1 / 30

Program Linking

Program Linking. System Software Emergency Resolution Lecture #1. Why This Presentation?. Due to unforeseen circumstances , the entire course was abruptly terminated . Class terminated means no lectures. No lectures means no materials for exam , which, unfortunately, still exists.

thai
Download Presentation

Program Linking

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. Program Linking System Software Emergency Resolution Lecture #1

  2. Why This Presentation? • Due to unforeseen circumstances, the entire course was abruptly terminated. • Class terminated means no lectures. No lectures means no materials for exam, which, unfortunately, still exists. • This file fills the gap by adding material to course, even without lecture.

  3. Agenda • Recap of our past: The SIC/XE Civilization • Program Linking Procedures • Solution #1 • Solution #2 • Linking Loader • Principles • Overview of Post-Assembly-Time

  4. The SIC/XE Civilization [BECK] • Allows “library sharing” at runtime • Very important, but we can’t talk right now… • Dynamic Linking • Linkage Editor • Lets us create “.exe” for faster loading • Allows us to NOT program linker in SIC or SIC/XE • Linking Loader • Enables Linking support • Control Section • Allows “fully multiple-file” programming • Relocating Loader (SIC or SIC/XE) • M-Record • Relocation Bit Mask • Absolute Loader • BSL, for example

  5. What is Program Linking? OBJ Load Module OBJ Linker OBJ

  6. Reasons for Program Linking (1) • Can we differentiate • MAIN.dump and MATH.asin, or • MAIN.mem and MATH.atan • by byte number? • How can we jump from an instruction in MAIN to, say, MATH.sin, when they “share” the same “address numbers”? • You can’t answer? Good. That’s what’s supposed to happen. 

  7. Reasons for Program Linking (2) • So why not just “include”? • Answer: It will work, but assembly will be slowed down. Libraries like “math.h” are usually pre-compiled (.o, .lib, .pyc, …), very large, and has only some headers to help you “reach” the functions inside. Don’t be fooled by their appearances. #include MATH MAIN MATH NOTE: In real-world, “headers” usually contain only declarations. So there can already be math.h and math.dll separately. This is actually linking, but still gives illusion of “including.”

  8. Types of Linking • Linking Loader • Link, Load later (Linkage Editor) OBJ OBJ OBJ OBJ OBJ OBJ Linker Linking Loader Load_Module.exe* Loader * Or “755”, you geek.

  9. Understanding Program Offsets SPROGA=0 PROGA • Files/CSs are joined end-to-head, like this diagram. • Each file/CS has its own Length. • First part starts at zero, or S1=0 • Subsequent parts start at {previous part’s start} + {previous part’s length}, or Sn=Sn-1+Ln-1 for positive int n LPROGA SPROGB=SPROGA+LPROGA PROGB LPROGB SPROGC=SPROGB+LPROGB PROGC LPROGC

  10. Linking Method #1: “Naïve” Linking [CCD1] • Simple • Easy to implement • Use 2-pass style • Fast (to run: O(2n), n: code lines) • Drawbacks: • Produces lots of M records • May or may not work with complex expressions

  11. Method #1: Pass 1/2 H,PROGA ,000000,000063 D,LISTA ,000040,ENDA ,000054 • Scan H and D records only • Keep results in ESTAB R,LISTB ,ENDB ,LISTC ,ENDC ... T RECORDS ...... M RECORDS ... E,000020 Current Offset: 0 63 E2 H,PROGB ,000000,00007F H,PROGC ,000000,000051 ESTAB Symbol Address Length D,LISTC ,000030,ENDC ,000042 D,LISTB ,000060,ENDB ,000070 PROGA 00000 00063 R,LISTA ,ENDA ,LISTC ,ENDC R,LISTA ,ENDA ,LISTB ,ENDB LISTA 00040 ... T RECORDS ...... M RECORDS ... ... T RECORDS ...... M RECORDS ... ENDA 00054 E E PROGB 00063 0007F LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  12. Method #1: Pass 2/2 H,PROGA ,000000,000063 D,LISTA ,000040,ENDA ,000054 • Time to modify our code. • Unify H&E • Delete D&R • No ext. symbols means no D/R • Shift T • Use ESTAB for length detect • Substitute into & Shift M • Use ESTAB R,LISTB ,ENDB ,LISTC ,ENDC ... T RECORDS ...... M RECORDS ... E,000020 H,PROGC ,000000,000051 H,PROGB ,000000,00007F D,LISTC ,000030,ENDC ,000042 D,LISTB ,000060,ENDB ,000070 R,LISTA ,ENDA ,LISTC ,ENDC R,LISTA ,ENDA ,LISTB ,ENDB ... T RECORDS ...... M RECORDS ... ... T RECORDS ...... M RECORDS ... E E

