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?
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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