在 gcc 的编译代码中，位置 0x284 处看似随机的 20 个字节是否有原因？
Is there a reason for the seemingly random twenty bytes at location 0x284 in the compiled code from gcc?
以下代码说明：
#include <stdio.h>
#define NUMBER_1 1
int main(void)
{
int a;
a = NUMBER_1;
printf("Output: %d\r\n", a);
return 0;
}
将 define 更改为 2 会导致 20 个字节完全更改。我在 Ubuntu 18.04 版下使用 gcc 7.5.0 版。我怀疑这是某种摘要，但如果是这样，为什么它在那里以及何时检查。使用十六进制编辑器编辑这些字节不会阻止代码执行。
来自readelf -a的输出：
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: DYN (Shared object file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x540
Start of program headers: 64 (bytes into file)
Start of section headers: 6448 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 9
Size of section headers: 64 (bytes)
Number of section headers: 29
Section header string table index: 28
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .interp PROGBITS 0000000000000238 00000238
000000000000001c 0000000000000000 A 0 0 1
[ 2] .note.ABI-tag NOTE 0000000000000254 00000254
0000000000000020 0000000000000000 A 0 0 4
[ 3] .note.gnu.build-i NOTE 0000000000000274 00000274
0000000000000024 0000000000000000 A 0 0 4
[ 4] .gnu.hash GNU_HASH 0000000000000298 00000298
000000000000001c 0000000000000000 A 5 0 8
[ 5] .dynsym DYNSYM 00000000000002b8 000002b8
00000000000000a8 0000000000000018 A 6 1 8
[ 6] .dynstr STRTAB 0000000000000360 00000360
0000000000000084 0000000000000000 A 0 0 1
[ 7] .gnu.version VERSYM 00000000000003e4 000003e4
000000000000000e 0000000000000002 A 5 0 2
[ 8] .gnu.version_r VERNEED 00000000000003f8 000003f8
0000000000000020 0000000000000000 A 6 1 8
[ 9] .rela.dyn RELA 0000000000000418 00000418
00000000000000c0 0000000000000018 A 5 0 8
[10] .rela.plt RELA 00000000000004d8 000004d8
0000000000000018 0000000000000018 AI 5 22 8
[11] .init PROGBITS 00000000000004f0 000004f0
0000000000000017 0000000000000000 AX 0 0 4
[12] .plt PROGBITS 0000000000000510 00000510
0000000000000020 0000000000000010 AX 0 0 16
[13] .plt.got PROGBITS 0000000000000530 00000530
0000000000000008 0000000000000008 AX 0 0 8
[14] .text PROGBITS 0000000000000540 00000540
00000000000001b2 0000000000000000 AX 0 0 16
[15] .fini PROGBITS 00000000000006f4 000006f4
0000000000000009 0000000000000000 AX 0 0 4
[16] .rodata PROGBITS 0000000000000700 00000700
0000000000000011 0000000000000000 A 0 0 4
[17] .eh_frame_hdr PROGBITS 0000000000000714 00000714
000000000000003c 0000000000000000 A 0 0 4
[18] .eh_frame PROGBITS 0000000000000750 00000750
0000000000000108 0000000000000000 A 0 0 8
[19] .init_array INIT_ARRAY 0000000000200db8 00000db8
0000000000000008 0000000000000008 WA 0 0 8
[20] .fini_array FINI_ARRAY 0000000000200dc0 00000dc0
0000000000000008 0000000000000008 WA 0 0 8
[21] .dynamic DYNAMIC 0000000000200dc8 00000dc8
00000000000001f0 0000000000000010 WA 6 0 8
[22] .got PROGBITS 0000000000200fb8 00000fb8
0000000000000048 0000000000000008 WA 0 0 8
[23] .data PROGBITS 0000000000201000 00001000
0000000000000010 0000000000000000 WA 0 0 8
[24] .bss NOBITS 0000000000201010 00001010
0000000000000008 0000000000000000 WA 0 0 1
[25] .comment PROGBITS 0000000000000000 00001010
0000000000000029 0000000000000001 MS 0 0 1
[26] .symtab SYMTAB 0000000000000000 00001040
00000000000005e8 0000000000000018 27 43 8
[27] .strtab STRTAB 0000000000000000 00001628
0000000000000205 0000000000000000 0 0 1
[28] .shstrtab STRTAB 0000000000000000 0000182d
00000000000000fe 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)
There are no section groups in this file.
