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Yaron Keren

2013-Oct-14 18:36 UTC

[LLVMdev] A weird, reproducable problem with MCJIT

Hi,

I had similar problems with EH in ELF in
RTDyldMemoryManager::registerEHFrames() calling __register_frame().

I'm not sure these problems are related to this problem since your crash
happens in  RuntimeDyldMachO::registerEHFrames() in its own processFDE
(there are two functions named processFDE(), one in
RuntimeDyldMachO.cpp and one in RTDyldMemoryManager.cpp)  *before*
RTDyldMemoryManager::registerEHFrames()
and __register_frame() are called.

It would seem that even if  RTDyldMemoryManager::registerEHFrames() and
__register_frame() got problematic input (as with the ELF dyn. linker) it
should not cause a crash in the calling code but either a malfunction of
exceptions or crash in RTDyldMemoryManager::registerEHFrames() /
__register_frame(). A crash like the one you see should be related
to RuntimeDyldMachO::registerEHFrames() inputs only.

Yaron



2013/10/14 Kaylor, Andrew <andrew.kaylor at intel.com>
> Hi Christian,
>
> Thanks for sharing this.
>
> Yaron Keren has been investigating some problems in the EH frame
> registration code recently, and I think this may be related.  It at least
> sounds similar to the type of variations in behavior based on code size
> that Yaron was seeing.
>
> -Andy
>
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On
> Behalf Of Christian Schafmeister
> Sent: Sunday, October 13, 2013 10:52 PM
> To: llvmdev at cs.uiuc.edu
> Subject: [LLVMdev] A weird, reproducable problem with MCJIT
>
>
> I switched my Common Lisp compiler to use MCJIT on the weekend and ran
> into a weird problem compiling one particular function.
>
> It crashes with an EXC_BAD_ACCESS error in MCJIT::finalizeObject when
> calling processFDE.
>
> The weird part is that the function does not appear to do anything special
> and I've whittled it down to the minimum size that still causes the
crash.
> If I remove even one statement it compiles fine.  Note: The function
> doesn't make much sense anymore but it does compile fine.
> It does have a lot of nested scopes.
>
> I can single step through processFDE and I see it pulls up a Length in
> processFDE of 1 and then a length of 16#1000000  - clearly something has
> been corrupted.
>
> Here is the top of the backtrace from lldb:
> ----------------------
> * thread #1: tid = 0x557509, 0x0000000107e6e066
> libLLVM-3.4svn.dylib`llvm::processFDE(unsigned char*, long, long) + 134 at
>
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:35,
> stop reason = EXC_BAD_ACCESS (code=2, address=0x1102adad1)
>     frame #0: 0x0000000107e6e066
> libLLVM-3.4svn.dylib`llvm::processFDE(unsigned char*, long, long) + 134 at
>
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:35
>     frame #1: 0x0000000107e6df04
> libLLVM-3.4svn.dylib`llvm::RuntimeDyldMachO::registerEHFrames() + 356 at
>
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:81
>     frame #2: 0x0000000107e36f39
> libLLVM-3.4svn.dylib`llvm::RuntimeDyld::registerEHFrames() + 25 at
>
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp:595
>     frame #3: 0x0000000107aca9c7
> libLLVM-3.4svn.dylib`llvm::MCJIT::finalizeObject() + 775 at
>
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp:226
>     frame #4: 0x0000000103da55d3
>
libllvmo_dbg.dylib`llvmo::ExecutionEngine_O::getCompiledFunction(mem::smart_ptr<core::Symbol_O>,
> mem::smart_ptr<llvmo::Function_O>,
mem::smart_ptr<core::ActivationFrame_O>,
> mem::smart_ptr<core::Symbol_O>) + 115 at
>
/Users/meister/Development/cando/brcl/src/llvmo/../../src/llvmo/llvmoExpose.cc:811
>
>
> Here is the function that causes the crash (it's Common Lisp and all
> macros have been expanded).
>
> (defun match-dimensions (array pat)
>   (let ((zzz (eq pat '*)))
>     (if zzz
>         zzz
>         (let ((rank (array-rank array) ))
>           (if (listp pat)
>               (BLOCK NIL
>                 (LET* (
>                        (%DOTIMES-VAR 100)
>                        (I 0)
>                        )
>                   (TAGBODY
>                      (GO bot)
>                    top
>                      (if (not t) (progn))
>                      (SETQ PAT (CDR PAT))
>                      (SETQ I (1+ I))
>                    bot
>                      (if (< I %DOTIMES-VAR) (GO top))
>                      )
>                   (NULL PAT))))))))
>
>
>
> The LLVM-IR file generated by compiling this function definition is
> here: https://dl.dropboxusercontent.com/u/6229900/broken.ll
>
> Any suggestions or pointers on how to debug this are welcome.
>
> _______________________________________________
> 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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Iain Sandoe

2013-Oct-14 18:49 UTC

head link

[LLVMdev] A weird, reproducable problem with MCJIT

Hi,

one possibility (discussed on IRC) is that zero-sized atoms are being created
where BBs contain only a single 'unreachable'.
This situation (BBs with only unreachable) occurs in a number of places in
Christian's code.

