Set the TZ env to get the UTC-ms since epoch.

runtime/vm/os_linux.cc

Index: runtime/vm/os_linux.cc
diff --git a/runtime/vm/os_linux.cc b/runtime/vm/os_linux.cc
index 52bdaf7b538f92e3abf87cdd86acc0d4a8f692ca..84080e4a9ddc31d89bc53d217cf304aafe03e8cb 100644
--- a/runtime/vm/os_linux.cc
+++ b/runtime/vm/os_linux.cc
@@ -25,8 +25,6 @@ bool OS::BreakDownSecondsSinceEpoch(time_t seconds_since_epoch,
   if (in_utc) {
     error_code = gmtime_r(&seconds_since_epoch, &tm_result);
   } else {
-    // TODO(floitsch): we should be able to call tzset only once during
-    // initialization.
     tzset();  // Make sure the libc knows about the local zone.
     error_code = localtime_r(&seconds_since_epoch, &tm_result);
   }
@@ -40,6 +38,15 @@ bool OS::BreakDownSecondsSinceEpoch(time_t seconds_since_epoch,
 }
 
 
+// TODO(floitsch): cache utc offset. Maybe look at V8's caching mechanism.
+static int UtcOffsetInSeconds(time_t seconds_since_epoch) {

[cshapiro, 2012/04/19 23:52:12]

This seems unnecessary, see below.

+  struct tm t;
+  struct tm* error_code = localtime_r(&seconds_since_epoch, &t);
+  ASSERT(error_code != NULL);
+  return t.tm_gmtoff;
+}
+
+
 bool OS::BrokenDownToSecondsSinceEpoch(
     const BrokenDownDate& broken_down, bool in_utc, time_t* result) {
   struct tm tm_broken_down;
@@ -53,27 +60,18 @@ bool OS::BrokenDownToSecondsSinceEpoch(
   // Set wday to an impossible day, so that we can catch bad input.
   tm_broken_down.tm_wday = -1;
   // Make sure the libc knows about the local zone.
-  // In case of 'in_utc' this call is mainly for multi-threading issues. If
-  // another thread uses a time-function it will set the timezone. The timezone
-  // adjustement below would then not work anymore.
   // TODO(floitsch): we should be able to call tzset only once during
   // initialization.
   tzset();
-  if (in_utc) {
-    // Disable daylight saving in utc mode.
-    tm_broken_down.tm_isdst = 0;
-    // mktime assumes that the given date is local time zone.
-    *result = mktime(&tm_broken_down);
-    // Remove the timezone.
-    *result -= timezone;
-  } else {
-    // Let libc figure out if daylight saving is active.
-    tm_broken_down.tm_isdst = -1;
-    *result = mktime(&tm_broken_down);
-  }
+  // Let libc figure out if daylight saving is active.
+  tm_broken_down.tm_isdst = -1;
+  *result = mktime(&tm_broken_down);
   if ((*result == -1) && (tm_broken_down.tm_wday == -1)) {
     return false;
   }
+  if (in_utc) {
+    *result += UtcOffsetInSeconds(*result);

[cshapiro, 2012/04/19 23:52:12]

See comment in os_macos.cc.

+  }
   return true;
 }