diff --git a/libcxx/test/localization/locale.categories/category.collate/locale.collate.byname/compare.pass.cpp b/libcxx/test/localization/locale.categories/category.collate/locale.collate.byname/compare.pass.cpp
index d64412521b7db..69af9ac1b7bf0 100644
--- a/libcxx/test/localization/locale.categories/category.collate/locale.collate.byname/compare.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.collate/locale.collate.byname/compare.pass.cpp
@@ -18,6 +18,11 @@
 //     has any difference from "C" collation.  But I do believe I'm picking
 //     up the OS's collation files.
 
+// TODO investigation needed.
+// Glibc seems to collate files differently from the way Apple's C library does
+// it.
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <string>
 #include <cassert>
diff --git a/libcxx/test/localization/locale.categories/category.monetary/locale.money.get/locale.money.get.members/get_long_double_zh_CN.pass.cpp b/libcxx/test/localization/locale.categories/category.monetary/locale.money.get/locale.money.get.members/get_long_double_zh_CN.pass.cpp
index 374443a2a9e68..07a33f7663b6d 100644
--- a/libcxx/test/localization/locale.categories/category.monetary/locale.money.get/locale.money.get.members/get_long_double_zh_CN.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.monetary/locale.money.get/locale.money.get.members/get_long_double_zh_CN.pass.cpp
@@ -16,6 +16,9 @@
 // iter_type get(iter_type b, iter_type e, bool intl, ios_base& iob,
 //               ios_base::iostate& err, long double& v) const;
 
+// TODO For zh_CN GLIBC puts the negative sign after the currency symbol.
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <ios>
 #include <streambuf>
diff --git a/libcxx/test/localization/locale.categories/category.monetary/locale.money.put/locale.money.put.members/put_long_double_zh_CN.pass.cpp b/libcxx/test/localization/locale.categories/category.monetary/locale.money.put/locale.money.put.members/put_long_double_zh_CN.pass.cpp
index 242701e26d765..633e1885e711d 100644
--- a/libcxx/test/localization/locale.categories/category.monetary/locale.money.put/locale.money.put.members/put_long_double_zh_CN.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.monetary/locale.money.put/locale.money.put.members/put_long_double_zh_CN.pass.cpp
@@ -16,6 +16,9 @@
 // iter_type put(iter_type s, bool intl, ios_base& f, char_type fill,
 //               long double units) const;
 
+// TODO For zh_CN GLIBC puts the negative sign after the currency symbol.
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <ios>
 #include <streambuf>
diff --git a/libcxx/test/localization/locale.categories/category.monetary/locale.moneypunct.byname/thousands_sep.pass.cpp b/libcxx/test/localization/locale.categories/category.monetary/locale.moneypunct.byname/thousands_sep.pass.cpp
index b7e16c6af8eca..a8782832de5cb 100644
--- a/libcxx/test/localization/locale.categories/category.monetary/locale.moneypunct.byname/thousands_sep.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.monetary/locale.moneypunct.byname/thousands_sep.pass.cpp
@@ -18,6 +18,12 @@
 
 // charT thousands_sep() const;
 
+// Failure related to GLIBC's use of U00A0 as mon_thousands_sep
+// and U002E as mon_decimal_point.
+// TODO: U00A0 should be investigated.
+// Possibly related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=16006
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <limits>
 #include <cassert>
diff --git a/libcxx/test/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp b/libcxx/test/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
index 2010dca4c61af..935961257ef2d 100644
--- a/libcxx/test/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp
@@ -13,6 +13,9 @@
 
 // iter_type put(iter_type s, ios_base& iob, char_type fill, long double v) const;
 
+// TODO GLIBC uses a different string for positive and negative NAN numbers.
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <ios>
 #include <cassert>
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one.pass.cpp
index 536859e933bcf..72b63278d71d2 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one.pass.cpp
@@ -19,6 +19,9 @@
 // iter_type get(iter_type s, iter_type end, ios_base& f,
 //               ios_base::iostate& err, tm *t, char format, char modifier = 0) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one_wide.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one_wide.pass.cpp
index 36c8a8e54ce0e..ae8bce22445af 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one_wide.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_one_wide.pass.cpp
@@ -19,6 +19,9 @@
 // iter_type get(iter_type s, iter_type end, ios_base& f,
 //               ios_base::iostate& err, tm *t, char format, char modifier = 0) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday.pass.cpp
index db070be90aba1..09055add75a91 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday.pass.cpp
@@ -20,6 +20,9 @@
 // get_weekday(iter_type s, iter_type end, ios_base& str,
 //             ios_base::iostate& err, tm* t) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday_wide.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday_wide.pass.cpp
index ac607bacce2db..31135a3494356 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday_wide.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.get.byname/get_weekday_wide.pass.cpp
@@ -20,6 +20,9 @@
 // get_weekday(iter_type s, iter_type end, ios_base& str,
 //             ios_base::iostate& err, tm* t) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.put.byname/put1.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.put.byname/put1.pass.cpp
index ff3bb823a3079..3e7538d6625b1 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.put.byname/put1.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.put.byname/put1.pass.cpp
@@ -24,6 +24,9 @@
 //     ~time_put_byname();
 // };
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/category.time/locale.time.put/locale.time.put.members/put2.pass.cpp b/libcxx/test/localization/locale.categories/category.time/locale.time.put/locale.time.put.members/put2.pass.cpp
index 577655f726383..427d7c5515fac 100644
--- a/libcxx/test/localization/locale.categories/category.time/locale.time.put/locale.time.put.members/put2.pass.cpp
+++ b/libcxx/test/localization/locale.categories/category.time/locale.time.put/locale.time.put.members/put2.pass.cpp
@@ -14,6 +14,9 @@
 // iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t,
 //               char format, char modifier = 0) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 #include "test_iterators.h"
diff --git a/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/grouping.pass.cpp b/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/grouping.pass.cpp
index b49eca487fa79..d5112a9508b7c 100644
--- a/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/grouping.pass.cpp
+++ b/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/grouping.pass.cpp
@@ -16,6 +16,9 @@
 
