Linux内核代码布局

上文参考：http://www.cnblogs.com/long123king/p/3545991.html

先分析一下linker script的语法。

#ifdef CONFIG_X86_32
#define LOAD_OFFSET __PAGE_OFFSET
#else
#define LOAD_OFFSET __START_KERNEL_map
#endif

    /* Text and read-only data */
    .text :  AT(ADDR(.text) - LOAD_OFFSET) {
        _text = .;
        /* bootstrapping code */
        HEAD_TEXT
#ifdef CONFIG_X86_32
        . = ALIGN(PAGE_SIZE);
        *(.text..page_aligned)
#endif
        . = ALIGN(8);
        _stext = .;
        TEXT_TEXT
        SCHED_TEXT
        LOCK_TEXT
        KPROBES_TEXT
        ENTRY_TEXT
        IRQENTRY_TEXT
        *(.fixup)
        *(.gnu.warning)
        /* End of text section */
        _etext = .;
    } :text = 0x9090

这一段定义了.text section中的内容，AT(ADDR(.text) - LOAD_OFFSET)定义了这个section的LMA(Load Memory Address)，说白了，而通过.定义的是VMA(Virtual Memory Address)。在x86平台，二者没有区别，都对应相对于加载起始点(LOAD_OFFSET，即0xC0000000, 3GB)的偏移地址。

:text = 0x9090指明这个.section要加载到text segment段中，0x9090指明了用于填充由于section对齐而产生的空隙。90是nop汇编语句。

我们看一下生成的内核映像文件vmlinux的布局

daniel@ubuntu:~/linux-3.0$ objdump vmlinux -h

vmlinux:     file format elf32-i386

Sections:
Idx Name                  Size      VMA       LMA       File off  Algn
  0 .interp               00000013  08048114  08048114  00000114  2**0                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  1 .init.text            0000b35f  08049000  08049000  00001000  2**0                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  2 .gnu.hash             000002b0  08055000  08055000  0000d000  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  3 .dynsym               00000b00  080552b0  080552b0  0000d2b0  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  4 .dynstr               00000622  08055db0  08055db0  0000ddb0  2**0                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  5 .gnu.version          00000160  080563d2  080563d2  0000e3d2  2**1                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  6 .gnu.version_r        000000a0  08056534  08056534  0000e534  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  7 .rel.got              00000008  080565d4  080565d4  0000e5d4  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  8 .rel.bss              00000010  080565dc  080565dc  0000e5dc  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  9 .rel.plt              00000460  080565ec  080565ec  0000e5ec  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 10 .init                 0000002e  08056a4c  08056a4c  0000ea4c  2**2                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 11 .plt                  000008d0  08056a80  08056a80  0000ea80  2**4                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 12 .text                 0016bcb0  08057350  08057350  0000f350  2**4                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 13 .syscall_stub         000000cc  081c3000  081c3000  0017b000  2**0                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 14 .fini                 0000001a  081c30cc  081c30cc  0017b0cc  2**2                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 15 .rodata               000592b0  081c4000  081c4000  0017c000  2**5                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 16 .eh_frame_hdr         00012554  0821d2b0  0821d2b0  001d52b0  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 17 __ksymtab             00004698  0822f808  0822f808  001e7808  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 18 __ksymtab_gpl         00001598  08233ea0  08233ea0  001ebea0  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 19 __ksymtab_strings     0000c299  08235438  08235438  001ed438  2**0                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 20 __param               00000110  082416d4  082416d4  001f96d4  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 21 __modver              0000081c  082417e4  082417e4  001f97e4  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 22 .note                 00000044  08242000  08242000  001fa000  2**2                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 23 __ex_table            00000130  08242044  08242044  001fa044  2**0                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 24 .uml.setup.init       00000090  08242178  08242178  001fa178  2**2                  CONTENTS, ALLOC, LOAD, DATA
 25 .uml.help.init        00000064  08242208  08242208  001fa208  2**2                  CONTENTS, ALLOC, LOAD, DATA
 26 .init.setup           000002ac  0824226c  0824226c  001fa26c  2**2                  CONTENTS, ALLOC, LOAD, DATA
 27 .initcall.init        00000270  08243000  08243000  001fb000  2**2                  CONTENTS, ALLOC, LOAD, DATA
 28 .con_initcall.init    00000004  08243270  08243270  001fb270  2**2                  CONTENTS, ALLOC, LOAD, DATA
 29 .exitcall             0000005c  08243274  08243274  001fb274  2**2                  CONTENTS, ALLOC, LOAD, DATA
 30 .uml.exitcall         00000024  082432d0  082432d0  001fb2d0  2**2                  CONTENTS, ALLOC, LOAD, DATA
 31 .altinstructions      00000030  082432f4  082432f4  001fb2f4  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 32 .altinstr_replacement 0000000c  08243324  08243324  001fb324  2**0                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 33 .exit.text            000002c3  08243330  08243330  001fb330  2**0                  CONTENTS, ALLOC, LOAD, READONLY, CODE
 34 init.data             00006ea0  08244000  08244000  001fc000  2**2                  CONTENTS, ALLOC, LOAD, DATA
 35 .data                 00014460  0824aea0  0824aea0  00202ea0  2**5                  CONTENTS, ALLOC, LOAD, DATA
 36 .eh_frame             0009fbc0  0825f300  0825f300  00217300  2**2                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 37 .dynamic              000000d8  082feec0  082feec0  002b6ec0  2**2                  CONTENTS, ALLOC, LOAD, DATA
 38 .ctors                00000008  082fef98  082fef98  002b6f98  2**2                  CONTENTS, ALLOC, LOAD, DATA
 39 .dtors                00000008  082fefa0  082fefa0  002b6fa0  2**2                  CONTENTS, ALLOC, LOAD, DATA
 40 .jcr                  00000004  082fefa8  082fefa8  002b6fa8  2**2                  CONTENTS, ALLOC, LOAD, DATA
 41 .got                  00000240  082fefac  082fefac  002b6fac  2**2                  CONTENTS, ALLOC, LOAD, DATA
 42 .bss                  0000d464  082ff200  082ff200  002b71ec  2**5                  ALLOC
 43 .comment              0000002a  00000000  00000000  002b71ec  2**0                  CONTENTS, READONLY
 44 .gnu_debuglink        00000024  00000000  00000000  002b7216  2**0                  CONTENTS, READONLY
 45 .debug_aranges        00005950  00000000  00000000  002b7240  2**3                  CONTENTS, READONLY, DEBUGGING
 46 .debug_info           01322c32  00000000  00000000  002bcb90  2**0                  CONTENTS, READONLY, DEBUGGING
 47 .debug_abbrev         000a2c21  00000000  00000000  015df7c2  2**0                  CONTENTS, READONLY, DEBUGGING
 48 .debug_line           0016b63c  00000000  00000000  016823e3  2**0                  CONTENTS, READONLY, DEBUGGING
 49 .debug_str            0008d834  00000000  00000000  017eda1f  2**0                  CONTENTS, READONLY, DEBUGGING
 50 .debug_loc            002823be  00000000  00000000  0187b253  2**0                  CONTENTS, READONLY, DEBUGGING
 51 .debug_ranges         00058c80  00000000  00000000  01afd618  2**3                  CONTENTS, READONLY, DEBUGGING

