电子商务网站建设案例,做三合一网站的好处,商务网站建设实训报告1600字,做拍福利爱福利视频网站为什么要动态链接
浪费内存和和磁盘空间 每个程序都得拥有相同的拷贝程序的发布、更新和部署困难 更新任何一个小的模块#xff0c;整个程序都需要重新链接
动态链接#xff1a;将链接的过程推迟到运行时
节省内存减少物理页面的换入换出、增加CPU的缓存命中率更新升级方便…为什么要动态链接
浪费内存和和磁盘空间 每个程序都得拥有相同的拷贝程序的发布、更新和部署困难 更新任何一个小的模块整个程序都需要重新链接
动态链接将链接的过程推迟到运行时
节省内存减少物理页面的换入换出、增加CPU的缓存命中率更新升级方便各个模块开发相互独立耦合度更小可扩展性和兼容性 兼容性体现在能够在操作系统和应用层增加中间层消除平台的依赖性
动态链接的例子
lib.so 保留了完整的符号信息链接器在链接时将符号标记为动态符号在装载时在进行地址重定位
// lib.h
#ifndef __LIB_H__
#define __LIB_H__
void foobar(int i);
#endif
// lib.c
#include stdio.h
void foobar(int i) {printf(Printing from lib.so %d\n, i);
}
// program1.c
#include lib.h
int main() {foobar(1);return 0;
}
// program2.c
#include lib.h
int main() {foobar(2);return 0;
}$ gcc -fPIC -shared -o lib.so lib.c
$ gcc -c program1 program1.c ./lib.so
$ gcc -o program2 program2.c ./lib.so
动态链接程序运行时地址空间分布
$ ./program1
[1] 3966895
Printing from lib.so 1
$ cat /proc/3966895/maps
563546b06000-563546b07000 r--p 00000000 fc:02 2601194 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/program1
563546b07000-563546b08000 r-xp 00001000 fc:02 2601194 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/program1
563546b08000-563546b09000 r--p 00002000 fc:02 2601194 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/program1
563546b09000-563546b0a000 r--p 00002000 fc:02 2601194 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/program1
563546b0a000-563546b0b000 rw-p 00003000 fc:02 2601194 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/program1
563547e2e000-563547e4f000 rw-p 00000000 00:00 0 [heap]
7f4d5c20a000-7f4d5c20d000 rw-p 00000000 00:00 0
7f4d5c20d000-7f4d5c22f000 r--p 00000000 fc:02 139834 /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f4d5c22f000-7f4d5c3a7000 r-xp 00022000 fc:02 139834 /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f4d5c3a7000-7f4d5c3f5000 r--p 0019a000 fc:02 139834 /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f4d5c3f5000-7f4d5c3f9000 r--p 001e7000 fc:02 139834 /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f4d5c3f9000-7f4d5c3fb000 rw-p 001eb000 fc:02 139834 /usr/lib/x86_64-linux-gnu/libc-2.31.so
7f4d5c3fb000-7f4d5c3ff000 rw-p 00000000 00:00 0
7f4d5c40a000-7f4d5c40b000 r--p 00000000 fc:02 2601193 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/lib.so
7f4d5c40b000-7f4d5c40c000 r-xp 00001000 fc:02 2601193 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/lib.so
7f4d5c40c000-7f4d5c40d000 r--p 00002000 fc:02 2601193 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/lib.so
7f4d5c40d000-7f4d5c40e000 r--p 00002000 fc:02 2601193 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/lib.so
7f4d5c40e000-7f4d5c40f000 rw-p 00003000 fc:02 2601193 /home/ubuntu/cpp_learn/effective_cpp/xiuyang07/lib.so
7f4d5c40f000-7f4d5c411000 rw-p 00000000 00:00 0
7f4d5c411000-7f4d5c412000 r--p 00000000 fc:02 130951 /usr/lib/x86_64-linux-gnu/ld-2.31.so
7f4d5c412000-7f4d5c435000 r-xp 00001000 fc:02 130951 /usr/lib/x86_64-linux-gnu/ld-2.31.so
7f4d5c435000-7f4d5c43d000 r--p 00024000 fc:02 130951 /usr/lib/x86_64-linux-gnu/ld-2.31.so
7f4d5c43e000-7f4d5c43f000 r--p 0002c000 fc:02 130951 /usr/lib/x86_64-linux-gnu/ld-2.31.so
7f4d5c43f000-7f4d5c440000 rw-p 0002d000 fc:02 130951 /usr/lib/x86_64-linux-gnu/ld-2.31.so
7f4d5c440000-7f4d5c441000 rw-p 00000000 00:00 0
7fff3218c000-7fff321ad000 rw-p 00000000 00:00 0 [stack]
7fff321dd000-7fff321e0000 r--p 00000000 00:00 0 [vvar]
7fff321e0000-7fff321e1000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]
lib.so 的装载属性
$ readelf -l lib.so Elf file type is DYN (Shared object file)
Entry point 0x1080
There are 11 program headers, starting at offset 64Program Headers:Type Offset VirtAddr PhysAddrFileSiz MemSiz Flags AlignLOAD 0x0000000000000000 0x0000000000000000 0x00000000000000000x0000000000000560 0x0000000000000560 R 0x1000LOAD 0x0000000000001000 0x0000000000001000 0x00000000000010000x000000000000017d 0x000000000000017d R E 0x1000LOAD 0x0000000000002000 0x0000000000002000 0x00000000000020000x00000000000000dc 0x00000000000000dc R 0x1000LOAD 0x0000000000002e10 0x0000000000003e10 0x0000000000003e100x0000000000000220 0x0000000000000228 RW 0x1000DYNAMIC 0x0000000000002e20 0x0000000000003e20 0x0000000000003e200x00000000000001c0 0x00000000000001c0 RW 0x8NOTE 0x00000000000002a8 0x00000000000002a8 0x00000000000002a80x0000000000000020 0x0000000000000020 R 0x8NOTE 0x00000000000002c8 0x00000000000002c8 0x00000000000002c80x0000000000000024 0x0000000000000024 R 0x4GNU_PROPERTY 0x00000000000002a8 0x00000000000002a8 0x00000000000002a80x0000000000000020 0x0000000000000020 R 0x8GNU_EH_FRAME 0x000000000000201c 0x000000000000201c 0x000000000000201c0x000000000000002c 0x000000000000002c R 0x4GNU_STACK 0x0000000000000000 0x0000000000000000 0x00000000000000000x0000000000000000 0x0000000000000000 RW 0x10GNU_RELRO 0x0000000000002e10 0x0000000000003e10 0x0000000000003e100x00000000000001f0 0x00000000000001f0 R 0x1Section to Segment mapping:Segment Sections...00 .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt 01 .init .plt .plt.got .plt.sec .text .fini 02 .rodata .eh_frame_hdr .eh_frame 03 .init_array .fini_array .dynamic .got .got.plt .data .bss 04 .dynamic 05 .note.gnu.property 06 .note.gnu.build-id 07 .note.gnu.property 08 .eh_frame_hdr 09 10 .init_array .fini_array .dynamic .got
