重定位类型分析(1)

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重定位类型分析(1)

2013年10月29日 ⁄ 综合 ⁄ 共 30940字 ⁄ 字号小中大 ⁄ 评论关闭

重定位目标文件:位置相关 gcc -c 1.c -o 1.o

PIC重定位目标文件:位置无关 gcc -fPIC -c 1.c -o 1.o

静态库文件:多个重定位目标文件的集合 ar c lib.a 1.o 2.o

共享库:动态链接库 ld -shared 1.o -o 1.so

可执行文件:静态链接 gcc 2.o 1.o -o 3 or gcc 2.o lib.a -o 3

可执行文件:动态链接 gcc 2.o 1.so -o 3

重定位分两个步骤

目标文件中的重定位信息,指导ld如何连接时重定位(静态)

可执行文件中的重定位信息，指导/lib/ld-linux.so.2如何执行时重定位(动态)

重定位类型解析(1)

由于是重定位目标文件，所以Offset是相对于节的偏移。.rel.text说明要重定位的节是.text.

找节表,.rel.text节的Inf指向1节，即.text.(可发现Addr全0)

Info字段分成两部分，第八位为重定位类型，高24位为符号表索引，据此可找到重定位的符号。

这里的符号表是.symtab.

0000000b 00901 R_386_32 00000000 s

而009在.symtab索引到的项为

9: 00000000 4 OBJECT GLOBAL DEFAULT 3 s

名字为s,值为全0，大小为4字节(指针变量)，节索引为3,即在.data节中.

00000027 00a01 R_386_32 00000004 t

可见00a在.symtab索引到的项为

10: 00000004 4 OBJECT GLOBAL DEFAULT 3 t

名字为t,值为4，大小为4字节(指针变量)，节索引为3,即在.data节中.

(还可以发现符号表中f和g的大小正好等于其代码长度,f大小25,代码长度0~0x18,...)

这里的值指的是该符号在所在的节中的偏移。

[root@proxy ~/3]# objdump -sj .data 1.o

1.o: file format elf32-i386

Contents of section .data:

0000 00000000 0e000000 ........

可见,s指向的值是0,t指向的值是0xe.这就是变量的s和t的值。

实际上，这两个值是指向.rodata节的偏移。

[root@proxy ~/3]# objdump -sj .rodata 1.o

1.o: file format elf32-i386

Contents of section .rodata:

0000 68656c6c 6f20576f 726c6421 0a006162 hello World!..ab

0010 630a00 c..

即s指向hello world!

t指向abc

和程序中的意思一样。

再看看重定位中的偏移Offset:[该offset指明了程序中需要重定位的位置]

Relocation section '.rel.text' at offset 0x40c contains 4 entries:

Offset Info Type Symbol's Value Symbol's Name

0000000b 00901 R_386_32 00000000 s

00000010 00c02 R_386_PC32 00000000 printf

00000027 00a01 R_386_32 00000004 t

0000002c 00c02 R_386_PC32 00000000 printf

可以在objdump -dj .text 1.o中查找对应的位置

假设现在1.o要和另一个目标文件2.o连接成可执行文件,由于ld要合并相同的节，1.o中符号原来的地址

变成无效地址了，因此1.o中的符号必须被重定位

R_386_32重定位方法: .data节被合并到新的地址处，假设为x,则s的值就修正为x+0,t的值被修正为x+4

(此时是地址，而不再是节偏移)，然后把该值写入Offset处

参看3.o调用1.o的f和g

R_386_PC32重定位方法: .text节被合并到新的地址处，假设为y,则f的值被修正为y+0,g的值被修正为y+0x1c.

然后把该值写到Offset处。

因此就不难理解下面的意思了

R_386_NONE 0 none none

R_386_32 1 word32 S + A

R_386_PC32 2 word32 S + A

S是节的新地址，A是Offset

附件1

1.c.txt

[root@proxy ~/3]# cat 1.c

#include <stdio.h>

char *s="hello World!/n";

char *t="abc/n";

void f()

{

printf(s);

}

void g()

{

printf(t);

}

[root@proxy ~/3]# gcc -c 1.c -o 1.o

[root@proxy ~/3]# objdump -dj .text 1.o

1.o: file format elf32-i386

Disassembly of section .text:

00000000 <f>:

