Flowchart Of The Design Of The Absolute Linker

The simplest is an absolute loader. By making the loader more sophisticated, more complex functions can be done by the loader, resulting in even better utilization of the computer. We consider the absolute loader first, and then based on some problems in the use of the absolute loader, discuss more sophisticated loaders. 7.1 ABSOLUTE LOADERS

Some systems have a linker to perform the linking operations and a separate loader to handle relocation and loading. 3.1 Introduction z The most fundamental functions of a loader - bringing an object program into memory and starting its execution. 3.1.1 Design of an Absolute Loader z An example object program is shown in Fig 3.1a.

4 3.1.1 Design of an Absolute Loader Absolute loader, in Figure 3.1 and 3.2. STL instruction, pair of characters 14, when these are read by loader, they will occupy two bytes of memory. 14 Hex 31 34 ----gt 00010100 one byte For execution, the operation code must be store in a single byte with hexadecimal value 14. Each pair of bytes must be packed together into one

3.1 Design of an Absolute Loader. For a simple absolute loader, all functions are accomplished in a single pass as follows The Header record of object programs is checked to verify that the correct program has been presented for loading. As each Text record is read, the object code it contains is moved to the indicated address in memory.

A linkeror linkage editor performs the linking operations and a separate loaderto handle relocation and loading. System Programming, Spring 2010 rsity 4. 3.1.1 Design of an Absolute Loader 3.1.2 A Simple Bootstrap Loader r 32Machine-DependentLoaderFeatures ical Eng 3.2 MachineDependent Loader Features 3.2.1 Relocation

The absolute loader is a kind of loader in which relocated object files are created, loader accepts these files and places them at a specified location in the memory. This type of loader is called absolute loader because no relocating information is needed, rather it is obtained from the programmer or assembler.

functions and design of all these types of loaders. 3.3.1 Absolute Loader The operation of absolute loader is very simple. The object code is loaded to specified locations in the memory. At the end the loader jumps to the specified address to begin execution of the loaded program. The role of absolute loader is as shown in the figure 3.3.1.

quotLoader and linkerquot may be a single system program Loader loading and relocation Linker linking Absolute loader No linking and relocation needed Records in object program perform Header record Check the Header record for program name, starting address, and length available

Figure 4.3 The Role of both Loader and Linker Type of Loaders The different types of loaders are, absolute loader, bootstrap loader, relocating loader relative loader, and, direct linking loader. The following sections discuss the functions and design of all these types of loaders. 4.1.1Design of Absolute Loader

Thus one system loader or linker can be used regardless of the original source programming language. Basic Loader Functions Design of an Absolute Loader. An absolute loader does not need to perform such functions as linking and program relocation, its operation is very simple. All functions are accomplished in a single pass.