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

The following reply was made to PR threads/103975; it has
been noted by GNATS.

From: "Takahiro Kurosawa"
<takahiro.kurosawagmail.com>
To: "Alexander Kabaev" <kabaevgmail.com>
Cc: "John Baldwin" <johnbaldwin.cx>,
freebsd-threadsfreebsd.org, 
	freebsd-gnats-submitfreebsd.org
Subject: Re: threads/103975: Implicit loading/unloading of
libpthread.so may crash user processes
Date: Fri, 6 Oct 2006 17:49:48 +0900

 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
 
 Thanks,
 --
 KUROSAWA, Takahiro
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