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
PHDR 0x0000000000000040 0x0000000000000040 0x0000000000000040
0x00000000000001f8 0x00000000000001f8 R 0x8
INTERP 0x0000000000000238 0x0000000000000238 0x0000000000000238
0x000000000000001c 0x000000000000001c R 0x1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000858 0x0000000000000858 R E 0x200000
LOAD 0x0000000000000db8 0x0000000000200db8 0x0000000000200db8
0x0000000000000258 0x0000000000000260 RW 0x200000
DYNAMIC 0x0000000000000dc8 0x0000000000200dc8 0x0000000000200dc8
0x00000000000001f0 0x00000000000001f0 RW 0x8
NOTE 0x0000000000000254 0x0000000000000254 0x0000000000000254
0x0000000000000044 0x0000000000000044 R 0x4
GNU_EH_FRAME 0x0000000000000714 0x0000000000000714 0x0000000000000714
0x000000000000003c 0x000000000000003c R 0x4
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 0x10
GNU_RELRO 0x0000000000000db8 0x0000000000200db8 0x0000000000200db8
0x0000000000000248 0x0000000000000248 R 0x1
Section to Segment mapping:
Segment Sections...
00
01 .interp
02 .interp .note.ABI-tag .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
03 .init_array .fini_array .dynamic .got .data .bss
04 .dynamic
05 .note.ABI-tag .note.gnu.build-id
06 .eh_frame_hdr
07
08 .init_array .fini_array .dynamic .got
Dynamic section at offset 0xdc8 contains 27 entries:
Tag Type Name/Value
0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
0x000000000000000c (INIT) 0x4f0
0x000000000000000d (FINI) 0x6f4
0x0000000000000019 (INIT_ARRAY) 0x200db8
0x000000000000001b (INIT_ARRAYSZ) 8 (bytes)
0x000000000000001a (FINI_ARRAY) 0x200dc0
0x000000000000001c (FINI_ARRAYSZ) 8 (bytes)
0x000000006ffffef5 (GNU_HASH) 0x298
0x0000000000000005 (STRTAB) 0x360
0x0000000000000006 (SYMTAB) 0x2b8
0x000000000000000a (STRSZ) 132 (bytes)
0x000000000000000b (SYMENT) 24 (bytes)
0x0000000000000015 (DEBUG) 0x0
0x0000000000000003 (PLTGOT) 0x200fb8
0x0000000000000002 (PLTRELSZ) 24 (bytes)
0x0000000000000014 (PLTREL) RELA
0x0000000000000017 (JMPREL) 0x4d8
0x0000000000000007 (RELA) 0x418
0x0000000000000008 (RELASZ) 192 (bytes)
0x0000000000000009 (RELAENT) 24 (bytes)
0x000000000000001e (FLAGS) BIND_NOW
0x000000006ffffffb (FLAGS_1) Flags: NOW PIE
0x000000006ffffffe (VERNEED) 0x3f8
0x000000006fffffff (VERNEEDNUM) 1
0x000000006ffffff0 (VERSYM) 0x3e4
0x000000006ffffff9 (RELACOUNT) 3
0x0000000000000000 (NULL) 0x0
Relocation section '.rela.dyn' at offset 0x418 contains 8 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000200db8 000000000008 R_X86_64_RELATIVE 640
000000200dc0 000000000008 R_X86_64_RELATIVE 600
000000201008 000000000008 R_X86_64_RELATIVE 201008
000000200fd8 000100000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_deregisterTMClone + 0
000000200fe0 000300000006 R_X86_64_GLOB_DAT 0000000000000000 __libc_start_main@GLIBC_2.2.5 + 0
000000200fe8 000400000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0
000000200ff0 000500000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_registerTMCloneTa + 0
000000200ff8 000600000006 R_X86_64_GLOB_DAT 0000000000000000 __cxa_finalize@GLIBC_2.2.5 + 0
Relocation section '.rela.plt' at offset 0x4d8 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000200fd0 000200000007 R_X86_64_JUMP_SLO 0000000000000000 printf@GLIBC_2.2.5 + 0
The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.