0: 55 push %ebp

1: 89 e5 mov %esp,%ebp

3: 83 ec 08 sub $0x8,%esp

6: 83 ec 0c sub $0xc,%esp

9: ff 35 00 00 00 00 pushl 0x0

f: e8 fc ff ff ff call 10 <f+0x10>

14: 83 c4 10 add $0x10,%esp

17: c9 leave

18: c3 ret

19: 8d 76 00 lea 0x0(%esi),%esi

0000001c <g>:

1c: 55 push %ebp

1d: 89 e5 mov %esp,%ebp

1f: 83 ec 08 sub $0x8,%esp

22: 83 ec 0c sub $0xc,%esp

25: ff 35 00 00 00 00 pushl 0x0

2b: e8 fc ff ff ff call 2c <g+0x10>

30: 83 c4 10 add $0x10,%esp

33: c9 leave

34: c3 ret

35: 8d 76 00 lea 0x0(%esi),%esi

[root@proxy ~/3]# readelf -a 1.o

ELF Header:

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: 296 (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: 12

Section header string table index: 9

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 000038 00 AX 0 0 4

[ 2] .rel.text REL 00000000 00040c 000020 08 10 1 4

[ 3] .data PROGBITS 00000000 00006c 000008 00 WA 0 0 4

[ 4] .rel.data REL 00000000 00042c 000010 08 10 3 4

[ 5] .bss NOBITS 00000000 000074 000000 00 WA 0 0 4

[ 6] .note NOTE 00000000 000074 000014 00 0 0 1

[ 7] .rodata PROGBITS 00000000 000088 000013 00 A 0 0 1

[ 8] .comment PROGBITS 00000000 00009b 000036 00 0 0 1

[ 9] .shstrtab STRTAB 00000000 0000d1 000057 00 0 0 1

[10] .symtab SYMTAB 00000000 000308 0000e0 10 11 9 4

[11] .strtab STRTAB 00000000 0003e8 000023 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)

There are no program headers in this file.

There is no dynamic segment in this file.

Relocation section '.rel.text' at offset 0x40c contains 4 entries:

Offset Info Type Symbol's Value Symbol's Name

0000000b 00901 R_386_32 00000000 s

00000010 00c02 R_386_PC32 00000000 printf

00000027 00a01 R_386_32 00000004 t

0000002c 00c02 R_386_PC32 00000000 printf

Relocation section '.rel.data' at offset 0x42c contains 2 entries:

Offset Info Type Symbol's Value Symbol's Name

00000000 00601 R_386_32 00000000 .rodata

00000004 00601 R_386_32 00000000 .rodata

There are no unwind sections in this file.

Symbol table '.symtab' contains 14 entries:

Num: Value Size Type Bind Vis Ndx Name

0: 00000000 0 NOTYPE LOCAL DEFAULT UND

1: 00000000 0 FILE LOCAL DEFAULT ABS 1.c

2: 00000000 0 SECTION LOCAL DEFAULT 1

3: 00000000 0 SECTION LOCAL DEFAULT 3

4: 00000000 0 SECTION LOCAL DEFAULT 5

5: 00000000 0 NOTYPE LOCAL DEFAULT 1 gcc2_compiled.

6: 00000000 0 SECTION LOCAL DEFAULT 7

7: 00000000 0 SECTION LOCAL DEFAULT 6

8: 00000000 0 SECTION LOCAL DEFAULT 8

9: 00000000 4 OBJECT GLOBAL DEFAULT 3 s

10: 00000004 4 OBJECT GLOBAL DEFAULT 3 t

11: 00000000 25 FUNC GLOBAL DEFAULT 1 f

12: 00000000 0 NOTYPE GLOBAL DEFAULT UND printf

13: 0000001c 25 FUNC GLOBAL DEFAULT 1 g

No version information found in this file.

附件2

3.c.txt

[root@proxy ~/3]# cat 3.c

void f();

int main()

{

f();

g();

return 0;

}

[root@proxy ~/3]# gcc -c 3.c -o 3.o

[root@proxy ~/3]# objdump -dj .text 3.o

3.o: file format elf32-i386

Disassembly of section .text:

00000000 <main>:

0: 55 push %ebp

1: 89 e5 mov %esp,%ebp

3: 83 ec 08 sub $0x8,%esp

6: e8 fc ff ff ff call 7 <main+0x7>

b: e8 fc ff ff ff call c <main+0xc>

10: b8 00 00 00 00 mov $0x0,%eax

15: c9 leave

16: c3 ret

17: 90 nop

[root@proxy ~/3]# readelf -a 3.o

ELF Header:

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: 220 (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: 10

Section header string table index: 7

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 000018 00 AX 0 0 4

[ 2] .rel.text REL 00000000 00033c 000010 08 8 1 4

[ 3] .data PROGBITS 00000000 00004c 000000 00 WA 0 0 4

[ 4] .bss NOBITS 00000000 00004c 000000 00 WA 0 0 4

[ 5] .note NOTE 00000000 00004c 000014 00 0 0 1

[ 6] .comment PROGBITS 00000000 000060 000036 00 0 0 1

[ 7] .shstrtab STRTAB 00000000 000096 000045 00 0 0 1

[ 8] .symtab SYMTAB 00000000 00026c 0000b0 10 9 8 4

[ 9] .strtab STRTAB 00000000 00031c 00001d 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)

There are no program headers in this file.

There is no dynamic segment in this file.

Relocation section '.rel.text' at offset 0x33c contains 2 entries:

Offset Info Type Symbol's Value Symbol's Name

00000007 00902 R_386_PC32 00000000 f

0000000c 00a02 R_386_PC32 00000000 g

There are no unwind sections in this file.

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 3.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 NOTYPE LOCAL DEFAULT 1 gcc2_compiled.

6: 00000000 0 SECTION LOCAL DEFAULT 5

7: 00000000 0 SECTION LOCAL DEFAULT 6

8: 00000000 23 FUNC GLOBAL DEFAULT 1 main

9: 00000000 0 NOTYPE GLOBAL DEFAULT UND f

10: 00000000 0 NOTYPE GLOBAL DEFAULT UND g

No version information found in this file.

附件3

4.c.txt

[root@proxy ~/3]# gcc 1.o 3.o -o 4

[root@proxy ~/3]# ./4

hello World!

abc

[root@proxy ~/3]# objdump -dj .text 4

4: file format elf32-i386

Disassembly of section .text:

08048360 <_start>:

8048360: 31 ed xor %ebp,%ebp

8048362: 5e pop %esi

8048363: 89 e1 mov %esp,%ecx

8048365: 83 e4 f0 and $0xfffffff0,%esp

8048368: 50 push %eax

8048369: 54 push %esp

804836a: 52 push %edx

804836b: 68 f0 84 04 08 push $0x80484f0

8048370: 68 e4 82 04 08 push $0x80482e4

8048375: 51 push %ecx

8048376: 56 push %esi

8048377: 68 98 84 04 08 push $0x8048498

804837c: e8 ab ff ff ff call 804832c <_init+0x48>

8048381: f4 hlt

8048382: 89 f6 mov %esi,%esi

08048384 <call_gmon_start>:

8048384: 55 push %ebp

8048385: 89 e5 mov %esp,%ebp

8048387: 53 push %ebx

8048388: 50 push %eax

8048389: e8 00 00 00 00 call 804838e <call_gmon_start+0xa>

804838e: 5b pop %ebx

804838f: 81 c3 ca 11 00 00 add $0x11ca,%ebx

8048395: 8b 83 20 00 00 00 mov 0x20(%ebx),%eax

804839b: 85 c0 test %eax,%eax

804839d: 74 02 je 80483a1 <call_gmon_start+0x1d>

804839f: ff d0 call *%eax

80483a1: 8b 5d fc mov 0xfffffffc(%ebp),%ebx

80483a4: c9 leave

80483a5: c3 ret

80483a6: 89 f6 mov %esi,%esi

80483a8: 90 nop

80483a9: 90 nop

80483aa: 90 nop

80483ab: 90 nop

80483ac: 90 nop

80483ad: 90 nop

80483ae: 90 nop

80483af: 90 nop

080483b0 <__do_global_dtors_aux>:

80483b0: 55 push %ebp

80483b1: 89 e5 mov %esp,%ebp

80483b3: 83 ec 08 sub $0x8,%esp

80483b6: 8b 15 38 95 04 08 mov 0x8049538,%edx

80483bc: 85 d2 test %edx,%edx

80483be: 75 49 jne 8048409 <__do_global_dtors_aux+0x59>

80483c0: 8b 15 34 95 04 08 mov 0x8049534,%edx

80483c6: 8b 02 mov (%edx),%eax

80483c8: 85 c0 test %eax,%eax

80483ca: 74 1a je 80483e6 <__do_global_dtors_aux+0x36>

80483cc: 8d 74 26 00 lea 0x0(%esi,1),%esi

80483d0: 8d 42 04 lea 0x4(%edx),%eax

80483d3: a3 34 95 04 08 mov %eax,0x8049534

80483d8: ff 12 call *(%edx)

80483da: 8b 15 34 95 04 08 mov 0x8049534,%edx

80483e0: 8b 0a mov (%edx),%ecx

80483e2: 85 c9 test %ecx,%ecx

80483e4: 75 ea jne 80483d0 <__do_global_dtors_aux+0x20>

80483e6: b8 1c 83 04 08 mov $0x804831c,%eax

80483eb: 85 c0 test %eax,%eax

80483ed: 74 10 je 80483ff <__do_global_dtors_aux+0x4f>

80483ef: 83 ec 0c sub $0xc,%esp

80483f2: 68 44 95 04 08 push $0x8049544

80483f7: e8 20 ff ff ff call 804831c <_init+0x38>

80483fc: 83 c4 10 add $0x10,%esp

80483ff: b8 01 00 00 00 mov $0x1,%eax

8048404: a3 38 95 04 08 mov %eax,0x8049538

8048409: 89 ec mov %ebp,%esp

804840b: 5d pop %ebp

804840c: c3 ret

804840d: 8d 76 00 lea 0x0(%esi),%esi

08048410 <fini_dummy>:

8048410: 55 push %ebp

8048411: 89 e5 mov %esp,%ebp

8048413: 83 ec 08 sub $0x8,%esp

8048416: 89 ec mov %ebp,%esp

8048418: 5d pop %ebp

8048419: c3 ret

804841a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi

08048420 <frame_dummy>:

8048420: 55 push %ebp

8048421: b8 0c 83 04 08 mov $0x804830c,%eax

8048426: 89 e5 mov %esp,%ebp

8048428: 83 ec 08 sub $0x8,%esp

804842b: 85 c0 test %eax,%eax

804842d: 74 15 je 8048444 <frame_dummy+0x24>

804842f: 83 ec 08 sub $0x8,%esp

8048432: 68 44 96 04 08 push $0x8049644

8048437: 68 44 95 04 08 push $0x8049544

804843c: e8 cb fe ff ff call 804830c <_init+0x28>

8048441: 83 c4 10 add $0x10,%esp

8048444: 89 ec mov %ebp,%esp

8048446: 5d pop %ebp

8048447: c3 ret

8048448: 90 nop

8048449: 8d b4 26 00 00 00 00 lea 0x0(%esi,1),%esi

08048450 <init_dummy>:

8048450: 55 push %ebp

8048451: 89 e5 mov %esp,%ebp

8048453: 83 ec 08 sub $0x8,%esp

8048456: 89 ec mov %ebp,%esp

8048458: 5d pop %ebp

8048459: c3 ret

804845a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi

08048460 <f>:

8048460: 55 push %ebp

8048461: 89 e5 mov %esp,%ebp

8048463: 83 ec 08 sub $0x8,%esp

8048466: 83 ec 0c sub $0xc,%esp

8048469: ff 35 3c 95 04 08 pushl 0x804953c

804846f: e8 c8 fe ff ff call 804833c <_init+0x58>

8048474: 83 c4 10 add $0x10,%esp

8048477: c9 leave

8048478: c3 ret

8048479: 8d 76 00 lea 0x0(%esi),%esi

0804847c <g>:

804847c: 55 push %ebp

804847d: 89 e5 mov %esp,%ebp

804847f: 83 ec 08 sub $0x8,%esp

8048482: 83 ec 0c sub $0xc,%esp

8048485: ff 35 40 95 04 08 pushl 0x8049540

804848b: e8 ac fe ff ff call 804833c <_init+0x58>

8048490: 83 c4 10 add $0x10,%esp

8048493: c9 leave

8048494: c3 ret

8048495: 8d 76 00 lea 0x0(%esi),%esi

08048498 <main>:

8048498: 55 push %ebp

8048499: 89 e5 mov %esp,%ebp

804849b: 83 ec 08 sub $0x8,%esp

804849e: e8 bd ff ff ff call 8048460 <f>

80484a3: e8 d4 ff ff ff call 804847c <g>

80484a8: b8 00 00 00 00 mov $0x0,%eax

80484ad: c9 leave

80484ae: c3 ret

80484af: 90 nop

080484b0 <__do_global_ctors_aux>:

80484b0: 55 push %ebp

80484b1: 89 e5 mov %esp,%ebp

80484b3: 53 push %ebx

80484b4: 83 ec 04 sub $0x4,%esp

80484b7: a1 48 95 04 08 mov 0x8049548,%eax

80484bc: bb 48 95 04 08 mov $0x8049548,%ebx

80484c1: 83 f8 ff cmp $0xffffffff,%eax

80484c4: 74 16 je 80484dc <__do_global_ctors_aux+0x2c>

80484c6: 8d 76 00 lea 0x0(%esi),%esi

80484c9: 8d bc 27 00 00 00 00 lea 0x0(%edi,1),%edi

80484d0: 83 eb 04 sub $0x4,%ebx

80484d3: ff d0 call *%eax

80484d5: 8b 03 mov (%ebx),%eax

80484d7: 83 f8 ff cmp $0xffffffff,%eax

80484da: 75 f4 jne 80484d0 <__do_global_ctors_aux+0x20>

80484dc: 58 pop %eax

80484dd: 5b pop %ebx

80484de: 5d pop %ebp

80484df: c3 ret

080484e0 <init_dummy>:

80484e0: 55 push %ebp

80484e1: 89 e5 mov %esp,%ebp

80484e3: 83 ec 08 sub $0x8,%esp

80484e6: 89 ec mov %ebp,%esp

80484e8: 5d pop %ebp

80484e9: c3 ret

80484ea: 8d b6 00 00 00 00 lea 0x0(%esi),%esi

[root@proxy ~/3]# readelf -a 4

ELF Header:

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: EXEC (Executable file)

Machine: Intel 80386

Version: 0x1

Entry point address: 0x8048360

Start of program headers: 52 (bytes into file)

Start of section headers: 10844 (bytes into file)

Flags: 0x0

Size of this header: 52 (bytes)

Size of program headers: 32 (bytes)

Number of program headers: 6

Size of section headers: 40 (bytes)

Number of section headers: 30

Section header string table index: 27

Section Headers:

[Nr] Name Type Addr Off Size ES Flg Lk Inf Al

[ 0] NULL 00000000 000000 000000 00 0 0 0

[ 1] .interp PROGBITS 080480f4 0000f4 000013 00 A 0 0 1

[ 2] .note.ABI-tag NOTE 08048108 000108 000020 00 A 0 0 4

[ 3] .hash HASH 08048128 000128 000034 04 A 4 0 4

[ 4] .dynsym DYNSYM 0804815c 00015c 000080 10 A 5 1 4

[ 5] .dynstr STRTAB 080481dc 0001dc 000095 00 A 0 0 1

[ 6] .gnu.version VERSYM 08048272 000272 000010 02 A 4 0 2

[ 7] .gnu.version_r VERNEED 08048284 000284 000030 00 A 5 1 4

[ 8] .rel.dyn REL 080482b4 0002b4 000008 08 A 4 0 4

[ 9] .rel.plt REL 080482bc 0002bc 000028 08 A 4 b 4

[10] .init PROGBITS 080482e4 0002e4 000018 00 AX 0 0 4

[11] .plt PROGBITS 080482fc 0002fc 000060 04 AX 0 0 4

[12] .text PROGBITS 08048360 000360 000190 00 AX 0 0 16

[13] .fini PROGBITS 080484f0 0004f0 00001e 00 AX 0 0 4

[14] .rodata PROGBITS 08048510 000510 00001b 00 A 0 0 4

[15] .data PROGBITS 0804952c 00052c 000018 00 WA 0 0 4

[16] .eh_frame PROGBITS 08049544 000544 000004 00 WA 0 0 4

[17] .ctors PROGBITS 08049548 000548 000008 00 WA 0 0 4

[18] .dtors PROGBITS 08049550 000550 000008 00 WA 0 0 4

[19] .got PROGBITS 08049558 000558 000024 04 WA 0 0 4

[20] .dynamic DYNAMIC 0804957c 00057c 0000c8 08 WA 5 0 4

[21] .sbss PROGBITS 08049644 000644 000000 00 W 0 0 1

[22] .bss NOBITS 08049644 000644 000018 00 WA 0 0 4

[23] .stab PROGBITS 00000000 000644 0007a4 0c 24 0 4

[24] .stabstr STRTAB 00000000 000de8 001983 00 0 0 1

[25] .comment PROGBITS 00000000 00276b 00017a 00 0 0 1

[26] .note NOTE 00000000 0028e5 00008c 00 0 0 1

[27] .shstrtab STRTAB 00000000 002971 0000e9 00 0 0 1

[28] .symtab SYMTAB 00000000 002f0c 000540 10 29 3d 4

[29] .strtab STRTAB 00000000 00344c 000234 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)

