Glibc 2.26 pulls in C-only builtins in <math.h> on some platforms.  This in turn
causes GCC to fail to override these in <cmath> when testing their existence.

This is an amalgamation of patches from a variety of upstream bug reports:

From <https://sourceware.org/bugzilla/show_bug.cgi?id=21930>:
https://sourceware.org/git/?p=glibc.git;a=commit;h=c2921b17a37e887b8a5ca9d84b875b9ba702b79c
https://sourceware.org/git/?p=glibc.git;a=commit;h=5e989c36934d0f0cf13b7a53ef2fa440bce39210
https://sourceware.org/git/?p=glibc.git;a=commit;h=ef8566d72af5e03c1b82cf02efb794268a347f8c
https://sourceware.org/git/?p=glibc.git;a=commit;h=35dded99a89db873b06270ca7f21245a0faf712a
https://sourceware.org/git/?p=glibc.git;a=commit;h=58270c0049404ef2f878fdd45df55f17f0b8c1f7

From <https://sourceware.org/bugzilla/show_bug.cgi?id=22235>:
https://sourceware.org/git/?p=glibc.git;a=commit;h=3b10c5d2abb0392d5ecfd865e2eb911ac109e36f
https://sourceware.org/git/?p=glibc.git;a=commit;h=dd3a7239fddff81ac31373d69978d7aa1902c65f

From <https://sourceware.org/bugzilla/show_bug.cgi?id=22146>:
https://sourceware.org/git/?p=glibc.git;a=commit;h=d37c951fde57e8acb320a9a7d437ba50a1fc3c8a

From <https://sourceware.org/bugzilla/show_bug.cgi?id=22296>:
https://sourceware.org/git/?p=glibc.git;a=commit;h=f8279a4b3cc66d3ec8bfb8519e9987b8f7727f53 

...with ChangeLog and NEWS entries removed.

From c2921b17a37e887b8a5ca9d84b875b9ba702b79c Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>
Date: Mon, 21 Aug 2017 14:23:27 +0200
Subject: [PATCH] Do not use __builtin_types_compatible_p in C++ mode (bug
 21930)
diff --git a/math/math.h b/math/math.h
index e217080..dea8dbe 100644
--- a/math/math.h
+++ b/math/math.h
@@ -442,8 +442,12 @@ enum
 
 /* Return nonzero value if X is positive or negative infinity.  */
 # if __HAVE_DISTINCT_FLOAT128 && !__GNUC_PREREQ (7,0) \
-     && !defined __SUPPORT_SNAN__
-   /* __builtin_isinf_sign is broken for float128 only before GCC 7.0.  */
+     && !defined __SUPPORT_SNAN__ && !defined __cplusplus
+   /* Since __builtin_isinf_sign is broken for float128 before GCC 7.0,
+      use the helper function, __isinff128, with older compilers.  This is
+      only provided for C mode, because in C++ mode, GCC has no support
+      for __builtin_types_compatible_p (and when in C++ mode, this macro is
+      not used anyway, because libstdc++ headers undefine it).  */
 #  define isinf(x) \
     (__builtin_types_compatible_p (__typeof (x), _Float128) \
      ? __isinff128 (x) : __builtin_isinf_sign (x))

From 5e989c36934d0f0cf13b7a53ef2fa440bce39210 Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>
Date: Mon, 14 Aug 2017 17:51:51 -0300
Subject: [PATCH] Do not use generic selection in C++ mode
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 06523bf..0c80821 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -464,17 +464,18 @@
 # define __glibc_macro_warning(msg)
 #endif
 
