[LLVMdev] Weird msan problem
Keno Fischer
kfischer at college.harvard.edu
Fri Aug 1 15:27:14 PDT 2014
I'm about to have another pass at this, so was wondering if this was
ever fixed (the reason I'm taking another pass is that I managed to
find the MCJIT issue that was causing this to take forever).
On Fri, Feb 7, 2014 at 12:06 AM, Keno Fischer
<kfischer at college.harvard.edu> wrote:
> Yes, it would be great to get that fixed.
>
>
> On Wed, Feb 5, 2014 at 4:09 PM, Evgeniy Stepanov <eugeni.stepanov at gmail.com>
> wrote:
>>
>> On Thu, Feb 6, 2014 at 12:21 AM, Keno Fischer
>> <kfischer at college.harvard.edu> wrote:
>> > Looks like when you materialize the stores, you should check the size of
>> > the
>> > the store and emit an appropriate amount of stores to the origin shadow
>> > (or
>> > just a memset intrinsic?).
>>
>> Yes. There is an old bug for that on the code.google.com site, but it
>> has _never_ caused problems. I guess partial reads at a non-zero
>> offset are pretty uncommon, and also LLVM IR tends to use smaller
>> stores (larger ones are transformed to memset/memcpy and we handle
>> those correctly). Should be fixed anyway.
>>
>> Note that __msan_print_shadow can lie about origin a bit if the
>> address is not 4-byte aligned (it would print origins for aligned
>> locations instead).
>>
>> >
>> >
>> > On Wed, Feb 5, 2014 at 2:13 PM, Keno Fischer
>> > <kfischer at college.harvard.edu>
>> > wrote:
>> >>
>> >> The @entry stuff is just a gdb artifact. I've been tracking this back a
>> >> little further, and it seems there's at least an origin propagation
>> >> problem:
>> >>
>> >> (gdb) list
>> >> 281 goto value_to_pointer_error;
>> >> 282 }
>> >> 283 else {
>> >> 284 if (jl_is_cpointer_type(jvt) && jl_tparam0(jvt) == jt)
>> >> {
>> >> 285 void *ptr = jl_unbox_voidpointer(v);
>> >> 286 assert(__msan_test_shadow(&ptr,sizeof(void**)) ==
>> >> -1);
>> >> 287 return (void*)ptr;
>> >> 288 }
>> >> 289 }
>> >> 290
>> >> (gdb) p __msan_print_shadow(v,16)
>> >> 00 00 00 00 00 00 00 00 ff ff ff ff ff ff ff ff
>> >> o: 40000e23 o: 40000e23 o: 40000e23 o: 40000e23
>> >> $21 = void
>> >> (gdb) p __msan_print_shadow(&ptr,8)
>> >> ff ff ff ff ff ff ff ff
>> >> o: 40000e23 o: 80007614
>> >> $22 = void
>> >>
>> >> Notice the origin of the lower bits is off. Any idea as to why?
>> >>
>> >>
>> >> On Mon, Feb 3, 2014 at 2:52 AM, Evgeniy Stepanov
>> >> <eugeni.stepanov at gmail.com> wrote:
>> >>>
>> >>> The code for ccall looks right. Sounds like you have a very small
>> >>> range of instructions where an uninitialized value appear. You could
>> >>> try debugging at asm level. Shadow for b should be passed at offset 0
>> >>> in __msan_param_tls.
>> >>>
>> >>> MSan could propagate shadow through arithmetic and even some logic
>> >>> operations (like select). It could be that b is clean on function
>> >>> entry, but then something uninitialized gets mixed in.
>> >>>
>> >>> Also, what is this @entry stuff? It looks like bitvector_any1 has 6
>> >>> arguments, but your ccall snippet only sets up tls for 3.
