Relocatable Code

Producing an object code, which can be placed to any specific area in memory.

Direct Address Table (DAT): contains offset locations of all direct addresses in the program (e.g., 8080 instructions that specify direct addresses are LDA, STA, all conditional jumps...). To relocate the program, the loader adds the loading point to all these locations.

assembly language program Assembler machine language program

and DAT

Figure 6. Assembler output for a relocatable code.

Example 3: Following relocatable object code and DAT are generated for Example 1.

assembly language memory object code

program address in memory

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

START

LDA #0 0000 01

0001 00

0002 00

LDX #0 0003 05

0004 00

0005 00

LOOP: ADD LIST, X 0006 18

0007 00

0008 12

TIX COUNT 0009 2C

000A 00

000B 15

JLT LOOP 000C 38

000D 00

000E 06

RSUB 000F 4C

0010 00

0011 00

LIST: WORD 200 0012 00

0013 02

0014 00

COUNT: WORD 6 0015 00

0016 00

0017 06

END

DAT

Forward and backward references in the machine code are generated relative to address 0000. To relocate the code, the loader adds the new load-point to the references in the machine code which are pointed by the DAT.

Date: 2015-01-11; view: 602