[PATCH v3 01/24] Feature test macros overhaul: sys/features.h

[Yaakov Selkowitz <yselkowi at redhat dot com>]

This is the complete rework of the feature tests macros for better
compatibility with GNU libc, primarily based on the Linux man pages
documentation:

http://man7.org/linux/man-pages/man7/feature_test_macros.7.html

The previous implementation was flawed in its approach that macros were
often used to hide symbols if defined (e.g. !defined __STRICT_ANSI__ or
!defined _POSIX_SOURCE), whereas the approach of glibc is that these macros
make symbols available when defined (e.g. defined _BSD_SOURCE, or as used
internally, #if __BSD_VISIBLE).  As much open-source software is written
with glibc in mind, this necessitated patching numerous packages just to
compile.

In particular, __STRICT_ANSI__ (which is defined by gcc -ansi or -std=c*)
was given too much importance.  This implementation limits the influence
of __STRICT_ANSI__ to controlling the default when no other feature test
macros are defined, and to the inclusion of <alloca.h> in <stdlib.h> as
documented.  These are the only places where __STRICT_ANSI__ should be
tested.

The following macros are now accepted: _ATFILE_SOURCE, _BSD_SOURCE,
_DEFAULT_SOURCE, _ISOC99_SOURCE, _ISOC11_SOURCE, _LARGEFILE_SOURCE,
_SVID_SOURCE, _XOPEN_SOURCE_EXTENDED.

The existing __*_VISIBLE internal macros have been kept mostly
compatible with the original BSD implementation, with some changes to
the criteria which controls them.  Several more macros in this style
have been added where needed for concision or accuracy.

Enabling C++11 or newer in the compiler also enables C99 and C11
functions.  Doing so should help move away from the need to define
_GNU_SOURCE in g++ for _GLIBCXX_USE_C99 support as on Linux:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51749

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>
---
 newlib/libc/include/sys/cdefs.h    | 126 ------------------------
 newlib/libc/include/sys/config.h   |   3 -
 newlib/libc/include/sys/features.h | 196 +++++++++++++++++++++++++++++++++----
 3 files changed, 177 insertions(+), 148 deletions(-)

diff --git a/newlib/libc/include/sys/cdefs.h b/newlib/libc/include/sys/cdefs.h
index 773ac25..2a55a92 100644
--- a/newlib/libc/include/sys/cdefs.h
+++ b/newlib/libc/include/sys/cdefs.h
@@ -624,132 +624,6 @@
 #define	__DEQUALIFY(type, var)	((type)(__uintptr_t)(const volatile void *)(var))
 #endif
 
