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Thu, 23 Apr 2026 17:56:31 -0700 (PDT) MIME-Version: 1.0 From: Shamil Abdulaev Date: Fri, 24 Apr 2026 03:55:54 +0300 X-Gm-Features: AQROBzAhoOng6W0eoyCsqZlbDqozmdnbeYc6Hn1rl_GWDdeCuj78N9aED3Lc1bA Message-ID: Subject: [PATCH v2] manual: clarify _FILE_OFFSET_BITS Y2038 implications [BZ #34095] To: libc-alpha@sourceware.org Cc: Paul Eggert X-Spam-Status: No, score=-8.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, GB_FREEMAIL_NUM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces~patchwork=sourceware.org@sourceware.org Changes in v2: - Instead of removing the Y2038 note, clarify its relationship to _FILE_OFFSET_BITS - Explicitly document the transitive dependency: _TIME_BITS=64 requires _FILE_OFFSET_BITS=64 - Address feedback from Mark Harris that the existing wording causes confusion --- The existing paragraph warning about _FILE_OFFSET_BITS default changes due to Y2038 is correct but confusing, as it does not explicitly state why time_t concerns affect _FILE_OFFSET_BITS. Clarify that _TIME_BITS=64 (needed for Y2038 safety) requires _FILE_OFFSET_BITS=64, so when systems migrate to 64-bit time_t by default, _FILE_OFFSET_BITS will also need to default to 64, even for applications that do not handle large files. This addresses the confusion noted in the bug report while keeping the warning in place, as the transitive dependency makes it relevant to the _FILE_OFFSET_BITS documentation. Signed-off-by: Shamil Abdulaev --- manual/creature.texi | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) handling large files. On @w{64 bit} systems this macro has no effect -- 2.54.0 diff --git a/manual/creature.texi b/manual/creature.texi index 90f9f8e35b..1a2c5e8f9d 100644 --- a/manual/creature.texi +++ b/manual/creature.texi @@ -161,10 +161,13 @@ under different names (as they are with @code{_LARGEFILE64_SOURCE}). Instead the old function names now reference the new functions, e.g., a call to @code{fseeko} now indeed calls @code{fseeko64}. If the macro is not defined it currently defaults to @code{32}, but -this default is planned to change due to a need to update -@code{time_t} for Y2038 safety, and applications should not rely on -the default. +this default is planned to change in the future. This is because +@code{_TIME_BITS=64} (required for @code{time_t} Y2038 safety) can +only be used together with @code{_FILE_OFFSET_BITS=64}. When systems +migrate to 64-bit @code{time_t} by default, @code{_FILE_OFFSET_BITS} +will also need to default to @code{64}, even for applications that +do not handle large files. Applications should not rely on the +current default. This macro should only be selected if the system provides mechanisms for