Re: [libc] dlclose gives "invalid shared object handle" without pthread combination.

[venki kaps <venkiece2005%gmail.com@localhost>]

Hi,

I have been porting NetBSD source in the Linux environment with our own
pthread library.

system environment:
Compiler: arm-linux-gcc-4.3.3
OS: Linux
Kernel: 2.6.29

Yes, it never even calls dlerr() in dlcose
but NetBSD __dlclose(void *handle) source sequence,

int
dlclose(void *handle)
{
        Obj_Entry *root = _rtld_dlcheck(handle);

        if (root == NULL)
                return -1;

        _rtld_debug.r_state = RT_DELETE;
        _rtld_debug_state();

        --root->dl_refcount;
        _rtld_unload_object(root, true);

        _rtld_debug.r_state = RT_CONSISTENT;
        _rtld_debug_state();

        return 0;
}

static Obj_Entry *
_rtld_dlcheck(void *handle)
{
        Obj_Entry *obj;

        for (obj = _rtld_objlist; obj != NULL; obj = obj->next)
                if (obj == (Obj_Entry *) handle)
                        break;
        xprintf("obj->dl_refcount is %d\n",obj->dl_refcount);
        if (obj == NULL || obj->dl_refcount == 0) {
                xwarnx("Invalid shared object handle %p", handle);
                return NULL;
        }
        return obj;
}

I have printed  xprintf("obj->dl_refcount is %d\n",obj->dl_refcount);
 obj->dl_refcount is getting zero(0).
So due to "obj->dl_refcount == 0"
the error "invalid shared object handle" is showing.

i do not know why this error is coming even though all the
constructor/destructor sequences are completed.

is it rtld_exit->fini->static C++ destructor->dlcose sequence problem?

Thanks & Regards,
Venkappa
On Wed, Jun 17, 2009 at 5:37 AM, Alexander Kabaev<kabaev%gmail.com@localhost> 
wrote:
> Hi,
>
> I do not think we on FreeBSD support NetBSD rtld with our pthread
> libraries, unless you already implemented all the necessary glue.
> The interface between threading library and rtld is rather intimate and
> tricky to get right.
>
> You provide no code to look at nor explicitly mention what OS and
> what version you are running your test on (FreeBSD?), I think you are
> on your own. Furthermore, your claim on 'correct'
> constructor/destructor is wrong given the sample code provided by
> NetBSD PR.
>
> Some more comments are inline.
>
> On Tue, 16 Jun 2009 14:59:36 +0530
> venki kaps <venkiece2005%gmail.com@localhost> wrote:
>
>> Hi,
>>
>> I am using the NetBSD implementation of rtld(src/libexec/ld.elf_so/)
>> for ARM/MIPS.
>>
>> I have C++ static constructor/destructor issue with my rtld.
>>
>> Problem Report:
>> "ld.elf_so does not execute .init/.fini functions in order" and [libc]
>> dlclose gives
>> "invalid shared object handle" when called through the fini function
>> of another module.
>>
>> The similar NetBSD/freeBSD issues are found from the following
>> References: [1] http://gnats.netbsd.org/37347
>> [2] http://updraft3.jp.freebsd.org/cgi/query-pr.cgi?pr=kern/42956
>>
>> The above issues are already commited in NetBSD-5-0-RELEASE.
>>
>> I have ported NetBSD-5-0-RELEASE rtld and tested Ref[1] provided
>> static constructor/destructor test and did not find any issues
>> with shared pthread combination but noticed [libc] dlclose gives
>> "invalid shared object handle" without pthread combination.
>>
>> The static constructor/destructor test results:
>>
>> It should be :
>> --------------
>>
>> $ ./foobar
>> foo_ctor
>> bar_ctor
>> tar_ctor
>> main_ctor
>> dep1_ctor
>> dep2_ctor
>> dll_ctor
>> dll_dtor
>> dep2_dtor
>> dep1_dtor
>> main_dtor
>> tar_dtor
>> bar_dtor
>> foo_dtor
>
> Given the test in Ref[1], both constructor and destructor orders are
> wrong above. libdep1 depends on libdep2, so dep2_ctor should be invoked
> before dep1_ctor and consequently dep2_dtor should be invoked after
> dep1_dtor.
>
>> While currently I get:
>> ----------------------
>>
>> with pthreads:
>>
>> $ ./foobar
>> foo_ctor
>> bar_ctor
>> tar_ctor
>> main_ctor
>> dep1_ctor
>> dep2_ctor
>> dll_ctor
>> dll_dtor
>> dep2_dtor
>> dep1_dtor
>> main_dtor
>> tar_dtor
>> bar_dtor
>> foo_dtor
>>
>> without pthreads:
>>
>> $ ./foobar
>> foo_ctor
>> bar_ctor
>> tar_ctor
>> main_ctor
>> dep1_ctor
>> dep2_ctor
>> dll_ctor
>> dll_dtor
>> dep2_dtor
>> dep1_dtor
>> main_dtor
>> tar_dtor
>> bar_dtor
>> foo_dtor
>> Invalid shared object handle 0xbdbed400
>
> Again, given the sample code from NetBSD PR cannot possibly print this
> message because it never even calls dlerr(). You must be looking at
> some other code and unless you provide it, understanding your problem
> and fixing it is next to impossible.
>
> Said that, thanks for pointing the FreeBSD PR to me. I will commit the
> fix for the problem described here shortly.
>
>> This gives a "invalid shared object handle" message
>> because the refcount field (obj->dl_refcount) for the handle is zero.
>>
>> I have little bit confused about dlclose destructor
>> with/without pthreads.
>>
>> I have some queries:
>> 1) Is it required any changes apart from the
>> NetBSD-5-0-RELEASE/{Ref[1],[2]}? 2) Are any changes required in
>> thread-stub?
>>
>> Could anyone provide any inputs to the my issue?
>>
>> Thanks in advance.
>>
>> Thanks & Regards,
>> Venkappa
>
> --
> Alexander Kabaev
>