-/* Support for generic selection (ISO C11) is available in GCC since
-   version 4.9.  Previous versions do not provide generic selection,
-   even though they might set __STDC_VERSION__ to 201112L, when in
-   -std=c11 mode.  Thus, we must check for !defined __GNUC__ when
-   testing __STDC_VERSION__ for generic selection support.
+/* Generic selection (ISO C11) is a C-only feature, available in GCC
+   since version 4.9.  Previous versions do not provide generic
+   selection, even though they might set __STDC_VERSION__ to 201112L,
+   when in -std=c11 mode.  Thus, we must check for !defined __GNUC__
+   when testing __STDC_VERSION__ for generic selection support.
    On the other hand, Clang also defines __GNUC__, so a clang-specific
    check is required to enable the use of generic selection.  */
-#if __GNUC_PREREQ (4, 9) \
-    || __glibc_clang_has_extension (c_generic_selections) \
-    || (!defined __GNUC__ && defined __STDC_VERSION__ \
-	&& __STDC_VERSION__ >= 201112L)
+#if !defined __cplusplus \
+    && (__GNUC_PREREQ (4, 9) \
+	|| __glibc_clang_has_extension (c_generic_selections) \
+	|| (!defined __GNUC__ && defined __STDC_VERSION__ \
+	    && __STDC_VERSION__ >= 201112L))
 # define __HAVE_GENERIC_SELECTION 1
 #else
 # define __HAVE_GENERIC_SELECTION 0


From ef8566d72af5e03c1b82cf02efb794268a347f8c Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>
Date: Mon, 14 Aug 2017 13:46:15 -0300
Subject: [PATCH] Provide a C++ version of issignaling that does not use
 __MATH_TG

diff --git a/math/Makefile b/math/Makefile
index e09b0c0..0130fcf 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -203,7 +203,7 @@ tests-static = test-fpucw-static test-fpucw-ieee-static \
 	       test-signgam-ullong-static test-signgam-ullong-init-static
 
 ifneq (,$(CXX))
-tests += test-math-isinff test-math-iszero
+tests += test-math-isinff test-math-iszero test-math-issignaling
 endif
 
 ifneq (no,$(PERL))
@@ -350,6 +350,7 @@ CFLAGS-test-signgam-ullong-init-static.c = -std=c99
 
 CFLAGS-test-math-isinff.cc = -std=gnu++11
 CFLAGS-test-math-iszero.cc = -std=gnu++11
+CFLAGS-test-math-issignaling.cc = -std=gnu++11
 
 CFLAGS-test-iszero-excess-precision.c = -fexcess-precision=standard
 CFLAGS-test-iseqsig-excess-precision.c = -fexcess-precision=standard
diff --git a/math/math.h b/math/math.h
index dea8dbe..add86af 100644
--- a/math/math.h
+++ b/math/math.h
@@ -474,7 +474,24 @@ enum
 # include <bits/iscanonical.h>
 
 /* Return nonzero value if X is a signaling NaN.  */
-# define issignaling(x) __MATH_TG ((x), __issignaling, (x))
+# ifndef __cplusplus
+#  define issignaling(x) __MATH_TG ((x), __issignaling, (x))
+# else
+   /* In C++ mode, __MATH_TG cannot be used, because it relies on
+      __builtin_types_compatible_p, which is a C-only builtin.  On the
+      other hand, overloading provides the means to distinguish between
+      the floating-point types.  The overloading resolution will match
+      the correct parameter (regardless of type qualifiers (i.e.: const
+      and volatile).  */
+extern "C++" {
+inline int issignaling (float __val) { return __issignalingf (__val); }
+inline int issignaling (double __val) { return __issignaling (__val); }
+inline int issignaling (long double __val) { return __issignalingl (__val); }
+#  if __HAVE_DISTINCT_FLOAT128
+inline int issignaling (_Float128 __val) { return __issignalingf128 (__val); }
+#  endif
+} /* extern C++ */
+# endif
 