-/*-
- * The following definitions are an extension of the behavior originally
- * implemented in <sys/_posix.h>, but with a different level of granularity.
- * POSIX.1 requires that the macros we test be defined before any standard
- * header file is included.
- *
- * Here's a quick run-down of the versions:
- *  defined(_POSIX_SOURCE)		1003.1-1988
- *  _POSIX_C_SOURCE == 1		1003.1-1990
- *  _POSIX_C_SOURCE == 2		1003.2-1992 C Language Binding Option
- *  _POSIX_C_SOURCE == 199309		1003.1b-1993
- *  _POSIX_C_SOURCE == 199506		1003.1c-1995, 1003.1i-1995,
- *					and the omnibus ISO/IEC 9945-1: 1996
- *  _POSIX_C_SOURCE == 200112		1003.1-2001
- *  _POSIX_C_SOURCE == 200809		1003.1-2008
- *
- * In addition, the X/Open Portability Guide, which is now the Single UNIX
- * Specification, defines a feature-test macro which indicates the version of
- * that specification, and which subsumes _POSIX_C_SOURCE.
- *
- * Our macros begin with two underscores to avoid namespace screwage.
- */
-
-/* Deal with _GNU_SOURCE, which implies everything and the kitchen sink */
-#ifdef _GNU_SOURCE
-#undef _XOPEN_SOURCE
-#define	_XOPEN_SOURCE		700
-#define	__BSD_VISIBLE		1
-#define	__GNU_VISIBLE		1
-#endif
-
-/* Deal with IEEE Std. 1003.1-1990, in which _POSIX_C_SOURCE == 1. */
-#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE == 1
-#undef _POSIX_C_SOURCE		/* Probably illegal, but beyond caring now. */
-#define	_POSIX_C_SOURCE		199009
-#endif
-
-/* Deal with IEEE Std. 1003.2-1992, in which _POSIX_C_SOURCE == 2. */
-#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE == 2
-#undef _POSIX_C_SOURCE
-#define	_POSIX_C_SOURCE		199209
-#endif
-
-/* Deal with various X/Open Portability Guides and Single UNIX Spec. */
-#ifdef _XOPEN_SOURCE
-#if _XOPEN_SOURCE - 0 >= 700
-#define	__XSI_VISIBLE		700
-#undef _POSIX_C_SOURCE
-#define	_POSIX_C_SOURCE		200809
-#elif _XOPEN_SOURCE - 0 >= 600
-#define	__XSI_VISIBLE		600
-#undef _POSIX_C_SOURCE
-#define	_POSIX_C_SOURCE		200112
-#elif _XOPEN_SOURCE - 0 >= 500
-#define	__XSI_VISIBLE		500
-#undef _POSIX_C_SOURCE
-#define	_POSIX_C_SOURCE		199506
-#endif
-#endif
-
-/*
- * Deal with all versions of POSIX.  The ordering relative to the tests above is
- * important.
- */
-#if defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE)
-#define	_POSIX_C_SOURCE		198808
-#endif
-#ifdef _POSIX_C_SOURCE
-#if _POSIX_C_SOURCE >= 200809
-#define	__POSIX_VISIBLE		200809
-#define	__ISO_C_VISIBLE		1999
-#elif _POSIX_C_SOURCE >= 200112
-#define	__POSIX_VISIBLE		200112
-#define	__ISO_C_VISIBLE		1999
-#elif _POSIX_C_SOURCE >= 199506
-#define	__POSIX_VISIBLE		199506
-#define	__ISO_C_VISIBLE		1990
-#elif _POSIX_C_SOURCE >= 199309
-#define	__POSIX_VISIBLE		199309
-#define	__ISO_C_VISIBLE		1990
-#elif _POSIX_C_SOURCE >= 199209
-#define	__POSIX_VISIBLE		199209
-#define	__ISO_C_VISIBLE		1990
-#elif _POSIX_C_SOURCE >= 199009
-#define	__POSIX_VISIBLE		199009
-#define	__ISO_C_VISIBLE		1990
-#else
-#define	__POSIX_VISIBLE		198808
-#define	__ISO_C_VISIBLE		0
-#endif /* _POSIX_C_SOURCE */
-#else
-/*-
- * Deal with _ANSI_SOURCE:
- * If it is defined, and no other compilation environment is explicitly
- * requested, then define our internal feature-test macros to zero.  This
- * makes no difference to the preprocessor (undefined symbols in preprocessing
- * expressions are defined to have value zero), but makes it more convenient for
- * a test program to print out the values.
- *
- * If a program mistakenly defines _ANSI_SOURCE and some other macro such as
- * _POSIX_C_SOURCE, we will assume that it wants the broader compilation
- * environment (and in fact we will never get here).
- */
-#if defined(_ANSI_SOURCE)	/* Hide almost everything. */
-#define	__POSIX_VISIBLE		0
-#define	__XSI_VISIBLE		0
-#define	__BSD_VISIBLE		0
-#define	__ISO_C_VISIBLE		1990
-#elif defined(_C99_SOURCE)	/* Localism to specify strict C99 env. */
-#define	__POSIX_VISIBLE		0
-#define	__XSI_VISIBLE		0
-#define	__BSD_VISIBLE		0
-#define	__ISO_C_VISIBLE		1999
-#elif defined(_C11_SOURCE)	/* Localism to specify strict C11 env. */
-#define	__POSIX_VISIBLE		0
-#define	__XSI_VISIBLE		0
-#define	__BSD_VISIBLE		0
-#define	__ISO_C_VISIBLE		2011
-#else				/* Default: everything except __GNU_VISIBLE. */
-#define	__POSIX_VISIBLE		200809
-#define	__XSI_VISIBLE		700
-#define	__BSD_VISIBLE		1
-#define	__ISO_C_VISIBLE		2011
-#endif
-#endif
-
 /*
  * Type Safety Checking
  *
diff --git a/newlib/libc/include/sys/config.h b/newlib/libc/include/sys/config.h
index 5297bef..c536698 100644
--- a/newlib/libc/include/sys/config.h
+++ b/newlib/libc/include/sys/config.h
@@ -232,9 +232,6 @@
 
 #if defined(__CYGWIN__)
 #include <cygwin/config.h>
-#if !defined (__STRICT_ANSI__) || (__STDC_VERSION__ >= 199901L)
-#define __USE_XOPEN2K 1
-#endif
 #endif
 
 #if defined(__rtems__)
diff --git a/newlib/libc/include/sys/features.h b/newlib/libc/include/sys/features.h
index cb6d1eb..d48413b 100644
--- a/newlib/libc/include/sys/features.h
+++ b/newlib/libc/include/sys/features.h
@@ -39,6 +39,183 @@ extern "C" {
 /* Version with trailing underscores for BSD compatibility. */
 #define	__GNUC_PREREQ__(ma, mi)	__GNUC_PREREQ(ma, mi)
 
