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先用 http://www.groad.net/bbs/read.php?tid-1391-fpage-3.html 中的 cpuid 作为例子来尝试下面的一个编译链接： $ as -o cpuid.o cpuid.s # 使用 as 编译出 *.o 目标文件
$ gcc cpuid.o -o cpuid
cpuid.o: In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/lib/gcc/i486-linux-gnu/4.3.2/../../../../lib/crt1.o:(.text+0x0): first defined here
/usr/lib/gcc/i486-linux-gnu/4.3.2/../../../../lib/crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
collect2: ld returned 1 exit status
上面使用 as 编译时没有问题，但在用 gcc 链接时出错了。提示出错的原因有两个，1 是没有定义 main 函数；2 是重复定义了 _start ，且这个 _start 在 crt1.o 中已有定义。然而，如果 cpuid.o 是一个由 c 文件产生的目标文件(gcc -c cpuid.c -o cpuid.o)，那么则不会出现错误。
从上面的错误提示中我们知道，_start 这个入口标号在 crt1.o 中有定义。
实际上，用 gcc 编译一个 C 文件要经过 3 个阶段，第一是生成汇编代码，第二是生成目标文件，第三是生成可执行文件，如：
gcc -S dumpstack.c # -S 选项生成汇编代码
gcc -c dumpstack.s # -c 选项生成目标文件
gcc dumpstack.o # 生成可执行文件，默认为 a.out
上面第三步生成可执行文件，实际上是用 ld 进行了必要的链接。这里，用 ld 来做一个试验，先如下链接：
$ ld dumpstack.o -o dumpstack
ld: warning: cannot find entry symbol _start; defaulting to 0000000008048074
dumpstack.o: In function `main':
dumpstack.c:(.text+0x26): undefined reference to `printf'
dumpstack.c:(.text+0x3e): undefined reference to `printf'
dumpstack.c:(.text+0x43): undefined reference to `environ'
dumpstack.c:(.text+0x53): undefined reference to `printf'
dumpstack.c:(.text+0x58): undefined reference to `environ'
dumpstack.c:(.text+0x6a): undefined reference to `printf'
dumpstack.c:(.text+0x7d): undefined reference to `printf'
dumpstack.c:(.text+0x90): undefined reference to `printf'
dumpstack.c:(.text+0xa3): undefined reference to `printf'
dumpstack.c:(.text+0xb6): undefined reference to `printf'
dumpstack.c:(.text+0xc2): undefined reference to `puts'
dumpstack.c:(.text+0xe0): undefined reference to `printf'
dumpstack.c:(.text+0x107): undefined reference to `printf'
dumpstack.c:(.text+0x124): undefined reference to `putchar'
dumpstack.c:(.text+0x14a): undefined reference to `puts'
dumpstack.c:(.text+0x179): undefined reference to `printf'
dumpstack.c:(.text+0x1a1): undefined reference to `printf'
dumpstack.c:(.text+0x1be): undefined reference to `printf'
dumpstack.c:(.text+0x20d): undefined reference to `putchar'
dumpstack.c:(.text+0x22a): undefined reference to `putchar'
上面输出，不但提示找不到 _start 符号还缺少了如 printf() 等基本函数。从上面知道，出错的原因实际上是在链接时一些必要的库文件没有加载进来，正确的链接方法是：
$ ld /usr/lib/crt1.o /usr/lib/crti.o dumpstack.o -o dumpstack -lc -dynamic-linker /lib/ld-linux.so.2
上面链接时用到了 crt1.o 和 crti.o 以及 ld-linux.so.2 动态链接库。其中在 crt1.o 里会提供 _start 入口点的定义，crti.o 里会提供 _init (初始化)和 _fini (完成返回) 这些标号入口，动态链接库 ld-linux.so.2 里会提供诸如 printf()，puts() 等函数的动态链接功能。
如下面是对 dumpstack 程序的反汇编： $ objdump -d dumpstack
dumpstack: file format elf32-i386
Disassembly of section .init:
08048324 <_init>: # 在 /usr/lib/crti.o 中定义
8048324: 55 push %ebp
8048325: 89 e5 mov %esp,%ebp
8048327: 53 push %ebx
8048328: 83 ec 04 sub $0x4,%esp
804832b: e8 00 00 00 00 call 8048330 <_init+0xc>
8048330: 5b pop %ebx
8048331: 81 c3 e4 15 00 00 add $0x15e4,%ebx
8048337: 8b 93 fc ff ff ff mov -0x4(%ebx),%edx
804833d: 85 d2 test %edx,%edx
804833f: 74 05 je 8048346 <_init+0x22>
8048341: e8 1e 00 00 00 call 8048364 <[email=__gmon_start__@plt]__gmon_start__@plt[/email]>
8048346: e8 05 01 00 00 call 8048450 <frame_dummy>
804834b: e8 f0 03 00 00 call 8048740 <__do_global_ctors_aux>
8048350: 58 pop %eax
8048351: 5b pop %ebx
8048352: c9 leave
8048353: c3 ret
Disassembly of section .plt:
08048354 <[email=__gmon_start__@plt-0x10]__gmon_start__@plt-0x10[/email]>:
8048354: ff 35 18 99 04 08 pushl 0x8049918
804835a: ff 25 1c 99 04 08 jmp *0x804991c
8048360: 00 00 add %al,(%eax)
...
