Let stddef.h respect __need_{wchar_t, size_t, NULL, ptrdiff_t, wint_t}.

glibc expects that stddef.h only defines a single thing if either of these
defines is set.  For example, before this change, a C file containing

  #include <stdlib.h>
  int ptrdiff_t = 0;

would compile with gcc but not with clang. Now it compiles with clang too.

This also fixes PR12997, where older versions of the Linux headers would define
NULL incorrectly, and glibc would define __need_NULL and expect stddef.h to
redefine NULL with the correct definition.

llvm-svn: 207606

1 files changed, 34 insertions, 4 deletions

diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index 97126ed1527..2dfe0a29b2a 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -23,9 +23,22 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef __STDDEF_H
+#if !defined(__STDDEF_H) || defined(__need_ptrdiff_t) ||                       \
+    defined(__need_size_t) || defined(__need_wchar_t) ||                       \
+    defined(__need_NULL) || defined(__need_wint_t)
+
+#if !defined(__need_ptrdiff_t) && !defined(__need_size_t) &&                   \
+    !defined(__need_wchar_t) && !defined(__need_NULL) &&                       \
+    !defined(__need_wint_t)
 #define __STDDEF_H
+#define __need_ptrdiff_t
+#define __need_size_t
+#define __need_wchar_t
+#define __need_NULL
+/* __need_wint_t is intentionally not defined here. */
+#endif
 
+#if defined(__need_ptrdiff_t)
 #if !defined(_PTRDIFF_T) || __has_feature(modules)
 /* Always define ptrdiff_t when modules are available. */
 #if !__has_feature(modules)
@@ -33,7 +46,10 @@
 #endif
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
 #endif
+#undef __need_ptrdiff_t
+#endif /* defined(__need_ptrdiff_t) */
 
+#if defined(__need_size_t)
 #if !defined(_SIZE_T) || __has_feature(modules)
 /* Always define size_t when modules are available. */
 #if !__has_feature(modules)
@@ -41,7 +57,10 @@ typedef __PTRDIFF_TYPE__ ptrdiff_t;
 #endif
 typedef __SIZE_TYPE__ size_t;
 #endif
+#undef __need_size_t
+#endif /*defined(__need_size_t) */
 
+#if defined(__STDDEF_H)
 /* ISO9899:2011 7.20 (C11 Annex K): Define rsize_t if __STDC_WANT_LIB_EXT1__ is
  * enabled. */
 #if (defined(__STDC_WANT_LIB_EXT1__) && __STDC_WANT_LIB_EXT1__ >= 1 && \
@@ -52,7 +71,9 @@ typedef __SIZE_TYPE__ size_t;
 #endif
 typedef __SIZE_TYPE__ rsize_t;
 #endif
+#endif /* defined(__STDDEF_H) */
 
+#if defined(__need_wchar_t)
 #ifndef __cplusplus
 /* Always define wchar_t when modules are available. */
 #if !defined(_WCHAR_T) || __has_feature(modules)
@@ -65,7 +86,10 @@ typedef __SIZE_TYPE__ rsize_t;
 typedef __WCHAR_TYPE__ wchar_t;
 #endif
 #endif
+#undef __need_wchar_t
+#endif /* defined(__need_wchar_t) */
 
+#if defined(__need_NULL)
 #undef NULL
 #ifdef __cplusplus
 #  if !defined(__MINGW32__) && !defined(_MSC_VER)
@@ -76,15 +100,19 @@ typedef __WCHAR_TYPE__ wchar_t;
 #else
 #  define NULL ((void*)0)
 #endif
-
 #ifdef __cplusplus
 #if defined(_MSC_EXTENSIONS) && defined(_NATIVE_NULLPTR_SUPPORTED)
 namespace std { typedef decltype(nullptr) nullptr_t; }
 using ::std::nullptr_t;
 #endif
 #endif
+#undef __need_NULL
+#endif /* defined(__need_NULL) */
+
+#if defined(__STDDEF_H)
 
 #if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) || __has_feature(modules)
 #ifndef _MSC_VER
 typedef struct {
   long long __clang_max_align_nonce1
@@ -97,10 +125,10 @@ typedef double max_align_t;
 #endif
 #define __CLANG_MAX_ALIGN_T_DEFINED
 #endif
+#endif
 
 #define offsetof(t, d) __builtin_offsetof(t, d)
-
-#endif /* __STDDEF_H */
+#endif  /* __STDDEF_H */
 
 /* Some C libraries expect to see a wint_t here. Others (notably MinGW) will use
 __WINT_TYPE__ directly; accommodate both by requiring __need_wint_t */
@@ -114,3 +142,5 @@ typedef __WINT_TYPE__ wint_t;
 #endif
 #undef __need_wint_t
 #endif /* __need_wint_t */
+
+#endif