Index: gcc/testsuite/gcc.target/i386/stack-prot-kernel.c
===================================================================
--- gcc/testsuite/gcc.target/i386/stack-prot-kernel.c	(revision 0)
+++ gcc/testsuite/gcc.target/i386/stack-prot-kernel.c	(revision 0)
@@ -0,0 +1,12 @@
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -fstack-protector-all -mcmodel=kernel" } */
+
+void test1 (int x)
+{
+  char p[40];
+  int i;
+  for (i=0; i<40; i++)
+	p[i] = x;
+}
+
+/* { dg-final { scan-assembler-not "%fs" } } */
Index: gcc/config/i386/i386.md
===================================================================
--- gcc/config/i386/i386.md	(revision 115220)
+++ gcc/config/i386/i386.md	(working copy)
@@ -20393,7 +20393,15 @@
    (set (match_scratch:DI 2 "=&r") (const_int 0))
    (clobber (reg:CC FLAGS_REG))]
   "TARGET_64BIT"
-  "mov{q}\t{%%fs:%P1, %2|%2, QWORD PTR %%fs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2"
+  {  
+     /* The kernel uses a different segment register for performance reasons; a
+        system call would not have to trash the userspace segment register, 
+        which would be expensive */
+     if (ix86_cmodel != CM_KERNEL)
+        return "mov{q}\t{%%fs:%P1, %2|%2, QWORD PTR %%fs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2";
+     else 
+        return "mov{q}\t{%%gs:%P1, %2|%2, QWORD PTR %%gs:%P1}\;mov{q}\t{%2, %0|%0, %2}\;xor{l}\t%k2, %k2";
+  }
   [(set_attr "type" "multi")])
 
 (define_expand "stack_protect_test"
@@ -20461,7 +20469,15 @@
 		    UNSPEC_SP_TLS_TEST))
    (clobber (match_scratch:DI 3 "=r"))]
   "TARGET_64BIT"
-  "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%fs:%P2, %3|%3, QWORD PTR %%fs:%P2}"
+  {
+     /* The kernel uses a different segment register for performance reasons; a
+        system call would not have to trash the userspace segment register, 
+        which would be expensive */
+     if (ix86_cmodel != CM_KERNEL)
+        return "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%fs:%P2, %3|%3, QWORD PTR %%fs:%P2}";
+     else
+        return "mov{q}\t{%1, %3|%3, %1}\;xor{q}\t{%%gs:%P2, %3|%3, QWORD PTR %%gs:%P2}";
+  }
   [(set_attr "type" "multi")])
 
 (include "sse.md")