08048364 <[email=__gmon_start__@plt]__gmon_start__@plt[/email]>:
8048364: ff 25 20 99 04 08 jmp *0x8049920
804836a: 68 00 00 00 00 push $0x0
804836f: e9 e0 ff ff ff jmp 8048354 <_init+0x30>
08048374 <[email=putchar@plt]putchar@plt[/email]>:
8048374: ff 25 24 99 04 08 jmp *0x8049924
804837a: 68 08 00 00 00 push $0x8
804837f: e9 d0 ff ff ff jmp 8048354 <_init+0x30>
08048384 <[email=__libc_start_main@plt]__libc_start_main@plt[/email]>:
8048384: ff 25 28 99 04 08 jmp *0x8049928
804838a: 68 10 00 00 00 push $0x10
804838f: e9 c0 ff ff ff jmp 8048354 <_init+0x30>
08048394 <[email=printf@plt]printf@plt[/email]>:
8048394: ff 25 2c 99 04 08 jmp *0x804992c
804839a: 68 18 00 00 00 push $0x18
804839f: e9 b0 ff ff ff jmp 8048354 <_init+0x30>
080483a4 <[email=puts@plt]puts@plt[/email]>:
80483a4: ff 25 30 99 04 08 jmp *0x8049930
80483aa: 68 20 00 00 00 push $0x20
80483af: e9 a0 ff ff ff jmp 8048354 <_init+0x30>
Disassembly of section .text:
080483c0 <_start>: # 在 /usr/lib/crt1.o 中有定义，程序从这里执行
80483c0: 31 ed xor %ebp,%ebp
80483c2: 5e pop %esi
80483c3: 89 e1 mov %esp,%ecx
80483c5: 83 e4 f0 and $0xfffffff0,%esp
80483c8: 50 push %eax
80483c9: 54 push %esp
80483ca: 52 push %edx
80483cb: 68 d0 86 04 08 push $0x80486d0
80483d0: 68 e0 86 04 08 push $0x80486e0
80483d5: 51 push %ecx
80483d6: 56 push %esi
80483d7: 68 74 84 04 08 push $0x8048474 # main 函数地址压栈
80483dc: e8 a3 ff ff ff call 8048384 <[email=__libc_start_main@plt]__libc_start_main@plt[/email]>
80483e1: f4 hlt
80483e2: 90 nop
80483e3: 90 nop
80483e4: 90 nop
80483e5: 90 nop
80483e6: 90 nop
80483e7: 90 nop
80483e8: 90 nop
80483e9: 90 nop
80483ea: 90 nop
80483eb: 90 nop
80483ec: 90 nop
80483ed: 90 nop
80483ee: 90 nop
80483ef: 90 nop
080483f0 <__do_global_dtors_aux>:
80483f0: 55 push %ebp
80483f1: 89 e5 mov %esp,%ebp
80483f3: 53 push %ebx
80483f4: 83 ec 04 sub $0x4,%esp
80483f7: 80 3d 44 99 04 08 00 cmpb $0x0,0x8049944
80483fe: 75 40 jne 8048440 <__do_global_dtors_aux+0x50>
8048400: 8b 15 48 99 04 08 mov 0x8049948,%edx
8048406: b8 38 98 04 08 mov $0x8049838,%eax
804840b: 2d 34 98 04 08 sub $0x8049834,%eax
8048410: c1 f8 02 sar $0x2,%eax
8048413: 8d 58 ff lea -0x1(%eax),%ebx
8048416: 39 da cmp %ebx,%edx
8048418: 73 1f jae 8048439 <__do_global_dtors_aux+0x49>
804841a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
8048420: 8d 42 01 lea 0x1(%edx),%eax
8048423: a3 48 99 04 08 mov %eax,0x8049948
8048428: ff 14 85 34 98 04 08 call *0x8049834(,%eax,4)
804842f: 8b 15 48 99 04 08 mov 0x8049948,%edx
8048435: 39 da cmp %ebx,%edx
8048437: 72 e7 jb 8048420 <__do_global_dtors_aux+0x30>
8048439: c6 05 44 99 04 08 01 movb $0x1,0x8049944
8048440: 83 c4 04 add $0x4,%esp
8048443: 5b pop %ebx
