gdb | マイノリティでいこう

C言語を挫折した人間なので、バイナリとかアセンブラとかは全く分からない。

スクリプト言語サイコーなのだが、どうしたってサーバを動かしていれば

C言語で書かれた、デーモンやら何やらでトラブルは起きる。

先日もデーモンプログラムで、どうも変な挙動をしていたのだが

古いプログラムで、しかもソースから入れていることもあって

なんとか自力で原因究明しなくてはならなくなった。

元々、デバッグ情報付きでコンパイルされてなく

オプションを付けてコンパイルしなくてはならなかったのだが

付けたはずのオプションが、どっかで無効になったのか

gdbで実行すると、デバッグ情報が無いよ! と怒られまくった。

デバッグ情報が付かなかったのは、Makefile内の修正箇所ミスだったのだが

都度gdbを実行してから怒られており、もっと簡単に知る方法はないのかと調査した。

結果

$ readelf -S 実行ファイル

1	$ readelf -S 実行ファイル

だそうです。

試しにやってみた

$ readelf -S httpd
There are 36 section headers, starting at offset 0x4f96dc:

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 009430 04   A  4   0  4
[ 4] .dynsym           DYNSYM          08051578 009578 015070 10   A  5   1  4
[ 5] .dynstr           STRTAB          080665e8 01e5e8 015ea1 00   A  0   0  1
[ 6] .gnu.version      VERSYM          0807c48a 03448a 002a0e 02   A  4   0  2
[ 7] .gnu.version_r    VERNEED         0807ee98 036e98 0000a0 00   A  5   3  4
[ 8] .rel.dyn          REL             0807ef38 036f38 000060 08   A  4   0  4
[ 9] .rel.plt          REL             0807ef98 036f98 0015c8 08   A  4   b  4
[10] .init             PROGBITS        08080560 038560 0000e7 00  AX  0   0 16
[11] .plt              PROGBITS        08080648 038648 002ba0 04  AX  0   0  4
[12] .text             PROGBITS        08083200 03b200 0f73a4 00  AX  0   0 64
[13] .fini             PROGBITS        0817a5a4 1325a4 00001b 00  AX  0   0  4
[14] .rodata           PROGBITS        0817a5c0 1325c0 043ddc 00   A  0   0 32
[15] .eh_frame_hdr     PROGBITS        081be39c 17639c 00004c 00   A  0   0  4
[16] .eh_frame         PROGBITS        081be3e8 1763e8 00021c 00   A  0   0  4
[17] .data             PROGBITS        081bf620 176620 011640 00  WA  0   0 32
[18] .dynamic          DYNAMIC         081d0c60 187c60 000118 08  WA  5   0  4
[19] .ctors            PROGBITS        081d0d78 187d78 000008 00  WA  0   0  4
[20] .dtors            PROGBITS        081d0d80 187d80 000008 00  WA  0   0  4
[21] .jcr              PROGBITS        081d0d88 187d88 000004 00  WA  0   0  4
[22] .got              PROGBITS        081d0d8c 187d8c 000af4 04  WA  0   0  4
[23] .bss              NOBITS          081d1880 188880 00822c 00  WA  0   0 32
[24] .comment          PROGBITS        00000000 188880 0059cd 00      0   0  1
[25] .debug_aranges    PROGBITS        00000000 18e250 000b18 00      0   0  8
[26] .debug_pubnames   PROGBITS        00000000 18ed68 00c7a5 00      0   0  1
[27] .debug_info       PROGBITS        00000000 19b50d 2ee565 00      0   0  1
[28] .debug_abbrev     PROGBITS        00000000 489a72 0125c5 00      0   0  1
[29] .debug_line       PROGBITS        00000000 49c037 02d6a8 00      0   0  1
[30] .debug_frame      PROGBITS        00000000 4c96e0 0101f0 00      0   0  4
[31] .debug_str        PROGBITS        00000000 4d98d0 01cc33 01  MS  0   0  1
[32] .debug_ranges     PROGBITS        00000000 4f6503 003090 00      0   0  1
[33] .shstrtab         STRTAB          00000000 4f9593 000147 00      0   0  1
[34] .symtab           SYMTAB          00000000 4f9c7c 0208b0 10     35 b85  4
[35] .strtab           STRTAB          00000000 51a52c 025b11 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)

