Merge pull request #119 from ethereum/loader

Generalize loader searching algorithm

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## [6.0.0-dev] - unreleased
 
+- Improved: [[#119](https://github.com/ethereum/evmc/pull/119)]
+  EVMC loader symbol searching has been generalized.
+
 ## [5.2.0] - 2018-08-28
 
 - Feature: [[#81](https://github.com/ethereum/evmc/pull/81)]

include/evmc/loader.h

@@ -60,15 +60,16 @@ enum evmc_loader_error_code
  *   "libexample-interpreter.so",
  * - the "lib" prefix and file extension are stripped from the name:
  *   "example-interpreter"
- * - all "-" are replaced with "_" to construct _full name_:
+ * - all "-" are replaced with "_" to construct _base name_:
  *   "example_interpreter",
- * - the _full name_ is split by "_" char and the last item is taken to form the _short name_:
- *   "interpreter",
- * - the name "evmc_create_" + _full name_ is checked in the library:
+ * - the function name "evmc_create_" + _base name_ is searched in the library:
  *   "evmc_create_example_interpreter",
- * - then, the name "evmc_create_" + _short name_ is checked in the library:
- *   "evmc_create_interpreter".
- * - lastly, the name "evmc_create" is checked in the library
+ * - if function not found, the _base name_ is shorten by skipping the first word separated by "_":
+ *   "interpreter",
+ * - then, the function of the shorter name "evmc_create_" + _base name_ is searched in the library:
+ *   "evmc_create_interpreter",
+ * - the name shortening continues until a function is found or the name cannot be shorten more,
+ * - lastly, when no function found, the function name "evmc_create" is searched in the library.
  *
  * If the create function is found in the library, the pointer to the function is returned.
  * Otherwise, the ::EVMC_LOADER_SYMBOL_NOT_FOUND error code is signaled and NULL is returned.

lib/loader/loader.c

@@ -69,8 +69,8 @@ evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* erro
     // Create name buffer with the prefix.
     const char prefix[] = "evmc_create_";
     const size_t prefix_length = strlen(prefix);
-    char name[sizeof(prefix) + PATH_MAX_LENGTH];
-    strcpy_s(name, sizeof(name), prefix);
+    char prefixed_name[sizeof(prefix) + PATH_MAX_LENGTH];
+    strcpy_s(prefixed_name, sizeof(prefixed_name), prefix);
 
     // Find filename in the path.
     const char* sep_pos = strrchr(filename, '/');
@@ -87,30 +87,28 @@ evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* erro
     if (strncmp(name_pos, lib_prefix, lib_prefix_length) == 0)
         name_pos += lib_prefix_length;
 
-    strcpy_s(name + prefix_length, PATH_MAX_LENGTH, name_pos);
+    char* base_name = prefixed_name + prefix_length;
+    strcpy_s(base_name, PATH_MAX_LENGTH, name_pos);
 
     // Trim the file extension.
-    char* ext_pos = strrchr(name, '.');
+    char* ext_pos = strrchr(prefixed_name, '.');
     if (ext_pos)
         *ext_pos = 0;
 
     // Replace all "-" with "_".
-    char* dash_pos = name;
+    char* dash_pos = base_name;
     while ((dash_pos = strchr(dash_pos, '-')) != NULL)
         *dash_pos++ = '_';
 
-    // Search for the "full name" based function name.
-    create_fn = DLL_GET_CREATE_FN(handle, name);
-    if (!create_fn)
+    // Search for the built function name.
+    while ((create_fn = DLL_GET_CREATE_FN(handle, prefixed_name)) == NULL)
     {
-        // Try the "short name" based function name.
-        const char* short_name_pos = strrchr(name, '_');
-        if (short_name_pos)
-        {
-            short_name_pos += 1;
-            memmove(name + prefix_length, short_name_pos, strlen(short_name_pos) + 1);
-            create_fn = DLL_GET_CREATE_FN(handle, name);
-        }
+        // Shorten the base name by skipping the `word_` segment.
+        const char* shorter_name_pos = strchr(base_name, '_');
+        if (!shorter_name_pos)
+            break;
+
+        memmove(base_name, shorter_name_pos + 1, strlen(shorter_name_pos) + 1);
     }
 
     if (!create_fn)