[libFuzzer][Windows] Use dllexport for all declarations in FuzzerInterface.h

[metzman]

Summary

Use dllexport for all declarations in FuzzerInterface.h Use it for clang
even though clang supports default visibility attribute to prevent a
warning from being thrown when LLVMFuzzerMutate is defined with dllexport.
This makes FUZZER_INTERFACE_VISIBILITY (FuzzerInterface.h) consistent with
ATTRIBUTE_INTERFACE (FuzzerDefs.h) when using clang on Windows.

[metzman]

Don't use default visibility with clang on Windows

[metzman]

Please take a look.
This change silences a warning when compiling libFuzzer for Windows with clang.
It shouldn't affect anything other than compiling libFuzzer with clang on Windows.

[morehouse]

compiler-rt/lib/fuzzer/FuzzerInterface.h

30 ↗

(On Diff #183766)

Why only 32-bit? Also, shouldn't this be #if defined(_WIN32)?

[metzman]

• check if _WIN32 is defined

[metzman]

compiler-rt/lib/fuzzer/FuzzerInterface.h

30 ↗

(On Diff #183766)

Why only 32-bit?

_WIN32 is defined for 64-bit and 32-bit builds. We use it in FuzzerDefs.h to set LIBFUZZER_WINDOWS.

Also, shouldn't this be #if defined(_WIN32)?

I've changed it to be this.

Funny that you noticed this though, since I came to the opposite conclusion when bikeshedding before uploading the initial patch.
#if defined(_WIN32) is more correct but #if _WIN32 works because undefined macros evaluate to false.
I did this to be consistent with FuzzerDefs.h which uses #if _WIN32 but should be using #if defined(_WIN32), (same for other platform macros).

[morehouse]

LGTM

compiler-rt/trunk/lib/fuzzer/FuzzerInterface.h

 #include <stdint.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif  // __cplusplus
 
 // Define FUZZER_INTERFACE_VISIBILITY to set default visibility in a way that
 // doesn't break MSVC.
-#if defined(_MSC_VER) && !defined(__clang__)
+#if defined(_WIN32)
 #define FUZZER_INTERFACE_VISIBILITY __declspec(dllexport)
 #else
 #define FUZZER_INTERFACE_VISIBILITY __attribute__((visibility("default")))
 #endif
 
 // Mandatory user-provided target function.
 // Executes the code under test with [Data, Data+Size) as the input.
 // libFuzzer will invoke this function *many* times with different inputs.