  13. Method #1: Pass 2/2: Unify H & E H,LDMODL,000000,000133 • H • Sum length, put at top • Program start = 0 • Absolute programs are usually not linkable… • E • Keep execution start address of Main CS • Put at end of program H,PROGA ,000000,000063 E,000020 H,PROGB ,000000,00007F E H,PROGC ,000000,000051 E E,000020

  14. Method #1: Pass 2/2: Shift T • To make program codes co-exist peacefully, we need to shift addresses. CS PROGA: Offset = 0 T,000020,0A,... ESTAB Symbol Address Length PROGA 00000 00063 +0 LISTA 00040 ENDA 00054 T,000020,0A,... PROGB 00063 0007F LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  15. Method #1: Pass 2/2: Shift T (2) • To make program codes co-exist peacefully, we need to shift addresses. CS PROGB: Offset = 0x63 T,000036,0B,... ESTAB Symbol Address Length PROGA 00000 00063 +63 LISTA 00040 ENDA 00054 T,000099,0B,... PROGB 00063 0007F LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  16. Method #1: Pass 2/2: Shift T (3) • To make program codes co-exist peacefully, we need to shift addresses. CS PROGC: Offset = 0x63+0x7F T,000018,0C,... ESTAB Symbol Address Length PROGA 00000 00063 +E2 LISTA 00040 ENDA 00054 T,0000FA,0C,... PROGB 00063 0007F LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  17. Method #1: Pass 2/2: Change M • Just use ESTAB. (No expressions allowed for now) • Don’t forget to add offset. CS PROGA: Offset = 0 M,000024,05,+LISTBM,000054,06,+LISTCM,000057,06,+ENDC  ESTAB Symbol Address Length PROGA 00000 00063 LISTA 00040 +0 Substitute ENDA 00054 PROGB 00063 0007F M,000024,05,+0000C3M,000054,06,+000112M,000057,06,+000124 LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  18. Method #1: Pass 2/2: Change M (2) • Don’t forget to add offset. CS PROGB: Offset = 0x63 M,000037,05,+LISTAM,00003E,05,+ENDAM,00003E,05,-LISTA  ESTAB Symbol Address Length PROGA 00000 00063 LISTA 00040 +63 Substitute ENDA 00054 PROGB 00063 0007F M,00009A,05,+000040M,0000A1,05,+000054M,0000A1,05,-000040 LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  19. Method #1: Pass 2/2: Change M (3) • Offsets add up! CS PROGC: Offset = 0x63+0x7F M,000019,05,+LISTAM,00001D,05,+LISTBM,000021,05,+ENDA  ESTAB Symbol Address Length PROGA 00000 00063 LISTA 00040 +E2 Substitute ENDA 00054 PROGB 00063 0007F M,0000FB,05,+000040M,0000FF,05,+0000C3M,000103,05,+000054 LISTB 000C3 ENDB 000D3 PROGC 000E2 00051 LISTC 00112 ENDC 00124

  20. Method #1: Ready for Loading H,LDMODL,000000,000133 • We put the H and E we processed earlier… • And the shifted T records… • Then the M records… • We call this a load module. T,000020,0A,... T,000099,0B,... T,0000FA,0C,... M,000024,05,+0000C3M,000054,06,+000112M,000057,06,+000124 M,00009A,05,+000040M,0000A1,05,+000054M,0000A1,05,-000040 M,0000FB,05,+000040M,0000FF,05,+0000C3M,000103,05,+000054 E,000020

  21. Method #1: Notes • Just one note: In pass-2, you just run it through and use string processing to determine line types and act automatically. You don’t and shouldn’t need to separate the code lines into types like I demonstrated.

