笔记和练习博客总目录见开始读TLPI。41-1尝试分别使用和不使用-static选项编译同一个程序对比动态链接 C 库与静态链接 C 库两种方式生成可执行文件的大小差异。根据gcc(1)-static的说明为-staticOn systems that support dynamic linking, this overrides -pie and prevents linking with the shared libraries. On other systems, this option has no effect.此练习需要预先安装静态版本的libc。$sudoyuminstallglibc-static Last metadata expiration check:0:56:41 ago on Thu 08 Oct202605:38:46 AM UTC. Dependencies resolved.Package Architecture Version Repository SizeInstalling: glibc-static x86_642.34-275.0.1.el9_8 ol9_codeready_builder1.5M Upgrading: glibc x86_642.34-275.0.1.el9_8 ol9_baseos_latest2.0M glibc-common x86_642.34-275.0.1.el9_8 ol9_baseos_latest334k glibc-devel x86_642.34-275.0.1.el9_8 ol9_appstream63k glibc-gconv-extra x86_642.34-275.0.1.el9_8 ol9_baseos_latest1.8M glibc-headers x86_642.34-275.0.1.el9_8 ol9_appstream925k glibc-langpack-de x86_642.34-275.0.1.el9_8 ol9_baseos_latest779k glibc-langpack-en x86_642.34-275.0.1.el9_8 ol9_baseos_latest973k glibc-langpack-es x86_642.34-275.0.1.el9_8 ol9_baseos_latest1.1M glibc-langpack-fr x86_642.34-275.0.1.el9_8 ol9_baseos_latest728k glibc-langpack-zh x86_642.34-275.0.1.el9_8 ol9_baseos_latest2.3M Installing dependencies: libxcrypt-static x86_644.4.18-3.el9 ol9_codeready_builder102k Transaction SummaryInstall2Packages Upgrade10Packages Total download size:12M Is this ok[y/N]: y Downloading Packages:(1/12): glibc-static-2.34-275.0.1.el9_8.x86_64.rpm1.5MB/s|1.5MB 00:00(2/12): glibc-common-2.34-275.0.1.el9_8.x86_64.rpm2.4MB/s|334kB 00:00(3/12): glibc-2.34-275.0.1.el9_8.x86_64.rpm1.7MB/s|2.0MB 00:01(4/12): glibc-langpack-de-2.34-275.0.1.el9_8.x86_64.rpm3.2MB/s|779kB 00:00(5/12): glibc-gconv-extra-2.34-275.0.1.el9_8.x86_64.rpm4.3MB/s|1.8MB 00:00(6/12): glibc-langpack-en-2.34-275.0.1.el9_8.x86_64.rpm4.1MB/s|973kB 00:00(7/12): glibc-langpack-fr-2.34-275.0.1.el9_8.x86_64.rpm7.2MB/s|728kB 00:00(8/12): glibc-langpack-es-2.34-275.0.1.el9_8.x86_64.rpm4.1MB/s|1.1MB 00:00(9/12): glibc-devel-2.34-275.0.1.el9_8.x86_64.rpm904kB/s|63kB 00:00(10/12): glibc-langpack-zh-2.34-275.0.1.el9_8.x86_64.rpm7.5MB/s|2.3MB 00:00(11/12): glibc-headers-2.34-275.0.1.el9_8.x86_64.rpm3.6MB/s|925kB 00:00(12/12): libxcrypt-static-4.4.18-3.el9.x86_64.rpm43kB/s|102kB 00:02 --------------------------------------------------------------------------------------------------------------- Total5.2MB/s|12MB 00:02 Running transaction check Transaction check succeeded. Running transactiontestTransactiontestsucceeded. Running transaction