<div dir="ltr">I don't think we're doing anything unusual. Here's the relevant snippet from the generated IR for ccall (after instrumentation):<div><br></div><div><div>ccall: ; preds = %pass6, %113</div>
<div> %114 = phi i8* [ %110, %113 ], [ %108, %pass6 ]</div><div> %115 = inttoptr i64 %17 to i64*</div><div> %116 = bitcast i8* %69 to i32*, !dbg !7</div><div> %117 = bitcast i8* %114 to i32 (i32*, i64, i64)*, !dbg !7</div>
<div> store i64 %_msret13, i64* getelementptr inbounds ([1000 x i64]* @__msan_param_tls, i64 0, i64 0), align 8, !dbg !7</div><div> store i32 %70, i32* getelementptr inbounds ([1000 x i32]* @__msan_param_origin_tls, i64 0, i64 0), align 4, !dbg !7</div>
<div> 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</div><div> 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</div>
<div> 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</div><div> 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</div>
<div> store i32 0, i32* bitcast ([8 x i64]* @__msan_retval_tls to i32*), align 8, !dbg !7</div><div> %118 = call i32 %117(i32* %116, i64 %87, i64 %107), !dbg !7, !julia_type !9</div></div><div><br></div></div><div class="gmail_extra">
<br><br><div class="gmail_quote">On Sun, Feb 2, 2014 at 6:18 AM, Evgeniy Stepanov <span dir="ltr"><<a href="mailto:eugeni.stepanov@gmail.com" target="_blank">eugeni.stepanov@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
How is ccall() implemented? If it manually sets up a stack frame, then<br>
it also needs to store argument shadow values in paramtls.<br>
<br>
I don't think there is an overflow, unless you have a _lot_ of<br>
arguments in a function call.<br>
<div class="HOEnZb"><div class="h5"><br>
On Sun, Feb 2, 2014 at 9:26 AM, Keno Fischer<br>
<<a href="mailto:kfischer@college.harvard.edu">kfischer@college.harvard.edu</a>> wrote:<br>
> Also, I was looking at the instrumented LLVM code and I noticed that the<br>
> LLVM global variable is generated with size 1000, while<br>
> kMsanParamTlsSizeInWords == 100, could there be some sort of overflow<br>
> happening?<br>
><br>
><br>
> On Sat, Feb 1, 2014 at 6:44 PM, Keno Fischer <<a href="mailto:kfischer@college.harvard.edu">kfischer@college.harvard.edu</a>><br>
> wrote:<br>
>><br>
>> I have verified that both TLS implementations indeed find the same area of<br>
>> memory. Anything else I could look for?<br>
>><br>
>><br>
>> On Tue, Jan 28, 2014 at 4:28 PM, Keno Fischer<br>
>> <<a href="mailto:kfischer@college.harvard.edu">kfischer@college.harvard.edu</a>> wrote:<br>
>>><br>
>>> Yes, both JIT code and the native runtime are instrumented. I am under<br>
>>> the impressions that the the C library should guarantee that from the way<br>
>>> the relocations are implemented as long as both native and JITed code are on<br>
>>> the same thread (but I will verify this and report back).<br>
>>><br>
>>><br>
>>> On Tue, Jan 28, 2014 at 2:41 AM, Evgeniy Stepanov<br>
>>> <<a href="mailto:eugeni.stepanov@gmail.com">eugeni.stepanov@gmail.com</a>> wrote:<br>
>>>><br>
>>>> I assume there are transitions between JITted code and native helper<br>
>>>> functions. How are you handling them? Are native functions<br>
>>>> MSan-instrumented?<br>
>>>> MSan is passing shadow across function calls in TLS slots. Does your<br>
>>>> TLS implementation guarantee that accesses to __msan_param_tls from<br>
>>>> JITted and from native code map to the same memory?<br>
>>>><br>
>>>><br>
>>>> On Mon, Jan 27, 2014 at 11:36 PM, Evgeniy Stepanov<br>
>>>> <<a href="mailto:eugeni.stepanov@gmail.com">eugeni.stepanov@gmail.com</a>> wrote:<br>
>>>> > This is really cool. I've not heard of anyone using MSan with MSJIT<br>
>>>> > before.<br>
>>>> ><br>
>>>> ><br>
>>>> > On Mon, Jan 27, 2014 at 7:44 PM, Keno Fischer<br>
>>>> > <<a href="mailto:kfischer@college.harvard.edu">kfischer@college.harvard.edu</a>> wrote:<br>
>>>> >> Hello everybody,<br>
>>>> >><br>
>>>> >> I've run into some strange behavior with memory sanitizer that I<br>
>>>> >> can't<br>
>>>> >> explain and hope somebody with more knowledge of the implementation<br>
>>>> >> would be<br>
>>>> >> able to help me out or at least point me into the right direction.<br>
>>>> >><br>
>>>> >> For background, I'm using memory sanitizer to check Julia<br>
>>>> >> (<a href="http://julialang.org" target="_blank">julialang.org</a>),<br>
>>>> >> which uses (or at least will once I track down a few bugs) MCJIT for<br>
>>>> >> the<br>
>>>> >> code compilation. So far I have rebuilt the runtime and all<br>
>>>> >> dependencies<br>
>>>> >> (including LLVM, libcxx, etc.) with memory sanitizer enabled and<br>
>>>> >> added the<br>
>>>> >> instrumentation pass in the appropriate place in the julia code<br>
>>>> >> generator.<br>
>>>> >><br>
>>>> >> I'm now going through the usual bootstrap which basically loads the<br>
>>>> >> standard<br>
>>>> >> library and compiles it, does inference, etc. This works fine for<br>
>>>> >> several<br>
>>>> >> hours (this is usually much faster - by which I mean several hundred<br>
>>>> >> time -<br>
>>>> >> I suspect the issue is with MCJIT having to process a ton more<br>
>>>> >> relocations<br>
>>>> >> and code and being inefficient at it, but I can't prove that). That's<br>
>>>> >> not<br>
>>>> >> the issue however. Eventually, I get<br>
>>>> >><br>
>>>> >> ==17150== WARNING: MemorySanitizer: use-of-uninitialized-value<br>
>>>> >> #0 0x7f417cea3189 in bitvector_any1<br>
>>>> >> /home/kfischer/julia-san/src/support/bitvector.c:177<br>
>>>> >> [ snip ]<br>
>>>> >><br>
>>>> >> Uninitialized value was created by a heap allocation<br>
>>>> >> #0 0x7f41815de543 in __interceptor_malloc<br>
>>>> >><br>
>>>> >> /home/kfischer/julia-san/deps/llvm-svn/projects/compiler-rt/lib/msan/msan_interceptors.cc:854<br>
>>>> >> #1 0x7f417cc7d7f1 in alloc_big<br>
>>>> >> /home/kfischer/julia-san/src/gc.c:355<br>
>>>> >> [snip]<br>
>>>> >><br>
>>>> >> Now, by going through it in the debugger, I see<br>
>>>> >><br>
>>>> >> (gdb) f 3<br>
>>>> >> #3 0x00007f417cea318a in bitvector_any1 (b=0x60c000607240,<br>
>>>> >> b@entry=<optimized out>, offs=0, offs@entry=<optimized out>,<br>
>>>> >> nbits=256,<br>
>>>> >> nbits@entry=<optimized out>)<br>
>>>> >> at bitvector.c:177<br>
>>>> >> 177 if ((b[0] & mask) != 0) return 1;<br>
>>>> >> (gdb) p __msan_print_shadow(&b,8)<br>
>>>> >> ff ff ff ff ff ff ff ff<br>
>>>> >> o: 3f0010a6 o: 80007666<br>
>>>> >><br>
>>>> >> which seems to indicate that the local variable b has uninitialized<br>
>>>> >> data.<br>
>>>> >> I'm having a hard time believing that though, since if I look at the<br>
>>>> >> functions before it, the place where it's coming from is initialized:<br>
>>>> >><br>
>>>> >> #4 0x00007f41755208a8 in julia_isempty248 ()<br>
>>>> >> #5 0x00007f417c163e3d in jl_apply (f=0x606000984d60,<br>
>>>> >> f@entry=<optimized<br>
>>>> >> out>, args=0x7fff9132da20, args@entry=<optimized out>, nargs=1,<br>
>>>> >> nargs@entry=<optimized out>) at ./julia.h:1043<br>
>>>> >><br>
>>>> >> (here's the code of that julia function for reference)<br>
>>>> >><br>
>>>> >> isempty(s::IntSet) =<br>
>>>> >> !s.fill1s && ccall(:bitvector_any1, Uint32, (Ptr{Uint32}, Uint64,<br>
>>>> >> Uint64), s.bits, 0, s.limit)==0<br>
>>>> >><br>
>>>> >> Looking at where that value is coming from:<br>
>>>> >><br>
>>>> >> (gdb) f 5<br>
>>>> >> #5 0x00007f417c163e3d in jl_apply (f=0x606000984d60,<br>
>>>> >> f@entry=<optimized<br>
>>>> >> out>, args=0x7fff9132da20, args@entry=<optimized out>, nargs=1,<br>
>>>> >> nargs@entry=<optimized out>) at ./julia.h:1043<br>
>>>> >> 1043 return f->fptr((jl_value_t*)f, args, nargs);<br>
>>>> >> (gdb) p ((jl_array_t*)((void**)args[0])[1])->data<br>
>>>> >> $43 = (void *) 0x60c000607240<br>
>>>> >> (gdb) p __msan_print_shadow(((jl_array_t*)((void**)args[0])[1]),0x30)<br>
>>>> >> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00<br>
>>>> >> 00 00<br>
>>>> >> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00<br>
>>>> >> o: d800496 o: d800496 o: d800496 o: d800496 o: d800496 o:<br>
>>>> >> d800496 o:<br>
>>>> >> d800496 o: d800496 o: d800496 o: d800496 o: d800496 o: d800496<br>
>>>> >><br>
>>>> >> There are no uninitialized values to be seen anywhere and the `b`<br>
>>>> >> value<br>
>>>> >> isn't touched before that line, so I'm a little stumped.<br>
>>>> >><br>
>>>> >> One note I should make is that I did have to implement TLS support<br>
>>>> >> myself in<br>
>>>> >> MCJIT for this to work (I'll upstream the patch soon), so I may have<br>
>>>> >> made a<br>
>>>> >> mistake, but I haven't found anything wrong yet. If nothing looks<br>
>>>> >> unusual,<br>
>>>> >> I'd also appreciate pointers on what to look for in the TLS<br>
>>>> >> variables.<br>
>>>> >><br>
>>>> >> Thank you for your help,<br>
>>>> >> Keno<br>
>>>> >><br>
>>>> >><br>
>>>> >> _______________________________________________<br>
>>>> >> LLVM Developers mailing list<br>
>>>> >> <a href="mailto:LLVMdev@cs.uiuc.edu">LLVMdev@cs.uiuc.edu</a> <a href="http://llvm.cs.uiuc.edu" target="_blank">http://llvm.cs.uiuc.edu</a><br>
>>>> >> <a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev" target="_blank">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><br>
>>>> >><br>
>>><br>
>>><br>
>><br>
><br>
</div></div></blockquote></div><br></div>