  22. Method #2: Introduction [CCD2] • Likeness with Method #1 • 2-pass • Utilizes ESTAB • Difference against Method #1 • More compact list of M records, which means faster Loading • Unified M record offset: No need to add/subtract by symbol addresses • However, you may need to implement Expression (-A+B+C-D+E…) • Creates M-Table, so this will use more memory in implementation • And uses more time: O(2n+ms) (m: M-table size, s: # of Symbols)

  23. Method #2: Pass 1: M-Table M,000024,05,+LISTBM,000054,06,+LISTCM,000057,06,+ENDC M,000057,06,-LISTC • While reading in Pass 1, we scan ALL M records to make M-table. • M-table should “summarize” the expression. Cut those loose ends. • For better illustration, we will add one more M-record per CS. M,000037,05,+LISTAM,00003E,05,+ENDAM,00003E,05,-LISTA M,000070,06,+ENDA M,000019,05,+LISTAM,00001D,05,+LISTBM,000021,05,+ENDA M,000021,05,-LISTA

  24. Method #2: Pass 1: Make the M-Table • Make M-table! Start = 0 Length = 0x63 M,000024,05,+LISTB M,000054,06,+LISTC M,000057,06,+ENDC M,000057,06,-LISTC Location Length Expression 00024 05 +LISTB 00054 06 +LISTC 00057 06 +ENDC - LISTC Start = 0x63 Length = 0x7F M,000037,05,+LISTA M,00003E,05,+ENDA M,00003E,05,-LISTA M,000070,06,+ENDA 0009A 05 +LISTA 000A1 05 +ENDA - LISTA 000D3 06 +ENDA M,000019,05,+LISTA M,00001D,05,+LISTB M,000021,05,+ENDA M,000021,05,-LISTA Start = 0xE2 Length = 0x51 000FB 05 +LISTA 000FF 05 +LISTB 00103 05 +ENDA - LISTA

  25. Method #2: Pass 1.5: Evaluate M-Table Result ESTAB Old M-Table Location Length Expression ESTAB Symbol Address Eval . Result Type (Abs/ Rel ) 00024 05 +LISTB PROGA 00000 000C3 R 00054 06 +LISTC LISTA 00040 000112 R 00057 06 +ENDC - LISTC ENDA 00054 000012 A 0009A 05 +LISTA PROGB 00063 00040 R 000A1 05 +ENDA - LISTA LISTB 000C3 00014 A 000D3 06 +ENDA ENDB 000D3 000054 R 000FB 05 +LISTA PROGC 000E2 00040 R 000FF 05 +LISTB LISTC 00112 000C3 R 00103 05 +ENDA - LISTA ENDC 00124 00014 A TIP: If (Number of +’s == Number of –’s) then Absolute, else Relative.

  26. Method #2: Pass 2 • Same thing as Method #1 • Process H and E records normally • However, … • You must add the M values right into the code • Since M records are already processed, we can just dump only Relative rows in.

  27. Method #2: Pass 2: Edit T records. T,000020,0A,03201D 77100004 ... Location Length Eval . Result Type 00024 05 000C3 R +000C3 00054 06 000112 R 00057 06 000012 A T,000020,0A,03201D 771000C7 ... 0009A 05 00040 R 000A1 05 00014 A T,000054,0F,000014 ... 000D3 06 000054 R +000112 000FB 05 00040 R 000FF 05 000C3 R T,000054,0F,000126 ... 00103 05 00014 A etc.

  28. Method #2: Dump the M Records • For R types only: • Dump “empty” M record to tell Loader to relocate. • Keep only Location and Length. Location Length Eval . Result Type 00024 05 000C3 R 00054 06 000112 R 00057 06 000012 A 0009A 05 00040 R 000A1 05 00014 A M,000024,05 M,000054,06 000D3 06 000054 R 000FB 05 00040 R M,00009A,05 M,0000D3,06 000FF 05 000C3 R 00103 05 00014 A M,0000FB,05 M,0000FF,05

  29. Method #2: Finished H,LDMODL,000000,000133 • Just dump the modified T records. • Add the M lines • The rest is no different. T,000020,0A,03201D 771000C7... T,000054,0F,000126 ... T ... T ... T ... M,000024,05 M,000054,06 M ... M ... M ... E,000020

  30. Further Reading • [BECK] L.L. Beck. "Loaders and Linkers" in System Software: An Introduction to Systems Programming, 3rd ed. Addison-Wesley, 1997, ch3. (ISBN: 0201423006) • [CCD1] C. Chatdokmaiprai. (2004, August 25). Load Module & Linker (Solution #1) [Online]. Available: http://cpe.ku.ac.th/~ccd/204331/lmdfmt1.pdf • [CCD2] ____________. (2004, August 25). Load Module & Linker (Solution #2)[Online]. Available: http://cpe.ku.ac.th/~ccd/204331/lmdfmt2.pdf • [CSSH] C.S. Shieh. (?). Linking Loader for SIC/XE Machine [Online]. Available: http://bit.kuas.edu.tw/~csshieh/teach/93A/sp/note/sp07.ppt

More Related