refactor: sandbox stack

runtime/include/sandbox_set_as_initialized.h

@@ -34,9 +34,9 @@ sandbox_set_as_initialized(struct sandbox *sandbox, struct sandbox_request *sand
 	sandbox->state                     = SANDBOX_SET_AS_INITIALIZED;
 
 	/* Initialize the sandbox's context, stack, and instruction pointer */
-	/* stack_start points to the bottom of the usable stack, so add stack_size to get to top */
+	/* stack.start points to the bottom of the usable stack, so add stack_size to get to top */
 	arch_context_init(&sandbox->ctxt, (reg_t)current_sandbox_start,
-	                  (reg_t)sandbox->stack_start + sandbox->stack_size);
+	                  (reg_t)sandbox->stack.start + sandbox->stack.size);
 
 	/* Initialize Parsec control structures */
 	ps_list_init_d(sandbox);

runtime/include/sandbox_types.h

@@ -30,18 +30,20 @@ struct sandbox_io_handle {
 	int file_descriptor;
 };
 
+struct sandbox_stack {
+	void *   start; /* points to the bottom of the usable stack */
+	uint32_t size;
+};
+
 struct sandbox {
 	uint64_t        id;
 	sandbox_state_t state;
-
 	uint32_t sandbox_size; /* The struct plus enough buffer to hold the request or response (sized off largest) */
 
-	struct wasm_memory memory;
-
-	void *   stack_start;
-	uint32_t stack_size;
-
-	struct arch_context ctxt; /* register context for context switch. */
+	/* Primitives that provide WebAssembly execution  */
+	struct arch_context  ctxt;
+	struct sandbox_stack stack;
+	struct wasm_memory   memory;
 
 	uint64_t request_arrival_timestamp;   /* Timestamp when request is received */
 	uint64_t allocation_timestamp;        /* Timestamp when sandbox is allocated */

runtime/include/wasm_types.h

@@ -2,6 +2,7 @@
 
 #include <stdint.h>
 
+/* bytes, not wasm pages */
 struct wasm_memory {
 	void *   start; /* after sandbox struct */
 	uint32_t size;  /* from after sandbox struct */

runtime/src/sandbox.c

@@ -94,8 +94,8 @@ sandbox_allocate_stack(struct sandbox *sandbox)
 	/* TODO: Fix leak here. Issue #132 */
 	if (addr_rw == MAP_FAILED) goto err_stack_allocation_failed;
 
-	sandbox->stack_start = addr_rw;
-	sandbox->stack_size  = sandbox->module->stack_size;
+	sandbox->stack.start = addr_rw;
+	sandbox->stack.size  = sandbox->module->stack_size;
 
 done:
 	return 0;
@@ -179,7 +179,7 @@ sandbox_free(struct sandbox *sandbox)
 	errno = 0;
 
 	/* The stack start is the bottom of the usable stack, but we allocated a guard page below this */
-	rc = munmap((char *)sandbox->stack_start - PAGE_SIZE, sandbox->stack_size + PAGE_SIZE);
+	rc = munmap((char *)sandbox->stack.start - PAGE_SIZE, sandbox->stack.size + PAGE_SIZE);
 	if (rc == -1) {
 		debuglog("Failed to unmap stack of Sandbox %lu\n", sandbox->id);
 		goto err_free_stack_failed;