[ASan] [MinGW] Avoid including headers for functions that will be redefined

[mstorsjo]

Summary

With mingw-w64 headers, including windows.h ends up including stdlib.h and malloc.h implicitly, with the following path:

compiler-rt/lib/asan/asan_malloc_win.cc
x86_64-w64-mingw32/include/windows.h
x86_64-w64-mingw32/include/windef.h
x86_64-w64-mingw32/include/minwindef.h
x86_64-w64-mingw32/include/winnt.h
lib/clang/8.0.0/include/x86intrin.h
lib/clang/8.0.0/include/immintrin.h
lib/clang/8.0.0/include/xmmintrin.h
lib/clang/8.0.0/include/mm_malloc.h
x86_64-w64-mingw32/include/c++/v1/stdlib.h
x86_64-w64-mingw32/include/stdlib.h

These headers include declarations of functions like e.g. free(), without the dllexport attribute, but other included headers also include inline functions that reference free().

If these functions have been declared before (either with or without dllimport), we can still redeclare them with dllexport, this only yields a warning. However, if they have been declared without dllimport and referenced by an inline function in the headers, it has already been emitted to IR and we can't add the dllexport attribute afterwards.

By undefining STDC_HOSTED, we avoid xmmintrin.h including mm_malloc.h.

[rnk]

ಠ_ಠ mm_malloc.h, you are a source of much complexity.

lib/asan/asan_malloc_win.cc

28

How badly do we need this include? It looks like we only get it for a few typedefs like HANDLE, LPVOID, and some other stuff that we could avoid without too much work. This file is intentionally isolated to avoid these kinds of conflicts. Should we just isolate it from windows.h too?

[mstorsjo]

lib/asan/asan_malloc_win.cc

28

That's probably a much less fragile approach - I'll see if I can make it build without it.

[mstorsjo]

Going with D51914 instead.

lib/asan/asan_malloc_win.cc

 //===-- asan_malloc_win.cc ------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is a part of AddressSanitizer, an address sanity checker.
 //
 // Windows-specific malloc interception.
 //===----------------------------------------------------------------------===//
 
+#ifdef __MINGW32__
+// mingw-w64 winnt.h pulls in x86intrin.h, which can pull in mm_malloc.h
+// if __STDC_HOSTED__ is defined. mm_malloc.h includes stdlib.h and malloc.h,
+// which include conflicting declarations of these functions. Having earlier
+// declarations with or without dllimport produces warnings, but if an
+// inline function in a header referenced one of the functions, we no longer
+// can redeclare them with dllexport below.
+#undef __STDC_HOSTED__
+#endif
+
 #include "sanitizer_common/sanitizer_platform.h"
 #if SANITIZER_WINDOWS
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 
 #include "asan_allocator.h"
 #include "asan_interceptors.h"
 #include "asan_internal.h"
 #include "asan_stack.h"
 #include "interception/interception.h"
 
 #include <stddef.h>