如何解读vmlinux.lds.S文件

vmlinux.lds.S用于对ld的输出进行组版，这个文件的格式在ld.info手册中有详细的说明。vmlinu
x.lds.S的主要目的是对输出文件中段进行排序，并定义相关的符号名，以下是简要注释。

/* ld script to make i386 Linux kernel
 * Written by Martin Mares ;
 */
OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
OUTPUT_ARCH(i386)        /* 输出格式 */
ENTRY(_start)            /* 定义_start作为入口点 */
SECTIONS
{
  . = PAGE_OFFSET_RAW + 0x100000; /* 定义当前段的偏移量（.代表当前计数器） */
  _text = .;            /* 定义符号_text为当前位置 */
  .text : {        /* 定义段.text （": {"是段定义符）*/
    *(.text)    /* 将所有输入文件中.text段合并到这里 */
    *(.fixup)    /* 将所有输入文件中的.fixup段合并到这里 */
    *(.gnu.warning) /* 将所有输入文件中的.gnu.warning段合并到这里 */
    } = 0x9090    /* 合并中的空隙用0x9090填充 */
            /* 以下的语法含义可以类推 */
  .text.lock : { *(.text.lock) }    /* out-of-line lock text */
  .rodata : { *(.rodata) }
  .kstrtab : { *(.kstrtab) }

  . = ALIGN(16);        /* Exception table */
  __start___ex_table = .;    /* 定义__start_ex_table符号为当前位置 */
  __ex_table : { *(__ex_table) }
  __stop___ex_table = .;

  __start___ksymtab = .;    /* Kernel symbol table */
  __ksymtab : { *(__ksymtab) }
  __stop___ksymtab = .;

  _etext = .;            /* End of text section */

  .data : {            /* Data */
    *(.data)
    CONSTRUCTORS        /* 将C++的构造函数指针段合并到这里 */
    }

  _edata = .;            /* End of data section */

  . = ALIGN(8192);        /* init_task */
  .data.init_task : { *(.data.init_task) }

  . = ALIGN(4096);        /* Init code and data */
  __init_begin = .;
  .text.init : { *(.text.init) }
  .data.init : { *(.data.init) }
  . = ALIGN(4096);        /* 输出计数器在页边界上对齐 */
  __init_end = .;

  . = ALIGN(32);
  .data.cacheline_aligned : { *(.data.cacheline_aligned) }

  . = ALIGN(4096);
  .data.page_aligned : { *(.data.idt) }


  __bss_start = .;        /* BSS */
  .bss : {
    *(.bss)
    }
  _end = . ;

  /* Stabs debugging sections. */
  .stab 0 : { *(.stab) }    /* 0 是段属性，代表段的起始地址 */
  .stabstr 0 : { *(.stabstr) }
  .stab.excl 0 : { *(.stab.excl) }
  .stab.exclstr 0 : { *(.stab.exclstr) }
  .stab.index 0 : { *(.stab.index) }
  .stab.indexstr 0 : { *(.stab.indexstr) }
  .comment 0 : { *(.comment) }
}

编译内核生成vmlinux
 objdump --headers vmlinux 可以对照着看一下。

以下：

 

[root@localhost linux-2.6.18.i686]# objdump --headers vmlinux

vmlinux: file format elf32-i386

Sections:
Idx Name Size VMA LMA File off Algn
  0 .text.head 000000a4 c0400000 00400000 00001000 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .text 0021f9e6 c0401000 00401000 00002000 2**12
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  2 __ex_table 00000ea0 c06209f0 006209f0 002219f0 2**3
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  3 .rodata 0004da85 c0622000 00622000 00223000 2**5
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  4 .pci_fixup 00000608 c066fa88 0066fa88 00270a88 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  5 __ksymtab 00005310 c0670090 00670090 00271090 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  6 __ksymtab_gpl 000015b0 c06753a0 006753a0 002763a0 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  7 __ksymtab_gpl_future 00000018 c0676950 00676950 00277950 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  8 __kcrctab 00002988 c0676968 00676968 00277968 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  9 __kcrctab_gpl 00000ad8 c06792f0 006792f0 0027a2f0 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
 10 __kcrctab_gpl_future 0000000c c0679dc8 00679dc8 0027adc8 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
 11 __ksymtab_strings 0000ea6c c0679de0 00679de0 0027ade0 2**5
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 12 __param 0000080c c0689000 00689000 0028a000 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
 13 .data 00069248 c068a000 0068a000 0028b000 2**7
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 14 .data_nosave 00002000 c06f4000 006f4000 002f5000 2**12
                  CONTENTS, ALLOC, LOAD, DATA
 15 .data.page_aligned 00000800 c06f6000 006f6000 002f7000 2**5
                  CONTENTS, ALLOC, LOAD, DATA
 16 .data.cacheline_aligned 0000c400 c06f6800 006f6800 002f7800 2**7
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 17 .data.read_mostly 00000dfc c0702c00 00702c00 00303c00 2**7
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 18 .data.init_task 00001000 c0704000 00704000 00305000 2**5
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 19 .smp_locks 000039d0 c0705000 00705000 00306000 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
 20 .init.text 0001f9fa c0709000 00709000 0030a000 2**0
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
 21 .init.data 0000e453 c0729000 00729000 0032a000 2**12
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 22 .init.setup 000006a8 c0737460 00737460 00338460 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 23 .initcall.init 00000458 c0737b08 00737b08 00338b08 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 24 .con_initcall.init 0000000c c0737f60 00737f60 00338f60 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 25 .security_initcall.init 00000008 c0737f6c 00737f6c 00338f6c 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 26 .altinstructions 00002b1f c0737f74 00737f74 00338f74 2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
 27 .altinstr_replacement 00000bf3 c073aa93 0073aa93 0033ba93 2**0
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
 28 .exit.text 00000b31 c073b686 0073b686 0033c686 2**0
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
 29 .init.ramfs 00000086 c073d000 0073d000 0033e000 2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 30 .data.percpu 00004e44 c073d100 0073d100 0033e100 2**7
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
 31 .bss 000b7000 c0742000 00742000 00342f44 2**12
                  ALLOC
 32 .comment 0000b188 00000000 00000000 00342f44 2**0
                  CONTENTS, READONLY
 33 .debug_aranges 00009898 00000000 00000000 0034e0cc 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING
 34 .debug_pubnames 000322f6 00000000 00000000 00357964 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING
 35 .debug_info 022f80a7 00000000 00000000 00389c5a 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING
 36 .debug_abbrev 001115b5 00000000 00000000 02681d01 2**0
                  CONTENTS, READONLY, DEBUGGING
 37 .debug_line 001db4e8 00000000 00000000 027932b6 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING
 38 .debug_frame 0008f154 00000000 00000000 0296e7a0 2**2
                  CONTENTS, RELOC, READONLY, DEBUGGING
 39 .debug_str 000dac29 00000000 00000000 029fd8f4 2**0
                  CONTENTS, READONLY, DEBUGGING
 40 .debug_loc 00322d57 00000000 00000000 02ad851d 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING
 41 .debug_ranges 0006d9f8 00000000 00000000 02dfb274 2**0
                  CONTENTS, RELOC, READONLY, DEBUGGING