 03 4D 45 54 80 01 00 2B 2A

    2 M E T 1 + *

80 - the tag of the absolute values for the numbers
2 and 1.

03 - the tag character values for the undefined symbols MET 3 
characters. ________________________________________