 /* Return nonzero value if X is subnormal.  */
 # define issubnormal(x) (fpclassify (x) == FP_SUBNORMAL)
diff --git a/math/test-math-issignaling.cc b/math/test-math-issignaling.cc
new file mode 100644
index 0000000..22ae9e1
--- /dev/null
+++ b/math/test-math-issignaling.cc
@@ -0,0 +1,113 @@
+/* Test for the C++ implementation of issignaling.
+   Copyright (C) 2017 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
+   <http://www.gnu.org/licenses/>.  */
+
+#define _GNU_SOURCE 1
+#include <math.h>
+#include <stdio.h>
+
+#include <limits>
+
+/* There is no signaling_NaN for _Float128 in std::numeric_limits.
+   Include ieee754_float128.h and use the bitfields in the union
+   ieee854_float128.ieee_nan to build a signaling NaN.  */
+#if __HAVE_DISTINCT_FLOAT128
+# include <ieee754_float128.h>
+#endif
+
+static bool errors;
+
+static void
+check (int actual, int expected, const char *actual_expr, int line)
+{
+  if (actual != expected)
+    {
+      errors = true;
+      printf ("%s:%d: error: %s\n", __FILE__, line, actual_expr);
+      printf ("%s:%d:   expected: %d\n", __FILE__, line, expected);
+      printf ("%s:%d:   actual: %d\n", __FILE__, line, actual);
+    }
+}
+
+#define CHECK(actual, expected) \
+  check ((actual), (expected), #actual, __LINE__)
+
+template <class T>
+static void
+check_type ()
+{
+  typedef std::numeric_limits<T> limits;
+  CHECK (issignaling (T{0}), 0);
+  if (limits::has_infinity)
+    {
+      CHECK (issignaling (limits::infinity ()), 0);
+      CHECK (issignaling (-limits::infinity ()), 0);
+    }
+  if (limits::has_quiet_NaN)
+    CHECK (issignaling (limits::quiet_NaN ()), 0);
+  if (limits::has_signaling_NaN)
+    CHECK (issignaling (limits::signaling_NaN ()), 1);
+}
+
+#if __HAVE_DISTINCT_FLOAT128
+static void
+check_float128 ()
+{
+  ieee854_float128 q;
+
+  q.d = 0;
+  CHECK (issignaling (q.d), 0);
+
+  /* Infinity.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x7FFF;
+  q.ieee.mantissa0 = 0x0000;
+  q.ieee.mantissa1 = 0x00000000;
+  q.ieee.mantissa2 = 0x00000000;
+  q.ieee.mantissa3 = 0x00000000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Quiet NaN.  */
+  q.ieee_nan.quiet_nan = 1;
+  q.ieee_nan.mantissa0 = 0x0000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Still a quiet NaN.  */
+  q.ieee_nan.quiet_nan = 1;
+  q.ieee_nan.mantissa0 = 0x4000;
+  CHECK (issignaling (q.d), 0);
+
+  /* Signaling NaN.  */
+  q.ieee_nan.quiet_nan = 0;
+  q.ieee_nan.mantissa0 = 0x4000;
+  CHECK (issignaling (q.d), 1);
+}
+#endif
+
+static int
+do_test (void)
+{
+  check_type<float> ();
+  check_type<double> ();
+  check_type<long double> ();
+#if __HAVE_DISTINCT_FLOAT128
+  check_float128 ();
+#endif
+  return errors;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/powerpc/powerpc64le/Makefile b/sysdeps/powerpc/powerpc64le/Makefile
index 77617b6..19adbfa 100644
--- a/sysdeps/powerpc/powerpc64le/Makefile
+++ b/sysdeps/powerpc/powerpc64le/Makefile
@@ -16,6 +16,7 @@ $(foreach suf,$(all-object-suffixes),%f128_r$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-float128%$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-ifloat128%$(suf)): CFLAGS += -mfloat128
 CFLAGS-libm-test-support-float128.c += -mfloat128
+CFLAGS-test-math-issignaling.cc += -mfloat128
 $(objpfx)test-float128% $(objpfx)test-ifloat128%: \
   gnulib-tests += $(f128-loader-link)
 endif

From 35dded99a89db873b06270ca7f21245a0faf712a Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>
Date: Wed, 23 Aug 2017 10:16:54 -0300
Subject: [PATCH] Fix the C++ version of issignaling when __NO_LONG_DOUBLE_MATH
 is defined

diff --git a/math/math.h b/math/math.h
index add86af..60dfa31 100644
--- a/math/math.h
+++ b/math/math.h
@@ -486,7 +486,15 @@ enum
 extern "C++" {
 inline int issignaling (float __val) { return __issignalingf (__val); }
 inline int issignaling (double __val) { return __issignaling (__val); }
-inline int issignaling (long double __val) { return __issignalingl (__val); }
+inline int
+issignaling (long double __val)
+{
+#  ifdef __NO_LONG_DOUBLE_MATH
+  return __issignaling (__val);
+#  else
+  return __issignalingl (__val);
+#  endif
+}
 #  if __HAVE_DISTINCT_FLOAT128
 inline int issignaling (_Float128 __val) { return __issignalingf128 (__val); }
 #  endif