>> >>>
>> >>>
>> >>> On Sun, Feb 2, 2014 at 10:39 PM, Keno Fischer
>> >>> <kfischer at college.harvard.edu> wrote:
>> >>> > I don't think we're doing anything unusual. Here's the relevant
>> >>> > snippet
>> >>> > from
>> >>> > the generated IR for ccall (after instrumentation):
>> >>> >
>> >>> > ccall: ; preds = %pass6,
>> >>> > %113
>> >>> > %114 = phi i8* [ %110, %113 ], [ %108, %pass6 ]
>> >>> > %115 = inttoptr i64 %17 to i64*
>> >>> > %116 = bitcast i8* %69 to i32*, !dbg !7
>> >>> > %117 = bitcast i8* %114 to i32 (i32*, i64, i64)*, !dbg !7
>> >>> > store i64 %_msret13, i64* getelementptr inbounds ([1000 x i64]*
>> >>> > @__msan_param_tls, i64 0, i64 0), align 8, !dbg !7
>> >>> > store i32 %70, i32* getelementptr inbounds ([1000 x i32]*
>> >>> > @__msan_param_origin_tls, i64 0, i64 0), align 4, !dbg !7
>> >>> > store i64 0, i64* inttoptr (i64 add (i64 ptrtoint ([1000 x i64]*
>> >>> > @__msan_param_tls to i64), i64 8) to i64*), align 8, !dbg !7
>> >>> > store i32 0, i32* inttoptr (i64 add (i64 ptrtoint ([1000 x i32]*
>> >>> > @__msan_param_origin_tls to i64), i64 8) to i32*), align 4, !dbg !7
>> >>> > store i64 0, i64* inttoptr (i64 add (i64 ptrtoint ([1000 x i64]*
>> >>> > @__msan_param_tls to i64), i64 16) to i64*), align 8, !dbg !7
>> >>> > store i32 0, i32* inttoptr (i64 add (i64 ptrtoint ([1000 x i32]*
>> >>> > @__msan_param_origin_tls to i64), i64 16) to i32*), align 4, !dbg !7
>> >>> > store i32 0, i32* bitcast ([8 x i64]* @__msan_retval_tls to i32*),
>> >>> > align
>> >>> > 8, !dbg !7
>> >>> > %118 = call i32 %117(i32* %116, i64 %87, i64 %107), !dbg !7,
>> >>> > !julia_type
>> >>> > !9
>> >>> >
>> >>> >
>> >>> >
>> >>> > On Sun, Feb 2, 2014 at 6:18 AM, Evgeniy Stepanov
>> >>> > <eugeni.stepanov at gmail.com>
>> >>> > wrote:
>> >>> >>
>> >>> >> How is ccall() implemented? If it manually sets up a stack frame,
>> >>> >> then
>> >>> >> it also needs to store argument shadow values in paramtls.
>> >>> >>
>> >>> >> I don't think there is an overflow, unless you have a _lot_ of
>> >>> >> arguments in a function call.
>> >>> >>
>> >>> >> On Sun, Feb 2, 2014 at 9:26 AM, Keno Fischer
>> >>> >> <kfischer at college.harvard.edu> wrote:
>> >>> >> > Also, I was looking at the instrumented LLVM code and I noticed
>> >>> >> > that
>> >>> >> > the
>> >>> >> > LLVM global variable is generated with size 1000, while
>> >>> >> > kMsanParamTlsSizeInWords == 100, could there be some sort of
>> >>> >> > overflow
>> >>> >> > happening?
>> >>> >> >
>> >>> >> >
>> >>> >> > On Sat, Feb 1, 2014 at 6:44 PM, Keno Fischer
>> >>> >> > <kfischer at college.harvard.edu>
>> >>> >> > wrote:
>> >>> >> >>
>> >>> >> >> I have verified that both TLS implementations indeed find the
>> >>> >> >> same
>> >>> >> >> area
>> >>> >> >> of
>> >>> >> >> memory. Anything else I could look for?