8048444: 5d pop %ebp
8048445: c3 ret
8048446: 8d 76 00 lea 0x0(%esi),%esi
8048449: 8d bc 27 00 00 00 00 lea 0x0(%edi),%edi
08048450 <frame_dummy>:
8048450: 55 push %ebp
8048451: 89 e5 mov %esp,%ebp
8048453: 83 ec 08 sub $0x8,%esp
8048456: a1 3c 98 04 08 mov 0x804983c,%eax
804845b: 85 c0 test %eax,%eax
804845d: 74 12 je 8048471 <frame_dummy+0x21>
804845f: b8 00 00 00 00 mov $0x0,%eax
8048464: 85 c0 test %eax,%eax
8048466: 74 09 je 8048471 <frame_dummy+0x21>
8048468: c7 04 24 3c 98 04 08 movl $0x804983c,(%esp)
804846f: ff d0 call *%eax
8048471: c9 leave
8048472: c3 ret
8048473: 90 nop
08048474 <main>: # C 程序中的 main
8048474: 8d 4c 24 04 lea 0x4(%esp),%ecx
8048478: 83 e4 f0 and $0xfffffff0,%esp
804847b: ff 71 fc pushl -0x4(%ecx)
804847e: 55 push %ebp
804847f: 89 e5 mov %esp,%ebp
8048481: 51 push %ecx
8048482: 83 ec 24 sub $0x24,%esp
8048485: 89 4d e4 mov %ecx,-0x1c(%ebp)
8048488: 8b 55 e4 mov -0x1c(%ebp),%edx
804848b: 8b 42 04 mov 0x4(%edx),%eax
804848e: 89 44 24 04 mov %eax,0x4(%esp)
8048492: c7 04 24 90 87 04 08 movl $0x8048790,(%esp)
8048499: e8 f6 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
804849e: 8b 4d e4 mov -0x1c(%ebp),%ecx
80484a1: 8b 41 04 mov 0x4(%ecx),%eax
80484a4: 8b 00 mov (%eax),%eax
80484a6: 89 44 24 04 mov %eax,0x4(%esp)
80484aa: c7 04 24 9d 87 04 08 movl $0x804879d,(%esp)
80484b1: e8 de fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
80484b6: a1 40 99 04 08 mov 0x8049940,%eax
80484bb: 89 44 24 04 mov %eax,0x4(%esp)
80484bf: c7 04 24 ad 87 04 08 movl $0x80487ad,(%esp)
80484c6: e8 c9 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
80484cb: a1 40 99 04 08 mov 0x8049940,%eax
80484d0: 8b 00 mov (%eax),%eax
80484d2: 89 44 24 04 mov %eax,0x4(%esp)
80484d6: c7 04 24 bd 87 04 08 movl $0x80487bd,(%esp)
80484dd: e8 b2 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
80484e2: 8d 45 f8 lea -0x8(%ebp),%eax
80484e5: 89 44 24 04 mov %eax,0x4(%esp)
80484e9: c7 04 24 d0 87 04 08 movl $0x80487d0,(%esp)
80484f0: e8 9f fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
80484f5: 8d 45 f4 lea -0xc(%ebp),%eax
80484f8: 89 44 24 04 mov %eax,0x4(%esp)
80484fc: c7 04 24 df 87 04 08 movl $0x80487df,(%esp)
8048503: e8 8c fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
8048508: 8d 45 f0 lea -0x10(%ebp),%eax
804850b: 89 44 24 04 mov %eax,0x4(%esp)
804850f: c7 04 24 ee 87 04 08 movl $0x80487ee,(%esp)
8048516: e8 79 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
804851b: 8d 45 ec lea -0x14(%ebp),%eax
804851e: 89 44 24 04 mov %eax,0x4(%esp)
8048522: c7 04 24 fd 87 04 08 movl $0x80487fd,(%esp)
8048529: e8 66 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
804852e: c7 04 24 0f 88 04 08 movl $0x804880f,(%esp)
