Index: sys/amd64/amd64/pmap.c
===================================================================
--- sys/amd64/amd64/pmap.c
+++ sys/amd64/amd64/pmap.c
@@ -705,6 +705,15 @@
 	invl_gen->next = (void *)PMAP_INVL_GEN_NEXT_INVALID;
 }
 
+/* Copied from atomic.h. */
+#ifdef __GCC_ASM_FLAG_OUTPUTS__
+#define	CC_FLAG_OUT_INST(cc, loc)
+#define	CC_FLAG_OUT_CONS(cc)		"=@cc" #cc
+#else
+#define	CC_FLAG_OUT_INST(cc, loc)	"set" #cc " " loc " ;	"
+#define	CC_FLAG_OUT_CONS(cc)		"=q"
+#endif
+
 static bool
 pmap_di_load_invl(struct pmap_invl_gen *ptr, struct pmap_invl_gen *out)
 {
@@ -714,8 +723,9 @@
 	old_low = new_low = 0;
 	old_high = new_high = (uintptr_t)0;
 
-	__asm volatile("lock;cmpxchg16b\t%1"
-	    : "=@cce" (res), "+m" (*ptr), "+a" (old_low), "+d" (old_high)
+	__asm volatile("lock;cmpxchg16b\t%1;" CC_FLAG_OUT_INST(e, "%0")
+	    : CC_FLAG_OUT_CONS(e) (res), "+m" (*ptr), "+a" (old_low),
+	      "+d" (old_high)
 	    : "b"(new_low), "c" (new_high)
 	    : "memory", "cc");
 	if (res == 0) {
@@ -742,8 +752,9 @@
 	old_low = old_val->gen;
 	old_high = (uintptr_t)old_val->next;
 
-	__asm volatile("lock;cmpxchg16b\t%1"
-	    : "=@cce" (res), "+m" (*ptr), "+a" (old_low), "+d" (old_high)
+	__asm volatile("lock;cmpxchg16b\t%1;" CC_FLAG_OUT_INST(e, "%0")
+	    : CC_FLAG_OUT_CONS(e) (res), "+m" (*ptr), "+a" (old_low),
+	      "+d" (old_high)
 	    : "b"(new_low), "c" (new_high)
 	    : "memory", "cc");
 	return (res);
Index: sys/amd64/include/atomic.h
===================================================================
--- sys/amd64/include/atomic.h
+++ sys/amd64/include/atomic.h
@@ -152,6 +152,19 @@
 #define	MPLOCKED
 #endif
 
+/*
+ * Newer versions of clang and gcc, including the in-tree compiler, support
+ * outputting status flags directly from asm blocks.  Provide support for
+ * older cross compilers, where the flag is extracted via setcc.
+ */
+#ifdef __GCC_ASM_FLAG_OUTPUTS__
+#define	CC_FLAG_OUT_INST(cc, loc)
+#define	CC_FLAG_OUT_CONS(cc)		"=@cc" #cc
+#else
+#define	CC_FLAG_OUT_INST(cc, loc)	"set" #cc " " loc " ;	"
+#define	CC_FLAG_OUT_CONS(cc)		"=q"
+#endif
+
 /*
  * The assembly is volatilized to avoid code chunk removal by the compiler.
  * GCC aggressively reorders operations and memory clobbering is necessary
@@ -201,8 +214,9 @@
 	__asm __volatile(				\
 	"	" MPLOCKED "		"		\
 	"	cmpxchg %3,%1 ;	"			\
+	CC_FLAG_OUT_INST(e, "%0")			\
 	"# atomic_cmpset_" #TYPE "	"		\
-	: "=@cce" (res),		/* 0 */		\
+	: CC_FLAG_OUT_CONS(e) (res),	/* 0 */		\
 	  "+m" (*dst),			/* 1 */		\
 	  "+a" (expect)			/* 2 */		\
 	: "r" (src)			/* 3 */		\
@@ -218,8 +232,9 @@
 	__asm __volatile(				\
 	"	" MPLOCKED "		"		\
 	"	cmpxchg %3,%1 ;		"		\
+	CC_FLAG_OUT_INST(e, "%0")			\
 	"# atomic_fcmpset_" #TYPE "	"		\
-	: "=@cce" (res),		/* 0 */		\
+	: CC_FLAG_OUT_CONS(e) (res),	/* 0 */		\
 	  "+m" (*dst),			/* 1 */		\
 	  "+a" (*expect)		/* 2 */		\
 	: "r" (src)			/* 3 */		\
@@ -276,8 +291,9 @@
 	__asm __volatile(
 	"	" MPLOCKED "		"
 	"	btsl	%2,%1 ;		"
+	CC_FLAG_OUT_INST(c, "%0")
 	"# atomic_testandset_int"
-	: "=@ccc" (res),		/* 0 */
+	: CC_FLAG_OUT_CONS(c) (res),	/* 0 */
 	  "+m" (*p)			/* 1 */
 	: "Ir" (v & 0x1f)		/* 2 */
 	: "cc");
@@ -292,8 +308,9 @@
 	__asm __volatile(
 	"	" MPLOCKED "		"
 	"	btsq	%2,%1 ;		"
+	CC_FLAG_OUT_INST(c, "%0")
 	"# atomic_testandset_long"
-	: "=@ccc" (res),		/* 0 */
+	: CC_FLAG_OUT_CONS(c) (res),	/* 0 */
 	  "+m" (*p)			/* 1 */
 	: "Jr" ((u_long)(v & 0x3f))	/* 2 */
 	: "cc");
@@ -308,8 +325,9 @@
 	__asm __volatile(
 	"	" MPLOCKED "		"
 	"	btrl	%2,%1 ;		"
+	CC_FLAG_OUT_INST(c, "%0")
 	"# atomic_testandclear_int"
-	: "=@ccc" (res),		/* 0 */
+	: CC_FLAG_OUT_CONS(c) (res),	/* 0 */
 	  "+m" (*p)			/* 1 */
 	: "Ir" (v & 0x1f)		/* 2 */
 	: "cc");
@@ -324,8 +342,9 @@
 	__asm __volatile(
 	"	" MPLOCKED "		"
 	"	btrq	%2,%1 ;		"
+	CC_FLAG_OUT_INST(c, "%0")
 	"# atomic_testandclear_long"
-	: "=@ccc" (res),		/* 0 */
+	: CC_FLAG_OUT_CONS(c) (res),	/* 0 */
 	  "+m" (*p)			/* 1 */
 	: "Jr" ((u_long)(v & 0x3f))	/* 2 */
 	: "cc");
@@ -463,6 +482,8 @@
 #undef ATOMIC_LOAD
 #undef ATOMIC_STORE
 #undef ATOMIC_LOADSTORE
+#undef CC_FLAG_OUT_INST
+#undef CC_FLAG_OUT_CONS
 #ifndef WANT_FUNCTIONS
 
 /* Read the current value and store a new value in the destination. */