from: http://www.ibm.com/developerworks/cn/aix/library/au-unixtools.html
級别: 中級
Bill Zimmerly ([email protected]), 自由撰稿人兼知識工程師, Author
2007 年 3 月 06 日
UNIX(R) 系統中運作的程式遵守一種稱為目标檔案格式的精心設計。了解更多關于目标檔案格式的内容,以及可以用來研究系統中目标檔案的工具。
計算機程式設計的最新技術将一種特殊的人性與一組特殊的工具結合在一起,用以生産出對其他人非常有幫助的一種神奇的産品,即軟體。計算機程式員是一群注重細節的人,他們可以處理計算機中各種各樣的困難。計算機的要求非常苛刻,并且不能容忍其中存在任何的偏差。毫無疑問,無論您的個性如何以及在工作中使用了何種輔助工具,計算機程式的編寫都是非常困難的。
在 UNIX® 和 Linux® 中,任何事物都是檔案。您可以認為,UNIX 和 Linux 程式設計實際上是編寫處理各種檔案的代碼。系統由許多類型的檔案組成,但目标檔案具有一種特殊的設計,提供了靈活和多樣的用途。
目标檔案是包含帶有附加位址和值的助記符号的路線圖。這些符号可以用來對各種代碼段和資料段進行命名,包括經過初始化的和未初始化的。它們也可以用來定位嵌入的調試資訊,就像語義 Web,非常适合由程式進行閱讀。
行業工具
計算機程式設計中使用的工具包括代碼編輯器,如 vi 或 Emacs,您可以使用這些工具輸入和編輯希望計算機在完成所需任務時執行的指令,以及編譯器和連接配接器,它們可以生成真正實作這些目标的機器代碼。
進階的工具,稱為內建調試環境 (IDE),它以統一的外觀內建了不同工具的功能。IDE 使得編輯器、編譯器、連接配接器和調試器之間的界限變得很模糊。是以,為了更深入地研究和了解系統,在使用內建的套件之前,最好先單獨地使用這些工具。(注意:IDE 也通常被稱為內建開發環境。)
編譯器可以将您在代碼編輯器中建立的文本轉換為目标檔案。最初,目标檔案被稱為代碼的中間表示形式,因為它用作連接配接編輯器(即連接配接器)的輸入,而連接配接編輯器最終完成整個任務并生成可執行的程式作為輸出。
從代碼到可執行代碼的轉換過程經過了良好的定義并實作了自動化,而目标檔案是這個鍊中有機的連接配接性環節。在這個轉換過程中,目标檔案作為連接配接編輯器所使用的映象,使得它們能夠解析各種符号并将不同的代碼和資料段連接配接在一起形成統一的整體。
曆史
計算機程式設計領域中存在許多著名的目标檔案格式。DOS 系列包括 COM、OBJ 和 EXE 格式。UNIX 和 Linux 使用 a.out、COFF 和 ELF。Microsoft® Windows® 使用可移植的執行檔案 (PE) 格式,而 Macintosh 使用 PEF、Mach-O 和其他檔案格式。
最初,各種類型的計算機具有自己獨特的目标檔案格式,但随着 UNIX 和其他在不同硬體平台上提供可移植性的作業系統的出現,一些常用的檔案格式上升為通用的标準。其中包括 a.out、COFF 和 ELF 格式。
要了解目标檔案,需要一組可以讀取目标檔案中不同部分并以更易于讀取的格式顯示這些内容的工具。本文将讨論這些工具中比較重要的方面。但首先,您必須建立一個工作台,并在其中建立一個研究對象。
工作台
啟動一個 xterm 會話,讓我們先建立一個空白的工作台,并開始對目标檔案進行研究。下面的指令建立了一個目錄,可以将目标檔案放到該目錄中進行研究:
cd
mkdir src
cd src
mkdir hw
cd hw |
然後,使用您最喜歡的代碼編輯器,在 $HOME/src/hw 目錄中輸入清單 1 中的程式,并命名為 hw.c。
清單 1. hw.c 程式
#include <stdio.h>
int main(void)
{
printf("Hello World!/n");
return 0;
}
|
要使用 UNIX 工具庫中提供的各種工具,可以将這個簡單的“Hello World”程式作為研究的對象。您将學習建構和檢視目标檔案的輸出,而不是使用任何快捷方法直接建立可執行檔案(的确有許多這樣的快捷方法)。
檔案格式
C
編譯器的正常輸出是用于您所指定的目标處理器的彙編代碼。彙編代碼是彙編器的輸入,在預設情況下,彙編器将生成所有目标檔案的祖先,即 a.out 檔案。這個名稱本身表示彙編輸出 (Assembler Output)。要建立 a.out 檔案,可以在 xterm 視窗中輸入下面的指令:
注意:如果出現了任何錯誤或者沒有建立 a.out 檔案,那麼您可能需要檢查自己的系統或源檔案 (hw.c),以找出其中的錯誤。還需要檢查是否已将 cc 定義為運作您的
C/C++
編譯器。
最新的
C
編譯器将編譯和彙編步驟組合成一個步驟。您可以指定不同開關選項以檢視
C
編譯器的彙編輸出。通過輸入下面的指令,您可以看到
C
編譯器的彙編輸出:
這個指令生成了一個新的檔案 hw.s,其中包含您通常無法看到的彙編輸入文本,因為編譯器在預設情況下将生成 a.out 檔案。正如所預期的,UNIX 彙程式設計式可以對這種輸入檔案進行彙編,以生成 a.out 檔案。
UNIX 特定的工具
假定編譯過程一切順利,那麼在該目錄中就有了一個 a.out 檔案,下面讓我們來對其進行研究。有許多可用于研究目标檔案的有價值的工具,下面便是其中一組:
- nm:列出目标檔案中的符号。
- objdump:顯示目标檔案中的詳細資訊。
- readelf:顯示關于 ELF 目标檔案的資訊。
清單中的第一個工具是 nm,它可以列出目标檔案中的符号。如果您輸入
nm
指令,您将注意到在預設情況下,它會尋找一個名為 a.out 的檔案。如果沒有找到該檔案,這個工具會給出相應的提示。然而,如果該工具找到了編譯器建立的 a.out 檔案,它将顯示類似清單 2 的清單。
清單 2. nm 指令的輸出
08049594 A __bss_start
080482e4 t call_gmon_start
08049594 b completed.4463
08049498 d __CTOR_END__
08049494 d __CTOR_LIST__
08049588 D __data_start
08049588 W data_start
0804842c t __do_global_ctors_aux
0804830c t __do_global_dtors_aux
0804958c D __dso_handle
080494a0 d __DTOR_END__
0804949c d __DTOR_LIST__
080494a8 d _DYNAMIC
08049594 A _edata
08049598 A _end
08048458 T _fini
08049494 a __fini_array_end
08049494 a __fini_array_start
08048478 R _fp_hw
0804833b t frame_dummy
08048490 r __FRAME_END__
08049574 d _GLOBAL_OFFSET_TABLE_
w __gmon_start__
08048308 T __i686.get_pc_thunk.bx
08048278 T _init
08049494 a __init_array_end
08049494 a __init_array_start
0804847c R _IO_stdin_used
080494a4 d __JCR_END__
080494a4 d __JCR_LIST__
w _Jv_RegisterClasses
080483e1 T __libc_csu_fini
08048390 T __libc_csu_init
U __libc_start_main@@GLIBC_2.0
08048360 T main
08049590 d p.4462
U puts@@GLIBC_2.0
080482c0 T _start
|
這些包含可執行代碼的段稱為正文段。同樣地,資料段包含了不可執行的資訊或資料。另一種類型的段,稱為 BSS 段,它包含以符号資料開頭的塊。
對于
nm
指令列出的每個符号,它們的值使用十六進制來表示(預設行為),并且在該符号前面加上了一個表示符号類型的編碼字元。常見的各種編碼包括:A 表示絕對 (absolute),這意味着不能将該值更改為其他的連接配接;B 表示 BSS 段中的符号;而 C 表示引用未初始化的資料的一般符号。
可以将目标檔案中所包含的不同的部分劃分為段。段可以包含可執行代碼、符号名稱、初始資料值和許多其他類型的資料。有關這些類型的資料的詳細資訊,可以閱讀 UNIX 中
nm
的 man 頁面,其中按照該指令輸出中的字元編碼分别對每種類型進行了描述。
細節,細節…
在目标檔案階段,即使是一個簡單的 Hello World 程式,其中也包含了大量的細節資訊。nm 程式可用于列舉符号及其類型和值,但是,要更仔細地研究目标檔案中這些命名段的内容,需要使用功能更強大的工具。
其中兩種功能強大的工具是 objdump 和 readelf 程式。通過輸入下面的指令,您可以看到目标檔案中包含可執行代碼的每個段的彙編清單。對于這麼一個小的程式,編譯器生成了這麼多的代碼,真的很令人驚異!
這個指令生成的輸出如清單 3 所示。每個可執行代碼段将在需要特定的事件時執行,這些事件包括庫的初始化和該程式本身主入口點。
清單 3. objdump 指令的輸出
a.out: file format elf32-i386
Disassembly of section .init:
08048278 <_init>:
8048278: 55 push %ebp
8048279: 89 e5 mov %esp,%ebp
804827b: 83 ec 08 sub $0x8,%esp
804827e: e8 61 00 00 00 call 80482e4 <call_gmon_start>
8048283: e8 b3 00 00 00 call 804833b <frame_dummy>
8048288: e8 9f 01 00 00 call 804842c <__do_global_ctors_aux>
804828d: c9 leave
804828e: c3 ret
Disassembly of section .plt:
08048290 <[email protected]>:
8048290: ff 35 78 95 04 08 pushl 0x8049578
8048296: ff 25 7c 95 04 08 jmp *0x804957c
804829c: 00 00 add %al,(%eax)
...
080482a0 <[email protected]>:
80482a0: ff 25 80 95 04 08 jmp *0x8049580
80482a6: 68 00 00 00 00 push $0x0
80482ab: e9 e0 ff ff ff jmp 8048290 <_init+0x18>
080482b0 <[email protected]>:
80482b0: ff 25 84 95 04 08 jmp *0x8049584
80482b6: 68 08 00 00 00 push $0x8
80482bb: e9 d0 ff ff ff jmp 8048290 <_init+0x18>
Disassembly of section .text:
080482c0 <_start>:
80482c0: 31 ed xor %ebp,%ebp
80482c2: 5e pop %esi
80482c3: 89 e1 mov %esp,%ecx
80482c5: 83 e4 f0 and $0xfffffff0,%esp
80482c8: 50 push %eax
80482c9: 54 push %esp
80482ca: 52 push %edx
80482cb: 68 e1 83 04 08 push $0x80483e1
80482d0: 68 90 83 04 08 push $0x8048390
80482d5: 51 push %ecx
80482d6: 56 push %esi
80482d7: 68 60 83 04 08 push $0x8048360
80482dc: e8 cf ff ff ff call 80482b0 <[email protected]>
80482e1: f4 hlt
80482e2: 90 nop
80482e3: 90 nop
080482e4 <call_gmon_start>:
80482e4: 55 push %ebp
80482e5: 89 e5 mov %esp,%ebp
80482e7: 53 push %ebx
80482e8: e8 1b 00 00 00 call 8048308 <__i686.get_pc_thunk.bx>
80482ed: 81 c3 87 12 00 00 add $0x1287,%ebx
80482f3: 83 ec 04 sub $0x4,%esp
80482f6: 8b 83 fc ff ff ff mov 0xfffffffc(%ebx),%eax
80482fc: 85 c0 test %eax,%eax
80482fe: 74 02 je 8048302 <call_gmon_start+0x1e>
8048300: ff d0 call *%eax
8048302: 83 c4 04 add $0x4,%esp
8048305: 5b pop %ebx
8048306: 5d pop %ebp
8048307: c3 ret
08048308 <__i686.get_pc_thunk.bx>:
8048308: 8b 1c 24 mov (%esp),%ebx
804830b: c3 ret
0804830c <__do_global_dtors_aux>:
804830c: 55 push %ebp
804830d: 89 e5 mov %esp,%ebp
804830f: 83 ec 08 sub $0x8,%esp
8048312: 80 3d 94 95 04 08 00 cmpb $0x0,0x8049594
8048319: 74 0c je 8048327 <__do_global_dtors_aux+0x1b>
804831b: eb 1c jmp 8048339 <__do_global_dtors_aux+0x2d>
804831d: 83 c0 04 add $0x4,%eax
8048320: a3 90 95 04 08 mov %eax,0x8049590
8048325: ff d2 call *%edx
8048327: a1 90 95 04 08 mov 0x8049590,%eax
804832c: 8b 10 mov (%eax),%edx
804832e: 85 d2 test %edx,%edx
8048330: 75 eb jne 804831d <__do_global_dtors_aux+0x11>
8048332: c6 05 94 95 04 08 01 movb $0x1,0x8049594
8048339: c9 leave
804833a: c3 ret
0804833b <frame_dummy>:
804833b: 55 push %ebp
804833c: 89 e5 mov %esp,%ebp
804833e: 83 ec 08 sub $0x8,%esp
8048341: a1 a4 94 04 08 mov 0x80494a4,%eax
8048346: 85 c0 test %eax,%eax
8048348: 74 12 je 804835c <frame_dummy+0x21>
804834a: b8 00 00 00 00 mov $0x0,%eax
804834f: 85 c0 test %eax,%eax
8048351: 74 09 je 804835c <frame_dummy+0x21>
8048353: c7 04 24 a4 94 04 08 movl $0x80494a4,(%esp)
804835a: ff d0 call *%eax
804835c: c9 leave
804835d: c3 ret
804835e: 90 nop
804835f: 90 nop
08048360 <main>:
8048360: 55 push %ebp
8048361: 89 e5 mov %esp,%ebp
8048363: 83 ec 08 sub $0x8,%esp
8048366: 83 e4 f0 and $0xfffffff0,%esp
8048369: b8 00 00 00 00 mov $0x0,%eax
804836e: 83 c0 0f add $0xf,%eax
8048371: 83 c0 0f add $0xf,%eax
8048374: c1 e8 04 shr $0x4,%eax
8048377: c1 e0 04 shl $0x4,%eax
804837a: 29 c4 sub %eax,%esp
804837c: c7 04 24 80 84 04 08 movl $0x8048480,(%esp)
8048383: e8 18 ff ff ff call 80482a0 <[email protected]>
8048388: b8 00 00 00 00 mov $0x0,%eax
804838d: c9 leave
804838e: c3 ret
804838f: 90 nop
08048390 <__libc_csu_init>:
