> Wiadomość napisana przez Krystian Lewandowski <k.lewandow...@me.com> w dniu
> 05.07.2019, o godz. 22:46:
>
> Based on information from Dimitry Andric:
> https://bugs.llvm.org/show_bug.cgi?id=42478
> - it does happen only for -triple aarch64-unknown-openbsd
> - with -stack-protector 2
> I tried to find a reason for this behaviour. Please note I have no knowledge
> about LLVM internals, dont trust me, double check.
>
> I'll point to OpenBSD (master branch) github links, I hope its fine with you.
>
> 1. So the crash is caused directly by:
> https://github.com/openbsd/src/blob/master/gnu/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp#L1500
> where getValue() is called on NULL pointer.
>
> 2. I think it is caused by Global being NULL here:
> https://github.com/openbsd/src/blob/master/gnu/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp#L766
> It should be returned from provided module as __stack_chk_guard function.
> https://github.com/openbsd/src/blob/master/gnu/llvm/lib/CodeGen/TargetLoweringBase.cpp#L1658
>
> 3. This "__stack_chk_guard" function should be registered here:
> https://github.com/openbsd/src/blob/master/gnu/llvm/lib/CodeGen/StackProtector.cpp#L341
> by
> insertSSPDeclarations() call but this piece of code is never executed because
> getStackGuard() returns earlier - getIRStackGuard() returns non-NULL value:
> https://github.com/openbsd/src/blob/master/gnu/llvm/lib/CodeGen/TargetLoweringBase.cpp#L1635
>
> Im not sure which one is valid:
> a. with TargetLoweringBase::getIRStackGuard() returning non-NULL value,
> TargetLoweringBase::getSDagStackGuard() should never be called by
> IRTranslator::getStackGuard() and this flow should be handled in a different
> manner
> b. or insertSSPDeclarations() should be called in
> StackProtector::getStackGuard()
> in both cases
>
> I was able to get rid of crash by the diff below (b. case).
>
> --
> Krystian
>
> Index: StackProtector.cpp
> ===================================================================
> RCS file: /cvs/src/gnu/llvm/lib/CodeGen/StackProtector.cpp,v
> retrieving revision 1.8
> diff -u -p -r1.8 StackProtector.cpp
> --- StackProtector.cpp 23 Jun 2019 22:05:12 -0000 1.8
> +++ StackProtector.cpp 5 Jul 2019 20:41:17 -0000
> @@ -322,8 +322,10 @@ bool StackProtector::RequiresStackProtec
> static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
> IRBuilder<> &B,
> bool *SupportsSelectionDAGSP = nullptr) {
> - if (Value *Guard = TLI->getIRStackGuard(B))
> + if (Value *Guard = TLI->getIRStackGuard(B)) {
> + TLI->insertSSPDeclarations(*M);
> return B.CreateLoad(Guard, true, "StackGuard");
> + }
>
> // Use SelectionDAG SSP handling, since there isn't an IR guard.
> //
Adding Jeremie to the thread, because he is working on devel/llvm 8.0.0.
--
Krystian