+
+/*
+ * Feature test macros control which symbols are exposed by the system
+ * headers.  Any of these must be defined before including any headers.
+ *
+ * __STRICT_ANSI__ (defined by gcc -ansi, -std=c90, -std=c99, or -std=c11)
+ *	ISO C
+ * _POSIX_SOURCE (deprecated by _POSIX_C_SOURCE=1)
+ * _POSIX_C_SOURCE >= 1
+ * 	POSIX.1-1990
+ * _POSIX_C_SOURCE >= 2
+ * 	POSIX.2-1992
+ * _POSIX_C_SOURCE >= 199309L
+ * 	POSIX.1b-1993 Real-time extensions
+ * _POSIX_C_SOURCE >= 199506L
+ * 	POSIX.1c-1995 Threads extensions
+ * _POSIX_C_SOURCE >= 200112L
+ * 	POSIX.1-2001 and C99
+ * _POSIX_C_SOURCE >= 200809L
+ * 	POSIX.1-2008
+ * _XOPEN_SOURCE
+ *	POSIX.1-1990 and XPG4
+ * _XOPEN_SOURCE_EXTENDED
+ *	SUSv1 (POSIX.2-1992 plus XPG4v2)
+ * _XOPEN_SOURCE >= 500
+ *	SUSv2 (POSIX.1c-1995 plus XSI)
+ * _XOPEN_SOURCE >= 600
+ *	SUSv3 (POSIX.1-2001 plus XSI) and C99
+ * _XOPEN_SOURCE >= 700
+ *	SUSv4 (POSIX.1-2008 plus XSI)
+ * _ISOC99_SOURCE or gcc -std=c99 or g++ -std=c++11
+ * 	ISO C99
+ * _ISOC11_SOURCE or gcc -std=c11 or g++ -std=c++11
+ * 	ISO C11
+ * _ATFILE_SOURCE (implied by _POSIX_C_SOURCE >= 200809L)
+ *	"at" functions
+ * _LARGEFILE_SOURCE (deprecated by _XOPEN_SOURCE >= 500)
+ *	fseeko, ftello
+ * _GNU_SOURCE
+ * 	All of the above plus GNU extensions
+ * _BSD_SOURCE (deprecated by _DEFAULT_SOURCE)
+ * _SVID_SOURCE (deprecated by _DEFAULT_SOURCE)
+ * _DEFAULT_SOURCE (or none of the above)
+ * 	POSIX-1.2008 with BSD and SVr4 extensions
+ */
+
+#ifdef _GNU_SOURCE
+#undef _ATFILE_SOURCE
+#define	_ATFILE_SOURCE		1
+#undef	_DEFAULT_SOURCE
+#define	_DEFAULT_SOURCE		1
+#undef _ISOC99_SOURCE
+#define	_ISOC99_SOURCE		1
+#undef _ISOC11_SOURCE
+#define	_ISOC11_SOURCE		1
+#undef _POSIX_SOURCE
+#define	_POSIX_SOURCE		1
+#undef _POSIX_C_SOURCE
+#define	_POSIX_C_SOURCE		200809L
+#undef _XOPEN_SOURCE
+#define	_XOPEN_SOURCE		700
+#undef _XOPEN_SOURCE_EXTENDED
+#define	_XOPEN_SOURCE_EXTENDED	1
+#endif /* _GNU_SOURCE */
+
+#if defined(_BSD_SOURCE) || defined(_SVID_SOURCE) || \
+   (!defined(__STRICT_ANSI__) && !defined(_ANSI_SOURCE) && \
+   !defined(_ISOC99_SOURCE) && !defined(_POSIX_SOURCE) && \
+   !defined(_POSIX_C_SOURCE) && !defined(_XOPEN_SOURCE))
+#undef _DEFAULT_SOURCE
+#define	_DEFAULT_SOURCE		1
+#endif
+
+#if defined(_DEFAULT_SOURCE)
+#undef _POSIX_SOURCE
+#define	_POSIX_SOURCE		1
+#undef _POSIX_C_SOURCE
+#define	_POSIX_C_SOURCE		200809L
+#endif
+
+#if !defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE) && \
+  ((!defined(__STRICT_ANSI__) && !defined(_ANSI_SOURCE)) || \
+   (_XOPEN_SOURCE - 0) >= 500)
+#define	_POSIX_SOURCE		1
+#if !defined(_XOPEN_SOURCE) || (_XOPEN_SOURCE - 0) >= 700
+#define	_POSIX_C_SOURCE		200809L
+#elif (_XOPEN_SOURCE - 0) >= 600
+#define	_POSIX_C_SOURCE		200112L
+#elif (_XOPEN_SOURCE - 0) >= 500
+#define	_POSIX_C_SOURCE		199506L
+#elif (_XOPEN_SOURCE - 0) < 500
+#define	_POSIX_C_SOURCE		2
+#endif
+#endif
+
+#if defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 200809
+#undef _ATFILE_SOURCE
+#define	_ATFILE_SOURCE		1
+#endif
+
+/* Our macros begin with two underscores to avoid namespace issues. */
+#ifdef _ATFILE_SOURCE
+#define	__ATFILE_VISIBLE	1
+#else
+#define	__ATFILE_VISIBLE	0
+#endif
+
+#ifdef _DEFAULT_SOURCE
+#define	__BSD_VISIBLE		1
+#else
+#define	__BSD_VISIBLE		0
+#endif
+
+#ifdef _GNU_SOURCE
+#define	__GNU_VISIBLE		1
+#else
+#define	__GNU_VISIBLE		0
+#endif
+
+#if defined(_ISOC11_SOURCE) || \
+  (__STDC_VERSION__ - 0) >= 201112L || (__cplusplus - 0) >= 201103L
+#define	__ISO_C_VISIBLE		2011
+#elif defined(_ISOC99_SOURCE) || \
+  (__STDC_VERSION__ - 0) >= 199901L || (_POSIX_C_SOURCE - 0) >= 200112L
+#define	__ISO_C_VISIBLE		1999
+#else
+#define	__ISO_C_VISIBLE		1990
+#endif
+
+#if defined(_LARGEFILE_SOURCE) || (_XOPEN_SOURCE - 0) >= 500
+#define	__LARGEFILE_VISIBLE	1
+#else
+#define	__LARGEFILE_VISIBLE	0
+#endif
+
+#ifdef _DEFAULT_SOURCE
+#define	__MISC_VISIBLE		1
+#else
+#define	__MISC_VISIBLE		0
+#endif
+
+#if (_POSIX_C_SOURCE - 0) >= 200809L
+#define	__POSIX_VISIBLE		200809
+#elif (_POSIX_C_SOURCE - 0) >= 200112L
+#define	__POSIX_VISIBLE		200112
+#elif (_POSIX_C_SOURCE - 0) >= 199506L
+#define	__POSIX_VISIBLE		199506
+#elif (_POSIX_C_SOURCE - 0) >= 199309L
+#define	__POSIX_VISIBLE		199309
+#elif (_POSIX_C_SOURCE - 0) >= 2 || defined(_XOPEN_SOURCE)
+#define	__POSIX_VISIBLE		199209
+#elif defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE)
+#define	__POSIX_VISIBLE		199009
+#else
+#define	__POSIX_VISIBLE		0
+#endif
+
+#ifdef _DEFAULT_SOURCE
+#define	__SVID_VISIBLE		1
+#else
+#define	__SVID_VISIBLE		0
+#endif
+
+#if (_XOPEN_SOURCE - 0) >= 700
+#define	__XSI_VISIBLE		700
+#elif (_XOPEN_SOURCE - 0) >= 600
+#define	__XSI_VISIBLE		600
+#elif (_XOPEN_SOURCE - 0) >= 500
+#define	__XSI_VISIBLE		500
+#elif defined(_XOPEN_SOURCE) && defined(_XOPEN_SOURCE_EXTENDED)
+#define	__XSI_VISIBLE		4
+#elif defined(_XOPEN_SOURCE)
+#define	__XSI_VISIBLE		1
+#else
+#define	__XSI_VISIBLE		0
+#endif
+
 /* RTEMS adheres to POSIX -- 1003.1b with some features from annexes.  */
 
