llvm dev - Apr 2005 - [LLVMdev] arguments to standard library functions

HI ,
 I understand that the standard C library functions are executed using the 
native  library  of the host machine. ( for example when we execute a bytecode
to extract the profile info )

Is it possible to extract for each standard library function that is
executed , the arguments that the function is called with.
For example if  printf ("%d", some_int )  when called during runtime
with some_int = 243 i want to get that info .

abhijit

On Mon, 21 Mar 2005, Abhijit Ray wrote:
> HI ,
> I understand that the standard C library functions are executed using the
> native  library  of the host machine. ( for example when we execute a
bytecode
> to extract the profile info )
>
> Is it possible to extract for each standard library function that is
> executed , the arguments that the function is called with.
> For example if  printf ("%d", some_int )  when called during
runtime
> with some_int = 243 i want to get that info .
Sure, you can do that multiple ways.  Perhaps the easiest would be to 
write an LLVM->LLVM pass which inspects all calls to external functions 
(e.g. printf) and inserts some code before or after it.  Thus it would 
turn:

   printf("%d", some_int);

into:

   log_printf_call(some_int);
   printf("%d", some_int);

Or something.  You can then provide an implementation of the logging 
runtime library to capture the data in any format you want.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.cs.uiuc.edu/

Right now I am trying to capture the function name and the number of 
arguments ,
so this following is the pass I wrote .


-------------------------------------------------------------
 struct pass06a : public ModulePass {
    virtual bool runOnModule(Module &M) {

      std::vector<const Type*> pList;
      pList.push_back( PointerType::get(Type::SByteTy) );
      pList.push_back( Type::UIntTy );

      FunctionType* FT = FunctionType::get( Type::IntTy, pList, /*is 
vararg*/ false); 
      Function* CF = new Function(FT, Function::ExternalLinkage, 
std::string("logExternalCalls"), &M);

      for(Module::iterator i = M.begin(), e = M.end(); i != e; i++ ){
        for(Function::iterator fi = i->begin(), fe = i->end(); fi != fe 
; fi++ ){
          for(BasicBlock::iterator bi = fi->begin(), be = fi->end(); bi 
!= be ; bi++ ){

            if(isa<CallInst>(*bi)){
              const CallInst* CI    = cast<CallInst>(bi);
              const Function* F     = CI->getCalledFunction() ;
              if( F->isExternal() ){
                std::vector<Value*> paramList;

                Constant *fname = ConstantArray::get(F->getName());
                Constant *GEP   = ConstantExpr::getGetElementPtr(fname, 
std::vector<Constant*>(2,Constant::getNullValue(Type::LongTy)));

                paramList.push_back( GEP);
                paramList.push_back( ConstantUInt::get( Type::UIntTy, 
CI->getNumOperands()) );

                CallInst* newCI = new CallInst( CF, paramList, "",  bi
);

              }
            }

          }
        }
      }

      return true;
    }
-------------------------------------------------------------------------------------------------------------------------------------------
and I have added the following function to tracelib.c

int logExternalCalls(char *fname, unsigned i){

  printf("function: %s \t No of args: %d\n", fname, i);
  return 0;
}

---------------------------------------------------------------------------------

The pass compiles fine but when i try to run it on a simple hello.c 
program i get the following error

 opt -load ~/work/llvm/Debug/lib/libpass06.so -pass06a <hello.bc  >
test.bc
opt: Constants.cpp:1431: static llvm::Constant* 
llvm::ConstantExpr::getGetElementPtr(llvm::Constant*, const 
std::vector<llvm::Constant*, std::allocator<llvm::Constant*>
>&):
Assertion `Ty && "GEP indices invalid!"' failed.
opt((anonymous namespace)::PrintStackTrace()+0x1a)[0x86a74d2]
opt((anonymous namespace)::SignalHandler(int)+0xcb)[0x86a7745]
/lib/libc.so.6[0x40149b68]
/lib/libc.so.6(abort+0x16d)[0x4014b05d]
/lib/libc.so.6(__assert_fail+0x10f)[0x40142e2f]
opt(llvm::ConstantExpr::getGetElementPtr(llvm::Constant*, 
std::vector<llvm::Constant*, std::allocator<llvm::Constant*> > 
const&)+0xd9)[0x85effc7]
/home/ary/work/llvm/Debug/lib/libpass06.so((anonymous 
namespace)::pass06a::runOnModule(llvm::Module&)+0x3dc)[0x40027902]
opt(llvm::PassManagerTraits<llvm::Module>::runPass(llvm::ModulePass*, 
llvm::Module*)+0x1f)[0x865476b]
opt(llvm::PassManagerT<llvm::Module>::runOnUnit(llvm::Module*)+0x5c3)[0x8648197]
opt(llvm::PassManagerTraits<llvm::Module>::runOnModule(llvm::Module&)+0x1f)[0x8649835]
opt(llvm::PassManager::run(llvm::Module&)+0x23)[0x85ff639]
opt(main+0x95e)[0x83ab362]
/lib/libc.so.6(__libc_start_main+0xbc)[0x4013610c]
opt[0x83aa961]
Aborted

======================looks like my invocation to getGetElementPtr() is not what
it should be
. But I am not sure what it should be :(

Thanks,
Abhijit Ray

On Thursday 07 April 2005 04:45, Abhijit Ray wrote:
> looks like my invocation to getGetElementPtr() is not what it should be
> . But I am not sure what it should be :(
The reason the above doesn't work is that the ConstantArray is not a pointer
type. You cannot use a non pointer type in a getelementptr instruction.

Instead you should create a GlobalVariable initialized with the ConstantArray 
(the name) and pass a ConstantExpr::getPtrPtrFromArrayPtr(<the global 
variable>) to the function call as the name of the function.

I hope this helps,

-- 

Alkis