8048535: e8 6a fe ff ff call 80483a4 <[email=puts@plt]puts@plt[/email]>
804853a: 8d 45 f8 lea -0x8(%ebp),%eax
804853d: 83 e0 f0 and $0xfffffff0,%eax
8048540: 89 45 f4 mov %eax,-0xc(%ebp)
8048543: eb 60 jmp 80485a5 <main+0x131>
8048545: 8b 45 f4 mov -0xc(%ebp),%eax
8048548: 89 44 24 04 mov %eax,0x4(%esp)
804854c: c7 04 24 11 88 04 08 movl $0x8048811,(%esp)
8048553: e8 3c fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
8048558: c7 45 f8 00 00 00 00 movl $0x0,-0x8(%ebp)
804855f: eb 27 jmp 8048588 <main+0x114>
8048561: 8b 55 f4 mov -0xc(%ebp),%edx
8048564: 8b 45 f8 mov -0x8(%ebp),%eax
8048567: c1 e0 02 shl $0x2,%eax
804856a: 8d 04 02 lea (%edx,%eax,1),%eax
804856d: 8b 00 mov (%eax),%eax
804856f: 89 44 24 04 mov %eax,0x4(%esp)
8048573: c7 04 24 17 88 04 08 movl $0x8048817,(%esp)
804857a: e8 15 fe ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
804857f: 8b 45 f8 mov -0x8(%ebp),%eax
8048582: 83 c0 01 add $0x1,%eax
8048585: 89 45 f8 mov %eax,-0x8(%ebp)
8048588: 8b 45 f8 mov -0x8(%ebp),%eax
804858b: 83 f8 03 cmp $0x3,%eax
804858e: 76 d1 jbe 8048561 <main+0xed>
8048590: c7 04 24 0a 00 00 00 movl $0xa,(%esp)
8048597: e8 d8 fd ff ff call 8048374 <[email=putchar@plt]putchar@plt[/email]>
804859c: 8b 45 f4 mov -0xc(%ebp),%eax
804859f: 83 c0 10 add $0x10,%eax
80485a2: 89 45 f4 mov %eax,-0xc(%ebp)
80485a5: 8b 45 f4 mov -0xc(%ebp),%eax
80485a8: 89 c2 mov %eax,%edx
80485aa: 8b 4d e4 mov -0x1c(%ebp),%ecx
80485ad: 8b 41 04 mov 0x4(%ecx),%eax
80485b0: 8b 00 mov (%eax),%eax
80485b2: 39 c2 cmp %eax,%edx
80485b4: 72 8f jb 8048545 <main+0xd1>
80485b6: c7 04 24 0f 88 04 08 movl $0x804880f,(%esp)
80485bd: e8 e2 fd ff ff call 80483a4 <[email=puts@plt]puts@plt[/email]>
80485c2: 8b 55 e4 mov -0x1c(%ebp),%edx
80485c5: 8b 42 04 mov 0x4(%edx),%eax
80485c8: 8b 00 mov (%eax),%eax
80485ca: 83 e0 f0 and $0xfffffff0,%eax
80485cd: 83 e8 10 sub $0x10,%eax
80485d0: 89 45 f0 mov %eax,-0x10(%ebp)
80485d3: 8b 45 f0 mov -0x10(%ebp),%eax
80485d6: 89 45 ec mov %eax,-0x14(%ebp)
80485d9: e9 cd 00 00 00 jmp 80486ab <main+0x237>
80485de: 8b 45 f0 mov -0x10(%ebp),%eax
80485e1: 89 44 24 04 mov %eax,0x4(%esp)
80485e5: c7 04 24 11 88 04 08 movl $0x8048811,(%esp)
80485ec: e8 a3 fd ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
80485f1: c7 45 f8 00 00 00 00 movl $0x0,-0x8(%ebp)
80485f8: eb 28 jmp 8048622 <main+0x1ae>
80485fa: 8b 55 f0 mov -0x10(%ebp),%edx
80485fd: 8b 45 f8 mov -0x8(%ebp),%eax
8048600: 8d 04 02 lea (%edx,%eax,1),%eax
8048603: 0f b6 00 movzbl (%eax),%eax
8048606: 0f b6 c0 movzbl %al,%eax
8048609: 89 44 24 04 mov %eax,0x4(%esp)
804860d: c7 04 24 1d 88 04 08 movl $0x804881d,(%esp)
