[llvm-dev] llvm dynamic execution trace

[Alex Susu via llvm-dev]

   Hello.
     Ammar, I come back to this old thread.
     Even with the current lli you can give
       lli --debug -force-interpreter -stats
     and you will obtain on stderr a trace of the instructions executed.

     Unfortunately, the information printed on stderr is not well formatted - I edited 
llvm/lib/ExecutionEngine/Interpreter/Execution.cpp, the Interpreter::run() method. You can 
find how the code looks now below.

     An important question I have is: how can I output the actual values the LLVM 
variables take during execution? I ask because the code below I wrote outputs the static 
values of the instruction operands, not the values taken at runtime.

     I'm also curious: is there a project adding a GUI frontend to lli in order to perform 
interactive debugging to an LLVM program (something like gdb -tui mode)? I wasn't able to 
find any after a few minutes of search on the Internet.

     void Interpreter::run() {
       while (!ECStack.empty()) {
         // Interpret a single instruction & increment the "PC".
         ExecutionContext &SF = ECStack.back();  // Current stack frame
         Instruction &I = *SF.CurInst++;         // Increment before execute

         // Track the number of dynamic instructions executed.
         ++NumDynamicInsts;

         DEBUG(dbgs() << "About to interpret: " << I);

         // Alex: new code
         DEBUG(dbgs() << "\n");

         const char *opcodeName = I.getOpcodeName();

         if ( (strcmp(opcodeName, "call") != 0) &&
              (strcmp(opcodeName, "br") != 0) ) {
             for (unsigned int i = 0; i < I.getNumOperands(); i++) {
                 DEBUG(dbgs() << "    arg " << i << ": " << * (I.getOperand(i)) << "\n");
             }
         }
         // Alex: END new code

         visit(I);   // Dispatch to one of the visit* methods...
       }
     }


   Thank you,
     Alex


On 5/4/2016 8:48 AM, Dean Michael Berris via llvm-dev wrote:
> On Wed, May 4, 2016 at 3:10 PM Ammar Naqvi via llvm-dev <llvm-dev at lists.llvm.org
> <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     Hi Dean, thank you for the response!
>
>     I'm a newbie to LLVM, a student working on an LLVM project so I'm not quite sure of
>     what you're suggesting, please excuse my naivety.
>
>     To clarify there used to exist
>     this http://llvm.org/releases/1.0/docs/CommandGuide/lli.html where you could type "lli
>     -trace 'filename.bc' and you would get a dump of the dynamic excutiion trace.
>
>       I need something like:
>      to record the execution (statement/instruction) trace of a program. For example, a C
>     program is like this:
>
>     1:    sum = 0;
>     2:    for(i = 0; i < 2; i++)
>     3:        sum += i;
>     4:    printf("%d", sum);
>
>         The execution trace would be something like 1->2->3->2->3->2->4.
>
>     Is there some way of achieving this, this was possible in previous verions of LLVM
>     <2.6 i believe; I need guidance of replicating this on the newer version(using 3.8).
>
>
> Ah, that's slightly different from what XRay allows. I'll let others respond more
> specifically on what you're after.
>
> Cheers
>
>
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