coroutine: Enable valgrind

Currently valgrind checks are disabled on the coroutine module,
because switching stacks tends to confuse it.  We can work around this
by using the valgrind client interface to explicitly inform it about
the stacks we create.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/coroutine/_info

@@ -37,8 +37,11 @@ int main(int argc, char *argv[])
 	}
 
 	if (strcmp(argv[1], "ccanlint") == 0) {
-		/* Context switching really confuses valgrind */
+#if !HAVE_VALGRIND_MEMCHECK_H
+		/* valgrind needs extra information to cope with stack
+		 * switching */
 		printf("tests_pass_valgrind FAIL\n");
+#endif
 		return 0;
 	}
 

ccan/coroutine/coroutine.c

@@ -14,11 +14,6 @@
  * Stack management
  */
 
-struct coroutine_stack {
-	uint64_t magic;
-	size_t size;
-};
-
 /* Returns lowest stack addres, regardless of growth direction */
 static UNNEEDED void *coroutine_stack_base(struct coroutine_stack *stack)
 {
@@ -29,12 +24,38 @@ static UNNEEDED void *coroutine_stack_base(struct coroutine_stack *stack)
 #endif
 }
 
+#if HAVE_VALGRIND_MEMCHECK_H
+#include <valgrind/memcheck.h>
+static void vg_register_stack(struct coroutine_stack *stack)
+{
+	char *base = coroutine_stack_base(stack);
+
+	VALGRIND_MAKE_MEM_UNDEFINED(base, stack->size);
+	stack->valgrind_id = VALGRIND_STACK_REGISTER(base,
+						     base + stack->size - 1);
+}
+
+static void vg_deregister_stack(struct coroutine_stack *stack)
+{
+	VALGRIND_MAKE_MEM_UNDEFINED(coroutine_stack_base(stack), stack->size);
+	VALGRIND_STACK_DEREGISTER(stack->valgrind_id);
+}
+static bool vg_addressable(void *p, size_t len)
+{
+	return !VALGRIND_CHECK_MEM_IS_ADDRESSABLE(p, len);
+}
+#else
+#define vg_register_stack(stack)		do { } while (0)
+#define vg_deregister_stack(stack)		do { } while (0)
+#define vg_addressable(p, len)			(true)
+#endif
+
 struct coroutine_stack *coroutine_stack_init(void *buf, size_t bufsize,
 					     size_t metasize)
 {
 	struct coroutine_stack *stack;
+	size_t size = bufsize - sizeof(*stack) - metasize;
 
-	BUILD_ASSERT(COROUTINE_STK_OVERHEAD == sizeof(*stack));
 #ifdef MINSIGSTKSZ
 	BUILD_ASSERT(COROUTINE_MIN_STKSZ >= MINSIGSTKSZ);
 #endif
@@ -50,20 +71,22 @@ struct coroutine_stack *coroutine_stack_init(void *buf, size_t bufsize,
 #endif
 
 	stack->magic = COROUTINE_STACK_MAGIC;
-	stack->size = bufsize - sizeof(*stack) - metasize;
-
+	stack->size = size;
+	vg_register_stack(stack);
 	return stack;
 }
 
 void coroutine_stack_release(struct coroutine_stack *stack, size_t metasize)
 {
+	vg_deregister_stack(stack);
 	memset(stack, 0, sizeof(*stack));
 }
 
 struct coroutine_stack *coroutine_stack_check(struct coroutine_stack *stack,
 					      const char *abortstr)
 {
-	if (stack && (stack->magic == COROUTINE_STACK_MAGIC)
+	if (stack && vg_addressable(stack, sizeof(*stack))
+	    && (stack->magic == COROUTINE_STACK_MAGIC)
 	    && (stack->size >= COROUTINE_MIN_STKSZ))
 		return stack;
 

ccan/coroutine/coroutine.h

@@ -18,7 +18,11 @@
  * Describes a stack suitable for executing a coroutine.  This
  * structure is always contained within the stack it describes.
  */
-struct coroutine_stack;
+struct coroutine_stack {
+	uint64_t magic;
+	size_t size;
+	int valgrind_id;
+};
 
 /**
  * struct coroutine_state
@@ -37,7 +41,7 @@ struct coroutine_state;
  * Number of bytes of a stack which coroutine needs for its own
  * tracking information.
  */
-#define COROUTINE_STK_OVERHEAD		(sizeof(uint64_t) + sizeof(size_t))
+#define COROUTINE_STK_OVERHEAD	sizeof(struct coroutine_stack)
 
 /**
  * COROUTINE_MIN_STKSZ - Minimum coroutine stack size