UML - fix x86_64 with !CONFIG_FRAME_POINTER

Index: linux-2.6.14-rc3/arch/um/sys-x86_64/stub_segv.c
===================================================================
@@ -10,6 +10,22 @@
 #include "uml-config.h"
 #include "sysdep/sigcontext.h"
 #include "sysdep/faultinfo.h"
+#include <stddef.h>
+
+/* Copied from sys-x86_64/signal.c - Can't find an equivalent definition
+ * in the libc headers anywhere.
+ */
+struct rt_sigframe
+{
+	char *pretcode;
+	struct ucontext uc;
+	struct siginfo info;
+};
+
+/* Copied here from <linux/kernel.h> - we're userspace. */
+#define container_of(ptr, type, member) ({                   \
+	const typeof( ((type *)0)->member ) *__mptr = (ptr); \
+	(type *)( (char *)__mptr - offsetof(type,member) );})
 
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_segv_handler(int sig)

@@ -17,16 +33,19 @@
 	struct ucontext *uc;
 
 	__asm__("movq %%rdx, %0" : "=g" (uc) :);
-        GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
-                              &uc->uc_mcontext);
+	GET_FAULTINFO_FROM_SC(*((struct faultinfo *) UML_CONFIG_STUB_DATA),
+			      &uc->uc_mcontext);
 
-	__asm__("movq %0, %%rax ; syscall": : "g" (__NR_getpid));
+	__asm__("movq %0, %%rax ; syscall": : "g" (__NR_getpid));	
 	__asm__("movq %%rax, %%rdi ; movq %0, %%rax ; movq %1, %%rsi ;"
-		"syscall": : "g" (__NR_kill), "g" (SIGUSR1));
-	/* Two popqs to restore the stack to the state just before entering
-	 * the handler, one pops the return address, the other pops the frame
-	 * pointer.
+		"syscall": : "g" (__NR_kill), "g" (SIGUSR1) : 
+		"%rdi", "%rax", "%rsi");
+	/* sys_sigreturn expects that the stack pointer will be 8 bytes into
+	 * the signal frame.  So, we use the ucontext pointer, which we know
+	 * already, to get the signal frame pointer, and add 8 to that.
 	 */
-	__asm__("popq %%rax ; popq %%rax ; movq %0, %%rax ; syscall" : : "g"
-		(__NR_rt_sigreturn));
+	__asm__("movq %0, %%rsp": : 
+		"g" ((unsigned long) container_of(uc, struct rt_sigframe, 
+						  uc) + 8));
+	__asm__("movq %0, %%rax ; syscall" : : "g" (__NR_rt_sigreturn));
 }