If this were the case (on OSX, with ld64) then ld64 would complain about it.
I'm not sure what happens if a similar situation is presented to MCJIT.

Also, now I see the debugging comment below - it seems that the size might be
'1' - rather than 0 - so perhaps a red-herring.

cheers
Iain


On 14 Oct 2013, at 19:36, Yaron Keren wrote:
> Hi,
> 
> I had similar problems with EH in ELF in
RTDyldMemoryManager::registerEHFrames() calling __register_frame().
> 
> I'm not sure these problems are related to this problem since your
crash happens in  RuntimeDyldMachO::registerEHFrames() in its own processFDE
(there are two functions named processFDE(), one in RuntimeDyldMachO.cpp and one
in RTDyldMemoryManager.cpp)  before RTDyldMemoryManager::registerEHFrames() and
__register_frame() are called.
> 
> It would seem that even if  RTDyldMemoryManager::registerEHFrames() and
__register_frame() got problematic input (as with the ELF dyn. linker) it should
not cause a crash in the calling code but either a malfunction of exceptions or
crash in RTDyldMemoryManager::registerEHFrames() / __register_frame(). A crash
like the one you see should be related to RuntimeDyldMachO::registerEHFrames()
inputs only.
> 
> Yaron
> 
> 
> 
> 2013/10/14 Kaylor, Andrew <andrew.kaylor at intel.com>
> Hi Christian,
> 
> Thanks for sharing this.
> 
> Yaron Keren has been investigating some problems in the EH frame
registration code recently, and I think this may be related.  It at least sounds
similar to the type of variations in behavior based on code size that Yaron was
seeing.
> 
> -Andy
> 
> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On Behalf Of Christian Schafmeister
> Sent: Sunday, October 13, 2013 10:52 PM
> To: llvmdev at cs.uiuc.edu
> Subject: [LLVMdev] A weird, reproducable problem with MCJIT
> 
> 
> I switched my Common Lisp compiler to use MCJIT on the weekend and ran into
a weird problem compiling one particular function.
> 
> It crashes with an EXC_BAD_ACCESS error in MCJIT::finalizeObject when
calling processFDE.
> 
> The weird part is that the function does not appear to do anything special
and I've whittled it down to the minimum size that still causes the crash.
If I remove even one statement it compiles fine.  Note: The function doesn't
make much sense anymore but it does compile fine.
> It does have a lot of nested scopes.
> 
> I can single step through processFDE and I see it pulls up a Length in
processFDE of 1 and then a length of 16#1000000  - clearly something has been
corrupted.
> 
> Here is the top of the backtrace from lldb:
> ----------------------
> * thread #1: tid = 0x557509, 0x0000000107e6e066
libLLVM-3.4svn.dylib`llvm::processFDE(unsigned char*, long, long) + 134 at
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:35,
stop reason = EXC_BAD_ACCESS (code=2, address=0x1102adad1)
>     frame #0: 0x0000000107e6e066
libLLVM-3.4svn.dylib`llvm::processFDE(unsigned char*, long, long) + 134 at
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:35
>     frame #1: 0x0000000107e6df04
libLLVM-3.4svn.dylib`llvm::RuntimeDyldMachO::registerEHFrames() + 356 at
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldMachO.cpp:81
>     frame #2: 0x0000000107e36f39
libLLVM-3.4svn.dylib`llvm::RuntimeDyld::registerEHFrames() + 25 at
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp:595
>     frame #3: 0x0000000107aca9c7
libLLVM-3.4svn.dylib`llvm::MCJIT::finalizeObject() + 775 at
/Users/meister/Development/cando/brcl/externals/src/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp:226
>     frame #4: 0x0000000103da55d3
libllvmo_dbg.dylib`llvmo::ExecutionEngine_O::getCompiledFunction(mem::smart_ptr<core::Symbol_O>,
mem::smart_ptr<llvmo::Function_O>,
mem::smart_ptr<core::ActivationFrame_O>,
mem::smart_ptr<core::Symbol_O>) + 115 at
/Users/meister/Development/cando/brcl/src/llvmo/../../src/llvmo/llvmoExpose.cc:811
> 
> 
> Here is the function that causes the crash (it's Common Lisp and all
macros have been expanded).
> 
> (defun match-dimensions (array pat)
>   (let ((zzz (eq pat '*)))
>     (if zzz
>         zzz
>         (let ((rank (array-rank array) ))
>           (if (listp pat)
>               (BLOCK NIL
>                 (LET* (
>                        (%DOTIMES-VAR 100)
>                        (I 0)
>                        )
>                   (TAGBODY
>                      (GO bot)
>                    top
>                      (if (not t) (progn))
>                      (SETQ PAT (CDR PAT))
>                      (SETQ I (1+ I))
>                    bot
>                      (if (< I %DOTIMES-VAR) (GO top))
>                      )
>                   (NULL PAT))))))))
> 
> 
> 
> The LLVM-IR file generated by compiling this function definition is
> here: https://dl.dropboxusercontent.com/u/6229900/broken.ll
> 
> Any suggestions or pointers on how to debug this are welcome.
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Christian Schafmeister