>> >>> >> >>
>> >>> >> >>
>> >>> >> >> On Tue, Jan 28, 2014 at 4:28 PM, Keno Fischer
>> >>> >> >> <kfischer at college.harvard.edu> wrote:
>> >>> >> >>>
>> >>> >> >>> Yes, both JIT code and the native runtime are instrumented. I
>> >>> >> >>> am
>> >>> >> >>> under
>> >>> >> >>> the impressions that the the C library should guarantee that
>> >>> >> >>> from
>> >>> >> >>> the
>> >>> >> >>> way
>> >>> >> >>> the relocations are implemented as long as both native and
>> >>> >> >>> JITed
>> >>> >> >>> code
>> >>> >> >>> are on
>> >>> >> >>> the same thread (but I will verify this and report back).
>> >>> >> >>>
>> >>> >> >>>
>> >>> >> >>> On Tue, Jan 28, 2014 at 2:41 AM, Evgeniy Stepanov
>> >>> >> >>> <eugeni.stepanov at gmail.com> wrote:
>> >>> >> >>>>
>> >>> >> >>>> I assume there are transitions between JITted code and native
>> >>> >> >>>> helper
>> >>> >> >>>> functions. How are you handling them? Are native functions
>> >>> >> >>>> MSan-instrumented?
>> >>> >> >>>> MSan is passing shadow across function calls in TLS slots.
>> >>> >> >>>> Does
>> >>> >> >>>> your
>> >>> >> >>>> TLS implementation guarantee that accesses to __msan_param_tls
>> >>> >> >>>> from
>> >>> >> >>>> JITted and from native code map to the same memory?
>> >>> >> >>>>
>> >>> >> >>>>
>> >>> >> >>>> On Mon, Jan 27, 2014 at 11:36 PM, Evgeniy Stepanov
>> >>> >> >>>> <eugeni.stepanov at gmail.com> wrote:
>> >>> >> >>>> > This is really cool. I've not heard of anyone using MSan
>> >>> >> >>>> > with
>> >>> >> >>>> > MSJIT
>> >>> >> >>>> > before.
>> >>> >> >>>> >
>> >>> >> >>>> >
>> >>> >> >>>> > On Mon, Jan 27, 2014 at 7:44 PM, Keno Fischer
>> >>> >> >>>> > <kfischer at college.harvard.edu> wrote:
>> >>> >> >>>> >> Hello everybody,
>> >>> >> >>>> >>
>> >>> >> >>>> >> I've run into some strange behavior with memory sanitizer
>> >>> >> >>>> >> that
>> >>> >> >>>> >> I
>> >>> >> >>>> >> can't
>> >>> >> >>>> >> explain and hope somebody with more knowledge of the
>> >>> >> >>>> >> implementation
>> >>> >> >>>> >> would be
>> >>> >> >>>> >> able to help me out or at least point me into the right
>> >>> >> >>>> >> direction.
>> >>> >> >>>> >>
>> >>> >> >>>> >> For background, I'm using memory sanitizer to check Julia
>> >>> >> >>>> >> (julialang.org),
>> >>> >> >>>> >> which uses (or at least will once I track down a few bugs)
>> >>> >> >>>> >> MCJIT
>> >>> >> >>>> >> for
>> >>> >> >>>> >> the
>> >>> >> >>>> >> code compilation. So far I have rebuilt the runtime and all
>> >>> >> >>>> >> dependencies
>> >>> >> >>>> >> (including LLVM, libcxx, etc.) with memory sanitizer
>> >>> >> >>>> >> enabled
>> >>> >> >>>> >> and
>> >>> >> >>>> >> added the
>> >>> >> >>>> >> instrumentation pass in the appropriate place in the julia
>> >>> >> >>>> >> code
>> >>> >> >>>> >> generator.