Symbol table '.dynsym' contains 7 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
2: 0000000000000000 0 FUNC GLOBAL DEFAULT UND printf@GLIBC_2.2.5 (2)
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_main@GLIBC_2.2.5 (2)
4: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
5: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMCloneTable
6: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.2.5 (2)
Symbol table '.symtab' contains 63 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000238 0 SECTION LOCAL DEFAULT 1
2: 0000000000000254 0 SECTION LOCAL DEFAULT 2
3: 0000000000000274 0 SECTION LOCAL DEFAULT 3
4: 0000000000000298 0 SECTION LOCAL DEFAULT 4
5: 00000000000002b8 0 SECTION LOCAL DEFAULT 5
6: 0000000000000360 0 SECTION LOCAL DEFAULT 6
7: 00000000000003e4 0 SECTION LOCAL DEFAULT 7
8: 00000000000003f8 0 SECTION LOCAL DEFAULT 8
9: 0000000000000418 0 SECTION LOCAL DEFAULT 9
10: 00000000000004d8 0 SECTION LOCAL DEFAULT 10
11: 00000000000004f0 0 SECTION LOCAL DEFAULT 11
12: 0000000000000510 0 SECTION LOCAL DEFAULT 12
13: 0000000000000530 0 SECTION LOCAL DEFAULT 13
14: 0000000000000540 0 SECTION LOCAL DEFAULT 14
15: 00000000000006f4 0 SECTION LOCAL DEFAULT 15
16: 0000000000000700 0 SECTION LOCAL DEFAULT 16
17: 0000000000000714 0 SECTION LOCAL DEFAULT 17
18: 0000000000000750 0 SECTION LOCAL DEFAULT 18
19: 0000000000200db8 0 SECTION LOCAL DEFAULT 19
20: 0000000000200dc0 0 SECTION LOCAL DEFAULT 20
21: 0000000000200dc8 0 SECTION LOCAL DEFAULT 21
22: 0000000000200fb8 0 SECTION LOCAL DEFAULT 22
23: 0000000000201000 0 SECTION LOCAL DEFAULT 23
24: 0000000000201010 0 SECTION LOCAL DEFAULT 24
25: 0000000000000000 0 SECTION LOCAL DEFAULT 25
26: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
27: 0000000000000570 0 FUNC LOCAL DEFAULT 14 deregister_tm_clones
28: 00000000000005b0 0 FUNC LOCAL DEFAULT 14 register_tm_clones
29: 0000000000000600 0 FUNC LOCAL DEFAULT 14 __do_global_dtors_aux
30: 0000000000201010 1 OBJECT LOCAL DEFAULT 24 completed.7698
31: 0000000000200dc0 0 OBJECT LOCAL DEFAULT 20 __do_global_dtors_aux_fin
32: 0000000000000640 0 FUNC LOCAL DEFAULT 14 frame_dummy
33: 0000000000200db8 0 OBJECT LOCAL DEFAULT 19 __frame_dummy_init_array_
34: 0000000000000000 0 FILE LOCAL DEFAULT ABS study.c
35: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
36: 0000000000000854 0 OBJECT LOCAL DEFAULT 18 __FRAME_END__
37: 0000000000000000 0 FILE LOCAL DEFAULT ABS
38: 0000000000200dc0 0 NOTYPE LOCAL DEFAULT 19 __init_array_end
39: 0000000000200dc8 0 OBJECT LOCAL DEFAULT 21 _DYNAMIC
40: 0000000000200db8 0 NOTYPE LOCAL DEFAULT 19 __init_array_start
41: 0000000000000714 0 NOTYPE LOCAL DEFAULT 17 __GNU_EH_FRAME_HDR