Preparing:1/1 Upgrading:glibc-common-2.34-275.0.1.el9_8.x86_641/22 Upgrading:glibc-gconv-extra-2.34-275.0.1.el9_8.x86_642/22 Running scriptlet: glibc-gconv-extra-2.34-275.0.1.el9_8.x86_642/22 Upgrading:glibc-langpack-de-2.34-275.0.1.el9_8.x86_643/22 Upgrading:glibc-langpack-en-2.34-275.0.1.el9_8.x86_644/22 Upgrading:glibc-langpack-es-2.34-275.0.1.el9_8.x86_645/22 Upgrading:glibc-langpack-fr-2.34-275.0.1.el9_8.x86_646/22 Upgrading:glibc-langpack-zh-2.34-275.0.1.el9_8.x86_647/22 Running scriptlet: glibc-2.34-275.0.1.el9_8.x86_648/22 Upgrading:glibc-2.34-275.0.1.el9_8.x86_648/22 Running scriptlet: glibc-2.34-275.0.1.el9_8.x86_648/22 Upgrading:glibc-headers-2.34-275.0.1.el9_8.x86_649/22 Upgrading:glibc-devel-2.34-275.0.1.el9_8.x86_6410/22 Installing:libxcrypt-static-4.4.18-3.el9.x86_6411/22 Installing:glibc-static-2.34-275.0.1.el9_8.x86_6412/22 Cleanup:glibc-devel-2.34-231.0.1.el9_7.10.x86_6413/22 Cleanup:glibc-headers-2.34-231.0.1.el9_7.10.x86_6414/22 Cleanup:glibc-langpack-en-2.34-231.0.1.el9_7.10.x86_6415/22 Cleanup:glibc-langpack-es-2.34-231.0.1.el9_7.10.x86_6416/22 Cleanup:glibc-langpack-fr-2.34-231.0.1.el9_7.10.x86_6417/22 Cleanup:glibc-langpack-zh-2.34-231.0.1.el9_7.10.x86_6418/22 Cleanup:glibc-2.34-231.0.1.el9_7.10.x86_6419/22 Cleanup:glibc-langpack-de-2.34-231.0.1.el9_7.10.x86_6420/22 Cleanup:glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_6421/22 Running scriptlet: glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_6421/22 Cleanup:glibc-common-2.34-231.0.1.el9_7.10.x86_6422/22 Running scriptlet: glibc-common-2.34-231.0.1.el9_7.10.x86_6422/22 Verifying:glibc-static-2.34-275.0.1.el9_8.x86_641/22 Verifying:libxcrypt-static-4.4.18-3.el9.x86_642/22 Verifying:glibc-2.34-275.0.1.el9_8.x86_643/22 Verifying:glibc-2.34-231.0.1.el9_7.10.x86_644/22 Verifying:glibc-common-2.34-275.0.1.el9_8.x86_645/22 Verifying:glibc-common-2.34-231.0.1.el9_7.10.x86_646/22 Verifying:glibc-gconv-extra-2.34-275.0.1.el9_8.x86_647/22 Verifying:glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_648/22 Verifying:glibc-langpack-de-2.34-275.0.1.el9_8.x86_649/22 Verifying:glibc-langpack-de-2.34-231.0.1.el9_7.10.x86_6410/22 Verifying:glibc-langpack-en-2.34-275.0.1.el9_8.x86_6411/22 Verifying:glibc-langpack-en-2.34-231.0.1.el9_7.10.x86_6412/22 Verifying:glibc-langpack-es-2.34-275.0.1.el9_8.x86_6413/22 Verifying:glibc-langpack-es-2.34-231.0.1.el9_7.10.x86_6414/22 Verifying:glibc-langpack-fr-2.34-275.0.1.el9_8.x86_6415/22 