Linux下Gcc 的编译过程-白红宇

Linux下Gcc 的编译过程

阅读量：5317 次

发布时间：2019-06-14

本文共 5826 字，大约阅读时间需要 19 分钟。

在linux下开发难免会用到gcc编译。GCC（GNU Compiler Collection。GNU编译器套装），是由 GNU 开发的编程语言编译器。它是GNU编译器套装以GPL许可证所发行的自由软件，也是 GNU计划的关键部分。

使用GCC编译程序时,编译过程能够被细分为四个阶段:

◆ 预处理(Pre-Processing)

◆ 编译(Compiling)

◆ 汇编(Assembling)

◆ 链接(Linking)

1、预处理对源码文件里的文件包括(include)、预编译语句(如宏定义define等)进行分析，编译选项为gcc -E *.c

#define DEBUG "debug"int main(){  char *a = DEBUG;  return 1;}

经过上面的预处理后，能够看到DEBUG被替换成了提前定义的内容

# 1 "hello.c"# 1 "
     
      "# 1 "
      
       "# 1 "hello.c"int main(){  char *a = "debug";  return 1;}

2、编译调用cc1进行编译，使用gcc -S选项就能够生成汇编代码，这个阶段依据输入文件生成以.o为后缀的目标文件。生成的汇编代码例如以下：

.file   "hello.c"        .section        .rodata.LC0:        .string "debug"        .text.globl main        .type   main, @functionmain:.LFB0:        .cfi_startproc        pushq   %rbp        .cfi_def_cfa_offset 16        .cfi_offset 6, -16        movq    %rsp, %rbp        .cfi_def_cfa_register 6        movq    $.LC0, -8(%rbp)        movl    $1, %eax        leave        .cfi_def_cfa 7, 8        ret        .cfi_endproc.LFE0:        .size   main, .-main        .ident  "GCC: (GNU) 4.4.6 20110731 (Red Hat 4.4.6-3)"        .section        .note.GNU-stack,"",@progbits

3、汇编汇编过程是针对汇编语言的步骤，调用as进行工作。一般来讲，.S为后缀的汇编语言源码文件和汇编、.s为后缀的汇编语言文件经过预编译和汇编之后都生成以.o为后缀的目标文件。此过程生成ELF格式的目标代码，使用gcc -c进行汇编

使用readelf -a hello.o能够看到具体的elf信息

ELF Header:  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00   Class:                             ELF64  Data:                              2's complement, little endian  Version:                           1 (current)  OS/ABI:                            UNIX - System V  ABI Version:                       0  Type:                              REL (Relocatable file)  Machine:                           Advanced Micro Devices X86-64  Version:                           0x1  Entry point address:               0x0  Start of program headers:          0 (bytes into file)  Start of section headers:          296 (bytes into file)  Flags:                             0x0  Size of this header:               64 (bytes)  Size of program headers:           0 (bytes)  Number of program headers:         0  Size of section headers:           64 (bytes)  Number of section headers:         13  Section header string table index: 10Section Headers:  [Nr] Name              Type             Address           Offset       Size              EntSize          Flags  Link  Info  Align  [ 0]                   NULL             0000000000000000  00000000       0000000000000000  0000000000000000           0     0     0  [ 1] .text             PROGBITS         0000000000000000  00000040       0000000000000013  0000000000000000  AX       0     0     4  [ 2] .rela.text        RELA             0000000000000000  00000568       0000000000000018  0000000000000018          11     1     8  [ 3] .data             PROGBITS         0000000000000000  00000054       0000000000000000  0000000000000000  WA       0     0     4  [ 4] .bss              NOBITS           0000000000000000  00000054       0000000000000000  0000000000000000  WA       0     0     4  [ 5] .rodata           PROGBITS         0000000000000000  00000054       0000000000000006  0000000000000000   A       0     0     1  [ 6] .comment          PROGBITS         0000000000000000  0000005a       000000000000002d  0000000000000001  MS       0     0     1  [ 7] .note.GNU-stack   PROGBITS         0000000000000000  00000087       0000000000000000  0000000000000000           0     0     1  [ 8] .eh_frame         PROGBITS         0000000000000000  00000088       0000000000000038  0000000000000000   A       0     0     8  [ 9] .rela.eh_frame    RELA             0000000000000000  00000580       0000000000000018  0000000000000018          11     8     8  [10] .shstrtab         STRTAB           0000000000000000  000000c0       0000000000000061  0000000000000000           0     0     1  [11] .symtab           SYMTAB           0000000000000000  00000468       00000000000000f0  0000000000000018          12     9     8  [12] .strtab           STRTAB           0000000000000000  00000558       000000000000000e  0000000000000000           0     0     1Key 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)There are no section groups in this file.There are no program headers in this file.Relocation section '.rela.text' at offset 0x568 contains 1 entries:  Offset          Info           Type           Sym. Value    Sym. Name + Addend000000000008  00050000000b R_X86_64_32S      0000000000000000 .rodata + 0Relocation section '.rela.eh_frame' at offset 0x580 contains 1 entries:  Offset          Info           Type           Sym. Value    Sym. Name + Addend000000000020  000200000002 R_X86_64_PC32     0000000000000000 .text + 0There are no unwind sections in this file.Symbol table '.symtab' contains 10 entries:   Num:    Value          Size Type    Bind   Vis      Ndx Name     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND      1: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS hello.c     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    1      3: 0000000000000000     0 SECTION LOCAL  DEFAULT    3      4: 0000000000000000     0 SECTION LOCAL  DEFAULT    4      5: 0000000000000000     0 SECTION LOCAL  DEFAULT    5      6: 0000000000000000     0 SECTION LOCAL  DEFAULT    7      7: 0000000000000000     0 SECTION LOCAL  DEFAULT    8      8: 0000000000000000     0 SECTION LOCAL  DEFAULT    6      9: 0000000000000000    19 FUNC    GLOBAL DEFAULT    1 main

4、链接链接过程。生成可运行代码。链接分为两种，一种是静态链接，第二种是动态链接。

使用静态链接的优点是，依赖的动态链接库较少，对动态链接库的版本号不会非常敏感，具有较好的兼容性。缺点是生成的程序比較大。使用动态链接的优点是，生成的程序比較小，占用较少的内存。

gcc hello.o -o hello 就能够完毕最后的链接操作并生成可运行文件，至于怎样生成动态库和静态库，以及怎样链接动态库和静态库，以后会再作介绍。

转载于:https://www.cnblogs.com/lxjshuju/p/6928091.html

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