On 23-12-2016 15:26, Sage Weil wrote:
> On Fri, 23 Dec 2016, Willem Jan Withagen wrote:
>> On 22-12-2016 23:01, Allen Samuels 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.
>>
>> Well the _raw class is properly initialised:
>> $8 = {_vptr$raw = 0x817578 <vtable for ceph::buffer::raw+16>,
>>
>> And is "upgraded" to a different class:
>> ceph::buffer::raw_combined
>>
>> But here is the problem...
>>
>> Hardware watchpoint 5: *0x1054048
>>
>> Old value = 8484744
>> New value = 0
>> 0x000000000049ab29 in denc_traits<unsigned long, void>::encode
>> (o=@0x10501d0: 123, p=..., f=0) at
>> /usr/srcs/Ceph/work/ceph/src/include/denc.h:228
>> 228 WRITE_INT_DENC(uint64_t, __le64);
>
> Ah, okay, this is making a bit more sense now.
>
> raw_combined is trying to be clever. It has a static create() method to
>
> - allocate an aligned buffer of size len + sizeof(raw_combined) (with some
> rounding up), call it *ptr
> - in-place initiailize raw_combined at ptr + len (rounded up), call it *this
> - store the the actual data at ptr
> - return the raw_combined *this
>
> It has an overloaded delete operator to free the entire allocate
> (roughly this - len) to make this work.
>
> It sounds a bit like the write into raw_combined's data portion (ptr) is
> clobbering vptr. Which probably suggests we wrote too much into the
> buffer. Can you print the contents of the raw_combined class and the
> appender?
Not sure if I understand the values you'd like, but this is a first attempt:
(gdb) p p
$1 = (ceph::buffer::list::contiguous_appender &) @0x7fffffffd948: {pbl =
0x7fffffffd978, pos = 0x105404f "", bp = {_raw = 0x1054048, _off = 0,
_len = 72}, deep = false,
out_of_band_offset = 0}
I do not know how to get to the raw_combined class
But I also found this morning that pos is actually point to 0x105404f
after adding 8 bytes of size .
So writing any value to that pointer before incrementing will clobber
vptr, since it points to 0x1054047.
--WjW
>
> sage
>
>
>>
>> The traceback:
>> #0 0x000000000049ab29 in denc_traits<unsigned long, void>::encode
>> (o=@0x10501d0: 123, p=..., f=0) at
>> /usr/srcs/Ceph/work/ceph/src/include/denc.h:228
>> #1 0x000000000049a7a8 in denc<unsigned long, denc_traits<unsigned long,
>> void> > (o=@0x10501d0: 123, p=..., features=0) at
>> /usr/srcs/Ceph/work/ceph/src/include/denc.h:479
>> #2 0x000000000049a6a5 in _denc_friend<foo_t const,
>> ceph::buffer::list::contiguous_appender> (v=..., p=...) at
>> /usr/srcs/Ceph/work/ceph/src/test/test_denc.cc:155
>> #3 0x000000000049a62d in foo_t::encode (this=0x10501c8, p=...) at
>> /usr/srcs/Ceph/work/ceph/src/test/test_denc.cc:152
>> #4 0x000000000049a601 in denc_traits<foo_t, void>::encode (v=...,
>> p=..., f=0) at /usr/srcs/Ceph/work/ceph/src/test/test_denc.cc:163
>> #5 0x000000000049a188 in denc<foo_t, denc_traits<foo_t, void> > (o=...,
>> p=..., features=0) at /usr/srcs/Ceph/work/ceph/src/include/denc.h:479
>> #6 0x000000000049a0ac in
>> denc_traits<std::__1::map<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >, foo_t,
>> std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>,
>> std::__1::allocator<char> > >,
>> std::__1::allocator<std::__1::pair<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> > const, foo_t> >
>>> , void>::encode<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> > > (v=..., p=...)
