From patchwork Wed Dec 12 15:57:07 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Albert ARIBAUD X-Patchwork-Id: 30649 Received: (qmail 6360 invoked by alias); 12 Dec 2018 15:57:22 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 6290 invoked by uid 89); 12 Dec 2018 15:57:21 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.4 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_LAZY_DOMAIN_SECURITY, KAM_NUMSUBJECT, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.2 spammy= X-HELO: smtp3-g21.free.fr From: "Albert ARIBAUD (3ADEV)" To: libc-alpha@sourceware.org Cc: "Albert ARIBAUD (3ADEV)" Subject: [PATCH v2] Y2038: add function __localtime64 Date: Wed, 12 Dec 2018 16:57:07 +0100 Message-Id: <20181212155707.2191-1-albert.aribaud@3adev.fr> In-Reply-To: <20181212012823.481-1-albert.aribaud@3adev.fr> References: <20181212012823.481-1-albert.aribaud@3adev.fr> Tested with 'make check' on x86_64-linux-gnu and i686-linux.gnu. * include/time.h (__localtime64): Add. * manual/maint.texi: Document Y2038 symbol handling. * time/localtime.c (__localtime64): Add. [__TIMERSIZE != 64] (__localtime): Turn into a wrapper. --- v2: fix 'Y2038' => @dfn{Y2038} in manual/maint.texi include/time.h | 9 +++- manual/maint.texi | 122 ++++++++++++++++++++++++++++++++++++++++++++++ time/localtime.c | 18 +++++-- 3 files changed, 145 insertions(+), 4 deletions(-) diff --git a/include/time.h b/include/time.h index 37964f7b76..251a2b0329 100644 --- a/include/time.h +++ b/include/time.h @@ -56,9 +56,16 @@ extern time_t __mktime_internal (struct tm *__tp, struct tm *(*__func) (const time_t *, struct tm *), long int *__offset) attribute_hidden; + +#if __TIMESIZE == 64 +# define __localtime64 localtime +#else +extern struct tm *__localtime64 (const __time64_t *__timer); +libc_hidden_proto (__localtime64) +#endif + extern struct tm *__localtime_r (const time_t *__timer, struct tm *__tp) attribute_hidden; - extern struct tm *__gmtime_r (const time_t *__restrict __timer, struct tm *__restrict __tp); libc_hidden_proto (__gmtime_r) diff --git a/manual/maint.texi b/manual/maint.texi index fce06bfa88..49be3621a0 100644 --- a/manual/maint.texi +++ b/manual/maint.texi @@ -5,6 +5,7 @@ @menu * Source Layout:: How to add new functions or header files to the GNU C Library. +* Symbol handling:: How to handle symbols in the GNU C Library. * Porting:: How to port the GNU C Library to a new machine or operating system. @end menu @@ -183,6 +184,127 @@ header file in the machine-specific directory, e.g., @file{sysdeps/powerpc/sys/platform/ppc.h}. +@node Symbol handling +@appendixsec Symbol handling in the GNU C Library + +@menu +* 64-bit time symbol handling :: How to handle 64-bit time related + symbols in the GNU C Library. +@end menu + +@node 64-bit time symbol handling +@appendixsubsec 64-bit time symbol handling in the GNU C Library + +Some of the architectures supported by @theglibc{} already use 64-bit +time (@code{__TIMESIZE == 64}), while other architectures use 32-bit time +(@code{__TIMESIZE != 64}) and therefore cannot handle dates beyond +2038-01-19 03:14:07 (aka @dfn{Y2038}). + +In order to make @theglibc{} Y2038-proof, 64-bit time support must be +added to those 32-bit-time-only architectures. When adding new code +for Y2038 support, some principles must be followed: + +@itemize @bullet + +@item +Y2038 support code added to @theglibc{} must not modify or remove +existing symbols on 32-bit time architectures. This ensures that +existing user object code will remain able to link against the newer +Y2038-proof @glibcadj{}. + +@item +Y2038 support code added to @theglibc{} must not add any new symbol +when building on 64-bit time architectures when existing symbols are +aleady Y2038-proof. + +@item +In public headers, @theglibc{} supports either 64- or 32-bit time with +a single set of names. On 64-bit time