Linux下共享库的系统路径和查找

文章由LinuxBoy分享于2019-03-27 06:03:27热评（623）

在使用qvfb做framebuffer模拟的时候,发现几个问题:第一个就是Ubuntu的确不专业,没有很多库的支持,最好使用RedHat,Fedora之类的发行版本,这样会少很多编译之类的麻烦.

由于在Ubuntu下编译qvfb缺少了很多库文件,而在没有网络的情况下,补齐这些库和头文件是非常麻烦的,所以准备在fedora中编译好后再放到Ubuntu中使用.由于Ubuntu和fedora下qtsdk的安装不一致,从而发现fedora下编译好的qvfb放到Ubuntu下执行,发现找不到库.

利用strace工具看一下这个过程,因为是在fedora下编译的,所以makefile中的链接选项有指明链接库的地址-rpath,这个地址就是sdk安装目录下的库目录.

所以在fedora下直接打开这个目录,加载相应的库文件.而在Ubuntu下sdk的安装目录不一致,系统的库搜索路径又没有这个库,所以执行肯定会报错.在Ubuntu下strace下这个过程,就会发现有很多open /usr/lib之类的操作.

man ld,该文档中给出了共享库的系统路径和查找优先级:

The linker uses the following search paths to locate required

shared libraries:

1. Any directories specified by -rpath-link options.

2. Any directories specified by -rpath options. The difference

between -rpath and -rpath-link is that directories specified by

-rpath options are included in the executable and used at

runtime, whereas the -rpath-link option is only effective at

link time. Searching -rpath in this way is only supported by

native linkers and cross linkers which have been configured

with the --with-sysroot option.

3. On an ELF system, for native linkers, if the -rpath and

-rpath-link options were not used, search the contents of the

environment variable "LD_RUN_PATH".

4. On SunOS, if the -rpath option was not used, search any

directories specified using -L options.

5. For a native linker, the search the contents of the environment

variable "LD_LIBRARY_PATH".

6. For a native ELF linker, the directories in "DT_RUNPATH" or

"DT_RPATH" of a shared library are searched for shared

libraries needed by it. The "DT_RPATH" entries are ignored if

"DT_RUNPATH" entries exist.

7. The default directories, normally /lib and /usr/lib.

8. For a native linker on an ELF system, if the file

/etc/ld.so.conf exists, the list of directories found in that

file.

If the required shared library is not found, the linker will issue

a warning and continue with the link.

所以,如果要想在ubuntu下运行fedora下编译的qvfb,可以在/usr/lib下做一下qt库的链接,将其指向qtsdk安装目录的库目录下的库.这样,就可以运行了.其实在嵌入式qt开发中也是这样的:所有的动态库我们都放在/lib下,这样应用程序就都可以找到库了。

相关阅读：关于Ubuntu添加共享库路径

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