From 58270c0049404ef2f878fdd45df55f17f0b8c1f7 Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>
Date: Tue, 22 Aug 2017 16:34:42 -0300
Subject: [PATCH] Provide a C++ version of iszero that does not use __MATH_TG
 (bug 21930)
diff --git a/math/math.h b/math/math.h
index 60dfa31..7c0fc6d 100644
--- a/math/math.h
+++ b/math/math.h
@@ -513,15 +513,40 @@ inline int issignaling (_Float128 __val) { return __issignalingf128 (__val); }
 #  endif
 # else	/* __cplusplus */
 extern "C++" {
+#  ifdef __SUPPORT_SNAN__
+inline int
+iszero (float __val)
+{
+  return __fpclassifyf (__val) == FP_ZERO;
+}
+inline int
+iszero (double __val)
+{
+  return __fpclassify (__val) == FP_ZERO;
+}
+inline int
+iszero (long double __val)
+{
+#   ifdef __NO_LONG_DOUBLE_MATH
+  return __fpclassify (__val) == FP_ZERO;
+#   else
+  return __fpclassifyl (__val) == FP_ZERO;
+#   endif
+}
+#   if __HAVE_DISTINCT_FLOAT128
+inline int
+iszero (_Float128 __val)
+{
+  return __fpclassifyf128 (__val) == FP_ZERO;
+}
+#   endif
+#  else
 template <class __T> inline bool
 iszero (__T __val)
 {
-#  ifdef __SUPPORT_SNAN__
-  return fpclassify (__val) == FP_ZERO;
-#  else
   return __val == 0;
-#  endif
 }
+#  endif
 } /* extern C++ */
 # endif	/* __cplusplus */
 #endif /* Use IEC_60559_BFP_EXT.  */
diff --git a/math/test-math-iszero.cc b/math/test-math-iszero.cc
index 027e972..5c07261 100644
--- a/math/test-math-iszero.cc
+++ b/math/test-math-iszero.cc
@@ -22,6 +22,13 @@
 
 #include <limits>
 
+/* Support for _Float128 in std::numeric_limits is limited.
+   Include ieee754_float128.h and use the bitfields in the union
+   ieee854_float128.ieee_nan to build corner-case inputs.  */
+#if __HAVE_DISTINCT_FLOAT128
+# include <ieee754_float128.h>
+#endif
+
 static bool errors;
 
 static void
@@ -72,12 +79,84 @@ check_type ()
          std::numeric_limits<T>::has_denorm == std::denorm_absent);
 }
 
+#if __HAVE_DISTINCT_FLOAT128
+static void
+check_float128 ()
+{
+  ieee854_float128 q;
+
+  q.d = 0.0Q;
+  CHECK (iszero (q.d), 1);
+  q.d = -0.0Q;
+  CHECK (iszero (q.d), 1);
+  q.d = 1.0Q;
+  CHECK (iszero (q.d), 0);
+  q.d = -1.0Q;
+  CHECK (iszero (q.d), 0);
+
+  /* Normal min.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x0001;
+  q.ieee.mantissa0 = 0x0000;
+  q.ieee.mantissa1 = 0x00000000;
+  q.ieee.mantissa2 = 0x00000000;
+  q.ieee.mantissa3 = 0x00000000;
+  CHECK (iszero (q.d), 0);
+  q.ieee.negative = 1;
+  CHECK (iszero (q.d), 0);
+
+  /* Normal max.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x7FFE;
+  q.ieee.mantissa0 = 0xFFFF;
+  q.ieee.mantissa1 = 0xFFFFFFFF;
+  q.ieee.mantissa2 = 0xFFFFFFFF;
+  q.ieee.mantissa3 = 0xFFFFFFFF;
+  CHECK (iszero (q.d), 0);
+  q.ieee.negative = 1;
+  CHECK (iszero (q.d), 0);
+
+  /* Infinity.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x7FFF;
+  q.ieee.mantissa0 = 0x0000;
+  q.ieee.mantissa1 = 0x00000000;
+  q.ieee.mantissa2 = 0x00000000;
+  q.ieee.mantissa3 = 0x00000000;
+  CHECK (iszero (q.d), 0);
+
+  /* Quiet NaN.  */
+  q.ieee_nan.quiet_nan = 1;
+  q.ieee_nan.mantissa0 = 0x0000;
+  CHECK (iszero (q.d), 0);
+
+  /* Signaling NaN.  */
+  q.ieee_nan.quiet_nan = 0;
+  q.ieee_nan.mantissa0 = 0x4000;
+  CHECK (iszero (q.d), 0);
+
+  /* Denormal min.  */
+  q.ieee.negative = 0;
+  q.ieee.exponent = 0x0000;
+  q.ieee.mantissa0 = 0x0000;
+  q.ieee.mantissa1 = 0x00000000;
+  q.ieee.mantissa2 = 0x00000000;
+  q.ieee.mantissa3 = 0x00000001;
+  CHECK (iszero (q.d), 0);
+  q.ieee.negative = 1;
+  CHECK (iszero (q.d), 0);
+}
+#endif
+
 static int
 do_test (void)
 {
   check_type<float> ();
   check_type<double> ();
   check_type<long double> ();
+#if __HAVE_DISTINCT_FLOAT128
+  check_float128 ();
+#endif
   return errors;
 }
 