Program Headers:

Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align

PHDR 0x000034 0x08048034 0x08048034 0x000c0 0x000c0 R E 0x4

INTERP 0x0000f4 0x080480f4 0x080480f4 0x00013 0x00013 R 0x1

[Requesting program interpreter: /lib/ld-linux.so.2]

LOAD 0x000000 0x08048000 0x08048000 0x0052b 0x0052b R E 0x1000

LOAD 0x00052c 0x0804952c 0x0804952c 0x00118 0x00130 RW 0x1000

DYNAMIC 0x00057c 0x0804957c 0x0804957c 0x000c8 0x000c8 RW 0x4

NOTE 0x000108 0x08048108 0x08048108 0x00020 0x00020 R 0x4

Section to Segment mapping:

Segment Sections...

01 .interp

02 .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version
.gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata

03 .data .eh_frame .ctors .dtors .got .dynamic .bss

04 .dynamic

05 .note.ABI-tag

Dynamic segment at offset 0x57c contains 20 entries:

Tag Type Name/Value

0x00000001 (NEEDED) Shared library: [libc.so.6]

0x0000000c (INIT) 0x80482e4

0x0000000d (FINI) 0x80484f0

0x00000004 (HASH) 0x8048128

0x00000005 (STRTAB) 0x80481dc

0x00000006 (SYMTAB) 0x804815c

0x0000000a (STRSZ) 127 (bytes)

0x0000000b (SYMENT) 16 (bytes)

0x00000015 (DEBUG) 0x0

0x00000003 (PLTGOT) 0x8049558

0x00000002 (PLTRELSZ) 40 (bytes)

0x00000014 (PLTREL) REL

0x00000017 (JMPREL) 0x80482bc

0x00000011 (REL) 0x80482b4

0x00000012 (RELSZ) 8 (bytes)

0x00000013 (RELENT) 8 (bytes)

0x6ffffffe (VERNEED) 0x8048284

0x6fffffff (VERNEEDNUM) 1

0x6ffffff0 (VERSYM) 0x8048272

0x00000000 (NULL) 0x0

Relocation section '.rel.dyn' at offset 0x2b4 contains 1 entries:

Offset Info Type Symbol's Value Symbol's Name

08049578 00706 R_386_GLOB_DAT 00000000 __gmon_start__

Relocation section '.rel.plt' at offset 0x2bc contains 5 entries:

Offset Info Type Symbol's Value Symbol's Name

08049564 00107 R_386_JUMP_SLOT 0804830c __register_frame_info

08049568 00207 R_386_JUMP_SLOT 0804831c __deregister_frame_info

0804956c 00307 R_386_JUMP_SLOT 0804832c __libc_start_main

08049570 00407 R_386_JUMP_SLOT 0804833c printf

08049574 00507 R_386_JUMP_SLOT 0804834c __cxa_finalize

There are no unwind sections in this file.

Symbol table '.dynsym' contains 8 entries:

Num: Value Size Type Bind Vis Ndx Name

0: 00000000 0 NOTYPE LOCAL DEFAULT UND

1: 0804830c 129 FUNC WEAK DEFAULT UND __register_frame_info@GLIBC_2.0

(2)

2: 0804831c 172 FUNC WEAK DEFAULT UND __deregister_frame_info@GLIBC_2.0

(2)

3: 0804832c 202 FUNC GLOBAL DEFAULT UND __libc_start_main@GLIBC_2.0

(2)

4: 0804833c 50 FUNC GLOBAL DEFAULT UND printf@GLIBC_2.0

(2)

5: 0804834c 157 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.1.3

(3)

6: 08048514 4 OBJECT GLOBAL DEFAULT 14 _IO_stdin_used

7: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__

Symbol table '.symtab' contains 84 entries:

Num: Value Size Type Bind Vis Ndx Name

0: 00000000 0 NOTYPE LOCAL DEFAULT UND

1: 080480f4 0 SECTION LOCAL DEFAULT 1

2: 08048108 0 SECTION LOCAL DEFAULT 2

3: 08048128 0 SECTION LOCAL DEFAULT 3

4: 0804815c 0 SECTION LOCAL DEFAULT 4

5: 080481dc 0 SECTION LOCAL DEFAULT 5

6: 08048272 0 SECTION LOCAL DEFAULT 6

7: 08048284 0 SECTION LOCAL DEFAULT 7

8: 080482b4 0 SECTION LOCAL DEFAULT 8

9: 080482bc 0 SECTION LOCAL DEFAULT 9

10: 080482e4 0 SECTION LOCAL DEFAULT 10

11: 080482fc 0 SECTION LOCAL DEFAULT 11

12: 08048360 0 SECTION LOCAL DEFAULT 12

13: 080484f0 0 SECTION LOCAL DEFAULT 13

14: 08048510 0 SECTION LOCAL DEFAULT 14

15: 0804952c 0 SECTION LOCAL DEFAULT 15

16: 08049544 0 SECTION LOCAL DEFAULT 16

17: 08049548 0 SECTION LOCAL DEFAULT 17

18: 08049550 0 SECTION LOCAL DEFAULT 18

19: 08049558 0 SECTION LOCAL DEFAULT 19

20: 0804957c 0 SECTION LOCAL DEFAULT 20

21: 08049644 0 SECTION LOCAL DEFAULT 21

22: 08049644 0 SECTION LOCAL DEFAULT 22

23: 00000000 0 SECTION LOCAL DEFAULT 23

24: 00000000 0 SECTION LOCAL DEFAULT 24

25: 00000000 0 SECTION LOCAL DEFAULT 25

26: 00000000 0 SECTION LOCAL DEFAULT 26

27: 00000000 0 SECTION LOCAL DEFAULT 27

28: 00000000 0 SECTION LOCAL DEFAULT 28

29: 00000000 0 SECTION LOCAL DEFAULT 29

30: 00000000 0 FILE LOCAL DEFAULT ABS initfini.c

31: 08048384 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

32: 08048384 0 FUNC LOCAL DEFAULT 12 call_gmon_start

33: 00000000 0 FILE LOCAL DEFAULT ABS init.c

34: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c

35: 080483b0 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

36: 08049534 0 OBJECT LOCAL DEFAULT 15 p.0

37: 08049550 0 OBJECT LOCAL DEFAULT 18 __DTOR_LIST__

38: 08049538 0 OBJECT LOCAL DEFAULT 15 completed.1

39: 080483b0 0 FUNC LOCAL DEFAULT 12 __do_global_dtors_aux

40: 08049544 0 OBJECT LOCAL DEFAULT 16 __EH_FRAME_BEGIN__

41: 08048410 0 FUNC LOCAL DEFAULT 12 fini_dummy

42: 08049644 24 OBJECT LOCAL DEFAULT 22 object.2

43: 08048420 0 FUNC LOCAL DEFAULT 12 frame_dummy

44: 08048450 0 FUNC LOCAL DEFAULT 12 init_dummy

45: 0804953c 0 OBJECT LOCAL DEFAULT 15 force_to_data

46: 08049548 0 OBJECT LOCAL DEFAULT 17 __CTOR_LIST__

47: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c

48: 080484b0 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

49: 080484b0 0 FUNC LOCAL DEFAULT 12 __do_global_ctors_aux

50: 0804954c 0 OBJECT LOCAL DEFAULT 17 __CTOR_END__

51: 080484e0 0 FUNC LOCAL DEFAULT 12 init_dummy

52: 08049544 0 OBJECT LOCAL DEFAULT 15 force_to_data

53: 08049554 0 OBJECT LOCAL DEFAULT 18 __DTOR_END__

54: 08049544 0 OBJECT LOCAL DEFAULT 16 __FRAME_END__

55: 00000000 0 FILE LOCAL DEFAULT ABS initfini.c

56: 080484f0 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

57: 00000000 0 FILE LOCAL DEFAULT ABS 1.c

58: 08048460 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

59: 00000000 0 FILE LOCAL DEFAULT ABS 3.c

60: 08048498 0 NOTYPE LOCAL DEFAULT 12 gcc2_compiled.