Verifying:glibc-langpack-fr-2.34-231.0.1.el9_7.10.x86_6416/22 Verifying:glibc-langpack-zh-2.34-275.0.1.el9_8.x86_6417/22 Verifying:glibc-langpack-zh-2.34-231.0.1.el9_7.10.x86_6418/22 Verifying:glibc-devel-2.34-275.0.1.el9_8.x86_6419/22 Verifying:glibc-devel-2.34-231.0.1.el9_7.10.x86_6420/22 Verifying:glibc-headers-2.34-275.0.1.el9_8.x86_6421/22 Verifying:glibc-headers-2.34-231.0.1.el9_7.10.x86_6422/22 Upgraded: glibc-2.34-275.0.1.el9_8.x86_64 glibc-common-2.34-275.0.1.el9_8.x86_64 glibc-devel-2.34-275.0.1.el9_8.x86_64 glibc-gconv-extra-2.34-275.0.1.el9_8.x86_64 glibc-headers-2.34-275.0.1.el9_8.x86_64 glibc-langpack-de-2.34-275.0.1.el9_8.x86_64 glibc-langpack-en-2.34-275.0.1.el9_8.x86_64 glibc-langpack-es-2.34-275.0.1.el9_8.x86_64 glibc-langpack-fr-2.34-275.0.1.el9_8.x86_64 glibc-langpack-zh-2.34-275.0.1.el9_8.x86_64 Installed: glibc-static-2.34-275.0.1.el9_8.x86_64 libxcrypt-static-4.4.18-3.el9.x86_64 Complete!样例程序hello.c如下#includestdio.hintmain(void){printf(Hello, world!\n);return0;}默认编译动态链接$ gcc hello.c-ohello_dynamic $ls-lhello_dynamic -rwxr-xr-x.1vagrant vagrant17496Oct806:38 hello_dynamic $ ./hello_dynamic Hello, world!指定-static选项静态编译$ gcc-statichello.c-ohello_static $ls-lhello_static -rwxr-xr-x.1vagrant vagrant875792Oct806:39 hello_static $ ./hello_static Hello, world!最后清理静态库$sudoyum remove glibc-static Dependencies resolved.Package Architecture Version Repository SizeRemoving: glibc-static x86_642.34-275.0.1.el9_8 ol9_codeready_builder9.8M Removing unused dependencies: libxcrypt-static x86_644.4.18-3.el9 ol9_codeready_builder466k Transaction SummaryRemove2Packages Freed space:10M Is this ok[y/N]: y Running transaction check Transaction check succeeded. Running transactiontestTransactiontestsucceeded. Running transaction Preparing:1/1 Erasing:glibc-static-2.34-275.0.1.el9_8.x86_641/2 Erasing:libxcrypt-static-4.4.18-3.el9.x86_642/2 Verifying:glibc-static-2.34-275.0.1.el9_8.x86_641/2 Verifying:libxcrypt-static-4.4.18-3.el9.x86_642/2 Removed: glibc-static-2.34-275.0.1.el9_8.x86_64 libxcrypt-static-4.4.18-3.el9.x86_64 Complete!41-2 (附加题)请熟悉本章的演示程序。本章的演示程序位于目录tlpi-book/shlibs/demo。$ls*.c mod1.c mod2.c mod3.c prog.c $ls*.sh Demo_no_lib.sh Demo_shared_lib.sh Demo_static_lib.sh三个shell脚本分别生成不使用库使用静态库使用动态库共享库的可执行程序$ls-lprog_* -rwxr-xr-x.1vagrant vagrant1460496Oct807:45 prog_nolib -rwxr-xr-x.1vagrant vagrant18936Oct807:46 prog_so -rwxr-xr-x.1vagrant vagrant1419984Oct807:46 prog_static虽然不使用库与使用静态库的可执行文件大小近似但这两种方式存在明显的差别项目方式1直接链接.o方式2静态库 .a中间产物一堆独立.o文件.o 归档文件libdemo.a链接行为所有传入的.o全部完整并入可执行文件仅提取被用到的.o模块未引用模块丢弃可执行体积更大全部目标代码都包含更小只包含用到的模块复用性每次链接都要列出一堆.o不方便复用libdemo.a可以给多个程序重复链接只需写库名符号规则全部目标文件符号全部参与链接链接器按符号依赖按需提取归档内的目标模块适用场景少量文件、一次性编译多个程序共用一组模块打包复用41-3 (附加题)请演示Figure 41-5中的全局符号引用。