Sebastian Steiger writes:
> The interesting part of the output when LD_DEBUG=all is this:
>
> 21475: file=libgomp.so.1 [0]; generating link map
> 21475: symbol=dlerror; lookup in file=python
> 21475: symbol=dlerror; lookup in
> file=/usr/lib64/libpython2.3.so.1.0
> 21475: symbol=dlerror; lookup in file=/lib64/tls/libpthread.so.0
> 21475: symbol=dlerror; lookup in file=/lib64/libdl.so.2
> 21475: binding file /usr/lib64/libpython2.3.so.1.0 to
> /lib64/libdl.so.2: normal symbol `dlerror' [GLIBC_2.2.5]
> 21475: symbol=__dcgettext; lookup in file=python
> 21475: symbol=__dcgettext; lookup in
> file=/usr/lib64/libpython2.3.so.1.0
> 21475: symbol=__dcgettext; lookup in
> file=/lib64/tls/libpthread.so.0
> 21475: symbol=__dcgettext; lookup in file=/lib64/libdl.so.2
> 21475: symbol=__dcgettext; lookup in file=/lib64/libutil.so.1
> 21475: symbol=__dcgettext; lookup in file=/lib64/tls/libm.so.6
> 21475: symbol=__dcgettext; lookup in file=/lib64/tls/libc.so.6
> 21475: binding file /lib64/libdl.so.2 to /lib64/tls/libc.so.6:
> normal symbol `__dcgettext' [GLIBC_2.2.5]
> 21475: symbol=__asprintf; lookup in file=python
> 21475: symbol=__asprintf; lookup in
> file=/usr/lib64/libpython2.3.so.1.0
> 21475: symbol=__asprintf; lookup in
> file=/lib64/tls/libpthread.so.0
> 21475: symbol=__asprintf; lookup in file=/lib64/libdl.so.2
>
> < The rest is just python stuff for error handling and screen output.>
>
>
>
> This encouraged me to take a sample C++ file for testing dlopen() which
> I found on the internet:
>
>
> #include <iostream>
> #include <dlfcn.h>
> using namespace std;
>
> int main()
> {
> void* handle = dlopen("(...)/libgomp.so.1", RTLD_LAZY);
>
> if (!handle) {
> cerr << "Cannot open library: " << dlerror() << '\n';
> return 1;
> }
> cout << "Loading was successful. Closing library...\n";
> dlclose(handle);
> }
>
>
>
> I compiled this file with g++4 -o dlopen_test.bin dlopen_test.cpp -ldl
> (I called the file dlopen_test.cpp) and got the following output:
>
> "Cannot open library: (...)/libgomp.so.1: shared object cannot be
> dlopen()ed"
>
>
> Obviously the output of the python shell was just dlerror(), but it is
> not very instructive.
>
> I also tried RTLD_NOW instead of RTLD_LAZY, but the error was the same.
This message comes from the dynamic linker:
/* Make sure we are not dlopen'ing an object
that has the DF_1_NOOPEN flag set. */
if (__builtin_expect (l->l_flags_1 & DF_1_NOOPEN, 0)
&& (mode & __RTLD_DLOPEN))
{
/* We are not supposed to load this object. Free all resources. */
__munmap ((void *) l->l_map_start, l->l_map_end - l->l_map_start);
...
errstring = N_("shared object cannot be dlopen()ed");
goto call_lose;
}
Because when you (or someone else) built libgomp.so.1, the object
was marked with the NOOPEN flag. From "info ld":
-z nodlopen
Marks the object not available to `dlopen'.