42: 0000000000200fb8 0 OBJECT LOCAL DEFAULT 22 _GLOBAL_OFFSET_TABLE_
43: 00000000000006f0 2 FUNC GLOBAL DEFAULT 14 __libc_csu_fini
44: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
45: 0000000000201000 0 NOTYPE WEAK DEFAULT 23 data_start
46: 0000000000201010 0 NOTYPE GLOBAL DEFAULT 23 _edata
47: 00000000000006f4 0 FUNC GLOBAL DEFAULT 15 _fini
48: 0000000000000000 0 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.2.5
49: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_main@@GLIBC_
50: 0000000000201000 0 NOTYPE GLOBAL DEFAULT 23 __data_start
51: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
52: 0000000000201008 0 OBJECT GLOBAL HIDDEN 23 __dso_handle
53: 0000000000000700 4 OBJECT GLOBAL DEFAULT 16 _IO_stdin_used
54: 0000000000000680 101 FUNC GLOBAL DEFAULT 14 __libc_csu_init
55: 0000000000201018 0 NOTYPE GLOBAL DEFAULT 24 _end
56: 0000000000000540 43 FUNC GLOBAL DEFAULT 14 _start
57: 0000000000201010 0 NOTYPE GLOBAL DEFAULT 24 __bss_start
58: 000000000000064a 44 FUNC GLOBAL DEFAULT 14 main
59: 0000000000201010 0 OBJECT GLOBAL HIDDEN 23 __TMC_END__
60: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMCloneTable
61: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@@GLIBC_2.2
62: 00000000000004f0 0 FUNC GLOBAL DEFAULT 11 _init
Version symbols section '.gnu.version' contains 7 entries:
Addr: 00000000000003e4 Offset: 0x0003e4 Link: 5 (.dynsym)
000: 0 (*local*) 0 (*local*) 2 (GLIBC_2.2.5) 2 (GLIBC_2.2.5)
004: 0 (*local*) 0 (*local*) 2 (GLIBC_2.2.5)
Version needs section '.gnu.version_r' contains 1 entry:
Addr: 0x00000000000003f8 Offset: 0x0003f8 Link: 6 (.dynstr)
000000: Version: 1 File: libc.so.6 Cnt: 1
0x0010: Name: GLIBC_2.2.5 Flags: none Version: 2
Displaying notes found in: .note.ABI-tag
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 3.2.0
Displaying notes found in: .note.gnu.build-id
Owner Data size Description
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: c095e6656212ec526608978b52cbe1108b59d0ef
如果对 readelf -a 的输出进行比较，您会发现 "Build ID" 字段发生了变化：
269c269
< Build ID: 5cee13af3549a15ae34a9a55fd49ec5e7d1f91ea
---
> Build ID: 0a2669d15ff23ae536f7496c1e0aa57051d29111
如果你对两个可执行文件的十六进制数据进行比较，你会看到：
48,49c48,49
< 000002f0: 474E5500 5CEE13AF 3549A15A E34A9A55 GNU.\...5I.Z.J.U
< 00000300: FD49EC5E 7D1F91EA 01000000 01000000 .I.^}...........
---
> 000002f0: 474E5500 0A2669D1 5FF23AE5 36F7496C GNU..&i._.:.6.Il
> 00000300: 1E0AA570 51D29111 01000000 01000000 ...pQ...........
276c276
< 00001130: FC010000 008B45FC 89C6BF10 204000B8 ......E..... @..
---
> 00001130: FC020000 008B45FC 89C6BF10 204000B8 ......E..... @..
第一个差异是构建 ID 的十六进制。
第二个是数据。就是NUMBER_1是1然后是2
的区别
我想我会说：别担心，开心点...
