threads/103975: Implicit loading/unloading of libpthread.so may crash user processes

[Daniel Eischen]

On Fri, 6 Oct 2006, Takahiro Kurosawa wrote:

> Alexander Kabaev <kabaev at gmail.com> wrote:
>> On Thu, 5 Oct 2006 09:06:20 -0400
>> John Baldwin <john at baldwin.cx> wrote:
>> 
>> > > To fix the problem, a function that has __attribute__((destructor))
>> > > in libpthread should probably be implemented in order to recover
>> > > the initial state before unloading.
>> >
>> > I'm not sure you can recover the state actually, hence why I think
>> > maybe we should make it so that libpthread doesn't unload once it has
>> > been loaded.
>
> I understand that it's way easier to prohibit unloading of libpthread
> than to change the code safely unloadable.
> Thanks for your explanation, John!
>
>> Linux does not allow pthread library to be unloaded presumably because
>> of reasons like this. From readelf -a /compat/linux/lib/libpthread.so.0:
>>
>>  0x6ffffffb (FLAGS_1)                    Flags: NODELETE INITFIRST
>> 
>> Infortunately, rtld does not implement NODELETE and INITFIRST. Both are
>> addressed in my patch that I am yet to commit.
>
> I'm looking forward to the commit of your patch into the CVS repository :-)
> Maybe the following line should be added to src/lib/libpthread/Makefile
> when rtld supports the NODELETE flag? :
> LDFLAGS+=-Wl,-znodelete

If that's the knob, then I'd agree.  You also want to make
the same change to libthr.

-- 
Dan