系統程式

1. 系統程式 Supplementation

2. #include <stdio.h> int main() { printf(“Hello World\n”); return 0; } $gcc hello.c $./a.out Hello World

3. The Compilation Process Source code hello.c Preprocessing (gcc -E) Header Files stdio.h … Compilation (cc1) Preprocessed hello.i Assembly (as) Assembly hello.s Object Files hello.o Linking (ld) Static Library libc.a … Executable a.out

4. Compilation Preprocessing gcc -E hello.c -o hello.i Compilation gcc -S hello.i -o hello.s Or cc1 hello.c

5. Assembly as hello.s -o hello.o or gcc -c hello.s -o hello.o Or gcc -c hello.c -o hello.o

6. Linking ld -static /usr/lib/crt1.o /usr/lib/crti.o … ld -static crt1.o crti.o crtbeginT.o hello.o –start-group –lgcc –lgcc_eh –llc –end-group crtend.o crtn.o

7. Object File Format • Executable • Windows: PE (Portable Executable) • Linux: ELF(Executable Linkable Format)

8. Section (Program Block) int g_init_var = 84; int g_uninit_var; void func1(int i) { printf(“%d\n”, i); } int main() { static int s_var = 85; static int s_var2; int a = 1; int b; func1(s_var + s_var2 + a + b); return 0; } BSS: Block Start by Symbol

9. gcc -c so.c objdump -h so.o

10. objdump –s -d so.o

12. ABI • Application Binary Interface • Issue • data type, size, and alignment • calling convention • Memory allocation of struct, union and array • system call •  C++ name mangling, exception propagation, and calling convention 

13. ELF file structure

14. readelf 7F 45 4C 46 readelf –h so.o ‘E’’L’’F’

15. Static Linking • gcc -c a.c b.c • We get a.o b.o • ld a.o b.o -e main -o ab • file ab • ab: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, not stripped

17. Objdump –d a.o Objdump –d ab

18. Memory Layout 0xFFFFFFFF Kernel Space 0xC0000000 Stack unused Heap Read/write sections (.data, .bss) Read only sections (.init, .rodata, .text) 0x08048000 reserved 0x00000000 Linux 2.4.x

19. Stack • Last In First Out (LIFO) ebp Stack pop esp push

20. Stack Frame (Active Record) Caller’s Freame ebp Callee’s Freame esp

22. Heap • malloc()