[OpenMP] Use weak attribute in interface only for static library

[protze.joachim]

Summary

This is to address the issue reported at:
https://bugs.llvm.org/show_bug.cgi?id=46863

From my understanding, the issue is that these omp_ symbols want to be both external and weak. Since weak is meaningless for a shared library interface function, this patch disables the attribute, when the OpenMP library is built as shared library.

The situation of ompt_start_tool is different. This is not an interface function, but a function implemented by an OMPT tool. This function needs to be weak if possible to allow overwriting ompt_start_tool with a function implementation built into the application.

[protze.joachim]

Updated to be a bit more specific, where the external version is used.

[mstorsjo]

FWIW, without verifying whether this works in detail, this sounds like a sensible solution, so +1 from me.

[hans]

Thanks! This fixes the link error I was hitting.

openmp/runtime/src/kmp_ftn_entry.h

 #else
   __kmp_entry_thread()->th.th_current_task->td_icvs.default_device =
       KMP_DEREF arg;
 #endif
 }
 
 // Get number of NON-HOST devices.
 // libomptarget, if loaded, provides this function in api.cpp.
-int FTN_STDCALL KMP_EXPAND_NAME(FTN_GET_NUM_DEVICES)(void) KMP_WEAK_ATTRIBUTE;
+int FTN_STDCALL KMP_EXPAND_NAME(FTN_GET_NUM_DEVICES)(void) KMP_WEAK_ATTRIBUTE_EXTERNAL;
 int FTN_STDCALL KMP_EXPAND_NAME(FTN_GET_NUM_DEVICES)(void) {
 #if KMP_MIC || KMP_OS_DARWIN || KMP_OS_WINDOWS || defined(KMP_STUB)
   return 0;
 #else
   int (*fptr)();
   if ((*(void **)(&fptr) = dlsym(RTLD_DEFAULT, "_Offload_number_of_devices"))) {
     return (*fptr)();
   } else if ((*(void **)(&fptr) = dlsym(RTLD_NEXT, "omp_get_num_devices"))) {
     return (*fptr)();
   } else { // liboffload & libomptarget don't exist
     return 0;
   }
 #endif // KMP_MIC || KMP_OS_DARWIN || KMP_OS_WINDOWS || defined(KMP_STUB)
 }
 
 // This function always returns true when called on host device.
 // Compiler/libomptarget should handle when it is called inside target region.
-int FTN_STDCALL KMP_EXPAND_NAME(FTN_IS_INITIAL_DEVICE)(void) KMP_WEAK_ATTRIBUTE;
+int FTN_STDCALL KMP_EXPAND_NAME(FTN_IS_INITIAL_DEVICE)(void) KMP_WEAK_ATTRIBUTE_EXTERNAL;
 int FTN_STDCALL KMP_EXPAND_NAME(FTN_IS_INITIAL_DEVICE)(void) {
   return 1; // This is the host
 }
 
 // libomptarget, if loaded, provides this function
-int FTN_STDCALL FTN_GET_INITIAL_DEVICE(void) KMP_WEAK_ATTRIBUTE;
+int FTN_STDCALL FTN_GET_INITIAL_DEVICE(void) KMP_WEAK_ATTRIBUTE_EXTERNAL;
 int FTN_STDCALL FTN_GET_INITIAL_DEVICE(void) {
 #if KMP_MIC || KMP_OS_DARWIN || KMP_OS_WINDOWS || defined(KMP_STUB)
   return KMP_HOST_DEVICE;
 #else
   int (*fptr)();
   if ((*(void **)(&fptr) = dlsym(RTLD_NEXT, "omp_get_initial_device"))) {
     return (*fptr)();
   } else { // liboffload & libomptarget don't exist
#else
   }
   return __kmp_max_task_priority;
 #endif
 }
 
 // This function will be defined in libomptarget. When libomptarget is not
 // loaded, we assume we are on the host and return KMP_HOST_DEVICE.
 // Compiler/libomptarget will handle this if called inside target.
-int FTN_STDCALL FTN_GET_DEVICE_NUM(void) KMP_WEAK_ATTRIBUTE;
+int FTN_STDCALL FTN_GET_DEVICE_NUM(void) KMP_WEAK_ATTRIBUTE_EXTERNAL;
 int FTN_STDCALL FTN_GET_DEVICE_NUM(void) { return KMP_HOST_DEVICE; }
 
 // Compiler will ensure that this is only called from host in sequential region
 int FTN_STDCALL FTN_PAUSE_RESOURCE(kmp_pause_status_t kind, int device_num) {
 #ifdef KMP_STUB
   return 1; // just fail
 #else
   if (device_num == KMP_HOST_DEVICE)

openmp/runtime/src/kmp_os.h

 #define KMP_THREAD_LOCAL __declspec(thread)
 #define KMP_ALIAS /* Nothing */
 #else
 #define KMP_ALIGN(bytes) __attribute__((aligned(bytes)))
 #define KMP_THREAD_LOCAL __thread
 #define KMP_ALIAS(alias_of) __attribute__((alias(alias_of)))
 #endif
 
+#if KMP_HAVE_WEAK_ATTRIBUTE && !KMP_DYNAMIC_LIB
+#define KMP_WEAK_ATTRIBUTE_EXTERNAL __attribute__((weak))
+#else
+#define KMP_WEAK_ATTRIBUTE_EXTERNAL /* Nothing */
+#endif
+
 #if KMP_HAVE_WEAK_ATTRIBUTE
-#define KMP_WEAK_ATTRIBUTE __attribute__((weak))
+#define KMP_WEAK_ATTRIBUTE_INTERNAL __attribute__((weak))
 #else
-#define KMP_WEAK_ATTRIBUTE /* Nothing */
+#define KMP_WEAK_ATTRIBUTE_INTERNAL /* Nothing */
 #endif
 
 // Define KMP_VERSION_SYMBOL and KMP_EXPAND_NAME
 #ifndef KMP_STR
 #define KMP_STR(x) _KMP_STR(x)
 #define _KMP_STR(x) #x
 #endif
 

openmp/runtime/src/ompt-specific.cpp

 #endif
 
 #if KMP_OS_WINDOWS
 #define THREAD_LOCAL __declspec(thread)
 #else
 #define THREAD_LOCAL __thread
 #endif
 
-#define OMPT_WEAK_ATTRIBUTE KMP_WEAK_ATTRIBUTE
+#define OMPT_WEAK_ATTRIBUTE KMP_WEAK_ATTRIBUTE_INTERNAL
 
 //******************************************************************************
 // macros
 //******************************************************************************
 
 #define LWT_FROM_TEAM(team) (team)->t.ompt_serialized_team_info
 
 #define OMPT_THREAD_ID_BITS 16