>> >>> >> >>>> >>
>> >>> >> >>>> >> I'm now going through the usual bootstrap which basically
>> >>> >> >>>> >> loads
>> >>> >> >>>> >> the
>> >>> >> >>>> >> standard
>> >>> >> >>>> >> library and compiles it, does inference, etc. This works
>> >>> >> >>>> >> fine
>> >>> >> >>>> >> for
>> >>> >> >>>> >> several
>> >>> >> >>>> >> hours (this is usually much faster - by which I mean
>> >>> >> >>>> >> several
>> >>> >> >>>> >> hundred
>> >>> >> >>>> >> time -
>> >>> >> >>>> >> I suspect the issue is with MCJIT having to process a ton
>> >>> >> >>>> >> more
>> >>> >> >>>> >> relocations
>> >>> >> >>>> >> and code and being inefficient at it, but I can't prove
>> >>> >> >>>> >> that).
>> >>> >> >>>> >> That's
>> >>> >> >>>> >> not
>> >>> >> >>>> >> the issue however. Eventually, I get
>> >>> >> >>>> >>
>> >>> >> >>>> >> ==17150== WARNING: MemorySanitizer:
>> >>> >> >>>> >> use-of-uninitialized-value
>> >>> >> >>>> >> #0 0x7f417cea3189 in bitvector_any1
>> >>> >> >>>> >> /home/kfischer/julia-san/src/support/bitvector.c:177
>> >>> >> >>>> >> [ snip ]
>> >>> >> >>>> >>
>> >>> >> >>>> >> Uninitialized value was created by a heap allocation
>> >>> >> >>>> >> #0 0x7f41815de543 in __interceptor_malloc
>> >>> >> >>>> >>
>> >>> >> >>>> >>
>> >>> >> >>>> >>
>> >>> >> >>>> >>
>> >>> >> >>>> >> /home/kfischer/julia-san/deps/llvm-svn/projects/compiler-rt/lib/msan/msan_interceptors.cc:854
>> >>> >> >>>> >> #1 0x7f417cc7d7f1 in alloc_big
>> >>> >> >>>> >> /home/kfischer/julia-san/src/gc.c:355
>> >>> >> >>>> >> [snip]
>> >>> >> >>>> >>
>> >>> >> >>>> >> Now, by going through it in the debugger, I see
>> >>> >> >>>> >>
>> >>> >> >>>> >> (gdb) f 3
>> >>> >> >>>> >> #3 0x00007f417cea318a in bitvector_any1 (b=0x60c000607240,
>> >>> >> >>>> >> b at entry=<optimized out>, offs=0, offs at entry=<optimized
>> >>> >> >>>> >> out>,
>> >>> >> >>>> >> nbits=256,
>> >>> >> >>>> >> nbits at entry=<optimized out>)
>> >>> >> >>>> >> at bitvector.c:177
>> >>> >> >>>> >> 177 if ((b[0] & mask) != 0) return 1;
>> >>> >> >>>> >> (gdb) p __msan_print_shadow(&b,8)
>> >>> >> >>>> >> ff ff ff ff ff ff ff ff
>> >>> >> >>>> >> o: 3f0010a6 o: 80007666
>> >>> >> >>>> >>
>> >>> >> >>>> >> which seems to indicate that the local variable b has
>> >>> >> >>>> >> uninitialized
>> >>> >> >>>> >> data.
