From dc495408beaecff343a66ccc531d148a6a01b754 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Bylica?= <chfast@gmail.com>
Date: Sat, 8 Sep 2018 18:23:27 +0200
Subject: [PATCH] Improve EVMC capabilities

---
 examples/example_vm.c   |  7 +++++++
 include/evmc/evmc.h     | 21 ++++++++++++++-------
 include/evmc/helpers.h  | 11 +++++++++++
 test/vmtester/tests.cpp |  7 +++++++
 4 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/examples/example_vm.c b/examples/example_vm.c
index 622c26b..6af5841 100644
--- a/examples/example_vm.c
+++ b/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,
     };
diff --git a/include/evmc/evmc.h b/include/evmc/evmc.h
index f7879c9..51496ef 100644
--- a/include/evmc/evmc.h
+++ b/include/evmc/evmc.h
@@ -768,20 +768,27 @@ typedef struct evmc_result (*evmc_execute_fn)(struct evmc_instance* instance,
  */
 enum evmc_capabilities
 {
-    EVMC_CAPABILITY_EVM1 = 1, /**< The VM is capable of executing EVM1 bytecode. */
-    EVMC_CAPABILITY_EWASM = 2 /**< The VM is capable of execution ewasm bytecode. */
+    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 set_option.
+ * 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.
+ * @param instance  The EVM instance.
+ * @return          The supported capabilities of the VM. @see evmc_capabilities.
  */
-typedef int (*evmc_get_capabilities_fn)(struct evmc_instance* instance);
+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;
@@ -890,7 +897,7 @@ struct evmc_instance
     evmc_execute_fn execute;
 
     /**
-     * Pointer to function returning capabilities supported by the EVM instance.
+     * Pointer to function returning capabilities supported by the VM instance.
      *
      * The value returned might change when different options are requested via set_option.
      *
diff --git a/include/evmc/helpers.h b/include/evmc/helpers.h
index a9ecd5f..601fa84 100644
--- a/include/evmc/helpers.h
+++ b/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.
  *
diff --git a/test/vmtester/tests.cpp b/test/vmtester/tests.cpp
index c844394..cebcef6 100644
--- a/test/vmtester/tests.cpp
+++ b/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));
+}