按图准备2个c语言文件。foo.c如下#includestdio.hvoidxyz(){printf(foo-xyz\n);}voidfunc(){xyz();}prog.c如下#includestdio.hexternvoidfunc();voidxyz(){printf(main-xyz\n);}intmain(){func();return0;}第一种行为调用的是主函数中的xyz函数$ gcc-g-c-fPIC-Wall-cfoo.c $ gcc-g-shared-olibfoo.so foo.o $ gcc-g-oprog prog.c libfoo.so $LD_LIBRARY_PATH. ./prog main-xyz第二种行为调用的是共享库中的xyz函数$ gcc-g-c-fPIC-Wall-cfoo.c $ gcc-g-shared-Wl,-Bsymbolic-olibfoo.so foo.o $ gcc-g-oprog prog.c libfoo.so $LD_LIBRARY_PATH. ./prog foo-xyz最后看一个小错误的修补。ldd显示libfoo.so找不到$ ldd prog linux-vdso.so.1(0x00007ffd927d2000)libfoo.sonot found libc.so.6/lib64/libc.so.6(0x00007fd3f72df000)/lib64/ld-linux-x86-64.so.2(0x00007fd3f74f2000)但是此文件是存在的$find.-namelibfoo.so*./libfoo.so $ objdump-pprog|grepNEEDED NEEDED libfoo.so NEEDED libc.so.6原因是当前目录不在ldd的搜索路径中。如下就可以了$LD_LIBRARY_PATH$PWDldd prog linux-vdso.so.1(0x00007ffee0db4000)libfoo.so/home/vagrant/test/bak/libfoo.so(0x00007f5ca65d5000)libc.so.6/lib64/libc.so.6(0x00007f5ca63c4000)/lib64/ld-linux-x86-64.so.2(0x00007f5ca65dc000)
笔记和练习博客总目录见开始读TLPI。41-1尝试分别使用和不使用-static选项编译同一个程序对比动态链接 C 库与静态链接 C 库两种方式生成可执行文件的大小差异。根据gcc(1)-static的说明为-staticOn systems that support dynamic linking, this overrides -pie and prevents linking with the shared libraries. On other systems, this option has no effect.此练习需要预先安装静态版本的libc。$sudoyuminstallglibc-static Last metadata expiration check:0:56:41 ago on Thu 08 Oct202605:38:46 AM UTC. Dependencies resolved.Package Architecture Version Repository SizeInstalling: glibc-static x86_642.34-275.0.1.el9_8 ol9_codeready_builder1.5M Upgrading: glibc x86_642.34-275.0.1.el9_8 ol9_baseos_latest2.0M glibc-common x86_642.34-275.0.1.el9_8 ol9_baseos_latest334k glibc-devel x86_642.34-275.0.1.el9_8 ol9_appstream63k glibc-gconv-extra x86_642.34-275.0.1.el9_8 ol9_baseos_latest1.8M glibc-headers x86_642.34-275.0.1.el9_8 ol9_appstream925k glibc-langpack-de x86_642.34-275.0.1.el9_8 ol9_baseos_latest779k glibc-langpack-en x86_642.34-275.0.1.el9_8 ol9_baseos_latest973k glibc-langpack-es x86_642.34-275.0.1.el9_8 ol9_baseos_latest1.1M glibc-langpack-fr x86_642.34-275.0.1.el9_8 ol9_baseos_latest728k glibc-langpack-zh x86_642.34-275.0.1.el9_8 ol9_baseos_latest2.3M Installing dependencies: libxcrypt-static x86_644.4.18-3.el9 