diff --git a/sysdeps/powerpc/powerpc64le/Makefile b/sysdeps/powerpc/powerpc64le/Makefile
index 19adbfa..dea2290 100644
--- a/sysdeps/powerpc/powerpc64le/Makefile
+++ b/sysdeps/powerpc/powerpc64le/Makefile
@@ -17,7 +17,8 @@ $(foreach suf,$(all-object-suffixes),$(objpfx)test-float128%$(suf)): CFLAGS += -
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-ifloat128%$(suf)): CFLAGS += -mfloat128
 CFLAGS-libm-test-support-float128.c += -mfloat128
 CFLAGS-test-math-issignaling.cc += -mfloat128
-$(objpfx)test-float128% $(objpfx)test-ifloat128%: \
+CFLAGS-test-math-iszero.cc += -mfloat128
+$(objpfx)test-float128% $(objpfx)test-ifloat128% $(objpfx)test-math-iszero: \
   gnulib-tests += $(f128-loader-link)
 endif

From d37c951fde57e8acb320a9a7d437ba50a1fc3c8a Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gabriel@inconstante.eti.br>
Date: Wed, 20 Sep 2017 15:10:26 -0300
Subject: [PATCH] Let fpclassify use the builtin when optimizing for size in
 C++ mode (bug 22146)
diff --git a/math/math.h b/math/math.h
index 7c0fc6d..f9348ec 100644
--- a/math/math.h
+++ b/math/math.h
@@ -402,7 +402,13 @@ enum
 
 /* Return number of classification appropriate for X.  */
 # if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__			      \
-     && !defined __OPTIMIZE_SIZE__
+     && (!defined __OPTIMIZE_SIZE__ || defined __cplusplus)
+     /* The check for __cplusplus allows the use of the builtin, even
+	when optimization for size is on.  This is provided for
+	libstdc++, only to let its configure test work when it is built
+	with -Os.  No further use of this definition of fpclassify is
+	expected in C++ mode, since libstdc++ provides its own version
+	of fpclassify in cmath (which undefines fpclassify).  */
 #  define fpclassify(x) __builtin_fpclassify (FP_NAN, FP_INFINITE,	      \
      FP_NORMAL, FP_SUBNORMAL, FP_ZERO, x)
 # else

From 3b10c5d2abb0392d5ecfd865e2eb911ac109e36f Mon Sep 17 00:00:00 2001
From: "Gabriel F. T. Gomes" <gabriel@inconstante.eti.br>
Date: Mon, 2 Oct 2017 14:46:35 -0300
Subject: [PATCH] Add C++ versions of iscanonical for ldbl-96 and ldbl-128ibm
 (bug 22235)
diff --git a/math/Makefile b/math/Makefile
index 0130fcf..2c17c68 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -203,7 +203,8 @@ tests-static = test-fpucw-static test-fpucw-ieee-static \
 	       test-signgam-ullong-static test-signgam-ullong-init-static
 
