[LLVMdev] Weird msan problem
Keno Fischer
kfischer at college.harvard.edu
Thu Feb 6 21:06:02 PST 2014
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
> >>> >> >>>> >>
> >>> >> >>>
> >>> >> >>>
> >>> >> >>
> >>> >> >
> >>> >
> >>> >
> >>
> >>
> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140207/fb2da76f/attachment.html>
More information about the llvm-dev
mailing list