8048390: 55 push %ebp
8048391: 89 e5 mov %esp,%ebp
8048393: 57 push %edi
8048394: 56 push %esi
8048395: 31 f6 xor %esi,%esi
8048397: 53 push %ebx
8048398: e8 6b ff ff ff call 8048308 <__i686.get_pc_thunk.bx>
804839d: 81 c3 d7 11 00 00 add $0x11d7,%ebx
80483a3: 83 ec 0c sub $0xc,%esp
80483a6: e8 cd fe ff ff call 8048278 <_init>
80483ab: 8d 83 20 ff ff ff lea 0xffffff20(%ebx),%eax
80483b1: 8d 93 20 ff ff ff lea 0xffffff20(%ebx),%edx
80483b7: 89 45 f0 mov %eax,0xfffffff0(%ebp)
80483ba: 29 d0 sub %edx,%eax
80483bc: c1 f8 02 sar $0x2,%eax
80483bf: 39 c6 cmp %eax,%esi
80483c1: 73 16 jae 80483d9 <__libc_csu_init+0x49>
80483c3: 89 d7 mov %edx,%edi
80483c5: ff 14 b2 call *(%edx,%esi,4)
80483c8: 8b 45 f0 mov 0xfffffff0(%ebp),%eax
80483cb: 83 c6 01 add $0x1,%esi
80483ce: 29 f8 sub %edi,%eax
80483d0: 89 fa mov %edi,%edx
80483d2: c1 f8 02 sar $0x2,%eax
80483d5: 39 c6 cmp %eax,%esi
80483d7: 72 ec jb 80483c5 <__libc_csu_init+0x35>
80483d9: 83 c4 0c add $0xc,%esp
80483dc: 5b pop %ebx
80483dd: 5e pop %esi
80483de: 5f pop %edi
80483df: 5d pop %ebp
80483e0: c3 ret
080483e1 <__libc_csu_fini>:
80483e1: 55 push %ebp
80483e2: 89 e5 mov %esp,%ebp
80483e4: 83 ec 18 sub $0x18,%esp
80483e7: 89 5d f4 mov %ebx,0xfffffff4(%ebp)
80483ea: e8 19 ff ff ff call 8048308 <__i686.get_pc_thunk.bx>
80483ef: 81 c3 85 11 00 00 add $0x1185,%ebx
80483f5: 89 75 f8 mov %esi,0xfffffff8(%ebp)
80483f8: 89 7d fc mov %edi,0xfffffffc(%ebp)
80483fb: 8d b3 20 ff ff ff lea 0xffffff20(%ebx),%esi
8048401: 8d bb 20 ff ff ff lea 0xffffff20(%ebx),%edi
8048407: 29 fe sub %edi,%esi
8048409: c1 fe 02 sar $0x2,%esi
804840c: eb 03 jmp 8048411 <__libc_csu_fini+0x30>
804840e: ff 14 b7 call *(%edi,%esi,4)
8048411: 83 ee 01 sub $0x1,%esi
8048414: 83 fe ff cmp $0xffffffff,%esi
8048417: 75 f5 jne 804840e <__libc_csu_fini+0x2d>
8048419: e8 3a 00 00 00 call 8048458 <_fini>
804841e: 8b 5d f4 mov 0xfffffff4(%ebp),%ebx
8048421: 8b 75 f8 mov 0xfffffff8(%ebp),%esi
8048424: 8b 7d fc mov 0xfffffffc(%ebp),%edi
8048427: 89 ec mov %ebp,%esp
8048429: 5d pop %ebp
804842a: c3 ret
804842b: 90 nop
0804842c <__do_global_ctors_aux>:
804842c: 55 push %ebp
804842d: 89 e5 mov %esp,%ebp
804842f: 53 push %ebx
8048430: 83 ec 04 sub $0x4,%esp
8048433: a1 94 94 04 08 mov 0x8049494,%eax
8048438: 83 f8 ff cmp $0xffffffff,%eax
804843b: 74 12 je 804844f <__do_global_ctors_aux+0x23>
804843d: bb 94 94 04 08 mov $0x8049494,%ebx
8048442: ff d0 call *%eax
8048444: 8b 43 fc mov 0xfffffffc(%ebx),%eax
8048447: 83 eb 04 sub $0x4,%ebx
804844a: 83 f8 ff cmp $0xffffffff,%eax
804844d: 75 f3 jne 8048442 <__do_global_ctors_aux+0x16>
804844f: 83 c4 04 add $0x4,%esp
8048452: 5b pop %ebx
8048453: 5d pop %ebp
8048454: c3 ret
8048455: 90 nop
8048456: 90 nop
8048457: 90 nop
Disassembly of section .fini:
08048458 <_fini>:
8048458: 55 push %ebp
8048459: 89 e5 mov %esp,%ebp
804845b: 53 push %ebx
804845c: e8 a7 fe ff ff call 8048308 <__i686.get_pc_thunk.bx>
8048461: 81 c3 13 11 00 00 add $0x1113,%ebx
8048467: 83 ec 04 sub $0x4,%esp
804846a: e8 9d fe ff ff call 804830c <__do_global_dtors_aux>
804846f: 83 c4 04 add $0x4,%esp
8048472: 5b pop %ebx
8048473: 5d pop %ebp
8048474: c3 ret
|
對于那些着迷于底層程式設計細節的程式員來說,這是一個功能非常強大的工具,可用于研究編譯器和彙編器的輸出。細節資訊,比如這段代碼中所顯示的這些資訊,可以揭示有關本地處理器本身運作方式的很多内容。對該處理器制造商提供的技術文檔進行深入的研究,您可以收集關于一些有價值的資訊,通過這些資訊可以深入地了解内部的運作機制,因為功能程式提供了清晰的輸出。
類似地,readelf 程式也可以清楚地列出目标檔案中的内容。輸入下面的指令,您将可以看到這一點:
這個指令生成的輸出如清單 4 所示。ELF Header 為該檔案中所有段入口顯示了詳細的摘要。在列舉出這些 Header 中的内容之前,您可以看到 Header 的具體數目。在研究一個較大的目标檔案時,該資訊可能非常有用。
清單 4. readelf 指令的輸出
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: 0x80482c0
Start of program headers: 52 (bytes into file)
Start of section headers: 3504 (bytes into file)
Flags: 0x0
Size of this header: 52 (bytes)
Size of program headers: 32 (bytes)
Number of program headers: 7
Size of section headers: 40 (bytes)
Number of section headers: 34