ol9_codeready_builder102k Transaction SummaryInstall2Packages Upgrade10Packages Total download size:12M Is this ok[y/N]: y Downloading Packages:(1/12): glibc-static-2.34-275.0.1.el9_8.x86_64.rpm1.5MB/s|1.5MB 00:00(2/12): glibc-common-2.34-275.0.1.el9_8.x86_64.rpm2.4MB/s|334kB 00:00(3/12): glibc-2.34-275.0.1.el9_8.x86_64.rpm1.7MB/s|2.0MB 00:01(4/12): glibc-langpack-de-2.34-275.0.1.el9_8.x86_64.rpm3.2MB/s|779kB 00:00(5/12): glibc-gconv-extra-2.34-275.0.1.el9_8.x86_64.rpm4.3MB/s|1.8MB 00:00(6/12): glibc-langpack-en-2.34-275.0.1.el9_8.x86_64.rpm4.1MB/s|973kB 00:00(7/12): glibc-langpack-fr-2.34-275.0.1.el9_8.x86_64.rpm7.2MB/s|728kB 00:00(8/12): glibc-langpack-es-2.34-275.0.1.el9_8.x86_64.rpm4.1MB/s|1.1MB 00:00(9/12): glibc-devel-2.34-275.0.1.el9_8.x86_64.rpm904kB/s|63kB 00:00(10/12): glibc-langpack-zh-2.34-275.0.1.el9_8.x86_64.rpm7.5MB/s|2.3MB 00:00(11/12): glibc-headers-2.34-275.0.1.el9_8.x86_64.rpm3.6MB/s|925kB 00:00(12/12): libxcrypt-static-4.4.18-3.el9.x86_64.rpm43kB/s|102kB 00:02 --------------------------------------------------------------------------------------------------------------- Total5.2MB/s|12MB 00:02 Running transaction check Transaction check succeeded. Running transactiontestTransactiontestsucceeded. Running transaction Preparing:1/1 Upgrading:glibc-common-2.34-275.0.1.el9_8.x86_641/22 Upgrading:glibc-gconv-extra-2.34-275.0.1.el9_8.x86_642/22 Running scriptlet: glibc-gconv-extra-2.34-275.0.1.el9_8.x86_642/22 Upgrading:glibc-langpack-de-2.34-275.0.1.el9_8.x86_643/22 Upgrading:glibc-langpack-en-2.34-275.0.1.el9_8.x86_644/22 Upgrading:glibc-langpack-es-2.34-275.0.1.el9_8.x86_645/22 Upgrading:glibc-langpack-fr-2.34-275.0.1.el9_8.x86_646/22 Upgrading:glibc-langpack-zh-2.34-275.0.1.el9_8.x86_647/22 Running scriptlet: glibc-2.34-275.0.1.el9_8.x86_648/22 Upgrading:glibc-2.34-275.0.1.el9_8.x86_648/22 Running scriptlet: glibc-2.34-275.0.1.el9_8.x86_648/22 Upgrading:glibc-headers-2.34-275.0.1.el9_8.x86_649/22 Upgrading:glibc-devel-2.34-275.0.1.el9_8.x86_6410/22 Installing:libxcrypt-static-4.4.18-3.el9.x86_6411/22 Installing:glibc-static-2.34-275.0.1.el9_8.x86_6412/22 Cleanup:glibc-devel-2.34-231.0.1.el9_7.10.x86_6413/22 Cleanup:glibc-headers-2.34-231.0.1.el9_7.10.x86_6414/22 Cleanup:glibc-langpack-en-2.34-231.0.1.el9_7.10.x86_6415/22 Cleanup:glibc-langpack-es-2.34-231.0.1.el9_7.10.x86_6416/22 Cleanup:glibc-langpack-fr-2.34-231.0.1.el9_7.10.x86_6417/22 Cleanup:glibc-langpack-zh-2.34-231.0.1.el9_7.10.x86_6418/22 