Anonymous function calls

[lks9]

1. We could save trace space if we do not record all numbers from function calls. When less methods are numbered, the method numbers are smaller, and this can result in a smaller trace, too.
2. We could even save more space if we do not record some function calls at all.

Well, but the problem is: How to decide on which function calls to skip?

• [ ] Static functions which are never referenced through a pointer?
• [x] Normal functions which are never referenced through a pointer? (#61 or approaches based on function_pointer_only)
• Small Functions which are often (and recursively) called as long as the trace keeps being reconstructable?
• [x] Inline functions (use --inline to instrument them anyway).
• [x] Use --anon to instrument all functions anonymously.
• [x] Skip all function calls instrumentations with --no-functions and --no-returns.

The problem is that we would need some static analysis to detect the first three.

[lks9]

We can open a new issue when there is hope to detect function access through pointers. Otherwise, there is no way to solve the first two. Task 3 (small functions) is too vague anyways.

[lks9]

I have a new approach which makes nasty use of the C pre processor:

Suppose we have a function with the following signature:

int foo(int x);

Replace it in the instrumentation with:

#undef foo
int foo(int x);
#define foo(...) foo_orig(__VA_ARGS__)
int foo(int x);

And the body:

int foo(int x) {
    CODE
}

Replace with:

int foo_orig(int x) {
    INSTRUMENTED_CODE
}
#undef foo
int foo(int x) { __FUNC(num)
    return foo_orig(x);
}
#define foo(...) foo_orig(__VA_ARGS__)

This way, a call to foo_orig() won't cause the function to be reported with __FUNC(num). Test:

  foo(1);
  int (*f)(int) = foo;
  f(2);
  (*foo)(2);

Only foo(1) is replaced with foo_orig(1) by the pre processor. foo(1) does not output the function number while f(2) and (*foo)(3) do. This is as it should be because the first is called by function name (hence without _FUNC(num) reconstructable) whereas the others are called by pointer.