wasmtime: branch execution path after wasm header interpretation

Signed-off-by: Maximilian Hüter <[email protected]>

Author: t4chib4ne

src/libcrun/handlers/handler-utils.c

@@ -75,15 +75,20 @@ wasm_encoding_t
 wasm_interpete_header (const char *header)
 {
   // Check for the WebAssembly magic bytes
+  // See: https://webassembly.github.io/spec/core/binary/modules.html#binary-module
   if (strncmp (header, "\0asm", 4))
     return WASM_ENC_INVALID;
 
-  // We don't care for the specific WebAssembly version
-  // so we only read the value of the `layer` field.
+  /* The next four bytes are the WebAssembly version.
+     We don't care for the specific WebAssembly version
+     so we only read the value of the `layer` field which
+     was defined by the component spec.
+     See: https://github.com/WebAssembly/component-model/blob/main/design/mvp/Binary.md#component-definitions
+  */
   if (header[6] == '\0' && header[7] == '\0')
     return WASM_ENC_MODULE;
 
-  // `layer` does not equal 0x00 0x00 so we are working
+  // `layer` does not equal `0x00 0x00` so we are working
   // with a component.
   return WASM_ENC_COMPONENT;
 }

src/libcrun/handlers/wasmtime.c

@@ -117,26 +117,16 @@ libwasmtime_exec (void *cookie, libcrun_container_t *container arg_unused,
       wasm = wasm_bytes;
     }
 
-  // Check if it is a valid webassembly module or
-  // a component.
-  bool is_wasm_module = true;
-  wasmtime_error_t *err = wasmtime_module_validate (engine, (uint8_t *) wasm.data, wasm.size);
-  if (err != NULL)
-    {
-      wasmtime_error_message (err, &error_message);
-      wasmtime_error_delete (err);
-
-      if (strcmp ((char *) error_message.data, "component passed to module validation") != 0)
-        error (EXIT_FAILURE, 0, "failed to validate module: %.*s", (int) error_message.size, error_message.data);
+  wasm_encoding_t wasm_enc = wasm_interpete_header (wasm.data);
+  if (wasm_enc == WASM_ENC_INVALID)
+    error (EXIT_FAILURE, 0, "invalid wasm binary header");
 
-      err = NULL;
-      is_wasm_module = false;
-    }
-
-  if (is_wasm_module)
+  if (wasm_enc == WASM_ENC_MODULE)
     libwasmtime_run_module (cookie, argv, engine, &wasm);
-  else
+  else if (wasm_enc == WASM_ENC_COMPONENT)
     libwasmtime_run_component (cookie, argv, engine, &wasm);
+  else
+    error (EXIT_FAILURE, 0, "unsupport wasm encoding detected");
 
   exit (EXIT_SUCCESS);
 }