On Wed, Nov 26, 2014 at 01:34:18PM +0200, Ants Aasma wrote: > glibc-2.3.4+ has a flag called RTLD_DEEPBIND for dlopen that prefers > symbols loaded by the library to those provided by the caller. Using > this flag fixes my issue, PostgreSQL gets the ldap functions from > libldap, Oracle client gets them from whatever it links to. Both work > fine. > > Attached is a patch that enables this flag on Linux when available. > This specific case could also be fixed by rewriting oracle_fdw to use > dlopen for libclntsh.so and pass this flag, but I think it would be > better to enable it for all PostgreSQL loaded extension modules. I > can't think of a sane use case where it would be correct to prefer > PostgreSQL loaded symbols to those the library was actually linked > against. > > Does anybody know of a case where this flag wouldn't be a good idea?
There's a meta-downside that any bug the flag prevents will still exist on non-glibc targets, and that's the primary reason not to make this change in core PostgreSQL. Most hackers use GNU/Linux as a primary development platform, so RTLD_DEEPBIND would delay discovery of still-present bugs. Standard POSIX symbol resolution has some advantages over RTLD_DEEPBIND. Any given program has at most one global symbol called "malloc", and so-named symbols usually get away with assuming they own the brk() space. LD_PRELOAD can overload any global symbol. Those points by themselves would not stop me from using RTLD_DEEPBIND in specific cases like oracle_fdw, though. > Are there any similar options for other platforms? Alternatively, does > anyone know of linker flags that would give a similar effect? It has some overlap with the -Bsymbolic linker option. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
