Features of a Symbol Table - System Software - GTU MCA

Ø  SYMTAB (symbol table)

Ø  Content

      Label name and its value (address)

      May also include flag (type, length) etc.

Ø  Usage

      Pass 1: labels are entered into SYMTAB with their address (from

                   LOCCTR) as they are encountered in the source program

       Pass 2: symbols used as operands are looked up in SYMTAB to

                   obtain the address to be inserted in the assembled instruction

Ø  Characteristic

        Dynamic table (insert, delete, search)

Ø  Implementation

        Hash table for efficiency of insertion and retrieval

COPY             1000

FIRST            1000

CLOOP          1003

ENDFIL         1015

EOF                1024

THREE          102D

ZERO             1030

RETADR       1033

LENGTH       1036

BUFFER        1039

RDREC         2039

            SYMBOL TABLE(SYMTAB)

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Example Of Assembly language along with the objectcode generated | System Software Example of Assembly Language. - GTU MCA SEM-3RD.

example of Assembly language along with the objectcode generated

Line    Loc         Source statement                                      Object code

5          1000    COPY             START         1000

10        1000    FIRST            STL              RETADR         141033

15        1003    CLOOP          JSUB            RDREC           482039

20        1006                             LDA            LENGTH         001036

25        1009                            COMP            ZERO             281030

30        100C                           JEQ                ENDFIL         301015

35        100F                            JSUB              WRREC        482061

40        1012                              J                    CLOOP          3C1003          

45        1015    ENDFIL         LDA                EOF                00102A

50        1018                            STA                BUFFER        0C1039

55        101B                           LDA               THREE          00102D

60        101E                           STA                LENGTH       0C1036

65        1021                            JSUB              WRREC        482061

70        1024                            LDL                RETADR       081033

75        1027                            RSUB                                     4C0000

80        102A   EOF                BYTE               C’EOF’        454F46

85        102D   THREE          WORD                   3              000003

90        1030    ZERO             WORD                   0               000000

95        1033    RETADR       RESW                                 1

100      1036    LENGTH       RESW                      1

105      1039    BUFFER        RESB               4096 

110                  .

115                  .           SUBROUTINE TO READ RECORD INTO BUFFER

120                  .

125      2039    RDREC         LDX                ZERO            041030

130      203C                           LDA                ZERO            001030

135      203F    RLOOP          TD                   INPUT          E0205D

140      2042                            JEQ                  RLOOP        30203D

145      2045                            RD                     INPUT        D8205D

150      2048                            COMP           ZERO             281030

155      204B                           JEQ                  EXIT                         302057

160      204E                           STCH            BUFFER,X     549039

165      2051                             TIX               MAXLEN       2C205E

170      2054                            JLT                 RLOOP          38203F

175      2057    EXIT                STX                 LENGTH    101036

180      205A                              RSUB                                  4C0000

185      205D   INPUT           BYTE X’F1’  F1

190      205E   MAXLEN      WORD           4096    001000

195                  .

200                  .           SUBROUTINE TO WRITE RECORD FROM BUFFER

205                  .

210      2061    WRREC                    LDX   ZERO 041030

215      2064    WLOOP         TD      OUTPUT       E02079

220      2067                            JEQ    WLOOP         302064

225      206A                           LDCH            BUFFER,X    509039

230      206D                           WD     OUTPUT       DC2079

235      2070                            TIX     LENGTH       2C1036

240      2073                            JLT     WLOOP         382064

245      2076                            RSUB                         4C0000

250      2079    OUTPUT       BYTE X’05’   05

255                                           END  FIRST

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What are the basic functions of an assembler | Assemler function in System Software. - GTU MCA MATERIAL

Functions of a Basic Assembler

Ø  Convert mnemonic operation codes to their machine

      language equivalents

           E.g. STL -> 14 (line 10)

Ø  Convert symbolic operands to their equivalent

      machine addresses

                  E.g. RETADR -> 1033 (line 10)

Ø  Build the machine instructions in the proper format

Ø  Convert the data constants to internal machine

        representations

                   E.g. EOF -> 454F46 (line 80)

Ø  Write the object program and the assembly listing

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