version 2, including all changes.
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DLOPEN |
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!!!DLOPEN |
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NAME |
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SYNOPSIS |
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DESCRIPTION |
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RETURN VALUE |
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EXAMPLE |
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ACKNOWLEDGEMENTS |
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SEE ALSO |
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---- |
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!!NAME |
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dlclose, dlerror, dlopen, dlsym - Programming interface to dynamic linking loader. |
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!!SYNOPSIS |
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__#include __ |
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__void *dlopen (const char *__''filename''__, int__ |
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''flag''__); |
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const char *dlerror(void); |
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void *dlsym(void *__''handle''__, char |
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*__''symbol''__); |
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int dlclose (void *__''handle''__);__ |
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Special symbols: ___init__, ___fini__. |
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!!DESCRIPTION |
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__dlopen__ loads a dynamic library from the file named by |
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the null terminated string ''filename'' and returns an |
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opaque |
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''filename'' is not an absolute path (i.e., it does not |
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begin with a |
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'' |
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A colon-separated list of directories in the user's |
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__LD_LIBRARY_PATH__ environment variable. |
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The list of libraries cached in |
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''/etc/ld.so.cache''. |
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''/usr/lib'', followed by ''/lib''. |
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If ''filename'' is a NULL pointer, then the returned |
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handle is for the main program. |
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External references in the library are resolved using the |
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libraries in that library's dependency list and any other |
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libraries previously opened with the __RTLD_GLOBAL__ |
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flag. If the executable was linked with the flag |
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__ |
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''flag'' must be either __RTLD_LAZY__, meaning resolve |
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undefined symbols as code from the dynamic library is |
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executed, or __RTLD_NOW__, meaning resolve all undefined |
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symbols before __dlopen__ returns, and fail if this |
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cannot be done. Optionally, __RTLD_GLOBAL__ may be or'ed |
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with ''flag,'' in which case the external symbols defined |
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in the library will be made available to subsequently loaded |
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libraries. |
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If the library exports a routine named ___init__, then |
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that code is executed before dlopen returns. If the same |
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library is loaded twice with __dlopen()__, the same file |
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handle is returned. The dl library maintains link counts for |
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dynamic file handles, so a dynamic library is not |
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deallocated until __dlclose__ has been called on it as |
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many times as __dlopen__ has succeeded on |
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it. |
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If __dlopen__ fails for any reason, it returns NULL. A |
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human readable string describing the most recent error that |
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occurred from any of the dl routines (dlopen, dlsym or |
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dlclose) can be extracted with __dlerror()__. |
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__dlerror__ returns NULL if no errors have occurred since |
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initialization or since it was last called. (Calling |
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__dlerror()__ twice consecutively, will always result in |
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the second call returning NULL.) |
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__dlsym__ takes a |
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__dlsym__ returns NULL; however, the |
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correct way to test for an error from __dlsym__ is to |
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save the result of __dlerror__ into a variable, and then |
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check if saved value is not NULL. This is because the value |
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of the symbol could actually be NULL. It is also necessary |
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to save the results of __dlerror__ into a variable |
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because if __dlerror__ is called again, it will return |
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NULL. |
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__dlclose__ decrements the reference count on the dynamic |
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library handle ''handle''. If the reference count drops |
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to zero and no other loaded libraries use symbols in it, |
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then the dynamic library is unloaded. If the dynamic library |
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exports a routine named ___fini__, then that routine is |
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called just before the library is unloaded. |
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!!RETURN VALUE |
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__dlclose__ returns 0 on success, and non-zero on |
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error. |
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!!EXAMPLE |
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__Load the math library, and print the cosine of |
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2.0:__ |
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#include |
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If this program were in a file named |
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gcc -rdynamic -o foo foo.c -ldl |
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!!ACKNOWLEDGEMENTS |
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The dlopen interface standard comes from Solaris. The Linux |
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dlopen implementation was primarily written by Eric |
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Youngdale with help from Mitch D'Souza, David Engel, Hongjiu |
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Lu, Andreas Schwab and others. The manual page was written |
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by Adam Richter. |
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!!SEE ALSO |
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2 |
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ld(1), ld.so(8), ldconfig(8), |
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ldd(1), __ld.so.info__ |
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---- |