以下代码说明：
#include <stdio.h>
#define NUMBER_1 1
int main(void)
{
int a;
a = NUMBER_1;
printf("Output: %d\r\n", a);
return 0;
}
将 define 更改为 2 会导致 20 个字节完全更改。我在 Ubuntu 18.04 版下使用 gcc 7.5.0 版。我怀疑这是某种摘要，但如果是这样，为什么它在那里以及何时检查。使用十六进制编辑器编辑这些字节不会阻止代码执行。
来自readelf -a的输出：
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: DYN (Shared object file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x540
Start of program headers: 64 (bytes into file)
Start of section headers: 6448 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 9
Size of section headers: 64 (bytes)
Number of section headers: 29
Section header string table index: 28
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .interp PROGBITS 0000000000000238 00000238
000000000000001c 0000000000000000 A 0 0 1
[ 2] .note.ABI-tag NOTE 0000000000000254 00000254
0000000000000020 0000000000000000 A 0 0 4
[ 3] .note.gnu.build-i NOTE 0000000000000274 00000274
0000000000000024 0000000000000000 A 0 0 4
[ 4] .gnu.hash GNU_HASH 0000000000000298 00000298
000000000000001c 0000000000000000 A 5 0 8
[ 5] .dynsym DYNSYM 00000000000002b8 000002b8
00000000000000a8 0000000000000018 A 6 1 8
[ 6] .dynstr STRTAB 0000000000000360 00000360
0000000000000084 0000000000000000 A 0 0 1
[ 7] .gnu.version VERSYM 00000000000003e4 000003e4
000000000000000e 0000000000000002 A 5 0 2
[ 8] .gnu.version_r VERNEED 00000000000003f8 000003f8
0000000000000020 0000000000000000 A 6 1 8
[ 9] .rela.dyn RELA 0000000000000418 00000418
00000000000000c0 0000000000000018 A 5 0 8
[10] .rela.plt RELA 00000000000004d8 000004d8
0000000000000018 0000000000000018 AI 5 22 8
[11] .init PROGBITS 00000000000004f0 000004f0
0000000000000017 0000000000000000 AX 0 0 4
[12] .plt PROGBITS 0000000000000510 00000510
0000000000000020 0000000000000010 AX 0 0 16
[13] .plt.got PROGBITS 0000000000000530 00000530
0000000000000008 0000000000000008 AX 0 0 8
[14] .text PROGBITS 0000000000000540 00000540
00000000000001b2 0000000000000000 AX 0 0 16
[15] .fini PROGBITS 00000000000006f4 000006f4
0000000000000009 0000000000000000 AX 0 0 4
[16] .rodata PROGBITS 0000000000000700 00000700
0000000000000011 0000000000000000 A 0 0 4
[17] .eh_frame_hdr PROGBITS 0000000000000714 00000714
000000000000003c 0000000000000000 A 0 0 4
[18] .eh_frame PROGBITS 0000000000000750 00000750
0000000000000108 0000000000000000 A 0 0 8
[19] .init_array INIT_ARRAY 0000000000200db8 00000db8
0000000000000008 0000000000000008 WA 0 0 8
[20] .fini_array FINI_ARRAY 0000000000200dc0 00000dc0
0000000000000008 0000000000000008 WA 0 0 8
[21] .dynamic DYNAMIC 0000000000200dc8 00000dc8
00000000000001f0 0000000000000010 WA 6 0 8
[22] .got PROGBITS 0000000000200fb8 00000fb8
0000000000000048 0000000000000008 WA 0 0 8
[23] .data PROGBITS 0000000000201000 00001000
0000000000000010 0000000000000000 WA 0 0 8
[24] .bss NOBITS 0000000000201010 00001010
0000000000000008 0000000000000000 WA 0 0 1
[25] .comment PROGBITS 0000000000000000 00001010
0000000000000029 0000000000000001 MS 0 0 1
[26] .symtab SYMTAB 0000000000000000 00001040
00000000000005e8 0000000000000018 27 43 8
[27] .strtab STRTAB 0000000000000000 00001628
0000000000000205 0000000000000000 0 0 1
[28] .shstrtab STRTAB 0000000000000000 0000182d
00000000000000fe 0000000000000000 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
l (large), p (processor specific)
There are no section groups in this file.