 ifneq (,$(CXX))
-tests += test-math-isinff test-math-iszero test-math-issignaling
+tests += test-math-isinff test-math-iszero test-math-issignaling \
+	 test-math-iscanonical
 endif
 
 ifneq (no,$(PERL))
@@ -351,6 +352,7 @@ CFLAGS-test-signgam-ullong-init-static.c = -std=c99
 CFLAGS-test-math-isinff.cc = -std=gnu++11
 CFLAGS-test-math-iszero.cc = -std=gnu++11
 CFLAGS-test-math-issignaling.cc = -std=gnu++11
+CFLAGS-test-math-iscanonical.cc = -std=gnu++11
 
 CFLAGS-test-iszero-excess-precision.c = -fexcess-precision=standard
 CFLAGS-test-iseqsig-excess-precision.c = -fexcess-precision=standard
diff --git a/math/math.h b/math/math.h
index f9348ec..2b216c6 100644
--- a/math/math.h
+++ b/math/math.h
@@ -488,7 +488,7 @@ enum
       other hand, overloading provides the means to distinguish between
       the floating-point types.  The overloading resolution will match
       the correct parameter (regardless of type qualifiers (i.e.: const
-      and volatile).  */
+      and volatile)).  */
 extern "C++" {
 inline int issignaling (float __val) { return __issignalingf (__val); }
 inline int issignaling (double __val) { return __issignaling (__val); }
diff --git a/math/test-math-iscanonical.cc b/math/test-math-iscanonical.cc
new file mode 100644
index 0000000..aba68ac
--- /dev/null
+++ b/math/test-math-iscanonical.cc
@@ -0,0 +1,48 @@
+/* Test for the C++ implementation of iscanonical.
+   Copyright (C) 2017 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
+   <http://www.gnu.org/licenses/>.  */
+
+#define _GNU_SOURCE 1
+#include <math.h>
+#include <stdio.h>
+
+static bool errors;
+
+template <class T>
+static void
+check_type ()
+{
+  T val = 0;
+
+  /* Check if iscanonical is available in C++ mode (bug 22235).  */
+  if (iscanonical (val) == 0)
+    errors++;
+}
+
+static int
+do_test (void)
+{
+  check_type<float> ();
+  check_type<double> ();
+  check_type<long double> ();
+#if __HAVE_DISTINCT_FLOAT128
+  check_type<_Float128> ();
+#endif
+  return errors;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h b/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
index 7ddb368..f756857 100644
--- a/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
+++ b/sysdeps/ieee754/ldbl-128ibm/bits/iscanonical.h
@@ -37,5 +37,22 @@ extern int __iscanonicall (long double __x)
    conversion, before being discarded; in IBM long double, there are
    encodings that are not consistently handled as corresponding to any
    particular value of the type, and we return 0 for those.  */
-# define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
-#endif
+# ifndef __cplusplus
+#  define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+# else
+/* In C++ mode, __MATH_TG cannot be used, because it relies on
+   __builtin_types_compatible_p, which is a C-only builtin.  On the
+   other hand, overloading provides the means to distinguish between
+   the floating-point types.  The overloading resolution will match
+   the correct parameter (regardless of type qualifiers (i.e.: const
+   and volatile)).  */
+extern "C++" {
+inline int iscanonical (float __val) { return __iscanonicalf (__val); }
+inline int iscanonical (double __val) { return __iscanonical (__val); }
+inline int iscanonical (long double __val) { return __iscanonicall (__val); }
+#  if __HAVE_DISTINCT_FLOAT128
+inline int iscanonical (_Float128 __val) { return __iscanonicalf128 (__val); }
+#  endif
+}
+# endif /* __cplusplus */
+#endif /* __NO_LONG_DOUBLE_MATH */
diff --git a/sysdeps/ieee754/ldbl-96/bits/iscanonical.h b/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
index 4a4f4ad..cfa36a0 100644
--- a/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
+++ b/sysdeps/ieee754/ldbl-96/bits/iscanonical.h
@@ -34,4 +34,21 @@ extern int __iscanonicall (long double __x)
    conversion, before being discarded; in extended precision, there
    are encodings that are not consistently handled as corresponding to
    any particular value of the type, and we return 0 for those.  */
-#define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+#ifndef __cplusplus
+# define iscanonical(x) __MATH_TG ((x), __iscanonical, (x))
+#else
+/* In C++ mode, __MATH_TG cannot be used, because it relies on
+   __builtin_types_compatible_p, which is a C-only builtin.  On the
+   other hand, overloading provides the means to distinguish between
+   the floating-point types.  The overloading resolution will match
+   the correct parameter (regardless of type qualifiers (i.e.: const
+   and volatile)).  */
+extern "C++" {
+inline int iscanonical (float __val) { return __iscanonicalf (__val); }
+inline int iscanonical (double __val) { return __iscanonical (__val); }
+inline int iscanonical (long double __val) { return __iscanonicall (__val); }
+# if __HAVE_DISTINCT_FLOAT128
+inline int iscanonical (_Float128 __val) { return __iscanonicalf128 (__val); }
+# endif
+}
+#endif /* __cplusplus */
diff --git a/sysdeps/powerpc/powerpc64le/Makefile b/sysdeps/powerpc/powerpc64le/Makefile
index dea2290..cf2dbfb 100644
--- a/sysdeps/powerpc/powerpc64le/Makefile
+++ b/sysdeps/powerpc/powerpc64le/Makefile
@@ -16,6 +16,7 @@ $(foreach suf,$(all-object-suffixes),%f128_r$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-float128%$(suf)): CFLAGS += -mfloat128
 $(foreach suf,$(all-object-suffixes),$(objpfx)test-ifloat128%$(suf)): CFLAGS += -mfloat128
 CFLAGS-libm-test-support-float128.c += -mfloat128
+CFLAGS-test-math-iscanonical.cc += -mfloat128
 CFLAGS-test-math-issignaling.cc += -mfloat128
 CFLAGS-test-math-iszero.cc += -mfloat128
 $(objpfx)test-float128% $(objpfx)test-ifloat128% $(objpfx)test-math-iszero: \

