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CS2422 Assembly Language & System Programming

This CS2422 Assembly Language & System Programming topic covers Beck's Section 3.2.3 algorithm and data structure for a linking loader, including two passes logic. Pass 1 assigns addresses to external symbols, while Pass 2 performs loading, relocation, and linking. It also discusses ESTAB (external symbol table).

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CS2422 Assembly Language & System Programming

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  1. CS2422 Assembly Language & System Programming January 2, 2007

  2. Today’s Topics • Beck’s Section 3.2.3: Algorithm and Data Structure for a Linking Loader

  3. Algorithm and Data Structure • Two Passes Logic • Pass 1: Assign addresses to all external symbols • Pass 2: Perform the actual loading, relocation, and linking • ESTAB (external symbol table) + +

  4. Pass 1 Program Logic • Pass 1: • Assign addresses to all external symbols • Variables & Data structures • PROGADDR (program load address) from OS • CSADDR (control section address) • CSLTH (control section length) • ESTAB • Fig. 3.11(a) • Process Define Record

  5. Fig. 3.11(a)

  6. Pass 2 Program Logic • Pass 2: • Perform the actual loading, relocation, and linking • Modification record • Lookup the symbol in ESTAB • End record for a main program • Transfer address • Fig. 3.11(b) • Process Text record and Modification record

  7. Fig. 3.11(b)

  8. Improve Efficiency • Use local searching instead of multiple searches of ESTAB for the same symbol • Assign a reference number to each external symbol • The reference number is used in Modification records • Implementation • 01: Control section name • Other: External reference symbols • Example • Fig. 3.12

  9. Fig. 3.12 (1/3)

  10. Fig. 3.12 (2/3)

  11. Fig. 3.12 (3/3)

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