Section header string table index: 31
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 08048114 000114 000013 00 A 0 0 1
[ 2] .note.ABI-tag NOTE 08048128 000128 000020 00 A 0 0 4
[ 3] .hash HASH 08048148 000148 00002c 04 A 4 0 4
[ 4] .dynsym DYNSYM 08048174 000174 000060 10 A 5 1 4
[ 5] .dynstr STRTAB 080481d4 0001d4 00005e 00 A 0 0 1
[ 6] .gnu.version VERSYM 08048232 000232 00000c 02 A 4 0 2
[ 7] .gnu.version_r VERNEED 08048240 000240 000020 00 A 5 1 4
[ 8] .rel.dyn REL 08048260 000260 000008 08 A 4 0 4
[ 9] .rel.plt REL 08048268 000268 000010 08 A 4 11 4
[10] .init PROGBITS 08048278 000278 000017 00 AX 0 0 1
[11] .plt PROGBITS 08048290 000290 000030 04 AX 0 0 4
[12] .text PROGBITS 080482c0 0002c0 000198 00 AX 0 0 4
[13] .fini PROGBITS 08048458 000458 00001d 00 AX 0 0 1
[14] .rodata PROGBITS 08048478 000478 000015 00 A 0 0 4
[15] .eh_frame PROGBITS 08048490 000490 000004 00 A 0 0 4
[16] .ctors PROGBITS 08049494 000494 000008 00 WA 0 0 4
[17] .dtors PROGBITS 0804949c 00049c 000008 00 WA 0 0 4
[18] .jcr PROGBITS 080494a4 0004a4 000004 00 WA 0 0 4
[19] .dynamic DYNAMIC 080494a8 0004a8 0000c8 08 WA 5 0 4
[20] .got PROGBITS 08049570 000570 000004 04 WA 0 0 4
[21] .got.plt PROGBITS 08049574 000574 000014 04 WA 0 0 4
[22] .data PROGBITS 08049588 000588 00000c 00 WA 0 0 4
[23] .bss NOBITS 08049594 000594 000004 00 WA 0 0 4
[24] .comment PROGBITS 00000000 000594 000126 00 0 0 1
[25] .debug_aranges PROGBITS 00000000 0006c0 000088 00 0 0 8
[26] .debug_pubnames PROGBITS 00000000 000748 000025 00 0 0 1
[27] .debug_info PROGBITS 00000000 00076d 00022b 00 0 0 1
[28] .debug_abbrev PROGBITS 00000000 000998 000076 00 0 0 1
[29] .debug_line PROGBITS 00000000 000a0e 0001bb 00 0 0 1
[30] .debug_str PROGBITS 00000000 000bc9 0000bf 01 MS 0 0 1
[31] .shstrtab STRTAB 00000000 000c88 000127 00 0 0 1
[32] .symtab SYMTAB 00000000 001300 000520 10 33 63 4
[33] .strtab STRTAB 00000000 001820 0002d2 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.
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000034 0x08048034 0x08048034 0x000e0 0x000e0 R E 0x4
INTERP 0x000114 0x08048114 0x08048114 0x00013 0x00013 R 0x1
[Requesting program interpreter: /lib/ld-linux.so.2]
LOAD 0x000000 0x08048000 0x08048000 0x00494 0x00494 R E 0x1000
LOAD 0x000494 0x08049494 0x08049494 0x00100 0x00104 RW 0x1000
DYNAMIC 0x0004a8 0x080494a8 0x080494a8 0x000c8 0x000c8 RW 0x4
NOTE 0x000128 0x08048128 0x08048128 0x00020 0x00020 R 0x4
GNU_STACK 0x000000 0x00000000 0x00000000 0x00000 0x00000 RW 0x4
Section to Segment mapping:
Segment Sections...
00
01 .interp
02 .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version
.gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame
03 .ctors .dtors .jcr .dynamic .got .got.plt .data .bss
04 .dynamic
05 .note.ABI-tag
06
Dynamic section at offset 0x4a8 contains 20 entries:
Tag Type Name/Value
0x00000001 (NEEDED) Shared library: [libc.so.6]
0x0000000c (INIT) 0x8048278
0x0000000d (FINI) 0x8048458
0x00000004 (HASH) 0x8048148
0x00000005 (STRTAB) 0x80481d4
0x00000006 (SYMTAB) 0x8048174
0x0000000a (STRSZ) 94 (bytes)
0x0000000b (SYMENT) 16 (bytes)
0x00000015 (DEBUG) 0x0
0x00000003 (PLTGOT) 0x8049574
0x00000002 (PLTRELSZ) 16 (bytes)
0x00000014 (PLTREL) REL
0x00000017 (JMPREL) 0x8048268
0x00000011 (REL) 0x8048260
0x00000012 (RELSZ) 8 (bytes)
0x00000013 (RELENT) 8 (bytes)
0x6ffffffe (VERNEED) 0x8048240
0x6fffffff (VERNEEDNUM) 1
0x6ffffff0 (VERSYM) 0x8048232
0x00000000 (NULL) 0x0
Relocation section '.rel.dyn' at offset 0x260 contains 1 entries:
Offset Info Type Sym.Value Sym. Name
08049570 00000506 R_386_GLOB_DAT 00000000 __gmon_start__
Relocation section '.rel.plt' at offset 0x268 contains 2 entries:
Offset Info Type Sym.Value Sym. Name
08049580 00000107 R_386_JUMP_SLOT 00000000 puts
08049584 00000207 R_386_JUMP_SLOT 00000000 __libc_start_main
There are no unwind sections in this file.
