From: Zack Weinberg <zackw@panix.com>
To: libc-alpha@sourceware.org
Subject: Re: [RFC PATCH] Deprecate _REENTRANT and _THREAD_SAFE.
Date: Tue, 06 Dec 2016 16:43:00 -0000 [thread overview]
Message-ID: <611abaa8-6ffe-50b9-d369-46f8161b2529@panix.com> (raw)
In-Reply-To: <8e3a2e59-8275-d188-6a7e-54d92cbd1417@redhat.com>
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On 12/06/2016 10:36 AM, Florian Weimer wrote:
> On 12/06/2016 04:22 PM, Zack Weinberg wrote:
>> 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).
>
> You should get rid of the internal #define and #undef of _REENTRANT, too.
Do you mean the ones in libc-symbols.h and check-installed-headers.sh?
Those are the only ones I see grepping.
This updated patch takes care of that and also the discussion in
creature.texi. (creature.texi needs a thorough overhaul, but let's not
worry about that now.) Also, it's been tested on x86-64-linux.
zw
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From 8e04a5fe9858410311c71da92cfa119e2710213a Mon Sep 17 00:00:00 2001
From: Zack Weinberg <zackw@panix.com>
Date: Tue, 6 Dec 2016 10:14:42 -0500
Subject: [PATCH] Deprecate _REENTRANT and _THREAD_SAFE.
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, I propose to make _REENTRANT and _THREAD_SAFE into aliases
for _POSIX_C_SOURCE=199506L, and issue a deprecation warning when a
higher conformance level was not selected some other way.
For instance, -std=c89 -D_REENTRANT will warn, 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. I could be persuaded to make that final
case also warn.
* NEWS: The feature selection macros _REENTRANT and _THREAD_SAFE
are deprecated.
* manual/creature.texi: Document them as obsolete.
* include/features.h: Treat them as synonyms for
_POSIX_C_SOURCE=199506L, if a higher POSIX conformance level
has not been selected by other macros.
* 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.
---
NEWS | 10 ++++++++++
include/features.h | 39 ++++++++++++++++++++++++--------------
include/libc-symbols.h | 2 --
manual/creature.texi | 12 ++++--------
posix/bits/unistd.h | 2 +-
posix/unistd.h | 2 +-
| 1 -
7 files changed, 41 insertions(+), 27 deletions(-)
diff --git a/NEWS b/NEWS
index c2e973d..4f72149 100644
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,16 @@ Version 2.25
from that TS. Note that most features from that TS are not supported by
the GNU C Library.
+* The feature test macros _REENTRANT and _THREAD_SAFE are deprecated, and
+ will henceforth be treated as synonyms for _POSIX_C_SOURCE=199506L.
+ For many years, their only effect has been to cause <unistd.h> to declare
+ getlogin_r; _POSIX_C_SOURCE=199506L has the same effect. Since the
+ GNU C Library defaults to a much newer revision of POSIX, this will
+ only affect programs that specifically request an old conformance mode.
+ (For instance, a program compiled with -std=c89 -D_REENTRANT will see a
+ change in the visible declarations, but a program compiled with
+ -std=c99 -D_POSIX_C_SOURCE=200809L -D_REENTRANT will not.)
+
* The inclusion of <sys/sysmacros.h> by <sys/types.h> is deprecated. This
means that in a future release, the macros “major”, “minor”, and “makedev”
will only be available from <sys/sysmacros.h>.
diff --git a/include/features.h b/include/features.h
index 650d4c5..5de950c 100644
--- a/include/features.h
+++ b/include/features.h
@@ -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 +273,17 @@
# define __USE_POSIX_IMPLICITLY 1
#endif
+/* _REENTRANT and _THREAD_SAFE are obsolete aliases for _POSIX_C_SOURCE=199506L.
