The following reply was made to PR threads/103975; it has
been noted by GNATS.
From: Daniel Eischen <deischen freebsd.org>
To: Takahiro Kurosawa <takahiro.kurosawagmail.com>
Cc: Alexander Kabaev <kabaevgmail.com>, John Baldwin
<johnbaldwin.cx>,
freebsd-gnats-submitfreebsd.org,
freebsd-threadsfreebsd.org
Subject: Re: threads/103975: Implicit loading/unloading of
libpthread.so may
crash user processes
Date: Fri, 6 Oct 2006 08:42:19 -0400 (EDT)
On Fri, 6 Oct 2006, Takahiro Kurosawa wrote:
> Alexander Kabaev <kabaevgmail.com> wrote:
>> On Thu, 5 Oct 2006 09:06:20 -0400
>> John Baldwin <johnbaldwin.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
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