Symbol table '.dynsym' contains 6 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 378 FUNC GLOBAL DEFAULT UND [email protected]_2.0 (2)
2: 00000000 230 FUNC GLOBAL DEFAULT UND [email protected]_2.0 (2)
3: 0804847c 4 OBJECT GLOBAL DEFAULT 14 _IO_stdin_used
4: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses
5: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__
Symbol table '.symtab' contains 82 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 08048114 0 SECTION LOCAL DEFAULT 1
2: 08048128 0 SECTION LOCAL DEFAULT 2
3: 08048148 0 SECTION LOCAL DEFAULT 3
4: 08048174 0 SECTION LOCAL DEFAULT 4
5: 080481d4 0 SECTION LOCAL DEFAULT 5
6: 08048232 0 SECTION LOCAL DEFAULT 6
7: 08048240 0 SECTION LOCAL DEFAULT 7
8: 08048260 0 SECTION LOCAL DEFAULT 8
9: 08048268 0 SECTION LOCAL DEFAULT 9
10: 08048278 0 SECTION LOCAL DEFAULT 10
11: 08048290 0 SECTION LOCAL DEFAULT 11
12: 080482c0 0 SECTION LOCAL DEFAULT 12
13: 08048458 0 SECTION LOCAL DEFAULT 13
14: 08048478 0 SECTION LOCAL DEFAULT 14
15: 08048490 0 SECTION LOCAL DEFAULT 15
16: 08049494 0 SECTION LOCAL DEFAULT 16
17: 0804949c 0 SECTION LOCAL DEFAULT 17
18: 080494a4 0 SECTION LOCAL DEFAULT 18
19: 080494a8 0 SECTION LOCAL DEFAULT 19
20: 08049570 0 SECTION LOCAL DEFAULT 20
21: 08049574 0 SECTION LOCAL DEFAULT 21
22: 08049588 0 SECTION LOCAL DEFAULT 22
23: 08049594 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 SECTION LOCAL DEFAULT 30
31: 00000000 0 SECTION LOCAL DEFAULT 31
32: 00000000 0 SECTION LOCAL DEFAULT 32
33: 00000000 0 SECTION LOCAL DEFAULT 33
34: 00000000 0 FILE LOCAL DEFAULT ABS abi-note.S
35: 00000000 0 FILE LOCAL DEFAULT ABS ../sysdeps/i386/elf/start
36: 00000000 0 FILE LOCAL DEFAULT ABS init.c
37: 00000000 0 FILE LOCAL DEFAULT ABS initfini.c
38: 00000000 0 FILE LOCAL DEFAULT ABS /build/buildd/glibc-2.3.6
39: 080482e4 0 FUNC LOCAL DEFAULT 12 call_gmon_start
40: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
41: 08049494 0 OBJECT LOCAL DEFAULT 16 __CTOR_LIST__
42: 0804949c 0 OBJECT LOCAL DEFAULT 17 __DTOR_LIST__
43: 080494a4 0 OBJECT LOCAL DEFAULT 18 __JCR_LIST__
44: 08049594 1 OBJECT LOCAL DEFAULT 23 completed.4463
45: 08049590 0 OBJECT LOCAL DEFAULT 22 p.4462
46: 0804830c 0 FUNC LOCAL DEFAULT 12 __do_global_dtors_aux
47: 0804833b 0 FUNC LOCAL DEFAULT 12 frame_dummy
48: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c
49: 08049498 0 OBJECT LOCAL DEFAULT 16 __CTOR_END__
50: 080494a0 0 OBJECT LOCAL DEFAULT 17 __DTOR_END__
51: 08048490 0 OBJECT LOCAL DEFAULT 15 __FRAME_END__
52: 080494a4 0 OBJECT LOCAL DEFAULT 18 __JCR_END__
53: 0804842c 0 FUNC LOCAL DEFAULT 12 __do_global_ctors_aux
54: 00000000 0 FILE LOCAL DEFAULT ABS initfini.c
55: 00000000 0 FILE LOCAL DEFAULT ABS /build/buildd/glibc-2.3.6
56: 00000000 0 FILE LOCAL DEFAULT ABS hw.c
57: 080494a8 0 OBJECT LOCAL HIDDEN 19 _DYNAMIC
58: 08049494 0 NOTYPE LOCAL HIDDEN ABS __fini_array_end
59: 08049494 0 NOTYPE LOCAL HIDDEN ABS __fini_array_start
60: 08049494 0 NOTYPE LOCAL HIDDEN ABS __init_array_end
61: 08049574 0 OBJECT LOCAL HIDDEN 21 _GLOBAL_OFFSET_TABLE_
62: 08049494 0 NOTYPE LOCAL HIDDEN ABS __init_array_start
63: 08048478 4 OBJECT GLOBAL DEFAULT 14 _fp_hw
64: 0804958c 0 OBJECT GLOBAL HIDDEN 22 __dso_handle
65: 080483e1 74 FUNC GLOBAL DEFAULT 12 __libc_csu_fini
66: 00000000 378 FUNC GLOBAL DEFAULT UND puts@@GLIBC_2.0
67: 08048278 0 FUNC GLOBAL DEFAULT 10 _init
68: 080482c0 0 FUNC GLOBAL DEFAULT 12 _start
69: 08048390 81 FUNC GLOBAL DEFAULT 12 __libc_csu_init
70: 08049594 0 NOTYPE GLOBAL DEFAULT ABS __bss_start
71: 08048360 47 FUNC GLOBAL DEFAULT 12 main
72: 00000000 230 FUNC GLOBAL DEFAULT UND __libc_start_main@@GLIBC_
73: 08049588 0 NOTYPE WEAK DEFAULT 22 data_start
74: 08048458 0 FUNC GLOBAL DEFAULT 13 _fini
75: 08049594 0 NOTYPE GLOBAL DEFAULT ABS _edata
76: 08048308 0 FUNC GLOBAL HIDDEN 12 __i686.get_pc_thunk.bx
77: 08049598 0 NOTYPE GLOBAL DEFAULT ABS _end
78: 0804847c 4 OBJECT GLOBAL DEFAULT 14 _IO_stdin_used
79: 08049588 0 NOTYPE GLOBAL DEFAULT 22 __data_start
80: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses
81: 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%) 20.0%
2 2 ( 66.7%) 100.0%
