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Make _REENTRANT and _THREAD_SAFE aliases for _POSIX_C_SOURCE=199506L.

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For many years, the only effect of these macros has been to make
unistd.h declare getlogin_r.  _POSIX_C_SOURCE >= 199506L also causes
this function to be declared.  However, people who don't carefully
read all the headers might be confused into thinking they need to
define _REENTRANT for any threaded code (as was indeed the case a long
time ago).

Therefore, remove __USE_REENTRANT, and make _REENTRANT and _THREAD_SAFE
into synonyms for _POSIX_C_SOURCE=199506L.  This will only affect
programs that don't select a higher conformance level some other way.
For instance, -std=c89 -D_REENTRANT will see a change in visible
declarations, but -std=c99 -D_POSIX_C_SOURCE=200809L -D_REENTRANT won't,
and -D_REENTRANT all by itself also won't, because _DEFAULT_SOURCE
implies _POSIX_C_SOURCE > 199506.

	* include/features.h: Remove __USE_REENTRANT.  Treat _REENTRANT
	and _THREAD_SAFE the same as _POSIX_C_SOURCE=199506L, if a higher
	POSIX conformance level has not been selected by other macros.
	* NEWS, manual/creature.texi: Document this change.

	* posix/unistd.h, posix/bits/unistd.h: Don't check __USE_REENTRANT.
	* include/libc-symbols.h: Don't define _REENTRANT.
	* scripts/check-installed-headers.sh: Don't undefine _REENTRANT.
This commit is contained in:
Zack Weinberg
2016-12-06 10:14:42 -05:00
parent 3d6bfcace1
commit c03073774f
7 changed files with 46 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

41
include/features.h
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@@ -24,10 +24,13 @@
__STRICT_ANSI__ ISO Standard C.
_ISOC99_SOURCE Extensions to ISO C89 from ISO C99.
_ISOC11_SOURCE Extensions to ISO C99 from ISO C11.
__STDC_WANT_LIB_EXT2__ Extensions to ISO C99 from TR 27431-2:2010.
__STDC_WANT_IEC_60559_BFP_EXT__ Extensions to ISO C11 from TS 18661-1:2014.
__STDC_WANT_IEC_60559_FUNCS_EXT__ Extensions to ISO C11 from
TS 18661-4:2015.
__STDC_WANT_LIB_EXT2__
Extensions to ISO C99 from TR 27431-2:2010.
__STDC_WANT_IEC_60559_BFP_EXT__
Extensions to ISO C11 from TS 18661-1:2014.
__STDC_WANT_IEC_60559_FUNCS_EXT__
Extensions to ISO C11 from TS 18661-4:2015.
_POSIX_SOURCE IEEE Std 1003.1.
_POSIX_C_SOURCE If ==1, like _POSIX_SOURCE; if >=2 add IEEE Std 1003.2;
if >=199309L, add IEEE Std 1003.1b-1993;
@@ -45,10 +48,12 @@
_GNU_SOURCE All of the above, plus GNU extensions.
_DEFAULT_SOURCE The default set of features (taking precedence over
__STRICT_ANSI__).
_REENTRANT Select additionally reentrant object.
_THREAD_SAFE Same as _REENTRANT, often used by other systems.
_FORTIFY_SOURCE If set to numeric value > 0 additional security
measures are defined, according to level.
_FORTIFY_SOURCE Add security hardening to many library functions.
Set to 1 or 2; 2 performs stricter checks than 1.
_REENTRANT, _THREAD_SAFE
Obsolete; equivalent to _POSIX_C_SOURCE=199506L.
The `-ansi' switch to the GNU C compiler, and standards conformance
options such as `-std=c99', define __STRICT_ANSI__. If none of
@@ -86,7 +91,6 @@
__USE_MISC Define things from 4.3BSD or System V Unix.
__USE_ATFILE Define *at interfaces and AT_* constants for them.
__USE_GNU Define GNU extensions.
__USE_REENTRANT Define reentrant/thread-safe *_r functions.
__USE_FORTIFY_LEVEL Additional security measures used, according to level.
The macros `__GNU_LIBRARY__', `__GLIBC__', and `__GLIBC_MINOR__' are
@@ -130,7 +134,6 @@
#undef __USE_MISC
#undef __USE_ATFILE
#undef __USE_GNU
#undef __USE_REENTRANT
#undef __USE_FORTIFY_LEVEL
#undef __KERNEL_STRICT_NAMES
@@ -253,6 +256,7 @@
# undef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 200809L
#endif
#if ((!defined __STRICT_ANSI__ \
|| (defined _XOPEN_SOURCE && (_XOPEN_SOURCE - 0) >= 500)) \
&& !defined _POSIX_SOURCE && !defined _POSIX_C_SOURCE)
@@ -269,6 +273,19 @@
# define __USE_POSIX_IMPLICITLY 1
#endif
/* Some C libraries once required _REENTRANT and/or _THREAD_SAFE to be
defined in all multithreaded code. GNU libc has not required this
for many years. We now treat them as compatibility synonyms for
_POSIX_C_SOURCE=199506L, which is the earliest level of POSIX with
comprehensive support for multithreaded code. Using them never
lowers the selected level of POSIX conformance, only raises it. */
#if ((!defined _POSIX_C_SOURCE || (_POSIX_C_SOURCE - 0) < 199506L) \
&& (defined _REENTRANT || defined _THREAD_SAFE))
# define _POSIX_SOURCE 1
# undef _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 199506L
#endif
#if (defined _POSIX_SOURCE \
|| (defined _POSIX_C_SOURCE && _POSIX_C_SOURCE >= 1) \
|| defined _XOPEN_SOURCE)
@@ -351,10 +368,6 @@
# define __USE_GNU 1
#endif
#if defined _REENTRANT || defined _THREAD_SAFE
# define __USE_REENTRANT 1
#endif
#if defined _FORTIFY_SOURCE && _FORTIFY_SOURCE > 0
# if !defined __OPTIMIZE__ || __OPTIMIZE__ <= 0
# warning _FORTIFY_SOURCE requires compiling with optimization (-O)