>> >>> >> >>>> >> I'm having a hard time believing that though, since if I
>> >>> >> >>>> >> look
>> >>> >> >>>> >> at
>> >>> >> >>>> >> the
>> >>> >> >>>> >> functions before it, the place where it's coming from is
>> >>> >> >>>> >> initialized:
>> >>> >> >>>> >>
>> >>> >> >>>> >> #4 0x00007f41755208a8 in julia_isempty248 ()
>> >>> >> >>>> >> #5 0x00007f417c163e3d in jl_apply (f=0x606000984d60,
>> >>> >> >>>> >> f at entry=<optimized
>> >>> >> >>>> >> out>, args=0x7fff9132da20, args at entry=<optimized out>,
>> >>> >> >>>> >> nargs=1,
>> >>> >> >>>> >> nargs at entry=<optimized out>) at ./julia.h:1043
>> >>> >> >>>> >>
>> >>> >> >>>> >> (here's the code of that julia function for reference)
>> >>> >> >>>> >>
>> >>> >> >>>> >> isempty(s::IntSet) =
>> >>> >> >>>> >> !s.fill1s && ccall(:bitvector_any1, Uint32,
>> >>> >> >>>> >> (Ptr{Uint32},
>> >>> >> >>>> >> Uint64,
>> >>> >> >>>> >> Uint64), s.bits, 0, s.limit)==0
>> >>> >> >>>> >>
>> >>> >> >>>> >> Looking at where that value is coming from:
>> >>> >> >>>> >>
>> >>> >> >>>> >> (gdb) f 5
>> >>> >> >>>> >> #5 0x00007f417c163e3d in jl_apply (f=0x606000984d60,
>> >>> >> >>>> >> f at entry=<optimized
>> >>> >> >>>> >> out>, args=0x7fff9132da20, args at entry=<optimized out>,
>> >>> >> >>>> >> nargs=1,
>> >>> >> >>>> >> nargs at entry=<optimized out>) at ./julia.h:1043
>> >>> >> >>>> >> 1043 return f->fptr((jl_value_t*)f, args, nargs);
>> >>> >> >>>> >> (gdb) p ((jl_array_t*)((void**)args[0])[1])->data
>> >>> >> >>>> >> $43 = (void *) 0x60c000607240
>> >>> >> >>>> >> (gdb) p
>> >>> >> >>>> >>
>> >>> >> >>>> >> __msan_print_shadow(((jl_array_t*)((void**)args[0])[1]),0x30)
>> >>> >> >>>> >> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> 00 00
>> >>> >> >>>> >> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> 00
>> >>> >> >>>> >> o: d800496 o: d800496 o: d800496 o: d800496 o: d800496
>> >>> >> >>>> >> o:
>> >>> >> >>>> >> d800496 o:
>> >>> >> >>>> >> d800496 o: d800496 o: d800496 o: d800496 o: d800496 o:
>> >>> >> >>>> >> d800496
>> >>> >> >>>> >>
>> >>> >> >>>> >> There are no uninitialized values to be seen anywhere and
>> >>> >> >>>> >> the
>> >>> >> >>>> >> `b`
>> >>> >> >>>> >> value
>> >>> >> >>>> >> isn't touched before that line, so I'm a little stumped.
>> >>> >> >>>> >>
>> >>> >> >>>> >> One note I should make is that I did have to implement TLS
>> >>> >> >>>> >> support
>> >>> >> >>>> >> myself in
>> >>> >> >>>> >> MCJIT for this to work (I'll upstream the patch soon), so I
>> >>> >> >>>> >> may
>> >>> >> >>>> >> have
>> >>> >> >>>> >> made a
>> >>> >> >>>> >> mistake, but I haven't found anything wrong yet. If nothing
>> >>> >> >>>> >> looks
>> >>> >> >>>> >> unusual,
>> >>> >> >>>> >> I'd also appreciate pointers on what to look for in the TLS
>> >>> >> >>>> >> variables.
>> >>> >> >>>> >>
>> >>> >> >>>> >> Thank you for your help,
>> >>> >> >>>> >> Keno
>> >>> >> >>>> >>
>> >>> >> >>>> >>
>> >>> >> >>>> >> _______________________________________________
>> >>> >> >>>> >> LLVM Developers mailing list
>> >>> >> >>>> >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>> >>> >> >>>> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> >>> >> >>>> >>
>> >>> >> >>>
>> >>> >> >>>
>> >>> >> >>
>> >>> >> >
>> >>> >
>> >>> >
>> >>
>> >>
>> >
>
>
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