From patchwork Tue Oct  1 12:15:11 2024
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
X-Patchwork-Submitter: Florian Weimer <fweimer@redhat.com>
X-Patchwork-Id: 1991449
Return-Path: <libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org>
X-Original-To: incoming@patchwork.ozlabs.org
Delivered-To: patchwork-incoming@legolas.ozlabs.org
Authentication-Results: legolas.ozlabs.org;
	dkim=pass (1024-bit key;
 unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256
 header.s=mimecast20190719 header.b=Im6FNyF8;
	dkim-atps=neutral
Authentication-Results: legolas.ozlabs.org;
 spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org
 (client-ip=2620:52:3:1:0:246e:9693:128c; helo=server2.sourceware.org;
 envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;
 receiver=patchwork.ozlabs.org)
Received: from server2.sourceware.org (server2.sourceware.org
 [IPv6:2620:52:3:1:0:246e:9693:128c])
	(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
	 key-exchange X25519 server-signature ECDSA (secp384r1) server-digest SHA384)
	(No client certificate requested)
	by legolas.ozlabs.org (Postfix) with ESMTPS id 4XHxkx2lNHz1xtY
	for <incoming@patchwork.ozlabs.org>; Tue,  1 Oct 2024 22:16:57 +1000 (AEST)
Received: from server2.sourceware.org (localhost [IPv6:::1])
	by sourceware.org (Postfix) with ESMTP id 28655386D626
	for <incoming@patchwork.ozlabs.org>; Tue,  1 Oct 2024 12:16:55 +0000 (GMT)
X-Original-To: libc-alpha@sourceware.org
Delivered-To: libc-alpha@sourceware.org
Received: from us-smtp-delivery-124.mimecast.com
 (us-smtp-delivery-124.mimecast.com [170.10.133.124])
 by sourceware.org (Postfix) with ESMTP id D0084386D600
 for <libc-alpha@sourceware.org>; Tue,  1 Oct 2024 12:15:17 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org D0084386D600
Authentication-Results: sourceware.org;
 dmarc=pass (p=none dis=none) header.from=redhat.com
Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com
ARC-Filter: OpenARC Filter v1.0.0 sourceware.org D0084386D600
Authentication-Results: server2.sourceware.org;
 arc=none smtp.remote-ip=170.10.133.124
ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1727784921; cv=none;
 b=Z3/t1KRx6V9dFJfaoFka/a3Yd4/MT5o9zYBsO+8yJJod+HDDxrRoFeUr58Tga2v2AGThi+mfIMCvBQuGsUP4VLhagevJVJo12qavqfGpJqKWXyzlSLP65Ah0Bf98+v/C9yipj+nruktFtqiEoIXxMF7kumYp1qNL6RHqory1aXg=
ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key;
 t=1727784921; c=relaxed/simple;
 bh=6/spxjblpTA7VSuxy1n2UbYR4JpjZFNe/0XAqjR3uRg=;
 h=DKIM-Signature:From:To:Subject:Message-ID:Date:MIME-Version;
 b=cmz7mgyso54y+6iYfKX+tmOA5D+cLSIRCqvuk/xANnBjON+tA3LN7p9UIy+Uq9SAmXsu0VeKOqzfRoaRV2xERcY9JbkpXkRG+kYYjLSu83fBLMw1eU2K2ObbtNYz/KGR3MpG6j5ahVTVnZ8l5anCduVQX1j5k6plmgm9zLZ6q+Q=
ARC-Authentication-Results: i=1; server2.sourceware.org
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
 s=mimecast20190719; t=1727784917;
 h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
 to:to:cc:mime-version:mime-version:content-type:content-type:
 in-reply-to:in-reply-to:references:references;
 bh=m4KjOQYzUegdv8iQVSs4eNw4ehmznF5atY4DiTEmoo8=;
 b=Im6FNyF85Adv1cPZlYjzH5ZdbrwqxOzlzsbniIhM/4bdl5TFuapxZKwMSkLAEHb6RN+Nba
 7WpNcohu962ZNz+2Aqb98EPDOTbXVGJ3ELRT3kUhyzAc45AM+A2QZphDXAi+x1otKgtPlY
 lttbou/v/eAXmeKE4Og3RXNfcEPgeoQ=
Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com
 (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by
 relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,
 cipher=TLS_AES_256_GCM_SHA384) id us-mta-606-QPAlzWCjPpqEGCDIfX4Flg-1; Tue,
 01 Oct 2024 08:15:15 -0400
X-MC-Unique: QPAlzWCjPpqEGCDIfX4Flg-1
Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (unknown
 [10.30.177.40])
 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
 key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest
 SHA256)
 (No client certificate requested)
 by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS
 id 1CA3C1943CCC
 for <libc-alpha@sourceware.org>; Tue,  1 Oct 2024 12:15:15 +0000 (UTC)
Received: from oldenburg.str.redhat.com (unknown [10.45.224.151])
 by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with
 ESMTPS
 id 3A7321944B2B
 for <libc-alpha@sourceware.org>; Tue,  1 Oct 2024 12:15:13 +0000 (UTC)
From: Florian Weimer <fweimer@redhat.com>
To: libc-alpha@sourceware.org
Subject: [PATCH 4/4] time: Implement the glibc.time.mktime_dst_adjustment
 tunable
In-Reply-To: <cover.1727784647.git.fweimer@redhat.com>
Message-ID: 
 <4b54ff2cd98520b5e1bf31da5b3ec0a2713ad3b3.1727784647.git.fweimer@redhat.com>
References: <cover.1727784647.git.fweimer@redhat.com>
X-From-Line: 4b54ff2cd98520b5e1bf31da5b3ec0a2713ad3b3 Mon Sep 17 00:00:00 2001
Date: Tue, 01 Oct 2024 14:15:11 +0200
User-Agent: Gnus/5.13 (Gnus v5.13)
MIME-Version: 1.0
X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40
X-Mimecast-Spam-Score: 0
X-Mimecast-Originator: redhat.com
X-Spam-Status: No, score=-10.8 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH,
 DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0,
 KAM_SHORT,
 RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,
 SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
 server2.sourceware.org
X-BeenThere: libc-alpha@sourceware.org
X-Mailman-Version: 2.1.30
Precedence: list
List-Id: Libc-alpha mailing list <libc-alpha.sourceware.org>
List-Unsubscribe: <https://sourceware.org/mailman/options/libc-alpha>,
 <mailto:libc-alpha-request@sourceware.org?subject=unsubscribe>
List-Archive: <https://sourceware.org/pipermail/libc-alpha/>
List-Post: <mailto:libc-alpha@sourceware.org>
List-Help: <mailto:libc-alpha-request@sourceware.org?subject=help>
List-Subscribe: <https://sourceware.org/mailman/listinfo/libc-alpha>,
 <mailto:libc-alpha-request@sourceware.org?subject=subscribe>
Errors-To: libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org

