1 / 28

Topics

Principles of Computer Architecture Miles Murdocca and Vincent Heuring Chapter 5: Languages and the Machine. Topics. 5.2 The Assembly Process 5.3 Linking and Loading 5.4 Macros. Assembler. Assembly lan. progs. Machine code. Prog1 (MC). Linker. exe file. Loader. Memory. prog2 (MC).

porter
Download Presentation

Topics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Principles of Computer ArchitectureMiles Murdocca and Vincent HeuringChapter 5: Languages and the Machine

  2. Topics 5.2 The Assembly Process 5.3 Linking and Loading 5.4 Macros Assembler Assembly lan. progs Machine code Prog1(MC) Linker exe file Loader Memory prog2(MC) … prog n(MC) libs

  3. The Assembly Process • The process of translating an assembly language program into a machine language program is referred to as the assembly process. • Assemblers generally provide this support: — Allow programmer to specify locations of data and code. — Provide assembly-language mnemonics for all machine instructions and addressing modes, and translate valid assembly language statements into the equivalent machine language. — Permit symbolic labels to represent addresses and constants. — Provide a means for the programmer to specify the starting address of the program, if there is one; and provide a degree of assemble-time arithmetic. — Include a mechanism that allows variables to be defined in one assembly language program and used in another, separately assembled program. — Support macro expansion.

  4. Assembly Example • We explore how the assembly process proceeds by “hand assembling” a simple ARC assembly language program.

  5. Macro Definition for PUSH

  6. Macro expansion for PUSH MACRO definition … PUSH %r2 PUSH %r3 PUSH %r1

  7. Instruc-tionFor-mats and PSR Format for the ARC

  8. Assembled Code ld [x], %r1 1100 0010 0000 0000 0010 1000 0001 0100 ld [y], %r2 1100 0100 0000 0000 0010 1000 0001 1000 addcc %r1,%r2,%r3 1000 0110 1000 0000 0100 0000 0000 0010 st %r3, [z] 1100 0110 0010 0000 0010 1000 0001 1100 jmpl %r15+4, %r0 1000 0001 1100 0011 1110 0000 0000 0100 15 0000 0000 0000 0000 0000 0000 0000 1111 9 0000 0000 0000 0000 0000 0000 0000 1001 0 0000 0000 0000 0000 0000 0000 0000 0000

  9. 2-PASS Assembler • Goes over the program twice • 1st pass: • Find out addresses for all DATA items and machine instructions • Employing location counter and forward referencing • Keep track of the addresses of the current instruction or data items as assembly proceeds • Create a symbolic table • Translate each assembly instruction into machine instruction • Mnemonics • Addressing modes • Has not generated machine code yet. • Location counter (similar to PC) • Initialized to what .org specifies/zero • Incremented by the size of each instruction

  10. Address for each instruction 2048 2052 2056 2060 2064 2068 2072 2076

  11. Symbol table • Contains all labels and constant values in the assembly program • After the first pass, the assembly will have identified and entered all symbols into the symbolic table • during the second pass, the assembler generates the machine code, inserting the values of symbols, which are known

  12. Symbol table • Symbol table for example 1: main 2048 x 2068 y 2072 z 2076

  13. Symbol table Symbol value a_start 3000 length -- address -- loop 2060 done 2088

  14. Symbol table cont’d Symbol value a_start 3000 length 2092 (1) address 2096 (2) loop 2060 done 2088

  15. Assembled Program

  16. Second pass • After the symbol table is created • the program is read a second time • Start from .begin • Machine code is generated using symbol table

  17. Final tasks of the assembler • Extra info to be added to the program for the linker and loader • Linker: linking modules together • Loader: putting the program into memory • Module name and size • Memory and segment info, such as code, data, stack • The address of start symbol (if defined) • The info about global and external symbols • The address of any global symbols • Info about any library routines that are referenced by the module • The value of any constants to be loaded to memory • Some loaders expect data initialization to be specified separately from the binary code • Relocation info

  18. Relocation info • Linker will link all the modules by concatenating them • To do so some of the modules need to be relocated • Example:

  19. Location of programs in memory • As long as program is in user-accessible segment • Might not in the address indicated by .org • Modules are concatenated one after the other • After linking, some modules are relocated to other addresses • Most of addresses we use are re-locatable • Exception: • fixed addresses (I/O devices)

  20. Linking and loading • A number of separately compiled/assembled modules • Linker: a software program • Combines separately assembled programs (object modules) into a single program (load module/exe) • Loader: a software program that places the load module into main memory • Load the various memory segments with the appropriate values and initialize certain registers (i.e. %sp, %pc)

  21. linking • Resolve address refs that are external to modules as it links them • Relocate each module in order to combine them • Specify the starting symbol of the load module • Identify different memory segments • Needs to know local symbol names from global symbol names • Only address labels can be global or external • Some addresses can not be relocated • External symbols defined in another module • Absolute numbers (defined by pseudo-code) • ONE .equ 1 • a_start .equ 3000 • Content of the address when relocated, do not change • i.e : x :105 • !relocate x, address changes, but content remains the same

  22. Linking: Using .global and .extern • A .global is used in the module where a symbol is defined and a .extern is used in every other module that refers to it.

  23. Linking and Loading: Symbol Tables • Symbol tables for the previous example:

  24. loading • Relocating loader • More than one modules, relocate by adding an offset to all re-locatable code in that module • Linking loader • Does both linking and loading • header info • An exe file contains a header (inserted by linker) • Where to load the program • Starting address • Relocation info • What routines are available externally • Dll (microsoft)

  25. Example ARC Program

  26. Recursive Macro Expansion

More Related