--- a/tools/misc/xen-detect.c   		2011-10-20 15:05:43.000000000 -0200
+++ b/tools/misc/xen-detect.c			2012-02-15 00:05:55.524455578 -0200
@@ -35,18 +35,21 @@
 
 static void cpuid(uint32_t idx, uint32_t *regs, int pv_context)
 {
-    asm volatile (
 #ifdef __i386__
-#define R(x) "%%e"#x"x"
-#else
-#define R(x) "%%r"#x"x"
-#endif
-        "push "R(a)"; push "R(b)"; push "R(c)"; push "R(d)"\n\t"
+/* Use the stack to avoid reg constraint failures with some gcc flags */
+    asm volatile (
+        "push %%eax; push %%ebx; push %%ecx; push %%edx\n\t"
         "test %1,%1 ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
         "mov %%eax,(%2); mov %%ebx,4(%2)\n\t"
         "mov %%ecx,8(%2); mov %%edx,12(%2)\n\t"
-        "pop "R(d)"; pop "R(c)"; pop "R(b)"; pop "R(a)"\n\t"
+        "pop %%edx; pop %%ecx; pop %%ebx; pop %%eax\n\t"
         : : "a" (idx), "c" (pv_context), "S" (regs) : "memory" );
+#else
+    asm volatile (
+       "test %5,%5 ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
+       : "=a" (regs[0]), "=b" (regs[1]), "=c" (regs[2]), "=d" (regs[3])
+       : "0" (idx), "1" (pv_context), "2" (0) );
+#endif
 }
 
 static int check_for_xen(int pv_context)