[LIBOMPTARGET]Ignore empty target descriptors.

[ABataev]

Summary

If the dynamically loaded module has been compiled with -fopenmp-targets
and has no target regions, it has empty target descriptor. It leads to a
crash at the runtime if another module has at least one target region
and at least one entry in its descriptor. The runtime library is unable
to load the empty binary descriptor and terminates the execution.
Caused by a clang-offload-wrapper.

[jdoerfert]

LGTM.

[merge_guards_bot]

Unit tests: pass. 61723 tests passed, 0 failed and 779 were skipped.

clang-tidy: fail. Please fix clang-tidy findings.

clang-format: fail. Please format your changes with clang-format by running git-clang-format HEAD^ or applying this patch.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[JonChesterfield]

Nice catch, thanks

[tianshilei1992]

I got a question: since there is no target region in the shared library at all, why is desc->NumDeviceImages = 1 where desc is the one in the shared library?

[ABataev]

In D72472#1817787, @tianshilei1992 wrote:

I got a question: since there is no target region in the shared library at all, why is desc->NumDeviceImages = 1 where desc is the one in the shared library?

It is an empty target region with no entries at all. It has some data inside (mostly, metadata, I assume), but no real target entries.

openmp/libomptarget/src/rtl.cpp

void RTLsTy::RegisterRequires(int64_t flags) {
   DP("New requires flags %ld compatible with existing %ld!\n",
      flags, RequiresFlags);
 }
 
 void RTLsTy::RegisterLib(__tgt_bin_desc *desc) {
   // Attempt to load all plugins available in the system.
   std::call_once(initFlag, &RTLsTy::LoadRTLs, this);
 
+  if (desc->HostEntriesBegin == desc->HostEntriesEnd)
+    return;
   RTLsMtx.lock();
   // Register the images with the RTLs that understand them, if any.
   for (int32_t i = 0; i < desc->NumDeviceImages; ++i) {
     // Obtain the image.
     __tgt_device_image *img = &desc->DeviceImages[i];
 
     RTLInfoTy *FoundRTL = NULL;
 
for (int32_t i = 0; i < desc->NumDeviceImages; ++i) {
     }
   }
   RTLsMtx.unlock();
 
 
   DP("Done registering entries!\n");
 }
 
 void RTLsTy::UnregisterLib(__tgt_bin_desc *desc) {
   DP("Unloading target library!\n");
 
+  if (desc->HostEntriesBegin == desc->HostEntriesEnd)
+    return;
   RTLsMtx.lock();
   // Find which RTL understands each image, if any.
   for (int32_t i = 0; i < desc->NumDeviceImages; ++i) {
     // Obtain the image.
     __tgt_device_image *img = &desc->DeviceImages[i];
 
     RTLInfoTy *FoundRTL = NULL;
 

openmp/libomptarget/test/offloading/dynamic_module.c

+// RUN: %libomptarget-compile-aarch64-unknown-linux-gnu -DSHARED -shared -o %t.so && %libomptarget-compile-aarch64-unknown-linux-gnu %t.so && %libomptarget-run-aarch64-unknown-linux-gnu 2>&1 | %fcheck-aarch64-unknown-linux-gnu
+// RUN: %libomptarget-compile-powerpc64-ibm-linux-gnu -DSHARED -shared -o %t.so && %libomptarget-compile-powerpc64-ibm-linux-gnu %t.so && %libomptarget-run-powerpc64-ibm-linux-gnu 2>&1 | %fcheck-powerpc64-ibm-linux-gnu
+// RUN: %libomptarget-compile-powerpc64le-ibm-linux-gnu -DSHARED -shared -o %t.so && %libomptarget-compile-powerpc64le-ibm-linux-gnu %t.so && %libomptarget-run-powerpc64le-ibm-linux-gnu 2>&1 | %fcheck-powerpc64le-ibm-linux-gnu
+// RUN: %libomptarget-compile-x86_64-pc-linux-gnu -DSHARED -shared -o %t.so && %libomptarget-compile-x86_64-pc-linux-gnu %t.so && %libomptarget-run-x86_64-pc-linux-gnu 2>&1 | %fcheck-x86_64-pc-linux-gnu
+
+#ifdef SHARED
+void foo() {}
+#else
+#include <stdio.h>
+int main() {
+#pragma omp target
+  ;
+  // CHECK: DONE.
+  printf("%s\n", "DONE.");
+  return 0;
+}
+#endif