Cleanup:glibc-2.34-231.0.1.el9_7.10.x86_6419/22 Cleanup:glibc-langpack-de-2.34-231.0.1.el9_7.10.x86_6420/22 Cleanup:glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_6421/22 Running scriptlet: glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_6421/22 Cleanup:glibc-common-2.34-231.0.1.el9_7.10.x86_6422/22 Running scriptlet: glibc-common-2.34-231.0.1.el9_7.10.x86_6422/22 Verifying:glibc-static-2.34-275.0.1.el9_8.x86_641/22 Verifying:libxcrypt-static-4.4.18-3.el9.x86_642/22 Verifying:glibc-2.34-275.0.1.el9_8.x86_643/22 Verifying:glibc-2.34-231.0.1.el9_7.10.x86_644/22 Verifying:glibc-common-2.34-275.0.1.el9_8.x86_645/22 Verifying:glibc-common-2.34-231.0.1.el9_7.10.x86_646/22 Verifying:glibc-gconv-extra-2.34-275.0.1.el9_8.x86_647/22 Verifying:glibc-gconv-extra-2.34-231.0.1.el9_7.10.x86_648/22 Verifying:glibc-langpack-de-2.34-275.0.1.el9_8.x86_649/22 Verifying:glibc-langpack-de-2.34-231.0.1.el9_7.10.x86_6410/22 Verifying:glibc-langpack-en-2.34-275.0.1.el9_8.x86_6411/22 Verifying:glibc-langpack-en-2.34-231.0.1.el9_7.10.x86_6412/22 Verifying:glibc-langpack-es-2.34-275.0.1.el9_8.x86_6413/22 Verifying:glibc-langpack-es-2.34-231.0.1.el9_7.10.x86_6414/22 Verifying:glibc-langpack-fr-2.34-275.0.1.el9_8.x86_6415/22 Verifying:glibc-langpack-fr-2.34-231.0.1.el9_7.10.x86_6416/22 Verifying:glibc-langpack-zh-2.34-275.0.1.el9_8.x86_6417/22 Verifying:glibc-langpack-zh-2.34-231.0.1.el9_7.10.x86_6418/22 Verifying:glibc-devel-2.34-275.0.1.el9_8.x86_6419/22 Verifying:glibc-devel-2.34-231.0.1.el9_7.10.x86_6420/22 Verifying:glibc-headers-2.34-275.0.1.el9_8.x86_6421/22 Verifying:glibc-headers-2.34-231.0.1.el9_7.10.x86_6422/22 Upgraded: glibc-2.34-275.0.1.el9_8.x86_64 glibc-common-2.34-275.0.1.el9_8.x86_64 glibc-devel-2.34-275.0.1.el9_8.x86_64 glibc-gconv-extra-2.34-275.0.1.el9_8.x86_64 glibc-headers-2.34-275.0.1.el9_8.x86_64 glibc-langpack-de-2.34-275.0.1.el9_8.x86_64 glibc-langpack-en-2.34-275.0.1.el9_8.x86_64 glibc-langpack-es-2.34-275.0.1.el9_8.x86_64 glibc-langpack-fr-2.34-275.0.1.el9_8.x86_64 glibc-langpack-zh-2.34-275.0.1.el9_8.x86_64 Installed: glibc-static-2.34-275.0.1.el9_8.x86_64 libxcrypt-static-4.4.18-3.el9.x86_64 Complete!样例程序hello.c如下#includestdio.hintmain(void){printf(Hello, world!\n);return0;}默认编译动态链接$ gcc hello.c-ohello_dynamic $ls-lhello_dynamic -rwxr-xr-x.1vagrant vagrant17496Oct806:38 hello_dynamic $ ./hello_dynamic Hello, world!指定-static选项静态编译$ gcc-statichello.c-ohello_static $ls-lhello_static -rwxr-xr-x.1vagrant vagrant875792Oct806:39 hello_static $ ./hello_static Hello, world!