$ readelf -S httpd

There are 36 section headers, starting at offset 0x4f96dc:

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 009430 04 A 4 0 4

[ 4] .dynsym DYNSYM 08051578 009578 015070 10 A 5 1 4

[ 5] .dynstr STRTAB 080665e8 01e5e8 015ea1 00 A 0 0 1

[ 6] .gnu.version VERSYM 0807c48a 03448a 002a0e 02 A 4 0 2

[ 7] .gnu.version_r VERNEED 0807ee98 036e98 0000a0 00 A 5 3 4

[ 8] .rel.dyn REL 0807ef38 036f38 000060 08 A 4 0 4

[ 9] .rel.plt REL 0807ef98 036f98 0015c8 08 A 4 b 4

[10] .init PROGBITS 08080560 038560 0000e7 00 AX 0 0 16

[11] .plt PROGBITS 08080648 038648 002ba0 04 AX 0 0 4

[12] .text PROGBITS 08083200 03b200 0f73a4 00 AX 0 0 64

[13] .fini PROGBITS 0817a5a4 1325a4 00001b 00 AX 0 0 4

[14] .rodata PROGBITS 0817a5c0 1325c0 043ddc 00 A 0 0 32

[15] .eh_frame_hdr PROGBITS 081be39c 17639c 00004c 00 A 0 0 4

[16] .eh_frame PROGBITS 081be3e8 1763e8 00021c 00 A 0 0 4

[17] .data PROGBITS 081bf620 176620 011640 00 WA 0 0 32

[18] .dynamic DYNAMIC 081d0c60 187c60 000118 08 WA 5 0 4

[19] .ctors PROGBITS 081d0d78 187d78 000008 00 WA 0 0 4

[20] .dtors PROGBITS 081d0d80 187d80 000008 00 WA 0 0 4

[21] .jcr PROGBITS 081d0d88 187d88 000004 00 WA 0 0 4

[22] .got PROGBITS 081d0d8c 187d8c 000af4 04 WA 0 0 4

[23] .bss NOBITS 081d1880 188880 00822c 00 WA 0 0 32

[24] .comment PROGBITS 00000000 188880 0059cd 00 0 0 1

[25] .debug_aranges PROGBITS 00000000 18e250 000b18 00 0 0 8

[26] .debug_pubnames PROGBITS 00000000 18ed68 00c7a5 00 0 0 1

[27] .debug_info PROGBITS 00000000 19b50d 2ee565 00 0 0 1

[28] .debug_abbrev PROGBITS 00000000 489a72 0125c5 00 0 0 1

[29] .debug_line PROGBITS 00000000 49c037 02d6a8 00 0 0 1

[30] .debug_frame PROGBITS 00000000 4c96e0 0101f0 00 0 0 4

[31] .debug_str PROGBITS 00000000 4d98d0 01cc33 01 MS 0 0 1

[32] .debug_ranges PROGBITS 00000000 4f6503 003090 00 0 0 1

[33] .shstrtab STRTAB 00000000 4f9593 000147 00 0 0 1

[34] .symtab SYMTAB 00000000 4f9c7c 0208b0 10 35 b85 4

[35] .strtab STRTAB 00000000 51a52c 025b11 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)

.debug_infoというセクションが有ると、デバッグ情報付きです。

とあるapacheはデバッグ情報付きでした。

$ readelf -S /usr/lib/firefox/firefox
There are 29 section headers, starting at offset 0x12180:

Section Headers:
[Nr] Name              Type             Address           Offset
Size              EntSize          Flags  Link  Info  Align
[ 0]                   NULL             0000000000000000  00000000
0000000000000000  0000000000000000           0     0     0
[ 1] .interp           PROGBITS         0000000000000270  00000270
000000000000001c  0000000000000000   A       0     0     1
[ 2] .note.ABI-tag     NOTE             000000000000028c  0000028c
0000000000000020  0000000000000000   A       0     0     4
[ 3] .note.gnu.build-i NOTE             00000000000002ac  000002ac
0000000000000024  0000000000000000   A       0     0     4
[ 4] .gnu.hash         GNU_HASH         00000000000002d0  000002d0
0000000000000174  0000000000000000   A       5     0     8
[ 5] .dynsym           DYNSYM           0000000000000448  00000448
0000000000000a20  0000000000000018   A       6     3     8
[ 6] .dynstr           STRTAB           0000000000000e68  00000e68
000000000000082e  0000000000000000   A       0     0     1
[ 7] .gnu.version      VERSYM           0000000000001696  00001696
00000000000000d8  0000000000000002   A       5     0     2
[ 8] .gnu.version_r    VERNEED          0000000000001770  00001770
0000000000000110  0000000000000000   A       6     6     8
[ 9] .rela.dyn         RELA             0000000000001880  00001880
00000000000003a8  0000000000000018   A       5     0     8
[10] .rela.plt         RELA             0000000000001c28  00001c28
0000000000000570  0000000000000018   A       5    12     8
[11] .init             PROGBITS         0000000000002198  00002198
0000000000000018  0000000000000000  AX       0     0     4
[12] .plt              PROGBITS         00000000000021b0  000021b0
00000000000003b0  0000000000000010  AX       0     0     16
[13] .text             PROGBITS         0000000000002560  00002560
000000000000ad68  0000000000000000  AX       0     0     16
[14] .fini             PROGBITS         000000000000d2c8  0000d2c8
000000000000000e  0000000000000000  AX       0     0     4
[15] .rodata           PROGBITS         000000000000d2e0  0000d2e0
0000000000000ef4  0000000000000000   A       0     0     16
[16] .eh_frame_hdr     PROGBITS         000000000000e1d4  0000e1d4
0000000000000784  0000000000000000   A       0     0     4
[17] .eh_frame         PROGBITS         000000000000e958  0000e958
0000000000002504  0000000000000000   A       0     0     8
[18] .tbss             NOBITS           0000000000211a20  00011a20
0000000000000009  0000000000000000 WAT       0     0     8
[19] .ctors            PROGBITS         0000000000211a20  00011a20
0000000000000010  0000000000000000  WA       0     0     8
[20] .dtors            PROGBITS         0000000000211a30  00011a30
0000000000000010  0000000000000000  WA       0     0     8
[21] .jcr              PROGBITS         0000000000211a40  00011a40
0000000000000008  0000000000000000  WA       0     0     8
[22] .data.rel.ro      PROGBITS         0000000000211a50  00011a50
0000000000000178  0000000000000000  WA       0     0     16
[23] .dynamic          DYNAMIC          0000000000211bc8  00011bc8
0000000000000200  0000000000000010  WA       6     0     8
[24] .got              PROGBITS         0000000000211dc8  00011dc8
0000000000000238  0000000000000008  WA       0     0     8
[25] .data             PROGBITS         0000000000212000  00012000
0000000000000070  0000000000000000  WA       0     0     16
[26] .bss              NOBITS           0000000000212070  00012070
00000000000003b8  0000000000000000  WA       0     0     16
[27] .gnu_debuglink    PROGBITS         0000000000000000  00012070
000000000000000c  0000000000000000           0     0     1
[28] .shstrtab         STRTAB           0000000000000000  0001207c
00000000000000fe  0000000000000000           0     0     1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)

$ readelf -S /usr/lib/firefox/firefox

There are 29 section headers, starting at offset 0x12180:

Section Headers:

[Nr] Name Type Address Offset

Size EntSize Flags Link Info Align

[ 0] NULL 0000000000000000 00000000

0000000000000000 0000000000000000 0 0 0

[ 1] .interp PROGBITS 0000000000000270 00000270

000000000000001c 0000000000000000 A 0 0 1

[ 2] .note.ABI-tag NOTE 000000000000028c 0000028c

0000000000000020 0000000000000000 A 0 0 4

[ 3] .note.gnu.build-i NOTE 00000000000002ac 000002ac

0000000000000024 0000000000000000 A 0 0 4

[ 4] .gnu.hash GNU_HASH 00000000000002d0 000002d0

0000000000000174 0000000000000000 A 5 0 8

[ 5] .dynsym DYNSYM 0000000000000448 00000448

0000000000000a20 0000000000000018 A 6 3 8

[ 6] .dynstr STRTAB 0000000000000e68 00000e68

000000000000082e 0000000000000000 A 0 0 1

[ 7] .gnu.version VERSYM 0000000000001696 00001696

00000000000000d8 0000000000000002 A 5 0 2

[ 8] .gnu.version_r VERNEED 0000000000001770 00001770

0000000000000110 0000000000000000 A 6 6 8

[ 9] .rela.dyn RELA 0000000000001880 00001880

00000000000003a8 0000000000000018 A 5 0 8

[10] .rela.plt RELA 0000000000001c28 00001c28

0000000000000570 0000000000000018 A 5 12 8

[11] .init PROGBITS 0000000000002198 00002198

0000000000000018 0000000000000000 AX 0 0 4

[12] .plt PROGBITS 00000000000021b0 000021b0

00000000000003b0 0000000000000010 AX 0 0 16

[13] .text PROGBITS 0000000000002560 00002560

000000000000ad68 0000000000000000 AX 0 0 16

[14] .fini PROGBITS 000000000000d2c8 0000d2c8

000000000000000e 0000000000000000 AX 0 0 4

[15] .rodata PROGBITS 000000000000d2e0 0000d2e0

0000000000000ef4 0000000000000000 A 0 0 16

[16] .eh_frame_hdr PROGBITS 000000000000e1d4 0000e1d4

0000000000000784 0000000000000000 A 0 0 4

[17] .eh_frame PROGBITS 000000000000e958 0000e958

0000000000002504 0000000000000000 A 0 0 8

[18] .tbss NOBITS 0000000000211a20 00011a20

0000000000000009 0000000000000000 WAT 0 0 8

[19] .ctors PROGBITS 0000000000211a20 00011a20

0000000000000010 0000000000000000 WA 0 0 8

[20] .dtors PROGBITS 0000000000211a30 00011a30

0000000000000010 0000000000000000 WA 0 0 8

[21] .jcr PROGBITS 0000000000211a40 00011a40

0000000000000008 0000000000000000 WA 0 0 8

[22] .data.rel.ro PROGBITS 0000000000211a50 00011a50

0000000000000178 0000000000000000 WA 0 0 16

[23] .dynamic DYNAMIC 0000000000211bc8 00011bc8

0000000000000200 0000000000000010 WA 6 0 8

[24] .got PROGBITS 0000000000211dc8 00011dc8

0000000000000238 0000000000000008 WA 0 0 8

[25] .data PROGBITS 0000000000212000 00012000

0000000000000070 0000000000000000 WA 0 0 16

[26] .bss NOBITS 0000000000212070 00012070

00000000000003b8 0000000000000000 WA 0 0 16

[27] .gnu_debuglink PROGBITS 0000000000000000 00012070

000000000000000c 0000000000000000 0 0 1

[28] .shstrtab STRTAB 0000000000000000 0001207c

00000000000000fe 0000000000000000 0 0 1

Key to Flags:

W (write), A (alloc), X (execute), M (merge), S (strings), l (large)

I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)

O (extra OS processing required) o (OS specific), p (processor specific)

ubuntu 12.04 amd64にパッケージで入れたfirefoxは.debug_infoというセクションはありません。

.gnu_debuglink があやしい気がしますが詳細は調べてません。

タグ: gdb

disownしたプロセスの標準出力や標準エラーを後から保存する

readelfなんて使ったことないし、バイナリに弱すぎ