[SYCL] Lookup versioned OpenCL adapter library as fallback

sycl/include/sycl/detail/os_util.hpp

@@ -106,27 +106,33 @@ void fileTreeWalk(const std::string Path,
                   std::function<void(const std::string)> Func,
                   bool ignoreErrors = false);
 
-void *dynLookup(const char *WinName, const char *LinName, const char *FunName);
+void *dynLookup(const char *WinName, const char *LinName,
+                const char *LinuxFallbackLibName, const char *FunName);
 
 // Look up a function name that was dynamically linked
 // This is used by the runtime where it needs to manipulate native handles (e.g.
 // retaining OpenCL handles). On Windows, the symbol name is looked up in
-// `WinName`. In Linux, it uses `LinName`.
+// `WinName`. In Linux, it uses `LinName` or `LinuxFallbackLibName`.
 //
 // The library must already have been loaded (perhaps by UR), otherwise this
 // function throws a SYCL runtime exception.
 template <typename fn>
 fn *dynLookupFunction(const char *WinName, const char *LinName,
-                      const char *FunName) {
-  return reinterpret_cast<fn *>(dynLookup(WinName, LinName, FunName));
+                      const char *LinuxFallbackLibName, const char *FunName) {
+  return reinterpret_cast<fn *>(
+      dynLookup(WinName, LinName, LinuxFallbackLibName, FunName));
 }
-// On Linux, the name of OpenCL that was used to link against may be either
-// `OpenCL.so`, `OpenCL.so.1` or possibly anything else.
-// `libur_adapter_opencl.so` is a more stable name, since it is hardcoded into
-// the loader.
+
+// On Linux, first try to load from libur_adapter_opencl.so, then
+// libur_adapter_opencl.so.0 if the first is not found. libur_adapter_opencl.so
+// and libur_adapter_opencl.so.0 might be different libraries if they are not
+// symlinked, which is the case with PyPi compiler distribution package.
+// We can't load libur_adapter_opencl.so.0 always as the first choice because
+// that would break SYCL unittests, which rely on mocking libur_adapter_opencl.
 #define __SYCL_OCL_CALL(FN, ...)                                               \
   (sycl::_V1::detail::dynLookupFunction<decltype(FN)>(                         \
-      "OpenCL", "libur_adapter_opencl.so", #FN)(__VA_ARGS__))
+      "OpenCL", "libur_adapter_opencl.so", "libur_adapter_opencl.so.0",        \
+      #FN)(__VA_ARGS__))
 
 } // namespace detail
 } // namespace _V1

sycl/source/detail/os_util.cpp

@@ -299,7 +299,9 @@ size_t getDirectorySize(const std::string &Path, bool ignoreErrors) {
 // The library must already have been loaded (perhaps by UR), otherwise this
 // function throws a SYCL runtime exception.
 void *dynLookup([[maybe_unused]] const char *WinName,
-                [[maybe_unused]] const char *LinName, const char *FunName) {
+                [[maybe_unused]] const char *LinName,
+                [[maybe_unused]] const char *LinuxFallbackLibName,
+                const char *FunName) {
 #ifdef __SYCL_RT_OS_WINDOWS
   auto handle = GetModuleHandleA(WinName);
   if (!handle) {
@@ -310,8 +312,14 @@ void *dynLookup([[maybe_unused]] const char *WinName,
 #else
   auto handle = dlopen(LinName, RTLD_LAZY | RTLD_NOLOAD);
   if (!handle) {
-    throw sycl::exception(make_error_code(errc::runtime),
-                          std::string(LinName) + " library is not loaded");
+
+    // Try to open fallback library if provided.
+    if (LinuxFallbackLibName)
+      handle = dlopen(LinuxFallbackLibName, RTLD_LAZY | RTLD_NOLOAD);
+
+    if (!handle)
+      throw sycl::exception(make_error_code(errc::runtime),
+                            std::string(LinName) + " library is not loaded");
   }
   auto *retVal = dlsym(handle, FunName);
   dlclose(handle);