8048614: e8 7b fd ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
8048619: 8b 45 f8 mov -0x8(%ebp),%eax
804861c: 83 c0 01 add $0x1,%eax
804861f: 89 45 f8 mov %eax,-0x8(%ebp)
8048622: 8b 45 f8 mov -0x8(%ebp),%eax
8048625: 83 f8 0f cmp $0xf,%eax
8048628: 76 d0 jbe 80485fa <main+0x186>
804862a: c7 04 24 23 88 04 08 movl $0x8048823,(%esp)
8048631: e8 5e fd ff ff call 8048394 <[email=printf@plt]printf@plt[/email]>
8048636: c7 45 f8 00 00 00 00 movl $0x0,-0x8(%ebp)
804863d: eb 4f jmp 804868e <main+0x21a>
804863f: 8b 55 f0 mov -0x10(%ebp),%edx
8048642: 8b 45 f8 mov -0x8(%ebp),%eax
8048645: 8d 04 02 lea (%edx,%eax,1),%eax
8048648: 0f b6 00 movzbl (%eax),%eax
804864b: 3c 20 cmp $0x20,%al
804864d: 76 24 jbe 8048673 <main+0x1ff>
804864f: 8b 55 f0 mov -0x10(%ebp),%edx
8048652: 8b 45 f8 mov -0x8(%ebp),%eax
8048655: 8d 04 02 lea (%edx,%eax,1),%eax
8048658: 0f b6 00 movzbl (%eax),%eax
804865b: 3c 7e cmp $0x7e,%al
804865d: 77 14 ja 8048673 <main+0x1ff>
804865f: 8b 55 f0 mov -0x10(%ebp),%edx
8048662: 8b 45 f8 mov -0x8(%ebp),%eax
8048665: 8d 04 02 lea (%edx,%eax,1),%eax
8048668: 0f b6 00 movzbl (%eax),%eax
804866b: 0f b6 c0 movzbl %al,%eax
804866e: 89 45 e8 mov %eax,-0x18(%ebp)
8048671: eb 07 jmp 804867a <main+0x206>
8048673: c7 45 e8 2e 00 00 00 movl $0x2e,-0x18(%ebp)
804867a: 8b 4d e8 mov -0x18(%ebp),%ecx
804867d: 89 0c 24 mov %ecx,(%esp)
8048680: e8 ef fc ff ff call 8048374 <[email=putchar@plt]putchar@plt[/email]>
8048685: 8b 45 f8 mov -0x8(%ebp),%eax
8048688: 83 c0 01 add $0x1,%eax
804868b: 89 45 f8 mov %eax,-0x8(%ebp)
804868e: 8b 45 f8 mov -0x8(%ebp),%eax
8048691: 83 f8 0f cmp $0xf,%eax
8048694: 76 a9 jbe 804863f <main+0x1cb>
8048696: c7 04 24 0a 00 00 00 movl $0xa,(%esp)
804869d: e8 d2 fc ff ff call 8048374 <[email=putchar@plt]putchar@plt[/email]>
80486a2: 8b 45 f0 mov -0x10(%ebp),%eax
80486a5: 83 c0 10 add $0x10,%eax
80486a8: 89 45 f0 mov %eax,-0x10(%ebp)
80486ab: 8b 45 f0 mov -0x10(%ebp),%eax
80486ae: 89 c2 mov %eax,%edx
80486b0: 8b 45 ec mov -0x14(%ebp),%eax
80486b3: 05 c0 05 00 00 add $0x5c0,%eax
80486b8: 39 c2 cmp %eax,%edx
80486ba: 0f 82 1e ff ff ff jb 80485de <main+0x16a>
80486c0: b8 00 00 00 00 mov $0x0,%eax
80486c5: 83 c4 24 add $0x24,%esp
80486c8: 59 pop %ecx
80486c9: 5d pop %ebp
80486ca: 8d 61 fc lea -0x4(%ecx),%esp
80486cd: c3 ret
80486ce: 90 nop
80486cf: 90 nop
080486d0 <__libc_csu_fini>:
80486d0: 55 push %ebp
80486d1: 89 e5 mov %esp,%ebp
80486d3: 5d pop %ebp
80486d4: c3 ret
80486d5: 8d 74 26 00 lea 0x0(%esi),%esi
80486d9: 8d bc 27 00 00 00 00 lea 0x0(%edi),%edi
080486e0 <__libc_csu_init>:
80486e0: 55 push %ebp
80486e1: 89 e5 mov %esp,%ebp
80486e3: 57 push %edi
80486e4: 56 push %esi
80486e5: 53 push %ebx
80486e6: e8 4f 00 00 00 call 804873a <__i686.get_pc_thunk.bx>