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
PHDR 0x0000000000000040 0x0000000000000040 0x0000000000000040
0x00000000000001f8 0x00000000000001f8 R 0x8
INTERP 0x0000000000000238 0x0000000000000238 0x0000000000000238
0x000000000000001c 0x000000000000001c R 0x1
[Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000858 0x0000000000000858 R E 0x200000
LOAD 0x0000000000000db8 0x0000000000200db8 0x0000000000200db8
0x0000000000000258 0x0000000000000260 RW 0x200000
DYNAMIC 0x0000000000000dc8 0x0000000000200dc8 0x0000000000200dc8
0x00000000000001f0 0x00000000000001f0 RW 0x8
NOTE 0x0000000000000254 0x0000000000000254 0x0000000000000254
0x0000000000000044 0x0000000000000044 R 0x4
GNU_EH_FRAME 0x0000000000000714 0x0000000000000714 0x0000000000000714
0x000000000000003c 0x000000000000003c R 0x4
GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x0000000000000000 0x0000000000000000 RW 0x10
GNU_RELRO 0x0000000000000db8 0x0000000000200db8 0x0000000000200db8
0x0000000000000248 0x0000000000000248 R 0x1
Section to Segment mapping:
Segment Sections...
00
01 .interp
02 .interp .note.ABI-tag .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame
03 .init_array .fini_array .dynamic .got .data .bss
04 .dynamic
05 .note.ABI-tag .note.gnu.build-id
06 .eh_frame_hdr
07
08 .init_array .fini_array .dynamic .got
Dynamic section at offset 0xdc8 contains 27 entries:
Tag Type Name/Value
0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
0x000000000000000c (INIT) 0x4f0
0x000000000000000d (FINI) 0x6f4
0x0000000000000019 (INIT_ARRAY) 0x200db8
0x000000000000001b (INIT_ARRAYSZ) 8 (bytes)
0x000000000000001a (FINI_ARRAY) 0x200dc0
0x000000000000001c (FINI_ARRAYSZ) 8 (bytes)
0x000000006ffffef5 (GNU_HASH) 0x298
0x0000000000000005 (STRTAB) 0x360
0x0000000000000006 (SYMTAB) 0x2b8
0x000000000000000a (STRSZ) 132 (bytes)
0x000000000000000b (SYMENT) 24 (bytes)
0x0000000000000015 (DEBUG) 0x0
0x0000000000000003 (PLTGOT) 0x200fb8
0x0000000000000002 (PLTRELSZ) 24 (bytes)
0x0000000000000014 (PLTREL) RELA
0x0000000000000017 (JMPREL) 0x4d8
0x0000000000000007 (RELA) 0x418
0x0000000000000008 (RELASZ) 192 (bytes)
0x0000000000000009 (RELAENT) 24 (bytes)
0x000000000000001e (FLAGS) BIND_NOW
0x000000006ffffffb (FLAGS_1) Flags: NOW PIE
0x000000006ffffffe (VERNEED) 0x3f8
0x000000006fffffff (VERNEEDNUM) 1
0x000000006ffffff0 (VERSYM) 0x3e4
0x000000006ffffff9 (RELACOUNT) 3
0x0000000000000000 (NULL) 0x0
Relocation section '.rela.dyn' at offset 0x418 contains 8 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000200db8 000000000008 R_X86_64_RELATIVE 640
000000200dc0 000000000008 R_X86_64_RELATIVE 600
000000201008 000000000008 R_X86_64_RELATIVE 201008
000000200fd8 000100000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_deregisterTMClone + 0
000000200fe0 000300000006 R_X86_64_GLOB_DAT 0000000000000000 __libc_start_main@GLIBC_2.2.5 + 0
000000200fe8 000400000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ + 0
000000200ff0 000500000006 R_X86_64_GLOB_DAT 0000000000000000 _ITM_registerTMCloneTa + 0
000000200ff8 000600000006 R_X86_64_GLOB_DAT 0000000000000000 __cxa_finalize@GLIBC_2.2.5 + 0
Relocation section '.rela.plt' at offset 0x4d8 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000200fd0 000200000007 R_X86_64_JUMP_SLO 0000000000000000 printf@GLIBC_2.2.5 + 0
The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.
