[llvm-dev] Moving to ORCv2 - Where are my global constructors and destructors? + More information

[Gaier, Bjoern via llvm-dev]

Sorry for the spam, but I made some progress with my issue and wanted to share what I found out.

I tried the following line before adding my module to the LLJIT:
“this->mainModule->getFunction("_GLOBAL__sub_I_VectorBIOS.cpp")->isDiscardableIfUnused();” This actually returned true
So I tried the following line:
“this->mainModule->getFunction("_GLOBAL__sub_I_VectorBIOS.cpp")->setLinkage(llvm::GlobalValue::ExternalLinkage);”
Now I was able to find the function and execute the global constructor. For a workaround this works for me.
However, running LLJITs ‘runConstructors’ does still not work, they are still empty.


From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Gaier, Bjoern via llvm-dev
Sent: 06 January 2020 15:02
To: David Blaikie <dblaikie at gmail.com>; Lang Hames <lhames at gmail.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Moving to ORCv2 - Where are my global constructors and destructors?

Is there a code example or maybe a documentation about this subject? Sadly it is an important part of my project to get the addresses of the constructors and destructors.
I really ran out of ideas though, every time when I try to look them up, they seem to be gone already .w.

From: David Blaikie <dblaikie at gmail.com<mailto:dblaikie at gmail.com>>
Sent: 19 December 2019 20:52
To: Gaier, Bjoern <Bjoern.Gaier at horiba.com<mailto:Bjoern.Gaier at horiba.com>>; Lang Hames <lhames at gmail.com<mailto:lhames at gmail.com>>
Cc: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
Subject: Re: [llvm-dev] Moving to ORCv2 - Where are my global constructors and destructors?

+Lang Hames<mailto:lhames at gmail.com> owner/author of the ORC JIT (though I think he's out of office at the moment, so replies from him might be delayed).

I believe there's a way to wire up the global ctors, but I don't know the details unfortunately - perhaps someone else will chime in if/before Lang gets a chance.

On Thu, Dec 19, 2019 at 5:53 AM Gaier, Bjoern via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Heyho,

Recently I tried out the ORCv2 JIT, especially the LLJIT. I gotta say, that I really like the new interface and the way you use it! However there is one thing I’m missing. I wrote a small bit code file, which should force having a global constructor.

int wuff();

__declspec(noinline) int miau()
{
       printf("Huhuhu");
       return wuff();
}

const int x = miau();

When I parse this IR file in my JIT and go through the ‘globals()’ of the llvm::Module, then I will encounter a symbol with the following name:
“_GLOBAL__sub_I_VectorBIOS.cpp” where VectorBIOS.cpp was the name of the source file I compiled to the bit code.

I then wanted to get the address of that symbol - from the MCJIT times I remember, that those functions are the global constructors, but when calling lookup on that name, I was not able to find the symbol.
So I tried a different way:
llvm::GlobalVariable *var = module->getNamedGlobal("llvm.global_ctors");
if(var)
{
       llvm::ConstantArray *InitList = (llvm::ConstantArray*)var->getInitializer();
       for(unsigned int n = 0; n < InitList->getNumOperands(); n++)
       {
             llvm::ConstantStruct *CS = (llvm::ConstantStruct*)InitList->getOperand(n);
             if(!CS)
             {
                    continue;
             }

             llvm::Constant *FP = CS->getOperand(1);
             if(FP->isNullValue())
                    continue;

             llvm::ConstantExpr *CE = (llvm::ConstantExpr*)FP;
             if(CE->isCast())
             {
                    FP = CE->getOperand(0);
             }

             ((llvm::Function*)FP)->getName();
       }
}
I then printed the name of the llvm::Function but it was exactly the name I expected “_GLOBAL__sub_I_VectorBIOS.cpp”. This code was executed before I added module to the JIT.
For various reasons I wanted to store the address to the constructor – so I don’t want to call the LLJIT runConstructor – simply because I want to execute those functions later, when the LLJIT does not exist anymore.

I hope someone can help me with this…

Kind Greetings
Björn
Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Takeshi Fukushima. Junichi Tajika
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Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Takeshi Fukushima. Junichi Tajika
Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Takeshi Fukushima. Junichi Tajika
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