[OpenMP] Load plugins from same directory as the libomptarget.so

[saiislam]

Summary

Introduce a fall back mechanism to load plugins from the same
directory as libomptarget.so if library does not exist or cannnot
be found. It avoids the need to set LD_LIBRARY_PATH to find
plugins.

[saiislam]

First of two patches after splitting D73657

[RaviNarayanaswamy]

openmp/libomptarget/src/rtl.cpp

111–127

Do we need to repeat this everytime in the for loop

[jdoerfert]

openmp/libomptarget/src/rtl.cpp

99

Not needed.

111–127

We do not. If needed, try to find the path of libomptarget once. Please put that code in a helper method.

113

126–127

[saiislam]

Moved the code to load plugins to a helper function and before loop on plugins.

[jdoerfert]

See comments below. High-level: Why don't we say FullPluginName = Name, then try to load, if that fails, get the CWD and prepend it to FullPluginName before trying again. So LoadLibFromCWD will become bool getOrCreateCWD(std::string &CachedCWD) { if (CachedCWD) return true; ... } and a lot of the logic should be simpler. Also consider moving the actual loading part DP("Loading library '%s'...\n", Name); void *dynlib_handle = dlopen(Name, RTLD_NOW); into a helper so you can just call it twice instead of duplicating logic there again.

openmp/libomptarget/src/rtl.cpp

65

Why char** ? I mean, you fiddle with a char** here and below you handle both a char * and a std::string. Just go with the string.

123

Now there are two problems.

1. You should not eagerly look into the CWD but only if we need to.
2. If we need to and it fails we should emit a proper error message.

openmp/libomptarget/src/rtl.cpp

 #include "device.h"
 #include "private.h"
 #include "rtl.h"
 
 #include <cassert>
 #include <cstdlib>
 #include <cstring>
 #include <dlfcn.h>
+#include <link.h>
 #include <mutex>
 #include <string>
 
 // List of all plugins that can support offloading.
 static const char *RTLNames[] = {
     /* PowerPC target       */ "libomptarget.rtl.ppc64.so",
     /* x86_64 target        */ "libomptarget.rtl.x86_64.so",
     /* CUDA target          */ "libomptarget.rtl.cuda.so",
__attribute__((destructor(101))) void deinit() {
   delete RTLs;
   delete RTLsMtx;
   delete HostEntriesBeginToTransTable;
   delete TrlTblMtx;
   delete HostPtrToTableMap;
   delete TblMapMtx;
 }
 
+/// Load plugins from same directory as libomptarget.so
+static bool LoadLibFromCWD(char **PathName) {
+  struct link_map *Map;
+
+  DP("Trying to load plugins from same directory as libomptarget.so: %s\n",
+     Name);
+  void *Handle = dlopen("libomptarget.so", RTLD_NOW);
+  if (!Handle) {
+    DP("Unable to load library : %s!\n", dlerror());
+    return false;
+  }
+  if (dlinfo(Handle, RTLD_DI_LINKMAP, &Map) == -1) {
+    DP("RTLD_DI_LINKMAP failed: %s\n", dlerror());
+    dlclose(Handle);
+    return false;
+  }
+  if (!Map->l_name) {
+    DP("Absolute pathname not found: %s\n", dlerror());
+    dlclose(Handle);
+    return false;
+  }
+  *PathName = Map->l_name;
+  return true;
+}
+
 void RTLsTy::LoadRTLs() {
   // Parse environment variable OMP_TARGET_OFFLOAD (if set)
   TargetOffloadPolicy = (kmp_target_offload_kind_t) __kmpc_get_target_offload();
   if (TargetOffloadPolicy == tgt_disabled) {
     return;
   }
 
   DP("Loading RTLs...\n");
 
+  std::string FullPluginName;
+  char *LibompPathName = NULL;
+  bool LibFoundInCWD = LoadLibFromCWD(&LibompPathName);
+
   // Attempt to open all the plugins and, if they exist, check if the interface
   // is correct and if they are supporting any devices.
   for (auto *Name : RTLNames) {
     DP("Loading library '%s'...\n", Name);
     void *dynlib_handle = dlopen(Name, RTLD_NOW);
 
     if (!dynlib_handle) {
       // Library does not exist or cannot be found.
-      DP("Unable to load library '%s': %s!\n", Name, dlerror());
+      // Try to load plugins from same directory as libomptarget.so
+
+      if (!LibFoundInCWD)
         continue;
+
+      FullPluginName.assign(LibompPathName).append("/").append(Name);
+      dynlib_handle = dlopen(FullPluginName.c_str(), RTLD_NOW);
+      if (!dynlib_handle) {
+        DP("Unable to load plugin '%s' from same directory as libomptarget.so: "
+           "%s\n",
+           Name, dlerror());
+        continue;
+      }
     }
 
-    DP("Successfully loaded library '%s'!\n", Name);
+    DP("Successfully loaded library '%s'!\n",
+       FullPluginName ? FullPluginName.c_str() : Name);
 
     // Retrieve the RTL information from the runtime library.
     RTLInfoTy R;
 
     R.LibraryHandler = dynlib_handle;
     R.isUsed = false;
 
 #ifdef OMPTARGET_DEBUG
     R.RTLName = Name;