Fix ABI regression in tbb::empty_task caused by switch to LTO

tbb-mark-empty_task-execute-with-gnu-used.patch

@@ -0,0 +1,26 @@
+From db2f2116adfb545bb76c92205f91e3e3f0f9e44a Mon Sep 17 00:00:00 2001
+From: Thomas Rodgers <rodgert@twrodgers.com>
+Date: Wed, 2 Jun 2021 15:18:30 -0700
+Subject: [PATCH] Mark tbb::empty_task::execute with [[gnu::used]]
+
+---
+ include/tbb/task.h | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/include/tbb/task.h b/include/tbb/task.h
+index 5e137c6..5b60163 100644
+--- a/include/tbb/task.h
++++ b/include/tbb/task.h
+@@ -1040,6 +1040,9 @@ inline void task::resume(suspend_point tag) {
+ //! task that does nothing.  Useful for synchronization.
+ /** @ingroup task_scheduling */
+ class __TBB_DEPRECATED_IN_VERBOSE_MODE empty_task: public task {
++#if __has_cpp_attribute(gnu::used)
++    [[gnu::used]]
++#endif
+     task* execute() __TBB_override {
+         return NULL;
+     }
+-- 
+2.31.1
+

tbb.spec

@@ -1,7 +1,7 @@
 Name:    tbb
 Summary: The Threading Building Blocks library abstracts low-level threading details
 Version: 2020.3
-Release: 5%{?dist}
+Release: 6%{?dist}
 License: ASL 2.0
 URL:     http://threadingbuildingblocks.org/
 
@@ -27,6 +27,10 @@ Patch2: tbb-2019-test-thread-monitor.patch
 # than 2 threads will be available to use it.
 Patch3: tbb-2019-test-task-scheduler-init.patch
 
+# Fix ABI break resulting from tbb::empty_task being removed from libtbb.so's
+# exported symbols
+Patch4: tbb-mark-empty_task-execute-with-gnu-used.patch
+
 BuildRequires: cmake
 BuildRequires: doxygen
 BuildRequires: gcc-c++
@@ -201,6 +205,9 @@ cmake \
 %{python3_sitearch}/__pycache__/TBB*
 
 %changelog
+* Thu Jun  3 2021 Thomas Rodgers <trodgers@redhat.com> - 2020.3-6
+- Fix ABI regression in tbb::empty_task caused by switch to LTO
+
 * Mon Feb 22 2021 Jerry James <loganjerry@gmail.com> - 2020.3-5
 - Fix cmake file installation some more (bz 1930389)