It helps with upgrades from older glibc versions (prior to 2.29)
which performed DST adjustments in fewer cases.
---
 elf/dl-tunables.list           |   9 ++
 elf/libc_early_init.c          |   3 +
 manual/time.texi               |   3 +-
 manual/tunables.texi           |  12 +++
 time/Makefile                  |   7 +-
 time/mktime.c                  |   8 +-
 time/time-tunables.c           |  29 +++++++
 time/tst-mktime-dst-adjust-0.c | 154 +++++++++++++++++++++++++++++++++
 time/tst-mktime-dst-adjust-1.c |   2 +
 time/tzset.h                   |   6 ++
 10 files changed, 228 insertions(+), 5 deletions(-)
 create mode 100644 time/time-tunables.c
 create mode 100644 time/tst-mktime-dst-adjust-0.c
 create mode 100644 time/tst-mktime-dst-adjust-1.c

diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index 40ac5b3776..af3eb4a37c 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -84,6 +84,15 @@ glibc {
     }
   }
 
+  time {
+    mktime_dst_adjustment {
+      type: INT_32
+      minval: 0
+      maxval: 1
+      default: 1
+    }
+  }
+
   elision {
     enable {
       type: INT_32
diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
index 575b837f8f..f99f12b6c8 100644
--- a/elf/libc_early_init.c
+++ b/elf/libc_early_init.c
@@ -23,6 +23,7 @@
 #include <lowlevellock.h>
 #include <pthread_early_init.h>
 #include <sys/single_threaded.h>
+#include <time/tzset.h>
 
 #ifdef SHARED
 _Bool __libc_initial;
@@ -46,4 +47,6 @@ __libc_early_init (_Bool initial)
 #if ENABLE_ELISION_SUPPORT
   __lll_elision_init ();
 #endif
+
+  __time_tunable_init ();
 }
diff --git a/manual/time.texi b/manual/time.texi
index c72febc7c6..0a158e742f 100644
--- a/manual/time.texi
+++ b/manual/time.texi
@@ -1324,7 +1324,8 @@ positive.  This forced adjustment only happens if time zone data
 indicates that there is at least one daylight saving transition (at any
 time).  For zones such as @samp{UTC} which never use daylight saving
 time, the adjustment does not happen even if @code{tm_isdst} is
-positive.
+positive.  The @code{glibc.time.mktime_dst_adjustment} tunable
+can be used to disable the adjustment heuristic.  @xref{Time Tunables}.
 
 The @code{mktime} function ignores the specified contents of the
 @code{tm_wday}, @code{tm_yday}, @code{tm_gmtoff}, and @code{tm_zone}
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 0b1b2898c0..e9e6759bf6 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -76,6 +76,7 @@ glibc.malloc.check: 0 (min: 0, max: 3)
 @menu
 * Tunable names::  The structure of a tunable name
 * Memory Allocation Tunables::  Tunables in the memory allocation subsystem
+* Time Tunables::  Tunables related to time and time zone processing.
 * Dynamic Linking Tunables:: Tunables in the dynamic linking subsystem
 * Elision Tunables::  Tunables in elision subsystem
 * POSIX Thread Tunables:: Tunables in the POSIX thread subsystem
@@ -294,6 +295,17 @@ supported ones.  If provided value is invalid, @code{MAP_HUGETLB} will not
 be used.
 @end deftp
 
+@node Time Tunables
+@section Time Tunables
+@cindex time tunables
+
+@deftp Tunable glibc.time.mktime_dst_adjustment
+If this tunable is @code{1}, the @code{mktime} function uses a heuristic
+if the the @code{tm_isdst} input value disagrees with available time
+zone data.  If the tunable is @code{0}, this heuristic is disabled.
+@xref{Broken-down Time}.
+@end deftp
+
 @node Dynamic Linking Tunables
 @section Dynamic Linking Tunables
 @cindex dynamic linking tunables
diff --git a/time/Makefile b/time/Makefile
index 0cfc4c9d51..ef7922cf35 100644
--- a/time/Makefile
+++ b/time/Makefile
@@ -30,7 +30,7 @@ headers := time.h sys/time.h sys/timeb.h bits/time.h			\
 	   bits/types/time_t.h bits/types/struct_timeb.h
 
 routines := offtime asctime clock ctime ctime_r difftime \
-	    gmtime localtime mktime time		 \
+	    gmtime localtime mktime time time-tunables	 \
 	    gettimeofday settimeofday settimezone	 \
 	    adjtime tzset tzfile getitimer setitimer	 \
 	    stime dysize timegm ftime			 \
@@ -65,6 +65,8 @@ tests := \
   tst-itimer \
   tst-mktime \
   tst-mktime-dst-adjust \
+  tst-mktime-dst-adjust-0 \
+  tst-mktime-dst-adjust-1 \
   tst-mktime2 \
   tst-mktime3 \
   tst-mktime4 \
@@ -147,3 +149,6 @@ CPPFLAGS-tst-tzname.c += -DTZDEFRULES='"$(posixrules-file)"'
 bug-getdate1-ARGS = ${objpfx}bug-getdate1-fmt
 
 tst-tzfile-fault-ENV = GLIBC_TUNABLES=glibc.rtld.enable_secure=1
+
+tst-mktime-dst-adjust-0-ENV = GLIBC_TUNABLES=glibc.time.mktime_dst_adjustment=0
+tst-mktime-dst-adjust-1-ENV = GLIBC_TUNABLES=glibc.time.mktime_dst_adjustment=1
diff --git a/time/mktime.c b/time/mktime.c
index ad371ba57f..0c9ef13ec3 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -435,9 +435,11 @@ __mktime_internal (struct tm *tp, bool local, mktime_offset_t *offset)
      value, if any.  */
   if (isdst_differ (isdst, tm.tm_isdst)
 #if _LIBC
-      /* Only perform the adjustment if the time zone ever uses DST.
-         This skips the adjustment for UTC, for example.  */
-      && __daylight
+      /* The glibc.time.mktime_dst_adjustment tunable disable all such
+         adjustments.  Otherwise, only perform the adjustment if the
+         time zone ever uses DST.  This skips the adjustment for UTC,
+         for example.  */
+      && __mktime_dst_adjustment && __daylight
 #endif
       )
     {
diff --git a/time/time-tunables.c b/time/time-tunables.c
new file mode 100644
index 0000000000..78d28f38e0
--- /dev/null
+++ b/time/time-tunables.c
@@ -0,0 +1,29 @@
+/* Tunables for time-related functions.
+   Copyright 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Paul Eggert <eggert@cs.ucla.edu>.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#define TUNABLE_NAMESPACE time
+#include <elf/dl-tunables.h>
+
+bool __mktime_dst_adjustment;
+
+void
+__time_tunable_init (void)
+{
+  __mktime_dst_adjustment = TUNABLE_GET (mktime_dst_adjustment, int32_t, NULL);
+}
diff --git a/time/tst-mktime-dst-adjust-0.c b/time/tst-mktime-dst-adjust-0.c
new file mode 100644
index 0000000000..386e69429f
--- /dev/null
+++ b/time/tst-mktime-dst-adjust-0.c
@@ -0,0 +1,154 @@
+/* Test lack of mktime DST adjustment with the adjustment heuristic disabled.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+#include <stdlib.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  TEST_COMPARE (setenv ("TZ", "UTC", 1), 0);
+
+  {
+    struct tm t =
+      {
+        .tm_year = 124,
+        .tm_mon = 9,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 1,            /* Not actually true.  */
+      };
+    TEST_COMPARE (mktime (&t), 1727774453);
+  }
+
+  /* IST used DST at one point, but no longer does.  */
+  {
+    char *path = realpath ("../timezone/testdata/IST", NULL);
+    TEST_VERIFY (path != NULL);
+    TEST_COMPARE (setenv ("TZ", path, 1), 0);
+    free (path);
+  }
+
+  {
+    struct tm t =
+      {
+        .tm_year = 124,
+        .tm_mon = 9,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 0,          /* Correct value.  */
+      };
+    TEST_COMPARE (mktime (&t), 1727774453 - (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_gmtoff, (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 0);
+  }
+
+  /* No adjustment for historic incorrect value.  */
+  {
+    struct tm t =
+      {
+        .tm_year = 124,
+        .tm_mon = 9,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 1,          /* Incorrect value.  */
+      };
+    TEST_COMPARE (mktime (&t), 1727774453 - (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_gmtoff, (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 0);
+  }
+
+  /* No adjustment for correct DST.  */
+  {
+    struct tm t =
+      {
+        .tm_year = 42,
+        .tm_mon = 9,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 1,          /* Correct value, DST was in effect.  */
+      };
+    TEST_COMPARE (mktime (&t), -860015347);
+    TEST_COMPARE (t.tm_gmtoff, (int) (6.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 1);
+  }
+
+  /* No adjustment for mismatch: DST incorrectly claimed not in effect.  */
+  {
+    struct tm t =
+      {
+        .tm_year = 42,
+        .tm_mon = 9,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 0,          /* Incorrect value.  */
+      };
+    TEST_COMPARE (mktime (&t), -860015347);
+    TEST_COMPARE (t.tm_gmtoff, (int) (6.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 1);
+  }
+
+  /* Test using correct standard time.  */
+  {
+    struct tm t =
+      {
+        .tm_year = 42,
+        .tm_mon = 7,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 0,          /* Correct value, standard time in effect.  */
+      };
+    TEST_COMPARE (mktime (&t), -865282147);
+    TEST_COMPARE (t.tm_gmtoff, (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 0);
+  }
+
+  /* No adjustment: Test using standard time with mismatch.  */
+  {
+    struct tm t =
+      {
+        .tm_year = 42,
+        .tm_mon = 7,
+        .tm_mday = 1,
+        .tm_hour = 9,
+        .tm_min = 20,
+        .tm_sec = 53,
+        .tm_isdst = 1,          /* Incorrect value.  */
+      };
+    TEST_COMPARE (mktime (&t), -865282147);
+    TEST_COMPARE (t.tm_gmtoff, (int) (5.5 * 3600));
+    TEST_COMPARE (t.tm_isdst, 0);
+  }
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/time/tst-mktime-dst-adjust-1.c b/time/tst-mktime-dst-adjust-1.c
new file mode 100644
index 0000000000..137d1e7411
--- /dev/null
+++ b/time/tst-mktime-dst-adjust-1.c
@@ -0,0 +1,2 @@
+/* Test with GLIBC_TUNABLES=glibc.time.mktime_dst_adjust=1 (default).  */
+#include "tst-mktime-dst-adjust.c"
diff --git a/time/tzset.h b/time/tzset.h
index 254540aa05..3999c71de6 100644
--- a/time/tzset.h
+++ b/time/tzset.h
@@ -31,4 +31,10 @@ extern void __tzset_unlocked (void) attribute_hidden;
 extern struct tm *__tz_convert (__time64_t timer, int use_localtime,
                                 struct tm *tp) attribute_hidden;
 
+/* True if mktime uses the DST adjustment heuristic based on tm_isdst.  */
+extern bool __mktime_dst_adjustment attribute_hidden;
+
+/* Initializes tunables.  Called from __libc_early_init.  */
+void __time_tunable_init (void) attribute_hidden;
+
 #endif /* _TZSET_H */