[OpenMP][libomp] Cleanup version script and exported symbols

[jlpeyton]

Summary

This patch is an attempt to fix issues seen once https://reviews.llvm.org/D135402 is applied.

The exports_so.txt file attempts to export functions which may not exist
depending on which features are enabled/disabled in the OpenMP
runtime library. There are not many of these so exporting dummy
symbols is feasible.

1. Export dummy __kmp_reset_stats() function when stats is disabled.
2. Export dummy debugging data when USE_DEBUGGER is disabled
3. Export dummy __kmp_itt_[fini|init]_ittlib() functions when ITT Notify is disabled
4. Export dummy __kmp_reap_monitor() function when KMP_USE_MONITOR is disabled
5. Remove __kmp_launch_monitor and __kmp_launch_worker from being exported. They have been static symbols since library inception.

Fixes: https://github.com/llvm/llvm-project/issues/58858

[ronlieb]

i applied the lld patch https://reviews.llvm.org/D135402 and this one, then ran the equivalent of our buildbot, all good, builds and passes.

[jhuber6]

I think multiple version scripts would've been more correct so we don't export symbols that the user can't do anything useful with. But realistically I'm not too attached to the idea given that it would probably take more effort for little gain. I'm fine with this, others and @MaskRay may wish to comment further.

[MaskRay]

Very appreciate your and jhuber6's efforts to fix the symbol versioning issues for OpenMP!

openmp/runtime/src/kmp_runtime.cpp

9205

Yes that I see a lot of FALSE in openmp/ since it was imported from a pretty old code base.
Does 0 or false apply?

[tianshilei1992]

openmp/runtime/src/kmp_runtime.cpp

9205

I think we should keep the same code style as before for consistence. That’s also one of the reasons that even new code for libomp still doesn’t use LLVM code style.

[jlpeyton]

In D138049#3939286, @MaskRay wrote:

Very appreciate your and jhuber6's efforts to fix the symbol versioning issues for OpenMP!

I agree with @tianshilei1992. I'd like to keep the code style consistent.

openmp/runtime/src/exports_so.txt

#if USE_ITT_BUILD
         __kmp_acquire_nested_tas_lock;
         __kmp_acquire_nested_ticket_lock;
         __kmp_acquire_queuing_lock;
         __kmp_acquire_tas_lock;
         __kmp_acquire_ticket_lock;
         __kmp_fork_call;
         __kmp_invoke_microtask;
 #if KMP_USE_MONITOR
-        __kmp_launch_monitor;
         __kmp_reap_monitor;
 #endif
-        __kmp_launch_worker;
         __kmp_reap_worker;
         __kmp_release_64;
         __kmp_wait_64;
         __kmp_wait_4;
 
         # ittnotify symbols to be used by debugger
         __kmp_itt_fini_ittlib;
         __kmp_itt_init_ittlib;

openmp/runtime/src/kmp_runtime.cpp

if (__kmp_nesting_mode > 1 && __kmp_nesting_mode_nlevels > __kmp_nesting_mode)
     __kmp_nesting_mode_nlevels = __kmp_nesting_mode;
   if (get__max_active_levels(thread) > 1) {
     // if max levels was set, set nesting mode levels to same
     __kmp_nesting_mode_nlevels = get__max_active_levels(thread);
   }
   if (__kmp_nesting_mode == 1) // turn on nesting for this case only
     set__max_active_levels(thread, __kmp_nesting_mode_nlevels);
 }
+
+// Empty symbols to export (see exports_so.txt) when feature is disabled
+extern "C" {
+#if !KMP_STATS_ENABLED
+void __kmp_reset_stats() {}
+#endif
+#if !USE_DEBUGGER
+int __kmp_omp_debug_struct_info = FALSE;
+int __kmp_debugging = FALSE;
+#endif
+#if !USE_ITT_BUILD || !USE_ITT_NOTIFY
+void __kmp_itt_fini_ittlib() {}
+void __kmp_itt_init_ittlib() {}
+#endif
+}
+
+// end of file

openmp/runtime/src/z_Linux_util.cpp

 
 void __kmp_exit_thread(int exit_status) {
   pthread_exit((void *)(intptr_t)exit_status);
 } // __kmp_exit_thread
 
 #if KMP_USE_MONITOR
 void __kmp_resume_monitor();
 
-void __kmp_reap_monitor(kmp_info_t *th) {
+extern "C" void __kmp_reap_monitor(kmp_info_t *th) {
   int status;
   void *exit_val;
 
   KA_TRACE(10, ("__kmp_reap_monitor: try to reap monitor thread with handle"
                 " %#.8lx\n",
                 th->th.th_info.ds.ds_thread));
 
   // If monitor has been created, its tid and gtid should be KMP_GTID_MONITOR.
extern "C" void __kmp_reap_monitor(kmp_info_t *th) {
   th->th.th_info.ds.ds_gtid = KMP_GTID_DNE;
 
   KA_TRACE(10, ("__kmp_reap_monitor: done reaping monitor thread with handle"
                 " %#.8lx\n",
                 th->th.th_info.ds.ds_thread));
 
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 }
+#else
+// Empty symbol to export (see exports_so.txt) when
+// monitor thread feature is disabled
+extern "C" void __kmp_reap_monitor(kmp_info_t *th) {
+  (void)th;
+}
 #endif // KMP_USE_MONITOR
 
 void __kmp_reap_worker(kmp_info_t *th) {
   int status;
   void *exit_val;
 
   KMP_MB(); /* Flush all pending memory write invalidates.  */