Version symbols section '.gnu.version' contains 6 entries:
Addr: 0000000008048232 Offset: 0x000232 Link: 4 (.dynsym)
000: 0 (*local*) 2 (GLIBC_2.0) 2 (GLIBC_2.0) 1 (*global*)
004: 0 (*local*) 0 (*local*)
Version needs section '.gnu.version_r' contains 1 entries:
Addr: 0x0000000008048240 Offset: 0x000240 Link to section: 5 (.dynstr)
000000: Version: 1 File: libc.so.6 Cnt: 1
0x0010: Name: GLIBC_2.0 Flags: none Version: 2
Notes at offset 0x00000128 with length 0x00000020:
Owner Data size Description
GNU 0x00000010 NT_VERSION (version)
|
正如從該輸出中看到的,簡單的 a.out Hello World 檔案中包含了大量有價值的細節資訊,包括版本資訊、柱狀圖、各種符号類型的表格,等等。通過使用本文中介紹的這幾種工具分析目标檔案,您可以慢慢地對可執行程式進行研究。
除了所有這些段之外,編譯器可以将調試資訊放入到目标檔案中,并且還可以顯示這些資訊。輸入下面的指令,仔細分析編譯器的輸出(假設您扮演了調試程式的角色):
readelf --debug-dump a.out | less
|
這個指令生成的輸出如清單 5 所示。調試工具,如 GDB,可以讀取這些調試資訊,并且當程式在調試器中運作的同時,您可以使用該工具顯示更具描述性的标記,而不是對代碼進行反彙編時的原始位址值。
清單 5. 該程式中的調試資訊
The section .debug_aranges contains:
Length: 28
Version: 2
Offset into .debug_info: 0
Pointer Size: 4
Segment Size: 0
Address Length
080482c0 34
Length: 52
Version: 2
Offset into .debug_info: 10b
Pointer Size: 4
Segment Size: 0
Address Length
08048308 4
08048458 18
08048278 11
080482e4 36
Length: 44
Version: 2
Offset into .debug_info: 19b
Pointer Size: 4
Segment Size: 0
Address Length
08048308 4
0804846f 6
0804828d 2
Contents of the .debug_pubnames section:
Length: 33
Version: 2
Offset into .debug_info section: 122
Size of area in .debug_info section: 145
Offset Name
121 _IO_stdin_used
The section .debug_info contains:
Compilation Unit @ offset 0x0:
Length: 118
Version: 2
Abbrev Offset: 0
Pointer Size: 4
<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
DW_AT_stmt_list : 0
DW_AT_low_pc : 0x80482c0
DW_AT_high_pc : 0x80482e2
DW_AT_name : ../sysdeps/i386/elf/start.S
DW_AT_comp_dir : /build/buildd/glibc-2.3.6/build-tree/glibc-2.3.6/csu
DW_AT_producer : GNU AS 2.16.91
DW_AT_language : 32769 (MIPS assembler)
Compilation Unit @ offset 0x7a:
Length: 141
Version: 2
Abbrev Offset: 20
Pointer Size: 4
<0><85>: Abbrev Number: 1 (DW_TAG_compile_unit)
DW_AT_stmt_list : 0x5b
DW_AT_high_pc : 0x80482e4
DW_AT_low_pc : 0x80482e4
DW_AT_producer : (indirect string, offset: 0x62): GNU C 3.4.6
DW_AT_language : 1 (ANSI C)
DW_AT_name : (indirect string, offset: 0x0): init.c
DW_AT_comp_dir : (indirect string, offset: 0x11): /build/buildd/...
<1><9f>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x90): unsigned int
DW_AT_byte_size : 4
DW_AT_encoding : 7 (unsigned)
<1><a6>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x54): unsigned char
DW_AT_byte_size : 1
DW_AT_encoding : 8 (unsigned char)
<1><ad>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x9d): short unsigned int
DW_AT_byte_size : 2
DW_AT_encoding : 7 (unsigned)
<1><b4>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x8b): long unsigned int
DW_AT_byte_size : 4
DW_AT_encoding : 7 (unsigned)
<1><bb>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x56): signed char
DW_AT_byte_size : 1
DW_AT_encoding : 6 (signed char)
<1><c2>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x7): short int
DW_AT_byte_size : 2
DW_AT_encoding : 5 (signed)
<1><c9>: Abbrev Number: 3 (DW_TAG_base_type)
DW_AT_name : int
DW_AT_byte_size : 4
DW_AT_encoding : 5 (signed)
<1><d0>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x46): long long int
DW_AT_byte_size : 8
DW_AT_encoding : 5 (signed)
<1><d7>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x86): long long unsigned int
DW_AT_byte_size : 8
DW_AT_encoding : 7 (unsigned)
<1><de>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x4b): long int
DW_AT_byte_size : 4
DW_AT_encoding : 5 (signed)
<1><e5>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x90): unsigned int
DW_AT_byte_size : 4
DW_AT_encoding : 7 (unsigned)
<1><ec>: Abbrev Number: 2 (DW_TAG_base_type)
DW_AT_name : (indirect string, offset: 0x5d): char
DW_AT_byte_size : 1
DW_AT_encoding : 6 (signed char)
<1><f3>: Abbrev Number: 4 (DW_TAG_variable)
DW_AT_name : (indirect string, offset: 0xb0): _IO_stdin_used
DW_AT_decl_file : 1
DW_AT_decl_line : 25
DW_AT_type : <105>
DW_AT_external : 1
DW_AT_location : 5 byte block: 3 7c 84 4 8 (DW_OP_addr: 804847c)
