From 32ae9c6127d21b8408f2573904fec8ab0b666d36 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Mon, 3 Oct 2016 20:22:53 +0530
Subject: [PATCH] build: Fix clock_gettime check with XCode 8

With XCode 8, clock_gettime will be incorrectly detected as being
available regardless of what OS X version we're targetting because the
symbol is available in the .tbd library as a weak symbol.
See: https://github.com/Homebrew/homebrew-core/issues/3727#issue-170086273

It's only starting from macOS 10.12 that clock_gettime is actually
available, so we can unconditionally disable it when targetting older
versions. We cannot simply do AC_CHECK_FUNCS with -Wl,-no_weak_imports
because the autoconf check does its own prototype declaration that
doesn't trigger that compiler flag.

https://bugzilla.gnome.org/show_bug.cgi?id=772451
---
 configure.ac       | 38 +++++++++++++++++++++++++++++++++++---
 m4/check-checks.m4 |  2 +-
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index 05ac220f72..b07dbf2c0c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -675,18 +675,50 @@ AC_CHECK_FUNCS([posix_memalign])
 AC_CHECK_FUNCS([getpagesize])
 
 dnl Check for POSIX timers
-AC_CHECK_FUNCS(clock_gettime, [], [
+CLOCK_GETTIME_FOUND="no"
+AC_CHECK_FUNC(clock_gettime, [CLOCK_GETTIME_FOUND="yes"], [
   AC_CHECK_LIB(rt, clock_gettime, [
-    AC_DEFINE(HAVE_CLOCK_GETTIME, 1)
+    CLOCK_GETTIME_FOUND="yes"
     LIBS="$LIBS -lrt"
   ], [
     AC_CHECK_LIB(pthread, clock_gettime, [
-      AC_DEFINE(HAVE_CLOCK_GETTIME, 1)
+      CLOCK_GETTIME_FOUND="yes"
       LIBS="$LIBS -lpthread"
     ])
   ])
 ])
 
+# With XCode 8, clock_gettime will be incorrectly detected as being available
+# regardless of what version of OS X you target because the symbol is available
+# in the .tbd file as a weak symbol.
+# See: https://bugzilla.gnome.org/show_bug.cgi?id=772451
+#
+# We cannot simply do AC_CHECK_FUNCS with -Wl,-no_weak_imports because the
+# autoconf check does its own prototype declaration that doesn't trigger that
+# compiler flag.
+#
+# It's only starting from macOS 10.12, that clock_gettime is actually available,
+# so we can unconditionally disable it when targetting older versions.
+case "$host_os" in
+  darwin*)
+    AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#include <AvailabilityMacros.h>
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_12
+#error "Not compiling for OS X 10.12 or later"
+#endif
+    ]])], [], [
+    if test "$CLOCK_GETTIME_FOUND" = "yes"; then
+      AC_MSG_NOTICE([Disabling incorrectly detected clock_gettime on OS X])
+    fi
+    CLOCK_GETTIME_FOUND="no"
+    ])
+    ;;
+esac
+
+if test "$CLOCK_GETTIME_FOUND" = "yes"; then
+  AC_DEFINE(HAVE_CLOCK_GETTIME, 1, [Have clock_gettime])
+fi
+
 AC_CACHE_CHECK(for posix timers, gst_cv_posix_timers,
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 #include <time.h>
diff --git a/m4/check-checks.m4 b/m4/check-checks.m4
index 16ba777d37..99aaa8ad7f 100644
--- a/m4/check-checks.m4
+++ b/m4/check-checks.m4
@@ -95,7 +95,7 @@ AC_CHECK_LIB([rt], [timer_create, timer_settime, timer_delete])
 AM_CONDITIONAL(HAVE_TIMER_CREATE_SETTIME_DELETE, test "x$ac_cv_lib_rt_timer_create__timer_settime__timer_delete" = "xyes")
 
 dnl Allow for checking HAVE_CLOCK_GETTIME in automake files
-AM_CONDITIONAL(HAVE_CLOCK_GETTIME, test "x$ac_cv_func_clock_gettime" = "xyes")
+AM_CONDITIONAL(HAVE_CLOCK_GETTIME, test "x$HAVE_CLOCK_GETTIME" = "xyes")
 
 dnl Create _stdint.h in the top-level directory
 AX_CREATE_STDINT_H