 #ifdef __rtems__
@@ -206,25 +383,6 @@ extern "C" {
 
 #endif /* __CYGWIN__ */
 
-/* Per the permission given in POSIX.1-2008 section 2.2.1, define
- * _POSIX_C_SOURCE if _XOPEN_SOURCE is defined and _POSIX_C_SOURCE is not.
- * (_XOPEN_SOURCE indicates that XSI extensions are desired by an application.)
- * This permission is first granted in 2008, but use it for older ones, also.
- * Allow for _XOPEN_SOURCE to be empty (from the earliest form of it, before it
- * was required to have specific values).
- */
-#if !defined(_POSIX_C_SOURCE)  &&  defined(_XOPEN_SOURCE) 
-  #if (_XOPEN_SOURCE - 0) == 700	/* POSIX.1-2008 */
-    #define _POSIX_C_SOURCE       200809L
-   #elif (_XOPEN_SOURCE - 0) == 600	/* POSIX.1-2001 or 2004 */
-    #define _POSIX_C_SOURCE       200112L
-   #elif (_XOPEN_SOURCE - 0) == 500	/* POSIX.1-1995 */
-    #define _POSIX_C_SOURCE       199506L
-   #elif (_XOPEN_SOURCE - 0) < 500	/* really old */
-    #define _POSIX_C_SOURCE       2
-  #endif
-#endif
-
 #ifdef __cplusplus
 }
 #endif
-- 
2.7.0