80486eb: 81 c3 29 12 00 00 add $0x1229,%ebx
80486f1: 83 ec 0c sub $0xc,%esp
80486f4: e8 2b fc ff ff call 8048324 <_init>
80486f9: 8d bb 18 ff ff ff lea -0xe8(%ebx),%edi
80486ff: 8d 83 18 ff ff ff lea -0xe8(%ebx),%eax
8048705: 29 c7 sub %eax,%edi
8048707: c1 ff 02 sar $0x2,%edi
804870a: 85 ff test %edi,%edi
804870c: 74 24 je 8048732 <__libc_csu_init+0x52>
804870e: 31 f6 xor %esi,%esi
8048710: 8b 45 10 mov 0x10(%ebp),%eax
8048713: 89 44 24 08 mov %eax,0x8(%esp)
8048717: 8b 45 0c mov 0xc(%ebp),%eax
804871a: 89 44 24 04 mov %eax,0x4(%esp)
804871e: 8b 45 08 mov 0x8(%ebp),%eax
8048721: 89 04 24 mov %eax,(%esp)
8048724: ff 94 b3 18 ff ff ff call *-0xe8(%ebx,%esi,4)
804872b: 83 c6 01 add $0x1,%esi
804872e: 39 fe cmp %edi,%esi
8048730: 72 de jb 8048710 <__libc_csu_init+0x30>
8048732: 83 c4 0c add $0xc,%esp
8048735: 5b pop %ebx
8048736: 5e pop %esi
8048737: 5f pop %edi
8048738: 5d pop %ebp
8048739: c3 ret
0804873a <__i686.get_pc_thunk.bx>:
804873a: 8b 1c 24 mov (%esp),%ebx
804873d: c3 ret
804873e: 90 nop
804873f: 90 nop
08048740 <__do_global_ctors_aux>:
8048740: 55 push %ebp
8048741: 89 e5 mov %esp,%ebp
8048743: 53 push %ebx
8048744: 83 ec 04 sub $0x4,%esp
8048747: a1 2c 98 04 08 mov 0x804982c,%eax
804874c: 83 f8 ff cmp $0xffffffff,%eax
804874f: 74 13 je 8048764 <__do_global_ctors_aux+0x24>
8048751: bb 2c 98 04 08 mov $0x804982c,%ebx
8048756: 66 90 xchg %ax,%ax
8048758: 83 eb 04 sub $0x4,%ebx
804875b: ff d0 call *%eax
804875d: 8b 03 mov (%ebx),%eax
804875f: 83 f8 ff cmp $0xffffffff,%eax
8048762: 75 f4 jne 8048758 <__do_global_ctors_aux+0x
8048764: 83 c4 04 add $0x4,%esp
8048767: 5b pop %ebx
8048768: 5d pop %ebp
8048769: c3 ret
804876a: 90 nop
804876b: 90 nop
Disassembly of section .fini:
0804876c <_fini>: # 在 /usr/lib/crti.o 中定义
804876c: 55 push %ebp
804876d: 89 e5 mov %esp,%ebp
804876f: 53 push %ebx
8048770: 83 ec 04 sub $0x4,%esp
8048773: e8 00 00 00 00 call 8048778 <_fini+0xc>
8048778: 5b pop %ebx
8048779: 81 c3 9c 11 00 00 add $0x119c,%ebx
804877f: e8 6c fc ff ff call 80483f0 <__do_global_dtors_aux>
8048784: 59 pop %ecx
8048785: 5b pop %ebx
8048786: c9 leave
8048787: c3 ret
上面，.plt 段用来协助完成动态链接功能。
另外，查看目标文件可以用 readelf 命令，如果只是关心符号信息，那么还可以使用 nm 命令，如下查看 crt1.o 和 crti.o 的符号信息：
C$ nm /usr/lib/crt1.o
00000000 R _IO_stdin_used
00000000 D __data_start
U __libc_csu_fini
U __libc_csu_init
U __libc_start_main
00000000 R _fp_hw
00000000 T _start
00000000 W data_start
U main
$ nm /usr/lib/crti.o
U _GLOBAL_OFFSET_TABLE_
w __gmon_start__
00000000 T _fini
00000000 T _init |
|
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发表于 2010-11-11 08:44:22
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