一些常用代码分析工具的使用
gcc -S hello.c -o hello.s
objdump -h hello.o
hello.o: file format elf32-i386
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000026 00000000 00000000 00000034 2**2 // 代码段
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000000 00000000 00000000 0000005c 2**2 //已初始化的全局变量和局部镜头变量
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 00000000 00000000 0000005c 2**2 // 未初始化的全局变量和局部镜头变量，实际大小0
ALLOC
3 .rodata 0000000c 00000000 00000000 0000005c 2**0 //只读数据段
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .comment 0000002a 00000000 00000000 00000068 2**0
CONTENTS, READONLY
5 .note.GNU-stack 00000000 00000000 00000000 00000092 2**0
CONTENTS, READONLY
size hello.o
text data bss dec hex filename
50 0 0 50 32 hello.o
两边大小有点不一致，呵呵。
readelf -h hello.o
Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
Class: ELF32
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Intel 80386
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 228 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 40 (bytes)
Number of section headers: 11
Section header string table index: 8
readelf -S hello.o
There are 11 section headers, starting at offset 0xe4:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .text PROGBITS 00000000 000034 000026 00 AX 0 0 4
[ 2] .rel.text REL 00000000 000350 000010 08 9 1 4 // 需要重新定位的
[ 3] .data PROGBITS 00000000 00005c 000000 00 WA 0 0 4
[ 4] .bss NOBITS 00000000 00005c 000000 00 WA 0 0 4
[ 5] .rodata PROGBITS 00000000 00005c 00000c 00 A 0 0 1
[ 6] .comment PROGBITS 00000000 000068 00002a 00 0 0 1
[ 7] .note.GNU-stack PROGBITS 00000000 000092 000000 00 0 0 1
[ 8] .shstrtab STRTAB 00000000 000092 000051 00 0 0 1
[ 9] .symtab SYMTAB 00000000 00029c 0000a0 10 10 8 4
[10] .strtab STRTAB 00000000 00033c 000013 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
Objdump -r hello.o
重定位表信息：表示需要外部link的函数和数据
更好的方法用：
readelf -s hello.o
Symbol table '.symtab' contains 11 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 FILE LOCAL DEFAULT ABS hello.c
2: 00000000 0 SECTION LOCAL DEFAULT 1
3: 00000000 0 SECTION LOCAL DEFAULT 3
4: 00000000 0 SECTION LOCAL DEFAULT 4
5: 00000000 0 SECTION LOCAL DEFAULT 5
6: 00000000 0 SECTION LOCAL DEFAULT 7
7: 00000000 0 SECTION LOCAL DEFAULT 6
8: 00000000 46 FUNC GLOBAL DEFAULT 1 main
9: 00000000 0 NOTYPE GLOBAL DEFAULT UND foo
10: 00000000 0 NOTYPE GLOBAL DEFAULT UND puts
里面UND 的函数就是需要外部link的函数
readelf -s ×.a | grep "UND"