逆アセンブルしてみる
objdump というコマンドで逆アセンブルできるみたいなのでちょっとやってみた。とりあえず、以下の HelloWorld プログラムを逆アセンブルしてみる。本当に Just Memo という内容だが。
#include <stdio.h> int main(void){ printf("HelloWorld!\n"); return 0; }
$ gcc hello.c $ ./a.out HelloWorld! $ objdump -d a.out a.out: file format elf64-x86-64 Disassembly of section .init: 00000000004003b8 <_init>: 4003b8: 48 83 ec 08 sub $0x8,%rsp 4003bc: e8 6b 00 00 00 callq 40042c <call_gmon_start> 4003c1: 48 83 c4 08 add $0x8,%rsp 4003c5: c3 retq Disassembly of section .plt: 00000000004003d0 <puts@plt-0x10>: 4003d0: ff 35 f2 04 20 00 pushq 0x2004f2(%rip) # 6008c8 <_GLOBAL_OFFSET_TABLE_+0x8> 4003d6: ff 25 f4 04 20 00 jmpq *0x2004f4(%rip) # 6008d0 <_GLOBAL_OFFSET_TABLE_+0x10> 4003dc: 0f 1f 40 00 nopl 0x0(%rax) 00000000004003e0 <puts@plt>: 4003e0: ff 25 f2 04 20 00 jmpq *0x2004f2(%rip) # 6008d8 <_GLOBAL_OFFSET_TABLE_+0x18> 4003e6: 68 00 00 00 00 pushq $0x0 4003eb: e9 e0 ff ff ff jmpq 4003d0 <_init+0x18> 00000000004003f0 <__libc_start_main@plt>: 4003f0: ff 25 ea 04 20 00 jmpq *0x2004ea(%rip) # 6008e0 <_GLOBAL_OFFSET_TABLE_+0x20> 4003f6: 68 01 00 00 00 pushq $0x1 4003fb: e9 d0 ff ff ff jmpq 4003d0 <_init+0x18> Disassembly of section .text: 0000000000400400 <_start>: 400400: 31 ed xor %ebp,%ebp 400402: 49 89 d1 mov %rdx,%r9 400405: 5e pop %rsi 400406: 48 89 e2 mov %rsp,%rdx 400409: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 40040d: 50 push %rax 40040e: 54 push %rsp 40040f: 49 c7 c0 30 05 40 00 mov $0x400530,%r8 400416: 48 c7 c1 40 05 40 00 mov $0x400540,%rcx 40041d: 48 c7 c7 0c 05 40 00 mov $0x40050c,%rdi 400424: e8 c7 ff ff ff callq 4003f0 <__libc_start_main@plt> 400429: f4 hlt 40042a: 90 nop 40042b: 90 nop 000000000040042c <call_gmon_start>: 40042c: 48 83 ec 08 sub $0x8,%rsp 400430: 48 8b 05 81 04 20 00 mov 0x200481(%rip),%rax # 6008b8 <_DYNAMIC+0x1e0> 400437: 48 85 c0 test %rax,%rax 40043a: 74 02 je 40043e <call_gmon_start+0x12> 40043c: ff d0 callq *%rax 40043e: 48 83 c4 08 add $0x8,%rsp 400442: c3 retq 400443: 90 nop 400444: 90 nop 400445: 90 nop 400446: 90 nop 400447: 90 nop 400448: 90 nop 400449: 90 nop 40044a: 90 nop 40044b: 90 nop 40044c: 90 nop 40044d: 90 nop 40044e: 90 nop 40044f: 90 nop 0000000000400450 <deregister_tm_clones>: 400450: b8 ff 08 60 00 mov $0x6008ff,%eax 400455: 55 push %rbp 400456: 48 2d f8 08 60 00 sub $0x6008f8,%rax 40045c: 48 83 f8 0e cmp $0xe,%rax 400460: 48 89 e5 mov %rsp,%rbp 400463: 77 02 ja 400467 <deregister_tm_clones+0x17> 400465: 5d pop %rbp 400466: c3 retq 400467: b8 00 00 00 00 mov $0x0,%eax 40046c: 48 85 c0 test %rax,%rax 40046f: 74 f4 je 400465 <deregister_tm_clones+0x15> 400471: 5d pop %rbp 400472: bf f8 08 60 00 mov $0x6008f8,%edi 400477: ff e0 jmpq *%rax 400479: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) 0000000000400480 <register_tm_clones>: 400480: b8 f8 08 60 00 mov $0x6008f8,%eax 400485: 55 push %rbp 400486: 48 2d f8 08 60 00 sub $0x6008f8,%rax 40048c: 48 c1 f8 03 sar $0x3,%rax 400490: 48 89 e5 mov %rsp,%rbp 400493: 48 89 c2 mov %rax,%rdx 400496: 48 c1 ea 3f shr $0x3f,%rdx 40049a: 48 01 d0 add %rdx,%rax 40049d: 48 89 c6 mov %rax,%rsi 4004a0: 48 d1 fe sar %rsi 4004a3: 75 02 jne 4004a7 <register_tm_clones+0x27> 4004a5: 5d pop %rbp 4004a6: c3 retq 4004a7: ba 00 00 00 00 mov $0x0,%edx 4004ac: 48 85 d2 test %rdx,%rdx 4004af: 74 f4 je 4004a5 <register_tm_clones+0x25> 4004b1: 5d pop %rbp 4004b2: bf f8 08 60 00 mov $0x6008f8,%edi 4004b7: ff e2 jmpq *%rdx 