[LLVMdev] r98459 break of ExceptionDemo

Chris Lattner clattner at apple.com
Fri Apr 16 11:23:42 PDT 2010

Hi Garrison,

Does r101453 fix this?


On Mar 22, 2010, at 12:35 PM, Garrison Venn wrote:

> Ok, I've isolated the recent additions that cause the issue and supplied a patch which is NOT meant
> to be applied, but instead solely exists for identification purposes for those who know what they are doing. :-)
> The patch is offset from HEAD.
> The patch is a hack which removes use of the MCSymbol::isDefined(...) method, as its use happens to break
> in the exception JIT context; both in MachineModuleInfo.:: TidyLandingPads(...) and in JITDwarfException::
> EmitFrameMoves(...). In this context these symbols are not defined but rather are temporaries. Beyond this
> I don't understand what the correct replacement is, or whether or not the use of MCSymbol::isDefined(...) can be 
> dropped from TidyLandingPads(...) since there are probably other dependencies.  In 2.7 JITDwarfException::
> EmitFrameMoves(...) used to check if the associated label id was deleted or folded into another. I guess the
> intent may now be to have this happen automatically to MCSymbol instances?
> I understand that trunk is being heavily thrashed in this area. Do you want me to turn ExceptionDemo into a related unit
> test case even though it only works on x86/x86_64 on UNIX systems, and requires exceptions to be turned on?
> Garrison
> On Mar 18, 2010, at 14:41, Garrison Venn wrote:
>> Forgot to add platform with issue: OS X 10.6.2. I have not tested elsewhere. 
>> Garrison
>> On Mar 18, 2010, at 14:20, Garrison Venn wrote:
>>> Hi Chris,
>>> The MCSymbol r98459 patch of llvm seems to have broken the ExceptionDemo example. As the example is dying in the
>>> associated personality's first unwind search phase, which happens to have no language specific context, and is returning
>>> a _URC_CONTINUE_UNWIND, I believe the issue is generic and not specific to the example. However I'm not sure why then
>>> this wasn't seen in one of the test cases. Anyway just wanted to give a heads up as I'm studying this, just in case the problem
>>> is obvious to you. One way to reproduce this in trunk from root is to:
>>> 1) set environment var BUILD_EXAMPLES 1
>>> 2) svn switch -r 98458 http://llvm.org/svn/llvm-project/llvm/trunk
>>> 3) make
>>> 4) Debug/examples/ExceptionDemo 2
>>> 5) example will complete successfully
>>> 6) svn switch -r 98459 http://llvm.org/svn/llvm-project/llvm/trunk
>>> 7) make
>>> 8) Debug/examples/ExceptionDemo 2
>>> 9) example will segv
>>> Sorry I'm late identifying this. I'll keep on trying to isolate it further, though I'm guessing that the sensitivity is in JITDwarfEmitter.
>>> Garrison
>>> PS: Patch ref: http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20100308/097798.html
> <NewMCAdds_ProbExceptionHack.patch>

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