在使用qvfb做framebuffer模擬的時候,發現幾個問題:第一個就是Ubuntu的確不專業,沒有很多庫的支持,最好使用RedHat,Fedora之類的發行版本,這樣會少很多編譯之類的麻煩.
由於在Ubuntu下編譯qvfb缺少了很多庫文件,而在沒有網絡的情況下,補齊這些庫和頭文件是非常麻煩的,所以准備在fedora中編譯好後再放到Ubuntu中使用.由於Ubuntu和fedora下qtsdk的安裝不一致,從而發現fedora下編譯好的qvfb放到Ubuntu下執行,發現找不到庫.
利用strace工具看一下這個過程,因為是在fedora下編譯的,所以makefile中的鏈接選項有指明鏈接庫的地址-rpath,這個地址就是sdk安裝目錄下的庫目錄.
所以在fedora下直接打開這個目錄,加載相應的庫文件.而在Ubuntu下sdk的安裝目錄不一致,系統的庫搜索路徑又沒有這個庫,所以執行肯定會報錯.在Ubuntu下strace下這個過程,就會發現有很多open /usr/lib之類的操作.
man ld,該文檔中給出了共享庫的系統路徑和查找優先級:
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下運行fedora下編譯的qvfb,可以在/usr/lib下做一下qt庫的鏈接,將其指向qtsdk安裝目錄的庫目錄下的庫.這樣,就可以運行了.其實在嵌入式qt開發中也是這樣的:所有的動態庫我們都放在/lib下,這樣應用程序就都可以找到庫了。
相關閱讀：關於Ubuntu添加共享庫路徑 http://www.linuxidc.com/Linux/2011-10/45745.htm
