loader: Expose DLL load error in hacky way

Only works on Linux and macos, otherwise returns null.
ethereum · Apr 3, 2019 · e8067fd · e8067fd
1 parent 4408da2
commit e8067fd
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Showing 5 changed files with 36 additions and 5 deletions.
diff --git a/bindings/go/evmc/evmc.go b/bindings/go/evmc/evmc.go
@@ -158,7 +158,13 @@ func Load(filename string) (instance *Instance, err error) {
 	case C.EVMC_LOADER_SUCCESS:
 		instance = &Instance{handle}
 	case C.EVMC_LOADER_CANNOT_OPEN:
-		err = fmt.Errorf("evmc loader: cannot open %s", filename)
+		optionalErrMsg := C.evmc_cannot_open_error()
+		if optionalErrMsg != nil {
+			msg := C.GoString(optionalErrMsg)
+			err = fmt.Errorf("evmc loader: %s", msg)
+		} else {
+			err = fmt.Errorf("evmc loader: cannot open %s", filename)
+		}
 	case C.EVMC_LOADER_SYMBOL_NOT_FOUND:
 		err = fmt.Errorf("evmc loader: the EVMC create function not found in %s", filename)
 	case C.EVMC_LOADER_INVALID_ARGUMENT:

diff --git a/include/evmc/loader.h b/include/evmc/loader.h
@@ -1,6 +1,6 @@
 /* EVMC: Ethereum Client-VM Connector API.
- * Copyright 2018 The EVMC Authors.
- * Licensed under the Apache License, Version 2.0. See the LICENSE file.
+ * Copyright 2019 The EVMC Authors.
+ * Licensed under the Apache License, Version 2.0.
  */
 
 /**
@@ -87,6 +87,15 @@ enum evmc_loader_error_code
  */
 evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* error_code);
 
+/**
+ * Exposes additional information about ::EVMC_LOADER_CANNOT_OPEN error.
+ *
+ * This function is not thread-safe and not supported on all operating systems.
+ *
+ * @return Error message or NULL if no additional information is available.
+ */
+const char* evmc_cannot_open_error();
+
 /**
  * Dynamically loads the VM DLL and creates the VM instance.
  *

diff --git a/lib/loader/loader.c b/lib/loader/loader.c
@@ -130,6 +130,16 @@ evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* erro
     return create_fn;
 }
 
+const char* evmc_cannot_open_error()
+{
+#if !defined(EVMC_LOADER_MOCK) && !_WIN32
+    const char* error = dlerror();
+    if (error)
+        return error;
+#endif
+    return NULL;
+}
+
 struct evmc_instance* evmc_load_and_create(const char* filename,
                                            enum evmc_loader_error_code* error_code)
 {

diff --git a/test/vmtester/CMakeLists.txt b/test/vmtester/CMakeLists.txt
@@ -18,7 +18,7 @@ add_test(NAME vmtester/help COMMAND evmc-vmtester --version --help)
 set_tests_properties(vmtester/help PROPERTIES PASS_REGULAR_EXPRESSION "Usage:")
 
 add_test(NAME vmtester/nonexistingvm COMMAND evmc-vmtester nonexistingvm)
-set_tests_properties(vmtester/nonexistingvm PROPERTIES PASS_REGULAR_EXPRESSION "Cannot open")
+set_tests_properties(vmtester/nonexistingvm PROPERTIES PASS_REGULAR_EXPRESSION "[Cc]annot open")
 
 add_test(NAME vmtester/noarg COMMAND evmc-vmtester)
 set_tests_properties(vmtester/noarg PROPERTIES PASS_REGULAR_EXPRESSION "is required")

diff --git a/test/vmtester/vmtester.cpp b/test/vmtester/vmtester.cpp
@@ -140,8 +140,14 @@ int main(int argc, char* argv[])
         case EVMC_LOADER_SUCCESS:
             break;
         case EVMC_LOADER_CANNOT_OPEN:
-            std::cerr << "Cannot open " << evmc_module << "\n";
+        {
+            const auto error = evmc_cannot_open_error();
+            if (error)
+                std::cerr << error << "\n";
+            else
+                std::cerr << "Cannot open " << evmc_module << "\n";
             return static_cast<int>(ec);
+        }
         case EVMC_LOADER_SYMBOL_NOT_FOUND:
             std::cerr << "EVMC create function not found in " << evmc_module << "\n";
             return static_cast<int>(ec);