<1><105>: Abbrev Number: 5 (DW_TAG_const_type)
DW_AT_type : <c9>
Compilation Unit @ offset 0x10b:
Length: 140
Version: 2
Abbrev Offset: 86
Pointer Size: 4
<0><116>: Abbrev Number: 1 (DW_TAG_compile_unit)
DW_AT_stmt_list : 0x82
DW_AT_name : /build/buildd/glibc-2.3.6/build-tree/i386-libc/csu/crti.S
DW_AT_comp_dir : /build/buildd/glibc-2.3.6/build-tree/glibc-2.3.6/csu
DW_AT_producer : GNU AS 2.16.91
DW_AT_language : 32769 (MIPS assembler)
Compilation Unit @ offset 0x19b:
Length: 140
Version: 2
Abbrev Offset: 102
Pointer Size: 4
<0><1a6>: Abbrev Number: 1 (DW_TAG_compile_unit)
DW_AT_stmt_list : 0x12f
DW_AT_name : /build/buildd/glibc-2.3.6/build-tree/i386-libc/csu/crtn.S
DW_AT_comp_dir : /build/buildd/glibc-2.3.6/build-tree/glibc-2.3.6/csu
DW_AT_producer : GNU AS 2.16.91
DW_AT_language : 32769 (MIPS assembler)
Contents of the .debug_abbrev section:
Number TAG
1 DW_TAG_compile_unit [no children]
DW_AT_stmt_list DW_FORM_data4
DW_AT_low_pc DW_FORM_addr
DW_AT_high_pc DW_FORM_addr
DW_AT_name DW_FORM_string
DW_AT_comp_dir DW_FORM_string
DW_AT_producer DW_FORM_string
DW_AT_language DW_FORM_data2
Number TAG
1 DW_TAG_compile_unit [has children]
DW_AT_stmt_list DW_FORM_data4
DW_AT_high_pc DW_FORM_addr
DW_AT_low_pc DW_FORM_addr
DW_AT_producer DW_FORM_strp
DW_AT_language DW_FORM_data1
DW_AT_name DW_FORM_strp
DW_AT_comp_dir DW_FORM_strp
2 DW_TAG_base_type [no children]
DW_AT_name DW_FORM_strp
DW_AT_byte_size DW_FORM_data1
DW_AT_encoding DW_FORM_data1
3 DW_TAG_base_type [no children]
DW_AT_name DW_FORM_string
DW_AT_byte_size DW_FORM_data1
DW_AT_encoding DW_FORM_data1
4 DW_TAG_variable [no children]
DW_AT_name DW_FORM_strp
DW_AT_decl_file DW_FORM_data1
DW_AT_decl_line DW_FORM_data1
DW_AT_type DW_FORM_ref4
DW_AT_external DW_FORM_flag
DW_AT_location DW_FORM_block1
5 DW_TAG_const_type [no children]
DW_AT_type DW_FORM_ref4
Number TAG
1 DW_TAG_compile_unit [no children]
DW_AT_stmt_list DW_FORM_data4
DW_AT_name DW_FORM_string
DW_AT_comp_dir DW_FORM_string
DW_AT_producer DW_FORM_string
DW_AT_language DW_FORM_data2
Number TAG
1 DW_TAG_compile_unit [no children]
DW_AT_stmt_list DW_FORM_data4
DW_AT_name DW_FORM_string
DW_AT_comp_dir DW_FORM_string
DW_AT_producer DW_FORM_string
DW_AT_language DW_FORM_data2
Dump of debug contents of section .debug_line:
Length: 87
DWARF Version: 2
Prologue Length: 50
Minimum Instruction Length: 1
Initial value of 'is_stmt': 1
Line Base: -5
Line Range: 14
Opcode Base: 13
(Pointer size: 4)
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
Opcode 10 has 0 args
Opcode 11 has 0 args
Opcode 12 has 1 args
The Directory Table:
../sysdeps/i386/elf
The File Name Table:
Entry Dir Time Size Name
1 1 0 0 start.S
Line Number Statements:
Extended opcode 2: set Address to 0x80482c0
Advance Line by 64 to 65
Copy
Special opcode 38: advance Address by 2 to 0x80482c2 and Line by 5 to 70
Special opcode 20: advance Address by 1 to 0x80482c3 and Line by 1 to 71
Special opcode 39: advance Address by 2 to 0x80482c5 and Line by 6 to 77
Special opcode 48: advance Address by 3 to 0x80482c8 and Line by 1 to 78
Special opcode 24: advance Address by 1 to 0x80482c9 and Line by 5 to 83
Special opcode 21: advance Address by 1 to 0x80482ca and Line by 2 to 85
Advance Line by 24 to 109
Special opcode 19: advance Address by 1 to 0x80482cb and Line by 0 to 109
Special opcode 76: advance Address by 5 to 0x80482d0 and Line by 1 to 110
Special opcode 77: advance Address by 5 to 0x80482d5 and Line by 2 to 112
Special opcode 20: advance Address by 1 to 0x80482d6 and Line by 1 to 113
Special opcode 21: advance Address by 1 to 0x80482d7 and Line by 2 to 115
Special opcode 79: advance Address by 5 to 0x80482dc and Line by 4 to 119
Special opcode 78: advance Address by 5 to 0x80482e1 and Line by 3 to 122
Advance PC by 1 to 0x80482e2
Extended opcode 1: End of Sequence
Length: 35
DWARF Version: 2
Prologue Length: 29
Minimum Instruction Length: 1
Initial value of 'is_stmt': 1
Line Base: -5
Line Range: 14
Opcode Base: 13
(Pointer size: 4)
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
Opcode 10 has 0 args
Opcode 11 has 0 args
Opcode 12 has 1 args
The Directory Table is empty.