Symbol table '.dynsym' contains 7 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
2: 0000000000000000 0 FUNC GLOBAL DEFAULT UND printf@GLIBC_2.2.5 (2)
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_main@GLIBC_2.2.5 (2)
4: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
5: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMCloneTable
6: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.2.5 (2)
Symbol table '.symtab' contains 63 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000238 0 SECTION LOCAL DEFAULT 1
2: 0000000000000254 0 SECTION LOCAL DEFAULT 2
3: 0000000000000274 0 SECTION LOCAL DEFAULT 3
4: 0000000000000298 0 SECTION LOCAL DEFAULT 4
5: 00000000000002b8 0 SECTION LOCAL DEFAULT 5
6: 0000000000000360 0 SECTION LOCAL DEFAULT 6
7: 00000000000003e4 0 SECTION LOCAL DEFAULT 7
8: 00000000000003f8 0 SECTION LOCAL DEFAULT 8
9: 0000000000000418 0 SECTION LOCAL DEFAULT 9
10: 00000000000004d8 0 SECTION LOCAL DEFAULT 10
11: 00000000000004f0 0 SECTION LOCAL DEFAULT 11
12: 0000000000000510 0 SECTION LOCAL DEFAULT 12
13: 0000000000000530 0 SECTION LOCAL DEFAULT 13
14: 0000000000000540 0 SECTION LOCAL DEFAULT 14
15: 00000000000006f4 0 SECTION LOCAL DEFAULT 15
16: 0000000000000700 0 SECTION LOCAL DEFAULT 16
17: 0000000000000714 0 SECTION LOCAL DEFAULT 17
18: 0000000000000750 0 SECTION LOCAL DEFAULT 18
19: 0000000000200db8 0 SECTION LOCAL DEFAULT 19
20: 0000000000200dc0 0 SECTION LOCAL DEFAULT 20
21: 0000000000200dc8 0 SECTION LOCAL DEFAULT 21
22: 0000000000200fb8 0 SECTION LOCAL DEFAULT 22
23: 0000000000201000 0 SECTION LOCAL DEFAULT 23
24: 0000000000201010 0 SECTION LOCAL DEFAULT 24
25: 0000000000000000 0 SECTION LOCAL DEFAULT 25
26: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
27: 0000000000000570 0 FUNC LOCAL DEFAULT 14 deregister_tm_clones
28: 00000000000005b0 0 FUNC LOCAL DEFAULT 14 register_tm_clones
29: 0000000000000600 0 FUNC LOCAL DEFAULT 14 __do_global_dtors_aux
30: 0000000000201010 1 OBJECT LOCAL DEFAULT 24 completed.7698
31: 0000000000200dc0 0 OBJECT LOCAL DEFAULT 20 __do_global_dtors_aux_fin
32: 0000000000000640 0 FUNC LOCAL DEFAULT 14 frame_dummy
33: 0000000000200db8 0 OBJECT LOCAL DEFAULT 19 __frame_dummy_init_array_
34: 0000000000000000 0 FILE LOCAL DEFAULT ABS study.c
35: 0000000000000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
36: 0000000000000854 0 OBJECT LOCAL DEFAULT 18 __FRAME_END__
37: 0000000000000000 0 FILE LOCAL DEFAULT ABS
38: 0000000000200dc0 0 NOTYPE LOCAL DEFAULT 19 __init_array_end
39: 0000000000200dc8 0 OBJECT LOCAL DEFAULT 21 _DYNAMIC
40: 0000000000200db8 0 NOTYPE LOCAL DEFAULT 19 __init_array_start
41: 0000000000000714 0 NOTYPE LOCAL DEFAULT 17 __GNU_EH_FRAME_HDR
