Index: sys/amd64/amd64/machdep.c
===================================================================
--- sys/amd64/amd64/machdep.c
+++ sys/amd64/amd64/machdep.c
@@ -2741,17 +2741,27 @@
 void    *memcpy_erms(void * _Nonnull dst, const void * _Nonnull src,
 	    size_t len);
 
-#ifdef KCSAN
 /*
  * These fail to build as ifuncs when used with KCSAN.
+ * AUTO_VAR_INIT calls memset before the ifunc resolver is called.
  */
+#if defined(KCSAN) || defined(AUTO_VAR_INIT)
 void *
 memset(void *buf, int c, size_t len)
 {
 
 	return (memset_std(buf, c, len));
 }
+#else
+DEFINE_IFUNC(, void *, memset, (void *, int, size_t))
+{
+
+	return ((cpu_stdext_feature & CPUID_STDEXT_ERMS) != 0 ?
+	    memset_erms : memset_std);
+}
+#endif
 
+#if defined(KCSAN)
 void *
 memmove(void * _Nonnull dst, const void * _Nonnull src, size_t len)
 {
@@ -2766,13 +2776,6 @@
 	return (memcpy_std(dst, src, len));
 }
 #else
-DEFINE_IFUNC(, void *, memset, (void *, int, size_t))
-{
-
-	return ((cpu_stdext_feature & CPUID_STDEXT_ERMS) != 0 ?
-	    memset_erms : memset_std);
-}
-
 DEFINE_IFUNC(, void *, memmove, (void * _Nonnull, const void * _Nonnull,
     size_t))
 {
Index: sys/amd64/conf/GENERIC
===================================================================
--- sys/amd64/conf/GENERIC
+++ sys/amd64/conf/GENERIC
@@ -84,6 +84,7 @@
 options 	RACCT			# Resource accounting framework
 options 	RACCT_DEFAULT_TO_DISABLED # Set kern.racct.enable=0 by default
 options 	RCTL			# Resource limits
+#options 	AUTO_VAR_INIT		# Init the stack on function entry
 
 # Debugging support.  Always need this:
 options 	KDB			# Enable kernel debugger support.
Index: sys/arm64/conf/GENERIC
===================================================================
--- sys/arm64/conf/GENERIC
+++ sys/arm64/conf/GENERIC
@@ -81,6 +81,7 @@
 options 	RCTL			# Resource limits
 options 	SMP
 options 	INTRNG
+options 	AUTO_VAR_INIT		# Init the stack on function entry
 
 # Debugging support.  Always need this:
 options 	KDB			# Enable kernel debugger support.
Index: sys/conf/kern.pre.mk
===================================================================
--- sys/conf/kern.pre.mk
+++ sys/conf/kern.pre.mk
@@ -146,6 +146,17 @@
 .endif
 .endif
 
+AUTO_VAR_INIT_ENABLED!= grep AUTO_VAR_INIT opt_global.h || true ; echo
+.if !empty(AUTO_VAR_INIT_ENABLED)
+.if ${COMPILER_TYPE} == "clang"
+CFLAGS+=	-ftrivial-auto-var-init=pattern
+MOD_CFLAGS+=	-ftrivial-auto-var-init=pattern
+.else
+.warning AUTO_VAR_INIT enabled, but no compiler support
+CFLAGS+=	-DAUTO_VAR_INIT_MISSING
+.endif
+.endif
+
 CFLAGS+=	${GCOV_CFLAGS}
 
 # Put configuration-specific C flags last (except for ${PROF}) so that they
Index: sys/conf/kmod.mk
===================================================================
--- sys/conf/kmod.mk
+++ sys/conf/kmod.mk
@@ -392,6 +392,9 @@
 # Add the gcov flags
 CFLAGS+=	${GCOV_CFLAGS}
 
+# Add flags based on config options
+CFLAGS+=	${MOD_CFLAGS}
+
 # Respect configuration-specific C flags.
 CFLAGS+=	${ARCH_FLAGS} ${CONF_CFLAGS}
 
Index: sys/conf/options
===================================================================
--- sys/conf/options
+++ sys/conf/options
@@ -74,6 +74,7 @@
 ALTERA_SDCARD_FAST_SIM	opt_altera_sdcard.h
 ATSE_CFI_HACK	opt_cfi.h
 AUDIT		opt_global.h
+AUTO_VAR_INIT	opt_global.h
 BOOTHOWTO	opt_global.h
 BOOTVERBOSE	opt_global.h
 CALLOUT_PROFILING
Index: sys/kern/init_main.c
===================================================================
--- sys/kern/init_main.c
+++ sys/kern/init_main.c
@@ -387,6 +387,15 @@
     print_caddr_t, diag_warn);
 #endif
 
+#ifdef AUTO_VAR_INIT_MISSING
+static char auto_var_warn[] =
+    "WARNING: AUTO_VAR_INIT option enable but no compiler support.\n";
+SYSINIT(sudo_var_warn, SI_SUB_COPYRIGHT, SI_ORDER_THIRD + 3,
+    print_caddr_t, auto_var_warn);
+SYSINIT(auto_var_warn2, SI_SUB_LAST, SI_ORDER_THIRD + 3,
+    print_caddr_t, auto_var_warn);
+#endif
+
 static int
 null_fetch_syscall_args(struct thread *td __unused)
 {