4004b9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) 00000000004004c0 <__do_global_dtors_aux>: 4004c0: 80 3d 31 04 20 00 00 cmpb $0x0,0x200431(%rip) # 6008f8 <__bss_start> 4004c7: 75 11 jne 4004da <__do_global_dtors_aux+0x1a> 4004c9: 55 push %rbp 4004ca: 48 89 e5 mov %rsp,%rbp 4004cd: e8 7e ff ff ff callq 400450 <deregister_tm_clones> 4004d2: 5d pop %rbp 4004d3: c6 05 1e 04 20 00 01 movb $0x1,0x20041e(%rip) # 6008f8 <__bss_start> 4004da: f3 c3 repz retq 4004dc: 0f 1f 40 00 nopl 0x0(%rax) 00000000004004e0 <frame_dummy>: 4004e0: 48 83 3d e8 01 20 00 cmpq $0x0,0x2001e8(%rip) # 6006d0 <__JCR_END__> 4004e7: 00 4004e8: 74 1b je 400505 <frame_dummy+0x25> 4004ea: b8 00 00 00 00 mov $0x0,%eax 4004ef: 48 85 c0 test %rax,%rax 4004f2: 74 11 je 400505 <frame_dummy+0x25> 4004f4: 55 push %rbp 4004f5: bf d0 06 60 00 mov $0x6006d0,%edi 4004fa: 48 89 e5 mov %rsp,%rbp 4004fd: ff d0 callq *%rax 4004ff: 5d pop %rbp 400500: e9 7b ff ff ff jmpq 400480 <register_tm_clones> 400505: e9 76 ff ff ff jmpq 400480 <register_tm_clones> 40050a: 90 nop 40050b: 90 nop 000000000040050c <main>: 40050c: 55 push %rbp 40050d: 48 89 e5 mov %rsp,%rbp 400510: bf dc 05 40 00 mov $0x4005dc,%edi 400515: e8 c6 fe ff ff callq 4003e0 <puts@plt> 40051a: b8 00 00 00 00 mov $0x0,%eax 40051f: 5d pop %rbp 400520: c3 retq 400521: 90 nop 400522: 90 nop 400523: 90 nop 400524: 90 nop 400525: 90 nop 400526: 90 nop 400527: 90 nop 400528: 90 nop 400529: 90 nop 40052a: 90 nop 40052b: 90 nop 40052c: 90 nop 40052d: 90 nop 40052e: 90 nop 40052f: 90 nop 0000000000400530 <__libc_csu_fini>: 400530: f3 c3 repz retq 400532: 66 66 66 66 66 2e 0f data32 data32 data32 data32 nopw %cs:0x0(%rax,%rax,1) 400539: 1f 84 00 00 00 00 00 0000000000400540 <__libc_csu_init>: 400540: 48 89 6c 24 d8 mov %rbp,-0x28(%rsp) 400545: 4c 89 64 24 e0 mov %r12,-0x20(%rsp) 40054a: 48 8d 2d 77 01 20 00 lea 0x200177(%rip),%rbp # 6006c8 <__init_array_end> 400551: 4c 8d 25 68 01 20 00 lea 0x200168(%rip),%r12 # 6006c0 <__frame_dummy_init_array_entry> 400558: 4c 89 6c 24 e8 mov %r13,-0x18(%rsp) 40055d: 4c 89 74 24 f0 mov %r14,-0x10(%rsp) 400562: 4c 89 7c 24 f8 mov %r15,-0x8(%rsp) 400567: 48 89 5c 24 d0 mov %rbx,-0x30(%rsp) 40056c: 48 83 ec 38 sub $0x38,%rsp 400570: 4c 29 e5 sub %r12,%rbp 400573: 41 89 fd mov %edi,%r13d 400576: 49 89 f6 mov %rsi,%r14 400579: 48 c1 fd 03 sar $0x3,%rbp 40057d: 49 89 d7 mov %rdx,%r15 400580: e8 33 fe ff ff callq 4003b8 <_init> 400585: 48 85 ed test %rbp,%rbp 400588: 74 1c je 4005a6 <__libc_csu_init+0x66> 40058a: 31 db xor %ebx,%ebx 40058c: 0f 1f 40 00 nopl 0x0(%rax) 400590: 4c 89 fa mov %r15,%rdx 400593: 4c 89 f6 mov %r14,%rsi 400596: 44 89 ef mov %r13d,%edi 400599: 41 ff 14 dc callq *(%r12,%rbx,8) 40059d: 48 83 c3 01 add $0x1,%rbx 4005a1: 48 39 eb cmp %rbp,%rbx 4005a4: 72 ea jb 400590 <__libc_csu_init+0x50> 4005a6: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx 4005ab: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp 4005b0: 4c 8b 64 24 18 mov 0x18(%rsp),%r12 4005b5: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13 4005ba: 4c 8b 74 24 28 mov 0x28(%rsp),%r14 4005bf: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15 4005c4: 48 83 c4 38 add $0x38,%rsp 4005c8: c3 retq 4005c9: 90 nop 4005ca: 90 nop 4005cb: 90 nop Disassembly of section .fini: 00000000004005cc <_fini>: 4005cc: 48 83 ec 08 sub $0x8,%rsp 4005d0: 48 83 c4 08 add $0x8,%rsp 4005d4: c3 retq $
うーん、nop というのが結構多いが。意味はよくわからない。