2013-Oct-14 19:40 UTC

head link

[LLVMdev] A weird, reproducable problem with MCJIT

Yaron,

Did you find a way around the problem?

It looks like the problem comes before processFDE because by the time it
gets to processFDE the eh_frame data is already corrupted.

Does ELF and MachO share the same eh_frame format?

I am developing this code in parallel on an Ubuntu Linux system but I
haven't tried to run it on there for a couple of weeks.   I'll bring it
up to date and try my test case on it and we'll see what happens.

Best,

.Chris.



Yaron Keren <yaron.keren at gmail.com> writes:
> Hi,
>
> I had similar problems with EH in ELF in
> RTDyldMemoryManager::registerEHFrames() calling __register_frame().
>
> I'm not sure these problems are related to this problem since your
> crash happens in  RuntimeDyldMachO::registerEHFrames() in its own
> processFDE (there are two functions named processFDE(), one in
> RuntimeDyldMachO.cpp and one in RTDyldMemoryManager.cpp)
>  before RTDyldMemoryManager::registerEHFrames() and __register_frame()
> are called.
>
> It would seem that even if  RTDyldMemoryManager::registerEHFrames()
> and __register_frame() got problematic input (as with the ELF dyn.
> linker) it should not cause a crash in the calling code but either a
> malfunction of exceptions or crash in
> RTDyldMemoryManager::registerEHFrames() / __register_frame(). A crash
> like the one you see should be related
> to RuntimeDyldMachO::registerEHFrames() inputs only.
>
> Yaron
>
>
>
> 2013/10/14 Kaylor, Andrew <andrew.kaylor at intel.com>
>
>     Hi Christian,
>     
>     Thanks for sharing this.
>     
>     Yaron Keren has been investigating some problems in the EH frame
>     registration code recently, and I think this may be related.  It
>     at least sounds similar to the type of variations in behavior
>     based on code size that Yaron was seeing.
>     
>     -Andy
>

Yaron Keren

2013-Oct-14 20:16 UTC

head link

[LLVMdev] A weird, reproducable problem with MCJIT

Hi,

There may be two problems with __register_frame usage. However based on

http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-April/061768.html

I think the existing code is correct for OS-X but likely buggy for Linux
and Windows systems.

Your crash is on OS-X, right?

Anyhow, the first problem is very easy to fix.  On Linux and Windows (at
least) __register_frame should be called once and not called on every FDE
as in processFDE in RTDyldMemoryManager,cpp does.

So RTDyldMemoryManager::registerEHFrames was modified to:

void RTDyldMemoryManager::registerEHFrames(uint8_t *Addr,
                                           uint64_t LoadAddr,
                                           size_t Size) {
  __register_frame(Addr);
}

On Windows 7 / MingW (gcc) this completely solved the problems I had with
erratic exception behaviour.

The second issue is a bit more complicated. With executable files, the
linker combines .eh frames with four zero bytes from crtend to marking
.eh_frame section end. As Rafael writes, this can't be done in codegen
since it's a linker function done when all .eh_frames are combined.

The dynamic linker must perform the same function, else
__register_frame(.eh_frame) might continue processing after .eh_frame,
depending if there were four zero bytes following it - or not - by chance.

However this again isn't likely to be your source of problem, as
__registerframe on OS-X processes one FDE at the time and the calling
function  processFDE() in RTDyldMemoryManager.cpp does know the size of
eh_frame so it will not overrun the frame.

The solution would be to allocate a larger buffer, copy .eh_frame into it
with four zero bytes appended. This buffer needs to live as long as long
it's registered in the runtime library.

Yaron
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