Page 139 - DCAP507_SYSTEM_SOFTWARE

Unit 9: Design of an Absolute Loader

Notes

9.2.2 Specification of Data Structures

The next step in our design process is to recognize the databases necessary by each pass of the
loader.

Format of Databases

Pass 1 databases:
1. Input object files.
2. A parameter, the Initial Program Load Address (IPLA) provided by the programmer or
the operating system that specifies the address to load the first segment.
3. A Program Load Address (PLA) counter, utilized to keep track of each segment's assigned
location.
4. A table, the Global External Symbol Table (GEST) that is used to amass each external
symbol and its corresponding assigned core address.

5. A copy of the input to be used later by pass 2. This may be amassed on an auxiliary storage
device, such as magnetic tape, disk, or drum, or the original object file may be reread by
the loader a second time for pass 2.
6. A printed listing, the load map, that states each external symbol and its assigned value.
Pass 2 databases:
1. Copy of object program to be inputted to pass 1.

2. The Initial Program Load Address parameter (IPLA).
3. The Program Load Address counter (PLA).
4. The Global External Symbol Table (GEST'), arranged by pass 1, comprising each external
symbol and its corresponding absolute address value.

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