Hello Guys我正在开始调试代码的航程,并根据本书运行以下命令,仅用于对下面的源代码进行一些分析
// hello_world-1.c
#include <stdio.h>
int main(void)
{
printf("hello world\n");
return 0;
gcc -Wall -Wextra -c hello_world-1.c // What is wall and wextra here
?
$ size hello_world-1 hello_world-1.o
text data bss dec hex filename
916 256 4 1176 498 hello_world-1
48 0 0 48 30 hello_world-1.o
$ objdump -h hello_world-1.o
hello_world-1.o: file format elf32-i386
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000023 00000000 00000000 00000034 2**2
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000000 00000000 00000000 00000058 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 00000000 00000000 00000058 2**2
ALLOC
3 .rodata 0000000d 00000000 00000000 00000058 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .note.GNU-stack 00000000 00000000 00000000 00000065 2**0
CONTENTS, READONLY
5 .comment 0000001b 00000000 00000000 00000065 2**0
CONTENTS, READONLY
48 0 0 48 30 hello_world-1.o
我在这里有一些问题
1)hello_world-1.c中没有全局变量。那么为什么大小报告数据和bss段的目标文件长度为零,而可执行文件的长度为零呢?
2)为什么size和objdump报告文本段的大小不同?
答案 0 :(得分:1)
关于你的问题:
“gcc -Wall -Wextra -c hello_world-1.c //这里有什么墙和wextra?”
(注意大小写计数)
-Wall告诉编译器启用大多数警告
-Wextra告诉编译器启用更多警告
-c告诉编译器只编译,而不是链接。
因为没有包含'-o objfilename.o'参数, 编译器将输出一个与输入文件同名的目标文件,扩展名为“.o”。
建议始终明确包含'-o objfilename.o'参数
建议在这些事情上进行一些在线谷歌搜索,其中你会发现类似于以下网页:
答案 1 :(得分:1)
目标文件包括.text(即二进制CPU指令),.rodata(只读数据 - “hello world”\ 10 \ 0 - 总共13个字节)和.comment(附加链接信息)。 可执行文件包含相同的减去.comment和标准库内容以及导入动态库数据(如果有)。 标准库至少添加了启动代码,这使得可执行文件变得更大。所以你的区别是:可执行文件.text = .object text + startup code + stdlibrary code(如果是静态链接)。
答案 2 :(得分:0)
这是&#39; size&#39;
的手册页的副本SIZE(1)GNU开发工具SIZE(1)
NAME 尺寸 - 列出截面尺寸和总尺寸。
概要 大小[-A | -B | --format = compatibility] [ - 救命] [-d | -o | -x | --radix =数] [ - 共同] [-t | --totals] [--target = bfdname] [-V | --version] [OBJFILE ...]
说明 GNU大小实用程序列出了部分大小---和总大小--- 每个对象或归档文件objfile在其参数列表中。通过 默认情况下,为每个目标文件或每个目标文件生成一行输出 存档中的模块。
objfile... are the object files to be examined. If none are specified,
the file "a.out" will be used.
OPTIONS 命令行选项具有以下含义:
-A
-B
--format=compatibility
Using one of these options, you can choose whether the output from
GNU size resembles output from System V size (using -A, or
--format=sysv), or Berkeley size (using -B, or --format=berkeley).
The default is the one-line format similar to Berkeley's.
Here is an example of the Berkeley (default) format of output from
size:
$ size --format=Berkeley ranlib size
text data bss dec hex filename
294880 81920 11592 388392 5ed28 ranlib
294880 81920 11888 388688 5ee50 size
This is the same data, but displayed closer to System V
conventions:
$ size --format=SysV ranlib size
ranlib :
section size addr
.text 294880 8192
.data 81920 303104
.bss 11592 385024
Total 388392
size :
section size addr
.text 294880 8192
.data 81920 303104
.bss 11888 385024
Total 388688
--help
Show a summary of acceptable arguments and options.
-d
-o
-x
--radix=number
Using one of these options, you can control whether the size of
each section is given in decimal (-d, or --radix=10); octal (-o, or
--radix=8); or hexadecimal (-x, or --radix=16). In --radix=number,
only the three values (8, 10, 16) are supported. The total size is
always given in two radices; decimal and hexadecimal for -d or -x
output, or octal and hexadecimal if you're using -o.
--common
Print total size of common symbols in each file. When using
Berkeley format these are included in the bss size.
-t
--totals
Show totals of all objects listed (Berkeley format listing mode
only).
--target=bfdname
Specify that the object-code format for objfile is bfdname. This
option may not be necessary; size can automatically recognize many
formats.
-V
--version
Display the version number of size.
@file
Read command-line options from file. The options read are inserted
in place of the original @file option. If file does not exist, or
cannot be read, then the option will be treated literally, and not
removed.
Options in file are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character (including
a backslash) may be included by prefixing the character to be
included with a backslash. The file may itself contain additional
@file options; any such options will be processed recursively.
另见 ar(1),objdump(1),readelf(1)和binutils的Info条目。
COPYRIGHT 版权所有(c)1991-2013 Free Software Foundation,Inc。
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
binutils-2.23.91 2013-11-18 SIZE(1)