在调试libdrm时，查看libdrm.so依赖哪些库，用到了readelf命令，简单记录下该命令的用法。
1、显示ELF文件头信息
root@ubuntu:/home/run/code# readelf -h libdrm.so.2.4.0
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: AArch64
Version: 0x1
Entry point address: 0x3cb0
Start of program headers: 64 (bytes into file)
Start of section headers: 58304 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 6
Size of section headers: 64 (bytes)
Number of section headers: 25
Section header string table index: 24
2、显示动态段信息
root@ubuntu:/home/run/code# readelf -d libdrm.so.2.4.0
Dynamic section at offset 0xddb8 contains 27 entries:
Tag Type Name/Value
0x0000000000000001 (NEEDED) Shared library: [libm.so.6]
0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
0x0000000000000001 (NEEDED) Shared library: [ld-linux-aarch64.so.1]
0x000000000000000e (SONAME) Library soname: [libdrm.so.2]
0x000000000000000c (INIT) 0x3720
0x000000000000000d (FINI) 0xbc34
0x0000000000000019 (INIT_ARRAY) 0x1dda0
0x000000000000001b (INIT_ARRAYSZ) 8 (bytes)
0x000000000000001a (FINI_ARRAY) 0x1dda8
0x000000000000001c (FINI_ARRAYSZ) 8 (bytes)
0x000000006ffffef5 (GNU_HASH) 0x1b8
0x0000000000000005 (STRTAB) 0x1e08
0x0000000000000006 (SYMTAB) 0x728
0x000000000000000a (STRSZ) 3554 (bytes)
0x000000000000000b (SYMENT) 24 (bytes)
0x0000000000000003 (PLTGOT) 0x1dfe8
0x0000000000000002 (PLTRELSZ) 2040 (bytes)
0x0000000000000014 (PLTREL) RELA
0x0000000000000017 (JMPREL) 0x2f28
0x0000000000000007 (RELA) 0x2e38
0x0000000000000008 (RELASZ) 240 (bytes)
0x0000000000000009 (RELAENT) 24 (bytes)
0x000000006ffffffe (VERNEED) 0x2dd8
0x000000006fffffff (VERNEEDNUM) 3
0x000000006ffffff0 (VERSYM) 0x2bea
0x000000006ffffff9 (RELACOUNT) 3
0x0000000000000000 (NULL) 0x0
该命令可查看该动态库依赖哪些库，方便动态库调试时，更新所需的动态库。
readelf可查看：可执行文件，动态库（.so）和静态库（.a）。
3.显示段表信息
root@ubuntu:/home/run/code# readelf -S libdrm.so.2.4.0
There are 25 section headers, starting at offset 0xe3c0:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .note.gnu.build-i NOTE 0000000000000190 00000190
0000000000000024 0000000000000000 A 0 0 4
[ 2] .gnu.hash GNU_HASH 00000000000001b8 000001b8
000000000000056c 0000000000000000 A 3 0 8
[ 3] .dynsym DYNSYM 0000000000000728 00000728
00000000000016e0 0000000000000018 A 4 3 8
[ 4] .dynstr STRTAB 0000000000001e08 00001e08
0000000000000de2 0000000000000000 A 0 0 1
[ 5] .gnu.version VERSYM 0000000000002bea 00002bea
00000000000001e8 0000000000000002 A 3 0 2
[ 6] .gnu.version_r VERNEED 0000000000002dd8 00002dd8
0000000000000060 0000000000000000 A 4 3 8
[ 7] .rela.dyn RELA 0000000000002e38 00002e38
00000000000000f0 0000000000000018 A 3 0 8
[ 8] .rela.plt RELA 0000000000002f28 00002f28
00000000000007f8 0000000000000018 AI 3 20 8
[ 9] .init PROGBITS 0000000000003720 00003720
0000000000000014 0000000000000000 AX 0 0 4
[10] .plt PROGBITS 0000000000003740 00003740
0000000000000570 0000000000000010 AX 0 0 16
[11] .text PROGBITS 0000000000003cb0 00003cb0
0000000000007f84 0000000000000000 AX 0 0 8
[12] .fini PROGBITS 000000000000bc34 0000bc34
0000000000000010 0000000000000000 AX 0 0 4
[13] .rodata PROGBITS 000000000000bc48 0000bc48
0000000000001658 0000000000000000 A 0 0 8
