{"id":2222415,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2222415/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/a08fa4509d28c856eb6063edf8285c00797b415b.1775912642.git.alvaro.begue@gmail.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"","date":"2026-04-11T13:33:05","name":"[1/5] libstdc++: Fix numeric save offset on Zone lines [PR 124851]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"b87c0c92e56aea963b56af6588098a7625c8a618","submitter":{"id":93119,"url":"http://patchwork.ozlabs.org/api/1.1/people/93119/?format=json","name":"Alvaro Begue","email":"alvaro.begue@gmail.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/a08fa4509d28c856eb6063edf8285c00797b415b.1775912642.git.alvaro.begue@gmail.com/mbox/","series":[{"id":499557,"url":"http://patchwork.ozlabs.org/api/1.1/series/499557/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499557","date":"2026-04-11T13:33:04","name":"libstdc++: chrono tzdb correctness fixes","version":1,"mbox":"http://patchwork.ozlabs.org/series/499557/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2222415/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2222415/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=BVwuaKT9;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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ZoneInfo::to() then returned that as\nsys_info::offset, dropping the numeric save and reporting a total\noffset that was wrong by the save amount.\n\nThis was inconsistent with the two ZoneInfo constructors that take a\nsys_info, which previously stored the *total* offset (stdoff + save) in\nm_offset. As a result m_offset's semantics depended on which code path\ncreated the ZoneInfo, and only the parser path's lines with non-zero\nnumeric save were observably broken.\n\nFix by giving m_offset a single semantics: always the standard offset\nonly. The two sys_info-taking constructors now subtract the save before\nstoring, and to() adds it back when reconstructing the sys_info.\n\nThe remaining .offset() callers inside _M_get_sys_info already expect\nthe standard offset (they are computing rule firing times, where the\nsave component is added separately from the active rule's save value),\nso no other call sites need adjustment.\n\nlibstdc++-v3/ChangeLog:\n\n\tPR libstdc++/124851\n\t* src/c++20/tzdb.cc (ZoneInfo::ZoneInfo(sys_info&&)): Store\n\tstdoff only in m_offset (subtract info.save).\n\t(ZoneInfo::ZoneInfo(const pair&)):\n\tLikewise.\n\t(ZoneInfo::offset()): Document new semantics.\n\t(ZoneInfo::to(sys_info&)): Add m_save back to offset() when\n\tpopulating sys_info::offset.\n\t* testsuite/std/time/time_zone/numeric_save.cc: New test.\n---\n libstdc++-v3/src/c++20/tzdb.cc | 13 ++--\n .../std/time/time_zone/numeric_save.cc | 66 +++++++++++++++++++\n 2 files changed, 75 insertions(+), 4 deletions(-)\n create mode 100644 libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc","diff":"diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc\nindex eb6ac7d07..33217f0a9 100644\n--- a/libstdc++-v3/src/c++20/tzdb.cc\n+++ b/libstdc++-v3/src/c++20/tzdb.cc\n@@ -478,11 +478,12 @@ namespace std::chrono\n \n ZoneInfo(sys_info&& info)\n : m_buf(std::move(info.abbrev)), m_expanded(true), m_save(info.save),\n-\tm_offset(info.offset), m_until(info.end)\n+\tm_offset(info.offset - seconds(info.save)), m_until(info.end)\n { }\n \n ZoneInfo(const pair& info)\n- : m_expanded(true), m_save(info.first.save), m_offset(info.first.offset),\n+ : m_expanded(true), m_save(info.first.save),\n+\tm_offset(info.first.offset - seconds(info.first.save)),\n \tm_until(info.first.end)\n {\n \tif (info.second.size())\n@@ -494,7 +495,9 @@ namespace std::chrono\n \tm_buf += info.first.abbrev;\n }\n \n- // STDOFF: Seconds from UTC during standard time.\n+ // STDOFF: Seconds from UTC during standard time. Always the\n+ // standard offset only; the saved value (if any) is in m_save and\n+ // is added back when reconstructing a sys_info via to().\n seconds\n offset() const noexcept { return m_offset; }\n \n@@ -539,7 +542,9 @@ namespace std::chrono\n \t return false;\n \n \tinfo.end = until();\n-\tinfo.offset = offset();\n+\t// m_offset is the standard offset only; add the saved value to\n+\t// reconstruct the total offset. See ZoneInfo's m_offset comment.\n+\tinfo.offset = offset() + seconds(m_save);\n \tinfo.save = minutes(m_save);\n \tinfo.abbrev = format();\n \tformat_abbrev_str(info); // expand %z\ndiff --git a/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc b/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc\nnew file mode 100644\nindex 000000000..d7b78f215\n--- /dev/null\n+++ b/libstdc++-v3/testsuite/std/time/time_zone/numeric_save.cc\n@@ -0,0 +1,66 @@\n+// { dg-do run { target c++20 } }\n+// { dg-require-effective-target tzdb }\n+// { dg-require-effective-target cxx11_abi }\n+// { dg-xfail-run-if \"no weak override on AIX\" { powerpc-ibm-aix* } }\n+\n+// Regression test: when a Zone line specifies a numeric value as its\n+// RULES field, that value is the constant DST save value for that zone\n+// line. ZoneInfo::to() previously set sys_info::offset to the zone\n+// line's STDOFF only, ignoring the parsed save. Per [time.zone.info.sys]\n+// sys_info::offset is the *total* UTC offset (stdoff + save), so any\n+// zone line with a non-zero numeric save reported the wrong offset.\n+//\n+// Mirrors Africa/Gaborone's tzdata, which uses\n+// 2 - CAT 1943 S 19 2\n+// 2 1 CAST 1944 Mar 19 2 <-- numeric \"1\" RULES, save = +1h\n+// 2 - CAT\n+// The middle line is what triggers the bug.\n+\n+#include \n+#include \n+#include \n+\n+static bool override_used = false;\n+\n+namespace __gnu_cxx\n+{\n+ const char* zoneinfo_dir_override() {\n+ override_used = true;\n+ return \"./\";\n+ }\n+}\n+\n+int\n+main()\n+{\n+ using namespace std::chrono;\n+\n+ std::ofstream(\"tzdata.zi\") << R\"(# version test_numeric_save\n+Z Test/Gaborone 2 - CAT 1943 Sep 19 2\n+ 2 1 CAST 1944 Mar 19 2\n+ 2 - CAT\n+)\";\n+\n+ const auto& db = reload_tzdb();\n+ VERIFY( override_used );\n+ VERIFY( db.version == \"test_numeric_save\" );\n+\n+ auto* tz = locate_zone(\"Test/Gaborone\");\n+\n+ // Sample well inside the CAST (numeric-save) zone line.\n+ auto info = tz->get_info(sys_days(1943y/December/15));\n+ VERIFY( info.offset == 3h ); // stdoff +2h + save +1h\n+ VERIFY( info.save == 60min );\n+ VERIFY( info.abbrev == \"CAST\" );\n+\n+ // Bordering zone lines should report the standard offset with save 0.\n+ auto before = tz->get_info(sys_days(1943y/September/1));\n+ VERIFY( before.offset == 2h );\n+ VERIFY( before.save == 0min );\n+ VERIFY( before.abbrev == \"CAT\" );\n+\n+ auto after = tz->get_info(sys_days(1944y/April/15));\n+ VERIFY( after.offset == 2h );\n+ VERIFY( after.save == 0min );\n+ VERIFY( after.abbrev == \"CAT\" );\n+}\n","prefixes":["1/5"]}