Linux环境下C语言编译、运行的底层工作原理.doc

Linux环境下C语言编译、运行的底层工作原理（3）借助readelf工具和hexdump工具查看目标文件的详细内容图1 linux环境下源代码、汇编代码、目标文件和可执行文件之间的关系图1反应的是linux环境下源代码（.c）、汇编代码（.s）、目标文件（.o）和可执行文件（.out）之间的关系。本文中，我们将要借助readelf工具和hexdump工具来查看目标文件的详细内容，因此要通过gcc-c命令生成print_address.o目标文件。由以上信息不难发现：1. ELF Header的起始文件地址是0，大小是64Bytes。由于文件开头第一字节的地址定义为0， 因此ELF Header的文件地址范围是0x000x3f。2. Section Header Table在文件中的起始位置是752，Section Header Table中有13个表项，每个表项占64bytes，13个表项共占832bytes（832=0x340）。因此Section Header Table对应的文件地址范围是0x2f00x62f。将上面截取的13个表项相关信息进行整理，注意Offset项对应起始文件地址，Size也就是section的size。整理后可以得到表1：表1 各个section及其对应的文件地址范围Section或Header文件地址范围SizeELF Header0x000x3f0x40.text0x400x12b0xec.data0x12c0.bss0x12c0x1330x08.rodata0x12c0x1e50xba.en_ment0x2600x28d0x2e.note.GNU-stack0x28e0.shstrtab0x28e0x2ee0x61Section Header Table0x2f00x62f0x340.symtab0x6300x7c70x198.strtab0x7c80x8370x70.rela.text0x8380xabf0x288.rela.en_frame0xac00xb070x48表1中有几个相邻的section之间首位地址不衔接。例如.rodata的尾地址是0x1e5，但临近的下一个section即.en_frame这个section的首地址并不是预期的0x1e6而是0x1e8。这里要看表项中的最后一个Align，有点类似内存对其的概念。.en_frame的Align值是8，这个section对应的地址必须是8的整数倍。因此.en_frame的起始文件地址是0x1e8而不是0x1e6。接下来我们用hexdump工具查看目标文件（.o）的具体内容。ELF Header，可以与readelf工具反馈的ELF Header信息对照着看。lirenjielocalhost $ hexdump -C print_address.o00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF.|00000010 01 00 3e 00 01 00 00 00 00 00 00 00 00 00 00 00 |.|00000020 00 00 00 00 00 00 00 00 f0 02 00 00 00 00 00 00 |.|00000030 00 00 00 00 40 00 00 00 00 00 40 00 0d 00 0a 00 |.|00000040 55 48 89 e5 48 83 ec 10 48 8d 75 fc bf 00 00 00 |UH.H.H.u.|00000050 00 b8 00 00 00 00 e8 00 00 00 00 be 00 00 00 00 |.|00000060 bf 00 00 00 00 b8 00 00 00 00 e8 00 00 00 00 c9 |.|00000070 c3 55 48 89 e5 48 83 ec 10 48 8d 75 fc bf 00 00 |.UH.H.H.u.|00000080 00 00 b8 00 00 00 00 e8 00 00 00 00 c9 c3 55 48 |.UH|00000090 89 e5 48 83 ec 10 be 00 00 00 00 bf 00 00 00 00 |.H.|000000a0 b8 00 00 00 00 e8 00 00 00 00 be 00 00 00 00 bf |.|000000b0 00 00 00 00 b8 00 00 00 00 e8 00 00 00 00 be 00 |.|.text000000c0 00 00 00 bf 00 00 00 00 b8 00 00 00 00 e8 00 00 |.|000000d0 00 00 be 00 00 00 00 bf 00 00 00 00 b8 00 00 00 |.|000000e0 00 e8 00 00 00 00 be 00 00 00 00 bf 00 00 00 00 |.|000000f0 b8 00 00 00 00 e8 00 00 00 00 e8 00 00 00 00 e8 |.|00000100 00 00 00 00 bf 04 00 00 00 e8 00 00 00 00 48 89 |.H.|00000110 45 f8 48 8b 75 f8 bf 00 00 00 00 b8 00 00 00 00 |E.H.u.|.rodata section的范围包括了8个字节的.bss section，它们的起始文件地址都是0x12c。00000120 e8 00 00 00 00 b8 00 00 00 00 c9 c3 26 66 75 6e |.&fun|00000130 63 31 5f 76 61 72 69 61 62 6c 65 09 09 25 70 0a |c1_variable.%p.|00000140 00 26 66 75 6e 63 31 5f 73 74 61 74 69 63 5f 76 |.&func1_static_v|00000150 61 72 69 61 62 6c 65 09 25 70 0a 00 26 66 75 6e |ariable.%p.&fun|00000160 63 32 5f 76 61 72 69 61 62 6c 65 09 09 25 70 0a |c2_variable.%p.|00000170 00 26 66 75 6e 63 31 09 09 09 25 70 0a 00 26 66 |.&func1.%p.&f|00000180 75 6e 63 32 09 09 09 25 70 0a 00 61 62 63 00 53 |unc2.%p.abc.S|00000190 74 72 69 6e 67 20 6c 69 74 65 72 61 6c 09 09 25 |tring literal.%|000001a0 70 0a 00 26 67 6c 6f 62 61 6c 5f 76 61 72 69 61 |p.&global_varia|000001b0 62 6c 65 09 25 70 0a 00 26 66 69 6c 65 5f 73 74 |ble.%p.