#28 Function with empty implementation gives wrong unfolding/xref

[Leonardo Solis Vasquez]

Taking the init_time() function of H.264 decoder as a study case.

We can find its node right after unfolding main(), This function has also been instrumented in win32.cil.c.

The issue is that init_time() has an empty implementation but unfolding it provides 2 nodes. These nodes also make reference to unrelated source code.

[Mihai T. Lazarescu]

Using the project I got from you:

• I cannot see an init_time() after unfolding main() (see
  attached main_unfold.pdf);
• no statements or data transfers are recorded in the profile
  file for the init_time() call stack (#2).

[Leonardo Solis Vasquez]

I forgot to mention:those project files were produced before updating ParTools.
The up-to-date results are attached here.
See also the screenshot: unfold_main_with_init_time.pdf

[Mihai T. Lazarescu]

Now I can see it. :-)

init_time() is not empty, see lcommon/src/win32.c:38:

void init_time(void)
{
  QueryPerformanceFrequency(&freq);
}

So, the bug appears to be that the cross-reference of the
statements in its body is not right.

This may have to do with calling a function that does NOT
return a value. Can you confirm that this is true also for
the other cases?

[Leonardo Solis Vasquez]

Yes, init_time() is defined in lcommon/src/win32.c.
However, its implementation depends on ___WIN32__:

/*file win32.c*/

#ifdef _WIN32

    static LARGE_INTEGER freq;

    // Other functions

    void init_time(void)
    {
      QueryPerformanceFrequency(&freq);
    }

#else

    // Other functions

    void init_time(void)
    {
    }


#endif

In this case ___WIN32__ has not been explicitly defined and I think the implementation is the empty one. I corroborated this with Eclipse IDE for C/C++ which provides a detailed call hierarchy view. By the way, no return value from both cases.

Moreover, we can find other functions with no return value using the same trace expansion view e.g: Configure(), defined in /ldecod/src/decoder_test.c:

/*file decoder_test.c*/

// declarations
static void Configure(InputParameters *p_Inp, int ac, char *av[])
{
  // Other statements

  ParseCommand(p_Inp, ac, av) // declared as void!

  // Other statements
}

The xref from the Configure() node to its source code works fine. The same is true for ParseCommand() (ldecod/src/configfile.c).

[Mihai T. Lazarescu]

The spurious statement nodes are due to the instrumentation
of the dependencies on global variables.

Currently, these are attached to the first function called in
a source file, which for win32.c appears to be init_time().

These are declared in the function partools_decl_globals()
that is attached at the end of each annotated source, e.g.:

static void
partools_decl_globals(void)
{
    {
        if (partools_decl_globals_done)
            return;

        partools_stmt_id_local_offset = partools_stmt_id_global_offset;
        partools_stmt_id_global_offset += 893;

        partools_loop_id_local_offset = partools_loop_id_global_offset;
        partools_loop_id_global_offset += 12;

        partools_decl("ColorComponent", (void *)(&ColorComponent), 4, 1, 1, "JM/ldecod/inc/defines.h", 239);
        partools_write(partools_stmt_id_local_offset + 892, "ColorComponent", (void *)(&ColorComponent), 4, "JM/ldecod/../lcommon/src/win32.c", 74, 0);

        partools_decl("tz", (void *)(&tz), 8, 1, 1, "JM/ldecod/../lcommon/src/win32.c", 54);
        partools_write(partools_stmt_id_local_offset + 891, "tz", (void *)(&tz), 8, "JM/ldecod/../lcommon/src/win32.c", 74, 0);

        partools_decl_globals_done = 1;
    }
}

Now, the issues are actually:

1. these dependencies should be displayed differently by the
   viewer, not as node statements;
2. the location should be that of the global
   variable declarations. Locations as
   "JM/ldecod/../lcommon/src/win32.c", 74 make no sense.

[Mihai T. Lazarescu]

Solved the location issue (item (2) above).