Have A Try: Dynamic Instrumentation

Prerequisites

After compiling and installing LLVM 13, the environment needs to have LLVM-related paths.

The inserted code needs to be compiled as a library

Take inserting a timing function as an example:

In the libins fold, we can compile the inserted timing function into a dynamic library:

gcc inslib.c -I . -shared -fPIC -o libinstrument.so

Build the new pass

llvm-config helps us to use flags of LLVM, which means we don't need to recompile the whole LLVM project when compiling a new PASS.

clang++ -fPIC -c InstruFunc.cpp  -o InstruFunc.o `llvm-config --cxxflags`
clang++ -shared -o InstruFunc.so InstruFunc.o `llvm-config --ldflags`

Test

Before Instrumentation

Unfortunately, the current method requires at least the instrumentation library to be included in the source code.

//#include "inslib.h" //Need to uncomment.
int M = 100;
int N = 100;
void test(){
  int x = 2;
  int A[M*N];
  for (int i = 0;i < N;i++){
    for(int j = 0;j < M;j++){
      A[i*M+j]+=x;
    }
  }
}
int main()
{
  test();
  return 0;
}

Method1: Using opt and lli (Already OK!)

In the test fold:

clang -S -L ../libins/ -linstrument -emit-llvm -I ../libins test_instrument.c -o test_instrument.ll
opt -load ../InstruFunc.so -instrufunc -enable-new-pm=0 test_instrument.ll -o test_instrument.bc
lli -load ../libins/libinstrument.so test_instrument.bc

Method2: Using Clang -Xclang (Need to be fixed)

In the test fold:

clang -Xclang  -load -Xclang ../InstruFunc.so -L ../libins -linstrument -I ../libins test_instrument.c -o test_instrument

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(topdir)/InstruFunc/libins
./test_instrument