[llvm] r271491 - [LibFuzzer] Reimplement how the optional user functions are called.

[Dan Liew via llvm-commits]

On 8 July 2017 at 01:40, Eric Christopher <echristo at gmail.com> wrote:
> Hi Dan,
>
> So this is causing warnings and breaking Werror builds:
>
> /usr/local/google/home/echristo/sources/llvm/lib/Fuzzer/FuzzerExtFunctions.def:29:10:
> warning: ISO C++ forbids casting between pointer-to-function and
> pointer-to-object [-Wpedantic]
>  EXT_FUNC(__lsan_enable, void, (), false);
>           ^
> /usr/local/google/home/echristo/sources/llvm/lib/Fuzzer/FuzzerExtFunctionsWeak.cpp:44:24:
> note: in definition of macro ‘EXT_FUNC’
>    CheckFnPtr((void *)::NAME, #NAME, WARN);
>                         ^
>
> Feel like fixing? :)

Is this GCC or Clang and which version is this with?

I can think of two options to fix this.

1. Use pragmas to disable warnings in the region. E.g.

```
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wpedantic"

// do stuff

#pragma GCC diagnostic pop
```

2. Make `CheckFnPtr a templated function so that the cast is no longer
necessary.

i.e. something like.
```
template <typename T>
static void CheckFnPtr(T FnPtr, const char *FnName, bool WarnIfMissing) {
  if (FnPtr == nullptr && WarnIfMissing) {
    Printf("WARNING: Failed to find function \"%s\".\n", FnName);
  }
}
```

I kind of prefer option 2 but I don't like the fact this will cause us
to emit a different implementation of `CheckFnPtr` for every single
function signature, just so we can avoid
a pedantic warning.

@kcc: Any thoughts on this? Do you have any preferences for option 1
or 2 or do you have an idea for a third option?

Dan.