Linux下動態共享庫 連線和載入路徑

mybwu_com發表於2014-02-19
Linux

1. 連線時找不到某一個函式，出現“ xxxxx undefined”，應該就是連線時找不到相應的動態庫，連線時動態庫的路徑如下：

1> 預設路徑是：/lib, /usr/lib/, /usr/local/lib

2> -L: 指定連線時動態庫的路徑

3> LD_LIBRARY_PATH: 指定連線路徑

2. 執行應用程式時出現“error<wbr>while loading shared libraries”，則是載入時找不到相應的動態庫</wbr>

下面的文章詳細介紹了動態庫的載入路徑：

http://blog.sina.com.cn/s/blog_6bf372530100o25v.html

對動態庫的實際應用還不太熟悉的讀者可能曾經遇到過類似“error<wbr>while loading shared libraries”這樣的錯誤，這是典型的因為需要的動態庫不在動態連結器ld.so的搜尋路徑設定當中導致的。</wbr>

　　具體說來，動態連結器ld.so按照下面的順序來搜尋需要的動態共享庫：

　　1．ELF可執行檔案中動態段中DT_RPATH所指定的路徑。這實際上是通過一種不算很常用，卻比較實用的方法所設定的：編譯目的碼時，可以對gcc加入連結引數“-Wl,-rpath”指定動態庫搜尋路徑；

　　2．環境變數LD_LIBRARY_PATH指定的動態庫搜尋路徑；

　　3．/etc/ld.so.cache中所快取的動態庫路徑（如果支援ld.so.cache的話）。這可以通過修改配置檔案/etc/ld.so.conf中指定的動態庫搜尋路徑來改變；

　　4．預設的動態庫搜尋路徑/lib；

　　5．預設的動態庫搜尋路徑/usr/lib。

　　在嵌入式Linux系統的實際應用中，1和2被經常使用，也有一些相對簡單的的嵌入式系統會採用4或5的路徑來規範動態庫。3在嵌入式系統中使用的比較少，因為有很多系統根本就不支援ld.so.cache。

　　4和5的方式非常簡單，只要將所需要的庫放到/lib或/usr/lib就可以解決找不到庫的問題，不過對於大一些的系統來說，不太方便管理。1和2的方式要稍微複雜一些，下面我們用一個非常簡單的例子來說明如何應用。

　　首先編寫一個最簡單的動態共享庫，原始碼pirnt.c如下：

　　1<wbr>#include &lt;stdio.h&gt;</wbr>

　　2

　　3<wbr>void print_foo()</wbr>

　　4<wbr>{</wbr>

　　5<wbr><wbr><wbr><wbr><wbr>printf("fooooooooo\n");</wbr></wbr></wbr></wbr></wbr>

　　6<wbr>}</wbr>

　　注意將它編譯成共享庫：

　　# gcc print.c -shared -o libprint.so

　　# file libprint.so

　　libprint.so: ELF 32-bit LSB shared object,<wbr><a target="_blank" href="http://www.dzsc.com/stock-ic/INTEL.html" style="color:rgb(0,0,0)">Intel</a><wbr>80386,<wbr><a target="_blank" href="http://www.dzsc.com/stock/V/VERSION.html" style="color:rgb(0,0,0)">version</a><wbr>1 (SYSV), not stripped</wbr></wbr></wbr></wbr>

　　呼叫該共享庫main.c程式碼如下：

　　1<wbr>#include &lt;stdio.h&gt;</wbr>

　　2

　　3<wbr>extern void print_foo();</wbr>

　　4

　　5<wbr>int main()</wbr>

　　6<wbr>{</wbr>

　　7<wbr><wbr><wbr><wbr><wbr>print_foo();</wbr></wbr></wbr></wbr></wbr>

　　8

　　9<wbr><wbr><wbr><wbr><wbr>return 0;</wbr></wbr></wbr></wbr></wbr>

　　10<wbr>}</wbr>

　　編譯之後的執行結果如下：

　　# gcc main.c -L./ -lprint -o pfoo

　　# ./pfoo

　　./pfoo: error while loading shared libraries: libprint.so: cannot<wbr><a target="_blank" href="http://www.dzsc.com/stock/O/OPEN.html" style="color:rgb(0,0,0)">open</a><wbr>shared object file: No such file or directory</wbr></wbr>