daniel@ubuntu:~/linux-3.0$ readelf -S vmlinux
There are 56 section headers, starting at offset 0x1b564bc:

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] .init.text        PROGBITS        08049000 001000 00b35f 00  AX  0   0  1
  [ 3] .gnu.hash         GNU_HASH        08055000 00d000 0002b0 04   A  4   0  4
  [ 4] .dynsym           DYNSYM          080552b0 00d2b0 000b00 10   A  5   1  4
  [ 5] .dynstr           STRTAB          08055db0 00ddb0 000622 00   A  0   0  1
  [ 6] .gnu.version      VERSYM          080563d2 00e3d2 000160 02   A  4   0  2
  [ 7] .gnu.version_r    VERNEED         08056534 00e534 0000a0 00   A  5   2  4
  [ 8] .rel.got          REL             080565d4 00e5d4 000008 08   A  4  42  4
  [ 9] .rel.bss          REL             080565dc 00e5dc 000010 08   A  4  43  4
  [10] .rel.plt          REL             080565ec 00e5ec 000460 08   A  4  12  4
  [11] .init             PROGBITS        08056a4c 00ea4c 00002e 00  AX  0   0  4
  [12] .plt              PROGBITS        08056a80 00ea80 0008d0 04  AX  0   0 16
  [13] .text             PROGBITS        08057350 00f350 16bcb0 00  AX  0   0 16
  [14] .syscall_stub     PROGBITS        081c3000 17b000 0000cc 00  AX  0   0  1
  [15] .fini             PROGBITS        081c30cc 17b0cc 00001a 00  AX  0   0  4
  [16] .rodata           PROGBITS        081c4000 17c000 0592b0 00   A  0   0 32
  [17] .eh_frame_hdr     PROGBITS        0821d2b0 1d52b0 012554 00   A  0   0  4
  [18] __ksymtab         PROGBITS        0822f808 1e7808 004698 00   A  0   0  4
  [19] __ksymtab_gpl     PROGBITS        08233ea0 1ebea0 001598 00   A  0   0  4
  [20] __ksymtab_strings PROGBITS        08235438 1ed438 00c299 00   A  0   0  1
  [21] __param           PROGBITS        082416d4 1f96d4 000110 00   A  0   0  4
  [22] __modver          PROGBITS        082417e4 1f97e4 00081c 00   A  0   0  4
  [23] .note             NOTE            08242000 1fa000 000044 00  AX  0   0  4
  [24] __ex_table        PROGBITS        08242044 1fa044 000130 00   A  0   0  1
  [25] .uml.setup.init   PROGBITS        08242178 1fa178 000090 00  WA  0   0  4
  [26] .uml.help.init    PROGBITS        08242208 1fa208 000064 00  WA  0   0  4
  [27] .init.setup       PROGBITS        0824226c 1fa26c 0002ac 00  WA  0   0  4
  [28] .initcall.init    PROGBITS        08243000 1fb000 000270 00  WA  0   0  4
  [29] .con_initcall.ini PROGBITS        08243270 1fb270 000004 00  WA  0   0  4
  [30] .exitcall         PROGBITS        08243274 1fb274 00005c 00  WA  0   0  4
  [31] .uml.exitcall     PROGBITS        082432d0 1fb2d0 000024 00  WA  0   0  4
  [32] .altinstructions  PROGBITS        082432f4 1fb2f4 000030 00   A  0   0  4
  [33] .altinstr_replace PROGBITS        08243324 1fb324 00000c 00  AX  0   0  1
  [34] .exit.text        PROGBITS        08243330 1fb330 0002c3 00  AX  0   0  1
  [35] init.data         PROGBITS        08244000 1fc000 006ea0 00  WA  0   0  4
