Usage of vptr shouldn't be very different between them. Allen Samuels SanDisk |a Western Digital brand 2880 Junction Avenue, San Jose, CA 95134 T: +1 408 801 7030| M: +1 408 780 6416 allen.samuels@xxxxxxxxxxx > -----Original Message----- > From: Willem Jan Withagen [mailto:wjw@xxxxxxxxxxx] > Sent: Thursday, December 22, 2016 4:48 PM > To: Brad Hubbard <bhubbard@xxxxxxxxxx>; Allen Samuels > <Allen.Samuels@xxxxxxxxxxx> > Cc: Ceph Development <ceph-devel@xxxxxxxxxxxxxxx> > Subject: Re: An empty vptr in an raw object > > On 23-12-2016 01:19, Brad Hubbard wrote: > > Any clue from Valgrind? > > > > Did you say this only happens with clang or doesn't happen with clang? > > I have to comment this piece of code to get unittest_denc to pass. > And with GCC this does not happen. > > But I'm not sure how GCC does its class function table stuff. > And whether that also involves a vptr? > > --WjW > > > On Fri, Dec 23, 2016 at 8:01 AM, Allen Samuels > > <Allen.Samuels@xxxxxxxxxxx> wrote: > >> I believe I mis-read the data. What I've seen before doesn't fit this data. > >> > >> If it fails in unit test, it shouldn't be hard to just set a HW breakpoint on > the vptr and see who the culprit is. > >> > >> > >> Allen Samuels > >> SanDisk |a Western Digital brand > >> 2880 Junction Avenue, San Jose, CA 95134 > >> T: +1 408 801 7030| M: +1 408 780 6416 allen.samuels@xxxxxxxxxxx > >> > >> > >>> -----Original Message----- > >>> From: Willem Jan Withagen [mailto:wjw@xxxxxxxxxxx] > >>> Sent: Thursday, December 22, 2016 10:37 AM > >>> To: Allen Samuels <Allen.Samuels@xxxxxxxxxxx>; Ceph Development > >>> <ceph-devel@xxxxxxxxxxxxxxx> > >>> Subject: Re: An empty vptr in an raw object > >>> > >>> On 22-12-2016 19:02, Allen Samuels wrote: > >>>> I have seen cases of null vptr due to an incompletely constructed > object, > >>> i.e., an object that's in the middle of being constructed. > >>> > >>> I going to believe you right away. > >>> But I'm having a hard time imagining such a case. > >>> > >>> Are you suggesting a object is referenced, whilest it is not yet complete. > who > >>> does the referencing then? due to threading? > >>> That would be even harder to find. > >>> > >>> --WjW > >>> > >>> > >>>> Allen Samuels > >>>> SanDisk |a Western Digital brand > >>>> 951 SanDisk Drive, Milpitas, CA 95035 > >>>> T: +1 408 801 7030| M: +1 408 780 6416 allen.samuels@xxxxxxxxxxx > >>>> > >>>> > >>>>> -----Original Message----- > >>>>> From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel- > >>>>> owner@xxxxxxxxxxxxxxx] On Behalf Of Willem Jan Withagen > >>>>> Sent: Thursday, December 22, 2016 9:41 AM > >>>>> To: Ceph Development <ceph-devel@xxxxxxxxxxxxxxx> > >>>>> Subject: An empty vptr in an raw object > >>>>> > >>>>>> I have a piece of code that actually seem to crash because the vptr > >>>>>> is not set: > >>>>>> (gdb) p *_raw > >>>>>> $2 = {_vptr$raw = 0x0, data = 0x10cc000 "\003", len = 72, nref = > >>>>>> {val = 1}, crc_spinlock = 0, crc_map = {__tree_ = { > >>>>>> __begin_node_ = 0x10cc078, > >>>>>> __pair1_ = > >>>>>> > >>>>> > >>> > {<std::__1::__libcpp_compressed_pair_imp<std::__1::__tree_end_node<st > >>>>> d::__1::__tree_node_base<void*>*>, > >>>>>> > >>>>> > std::__1::allocator<std::__1::__tree_node<std::__1::__value_type<std: > >>>>> :__1 > >>>>> ::pair<unsigned > >>>>>> long, unsigned long>, std::__1::pair<unsigned int, unsigned int> >, > >>>>>> void*> >, 2>> = > >>>>>> > >>>>> > {<std::__1::allocator<std::__1::__tree_node<std::__1::__value_type<st > >>>>> d::_ > >>>>> _1::pair<unsigned > >>>>>> long, unsigned long>, std::__1::pair<unsigned int, unsigned int> >, > >>>>>> void*> >> = {<No data fields>}, __first_ = { > >>>>>> __left_ = 0x0}}, <No data fields>}, > >>>>>> > >>>>>> The function that crashes: > >>>>>> char *buffer::ptr::c_str() { > >>>>>> assert(_raw); > >>>>>> if (buffer_track_c_str) > >>>>>> buffer_c_str_accesses.inc(); > >>>>>> char *p = _raw->get_data(); > >>>>>> return p + _off; > >>>>>> } > >>>>>> > >>>>>> And crash is actually on the return line. > >>>>>> > >>>>>> Any ideas as how the vptr can be empty? > >>>>> > >>>>> Now the _vptr$raw point is part of the internal code of the clang > >>>>> class function table/constructor. Overwriting that means that > >>>>> class-function references are problematic to say the least. (in this > >>> example get_data()). > >>>>> > >>>>> The major reason why this occurs is because an object is being zeroed > >>>>> in C-style way: memset( &obj, 0, sizeof(obj)) And thus overwriting > >>>>> the _vptr. > >>>>> > >>>>> Note that this does not bite the FreeBSD compilation, but also any > >>>>> other attempts to build Ceph with clang. > >>>>> > >>>>> Now the strange thing is that this does not bite Clang compilation > >>>>> much more. But the only test that fails is unittest_denc. So I guess > >>>>> that most of the code is rather well behaved. > >>>>> > >>>>> And I'm off on a search to find the culprit. > >>>>> > >>>>> --WjW > >>>>> > >>>>> > >>>>> > >>>>> -- > >>>>> To unsubscribe from this list: send the line "unsubscribe ceph-devel" > >>>>> in the body of a message to majordomo@xxxxxxxxxxxxxxx More > >>> majordomo > >>>>> info at http://vger.kernel.org/majordomo-info.html > >> > > > > > > ��.n��������+%������w��{.n����z��u���ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