From dd3a7239fddff81ac31373d69978d7aa1902c65f Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 3 Oct 2017 17:41:32 -0700
Subject: [PATCH] test-math-iscanonical.cc: Replace bool with int
diff --git a/math/test-math-iscanonical.cc b/math/test-math-iscanonical.cc
index aba68ac..4cfb1c5 100644
--- a/math/test-math-iscanonical.cc
+++ b/math/test-math-iscanonical.cc
@@ -20,7 +20,7 @@
 #include <math.h>
 #include <stdio.h>
 
-static bool errors;
+static int errors;
 
 template <class T>
 static void
@@ -42,7 +42,7 @@ do_test (void)
 #if __HAVE_DISTINCT_FLOAT128
   check_type<_Float128> ();
 #endif
-  return errors;
+  return errors != 0;
 }
 
 #include <support/test-driver.c>
 
From f8279a4b3cc66d3ec8bfb8519e9987b8f7727f53 Mon Sep 17 00:00:00 2001
From: Romain Naour <romain.naour@gmail.com>
Date: Mon, 16 Oct 2017 23:21:56 +0200
Subject: [PATCH] Let signbit use the builtin in C++ mode with gcc < 6.x (bug
 22296)
diff --git a/math/math.h b/math/math.h
index 2b216c6..ba26624 100644
--- a/math/math.h
+++ b/math/math.h
@@ -418,6 +418,15 @@ enum
 /* Return nonzero value if sign of X is negative.  */
 # if __GNUC_PREREQ (6,0)
 #  define signbit(x) __builtin_signbit (x)
+# elif defined __cplusplus
+  /* In C++ mode, __MATH_TG cannot be used, because it relies on
+     __builtin_types_compatible_p, which is a C-only builtin.
+     The check for __cplusplus allows the use of the builtin instead of
+     __MATH_TG. This is provided for libstdc++, only to let its configure
+     test work. No further use of this definition of signbit is expected
+     in C++ mode, since libstdc++ provides its own version of signbit
+     in cmath (which undefines signbit). */
+#  define signbit(x) __builtin_signbitl (x)
 # elif __GNUC_PREREQ (4,0)
 #  define signbit(x) __MATH_TG ((x), __builtin_signbit, (x))
 # else