[14] .eh_frame PROGBITS 000000000000d2a0 0000d2a0
0000000000000004 0000000000000000 A 0 0 4
[15] .init_array INIT_ARRAY 000000000001dda0 0000dda0
0000000000000008 0000000000000008 WA 0 0 8
[16] .fini_array FINI_ARRAY 000000000001dda8 0000dda8
0000000000000008 0000000000000008 WA 0 0 8
[17] .jcr PROGBITS 000000000001ddb0 0000ddb0
0000000000000008 0000000000000000 WA 0 0 8
[18] .dynamic DYNAMIC 000000000001ddb8 0000ddb8
00000000000001f0 0000000000000010 WA 4 0 8
[19] .got PROGBITS 000000000001dfa8 0000dfa8
0000000000000040 0000000000000008 WA 0 0 8
[20] .got.plt PROGBITS 000000000001dfe8 0000dfe8
00000000000002c0 0000000000000008 WA 0 0 8
[21] .data PROGBITS 000000000001e2a8 0000e2a8
0000000000000008 0000000000000000 WA 0 0 8
[22] .bss NOBITS 000000000001e2b0 0000e2b0
00000000000009b8 0000000000000000 WA 0 0 8
[23] .gnu_debuglink PROGBITS 0000000000000000 0000e2b0
0000000000000034 0000000000000000 0 0 1
[24] .shstrtab STRTAB 0000000000000000 0000e2e4
00000000000000da 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),
p (processor specific)
4）显示符号表信息
root@ubuntu:/home/run/code# readelf -s libdrm.so.2.4.0
Symbol table '.dynsym' contains 244 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000003720 0 SECTION LOCAL DEFAULT 9
2: 000000000001ddb0 0 SECTION LOCAL DEFAULT 17
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND memcpy@GLIBC_2.17 (2)
4: 0000000000000000 0 FUNC GLOBAL DEFAULT UND memmove@GLIBC_2.17 (2)
5: 0000000000000000 0 FUNC GLOBAL DEFAULT UND strlen@GLIBC_2.17 (2)
6: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __sprintf_chk@GLIBC_2.17 (2)
7: 0000000000000000 0 NOTYPE WEAK DEFAULT UND _ITM_deregisterTMCloneTab
8: 0000000000000000 0 FUNC GLOBAL DEFAULT UND readlink@GLIBC_2.17 (2)
9: 0000000000000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.17 (2)
10: 0000000000000000 0 FUNC GLOBAL DEFAULT UND opendir@GLIBC_2.17 (2)
11: 0000000000000000 0 FUNC GLOBAL DEFAULT UND clock_gettime@GLIBC_2.17 (2)
12: 0000000000000000 0 OBJECT GLOBAL DEFAULT UND stderr@GLIBC_2.17 (2)
13: 0000000000000000 0 FUNC GLOBAL DEFAULT UND qsort@GLIBC_2.17 (2)
...
符号表保存程序定义或使用的所有全局变量和函数。
5）显示所有信息
等同于-h -l -S -s -r -d -V -A -I。
root@ubuntu:/home/run/code# readelf -a libdrm.so.2.4.0
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: AArch64
Version: 0x1
Entry point address: 0x3cb0
Start of program headers: 64 (bytes into file)
Start of section headers: 58304 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 6
Size of section headers: 64 (bytes)
Number of section headers: 25
Section header string table index: 24
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .note.gnu.build-i NOTE 0000000000000190 00000190
0000000000000024 0000000000000000 A 0 0 4
[ 2] .gnu.hash GNU_HASH 00000000000001b8 000001b8
000000000000056c 0000000000000000 A 3 0 8
[ 3] .dynsym DYNSYM 0000000000000728 00000728
00000000000016e0 0000000000000018 A 4 3 8
[ 4] .dynstr STRTAB 0000000000001e08 00001e08
0000000000000de2 0000000000000000 A 0 0 1
[ 5] .gnu.version VERSYM 0000000000002bea 00002bea
readelf命令可以使用readelf -h获取其它参数的用法。
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