Make spinlocks constructable without initlock

These locks can be statically constructed in the .data segment, since the constructor is constexpr. Currently this only works for locks that aren't tracked by lockstat.

Make spinlocks constructable without initlock
b6308520 · Austin Clements · d0b095e0 · b6308520 · b6308520
--- a/include/spinlock.h
+++ b/include/spinlock.h
@@ -16,6 +16,31 @@ struct spinlock {
 #if LOCKSTAT
  struct klockstat *stat;
 #endif
+  // Create a spinlock that will later be initialized by initlock.
+  // XXX(austin) Remove this and initlock in favor of the other ctor.
+  constexpr spinlock()
+    : locked(0)
+#if SPINLOCK_DEBUG
+    , name(nullptr), cpu(nullptr), pcs{}
+#endif
+#if LOCKSTAT
+    , stat(nullptr)
+#endif
+  { }
+  // Create a spinlock without lockstat tracking.  This is constexpr,
+  // so it can be used for global spinlocks without incurring a static
+  // constructor.
+  constexpr spinlock(const char *name)
+    : locked(0)
+#if SPINLOCK_DEBUG
+    , name(name), cpu(nullptr), pcs{}
+#endif
+#if LOCKSTAT
+    , stat(nullptr)
+#endif
+  { }
 };
 #if SPINLOCK_DEBUG

--- a/kernel/spinlock.cc
+++ b/kernel/spinlock.cc
@@ -117,13 +117,7 @@ holding(struct spinlock *lock)
 #if LOCKSTAT
 LIST_HEAD(lockstat_list, klockstat);
 static struct lockstat_list lockstat_list = { (struct klockstat*) nullptr };
-static struct spinlock lockstat_lock = { 
+static struct spinlock lockstat_lock("lockstat");
- locked: 0,
-#if SPINLOCK_DEBUG
- name: "lockstat",
- cpu: (struct cpu*) nullptr,
-#endif
-};
 klockstat::klockstat(const char *name) : 
  rcu_freed("klockstat")