LLDB C++ API function tracer

Intro

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When I run the tracer, the return value (the value of rax after stepping out of the thread) is always zero. 
I'm breaking on malloc, so the output should be some pointery looking value. I tried with other functions as well, 
and I get the same issue. I also tried checking for the process state, and that says it's invalid.

Output of tracer.mm

Creating debugger...
Creating target...
Creating breakpoint...
Now in function named : malloc in process with pid = 12511
	Requested size : 32
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 32
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 32
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 45
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 47
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 46
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 52
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 50
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 48
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 40
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 45
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 47
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 46
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 50
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 48
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 45
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 47
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 50
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 48
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 231
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 32768
	Returned : 0
Now in function named : malloc in process with pid = 12511
	Requested size : 4096
	Returned : 0
Program exited!
Done.
Terminating debugger...

tracer.mm

// tracer.mm

#include <iostream>
#include <lldb/API/LLDB.h>
#include <utils/scope_exit_guard.h>
#include <utils/compute.h>

int main(int argc, const char **argv) {
  // Setup debugger environment
  lldb::SBDebugger::Initialize();
  scope_exit_guard_t guard([&] {
    std::cout << "Terminating debugger..." << std::endl;
    lldb::SBDebugger::Terminate();
  });
  // Create debugger
  lldb::SBDebugger debugger = COMPUTE({
    std::cout << "Creating debugger..." << std::endl;
    lldb::SBDebugger resp = lldb::SBDebugger::Create();
    assert(resp.IsValid() && "Could not create a valid debugger!");
    resp.SetAsync(false);
    return resp;
  });
  // Create target
  lldb::SBTarget target = COMPUTE({
    std::cout << "Creating target..." << std::endl;
    lldb::SBError error;
    lldb::SBTarget resp = debugger.CreateTarget(
      "/bin/ls", "x86_64", NULL, true, error
    );
    assert(error.Success() && "Failed to create target!");
    assert(resp.IsValid() && "Target created but is invalid!");
    return resp;
  });
  // Add breakpoints
  lldb::SBBreakpoint breakpoint = COMPUTE({
    std::cout << "Creating breakpoint..." << std::endl;
    lldb::SBBreakpoint resp = target.BreakpointCreateByName("malloc");
    auto callback = [](void *baton, lldb::SBProcess& process, lldb::SBThread& thread, lldb::SBBreakpointLocation& location) -> bool {
      // Log where we're at
      lldb::SBFrame frame = thread.GetFrameAtIndex(0);
      std::cout << "Now in function named : " << frame.GetFunctionName() << " in process with pid = " << process.GetProcessID() << std::endl;
      // Print the argument
      // x86_64 calling convention : RDI, RSI, RDX, RCX, R8, R9, XMM0–7
      lldb::SBValue rdiValue = frame.FindValue("rdi", lldb::eValueTypeRegister);
      std::cout << "\tRequested size : " << rdiValue.GetValueAsUnsigned() << std::endl;
      // Next, step out
      thread.StepOut();
      // Then log return value
      lldb::SBValue raxValue = frame.FindValue("rax", lldb::eValueTypeRegister);
      std::cout << "\tReturned : " << raxValue.GetValueAsUnsigned() << std::endl;
      return true;
    };
    resp.SetCallback(callback, 0);
    return resp;
  });
  // Launch process
  lldb::SBProcess process = COMPUTE({
    lldb::SBProcess resp = target.LaunchSimple(nullptr, nullptr, "/Users/Bibhas/Desktop");
    assert(resp.IsValid() && "Failed to attach to remote process!");
    return resp;
  });
  // Poll process for state changes
  while (1) {
    lldb::StateType state = process.GetState();
    if (state == lldb::eStateStopped) {
      process.Continue();
    }
    else if (state == lldb::eStateExited) {
      std::cerr << "Program exited!" << std::endl;
      break;
    }
  }
  // We're done
  std::cout << "Done." << std::endl;
  return 0; 
}