commit 6099f062f5d0e79586149d9a8963525a59f89557
Author: Makoto Kato <m_kato@ga2.so-net.ne.jp>
Date:   Fri Nov 22 16:51:30 2019 +0900

    ICU-11992 uprv_tzname doesn't return valid time zone on Android

# ICU bug report:
# https://unicode-org.atlassian.net/browse/ICU-11992
#
# Pull request:
# https://github.com/unicode-org/icu/pull/605
#
# Commit:
# https://github.com/unicode-org/icu/commit/c9037ca8d3c0738f1a044dd845bdc0dc646f3e97.patch

diff --git a/intl/icu/source/common/putil.cpp b/intl/icu/source/common/putil.cpp
--- a/intl/icu/source/common/putil.cpp
+++ b/intl/icu/source/common/putil.cpp
@@ -116,15 +116,19 @@
 #   include <unistd.h>
 #   if U_PLATFORM == U_PF_SOLARIS
 #       ifndef _XPG4_2
 #           define _XPG4_2
 #       endif
+#   elif U_PLATFORM == U_PF_ANDROID
+#       include <sys/system_properties.h>
+#       include <dlfcn.h>
 #   endif
 #elif U_PLATFORM == U_PF_QNX
 #   include <sys/neutrino.h>
 #endif
 
+
 /*
  * Only include langinfo.h if we have a way to get the codeset. If we later
  * depend on more feature, we can test on U_HAVE_NL_LANGINFO.
  *
  */
@@ -1041,13 +1045,57 @@ static char* searchForTZFile(const char* path, DefaultTZInfo* tzInfo) {
     }
     return result;
 }
 #endif
 
+#if U_PLATFORM == U_PF_ANDROID
+typedef int(system_property_read_callback)(const prop_info* info,
+                                           void (*callback)(void* cookie,
+                                                            const char* name,
+                                                            const char* value,
+                                                            uint32_t serial),
+                                           void* cookie);
+typedef int(system_property_get)(const char*, char*);
+
+static char gAndroidTimeZone[PROP_VALUE_MAX] = { '\0' };
+
+static void u_property_read(void* cookie, const char* name, const char* value,
+                            uint32_t serial) {
+    uprv_strcpy((char* )cookie, value);
+}
+#endif
+
 U_CAPI void U_EXPORT2
 uprv_tzname_clear_cache()
 {
+#if U_PLATFORM == U_PF_ANDROID
+    /* Android's timezone is stored in system property. */
+    gAndroidTimeZone[0] = '\0';
+    void* libc = dlopen("libc.so", RTLD_NOLOAD);
+    if (libc) {
+        /* Android API 26+ has new API to get system property and old API
+         * (__system_property_get) is deprecated */
+        system_property_read_callback* property_read_callback =
+            (system_property_read_callback*)dlsym(
+                libc, "__system_property_read_callback");
+        if (property_read_callback) {
+            const prop_info* info =
+                __system_property_find("persist.sys.timezone");
+            if (info) {
+                property_read_callback(info, &u_property_read, gAndroidTimeZone);
+            }
+        } else {
+            system_property_get* property_get =
+                (system_property_get*)dlsym(libc, "__system_property_get");
+            if (property_get) {
+                property_get("persist.sys.timezone", gAndroidTimeZone);
+            }
+        }
+        dlclose(libc);
+    }
+#endif
+
 #if defined(CHECK_LOCALTIME_LINK) && !defined(DEBUG_SKIP_LOCALTIME_LINK)
     gTimeZoneBufferPtr = NULL;
 #endif
 }
 
@@ -1082,11 +1130,15 @@ uprv_tzname(int n)
     }
 #endif*/
 
 /* This code can be temporarily disabled to test tzname resolution later on. */
 #ifndef DEBUG_TZNAME
+#if U_PLATFORM == U_PF_ANDROID
+    tzid = gAndroidTimeZone;
+#else
     tzid = getenv("TZ");
+#endif
     if (tzid != NULL && isValidOlsonID(tzid)
 #if U_PLATFORM == U_PF_SOLARIS
     /* When TZ equals localtime on Solaris, check the /etc/localtime file. */
         && uprv_strcmp(tzid, TZ_ENV_CHECK) != 0
 #endif