architectures, only 64-bit time +is supporte (@code{time_t} is 64-bit, @code{time()} returns a 64-bit time +etc); on 32-bit architectures, 32-bit time is supported (@code{time_t} +is 32-bit, @code{time()} returns a 32-bit time etc) unless +@code{_TIME_BITS} is defined equal to @code{64} before including +headers from @theglibc{}, in which case 64-bit time is supported. + +@end itemize + +In order to simplify Y2038 support, all Y2038 proofing follows the +same mechanism: for each non-Y2038-proof 32-bit-time function, a +Y2038-proof 64-bit-time version is created, and the 32-bit-time function +is rewritten as a wrapper around the 64-bit-time function. + +Here is an example with @code{localtime}: + +Function @code{localtime} is declared in @file{time/time.h} as +@smallexample +extern struct tm *localtime (const time_t *__timer) __THROW; +libc_hidden_proto (localtime) +@end smallexample + +On 64-bit time architectures, we declare @code{__localtime64} to be a +macro which evaluates to @code{localtime}, so that +@smallexample +extern struct tm *__localtime64 (const __time64_t *__timer) __THROW; +@end smallexample +evaluates to +@smallexample +extern struct tm *localtime (const time_t *__timer) __THROW; +@end smallexample + +(for 64-bit-time architectures, @code{__time64_t} is declared as a +macro which evaluates to @code{time_t}) + +On 32-bit time architectures, we declare @code{__localtime64} similar +to @code{localtime} except it uses Y2038-proof types: +@smallexample +#if __TIMESIZE == 64 +# define __localtime64 localtime +#else +extern struct tm *__localtime64 (const __time64_t *__timer) __THROW; +libc_hidden_proto (__localtime64) +#endif +@end smallexample + +(type @code{time_t} is replaced with @code{__time64_t} because +@code{time_t} is not Y2038-proof, whereas @code{struct tm} is not +replaced because it is already Y2038-proof.) + +The implementation of @code{localtime} is replaced as follows: + +@smallexample +struct tm * +__localtime64 (const __time64_t *t) +( + return __tz_convert (*t, 1, &_tmbuf); +) +libc_hidden_def (__localtime64) + +/* Provide a 32-bit variant if needed */ + +#if __TIMESIZE != 64 + +struct tm * +localtime (const time_t *t) +( + __time64_t t64 = *t; + return __localtime64 (&t64); +) +libc_hidden_def (localtime) + +#endif +@end smallexample + +For 64-bit-time architectures, @code{__localtime64} is a macro which +evaluates to @code{localtime} and @code{__time64} is a macro which +evaluates to @code{time_t}, so the first definition above amounts to +the original definition of @code{localtime}; and since @code{__TIMESIZE} +equals 64, the second definition is removed by the preprocessor. + +For 32-bit architectures, the first definition creates the new function +@code{__localtime64} which uses Y2038-proof types, and since +@code{__TIMESIZE} is different from 64, the second definition provides +@code{localtime} as a wrapper around @code{__localtime64}. + @node Porting @appendixsec Porting @theglibc{} diff --git a/time/localtime.c b/time/localtime.c index 92dbfe0f8c..50e0be2272 100644 --- a/time/localtime.c +++ b/time/localtime.c @@ -21,7 +21,6 @@ /* The C Standard says that localtime and gmtime return the same pointer. */ struct tm _tmbuf; - /* Return the `struct tm' representation of *T in local time, using *TP to store the result. */ struct tm * @@ -31,11 +30,24 @@ __localtime_r (const time_t *t, struct tm *tp) } weak_alias (__localtime_r, localtime_r) - /* Return the `struct tm' representation of *T in local time. */ struct tm * -localtime (const time_t *t) +__localtime64 (const __time64_t *t) { return __tz_convert (*t, 1, &_tmbuf); } +libc_hidden_def (__localtime64) + +/* Provide a 32-bit variant if needed */ + +#if __TIMESIZE != 64 + +struct tm * +localtime (const time_t *t) +{ + __time64_t t64 = *t; + return __localtime64 (&t64); +} libc_hidden_def (localtime) + +#endif