llvm dev - Jan 2013 - [LLVMdev] Dynamic Profiling - Instrumentation basic query

Hi Alastair,
Thank you so much for the information on the tools. Actually, I need to
analyze which sections of code are prone to misses and mis predicts, and
would have to eventually instrument the code. 

I was able to instrument and call an external function, but faced an issue
while passing an argument to the function. I am following EdgeProfiling.cpp
but couldn't figure out the problem. Could you please see where I am going
wrong here - 

 virtual bool runOnModule(Module &M) 
        { 
            Constant *hookFunc; 
            LLVMContext& context = M.getContext(); 
            hookFunc
M.getOrInsertFunction("cacheCounter",Type::getVoidTy(M.getContext()),
                                                           
llvm::Type::getInt32Ty(M.getContext()), 
                                                            (Type*)0); 
            cacheCounter= cast<Function>(hookFunc); 
 
            for(Module::iterator F = M.begin(), E = M.end(); F!= E; ++F) 
            { 
 
                for(Function::iterator BB = F->begin(), E = F->end(); BB
!E; ++BB)
                { 
                    cacheProf::runOnBasicBlock(BB, hookFunc, context); 
                } 
            } 
 
            return false; 
        } 
        virtual bool runOnBasicBlock(Function::iterator &BB, Constant*
hookFunc, LLVMContext& context) 
        { 
 
            for(BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI
!BE; ++BI)
            { 
                std::vector<Value*> Args(1); 
                unsigned a =100; 
                Args[0] =  ConstantInt::get(Type::getInt32Ty(context), a); 
                if(isa<LoadInst>(&(*BI)) ) 
                    { 
                        CallInst *newInst = CallInst::Create(hookFunc, Args,
"",BI); 
                    } 
                    
            } 
            return true; 
        } 

The C code is as follows - 

extern "C" void cacheCounter(unsigned a){
    std::cout<<a<<" Load instruction\n";
}


Error:
line 8: 18499 Segmentation fault      (core dumped) lli out.bc

Also, the code works fine when I don't try to print out 'a'. 

Thanks for your help.

Regards,
Silky



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Hi Silky,

Sorry for the slow reply.  You probably already fixed this, but just in 
case I'll reply anyway.

Comments inline below

On 15/01/13 19:38, SArora wrote:
> Hi Alastair,
> Thank you so much for the information on the tools. Actually, I need to
> analyze which sections of code are prone to misses and mis predicts, and
> would have to eventually instrument the code.
>
> I was able to instrument and call an external function, but faced an issue
> while passing an argument to the function. I am following EdgeProfiling.cpp
> but couldn't figure out the problem. Could you please see where I am
going
> wrong here -
>
>   virtual bool runOnModule(Module &M)
>          {
>              Constant *hookFunc;
>              LLVMContext& context = M.getContext();
>              hookFunc >
M.getOrInsertFunction("cacheCounter",Type::getVoidTy(M.getContext()),
>
> llvm::Type::getInt32Ty(M.getContext()),
>                                                              (Type*)0);
>              cacheCounter= cast<Function>(hookFunc);
>
>              for(Module::iterator F = M.begin(), E = M.end(); F!= E; ++F)
>              {
>
>                  for(Function::iterator BB = F->begin(), E =
F->end(); BB !> E; ++BB)
>                  {
>                      cacheProf::runOnBasicBlock(BB, hookFunc, context);
>                  }
>              }
>
>              return false;
>          }
>          virtual bool runOnBasicBlock(Function::iterator &BB, Constant*
> hookFunc, LLVMContext& context)
>          {
>
>              for(BasicBlock::iterator BI = BB->begin(), BE =
BB->end(); BI !> BE; ++BI)
>              {
>                  std::vector<Value*> Args(1);
>                  unsigned a =100;
>                  Args[0] =  ConstantInt::get(Type::getInt32Ty(context), a);
>                  if(isa<LoadInst>(&(*BI)) )
>                      {
>                          CallInst *newInst = CallInst::Create(hookFunc,
Args,
> "",BI);
Did this line compile without warning?  Shouldn't 'BI' be
'&(*BI)' or
something?
>                      }
>
>              }
>              return true;
>          }
>
> The C code is as follows -
>
> extern "C" void cacheCounter(unsigned a){
>      std::cout<<a<<" Load instruction\n";
> }
I was kind of surprised that this worked, so I tried it out and it does! 
  In general libprofile_rt.so is written in C though, if you write it in 
C++ it will require a C++ library at run-time.
>
> Error:
> line 8: 18499 Segmentation fault      (core dumped) lli out.bc
>
> Also, the code works fine when I don't try to print out 'a'.
>
> Thanks for your help.
>
> Regards,
> Silky
You could look at the IR for out.bc before running it, if there is 
something wrong it will probably be pretty obvious there.

Regards,
Alastair.

Hi Alastair,

You're right. I figured out that I wasn't linking the files properly.
Instead of using llvm-link command I used the following commands, and it
worked.

opt -load /x/ext_students/silkyar/llvm/Debug+Asserts/lib/cacheProf.so
-cacheProf a.bc>out.bc
llc out.bc -o out.s
g++ -o cache.exe out.s cacheSim.o
./cache.exe

Regards,
Silky



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