&file_st|000001c0 61 74 69 63 5f 76 61 72 69 61 62 6c 65 09 25 70 |atic_variable.%p|000001d0 0a 00 6d 61 6c 6c 6f 63 20 61 64 64 72 65 73 73 |.malloc address|000001e0 09 09 25 70 0a 00 00 00 14 00 00 00 00 00 00 00 |.%p.|.comment.en_frame000001f0 01 7a 52 00 01 78 10 01 03 0c 07 08 90 01 00 00 |.zR.x.|00000200 1c 00 00 00 1c 00 00 00 00 00 00 00 31 00 00 00 |.1.|00000210 00 41 0e 10 86 02 43 0d 06 00 00 00 00 00 00 00 |.A.C.|00000220 1c 00 00 00 3c 00 00 00 00 00 00 00 1d 00 00 00 |.|00000480 00 00 00 00 00 00 00 00 e8 01 00 00 00 00 00 00 |.|00000490 78 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |x.|000004a0 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|000004b0 39 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 |9.|000004c0 00 00 00 00 00 00 00 00 c0 0a 00 00 00 00 00 00 |.|000004d0 48 00 00 00 00 00 00 00 0b 00 00 00 06 00 00 00 |H.|000004e0 08 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00 |.|000004f0 48 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 |H.|00000500 00 00 00 00 00 00 00 00 60 02 00 00 00 00 00 00 |.|00000510 2e 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000520 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000530 51 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 |Q.|00000540 00 00 00 00 00 00 00 00 8e 02 00 00 00 00 00 00 |.|00000550 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000560 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000570 11 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 |.|00000580 00 00 00 00 00 00 00 00 8e 02 00 00 00 00 00 00 |.|Section Header Table00000590 61 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |a.|000005a0 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|000005b0 01 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 |.|000005c0 00 00 00 00 00 00 00 00 30 06 00 00 00 00 00 00 |.0.|000005d0 98 01 00 00 00 00 00 00 0c 00 00 00 0b 00 00 00 |.|000005e0 08 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00 |.|000005f0 09 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 |.|00000600 00 00 00 00 00 00 00 00 c8 07 00 00 00 00 00 00 |.|00000610 70 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |p.|00000620 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000630 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000640 00 00 00 00 00 00 00 00 01 00 00 00 04 00 f1 ff |.|00000650 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000660 00 00 00 00 03 00 01 00 00 00 00 00 00 00 00 00 |.|00000670 00 00 00 00 00 00 00 00 00 00 00 00 03 00 03 00 |.|00000680 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|00000690 00 00 00 00 03 00 04 00 00 00 00 00 00 00 00 00 |.|000006a0 00 00 00 00 00 00 00 00 11 00 00 00 01 00 04 00 |.|000006b0 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 |.|000006c0 00 00 00 00 03 00 05 00 00 00 00 00 00 00 00 00 |.|000006d0 00 00 00 00 00 00 00 00 2c 00 00 00 01 00 04 00 |.,.|000006e0 04 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 |.|000006f0 00 00 00 00 03 00 06 00 00 00 00 00 00 00 00 00 |.|00000700 00 00 00 00 00 00 00 00 00 00 00 00 03 00 09 00 |.|00000710 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |.|.strtab.symtab00000720 00 00 00 00 03 00 08 00 00 00 00 00 00 00 00 00 |.|00000730 00 00 00 00 00 00 00 00 41 00 00 00 12 00 01 00 |.A.|00000740 00 00 00 00 00 00 00 00 31 00 00 00 00 00 00 00 |.1.|00000750 47 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 |G.|00000760 00 00 00 00 00 00 00 00 4e 00 00 00 12 00 01 00 |.N.|00000770 31 00 00 00 00 00 00 00 1d 00 00 00 00 00 00 00 |1.|00000780 54 00 00 00 12 00 01 00 4e 00 00 00 00 00 00 00 |T.N.|00000790 9e 00 00 00 00 00 00 00 59 00 00 00 11 00 f2 ff |.Y.|000007a0 04 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 |.|000007b0 69 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 |i.|000007c0 00 00 00 00 00 00 00 00 00 70 72 69 6e 74 5f 61 |.print_a|000007d0 64 64 72 65 73 73 2e 63 00 66 75 6e 63 31 5f 73 |ddress.c.func1_s|000007e0 74 61 74 69 63 5f 76 61 72 69 61 62 6c 65 2e 32 |tatic_variable.2|000007f0 36 35 35 00 66 69 6c 65 5f 73 74 61 74 69 63 5f |655.file_static_|00000800 76 61 72 69 61 62 6c 65 00 66 75 6e 63 31 00 70 |variable.func1.p|00000810 72 69 6e 74 66 00 66 75 6e 63 32 00 6d 61 69 6e |rintf.func2.main|00000820 00 67 6c 6f 62 61 6c 5f 76 61 72 69 61 62 6c 65 |.global_variable|00000830 00 6d 61 6c 6c 6f 63 00 0d 00 00 00 00 00 00 00 |.malloc.|00000840 0a 00 00 00 06 00 00 00 00 00 00 00 00 00 00 00 |.|00000850 17 00 00 00 00 00 00 00 02 00 00 00 0c 00 00 00 |.|00000860 fc ff ff ff ff ff ff ff 1c 00 00 00 00 00 00 00 |.|00000870 0a 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 |.|00000880 21 00 00 00 00 00 00 00 0a 00 00 00 06 00 00 00 |!.|00000890 15 00 00 00 00 00 00 00 2b 00 00 00 00 00 00 00 |.+.|000008a0 02 00 00 00 0c 00 00 00 fc ff ff ff ff ff ff ff |.|000008b0 3e 00 00 00 00 00 00 00 0a 00 00 00 06 00 00 00 |.|000008c0 30 00 00 00 00 00 00 00 48 00 00 00 00 00 00 00 |0.H.|000008d0 02 00 00 00 0c 00 00 00 fc ff ff ff ff ff ff ff |.|000008e0 57 00 00 00 00 00 00 00 0a 00 00 00 0b 00 00 00 |W.|000008f0 00 00 00 00 00 00 00 00 5c 00 00 00 00 00 00 00 |.|00000900 0a 00 00 00 06 00 00 00 45 00 00 00 00 00 00 00 |.E.|00000910 66 00 00 00 00 00 00 00 02 00 00 00 0c 00 00 00 |f.|00000920 fc ff ff ff ff ff ff ff 6b 00 00 00 00 00 00 00 |.k.|00000930 0a 00 00 00 0d 00 00 00 00 00 00 00 00 00 00 00 |.|00000940 70 00 00 00 00 00 00 00 0a 00 00 00 06 00 00 00 |p.|00000950 52 00 00 00 00 00 00 00 7a 00 00 00 00 00 00 00 |R.z.|00000960 02 00 00 00 0c 00 00 00 fc ff ff ff ff ff ff ff |.|00000970 7f 00 00 00 00 00 00 00 0a 00 00 00 06 00 00 00 |.|00000980 5f 00 00 00 00 00 00 00 84 00 00 00 00 00 00 00 |_.|00000990 0a 00 00 00 06 00 00 00 63 00 00 00 00 00 00 00 |.c.|000009a0 8e 00 00 00 00 00 00 00 02 00 00 00 0c 00 00 00 |.|000009b0 fc ff ff ff ff ff ff ff 93 00 00 00 00 00 00 00 |.|000009c0 0a 00 00 00 0f 00 00 00 00 00 00 00 00 00 00 00 |.|000009d0 98 00 00 00 00 00 00 00 0a 00 00 00 06 00 00 00 |.|000009e0 77 00 00 00 00 00 00 00 a2 00 00 00 00 00 00 00 |w.|000009f0 02 00 00 00 0c 00 00 00 fc ff ff ff ff ff ff ff |.|00000a00 a7 00 00 00 00 00 00 00 0a 00 00 00 04 00 00 00 |.|00000a10 04 00 00 00 00 00 00 00 ac 00 00 00 00 00 00 00 |.|00000a20 0a 00 00 00 06 00 00 00 8c 00 00 00