42: 0000000000200fb8 0 OBJECT LOCAL DEFAULT 22 _GLOBAL_OFFSET_TABLE_
43: 00000000000006f0 2 FUNC GLOBAL DEFAULT 14 __libc_csu_fini
44: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
45: 0000000000201000 0 NOTYPE WEAK DEFAULT 23 data_start
46: 0000000000201010 0 NOTYPE GLOBAL DEFAULT 23 _edata
47: 00000000000006f4 0 FUNC GLOBAL DEFAULT 15 _fini
48: 0000000000000000 0 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.2.5
49: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __libc_start_main@@GLIBC_
50: 0000000000201000 0 NOTYPE GLOBAL DEFAULT 23 __data_start
51: 0000000000000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
52: 0000000000201008 0 OBJECT GLOBAL HIDDEN 23 __dso_handle
53: 0000000000000700 4 OBJECT GLOBAL DEFAULT 16 _IO_stdin_used
54: 0000000000000680 101 FUNC GLOBAL DEFAULT 14 __libc_csu_init
55: 0000000000201018 0 NOTYPE GLOBAL DEFAULT 24 _end
56: 0000000000000540 43 FUNC GLOBAL DEFAULT 14 _start
57: 0000000000201010 0 NOTYPE GLOBAL DEFAULT 24 __bss_start
58: 000000000000064a 44 FUNC GLOBAL DEFAULT 14 main
59: 0000000000201010 0 OBJECT GLOBAL HIDDEN 23 __TMC_END__
60: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_registerTMCloneTable
61: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@@GLIBC_2.2
62: 00000000000004f0 0 FUNC GLOBAL DEFAULT 11 _init
Version symbols section '.gnu.version' contains 7 entries:
Addr: 00000000000003e4 Offset: 0x0003e4 Link: 5 (.dynsym)
000: 0 (*local*) 0 (*local*) 2 (GLIBC_2.2.5) 2 (GLIBC_2.2.5)
004: 0 (*local*) 0 (*local*) 2 (GLIBC_2.2.5)
Version needs section '.gnu.version_r' contains 1 entry:
Addr: 0x00000000000003f8 Offset: 0x0003f8 Link: 6 (.dynstr)
000000: Version: 1 File: libc.so.6 Cnt: 1
0x0010: Name: GLIBC_2.2.5 Flags: none Version: 2
Displaying notes found in: .note.ABI-tag
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 3.2.0
Displaying notes found in: .note.gnu.build-id
Owner Data size Description
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: c095e6656212ec526608978b52cbe1108b59d0ef
如果对 readelf -a 的输出进行比较，您会发现 "Build ID" 字段发生了变化：
269c269
< Build ID: 5cee13af3549a15ae34a9a55fd49ec5e7d1f91ea
---
> Build ID: 0a2669d15ff23ae536f7496c1e0aa57051d29111
如果你对两个可执行文件的十六进制数据进行比较，你会看到：
48,49c48,49
< 000002f0: 474E5500 5CEE13AF 3549A15A E34A9A55 GNU.\...5I.Z.J.U
< 00000300: FD49EC5E 7D1F91EA 01000000 01000000 .I.^}...........
---
> 000002f0: 474E5500 0A2669D1 5FF23AE5 36F7496C GNU..&i._.:.6.Il
> 00000300: 1E0AA570 51D29111 01000000 01000000 ...pQ...........
276c276
< 00001130: FC010000 008B45FC 89C6BF10 204000B8 ......E..... @..
---
> 00001130: FC020000 008B45FC 89C6BF10 204000B8 ......E..... @..
第一个差异是构建 ID 的十六进制。
第二个是数据。就是NUMBER_1是1然后是2
我想我会说：别担心，开心点...