61: 08049540 4 OBJECT GLOBAL DEFAULT 15 t

62: 0804957c 0 OBJECT GLOBAL DEFAULT 20 _DYNAMIC

63: 08048460 25 FUNC GLOBAL DEFAULT 12 f

64: 0804830c 129 FUNC WEAK DEFAULT UND __register_frame_info@@GLIBC_2.0

65: 08048510 4 NOTYPE GLOBAL DEFAULT 14 _fp_hw

66: 0804847c 25 FUNC GLOBAL DEFAULT 12 g

67: 080482e4 0 FUNC GLOBAL DEFAULT 10 _init

68: 0804831c 172 FUNC WEAK DEFAULT UND __deregister_frame_info@@GLIBC_2.0

69: 08048360 0 FUNC GLOBAL DEFAULT 12 _start

70: 08049644 0 OBJECT GLOBAL DEFAULT ABS __bss_start

71: 08048498 23 FUNC GLOBAL DEFAULT 12 main

72: 0804832c 202 FUNC GLOBAL DEFAULT UND __libc_start_main@@GLIBC_2.0

73: 0804952c 0 NOTYPE WEAK DEFAULT 15 data_start

74: 0804833c 50 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.0

75: 080484f0 0 FUNC GLOBAL DEFAULT 13 _fini

76: 0804953c 4 OBJECT GLOBAL DEFAULT 15 s

77: 0804834c 157 FUNC WEAK DEFAULT UND __cxa_finalize@@GLIBC_2.1.3

78: 08049644 0 OBJECT GLOBAL DEFAULT ABS _edata

79: 08049558 0 OBJECT GLOBAL DEFAULT 19 _GLOBAL_OFFSET_TABLE_

80: 0804965c 0 OBJECT GLOBAL DEFAULT ABS _end

81: 08048514 4 OBJECT GLOBAL DEFAULT 14 _IO_stdin_used

82: 0804952c 0 NOTYPE GLOBAL DEFAULT 15 __data_start

83: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__

Histogram for bucket list length (total of 3 buckets):

Length Number % of total Coverage

0 0 ( 0.0%)

1 1 ( 33.3%) 14.3%

2 0 ( 0.0%) 14.3%

3 2 ( 66.7%) 100.0%

Version symbols section '.gnu.version' contains 8 entries:

Addr: 0000000008048272 Offset: 0x000272 Link: 4 (.dynsym)

000: 0 (*local*) 2 (GLIBC_2.0) 2 (GLIBC_2.0) 2 (GLIBC_2.0)

004: 2 (GLIBC_2.0) 3 (GLIBC_2.1.3) 1 (*global*) 0 (*local*)

Version needs section '.gnu.version_r' contains 1 entries:

Addr: 0x0000000008048284 Offset: 0x000284 Link to section: 5 (.dynstr)

000000: Version: 1 File: libc.so.6 Cnt: 2

0x0010: Name: GLIBC_2.1.3 Flags: none Version: 3

0x0020: Name: GLIBC_2.0 Flags: none Version: 2

补充:

注意1.c.txt中这个重定位节
Relocation section '.rel.data' at offset 0x42c contains 2 entries:
Offset    Info Type            Symbol's Value Symbol's Name
00000000 00601 R_386_32              00000000 .rodata
00000004 00601 R_386_32              00000000 .rodata

分析一下可以发现，它也是用来重定位s和t的。这又是为什么呢？

原来,s指向的字符串是在.rodata节中，节被合并后,.rodata中数据的

地址也会变动，而s和t处的值正是指向.rodata的地址值，因此也需要重定位。

重定位方法同上。只不过有点不同.

006索引的符号是

6: 00000000 0 SECTION LOCAL DEFAULT 7

7节是

[ 7] .rodata PROGBITS 00000000 000088 000013 00 A 0 0 1

符号类型是SECTION,说明该符号和节相关，因此重定位时的S就是修正后.rodata的地址.

总结：
当编译器编译1.c 生成 1.o文件时，是否需要生成 .rel.text 节，我觉得应该由 .text
节中是否使用了需要重定位的符号决定：
全局变量符号，外部函数符号。【这个需要实验一下：局部变量是否需要定位[根据x86的
函数局部变量都是放在堆栈中可知这是不需要定位的]；对静态的局部变量呢？；对于全局的
静态变量呢？对本编译单元内部中函数的调用是否需要定位】而且由于这种.rel.text 是链
接阶段的重定位，所以只有object文件中才有。

.rel.data 是否需要生成，应该由变量中是否使用了常量来决定。不管这个变量是全局变量
还是局部变量。这个还需要实验一下。

【上篇】动易2006最新漏洞公告（2007-2-15）
【下篇】Android NDK带来了什么

作者: reclaimed

该日志由 reclaimed 于11年前发表在综合分类下，最后更新于 2013年10月29日.
转载请注明: 重定位类型分析(1) | 学步园 +复制链接

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重定位类型分析(1)

作者: reclaimed

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