服务器评测
使用objdump 和readelf 两个命令，我们可以看到elf的各个节段的 信息还有 运行时需要那些动态链接库，elf中的汇编代码等等。 我就是想用来查看 这个elf运行需要哪些 *.so 文件
#include<stdio.h>
int test()
{
return 0;
}
int main(void)
{
int i;
int j =0;
//printf (“sizeof (int)=%d\n”,sizeof (int));
if ( i = j )
printf (“\ntrue\n”,i);
return 0;
}
gcc main.c 编译后，
www.lnuxidc.com@linuxidc:~/桌面$ readelf -a a.out
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: 0x8048310
Start of program headers: 52 (bytes into file)
Start of section headers: 5996 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 8
Size of section headers: 40 (bytes)
Number of section headers: 36
Section header string table index: 33
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 08048134 000134 000013 00 A 0 0 1
[ 2] .note.ABI-tag NOTE 08048148 000148 000020 00 A 0 0 4
[ 3] .hash HASH 08048168 000168 000028 04 A 5 0 4
[ 4] .gnu.hash GNU_HASH 08048190 000190 000020 04 A 5 0 4
[ 5] .dynsym DYNSYM 080481b0 0001b0 000050 10 A 6 1 4
[ 6] .dynstr STRTAB 08048200 000200 00004c 00 A 0 0 1
[ 7] .gnu.version VERSYM 0804824c 00024c 00000a 02 A 5 0 2
[ 8] .gnu.version_r VERNEED 08048258 000258 000020 00 A 6 1 4
[ 9] .rel.dyn REL 08048278 000278 000008 08 A 5 0 4
[10] .rel.plt REL 08048280 000280 000018 08 A 5 12 4
[11] .init PROGBITS 08048298 000298 000030 00 AX 0 0 4
[12] .plt PROGBITS 080482c8 0002c8 000040 04 AX 0 0 4
[13] .text PROGBITS 08048310 000310 0001ac 00 AX 0 0 16
[14] .fini PROGBITS 080484bc 0004bc 00001c 00 AX 0 0 4
[15] .rodata PROGBITS 080484d8 0004d8 00000f 00 A 0 0 4
[16] .eh_frame PROGBITS 080484e8 0004e8 000004 00 A 0 0 4
[17] .ctors PROGBITS 08049f0c 000f0c 000008 00 WA 0 0 4
[18] .dtors PROGBITS 08049f14 000f14 000008 00 WA 0 0 4
[19] .jcr PROGBITS 08049f1c 000f1c 000004 00 WA 0 0 4
[20] .dynamic DYNAMIC 08049f20 000f20 0000d0 08 WA 6 0 4
[21] .got PROGBITS 08049ff0 000ff0 000004 04 WA 0 0 4
[22] .got.plt PROGBITS 08049ff4 000ff4 000018 04 WA 0 0 4
[23] .data PROGBITS 0804a00c 00100c 000008 00 WA 0 0 4
[24] .bss NOBITS 0804a014 001014 000008 00 WA 0 0 4
[25] .comment PROGBITS 00000000 001014 0000fc 00 0 0 1
[26] .debug_aranges PROGBITS 00000000 001110 000070 00 0 0 8
[27] .debug_pubnames PROGBITS 00000000 001180 000025 00 0 0 1
[28] .debug_info PROGBITS 00000000 0011a5 0001b5 00 0 0 1
[29] .debug_abbrev PROGBITS 00000000 00135a 000083 00 0 0 1
[30] .debug_line PROGBITS 00000000 0013dd 000180 00 0 0 1
[31] .debug_str PROGBITS 00000000 00155d 00008e 01 MS 0 0 1
[32] .debug_ranges PROGBITS 00000000 0015f0 000040 00 0 0 8
[33] .shstrtab STRTAB 00000000 001630 000139 00 0 0 1
[34] .symtab SYMTAB 00000000 001d0c 0004b0 10 35 54 4
[35] .strtab STRTAB 00000000 0021bc 000213 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 section groups in this file.
Dynamic section at offset 0xf20 contains 21 entries: 用 readelf -d 命令可以单独查看这个Dynamic section
Tag Type Name/Value
0x00000001 (NEEDED) Shared library: [libc.so.6] 需要的动态链接库
0x0000000c (INIT) 0x8048298
0x0000000d (FINI) 0x80484bc
0x00000004 (HASH) 0x8048168
0x6ffffef5 (GNU_HASH) 0x8048190
0x00000005 (STRTAB) 0x8048200
0x00000006 (SYMTAB) 0x80481b0
0x0000000a (STRSZ) 76 (bytes)
0x0000000b (SYMENT) 16 (bytes)
0x00000015 (DEBUG) 0x0
0x00000003 (PLTGOT) 0x8049ff4
0x00000002 (PLTRELSZ) 24 (bytes)
0x00000014 (PLTREL) REL
0x00000017 (JMPREL) 0x8048280
0x00000011 (REL) 0x8048278
0x00000012 (RELSZ) 8 (bytes)
0x00000013 (RELENT) 8 (bytes)
0x6ffffffe (VERNEED) 0x8048258
0x6fffffff (VERNEEDNUM) 1
0x6ffffff0 (VERSYM) 0x804824c
0x00000000 (NULL) 0x0
Relocation section ‘.rel.dyn’ at offset 0x278 contains 1 entries:
Offset Info Type Sym.Value Sym. Name
08049ff0 00000106 R_386_GLOB_DAT 00000000 __gmon_start__
Relocation section ‘.rel.plt’ at offset 0x280 contains 3 entries:
Offset Info Type Sym.Value Sym. Name
0804a000 00000107 R_386_JUMP_SLOT 00000000 __gmon_start__
0804a004 00000207 R_386_JUMP_SLOT 00000000 __libc_start_main
0804a008 00000307 R_386_JUMP_SLOT 00000000 printf
There are no unwind sections in this file.
