FIT

the Flexible Instrumentation Toolkit

Using FIT is fairly straightforward. We've designed it to be compatible with ATOM's interface, so if you've ever used that, using FIT should not be a problem. In this section we will give a high-level overview of the process of creating a custom instrumentor. For a detailed description of how to use FIT, we refer to the MANUAL file included in the FIT distribution.

Suppose you want to create btrace, an instrumentor that prints out a basic block trace of the instrumented program to a file. To do this, you need to create two files, btrace.anal.c and btrace.inst.c. The first file describes the analysis procedures your instrumentor will insert into the program, and the second file describes where to insert them, and what parameters you want to pass to them.

The code in those files is pretty self-explanatory, so let's just take a look at it:

void * fd;

void Init()
{
  fd = fopen("trace.out","w");
}

void Fini()
{
  fclose(fd);
}

void TraceBlock(void * block_address)
{
  fprintf(fd,"0x%x\n",block_address);
}
	

#include <cmplrs/atom.inst.h>

void InstrumentInit(int argc, char ** argv)
{
  AddCallProto("Init()");
  AddCallProto("Fini()");
  AddCallProto("TraceBlock(REGV)");
}

void Instrument(int argc, char ** argv, Obj *obj)
{
  Proc *p; Block *b;
  AddCallProgram(ProgramBefore, "Init");
  AddCallProgram(ProgramAfter , "Fini");
  for (p = GetFirstObjProc(obj); p != NULL; p = GetNextProc(p))
    for (b = GetFirstBlock(p); b != NULL; b = GetNextBlock(b))
      AddCallBlock(b,BlockBefore,"TraceBlock",REG_PC);
}
	

• InstrumentInit(): In this procedure the prototypes of the analysis routines are declared.
• Instrument(): In this procedure, the actual instrumentation is added to the program. The Init() procedure will be called before the program starts executing, the Fini() procedure will be called after the program is done, and the TraceBlock() procedure will be called at the start of each basic block in the program. In addition, it will take one argument at each call site, consisting of the value of the program counter (thus, effectively the basic block address) at that point.

The following diagram shows how FIT builds an instrumentor based on the analysis and instrumentation files: