Linking Loader Pass 1

Introduction linking loader pass1 :

Pass 1 of a Linking Loader is responsible for preparing and analyzing object modules before loading and linking. In this pass, the loader performs several important tasks:

1. Memory Allocation: The loader determines the memory space required for each module and allocates it accordingly. It establishes where code and data will reside in memory.

2. Symbol Table Creation: All symbols (such as variables and functions) used across modules are identified and stored in a symbol table. This table tracks each symbol's location and attributes.

3. External References Resolution: External symbols (those used in one module but defined in another) are flagged for resolution in Pass 2. These references cannot be fully processed until the modules are linked.

4. Relocation Information: The loader generates relocation details, specifying where addresses need adjustment. This ensures that after loading, all memory references are valid.

Pass 1 prepares all modules for the actual linking, relocation, and final execution in Pass 2.

Algorithm of Linking Loader Pass 1:

Begin

get PROOADDR from operating system

set CSADDR to PROOADDR {for first control section}

while not end of input do

begin

read next input record {Header record for control section}

set CSLTH to control section length

search ESTAB for control section name

if found then

set error flag {duplicate external symbol}

else

enter control section name into ESTAB with value CSADDR

while record type ~ 'E' do

begin

read next input record

if record type = 'D' then

for each symbol in the record do

begin

search ESTAB for symbol name

if found then

set error flag (duplicate external symbol)

else

enter symbol into ESTAB with value(CSADDR + indicated address)

end {for}

end {while ~ 'E'}

add CSLTH to CSADDR {starting address for next control section}

end {while not EOF}

end {Pass 1}