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This works by linking the code for the modules into theapplication in advance, and then looking up the addresses of the alreadyloaded symbols when <CODE>lt_dlsym</CODE> is called. We call this mechanism<EM>dlpreopening</EM> -- so named because the modules must be loaded atlink time, not because the API to use modules loaded in this way isany different.</P><P>This feature is extremely useful for debugging, allowing you to make afully statically linked application from the executable and moduleobjects, without changing any source code to work around the moduleloading calls. As far as the code outside the libltdl APIcan tell, these modules really are being loaded dynamically. Driving asymbolic debugger across module boundaries is however much easier whenblocks of code aren't moving in and out of memory during execution.</P><P>You may have wondered about the purpose of the following line in thedynamic module code in <A HREF="autobook_170.html#SEC170">Dependent Libraries</A>:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>#define run ltdl_module_LTX_run</pre></td></tr></table></P><P>The reason for redefining the entry point symbol in this way is toprevent a symbol clash when two or more modules that provideidentically named entry point functions are preloaded into anexecutable. It would be otherwise impossible to preload both<TT>`simple-module.c'</TT> and <TT>`ltdl-module.c'</TT>, for example, sinceeach defines the symbol <SAMP>`run'</SAMP>. To allow us to write dynamicmodules that are potentially preloaded, <CODE>lt_dlsym</CODE> will first tryto lookup the address of a named symbol with a prefix consisting of thecanonicalized name of the module being searched, followed by the?? 快捷鍵說明
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