Merge pull request #144 from ethereum/capabilities

Introduce evmc_capabilities and emvc_get_capabilities_fn

examples/example_vm.c

@@ -28,6 +28,12 @@ static void destroy(struct evmc_instance* evm)
     free(evm);
 }
 
+static evmc_capabilities_flagset get_capabilities(struct evmc_instance* vm)
+{
+    (void)vm;
+    return EVMC_CAPABILITY_EVM1 | EVMC_CAPABILITY_EWASM;
+}
+
 /// Example options.
 ///
 /// VMs are allowed to omit this function implementation.
@@ -150,6 +156,7 @@ struct evmc_instance* evmc_create_example_vm()
         .version = STR(PROJECT_VERSION),
         .destroy = destroy,
         .execute = execute,
+        .get_capabilites = get_capabilities,
         .set_option = set_option,
         .set_tracer = set_tracer,
     };

include/evmc/evmc.h

@@ -763,6 +763,32 @@ typedef struct evmc_result (*evmc_execute_fn)(struct evmc_instance* instance,
                                               uint8_t const* code,
                                               size_t code_size);
 
+/**
+ * Possible capabilities of a VM.
+ */
+enum evmc_capabilities
+{
+    EVMC_CAPABILITY_EVM1 = (1u << 0), /**< The VM is capable of executing EVM1 bytecode. */
+    EVMC_CAPABILITY_EWASM = (1u << 1) /**< The VM is capable of execution ewasm bytecode. */
+};
+
+/**
+ * Alias for unsigned integer representing a set of bit flags of EVMC capabilities.
+ *
+ * @see evmc_capabilities
+ */
+typedef uint32_t evmc_capabilities_flagset;
+
+/**
+ * Return the supported capabilities of the VM instance.
+ *
+ * This function MAY be invoked multiple times for a single VM instance,
+ * and its value MAY be influenced by calls to evmc_instance::set_option.
+ *
+ * @param instance  The EVM instance.
+ * @return          The supported capabilities of the VM. @see evmc_capabilities.
+ */
+typedef evmc_capabilities_flagset (*evmc_get_capabilities_fn)(struct evmc_instance* instance);
 
 /** The opaque type representing a Client-side tracer object. */
 struct evmc_tracer_context;
@@ -870,6 +896,16 @@ struct evmc_instance
     /** Pointer to function executing a code by the EVM instance. */
     evmc_execute_fn execute;
 
+    /**
+     * Pointer to function returning capabilities supported by the VM instance.
+     *
+     * The value returned might change when different options are requested via set_option.
+     *
+     * A Client SHOULD only rely on the value returned here if it has queried it after
+     * it has called set_option.
+     */
+    evmc_get_capabilities_fn get_capabilites;
+
     /**
      * Optional pointer to function setting the EVM instruction tracer.
      *

include/evmc/helpers.h

@@ -41,6 +41,17 @@ static inline const char* evmc_vm_version(struct evmc_instance* instance)
     return instance->version;
 }
 
+/**
+ * Checks if the VM instance has the given capability.
+ *
+ * @see evmc_get_capabilities_fn
+ */
+static inline bool evmc_vm_has_capability(struct evmc_instance* vm,
+                                          enum evmc_capabilities capability)
+{
+    return (vm->get_capabilites(vm) & (evmc_capabilities_flagset)capability) != 0;
+}
+
 /**
  * Destroys the VM instance.
  *

test/vmtester/tests.cpp

@@ -117,3 +117,10 @@ TEST_F(evmc_vm_test, set_tracer)
     if (vm->set_tracer)
         vm->set_tracer(vm, tracer_callback, nullptr);
 }
+
+TEST_F(evmc_vm_test, capabilities)
+{
+    // The VM should have at least one of EVM1 or EWASM capabilities.
+    EXPECT_TRUE(evmc_vm_has_capability(vm, EVMC_CAPABILITY_EVM1) ||
+                evmc_vm_has_capability(vm, EVMC_CAPABILITY_EWASM));
+}