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
