restorer: introduced the macro SIGFRAME_OFFSET

The macro is designated to tune the beginning of a sigframe on different architectures.
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

arch/x86/include/asm/restorer.h

@@ -131,6 +131,8 @@ struct rt_sigframe {
 
 #define RT_SIGFRAME_UC(rt_sigframe) rt_sigframe->uc
 
+#define SIGFRAME_OFFSET 8
+
 
 int restore_gpregs(struct rt_sigframe *f, UserX86RegsEntry *r);
 

pie/restorer.c

@@ -210,7 +210,7 @@ long __export_restore_thread(struct thread_restore_args *args)
 
 	futex_dec_and_wake(&thread_inprogress);
 
-	new_sp = (long)rt_sigframe + 8;
+	new_sp = (long)rt_sigframe + SIGFRAME_OFFSET;
 	ARCH_RT_SIGRETURN(new_sp);
 
 core_restore_end:
@@ -715,7 +715,7 @@ long __export_restore_task(struct task_restore_core_args *args)
 	/*
 	 * Sigframe stack.
 	 */
-	new_sp = (long)rt_sigframe + 8;
+	new_sp = (long)rt_sigframe + SIGFRAME_OFFSET;
 
 	/*
 	 * Prepare the stack and call for sigreturn,