>> at /usr/srcs/Ceph/work/ceph/src/include/denc.h:1010
>> #7 0x0000000000494581 in
>> denc<std::__1::map<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >, foo_t,
>> std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>,
>> std::__1::allocator<char> > >,
>> std::__1::allocator<std::__1::pair<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> > const, foo_t> >
>>> , denc_traits<std::__1::map<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >, foo_t,
>> std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>,
>> std::__1::allocator<char> > >,
>> std::__1::allocator<std::__1::pair<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> > const, foo_t> >
>>> , void> > (o=..., p=..., features=0) at
>> /usr/srcs/Ceph/work/ceph/src/include/denc.h:479
>> #8 0x0000000000490fb1 in
>> test_denc<std::__1::map<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >, foo_t,
>> std::__1::less<std::__1::basic_string<char, std::__1::char_traits<char>,
>> std::__1::allocator<char> > >,
>> std::__1::allocator<std::__1::pair<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> > const, foo_t> >
>>>> (v=...) at /usr/srcs/Ceph/work/ceph/src/test/test_denc.cc:49
>> #9 0x00000000004904e0 in denc_map_Test::TestBody (this=0x1038030) at
>> /usr/srcs/Ceph/work/ceph/src/test/test_denc.cc:206
>>
>> (gdb) p p
>> $10 = (ceph::buffer::list::contiguous_appender &) @0x7fffffffd948: {pbl
>> = 0x7fffffffd978, pos = 0x105404f "", bp = {_raw = 0x1054048, _off = 0,
>> _len = 72}, deep = false,
>> out_of_band_offset = 0}
>> (gdb) p *p.bp._raw
>> $17 = {_vptr$raw = 0x0, data = 0x1054000 "\003", len = 72, nref = {val =
>> 1}, crc_spinlock = 0, crc_map = {__tree_ = {__begin_node_ = 0x1054078,
>> __pair1_ =
>> {<std::__1::__libcpp_compressed_pair_imp<std::__1::__tree_end_node<std::__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<std::__1::pair<unsigned
>> long, unsigned long>, std::__1::pair<unsigned int, unsigned int> >,
>> void*> >> = {<No data fields>}, __first_ = {
>> __left_ = 0x0}}, <No data fields>},
>> __pair3_ = {<std::__1::__libcpp_compressed_pair_imp<unsigned long,
>> std::__1::__map_value_compare<std::__1::pair<unsigned long, unsigned
>> long>, std::__1::__value_type<std::__1::pair<unsigned long, unsigned
>> long>, std::__1::pair<unsigned int, unsigned int> >,
>> std::__1::less<std::__1::pair<unsigned long, unsigned long> >, true>,
>> 2>> = {<std::__1::__map_value_compare<std::__1::pair<unsigned long,
>> unsigned long>, std::__1::__value_type<std::__1::pair<unsigned long,
>> unsigned long>, std::__1::pair<unsigned int, unsigned int> >,
>> std::__1::less<std::__1::pair<unsigned long, unsigned long> >, true>> =
>> {<std::__1::less<std::__1::pair<unsigned long, unsigned long> >> =
>> {<std::__1::binary_function<std::__1::pair<unsigned long, unsigned
>> long>, std::__1::pair<unsigned long, unsigned long>, bool>> = {<No data
>> fields>}, <No data fields>}, <No data fields>},
>> __first_ = 0}, <No data fields>}}}}
>>
>> (gdb) disassemble
>> Dump of assembler code for function denc_traits<unsigned long,
>> void>::encode(unsigned long const&,
>> ceph::buffer::list::contiguous_appender&, unsigned long):
>> 0x000000000049aaf0 <+0>: push %rbp
>> 0x000000000049aaf1 <+1>: mov %rsp,%rbp
>> 0x000000000049aaf4 <+4>: sub $0x20,%rsp
>> 0x000000000049aaf8 <+8>: mov $0x8,%eax
>> 0x000000000049aafd <+13>: mov %eax,%ecx
>> 0x000000000049aaff <+15>: mov %rdi,-0x8(%rbp)
>> 0x000000000049ab03 <+19>: mov %rsi,-0x10(%rbp)
>> 0x000000000049ab07 <+23>: mov %rdx,-0x18(%rbp)
>> 0x000000000049ab0b <+27>: mov -0x8(%rbp),%rdx
>> 0x000000000049ab0f <+31>: mov (%rdx),%rdx
>> 0x000000000049ab12 <+34>: mov -0x10(%rbp),%rdi
>> 0x000000000049ab16 <+38>: mov %rcx,%rsi
>> 0x000000000049ab19 <+41>: mov %rdx,-0x20(%rbp)
>> 0x000000000049ab1d <+45>: callq 0x49a1d0
>> <ceph::buffer::list::contiguous_appender::get_pos_add(unsigned long)>
>> 0x000000000049ab22 <+50>: mov -0x20(%rbp),%rcx
>> 0x000000000049ab26 <+54>: mov %rcx,(%rax)
>> => 0x000000000049ab29 <+57>: add $0x20,%rsp
>> 0x000000000049ab2d <+61>: pop %rbp
>> 0x000000000049ab2e <+62>: retq
>> End of assembler dump.
>>
>> (gdb) info registers
>> rax 0x1054047 17121351
>> rbx 0x0 0
>> rcx 0x7b 123
>> rdx 0x7b 123
>> rsi 0x7fffffffd948 140737488345416
>> rdi 0x105404f 17121359
>> rbp 0x7fffffffd4f0 0x7fffffffd4f0
>> rsp 0x7fffffffd4d0 0x7fffffffd4d0
>> r8 0x0 0
>> r9 0x0 0
>> r10 0x0 0
>> r11 0x829100 8556800
>> r12 0x7fffffffe910 140737488349456
>> r13 0x7fffffffe928 140737488349480
>> r14 0x7fffffffe918 140737488349464
>> r15 0x1 1
>> rip 0x49ab29 0x49ab29 <denc_traits<unsigned long,
>> void>::encode(unsigned long const&,
>> ceph::buffer::list::contiguous_appender&, unsigned long)+57>
>>
>> And this is wierd:
>> %rax contains 0x1054047
>> _raw is 0x1054048
>>
>> So writing %rcx to (%rax) is definitly going to overwrite the larger
>> part of _raw.
>>
>> So now the question transforms into:
>> Why does %rax hold this wierd value ??
>> or Why does get_pos_add(sizeof(etype)) a negative offset ??
>>
>> Got to go and do real dayjob work.
>>
>> --WjW
>> --
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