The underlying cause appears to be that libm is referencing _LIB_VERSION in libperl.
I suspect the Oracle client libraries have dlopen()ed a library that depends on libm, and that isn't dlclosed() when mod_perl unloads DBD::Oracle. So the process that leads to the crash: 1) Apache starts it configuration check[1], loads mod_perl, which implicitly loads libperl (with PL_keyword_plugin set to its default) 2) mod_perl runs the startup script, loading Syntax::Keyword::Try (which points PL_keyword_plugin at its keyword handler) and DBD::Oracle (which presumably dlopen()s a shared object that depends on libm). 3) Apache unloads mod_perl, which unloads the shared objects for Syntax::Keyword::Try and DBD::Oracle. Since something still loaded depends on libm, and that depends on the _LIB_VERSION symbol defined by libperl, libperl remains loaded. PL_keyword_plugin now points to where the Syntax::Keyword::Try keyword handler *used* to be. 4) Apache loads mod_perl again, and attempts to parse the perl startup script. Since PL_keyword_plugin points to unmapped memory, libperl segfaults. Without something else depending on libm, libperl would normally be unloaded at step 3), and step 4) would reload libperl, with PL_keyword_plugin pointing at the default keyword plugin function. The patch incidentally prevents libm depending on the _LIB_VERSION symbol in libperl, so libperl can unload when mod_perl unloads. Tony [1] https://wiki.apache.org/httpd/ModuleLife