Symbol table ‘.dynsym’ contains 5 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
2: 00000000 0 FUNC GLOBAL DEFAULT UND __libc_start_main@GLIBC_2.0 (2)
3: 00000000 0 FUNC GLOBAL DEFAULT UND printf@GLIBC_2.0 (2)
4: 080484dc 4 OBJECT GLOBAL DEFAULT 15 _IO_stdin_used
Symbol table ‘.symtab’ contains 75 entries:
Num: Value Size Type Bind Vis Ndx Name
。。。。。。
67: 00000000 0 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.0
68: 0804a014 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
69: 080483c4 10 FUNC GLOBAL DEFAULT 13 test
70: 0804a01c 0 NOTYPE GLOBAL DEFAULT ABS _end
71: 0804a014 0 NOTYPE GLOBAL DEFAULT ABS _edata
72: 0804848a 0 FUNC GLOBAL HIDDEN 13 __i686.get_pc_thunk.bx
73: 080483ce 69 FUNC GLOBAL DEFAULT 13 main
74: 08048298 0 FUNC GLOBAL DEFAULT 11 _init
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－
www.lnuxidc.com@linuxidc:~/桌面$ objdump -d a.out 反汇编
a.out: file format elf32-i386
…
080482f8 <printf@plt>:
80482f8: ff 25 08 a0 04 08 jmp *0x804a008
80482fe: 68 10 00 00 00 push $0x10
8048303: e9 c0 ff ff ff jmp 80482c8 <_init+0x30>
Disassembly of section .text:
080483ce <main>:
80483ce: 8d 4c 24 04 lea 0x4(%esp),%ecx
80483d2: 83 e4 f0 and $0xfffffff0,%esp
80483d5: ff 71 fc pushl -0x4(%ecx)
80483d8: 55 push %ebp
80483d9: 89 e5 mov %esp,%ebp
80483db: 51 push %ecx
80483dc: 83 ec 24 sub $0x24,%esp
80483df: c7 45 f4 00 00 00 00 movl $0x0,-0xc(%ebp)
80483e6: 8b 45 f4 mov -0xc(%ebp),%eax
80483e9: 89 45 f8 mov %eax,-0x8(%ebp)
80483ec: 83 7d f8 00 cmpl $0x0,-0x8(%ebp)
80483f0: 74 13 je 8048405 <main+0x37>
80483f2: 8b 45 f8 mov -0x8(%ebp),%eax
80483f5: 89 44 24 04 mov %eax,0x4(%esp)
80483f9: c7 04 24 e0 84 04 08 movl $0x80484e0,(%esp)
8048400: e8 f3 fe ff ff call 80482f8 <printf@plt>
8048405: b8 00 00 00 00 mov $0x0,%eax
804840a: 83 c4 24 add $0x24,%esp
804840d: 59 pop %ecx
804840e: 5d pop %ebp
804840f: 8d 61 fc lea -0x4(%ecx),%esp
8048412: c3 ret
8048413: 90 nop
8048414: 90 nop
8048415: 90 nop
8048416: 90 nop
8048417: 90 nop
8048418: 90 nop
8048419: 90 nop
804841a: 90 nop
804841b: 90 nop
804841c: 90 nop
804841d: 90 nop
804841e: 90 nop
804841f: 90 nop
======================================================
关于ELF格式的链接 可以看
1. Intel平台下Linux中 ELF文件动态链接的加载、解析及实例分析）: 加载
IBM developerWorks 中国网站 王瑞川 (jeppeterone@163.com)
2. Linkers and Loaders
http://www.iecc.com/linker/
=======================================
2009－05－06 widebright 补充
上面两个命令都是 gnu binutils工具附带的，可能比较有帮助的还有addr2line 可以根据 你出错的堆栈地址找到对应的代码的行数吧。
http://www.gnu.org/software/binutils/
GNU Binutils
The GNU Binutils are a collection of binary tools. The main ones are:
ld – the GNU linker.
as – the GNU assembler.
But they also include:
addr2line – Converts addresses into filenames and line numbers.
ar – A utility for creating, modifying and extracting from archives.
c++filt – Filter to demangle encoded C++ symbols.
dlltool – Creates files for building and using DLLs.
gold – A new, faster, ELF only linker, still in beta test.
gprof – Displays profiling information.
nlmconv – Converts object code into an NLM.
nm – Lists symbols from object files.
objcopy – Copys and translates object files.
objdump – Displays information from object files.
ranlib – Generates an index to the contents of an archive.
readelf – Displays information from any ELF format object file.
size – Lists the section sizes of an object or archive file.
strings – Lists printable strings from files.
strip – Discards symbols.
windmc – A Windows compatible message compiler.
windres – A compiler for Windows resource files.
