1. CS 140 Lecture Notes: LinkersSlide 1 Memory Layout for Process Code 0 ∞ Data Stack

2. CS 140 Lecture Notes: LinkersSlide 2 Creating a Process Code 0 ∞ Data Stack 10101010 10101010 10101010 ccx.cx.sasx.o 10101010 10101010 10101010 ccy.cy.sasy.o 10101010 10101010 10101010 ccz.cz.sasz.o 10101010 10101010 10101010 Source Code Assembly Code Object Code Executable a.out CompilerAssemblerLinkerLoader ld OS

3. CS 140 Lecture Notes: LinkersSlide 3 A Simple Example extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } main.c FILE* stdin, stdout; int printf(const char* format,...) {... fputc(c, stdout);... } int scanf(const char* format,...) {... c = fgetc(stdin);... } FILE* stdin, stdout; int printf(const char* format,...) {... fputc(c, stdout);... } int scanf(const char* format,...) {... c = fgetc(stdin);... } stdio.c double sin(double x) {... } double sin(double x) {... } math.c

4. CS 140 Lecture Notes: LinkersSlide 4 Object File extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } extern float sin(); extern printf(), scanf(); main() { double x, result; printf("Type number: "); scanf("%f", &x); result = sin(x); printf("Sine is %f\n", result); } main.cmain.o 0 20 32 40 56 main:... call printf... call scanf... call sin... call printf main T[0] printf T[20] printf T[56] scanf T[32] sin T[40] main:... call printf... call scanf... call sin... call printf main T[0] printf T[20] printf T[56] scanf T[32] sin T[40] text section symbols relocation “Store the final location of printf at offset 20 in the text section”

5. CS 140 Lecture Notes: LinkersSlide 5 Object File FILE* stdin, stdout; int printf(const char* format,...) {... fputc(c, stdout);... } int scanf(const char* format,...) {... c = fgetc(stdin);... } FILE* stdin, stdout; int printf(const char* format,...) {... fputc(c, stdout);... } int scanf(const char* format,...) {... c = fgetc(stdin);... } printf.cprintf.o 44 118 232 306 0 8... printf:... load stdout... scanf:... load stdin... stdin: stdout: printf T[44] scanf T[232] stdin D[0] stdout D[8] stdout T[118] stdin T[306]... printf:... load stdout... scanf:... load stdin... stdin: stdout: printf T[44] scanf T[232] stdin D[0] stdout D[8] stdout T[118] stdin T[306] text section data section relocation symbols

6. CS 140 Lecture Notes: LinkersSlide 6 During Pass 1 main.o text 0 64 276 700 math.o text stdio.o text math.o data 728 stdio.o data 836 NameFileSecOffsetAddr main:mainT0?? sin:mathT0?? printf:stdioT38?? scanf:stdioT232?? stdin:stdioD0?? stdout:stdioD8?? Memory map:Symbol table:

7. CS 140 Lecture Notes: LinkersSlide 7 After Pass 1 main.o text 0 64 276 700 math.o text stdio.o text math.o data 728 stdio.o data 836 NameFileSecOffsetAddr main:mainT00 sin:mathT064 printf:stdioT38314 scanf:stdioT232508 stdin:stdioD0728 stdout:stdioD8736 Memory map:Symbol table:

8. CS 140 Lecture Notes: LinkersSlide 8 Relocation text section in main.o 20... call 0... printf T[20] relocation record in main.o printf 314 symbol table text section in a.out 20... call 314...

9. CS 140 Lecture Notes: LinkersSlide 9