C語言 - 常量和變量的存儲位置
〇、環境
| 項 | 值 |
|---|---|
| 語言 | C |
| 編譯器 | gcc |
| 編譯環境 | x86_64-linux-gnu |
一、常量和變量的存儲位置
1.1 實驗方法
靜態觀察：對編譯得到的可執行文件進行分析
動態觀察：運行時獲取變量的地址，並分析變量在進程地址空間的位置
1.2 示例程序
示例程序1
#include <stdio.h>
#include <unistd.h>
static int local_static_uninit;
static int local_static_init = 0x88;
static int localarr_static_uninit[1024];
static int localarr_static_init[1024] = {1,2,3};
int global_uninit;
int gloabl_init = 0x88;
int globalarr_uninit[1024];
int globalarr_init[1024] = {1,2,3};
int add(int a, int b)
{
static int infun_static_uninit;
static int infun_static_init = 0x88;
static int infunarr_static_uninit[1024];
static int infunarr_static_init[1024] = {1,2,3};
int c;
int d = 0;
int e = a + b;
printf (
"&local_static_uninit=%p\n"
"&local_static_init=%p\n"
"&localarr_static_uninit[0]=%p\n"
"&localarr_static_init[0]=%p\n"
"&global_uninit=%p\n"
"&gloabl_init=%p\n"
"&globalarr_uninit[0]=%p\n"
"&globalarr_init[0]=%p\n"
"&infun_static_uninit=%p\n"
"&infun_static_init=%p\n"
"&infunarr_static_uninit[0]=%p\n"
"&infunarr_static_init[0]=%p\n"
"&a=%p\n"
"&b=%p\n"
"&c=%p\n"
"&d=%p\n"
,
&local_static_uninit,
&local_static_init,
&localarr_static_uninit[0],
&localarr_static_init[0],
&global_uninit,
&gloabl_init,
&globalarr_uninit[0],
&globalarr_init[0],
&infun_static_uninit,
&infun_static_init,
&infunarr_static_uninit[0],
&infunarr_static_init[0],
&a, &b, &c, &d
);
while (1)
{
sleep (5);
}
return e;
}
int main()
{
add(1,2);
return 0;
}
文件布局：
運行輸出：
./a.out
&local_static_uninit=0x6040e0
&local_static_init=0x601060
&localarr_static_uninit[0]=0x604100
&localarr_static_init[0]=0x601080
&global_uninit=0x606120
&gloabl_init=0x602080
&globalarr_uninit[0]=0x606140
&globalarr_init[0]=0x6020a0
&infun_static_uninit=0x605100
&infun_static_init=0x6030a0
&infunarr_static_uninit[0]=0x605120
&infunarr_static_init[0]=0x6030c0
&a=0x7ffd0ee30b1c
&b=0x7ffd0ee30b18
&c=0x7ffd0ee30b2c
&d=0x7ffd0ee30b30
進程地址布局：
cat /proc/2446/maps
00400000-00401000 r-xp 00000000 fc:00 130819 /home/ttt/test/a.out
00600000-00601000 r--p 00000000 fc:00 130819 /home/ttt/test/a.out
00601000-00605000 rw-p 00001000 fc:00 130819 /home/ttt/test/a.out
00605000-00608000 rw-p 00000000 00:00 0
007cf000-007f0000 rw-p 00000000 00:00 0 [heap]
7f54a3458000-7f54a3618000 r-xp 00000000 fc:00 659982 /lib/x86_64-linux-gnu/libc-2.23.so
7f54a3618000-7f54a3818000 ---p 001c0000 fc:00 659982 /lib/x86_64-linux-gnu/libc-2.23.so
7f54a3818000-7f54a381c000 r--p 001c0000 fc:00 659982 /lib/x86_64-linux-gnu/libc-2.23.so
7f54a381c000-7f54a381e000 rw-p 001c4000 fc:00 659982 /lib/x86_64-linux-gnu/libc-2.23.so
7f54a381e000-7f54a3822000 rw-p 00000000 00:00 0
7f54a3822000-7f54a3848000 r-xp 00000000 fc:00 659993 /lib/x86_64-linux-gnu/ld-2.23.so
7f54a3a3c000-7f54a3a3f000 rw-p 00000000 00:00 0
7f54a3a47000-7f54a3a48000 r--p 00025000 fc:00 659993 /lib/x86_64-linux-gnu/ld-2.23.so
7f54a3a48000-7f54a3a49000 rw-p 00026000 fc:00 659993 /lib/x86_64-linux-gnu/ld-2.23.so
7f54a3a49000-7f54a3a4a000 rw-p 00000000 00:00 0
7ffd0ee11000-7ffd0ee32000 rw-p 00000000 00:00 0 [stack]
7ffd0eff3000-7ffd0eff6000 r--p 00000000 00:00 0 [vvar]
7ffd0eff6000-7ffd0eff8000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
1.3 結果分析
1.3.1 運行時結果
- 源文件中的全局變量，包括普通全局變量、靜態全局變量，不論是否初始化，均在程序段（可寫數據段）
- 函數內部的靜態變量，不論是否初始化，均在程序段（可寫數據段）。（和全局變量一致）
- 函數內部的局部變量，函數傳參，均在棧段。
1.3.2 靜態分析結果
說明一點，未初始化的全局變量（包括函數內靜態變量）位於.bss段，並不占用可執行文件的空間。以后再表。