最后清理静态库$sudoyum remove glibc-static Dependencies resolved.Package Architecture Version Repository SizeRemoving: glibc-static x86_642.34-275.0.1.el9_8 ol9_codeready_builder9.8M Removing unused dependencies: libxcrypt-static x86_644.4.18-3.el9 ol9_codeready_builder466k Transaction SummaryRemove2Packages Freed space:10M Is this ok[y/N]: y Running transaction check Transaction check succeeded. Running transactiontestTransactiontestsucceeded. Running transaction Preparing:1/1 Erasing:glibc-static-2.34-275.0.1.el9_8.x86_641/2 Erasing:libxcrypt-static-4.4.18-3.el9.x86_642/2 Verifying:glibc-static-2.34-275.0.1.el9_8.x86_641/2 Verifying:libxcrypt-static-4.4.18-3.el9.x86_642/2 Removed: glibc-static-2.34-275.0.1.el9_8.x86_64 libxcrypt-static-4.4.18-3.el9.x86_64 Complete!41-2 (附加题)请熟悉本章的演示程序。本章的演示程序位于目录tlpi-book/shlibs/demo。$ls*.c mod1.c mod2.c mod3.c prog.c $ls*.sh Demo_no_lib.sh Demo_shared_lib.sh Demo_static_lib.sh三个shell脚本分别生成不使用库使用静态库使用动态库共享库的可执行程序$ls-lprog_* -rwxr-xr-x.1vagrant vagrant1460496Oct807:45 prog_nolib -rwxr-xr-x.1vagrant vagrant18936Oct807:46 prog_so -rwxr-xr-x.1vagrant vagrant1419984Oct807:46 prog_static虽然不使用库与使用静态库的可执行文件大小近似但这两种方式存在明显的差别项目方式1直接链接.o方式2静态库 .a中间产物一堆独立.o文件.o 归档文件libdemo.a链接行为所有传入的.o全部完整并入可执行文件仅提取被用到的.o模块未引用模块丢弃可执行体积更大全部目标代码都包含更小只包含用到的模块复用性每次链接都要列出一堆.o不方便复用libdemo.a可以给多个程序重复链接只需写库名符号规则全部目标文件符号全部参与链接链接器按符号依赖按需提取归档内的目标模块适用场景少量文件、一次性编译多个程序共用一组模块打包复用41-3 (附加题)请演示Figure 41-5中的全局符号引用。按图准备2个c语言文件。foo.c如下#includestdio.hvoidxyz(){printf(foo-xyz\n);}voidfunc(){xyz();}prog.c如下#includestdio.hexternvoidfunc();voidxyz(){printf(main-xyz\n);}intmain(){func();return0;}第一种行为调用的是主函数中的xyz函数$ gcc-g-c-fPIC-Wall-cfoo.c $ gcc-g-shared-olibfoo.so foo.o $ gcc-g-oprog prog.c libfoo.so $LD_LIBRARY_PATH. ./prog main-xyz第二种行为调用的是共享库中的xyz函数$ gcc-g-c-fPIC-Wall-cfoo.c $ gcc-g-shared-Wl,-Bsymbolic-olibfoo.so foo.o $ gcc-g-oprog prog.c libfoo.so $LD_LIBRARY_PATH. ./prog foo-xyz最后看一个小错误的修补。ldd显示libfoo.so找不到$ ldd prog linux-vdso.so.1(0x00007ffd927d2000)libfoo.sonot found libc.so.6/lib64/libc.so.6(0x00007fd3f72df000)/lib64/ld-linux-x86-64.so.2(0x00007fd3f74f2000)但是此文件是存在的$find.-namelibfoo.so*./libfoo.so $ objdump-pprog|grepNEEDED NEEDED libfoo.so NEEDED libc.so.6原因是当前目录不在ldd的搜索路径中。如下就可以了$LD_LIBRARY_PATH$PWDldd prog linux-vdso.so.1(0x00007ffee0db4000)libfoo.so/home/vagrant/test/bak/libfoo.so(0x00007f5ca65d5000)libc.so.6/lib64/libc.so.6(0x00007f5ca63c4000)/lib64/ld-linux-x86-64.so.2(0x00007f5ca65dc000)