 // string grouping() const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 
diff --git a/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/thousands_sep.pass.cpp b/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/thousands_sep.pass.cpp
index 80b440ac9305f..b1bd03ff73645 100644
--- a/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/thousands_sep.pass.cpp
+++ b/libcxx/test/localization/locale.categories/facet.numpunct/locale.numpunct.byname/thousands_sep.pass.cpp
@@ -16,6 +16,9 @@
 
 // char_type thousands_sep() const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <locale>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.match/basic.pass.cpp b/libcxx/test/re/re.alg/re.alg.match/basic.pass.cpp
index d63817d03e6e1..4139cea35f80a 100644
--- a/libcxx/test/re/re.alg/re.alg.match/basic.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.match/basic.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.match/ecma.pass.cpp b/libcxx/test/re/re.alg/re.alg.match/ecma.pass.cpp
index 67df410282a6c..38540560452da 100644
--- a/libcxx/test/re/re.alg/re.alg.match/ecma.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.match/ecma.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.match/extended.pass.cpp b/libcxx/test/re/re.alg/re.alg.match/extended.pass.cpp
index 733c16ec432a9..c54825de584ab 100644
--- a/libcxx/test/re/re.alg/re.alg.match/extended.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.match/extended.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.search/awk.pass.cpp b/libcxx/test/re/re.alg/re.alg.search/awk.pass.cpp
index 74c25c1a53d69..521e98b3a880a 100644
--- a/libcxx/test/re/re.alg/re.alg.search/awk.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.search/awk.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.search/basic.pass.cpp b/libcxx/test/re/re.alg/re.alg.search/basic.pass.cpp
index c8a5051d585c4..838294e984c74 100644
--- a/libcxx/test/re/re.alg/re.alg.search/basic.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.search/basic.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.search/ecma.pass.cpp b/libcxx/test/re/re.alg/re.alg.search/ecma.pass.cpp
index 965c29d6cf631..2796850fbd591 100644
--- a/libcxx/test/re/re.alg/re.alg.search/ecma.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.search/ecma.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.alg/re.alg.search/extended.pass.cpp b/libcxx/test/re/re.alg/re.alg.search/extended.pass.cpp
index c181cff4728db..a8a121bdd45b3 100644
--- a/libcxx/test/re/re.alg/re.alg.search/extended.pass.cpp
+++ b/libcxx/test/re/re.alg/re.alg.search/extended.pass.cpp
@@ -18,6 +18,9 @@
 //                  const basic_regex<charT, traits>& e,
 //                  regex_constants::match_flag_type flags = regex_constants::match_default);
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>
 
diff --git a/libcxx/test/re/re.traits/lookup_collatename.pass.cpp b/libcxx/test/re/re.traits/lookup_collatename.pass.cpp
index 049246ed1b1c4..d495f8aaf070e 100644
--- a/libcxx/test/re/re.traits/lookup_collatename.pass.cpp
+++ b/libcxx/test/re/re.traits/lookup_collatename.pass.cpp
@@ -17,6 +17,9 @@
 //   string_type
 //   lookup_collatename(ForwardIterator first, ForwardIterator last) const;
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <iterator>
 #include <cassert>
diff --git a/libcxx/test/re/re.traits/translate_nocase.pass.cpp b/libcxx/test/re/re.traits/translate_nocase.pass.cpp
index 5e042aead86c4..37d277450a751 100644
--- a/libcxx/test/re/re.traits/translate_nocase.pass.cpp
+++ b/libcxx/test/re/re.traits/translate_nocase.pass.cpp
@@ -17,6 +17,9 @@
 // XFAIL: with_system_lib=x86_64-apple-darwin11
 // XFAIL: with_system_lib=x86_64-apple-darwin12
 
+// TODO: investigation needed
+// XFAIL: linux-gnu
+
 #include <regex>
 #include <cassert>