Assembly-and-Linking-From-Instructions-to-Execution.pptx
- 1. Assembly and Linking: From Instructions to Execution Assembly and linking are crucial steps in the compilation process, transforming instructions into a program's memory image. Loading then places the program in memory for execution. This presentation explores the techniques required for assembly and linking, providing insights into the complete compilation and loading process. by ARTHI Thenraj
- 2. The Role of Assemblers and Linkers Assembler Translates symbolic assembly language into bit-level representations of instructions, known as object code. It handles instruction formats and partially translates labels into addresses. Linker Completes the translation of labels into addresses and produces an executable binary file. It combines multiple object files into a single executable program. Compilers often generate human-readable assembly language, freeing them from instruction format and address details. The linker ensures the executable is ready for loading into memory.
- 3. Assembler Functionality: Translating Assembly to Object Code 1 Opcode Translation Translates assembly code opcodes into their binary equivalents. 2 Instruction Formatting Formats the bits in each instruction according to the architecture's specifications. 3 Label Translation Translates labels into memory addresses, enabling symbolic addressing. The assembler translates assembly code into object code, handling opcodes, instruction formats, and labels. Labels are a crucial abstraction, allowing programmers to avoid specifying exact memory locations.
- 4. Two-Pass Assembly Process First Pass: Symbol Table Creation Scans the assembly code to determine the address of each label, storing the name and address in a symbol table. Second Pass: Instruction Assembly Assembles the instructions using the label values computed in the first pass, substituting label names with their corresponding addresses. The assembly process involves two passes. The first pass identifies label addresses, and the second pass assembles instructions using these addresses. The program location counter (PLC) tracks the current memory location during the first pass.
- 5. Program Location Counter (PLC) and Origin Program Location Counter (PLC) Keeps track of the current location in memory during the assembly process. It is incremented as the assembler scans through the code. Origin (ORG) A pseudo-op that specifies the starting address of the program. It sets the PLC's value to the specified address, determining where the program begins in memory. The PLC assigns memory locations to labels during assembly, while the ORG statement sets the program's starting address. Assemblers allow multiple ORG statements to spread instructions and data across memory.
- 6. Linking: Stitching Together Program Pieces Modularity Breaking a large program into smaller files helps delineate program modularity. 1 Library Routines If the program uses library routines, those will already be preassembled. 2 Linker A linker allows a program to be stitched together out of several smaller pieces. 3 The linker combines smaller program pieces, operating on object files and modifying assembled code to link files. Breaking programs into smaller files enhances modularity and allows the use of preassembled library routines.
- 7. Entry Points and External References 1 Entry Point The location in a file where a label is defined. 2 External Reference The location in a file where a label is used but not defined. Labels can be defined and used in the same file, or defined in one file and used in others. Entry points define labels, while external references use them. The linker resolves these references.
- 8. Loader's Role: Resolving External References Resolve The main job of the loader is to resolve external references based on available entry points. Symbol Table As a result of the need to know how definitions and references connect, the assembler passes to the linker not only the object file but also the symbol table. The loader resolves external references using entry points, requiring the assembler to pass the object file and symbol table to the linker. This ensures that all references are correctly linked.
- 9. Linker's Two-Phase Process 1 Phase 1: Address Determination Determines the starting address of each object file based on the load order specified by the user or a load map file. 2 Phase 2: Symbol Table Merging and Address Editing Merges all symbol tables from the object files into a single table and edits the object files to change relative addresses into absolute addresses. The linker operates in two phases. First, it determines the starting address of each object file. Second, it merges symbol tables and edits object files to convert relative addresses to absolute addresses.
- 10. Key Takeaways and Next Steps Assembly and Linking Essential steps in transforming code into executable programs. Assemblers and Linkers Play distinct roles in translating and combining code. Understanding the Process Provides insights into software compilation and execution. Assembly and linking are vital for creating executable programs. Assemblers and linkers have distinct roles in translating and combining code. Understanding this process provides valuable insights into software compilation and execution.