+ Only issue a warning if _POSIX_C_SOURCE was not already defined to
+ an equivalent or higher level some other way. */
+#if ((!defined _POSIX_C_SOURCE || (_POSIX_C_SOURCE - 0) < 199506L) \
+ && (defined _REENTRANT || defined _THREAD_SAFE))
+# warning "_REENTRANT and _THREAD_SAFE are deprecated, use _POSIX_C_SOURCE"
+# 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 +366,6 @@
# 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)
diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index 1c91f2e..4238d79 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -52,8 +52,6 @@
/* Enable declarations of GNU extensions, since we are compiling them. */
#define _GNU_SOURCE 1
-/* And we also need the data for the reentrant functions. */
-#define _REENTRANT 1
#include <config.h>
diff --git a/manual/creature.texi b/manual/creature.texi
index 257f871..5048886 100644
--- a/manual/creature.texi
+++ b/manual/creature.texi
@@ -219,15 +219,11 @@ cause them to be disabled.
@comment GNU
@defvr Macro _REENTRANT
@defvrx Macro _THREAD_SAFE
-If you define one of these macros, reentrant versions of several functions get
-declared. Some of the functions are specified in POSIX.1c but many others
-are only available on a few other systems or are unique to @theglibc{}.
-The problem is the delay in the standardization of the thread safe C library
-interface.
+These macros are obsolete. They have the same effect as defining
+@code{_POSIX_C_SOURCE} with the value @code{199506L}.
-Unlike on some other systems, no special version of the C library must be
-used for linking. There is only one version but while compiling this
-it must have been specified to compile as thread safe.
+Some very old C libraries required one of these macros to be defined
+for basic functionality (e.g.@: @code{getchar}) to be thread-safe.
@end defvr
We recommend you use @code{_GNU_SOURCE} in new programs. If you don't
diff --git a/posix/bits/unistd.h b/posix/bits/unistd.h
index 0105f04..4a5f42e 100644
--- a/posix/bits/unistd.h
+++ b/posix/bits/unistd.h
@@ -302,7 +302,7 @@ __NTH (ttyname_r (int __fd, char *__buf, size_t __buflen))
}
-#if defined __USE_REENTRANT || defined __USE_POSIX199506
+#ifdef __USE_POSIX199506
extern int __getlogin_r_chk (char *__buf, size_t __buflen, size_t __nreal)
__nonnull ((1));
extern int __REDIRECT (__getlogin_r_alias, (char *__buf, size_t __buflen),
diff --git a/posix/unistd.h b/posix/unistd.h
index 625ba77..392dc0e 100644
--- a/posix/unistd.h
+++ b/posix/unistd.h
@@ -849,7 +849,7 @@ extern int tcsetpgrp (int __fd, __pid_t __pgrp_id) __THROW;
This function is a possible cancellation point and therefore not
marked with __THROW. */
extern char *getlogin (void);
-#if defined __USE_REENTRANT || defined __USE_POSIX199506
+#ifdef __USE_POSIX199506
/* Return at most NAME_LEN characters of the login name of the user in NAME.
If it cannot be determined or some other error occurred, return the error
code. Otherwise return 0.
--git a/scripts/check-installed-headers.sh b/scripts/check-installed-headers.sh
index a245fe6..89e1514 100644
--- a/scripts/check-installed-headers.sh
+++ b/scripts/check-installed-headers.sh
@@ -143,7 +143,6 @@ EOF
inappropriate for this test. */
#undef _LIBC
#undef _GNU_SOURCE
-#undef _REENTRANT
/* The library mode is selected here rather than on the command line to
ensure that this selection wins. */
$expanded_lib_mode
--
2.10.2
next prev parent reply other threads:[~2016-12-06 16:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-06 15:22 Zack Weinberg
2016-12-06 15:36 ` Florian Weimer
2016-12-06 16:43 ` Zack Weinberg [this message]
2016-12-07 9:06 ` Florian Weimer
2016-12-07 13:52 ` Zack Weinberg
2016-12-08 19:51 ` Carlos O'Donell
2016-12-08 20:41 ` Zack Weinberg
2016-12-06 16:46 ` Joseph Myers
2016-12-06 16:48 ` Zack Weinberg
2016-12-08 18:21 ` Mike Frysinger
2016-12-08 9:01 ` Michael Kerrisk
2016-12-08 14:01 ` Zack Weinberg
2016-12-09 10:33 ` Michael Kerrisk (man-pages)
2016-12-09 18:07 ` Zack Weinberg
2016-12-10 12:01 ` Michael Kerrisk (man-pages)
2016-12-10 13:56 ` Zack Weinberg
2016-12-10 14:23 ` Michael Kerrisk (man-pages)
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