  [36] .data             PROGBITS        0824aea0 202ea0 014460 00  WA  0   0 32
  [37] .eh_frame         PROGBITS        0825f300 217300 09fbc0 00   A  0   0  4
  [38] .dynamic          DYNAMIC         082feec0 2b6ec0 0000d8 08  WA  5   0  4
  [39] .ctors            PROGBITS        082fef98 2b6f98 000008 00  WA  0   0  4
  [40] .dtors            PROGBITS        082fefa0 2b6fa0 000008 00  WA  0   0  4
  [41] .jcr              PROGBITS        082fefa8 2b6fa8 000004 00  WA  0   0  4
  [42] .got              PROGBITS        082fefac 2b6fac 000240 04  WA  0   0  4
  [43] .bss              NOBITS          082ff200 2b71ec 00d464 00  WA  0   0 32
  [44] .comment          PROGBITS        00000000 2b71ec 00002a 01  MS  0   0  1
  [45] .gnu_debuglink    PROGBITS        00000000 2b7216 000024 00      0   0  1
  [46] .debug_aranges    PROGBITS        00000000 2b7240 005950 00      0   0  8
  [47] .debug_info       PROGBITS        00000000 2bcb90 1322c32 00      0   0  1
  [48] .debug_abbrev     PROGBITS        00000000 15df7c2 0a2c21 00      0   0  1
  [49] .debug_line       PROGBITS        00000000 16823e3 16b63c 00      0   0  1
  [50] .debug_str        PROGBITS        00000000 17eda1f 08d834 01  MS  0   0  1
  [51] .debug_loc        PROGBITS        00000000 187b253 2823be 00      0   0  1
  [52] .debug_ranges     PROGBITS        00000000 1afd618 058c80 00      0   0  8
  [53] .shstrtab         STRTAB          00000000 1b56298 000223 00      0   0  1
  [54] .symtab           SYMTAB          00000000 1b56d7c 04e810 10     55 13787  4
  [55] .strtab           STRTAB          00000000 1ba558c 060090 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

daniel@ubuntu:~/linux-3.0$ readelf -s vmlinux | grep _stext
 16700: 08049000     0 NOTYPE  GLOBAL DEFAULT  ABS _stext
daniel@ubuntu:~/linux-3.0$ readelf -s vmlinux | grep _etext
 17219: 081c30e6     0 NOTYPE  GLOBAL DEFAULT  ABS _etext
daniel@ubuntu:~/linux-3.0$ readelf -s vmlinux | grep _sdata
 14535: 081c4000     0 NOTYPE  GLOBAL DEFAULT  ABS _sdata
daniel@ubuntu:~/linux-3.0$ readelf -s vmlinux | grep _edata
 19451: 082ff1ec     0 NOTYPE  GLOBAL DEFAULT  ABS _edata

因此，内核中的.text section被加载到0x08049000~0x081c30e6范围内，而.data section被加载到0x081c4000~0x082ff1ec范围内，这里面的地址都是指物理地址。

    /* Text and read-only data */
    .text :  AT(ADDR(.text) - LOAD_OFFSET) {
        _text = .;
        /* bootstrapping code */
        HEAD_TEXT
#ifdef CONFIG_X86_32
        . = ALIGN(PAGE_SIZE);
        *(.text..page_aligned)
#endif
        . = ALIGN(8);
        _stext = .;
        TEXT_TEXT
        SCHED_TEXT
        LOCK_TEXT
        KPROBES_TEXT
        ENTRY_TEXT
        IRQENTRY_TEXT
        *(.fixup)
        *(.gnu.warning)
        /* End of text section */
        _etext = .;
    } :text = 0x9090

而内核代码段的各个子section，比如HEAD_TEXT, TEXT_TEXT……IRQENTRY_TEXT都按顺序排列在0x08049000~0x081c30e6物理地址范围内。