　　這便是典型的找不到動態庫的錯誤。通常我們可以通過設定環境變數LD_LIBRARY_PATH來指定動態庫的搜尋路徑（即上面的方法2），比如這樣就可以正確執行了：

　　# export LD_LIBRARY_PATH=./

　　# ./pfoo

　　fooooooooo

　　但這種方法有一個明顯的缺點：一旦LD_LIBRARY_PATH被設定，則在這個環境變數生效的範圍之內，所有其他的ELF可執行程式也會按照這個順序去搜尋動態庫，這樣勢必會造成搜尋時的一些浪費。

　　我們也可以使用另外一種方案來解決這種問題，即利用引數“-Wl,-rpath”在編譯時指定執行時的搜尋路徑（即上面的方法1），如下所示：

　　# unset LD_LIBRARY_PATH

　　# echo $LD_LIBRARY_PATH

　　# gcc main.c -L./ -lprint -o pfoo_r -Wl,-rpath=./

　　# ./pfoo

　　./pfoo: error while loading shared libraries: libprint.so: cannot open shared object file: No such file or directory

　　# ./pfoo_r

　　fooooooooo

　　我們首先unset了LD_LIBRARY_PATH，可以看到它已經不再有效了（當然這不是使用引數“-Wl,-rpath”的必要步驟，在這裡只是為了說明它已經不再起作用了），而且”pfoo”程式執行時也會發生找不到庫的錯誤，而我們加入編譯引數“-Wl,-rpath,./”之後得到的pfoo_r程式則能正常執行。

　　事實上我們可以通過readelf工具來檢視兩個檔案的差異：

　　# readelf -d pfoo

　　Dynamic segment at offset 0x514 contains 21 entries:

　　Tag<wbr><wbr><wbr><wbr><wbr><wbr><wbr>Type<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Name/Value</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000001 (NEEDED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Shared library: [libprint.so]</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000001 (NEEDED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Shared library: [libc.so.6]</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000c (INIT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048344</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000d (FINI)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x80484e0</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000004 (HASH)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048128</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000005 (STRTAB)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048240</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000006 (SYMTAB)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048170</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000a (STRSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>178 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000b (SYMENT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>16 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000015 (DEBUG)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x0</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000003 (PLTGOT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x80495f8</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000002 (PLTRELSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>16 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000014 (PLTREL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>REL</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000017 (JMPREL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048334</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000011 (REL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x804832c</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000012 (RELSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>8 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000013 (RELENT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>8 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6ffffffe (VERNEED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x804830c</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6fffffff (VERNEEDNUM)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>1</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6ffffff0 (VERSYM)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x80482f2</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000000 (NULL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x0</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　[root@localhost ldpath]# readelf -d pfoo_r

　　Dynamic segment at offset 0x518 contains 22 entries:

　　Tag<wbr><wbr><wbr><wbr><wbr><wbr><wbr>Type<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Name/Value</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000001 (NEEDED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Shared library: [libprint.so]</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000001 (NEEDED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Shared library: [libc.so.6]</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000f (RPATH)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Library rpath: [./]</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000c (INIT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048348</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000d (FINI)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x80484e4</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000004 (HASH)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048128</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000005 (STRTAB)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048240</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000006 (SYMTAB)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048170</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000a (STRSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>181 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x0000000b (SYMENT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>16 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000015 (DEBUG)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x0</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000003 (PLTGOT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8049*</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000002 (PLTRELSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>16 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000014 (PLTREL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>REL</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000017 (JMPREL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048338</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000011 (REL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048330</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000012 (RELSZ)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>8 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000013 (RELENT)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>8 (bytes)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6ffffffe (VERNEED)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x8048310</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6fffffff (VERNEEDNUM)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>1</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x6ffffff0 (VERSYM)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x80482f6</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　0x00000000 (NULL)<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>0x0</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

　　“readelf -d”可以用來檢視ELF檔案的動態節(Dynamic Section)。對比pfoo 和pfoo_r的結果我們可以發現，pfoo_r中多出來了RPATH項，指定”Library rpath: [./]”。通過這種方式，我們可以用非常小的代價（僅增加幾乎可以忽略的空間開銷），對每個ELF檔案都指定最優化的搜尋路徑，達到提升效能的目的。這是我們比較推薦的一種方法。當然了，具體如果操作依賴於具體的軟體系統的情況，簡單的系統中直接將所有的庫都放到/lib下也未嘗不是一種簡單易行的優化方案。

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