allocator: heap_quarantine_empty int return

sdk/core/allocator/main.cc

diff --git a/sdk/core/allocator/main.cc b/sdk/core/allocator/main.cc
index 3b8e6cd..359134c 100644
--- a/sdk/core/allocator/main.cc
+++ b/sdk/core/allocator/main.cc
@@ -852,7 +852,7 @@
 	return cap->quota;
 }
 
-__cheriot_minimum_stack(0xc0) void heap_quarantine_empty()
+__cheriot_minimum_stack(0xc0) int heap_quarantine_empty()
 {
 	STACK_CHECK(0xc0);
 	LockGuard g{lock};
@@ -866,6 +866,8 @@
 		yield();
 		g.lock();
 	}
+
+	return 0;
 }
 
 __cheriot_minimum_stack(0x210) void *heap_allocate(Timeout *timeout,

sdk/include/stdlib.h

diff --git a/sdk/include/stdlib.h b/sdk/include/stdlib.h
index 2dca318..26e5180 100644
--- a/sdk/include/stdlib.h
+++ b/sdk/include/stdlib.h
@@ -281,8 +281,12 @@
  * This should be used only in testing, to place the system in a quiesced
  * state.  It can block indefinitely if another thread is allocating and
  * freeing memory while this runs.
+ *
+ * Returns 0 on success, a compartment invocation failure indication
+ * (-ENOTENOUGHSTACK, -ENOTENOUGHTRUSTEDSTACK) if it cannot be invoked, or
+ * possibly -ECOMPARTMENTFAIL if the allocator compartment is damaged.
  */
-void __cheri_compartment("alloc") heap_quarantine_empty(void);
+int __cheri_compartment("alloc") heap_quarantine_empty(void);
 
 /**
  * Returns true if `object` points to a valid heap address, false otherwise.