The File Name Table:
Entry Dir Time Size Name
1 0 0 0 init.c
Line Number Statements:
Length: 169
DWARF Version: 2
Prologue Length: 80
Minimum Instruction Length: 1
Initial value of 'is_stmt': 1
Line Base: -5
Line Range: 14
Opcode Base: 13
(Pointer size: 4)
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
Opcode 10 has 0 args
Opcode 11 has 0 args
Opcode 12 has 1 args
The Directory Table:
/build/buildd/glibc-2.3.6/build-tree/i386-libc/csu
The File Name Table:
Entry Dir Time Size Name
1 1 0 0 crti.S
Line Number Statements:
Extended opcode 2: set Address to 0x8048308
Advance Line by 64 to 65
Copy
Special opcode 48: advance Address by 3 to 0x804830b and Line by 1 to 66
Advance PC by 1 to 0x804830c
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x8048458
Advance Line by 46 to 47
Copy
Special opcode 20: advance Address by 1 to 0x8048459 and Line by 1 to 48
Special opcode 34: advance Address by 2 to 0x804845b and Line by 1 to 49
Special opcode 20: advance Address by 1 to 0x804845c and Line by 1 to 50
Special opcode 76: advance Address by 5 to 0x8048461 and Line by 1 to 51
Special opcode 90: advance Address by 6 to 0x8048467 and Line by 1 to 52
Advance PC by 3 to 0x804846a
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x8048278
Advance Line by 31 to 32
Copy
Special opcode 20: advance Address by 1 to 0x8048279 and Line by 1 to 33
Special opcode 34: advance Address by 2 to 0x804827b and Line by 1 to 34
Special opcode 48: advance Address by 3 to 0x804827e and Line by 1 to 35
Advance PC by 5 to 0x8048283
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x80482e4
Advance Line by 10 to 11
Copy
Special opcode 20: advance Address by 1 to 0x80482e5 and Line by 1 to 12
Special opcode 34: advance Address by 2 to 0x80482e7 and Line by 1 to 13
Special opcode 20: advance Address by 1 to 0x80482e8 and Line by 1 to 14
Special opcode 76: advance Address by 5 to 0x80482ed and Line by 1 to 15
Special opcode 90: advance Address by 6 to 0x80482f3 and Line by 1 to 16
Special opcode 48: advance Address by 3 to 0x80482f6 and Line by 1 to 17
Special opcode 90: advance Address by 6 to 0x80482fc and Line by 1 to 18
Special opcode 34: advance Address by 2 to 0x80482fe and Line by 1 to 19
Special opcode 34: advance Address by 2 to 0x8048300 and Line by 1 to 20
Special opcode 35: advance Address by 2 to 0x8048302 and Line by 2 to 22
Special opcode 48: advance Address by 3 to 0x8048305 and Line by 1 to 23
Special opcode 20: advance Address by 1 to 0x8048306 and Line by 1 to 24
Special opcode 20: advance Address by 1 to 0x8048307 and Line by 1 to 25
Advance PC by 1 to 0x8048308
Extended opcode 1: End of Sequence
Length: 136
DWARF Version: 2
Prologue Length: 80
Minimum Instruction Length: 1
Initial value of 'is_stmt': 1
Line Base: -5
Line Range: 14
Opcode Base: 13
(Pointer size: 4)
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
Opcode 10 has 0 args
Opcode 11 has 0 args
Opcode 12 has 1 args
The Directory Table:
/build/buildd/glibc-2.3.6/build-tree/i386-libc/csu
The File Name Table:
Entry Dir Time Size Name
1 1 0 0 crtn.S
Line Number Statements:
Extended opcode 2: set Address to 0x8048308
Advance Line by 33 to 34
Copy
Special opcode 48: advance Address by 3 to 0x804830b and Line by 1 to 35
Advance PC by 1 to 0x804830c
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x804846f
Advance Line by 18 to 19
Copy
Special opcode 48: advance Address by 3 to 0x8048472 and Line by 1 to 20
Special opcode 20: advance Address by 1 to 0x8048473 and Line by 1 to 21
Special opcode 20: advance Address by 1 to 0x8048474 and Line by 1 to 22
Advance PC by 1 to 0x8048475
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x804828d
Advance Line by 9 to 10
Copy
Special opcode 20: advance Address by 1 to 0x804828e and Line by 1 to 11
Advance PC by 1 to 0x804828f
Extended opcode 1: End of Sequence
Contents of the .debug_str section:
0x00000000 696e6974 2e630073 686f7274 20696e74 init.c.short int
0x00000010 002f6275 696c642f 6275696c 64642f67 ./build/buildd/g
0x00000020 6c696263 2d322e33 2e362f62 75696c64 libc-2.3.6/build
0x00000030 2d747265 652f676c 6962632d 322e332e -tree/glibc-2.3.
0x00000040 362f6373 75006c6f 6e67206c 6f6e6720 6/csu.long long
0x00000050 696e7400 756e7369 676e6564 20636861 int.unsigned cha
0x00000060 7200474e 55204320 332e342e 36202855 r.GNU C 3.4.6 (U
0x00000070 62756e74 7520332e 342e362d 31756275 buntu 3.4.6-1ubu
0x00000080 6e747532 29006c6f 6e67206c 6f6e6720 ntu2).long long
0x00000090 756e7369 676e6564 20696e74 0073686f unsigned int.sho
0x000000a0 72742075 6e736967 6e656420 696e7400 rt unsigned int.
0x000000b0 5f494f5f 73746469 6e5f7573 656400 _IO_stdin_used.
|
可執行檔案是目标檔案
在 UNIX 中,可執行檔案是 目标檔案,并且您可以像對 a.out 檔案那樣對它們進行分析。可以進行一次有益的練習,更改到 /bin 或 /local/bin 目錄,然後針對一些您最常用的指令,如
pwd
、
ps
、
cat
或
rm
,運作
nm
、
objdump
和
readelf
。通常,在您編寫需要某種功能的程式時,如果标準的工具已經提供了這個功能,那麼通過運作
objdump -d <command>
,可以檢視這些工具究竟如何完成這項任務。
如果您傾向于使用編譯器和其他的語言工具,那麼您可以對組成計算機系統的各種目标檔案進行仔細研究,并且您将會發現這項工作是非常值得的。UNIX 作業系統具有許多層次,那些通過工具檢視目标檔案所公開的層次,非常接近底層硬體。通過這種方式,您可以真實地接觸到系統。
結束語
研究目标檔案可以極大地加深您對 UNIX 作業系統的認識,并且可以更深入地了解如何對軟體的源代碼進行彙編。我鼓勵您使用本文中介紹的目标檔案工具對系統中 /bin 或 /local/bin 目錄中的程式進行分析,仔細研究其輸出結果,并找出您的硬體制造商所提供的系統文檔。
參考資料
學習
- 您可以參閱本文在 developerWorks 全球站點上的 英文原文 。
- Executable file formats:有關可執行檔案格式的更多内容,請通路 Wikipedia。
- Executable and Linking Format (ELF):通路加州大學 Davis 站點以獲得更多的資訊。
- AIX and UNIX 文章:檢視 William Zimmerly 撰寫的其他文章。
- AIX and UNIX developerWorks 專區提供了大量與 AIX 系統管理的所有方面相關并擴充您的 UNIX 技能的資訊。
- New to AIX and UNIX:通路“New to AIX and UNIX”頁面以了解更多關于 AIX 和 UNIX 的内容。
- developerWorks 技術事件和網絡廣播:跟蹤最新的 developerWorks 技術事件與網絡廣播。
- AIX 5L Wiki:AIX 相關技術資訊的協作環境。
- 技術書店:浏覽這個站點,以了解相關的書籍和其他技術主題。
- 播客:收聽播客并與 IBM 技術專家保持同步。